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The Florida Institute of Phosphate Research was created in 1978 by the Florida Legislature(Chapter 378.101, Florida- Statutes) and empowered to conduct research supportive to theresponsible development of the states phosphate resources. The Institute has targeted areaof research responsibility. These are: reclamation alternatives in mining and processing,including wetlands reclamation, phosphogypsum storage areas and phosphatic claycontainment areas; methods for more efficient, economical and environmentally balanced
phosphate recovery and processing; disposal and utilization of phosphatic clay; andenvironmental effects involving the health and welfare of the people, including those effectrelated to radiation and water consumption.
FIPR is located in Polk County, in the heart of the central Florida phosphate district. TheInstitute seeks to serve as an information center on phosphate-related topics and welcomesinformation requests made in person, by mail, or by telephone.
Research Staff
Executive DirectorPaul R.Clifford
Research Directors
G.MichaelLloyd Jr. -ChemicalProcessingJinrongP.Zhang -Mining & BeneficiationStevenG.Richardson -ReclamationGordon D.Nifong -Environmental Services
Florida Institute of Phosphate Research1855 West Main StreetBartow, Florida 33830
(863) 534-7160Fax:(863) 534-7165
http://www.fipr.state.fl.us
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BACTERIA AS FLOTATION REAGENTS FOR THE FLOTATION
OF A DOLOMITIC PHOSPHATE ROCK
FINAL REPORT
Ross W. Smith
Principal Investigator
with
Manoranjan Misra, Rajendra K. Mehta, and Xiapeng Zheng
UNIVERSITY OF NEVADA RENO
Reno, Nevada 89557
Prepared for
FLORIDA INSTITUTE OF PHOSPHATE RESEARCH
1855 West Main Street
Bartow, Florida 33830
Contract Manager: Patrick Zhang
FIPR Contract Number: 94-02-l06R
January 1997
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DISCLAIMER
The contents of this report are reproduced herein as received from the contractor.
The opinions, findings and conclusions expressed herein are not necessarily those of the Florida
Institute of Phosphate Research, nor does mention of company names or products constitute
endorsement by the Florida Institute of Phosphate Research.
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PERSPECTIVE
Patrick Zhang, Research Director - Beneficiation & Mining
With the depletion of the higher grade, easy-to-process Bone Valley deposits, the central
Florida phosphate industry has been forced to move into the lower grade, more
contaminated (mainly by dolomite) ore bodies from the Southern Extension. Although
extensive resources have been directed at developing processes for separating dolomite
from phosphate, no practical and economical approach is available to date, except for the
IMC-Agrico heavy media process.
In an effort to identify the most feasible technique for processing Florida dolomitic ores,
FIPR has conducted an in-house research project to evaluate five flotation separation
processes utilizing the same high dolomite pebble feed. Only one of the processes
achieved successful removal of dolomite at a seemingly reasonable cost, but with arecovery ofPZOS only about 60% from the original pebble feed.
Flotation is generally the least expensive mineral processing technique. There are two
basic approaches for separating dolomite from phosphate by flotation: floating phosphate
while depressing carbonate, or floating carbonate while depressing phosphate. The former
is restricted by the lack of carbonate depressants, and the latter is limited by poor
selectivity of anionic collectors as well as the low efficiency of phosphate depressants.
The use of microorganisms as flotation reagents is one of the new frontiers of bio-mineral
processing. Research has established that mineral surface properties can be modified
biologically. Some microorganisms may act as depressants, activators or collectors fordifferent minerals under different conditions. Thiobacillus ferrooxidans was used as
conditioning reagents for sphalerrite and galena; biosurface modification was studied in
separating pyrite from coal; mycobacterium phlei was found to be an efficient hematite
collector; and some bacteria were found to be effective flocculants for finely sized clay
suspensions.
The major goal of this project was to develop alternative, environmentally friendly, and
cost effective flotation reagents for depressing dolomite and/or promoting phosphate in
processing Florida phosphate deposits of the future.
Potential benefits of research in this field to the State of Florida and its citizens as well asthe phosphate industry may include: a) processing phosphate minerals in a more
environmentally sound manner by replacing chemicals with microorganism; b) extending
phosphate resources significantly by successful processing of the dolomitic deposits; and
c) insulating the industry against dramatic price increases due to possible shortages of
certain flotation reagents.
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ABSTRACT
The mineralogical characteristics of two Florida dolomitic phosphates were investigated by
microscopic analysis, liberation degree analysis, and BET surface. area measurement. The growth
of two bacteria,Mycobacteria phlei andBacillus licheniformis JF-2,and study on some of theirproperties in aqueous solutions were conducted through electrokinetics, contact angle, and surface
tension measurements. The experimental work on the micro-flotation of pure apatite and dolomite
and flotation of the real Florida dolomitic phosphate pebble samples were also conducted using
bacteria as both collector and depressant in anionic collector flotation. The results of the
investigations and experiments indicated that apatite in the phosphate pebble samples has good
liberation from other minerals and a very large surface area, which is the major reason for high
reagent consumption and low flotation selectivity. The cell walls of both M.phlei and B.licheniformisJF-2 include very active biosurfactants, which can remarkably reduce the surface tension of the
suspensions and increase the contact angle of minerals they adsorb onto in aqueous solution. The
results of experiments indicate thatM.phlei was markedly adsorbed on the dolomite and apatite
surfaces. The bacterium demonstrated more affinity towards dolomite than apatite, and thatB. licheniformis JF-2has even more affinity than M.phlei for adhesion onto dolomite. Flotation testsrevealed that both bacteria act as a depressant of dolomite during phosphate flotation using anionic
collectors. A flotation concentrate less than 1% MgO content can be obtained from Florida
phosphate pebble flotation.
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ACKNOWLEDGMENTS
We are grateful to Dr. Malcolm J. Hibbard, professor of Department of Geological Science,
University of Nevada Reno (UNR), for advice on mineralogical analysis and for help with obtaining
the micrographs, to Dr. Ashok M. Raichur, Research Associate of the Department of Chemical and
Metallurgical Engineering, UNR, for assistance on preparation of bacteria, and to Mr. Chan C. Lee,
undergraduate in Chemical Engineering, UNR, for his help with phosphate analysis of the samples.
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EXECUTIVE SUMMARY
This report summarizes the progress made during one and half years of work on the research
project Bacteria as Flotation Reagents for the Flotation of a Dolomitic Phosphate Rock. The
description of work done is in accordance with the proposal approved by The Florida Institute of
Phosphate Research under the Contract Number of 94-02-106R.
As Florida low dolomitic phosphate reserves become exhausted, the remaining Florida
phosphate rock contains less phosphate and significantly more dolomite. It is generally difficult to
obtain, from such materials, a phosphate concentrate containing less than the desired maximum
magnesium content of 1% MgO. Microorganisms and products derived from them can function as
modifying agents or even collectors in mineral flotation due to their selective adhesion onto specific
minerals. The microorganism adhesion onto the minerals result from their specific metal-binding
ability.
The work on using the bacteriaMycobacterium phlei andBacillus licheniformis JF-2(wholecells and products derived from cell rupture) as flotation modifiers/collectors of dolomitic Floridaphosphate rock was performed at the University of Nevada, Reno. The experimentation included
mineralogical analysis of Florida phosphate pebble samples, properties analysis of the two bacteria
in aqueous solutions, evaluation of the surface chemical nature of the microorganisms and their
derivatives and the minerals present in dolomitic Florida phosphate rocks. The experimentation was
performed through microflotation, electrokinetic, contact angle, adsorption and surface tension
studies. At the same time experimental work on the flotation of actual dolomitic Florida phosphate
rocks was performed using cells/cell products of the microorganisms both as modifiers in anionic
flotation and as flotation collectors.
The results of analysis and experimentation reveal that it is possible to use successfullymicroorganisms in Florida phosphate flotation. The three main mineralogical characteristics of
phosphate minerals in Florida dolomitic phosphate rock, cryptocrystalline character, CO2substitution, and porous structure, make it difficult to separate them from dolomite. Both bacteria
studied exhibit high, negative, zeta potentials and strongly adsorb calcium and magnesium ions in
the aqueous solutions depending on the pH values. The Florida sedimentary apatite, francolite, and
sedimentary dolomite demonstrate different electrokinetic behavior from that of crystalline apatite
and dolomite. The cells or soluble products from cells of the two microorganisms demonstrated very
high surface activity to magnesium or calcium ions in the aqueous solution. In particular,Bacilluslicheniformis JF-2 shows remarkable affinity to magnesium over calcium ions. The results of bothmicro flotation and actual sample flotation indicates that the two microorganisms can act as a
dolomite depressant but not as a collector for phosphate or dolomite. Using fatty acid or
diphosphonic acid as collector and bacteria as depressants in alkaline medium, a concentrate
containing less than 1% MgO can be obtained at 60 -70% P,O, recoveries.
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INTRODUCTION
PURPOSE OF STUDY
The United States is the largest phosphate rock producer in the world. About 30% of the
world production in 1990 was produced by the United States (Bartels and Gurr, 1994). This level
of production has continued to the present. Florida accounts for approximately 80% of U.S.
phosphate production (Harben, 1980). During the past 100 years the Florida phosphate industry has
produced high quality products having a MgO content of less than 0.5%. Phosphate reserves and
resources in Florida have the potential to continue production at a rate of about 40-55 million metric
tons/year for hundreds of years (Sandvik, 1979). The Florida phosphate rock deposits are located in
the states central and northern land pebble districts (Moudgil and Ince, 1991). The land-pebble
phosphate district of Florida, also called the Central Florida phosphate district, is the major district
where phosphate is produced. The reserves of phosphate in this district are being rapidly depleted
and future production will shift to the southern extension (Bernard and Hall, 1980). The southernreserves have a lower phosphate concentration and a severe MgO contaminant, i.e., significant
quantities of dolomitic carbonates (Lawver et al., 1982). The processing of these reserves will
require special beneficiation techniques to produce concentrates containing less than the practical
limit of about 1% MgO. Thus, for Florida phosphorus resource conservation, study on the dolomite
separation processes is a very important item.
As it is generally difficult to obtain from such materials a phosphate concentrate containing
less than the desired maximum content of 1% MgO, many attempts have been made to study the
separation processes. The past studies mainly focused on the flotation of dolomite from phosphate,
and a dozen reagents have been found to be effective in depressing phosphate. The flotation of
phosphate from dolomite is hard to perform due to the lack of the proper dolomite depressants. Sofar, only two main carbonate depressants, sodium silicate and sodium hydroxide, have been
identified (Zhang, 1994). Development of the flotation of phosphate from dolomite, however, is also
attractive because this process is considered to be simple, and would discharge the dolomite and
quartz together. In order to further exploit Florida dolomitic phosphate pebble ores, the development
of effective and economical dolomite depressants for the flotation of phosphate from dolomite
appears to be essential.
The Center for Mineral Bioprocessing and Remediation, University of Nevada-Reno, has
been engaged in the development of dolomite depressants for anionic collector flotation in recent
years. One approach has been using bacteria as depressants for dolomite.
PRELIMINARY SURVEY
Over the past years, five flotation processes have been developed to separate dolomite from
phosphate or phosphate from dolomite. They are the TVA (Tennessee Valley Authority) phosphonic
Process (Lehr and Hsieh, 1981) the UF (University of Florida) two-stage conditioning Process
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(Moudgil and Chanchani, 1985), the Alabama non-conditioning Process (Anazia and Hanna, 1987),
USBM (United States Bureau of Mines) Process (Davis, Liewellyn and Smith, 1984), and the IMC
(International Minerals and Chemical Corporation) cationic Process (Snow, 1979). These processes
require the secondary stage operation to separate the final phosphate from quartz or dolomite, and
the change of conditions from alkaline to acidic pH which lead to their complexity. Many of the
reagent systems developed are not attractive because they require high doses and are more expensive
than the conventional reagent systems.
Biomass, such as algae, fungi, and bacteria, has been long known to absorb metal ions from
aqueous solution in some environmental and metallurgical processes applications (Brierley et al.,
1986, Thompson, 1986). But there have been almost no studies and/or applications of them as
mineral flotation reagents. Only one attempt has been tried to use a kind of bacterium as flotation
collector (Smith et al., 1993).
Mycobacterium phlei is a bacterium that is not readily classified as being either gram
positive or gram negative because of its fatty acid surface. It is highly hydrophobic, and will producea hydrophobic substance, mycobactin (Van Loosdrecht, 1987). It is non-pathogenic in humans and
in all animals thus far tested and is easily and readily cultured (Laskin and Lechevalier, 1977). Not
only is Mycobacterium phlei highly hydrophobic (contact angle 65-70 degree), it also is highlynegatively charged with an isoelectric point (iep) at about pH 2.5. It should, thus, readily adhere onto
a hydrophilic mineral surface if the mineral is of low negative, neutral or positive charge. The lipids
ofM.phlei may constitute more than 50% cell dry weight. Various saturated, monosaturated, andmethyl-branched fatty acids are important components of these lipids, both in esterified form, and
as precursors of long chain mycolic acids. It is reported that in the growth ofM.phlei, fatty acidunsaturation increases with decreasing temperature, and consequently, fatty acid branching decreases
and mean chain length increases as the temperature is reduced (Suutari and Laakso, 1993).
Bacillus licheniformis JF-2, isolated from oilfield injection brine (Jenneman et al., 1983), isa gram-positive bacterium. It is able to grow and produce a very effective biosurfactant under both
aerobic and anaerobic conditions at a very wide range of temperature and in the presence of high
concentrations of salts. The surface tension of the medium in which it is cultured can be remarkably
reduced from 70 to 74 mN/m to as low as 28 mN/m due to production of an anionic biosurfactant
(Javaheri et al., 1985). Bacterial surfaces of this species are typically anionic and, therefore, interact
with metal cations leading to metal binding. The metal binding can be partially attributed to the
chemical properties of the metallic aqua ions involved. The cell walls of another gram positive
bacterium,Bacillus subtilis, containing teichoic acid-peptidoglycans, are strongly anionic and bind
metal avidly. In the case ofB. subtilis, Mg* binds much more strongly than Ca*+ (Beveridge andMurray, 1976). This example implies that the metal binding of specific bacteria species is selectivein nature, and that teichoic acid, which is present in amounts up to 70% dry weight ofB.subtiliswhen grown in phosphate- and glucose-containing medium, is responsible for Mg*+ and not Ca*binding. Bacillus licheniformis JF-2 has a wall which contains teichuronic acid in combination withteichoic acid-peptidoglycan polymers. This added complexity makes the B.licheniformis wall a goodcomparison for the B.sublitis system. Experimental results indicate that teichoic and teichuronic
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acids are the prime sites of the metal binding inB.licheniformis (Beveridge et al., 1982)
The binding characteristics of these bacteria should, thus, contribute to bacterial adhesion to
the minerals containing Ca2+ and Mg* at their surfaces. Further, it is probable that the selectivity ofmetal binding also occurs in mineral adhesion.
APPROACH AND STRATEGY
The objective of this research is to evaluate the effectiveness of two microorganisms,
Mycobacterium phlei andBacillus licheniformis JF-2 as collectors or regulators for the flotation of,Florida dolomitic phosphate rock. Data on the mineralogical characteristics of the Florida phosphate
pebble samples, and the properties of the two bacteria in aqueous solution are needed in for the
guidance of subsequent flotation tests. Flotation tests of the Florida dolomitic pebble samples were
conducted using bacteria as reagents after flotation tests of pure minerals were initiated. The final
target for flotation of Florida phosphate rock was to obtain a concentrate containing less than 1%
MgO at a reasonable recovery of phosphate values. During the reporting period, experiments suchas electrokinetic, contact angle, surface tension, and surface area measurements were conducted to
help explain the mechanisms of reactions between bacteria and minerals.
METHODOLOGY
MATERIALS AND THEIR PREPARATIONS
1. Pure Mineral Samples
Unless otherwise stated, all the pure mineral samples were obtained from Wards Natural
Science Establishment, Inc. Crystallized fluorapatite, Ca,[PO,],(F,Cl,OH), with blue-green colorand massive shape, was from Ontario, Canada. Sedimentary apatite, francolite was from Florida,
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U.S.A. Crystallized dolomite, CaMg(CO,),, excellently crystallized with large and gray cleavages,which was from Selasvann, Norway. Sedimentary dolomite was from Minnesota, U.S.A. Quartz,
with milky appearance, was from Boulder County, Colorado, USA. All the mineral samples were
first hand crushed, followed by grinding in a porcelain mortar with a pestle, and then screened to the
desired size fraction. The different size fractions were used for the various measurements and tests.
2. Florida Dolomitic Phosphate Pebbles
Two dolomitic phosphate pebble samples used in this study were obtained from the Florida
Institute of Phosphate Research and IMC Agrico Company. The P,O, content of samples wasanalyzed using the spectrophotometric method adopted by the Association of Florida Phosphate
Chemists. A Spectronic 21 UVD spectrophotometer, Bausch & Lomb Inc., USA, was used forP,O,analysis. Chemical analyses of MgO and CaO were performed using an ICP chemical analysis
system. The particle size distribution and chemical analysis of these pebble samples are shown in
Tables 2 & 3, where the content of head samples was calculated by material balance.
The pebble samples were dried, crushed and ground to -35 mesh (-500 pm). The -35+150
(-500+106 urn) mesh size fraction was used as flotation feed while the -150 (-106 urn) mesh sizefraction was removed after the wet screening. Tables 4 & 5 show the particle size and chemical
analysis results for the -35 mesh (-500 pm) fraction.
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TABLE 3: SIZE AND CHEMICAL ANALYSIS OF THE,# 2 SAMPLE
Analysis, % Distribution, %mo CaO Ins0164.28 49.14 43.5014.52 19.51 16.58
1 -12+18 1 21.3 24.18 1 2.62 1 42.83 12.39 1 22.23 14.28 1 20.59 1 18.63 11 -18+28 1 4.21 21.45 1 2.56 1 42.47 17.54 I 3.90
17.79 ( 2.33 1 42.52 32.66 1 5.35ITotal I 100.00 23.17 1 3.91 1 40.87 14.16 1 100.0TABLE 4: SIZE AND CHEMICAL ANALYSIS OF THE # 1 SAMPLE AFTER GROUND
An; lysis, % Distribution, %ize, wt.mesh % PA I MU CaO I Ins01 W5 MN CaO Ins0130.38 35.10 31.3010.85 13.37 18.059.35 11.99 14.956.46 7.72 9.96
43.02 13.91 37.1642.09 20.61 13.2742.83 19.37 11.7642.47 19.87 7.61
-150+200 1 4.29 24.05 1 1.74 42.52 1 14.60 ~ 4.42 3.38 ) 4.32 1 4.0921.19 1 3.08 40.87 1 11.67 25.78 39.58 I 27.5 1 1 21.6623.34 1 2.21 42.20 1 15.30 100.0 ~100.0 100.0 100.0
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Except for the -200 (-75 pm) mesh fractions, which are higher in MgO in both # 1 and # 2ground samples and lower in insoluble material, the size fractions of the ground sample do not show
significant differences in chemical and mineral compositions. After the -150 (-106 pm) meshfractions were removed, the # 1 flotation feed contained 24.20 % P,O,, 1.87 % MgO, 42.73 % CaOand 16.88 % insoluble matter, and the # 2 flotation feed contained 24.27 % P20s, 3.09 % MgO,40.74 % CaO and 15.8 % insoluble matter, about the same composition as the original pebble
samples. The phosphate pebbles in samples were observed to be rounded black or gray pelleted
grains, containing about 27-32 % P,O,, 10% insoluble matter and less than 0.2 % MgO. Thedolomite and other carbonates occurred as liberated white, yellow or gray fragments, usually with
sharp edges, which contained less than 3% P2O5, 10-15 % MgO and less than 5% insoluble matter.
3. Bacteria
Mycobacterium phleiThe freeze-dried culture of microorganism,M. phlei, was first transferred to a rehydration
medium (both supplied by Carolina Biological Supply Company) and incubated at 35C for 48
hours. The M. phlei was grown in a culture medium consisting of the following: 10 g/l D-(+)-glucose, 1 g/l beef extract, 1 g/l yeast extract, and 2 g/l enzymatic hydrolyzed casein. The above
materials were supplied by Sigma Chemical Company, St. Louis, MO. The culture medium was
sterilized at 121C for 25 minutes in a Spectroline Model 750 autoclave. The sterilized culture
medium was cooled and the incubated bacteria were inoculated into the medium. Culturing was
carried out in 250 mL flasks continuously shaken at 150 rpm at 35C in a G24 environmental
incubator shaker (New Brunswick Scientific Co. Inc., NJ, USA). After about 30 hours of culturing,
the M. phlei suspension was centrifuged using an IEC Model K centrifuger (International EquipmentCompany, MS, USA), then filtered using a 0.45 pm Millipore filter paper, washed twice and then
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resuspended in distilled water. Sterilized glassware and distilled water were used throughout the
investigation. The concentration of bacteria in aqueous solution was obtained by filtering a certain
amount of bacterial suspension and weighing the dried residue on the filter. However, in the
adsorption measurements, the cell accounting method was used and then converted to ppm dry
weight.
The soluble fraction of a bacterium is usually about 40% of the total cell weight. Study of
the properties of the soluble fraction helps elucidate the mechanism of reaction of a bacterium with
mineral particles. The soluble fraction ofM.phlei was obtained using an ultrasonic vibration method.About 100 ml ofM.phlei whole cell suspension (concentration about 2,000 ppm) was sonicated(Branson Sonic Power Co., CT, USA) to release the soluble fraction in the bacteria. The soluble .
fraction ofM.phlei was separated from the solid cell mass by centrifugation and filtration. Theseparate suspensions of the whole cells, cell wall materials and soluble fractions were stored in the
refrigerator at most for a week before use. After this time period the suspensions appeared to
deteriorate. However,M.phlei in rehydration medium or in culturing medium can be kept in the
refrigerator for months without evidence of decay.M.phlei in culturing medium saved in this waycan be used to produce the second or third generation of bacteria. Although it appeared that suchsubsequent generation of bacteria had the same characteristics as the first, in the present investigation
only the first generation was used.
Bacillus licheniformis JF-2The freeze-dried culture of the microorganism,Bacillus licheniformis JF-2, ATCC 39307,
was first transferred to a medium including 10.0 g of sucrose, 50.0 g of NaCl, 1.0 g of(NH,),SO,,0.25 g ofMgSO,, 10.6 g ofK,HPO,, 5.3 g ofKH*PO,, and 10.0 ml of trace salts solution in the 1.0liter of deionized water. The trace salt solution consists of 1,000 ppm ofNa,EDTA, 3,000 ppm ofMnSO,*H,O, 100 ppm ofFeSO,.7H,O, 100 ppm ofCaCl,.H,O, 100 ppm ofCoCl,*GH,O, 100 ppmofZnSO,*7H,O, 10 ppm ofCuSO,*SH,O, 10 ppm ofA1K(S0,),.12H20, 10 ppm ofH,BO,, and 10
ppm ofNa,Mo0,*2H20. The culture medium was sterilized at 121C for 25 minutes in a SpectrolineModel 750 autoclave. The sterilized culture medium was cooled and the Bacillus licheniformis JF-2was inoculated into the medium. Culturing was carried out in 250 mL flasks continuously shaken
at 150 rpm at 40C in a G24 environmental incubator shaker (New Brunswick Scientific Co. Inc.,
NJ, USA). After about 48 hours of culturing, Bacillus licheniformis JF-2 suspensions werecentrifuged using an IEC Model K centrifuger (International Equipment Company, MS, USA). Then
the residues were suspended in deionized water. Sterilized glassware and distilled water were used
throughout the investigation.
The production of the soluble fraction ofB. licheniformis JF-2 was similar to that ofM.phlei.The only difference in this case was the use of 0.2 pm filtration paper instead of 0.45 pm filtration
paper.
4. Chemicals
Purified sodium oleate, obtained from Fisher Scientific Co., was used as collector in the
micro flotation experiments. In addition, a new phosphate collector, diphosphonic acid, whose main
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compounds are disodium salt of 1-hydroxyoctylidene 1, 1-diphosphonic acid, DPA, synthesized by
the Center of Mineral Bioprocessing and Remediation, University of Nevada Reno, was also used
in flotation experiments. ACS certified grade KOH, HNO,, Na,CO,, and Na,SiO, were used for pHadjustment or pulp modification in measurements, micro flotation and actual sample flotation. Tall
oil, No. 154 (obtained from Westvaco Chemicals Co.) plus kerosene was used as collector mixture
in the bench scale flotation tests. All measurements and micro flotation experiments with the pure
mineral samples were conducted using deionized water with more than 17 MQcm resistivity value.Tap water was employed for bench scale flotation tests.
EXPERIMENTAL METHODS AND PROCEDURES
1. Mineralogical Measurements for Florida Dolomitic Pebble Samples
For understanding the reaction between bacteria/reagents and minerals, mineralogical
measurements were conducted. Included were XRD (X-Ray Diffraction) analysis using a XRG 3 100
X-ray diffraction meter (Philips Co.) and Jade X-ray Pattern Processing software (Materials Data,
Inc.), microscopic analysis of Florida phosphate pebble samples to evaluate the relationships amongphosphate minerals and associated minerals, and analysis of the liberation degree for phosphate
minerals, carbonates, and silicates after grinding. The surface areas of pebble samples also were
measured using the BET method.
2. Electrokinetic Measurements for Minerals and/with Bacteria
Electrokinetic potentials of mineral samples and bacterial suspensions were measured by
electrophoresis using a Laser Zee Meter (Model 501, Pen Ken Inc., USA). In the experimentation
5 mg samples of minerals, of -38 pm (-400 mesh) size, were aged overnight in 50 ml of deionizedwater with 10
-3mol/l KNO,. The pH of suspension was adjusted 3 minutes before making the
measurements. In the case of bacteria, 200 pl of about 2,000 ppm of bacteria suspension was usedto make the same 50 ml of suspension. When studying the minerals with the soluble fraction, 5 mgof a mineral sample was put into the suspension with the soluble bacterial fraction at a given
concentration. All experiments were conducted at the temperature of about 22&2C.3. Surface Tension Measurements for Soluble Bacteria
Surface tension measurements, by the du Nouy ring method, were conducted using a Model
215 Autotensiomat Surface Tension Analyzer (Fisher Scientific Company, USA). A platinum-
iridium ring, with 53.79 of R/r ratio and 6.005 cm of mean circumference, was used. The variations
of the surface tension for the soluble fractions of bacteria were investigated as a function of pH and
concentration of the soluble fraction of bacteria. The apparent surface tension was converted into the
absolute surface tension by using a correction factor, F, which is given by: y = y,FF = 0.725 + (O.O1425y$(2r~R)~p)* - 1.679r/R + 0.04534
where y is absolute surface tension, ya is the apparent surface tension, R is the radius of the ring,r is the radius of the wire of the ring, and is the density of water.
4. Adhesion Measurements
Adhesion measurements were performed using one gram of mineral particles in 100 ml of
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deionized water. The mixture of minerals and water was put into a cone beaker and shaken in a G24
environmental incubator shaker for five minutes after pH was adjusted. After shaking, the mineral
particles were allowed to settle for two minutes and the supernatant was taken out for measuring the
remaining bacterial concentration. The measurement of bacterial concentration in the supernatant
was completed by cell counting. The number of the cells counted was then converted to weight
percentage (ppm).
5. Contact Angle Measurements for Minerals with Soluble Bacteria
Contact angle measurements were conducted using an A-100 Contact Angle Goniometer
(Rame-Hart Inc., USA). Mineral samples of approximate dimensions 2 x 2 x 1.5 cm were molded
with an epoxy resin. The surface of each sample was polished using 1,000 and 4,000 grits SiC
polishing paper followed by fine polishing with 0.05 pm alumina suspensions. The samples wererubbed over the wet polishing cloth, and washed with distilled water before each measurement.
Contact angles of pure apatite and dolomite were measured using the captive bubble technique
(Misra, Miller and Song, 1984). In this method an air/mineral/water perimeter of contact was
produced at a horizontal mineral surface. This technique involves immersing the freshly polishedsample into an optical glass cell containing water and then attaching an air bubble to the mineral
surface. The holder was raised to a fixed distance until the area of contact between the bubble and
a solid surface was seen to contract. The holder was then gently tapped to avoid any slackness in the
bubble. The angle at each side of the bubble was noted, and the five measurements were made for
each condition. All the measurements were made after three minutes under the conditions of the test
although no significant variation was observed for extended time. The cell was cleaned with chromic
acid and rinsed with deionized water for each experiment to prevent the samples from contamination.
All measurements were carried out at 22*2C.6. Pure Mineral Flotation
The apatite and dolomite flotation experiments were performed using a Hallimond tube. Incarrying out the micro flotation experiments, three grams of the ground mineral (-200+400 or -
100+200 mesh) were added to 150 ml of deionized water and conditioned for 3 minutes in a beaker.
The pH was adjusted to the desired value with HNO, and KOH. Bacteria were added andconditioned for 5 minutes before collectors were added and conditioned for three minutes. All
contents were transferred to the Hallimond tube and conditioned for two more minutes. In the case
of flotation of sedimentary phosphate and dolomite, a shorter Hallimond tube and 100 ml of water
were used to float concentrates, and 10 ml of water were used to condition in a beak. Flotation was
completed in 3 minutes. Pure mineral flotation tests were divided into three categories, single
mineral flotation, 1:1 mixed mineral flotation, and 2:1 mixed mineral flotation.
7. Florida Dolomitic Phosphate Pebble Flotation
In bench scale tests, a 200 g sample (dry basis) was conditioned for 5 minutes in 200 ml of
tap water. A Denver D-12 flotation machine (Denver Equipment Co., CO, USA) was used. Agitation
speed was set at approximately 1,000 rpm. Bacteria were added and conditioned for 7 minutes after
Na,CO, and/orNa,SiO, were added. After collectors were added and agitation, the pulp was dilutedto 40 wt% solid with tap water, and phosphate values were recovered as froth products.
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RESULTS
MINERALOGICAL MEASUREMENTS
Phosphate most commonly is derived from the mineral apatite, which is chemically describedas Ca,(F,Cl,OH)(PO,),. Carbonate, CO3, can partly substitute for PO4 forming carbonate apatitecalled francolite. On the other hand, cellophane is a name given to cryptocrystalline apatite found
in phosphate rock in fossil form (Bartels and Gurr, 1994). The apatite of all of the phosphate deposits
of Florida is francolite (carbonate fluorapatite) (Cathcart, 1989) and/or cellophane. Both
characteristics of carbonate substitution and cryptocrystalline structure make it much more difficult
to separate phosphate values from gangue material containing a high concentration of magnesium.
Two dolomitic phosphate pebble samples, obtained from The Florida Institute of Phosphate
Research and The IMC Agrico Company, were used in this study.
1. Carbonate ContentAll of the apatite from Florida phosphate contains some carbonate. The substitution of
carbonate for phosphate is usually expressed as the content of CO,. The CO2 content of the apatite
is difficult to measure because of included very small particles of calcite and dolomite in an apatite
particle. An investigation has demonstrated that the measurement of an x-ray diffraction pattern, of
the difference in degrees 28, of the 410 and 004 peaks of francolite could be used to estimate its CO 2content, and therefore, the approximate degree of substitution (Gulbrandsen, 1970). According to
the scatter diagram, which shows the relationship of CO2 content and A28, the difference ofdiffraction angles of the 410 and 004 crystal plans, the samples 1 and 2 contain about 3.5% and 4%
CO2, corresponding to theA28 value of 1.3 and 1.2 respectively (Figures 1 and 2).2. Optical Microscopy ObservationsThe shape of phosphate intra clusters is very distinctive. Within each size fraction, most
phosphate grains of the sample are highly rounded (Figure 3), although some of them are irregular
shaped (Figure 4). Most gangue minerals, such as carbonate minerals and quartz, are rounded or
bounded by a phosphate matrix. It is believed that the different colors of phosphate matrices are
caused by differing iron concentration. The colors vary from deep dark to brown. The dark color
represents a greater iron content. Some phosphorite of one color were wrapped by the others of
different colors.
The inclusions in apatite are very important economically since the inclusions are to contain
magnesium. The magnesium in the apatite structure cannot be removed by beneficiation. From the
photographs taken under the polarized microscope, most of the dolomite exists as aggregation of
microcrystalline materials (Figure 5). Their shapes are mostly irregular. They contact phosphate
matrices with an instinct boundary. However, some fine crystalline dolomite is also found in
phosphate matrices.
Quartz is the major part of insoluble materials in the ore samples. Most quartz, exhibiting an
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angular shape and a size of 0.1 to 0.5 mm, are mounted in phosphate matrixes (Figure 6). Some of
them are believed to be less than 5 pm in size (Figure 7). This quartz is very hard to separate fromphosphate by mechanical methods. There is also some macrocrystalline quartz to contact with
phosphorite which can be easily separated under grinding.
3. Grinding and LiberationAfter grinding, the pebble phosphate samples demonstrate a good liberation of the associated
minerals. The degree of liberation of phosphate is estimated as much as 95% in the each size range
of -35+48 (-425+300 pm), -48+65 (-300+212 pm), -65+100 (-212+150 pm), -100+150 (-150+106p), -150+200 (-106+75 pm), and -200 (75 pm) mesh. It is seen that most quartz has been liberatedfrom phosphate matrixes except of very fine dispersed grains of quartz (Figures 8 and 10). Dolomite
brakes as very fine particles, which lead a higher MgO content, 3.08% and 7.98%, in the -200 mesh
(75 pm) fraction of the samples 1 and 2, compared to the MgO content in the original samples,2.21% and 4.07%.
4. Specific Surface Area
An important factor affecting mineral flotation is the specific surface area of minerals. Alarger surface area will lead to greater reagent consumption. Also, like the effect of fine particle size,
the larger specific surface area will cause the loss of selectivity. Data on the specific surface area of
the two Florida pebble samples were obtained using nitrogen adsorption. The surface area of
crystallized apatite was also measured for comparison. From the data listed in Table 6, it is seen that
the specific surface area of francolite is much more than that of crystalline apatite. The difference
in surface areas for the finest size (-400 mesh) and the coarsest size (-65+100 mesh) of the francolite
is about double. The difference between sedimentary and crystalline apatite is more than ten times.
Thus, the Florida phosphate minerals contain considerable porosity.
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FIGURE 3: ROUNDED PHOSPHATE, WRAPPED QUARTZ, AND DOUBLE ANDDOUBLE PHOSPHATE (POLARIZED, FIELD WIDTH 3.5 MM)
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FIGURE 4: IRREGULAR SHAPE OF PHOSPHATE(35X48 MESH, FIELD WIDTH 0.8 MM)
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FIGURE 5: AGGREGATION OF DOLOMITE IN FLORIDA PHOSPHATE PEBBLE( DOLOMITE AND QUARTZ CLUSTER, FIELD WIDTH 0.8 MM)
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FIGURE 6: PHOSPHATE WITH QUARTZ INCLUSIONS(POLARIZED, FIELD WIDTH 3.5 MM)
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FIGURE 7: PHOSPHATE WITH TINY QUARTZ GRAINS INCLUSIONS(POLARIZED, FIELD WIDTH 3.5 MM)
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FIGURE 8: FLORIDA PHOSPHATE PEBBLE AFTER GROUND(35X48 MESH, FIELD WIDTH 0.8 MM)
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FICURE9:FLORIDAPHOSPHATEPEBBLEAFTERCROU1\1:D(65X100 MESH, FIELD WIDTH 0.8 MM)
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FIGURE 10: FLORIDA PHOSPHATE PEBBLE AFTER GROUND(100x150 MESH, FIELD WIDTH 0.8 MM)
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liberation of particles, but because of the large surface area of the phosphate minerals, carbonate
substitution in apatite and the crypocrystalline structure of the minerals.
ELECTROKINETIC MEASUREMENTS
The zeta potential of francolite and sedimentary dolomite as a function of pH, with andwithout lOA and lo5 M Ca(II) or Mg(II) are shown in Figures 11 through 14. In both cases, additionof10m4 M of Ca(II) or Mg(II) caused the isoelectric point (IEP) of the two mineral samples to shiftto more basic values. The electrokinetic properties of both francolite and sedimentary dolomite are
quite different from that of crystallized apatite and dolomite. In the case of crystallized apatite and
dolomite, IEPs of two minerals are at about pH 5.5 and 7 respectively. But the IEPs of both
francolite and sedimentary dolomite are below pH 2, which is rather comparable to the IEPs of
many silicate minerals. However, unlike the variation of zeta potential with increasing pH for
silicates, the zeta potential of the two minerals display an increase in zeta potential at moderately
alkaline pH values. Probably dissolved cations from the minerals readsorb again as pH is increased.
When 10m3 M Ca(II) was added, the zeta potential of francolite remains positive regardless of pH.The experimental data implies that calcium and magnesium species can adsorb onto both themineral surfaces over the whole pH range. The sharp increase of adsorption of cations at higher pH
is due to the adsorption of calcium and magnesium hydroxy complexes. A significant phenomenon
is that the zeta potential of sedimentary dolomite drops and rises as pH is increased.
On the other hand, the electrokinetic behavior ofM.phlei, shown in Figures 15 and 16, issomewhat similar to that of quartz and francolite in aqueous solution. At lower pH values, calcium
species adsorb more onto the bacterium than magnesium species. Above pH 11, magnesium species
adsorbed onto bacteria give rise to the much more positive potentials. The results of electrokinetic
measurements forM.phlei indicate that calcium and magnesium ion species can absorb onto M.phlei,and adsorption is dependent on pH and concentration of calcium and magnesium species. The
electrokinetic behavior ofB. licheniformis JF-2 in aqueous solutions was similar to that ofM.phlei(Figures 17 and 18). However, its zeta potential values are about 10 mV more negative than that of
M.phlei, especially over the basic range. This indicates that the cell walls ofB.licheniformis JF-2 aremore negatively charged than the cell wallsM.phlei.
The Figures 1.9 and 20 show zeta potentials of both minerals as a function of pH in the
presence and absence of the water soluble fraction derived from M.phlei and B.licheniformis JF-2.Addition of the water soluble fractions greatly decreased the zeta potentials on the minerals. Thus,
the water soluble fraction adsorbed onto mineral surfaces seems to be responsible for the decreasing
zeta potentials. The water soluble fraction ofB.licheniformis JF-2 led to more negative zeta
potentials of minerals than that ofM.phlei.
SURFACE TENSION MEASUREMENTS
The water soluble fractions of both M.phlei and B.licheniformis JF-2 at concentrations of 10ppm and greater decreases the surface tension of water (Figure 21). Maximum surface tension
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depression occurs at a soluble M.phlei concentration of about 1,000 ppm, and at a solubleB. licheniformis JF-2 concentration of about 400 ppm. Also, the surface tension of solubleM.phleiincreases rapidly with the increase in pH (Figure 22). These phenomena seem to be attributed to the
characteristics of soluble compounds of the cell walls from bacteria. Maybe polar groups with the
carboxyl, hydroxyl and phosphate functional groups at the cell walls of bacteria have changed when
pH increases.
ADHESION MEASUREMENTS
The Figures 23 through 26 show the experimental results of adhesion of two bacteria on both
dolomite and phosphate minerals. The adhesion ofM.phlei to dolomite happened at a very low levelof the bacteria concentration. The saturated adhesion amount was 7 - 8 mg/g dolomite when the
bacterial concentration was more than 300 ppm. ForB. licheniformis JF-2, the saturated adhesion ofbacteria onto apatite, at 400 ppm of bacterial concentration, was 5- 6 mg/l (Figure 24).
Francolite and sedimentary dolomite behaved differently. Concentration at saturated adhesion
dramatically increased to about 2,000 ppm in the case of sedimentary dolomite, and to 5,000 ppmin the case of francolite. But the same adhesion comparative properties as crystallized minerals, i.e.,
B. licheniformis JF-2 overM.phlei on dolomite, and less M.phlei on phosphate, were obtained.
CONTACT ANGLE MEASUREMENTS
The contact angles on dolomite and apatite increase with concentration of solubleM.phleiandB.licheniformis JF-2 (Figure 27). It is, thus, indicated that while bacteria decrease the surfacetension of the solution/air interface, they also decrease the interfacial tension of the air/mineral
interface and leads to a larger contact angle. It is evident that both M.phlei and B. licheniformis JF-2adhere onto the mineral surfaces, and that the increase of contact angles of the minerals is due to the
hydrophobic property of the soluble fractions of bacteria. Figure 28 demonstrates the dependence
of contact angles of both minerals on pH in the presence ofM.phlei.
PURE MINERAL FLOTATION
1. Single Mineral Flotation with M.phlei as Collector
The Figure 29 shows the flotation of -200+400 (-75+38 pm) mesh apatite and dolomite asa function ofM.phlei concentration at pH 8.8 and 9.5. However, if particle size is greater than 200mesh there is no significant flotation of either mineral. Quartz cannot be floated even when the -
200+400 mesh sample was used. The similar results usingB.licheniformis JF-2 as collector werealso obtained.
2. Single Mineral Flotation with Bacteria as Depressants
When larger size mineral particles (-100+200 mesh, -150+75 pm) are floated using otheranionic collectors, both M.phlei andB. licheniformis JF-2acts as depressants. Two collectors, sodiumoleate and diphosphonic acid, were studied, and their collecting abilities as a function of pH are
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shown Figure 30. It is seen that diphosphonic acid, DPA, shows different collecting characteristics
from sodium oleate for the four minerals. At a given pH value, the collecting ability of DPA for
apatite is more than for dolomite, whether crystallized or sedimentary minerals. However, the
collecting ability of sodium oleate for phosphates is less than for dolomites.
The Tables 7 and 8 show flotation results for the two minerals using sodium oleate ascollector andM.phlei as depressant. The results indicate thatM.phlei is a strong depressant for
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containing minerals when oleate is used as collector. But depression of dolomite is much stronger
than that of apatite. At pH 9.7, only 10 ppm dosage ofM.phlei can lead to about 30% depression ofdolomite and 15% depression of apatite. When 50 ppm M.phlei was used, the floated fraction ofdolomite flotation decreased by 80% and that of apatite flotation by 50% at pH 9.7. At pH 11.2, the
depression effect ofM.phlei decreased for both minerals, although the amount of dolomite depressed
was still more than that of apatite. When DPA was used as flotation reagent,M.phleiperforms thesame depressing function for dolomite and apatite.
The Figure 31 shows the depressing effect of two microorganisms for dolomite flotation
when sodium oleate was used as collector. Bacteria successful depressed flotation of dolomite within
very wide pH range. At the basic pH range, say over pH 10, the flotation recovery of dolomite
deceased mainly due to competition of OK cations but not bacteria. B.licheniformis JF-2demonstrated an advantage overM.phlei in depressing, which is in correspondence with the resultsof electrokinetic, adsorption, and surface tension experiments. Figure 32 shows the depressing effect
of two microorganisms for apatite flotation when sodium oleate was used as collector. The
depressing effect of microorganisms on apatite was less than on dolomite. When DPA was used as
collector, this general trend of difference was still kept, but depressing effect of bacteria on dolomite
was better because of the good selectivity of DPA between two minerals (Figures 33 and 34).
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>E
l without Mg(NO,),w10.0 - A with lOA M Mg(NO,),with low3 M Mg(NO,),
-10.0 -
-30.0 -
0
-50.0' I I I I I I I 1 I I I I0 2 4 6 8 IO 12
PHFIGURE 12: ZETA POTENTIAL OF FRANCOLITE AS A FUNCTION
OF PH WITH AND WITHOUT Mg(NO,),
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20.0 1 I I I I I I I I I I I I It a without Ca(NO&10.0 t-
0 with IO4 M Ca(NO&n with 1 Om3M Ca(NO,),
-30.0 a-40.0 v
-50.0 I-60.0 I I I I I I I I I I I I I I
0 2 4 6 8 10 12 14PH
FIGURE 13: ZETA POTENTIAL OF SEDIMENTARY DOLOMITE ASA FUNCTION OF PH WITH AND WITHOUT Ca(NO&
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20.0 I I I I I I I I I I I I I0 without Mg(NO&
10.0 - * O with 10e4 M Mg(NO&n with 10e3 M Mg(NO,),0.0 -
-10.0 -
-20.0 -
-30.0 -
-40.0 -
-50.0 -
-60.0 - I I I I I I I I I I I I I0 2 4 6 .8 IO, 12 14
PHFIGURE 14: ZETA POTENTIAL OF SF$DIMENTARY DOLOMITE AS
A FUNCTION OF PH WITH AND WITHOUT Mg(NO,),
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20.0
10.0
>E 0.0.cog-5 -10.0a.m
-55 -20.0
-30.0
-40.0
I I I I I I I I I I I I I
.e without Ca(NO,),0 with lOA M Ca(NO,),n . with 10s3 M Ca(NO,),
.
2
.
0 2 4 6 8 IO 12 14PH
FIGURE 15: ZETA POTENTIAL OF Mphlei AS A FUNCTIONOF PH WITH AND WITHOUT Ca(NO&
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10.0 I I I I I I I I I I I I I
0.0 -
-10.0 -
-20.0 -
-30.0 -
-40.0 -
-50.0 -
l without Ca(NO&0 with IO4 M Ca(NO&w with 10D3 M Ca(NO&
I I I I I I I I I I I I I-60.0' I0 2 4 6 8 10 12 14PH
FIGURE 17: ZETA POTENTIAL OF B. Zicheniformis JF-2 AS AFUNCTION OF PH WITH AND WITHOUT Ca(NO&
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I u.uI l without Mg(NO,),
00.0 - with IO4 M Mg(NO,),w with 10e3 M Mg(NO,),
-10.0 - l
-20.0 -
-30.0 - -v\ l
-40.0 -
-50.0 -
-60.0 I I I I I I I I I I I I I0 2 4 6 8 10 12 14PH
FIGURE 18: ZETA POTENTIAL OF B. licheniformis JF-2 AS AFUNCTION OF PH WITH AND WITHOUT M&NO,),
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0.0 I I I l I I I I I I I I Iwithout bacteria0
2.with 200 ppm soluble M.ph/eiwith 200 ppm soluble B./icheniformis JF-2
0 2 4 6 8 10 12PH
FIGURE 19: ZETA POTENTIAL OF FRANCOLITE AS A FUNCTIONOF PH WITH AND WITHOUT SOLUBLE BACTERIA
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I I I I I I I I I I I I I. a without bacteria\ 0 with 200 ppm soluble M.ph/ei
0 2 4 6 8 10 12PH
FIGURE20:ZETAPOTENTIALOFSEDIMENTARYDOLOMITEASAFUNCTI~NOFPHWITHANDWITH~UTS~LUBLEBA~TERIA
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80.0
70.0
60.0
50.0
40.0
30.0 0 I 2 3 4 5 6 7Ln(concentration), ppm
FIGURE 21: SURFACE TENSION OF WATER AS A FUNCTION OFCONCENTRATION OF SOLUBLE BACTERIA
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80.0
65.0
60.0 0 2 4 6 8 IO 12 14PH
FIGURE 22: SURFACE TENSION OF SOLUBLE Mphlei SUSPENSION(50 ppm) AS A FUNCTION OF PH
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10.0 I 1 I I I I I I I I I I I I I
8.0 - * 00
a with Mphlei0 with B./icheniformis JF-2
I0 2 4 6 8 10 12 14 16
Concentration of bacteria, x10* ppmFIGURE 23: AMOUNT OF BACTERIA ADHERING ON DOLOMITE AS
A FUCTION OF THEIR CONCENTRATION AT PH 9
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10.0 I I I I I I I I I I I I I I I
8.0
6.0
4.0
2.c
0.c
I -
I -
with M.phleiwith B. iicheniformis J F-2
0 2 4 6 8 10 12 14 16Concentration of bacteria, x10* ppm
FIGURE 24: AMOUNT OF BACTERIA ADHERING ON APATITE ASA FUCTION OF THEIR CONCENTRATION AT PH 9
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60.0
~ 50.03E-iz 40.0ii5
5 30.0z2E6 20.0
10.0
0.0
I I I I I I I I I I I I I I I I I I I
0 with M.phleiwith Blicheniformis JF-2
0 IO 20 30 40 50 60 70 80 90 100Concentration of bacteria, x10* ppm
FIGURE 25: AMOUNT OF BACTERIA ADHERING ON SEDIMENTARY DOLOMITEAS A FUCTION OF THEIR CONCENTRATION AT PH 9
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60.0
~ 50.032E-ii!- 40.0'La,% 30.0EsEQ, 20.0
10.0
0.0
I I I I I I,, 1 I I I I I I I I I I I I
with f3.licheniformi.s JF-2ith f3.licheniformi.s JF-2
0 10 20 30 40 50 60 70 80 90 100Concentration of bacteria, x10* ppm
FIGURE 26: AMOUNT OF BACTERIA ADHERING ON FRANCOLITEAS A FUCTION OF THEIR CONCENTRATION AT PH 9
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I I I 11111~I 11111~ I I ll1lll~ll1lll~ I I llllrllllrl apatite with M.phfeipatite with M.phfei0 dolomite with M.ph/eiolomite with M.ph/eim apatite with BJicheniformis JF-2patite with BJicheniformis JF-2cll dolomite with BJicheniformis JF-2olomite with BJicheniformis JF-2
75.0 -
65.0 -
45.0 -
35.0 t I I l111111 I I IIIIIIO0 IO IO2
Concentration of soluble bacteriaFIGURE 27: EFFECT OF SOLUBLE FRACTION OF BACTERIA
ON CONTACT ANGLE OF MINERALS
IO3
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75.0
65.0
55.0
45.0
35.0 2
I I I0 apatite with M.phlei0 dolomite with M.phlein aDatite with B./icheniformis JF-2
I I I0 apatite with M.phlei0 dolomite with M.phlein apatite with B./icheniformis JF-2dolomite with BJicheniformis JF-2
4 6 8 10Concentration of soluble bacteria
12
FIGURE 28: CONTACT ANGLE OF MINERALS AS A FUNCTIONOF 350 ppm SOLUBLE FRACTION OF BACTERIA
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90.0 I) I I111111( I I 111111~ I I Illlll~ I I111111~l apatite with whole cell, pH 8.8
80.0 - 0 dolomite with whole cell , pH 9.5I apatite with soluble part, pH 8.8cl dolomite with soluble part, pH 9.5
70.0 -
60.0 -
50.0 -
40.0 -
30.0 -
20.0 -
10.0 II I I l1lllll I I I111111 I I I llllll I I IIIrlrl10-1.0 l()O.O 1 O'*O I 02.0 1 03-0M.ph/ei concentration, ppm
FIGURE 29: FLOTATION RESULTS OF 200x400 MESH MINERALSAS A FUCTION OF Mphlei CONCENTRATION
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IO -IO'
I I I I II II1 I I )2 3 4 5 6 7 8 9102 2 3
Collector concentration, mg/l0 apatite with DPA, pH 8.5n dolomite with DPA, pH 8.5A cellophane with DPA, pH 8.0+ sedimentary dolomite with DPA, pH 8.00 apatite with oleate, pH 9.8q dolomite with oleate, pH 9.8A cellophane with oleate, pH IO0 sedimentary dolomite with oleate, pH 10
FIGURE 30: FLOTATION OF MINEXALS AS A FUNCTIONOF COLLECTOR CONCENTRATION
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100.0
80.0sx5-2 60.0a0Y-c0.-%
40.0It
20.0
0.0
- a without bacteria0 with 50 ppm M.ph/ein with 50 ppm Blicheniformis JF-2
I I I I I
6 8 10PH12
FIGURE 31: FLOTATION OF DOLOMITE AS A FUNCTIONOF PH WITH 40 MG/L SODIUM OLEATE
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80.0
60.0
40.0
0 with 50 ppm M.phlein with 50 ppm Bhheniformis JF-2e without bacteria0 with 50 ppm M.phlein with 50 ppm Bhheniformis JF-2
I I I I I6 8 IO 12
,. PHFIGURE 32: FLOTATION OF APATITE AS A FUNCTION
OF PH WITH 80 MG/L SODIUM OLEATE
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60.0
60.0s-lif5u- 40.05.-
HIL20.0
0.0
1 I I I 1
0 without bacteriawith 50 ppm M.phleiwith 50 ppm B.licheniformis JF-2
FIGURE 33: FLOTATION OF DOLOMITlil AS A FUNCTIONOF PH WITH 50 MG/L DIPHOSPHONIC ACID
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80.0sz5rc 60.0E.-
2LL
40.0 0 without bacteria0 with 50 ppm M.phlein with 50 ppm f3.licheniformi.s JF-2
20.0 I I I I I I I I I2 4 6 8 IO 12PHFIGURE 34: FLOTATION OF APATITE AS A FUNCTION
OF PH WITH 50 MG/L DIPHOSPHONIC ACID
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3. Mixed Mineral Flotation with Bacteria as Depressants
The results of 1:1 dolomite/apatite mixed mineral flotation with M.phlei are shown in Table8. It can be seen, from the data, thatM.phlei acted as depressant for dolomite and also for apatite.Addition ofM.phlei, however, led to a greater decrease in recovery of MgO than of P
2O
5when oleate
was used as collector. Note that 50 ppmM.phlei decreased recovery of P2O5 by about 35%, butrecovery of dolomite by about 50%, and increased the grade of P2O5 in the float at pH 9.5. Also, at
lower and higher pH values, there are decreased MgO and increasedP,O, recoveries. When DPAwas used as collector, best results were obtained at pH 7. When 50 ppmM.phlei was added, thegrade of P,O, in the froth product increased from 29.39% to 33.26% and MgO decreased from 5.4%to 3.41%, with a decrease ofP,O, recovery by 18.75% and a decrease of MgO recovery by 54.70%,when 50 ppmM.phlei was added. The results of 1:1 mixed mineral flotation indicate thatM.phleican more markedly depress dolomite than apatite. A decrease of MgO and increase ofP,O, in theflotation concentrate can be obtained usingM.phlei as depressant at a sacrifice in recovery of P2O5.Also the results again show that DPA has better collecting selectivity for apatite flotation than
sodium oleate.
The results of 2:1 dolomite/apatite mixed mineral flotation with both M.phlei andB.licheniformis JF-2 are shown in Table 10. The results show thatB.licheniformis JF-2 was betterthanM.phlei in depressing dolomite, regardless of the collector used. A concentrate, with a gradeof 37% P,O,, less than 1% MgO, and the recovery of 95%, was obtained when using DPA ascollector without any bacterium as depressant at pH 6.8. Addition of bacteria decreased the recovery
ofP,O, and increased the grade ofP,O, in the concentrate at a lower MgO content.The results of Flotation of 2:1 mixture of Florida francolite and Minnesota sedimentary
dolomite were poorer than that of 2:1 mixture of crystalline apatite and dolomite. It is seen, from the
Table 11, that oleate flotation did not reach the target of the proper level of bothP,O, and MgO. Useof DPA improved the results, and a concentrate containing 29% P,O, and nearly 1% MgO wasobtained at a recovery of 63% P,O,.
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TABLE 9: FLOTATION RESULTS OF 1:l MIXTURE OF APATITE AND DOLOMITEWITH AND WITHOUT MPHLEICollector Mphlei pH Item Wt, Analysis, % Distribution, %
%reagent mg/l mgll p&4 mo p*05 ME30oleate 40 0 9.5 float 86.65 20.05 10.24 87.27 86.06
sink 13.35 19.03 10.77 12.76 13.94oleate 40 50 9.5 float 40.85 22.19 9.13 45.52 36.18
sink 59.15 18.34 11.12 54.48 63.82oleate 40 0 11.0 float 82.85 20.44 10.04 85.04 80.66
sink 17.15 17.37 11.63 14.96 19.34oleate 40 50 11.0 float 57.08 22.37 9.04 64.12, 50.03
sink 42.92 16.65 12.01 35.88 49.97oleate 40 0 7.0 float 95.32 19.34 10.61 92.57 98.00
sink 4.68 31.6 4.40 7.43 2.00oleate 40 50 7.0 float 48.73 18.94 10.81 46.35 51.11
sink 5 I .27 20.84 9.83 53.65 48.89DPA 40 0 9.5 float 42.89 29.63 5.28 63.83 21.96
sink 57.11 12.61 14.09 36.17 78.04DPA 40 50 9.5 float 34.75 3 1.99 4.06 55.83 13.68
sink 65.25 13.48 13.64 44.17 86.32DPA 40 0 10.8 float 32.04 28.44 5.90 45.76 18.33
sink 67.96 15.89 12.39 54.24 81.67DPA 40 50 10.8 float 16.45 30.13 5.02 24.89 8.01
sink 83.55 17.90 11.35 75.11 91.99DPA 40 0 7.0 float 48.29 29.39 5.40 71.28 25.30
sink 51.71 11.06 14.89 28.72 74.70DPA 40 50 7.0 float 34.67 33.26 3.41 57.91 11.46
sink 65.33 12.83 13.98 42.09 88.54
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TABLE 10: FLOTATION RESULTS OF 2:l MIXTURE OF APATITE ANDDOLOMITE WITH AND WITHOUT BACTERIA
Collector Bacteria pHreagent mg/l mg/loleate 60I I 0 10.8
oleate 60 Mphlei 10.850
oleate 60 JF-2 10.850
DPA 100 0 6.8
DPA 100 Mphlei 6.850
DPA 100 JF-2 6.850
Item Wt,I I Analysis, % I Distribution, % Iw5 MgO ho,
float 1 57.50 1 28.31 ) 4.05 ) 70.22I I I Isink 1 42.50 1 16.24 1 10.26 1 29.78
feed 100.00 23.18 6.69 100.00float 43.74 30.48 2.87 56.85sink 56.26 17.98 9.81 43.15feed 100.00 23.45 6.77 100.00float 1 40.56 1 32.65 1 2.43 1 55.88sink 1 59.44 ( 17.59 1 9.61 1 44.12feed 100.00 23.70 6.70 100.00float 59.70 37.67 0.99 95.32sink 40.30 2.74 15.28 4.68feed 100.00 23.59 6.75 100.00I I I I
Ifloat 1 56.83 I 38.41 ( 0.82 I 92.15sink 43.17 4.31 14.38 7.85feed 100.00 23.69 6.67 100.00
MgO34.8165.19
100.0018.4881.52
100.0014.7285.28
100.008.77
91.23100.00
6.9993.01 )
100.00 I6.53 1
93.47 1100.00
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TABLE 11: FLOTATION RESULTS OF 2:l MIXTURE OF FRANCOLITE ANDSEDIMENTARY DOLOMITE WITH AND WITHOUT BACTERIA
rollector Bacteriamg/l PH Item Wt,% Analysis, % Distribution, %reagent mg/l WA21.4121.29
MgO w, mo0 10.5leate 60 5.62 1 62.66 1 62.28 1loat
sink62.5337.47 5.68 1 37.34 1 37.72 1
feed ) 100.00 1 21.37 1 5.64 1 100.00 ( 100.00 Ioleate 60 Mphlei 10.5 float 1 54.47 1 23.67 1 4.53 1 60.03 1 43.52 1
100 sit i 1 45.43 1 18.90 1 7.05 1 39.97 ) 56.48 1feed 1 100.00 1 21.48 1 5.67 1 100.00 I 100.00 I
oleate 60 10.5 float 1 52.38 1 23.91 I 4.21 I 58.99 1 38.33 Isink I 47.62 I 18.28 I 7.45 I 41.01 I 61.67 I
JF-2100
0feed I 100.00 1 21.23 I 5.75 I 100.00 I 100.00 I
DPA 100 8.0 float I 52.53 I 28.17 I 1.50 1 69.31 1 13.95 Isink 1 47.47 ( 13.80 ( 10.24 ( 30.69 1 86.05 1feed 100.00 21.35 5.65 100.00
1.20 63.869.93 36.145.68 100.00
100.00! 10.28
89.72100 float 48.67phlei
1008.0 28.69
sink 15.40feed 21.87 100.00
JF-2 8.0 float
51.33100.0046.34 29.12 1.18 1 63.20 9.56
100 sink 1 53.66 ) 14.64 1 9.64 I 36.80 1 90.44 I
DPA
DPA 100
feed 100.00 21.35 5.72 100.00 100.00
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FLORIDA DOLOMITIC PHOSPHATE PEBBLE FLOTATION
The selective flotation of Florida dolomitic phosphate pebble samples was more difficult thanthat of natural mineral samples because of the composition and similarity of the surface
characteristics of phosphate and carbonate minerals. The addition of bacteria increased the P,O,grade of the concentrate and decreased MgO content in it when tall oil/kerosene or sodium oleatewas used as collectors (Tables 12 and 13). The optimum pH value seems to be around 10.6 for both
#1 and #2 samples. Flotation concentrates with less than 1% MgO can be obtained from the #l
phosphate sample at this pH value with 62.07% recovery ofP,O,. However, the target level of aconcentrate for the #2 sample was far from satisfactory. In order to decrease the concentrate content
of MgO to less than 1%, the recovery of P2O5 is 50% or less, which is unacceptable for commercial
applications. From the test data of actual sample flotation, other modifiers may have positive effect
on the depression of dolomite. It is seen that N%CO, demonstrated some depression of MgO-containing carbonates. Also, there may be a synergistic effect of bacteria with other regulators. The
depression behavior ofNa&O, on dolomite and possible synergistic effect using bacteria with otherregulators is now under investigation by Department of Chemical and Metallurgical Engineering,
University of Nevada Reno.
When oleate was used as collector, the grades of obtained concentrates went up, and the
contents of MgO went down. B.licheniformis JF-2 still had an advantage overM.phlei in enhancinggrade and lowering MgO content. Using combination of oleate and B.licheniformis JF-2, aconcentrate with 28.48% P,O,, less than 1% MgO at a recovery of 60% P,OS was obtained. DPAdemonstrated better performances with or without bacteria. The concentrate with a grade of 29-30%
P,O, and recovery 60- 65% can be obtained from the # 1 sample at the same level of less than 1%MgO content (Table 14). For the # 2 sample, use of oleate was hard to perform well enough. When
using DPA, it was possible to obtain a concentrate containing 30.01% P,O,, less than 1% MgO ata recovery of 56.39% recovery (Table 15).
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TABLE 12: FLOTATION RESULTS OF THE # 1 FLORIDA PHOSPHATE PEBBLEUSING TALL OIL AS COLLECTOR
Collector Regulator Bacteria pH wt., % Analysis, % Distribution, %kg/ton kg/ton kg/ton m MgO Insol P,O, MgO Insol
tall oil, Na,SiO,, 0 9.2 C 67.83 26.03 1.88 8.93 73.06 68.06 35.832.5 1kerosene T 32.17 20.24 1.86 33.72 26.94 31.94 64.170.5 F 100.0 24.17 1.87 16.90 100.0 100.0 100.0tall oil, Na,SiO,, MphleiO 9.2 C 59.74 27.13 1.65 8.23 66.98 52.33 28.832.5 1 .25kerosene T 40.26 19.85 2.23 30.14 33.02 47.67 71.170.5 F 100.0 24.20 1.88 17.05 100.0 100.0 100.0tall oil, Na,SiO,, JF-2 9.2 C 58.46 27.15 1.67 8.15 65.00 51.38 26.442.5 1 0.25kerosene T 41.54 20.58 2.22 31.91 35.00 48.62 73.560.5 F 100.0 24.42 1.90 18.02 100.0 100.0 100.0tall oil, Na,SiO,, 0 10.6 C 62.92 26.98 1.23 8.16 70.37 41.35 29.432.5 1kerosene NGQ, T 37.08 19.28 2.96 33.21 29.63 58.65 70.570.5 2.5 F 100.0 24.12 1.87 17.45 100.0 100.0 100.0tall oil, Na,SiO,, M.phleiO 10.6 C 53.85 27.89 0.98 7.98 62.07 27.93 25.462.5 1 .25kerosene Na,CO,, T 46.15 19.89 2.95 27.26 37.93 72.07 74.540.5 2.5 F 100.0 24.20 1.89 16.88 100.0 100.0 100.0tall oil, Na,SiO,, JF-2 10.6 C 49.87 27.57 0.96 7.21 55.87 25.88 20.692.5 1 0.25kerosene NW&, T 50.13 21.67 2.74 27.50 44.13 74.12 79.310.5 2.5 F 100.0 24.61 1.85 17.38 100.0 100.0 100.0* c: concentrate, T: tail, F: feed
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TABLE 13: FLOTATION RESULTS OF THE # 2 FLORIDA PHOSPHATE PEBBLEUSING TALL OIL AS COLLECTOR
Collector Regulator Bacteria PH wt.,% I Analysis, % I Distribution % Ikg/ton kg/ton kg/ton I PA I mo I Ins01w, I M@ Ins01 I
tall oil,2.5kerosene0.5
tall oil,2.5kerosene0.5
tall oil,2.5kerosene0.5
tall oil,2.5kerosene0.5
tall oil,2.5kerosene0.5
tall oil,2.5kerosene0.5
0 9.2 C 1 75.69 1 25.78 1 2.92 1 9.13 1 79.60 1 71.52a$iO,,1 T 1 24.31 1 20.57 1 3.62 1 37.21 1 20.40 1 28.48F 1 100.0 1 24.51 1 3.09 1 15.96 1 100.0 1 100.0 100.0
37.9562.05100.034.3765.63100.039.3760.63100.029.8570.15100.026.0473.96100.0
Na,,SiO,, M.phlei1 0.25 C 65.87 26.34 2.66 9.03 71.39 56.58T 34.13 20.37 3.94 28.49 28.61 43.42i; 100.0 24.30 3.10 15.67 100.0 100.0C 63.28 26.81 2.62 9.25 70.16 54.01T 36.72 19.65 3.85 30.44 29.84 45.99
9.2
N+SiO,, JF:21 0.25
F 1 100.0 1 24.18 1 3.07 1 17.03 1 100.0 1 100.0Na$iO,,1KOH
0 10.6
NqSiO,,1KOHM.phlei0.25 10.6 C 59.38 27.49 2.24 8.13 67.60 44.22T 40.62 19.26 4.13 27.93 32.40 55.78
F 100.0 24.15 3.01 16.17 100.0 100.0C 55.89 27.62 2.19 7.39 62.70 39.11T 44.11 20.82 4.32 26.59 37.30 60.89F 100.0 24.62 3.13 15.86 100.0 100.0
Na$iO,,1KOHJF-2
* C: concentrate, I
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TABLE 14: FLOTATION RESULTS OF THE # 1 FLORIDA PHOSPHATE PEBBLEUSING OLEATE AND DPA AS COLL&ZTORS
Collectorkg/ton
Regulatorkg/ton
Bacteriakg/ton
PH wt., % Distribution, %nalysis, %PA MgO Insol27.72 1.21 7.9519.25 2.90 30.9324.36 1.88 17.0728.19 1 1.02 1 7.4319.79 ( 2.86 ( 3 1.3224.22 1 1.89 1 18.7228.48 1 0.97 1 6.9419.69 1 2.79 1 29.4324.19 I 1.86 I 17.9229.13 I 0.95 I 7.3918.49 ) 2.98 ) 29.4124.26 ( 1.88 ( 17.4729.97 1 0.93 1 8.13
oleate2
Na,SiO,,1NC%2.5
0 10.6
100.0 1 100.0 1 100.0 1oleate2 Na,SiO,,1
Na,C%2.5Mphlei0.25 10.6 C 1 52.74 61.38 1 28.46 1 20.93 1T ( 47.26 38.62 1 71.54 ( 79.07 (
F 1 100.0 100.0 I 100.0 I 100.0 Ioleate2 Na,SiO,,1
Na,CQ,2.5
JF-20.25 10.6 C 1 51.18 60.26 1 26.69 1 19.82 )T 1 48.82 39.74 I 73.31 I 80.18 I
F ) 100.0DPA2 Na,SiO,,1 0 7.2 C 1 54.23T ) 45.77 34.88 ) 72.60 ) 77.06 1
F 1 100.0 100.0 I 100.0 I 100.0 IDPA2 C 1 51.21 63.47 1 25.63 23.09 1.2
7.2
Na,SiO,,1
DPA Na,SiO,,2 1
Mphlei0.25
JF-2
T 1 48.79 18.10 1 2.82 1 28.42 36.52 74.37 76.91100.0 1oo;o 100.0100.0
tC 48.16T ) 47.84
I II I I
F ( 100.0 1 24.31 1 1.87 1 16.98tai 1, F: feet: concentrate, T:
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TABLE 15: FLOTATION RESULTS OF THE # 2 FLORIDA PHOSPHATE PEBBLEUSING OLEATE AND DPA AS COLLECTORS
* C: concentrate, T: I
Collectorkg/ton
oleate2
oleate2
oleate2
DPA2
DPA2
DPA2
Regulatorkg/ton
Na,SiO,,1NaPA,2.5Na,SiO,,1NaPA,2.5
Na,SiO,,1NaPA,2.5
Na,SiO,,1
Na,SiO,,1
Na,SiO,,1
Bacteriakg/ton
0
M.phlei0.25
JF-20.25
0
Mphlei0.25
JF-2
.I, F: fee
PH wt., % Analysis, % Distribution, %PA MgO Insol P,O, MgO Insol
10.6 C 72.18 27.68 2.57 8.97 81.38 58.71 41.35T 27.82 16.43 4.69 33.01 18.62 41.29 58.65
F 100.0 24.70 3.12 16.12 100.0 100.0 100.07.2 C 57.28 29.12 1.05 6.93 67.20 19.03 24.43
T 42.72 19.05 5.99 28.75 32.80 80.97 75.57F 100.0 24.82 3.16 16.25 100.0 100.0 100.0
7.2 C 45.83 30.01 0.98 7.10 56.39 14.40 19.63T 54.17 19.63 4.93 24.60 43.61 85.60 80.37F 100.0 24.39 3.12 16.58 100.0 100.0 100.0
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CONCLUSIONS AND RECOMMENDATIONS
CONCLUSIONS
The following conclusions are drawn from the experimental results and analysis of these resultsbased on the phenomena and potential mechanisms.
1. Florida phosphate in a dolomitic pebble sample can be called as francolite based on its
carbonate substitution or collophane due to its cryptocrystalline formation from sedimentation. The
difficulty of separation of phosphate from dolomite is due to its cryptocrystalline character, carbonate
substitution and huge specific surface area.
2. In the aqueous solutions, Florida phosphate in a dolomitic pebble sample, as sedimentary
dolomite, has a high negative charge on its surface. Its IEP is at about pH 2, which is much different
from the crystalline apatite. The calcium and magnesium ions, adding or getting rid of minerals
surface, adsorb on the surface of the phosphate, and lead to fewer negative potentials or positivepotentials, especially at the high pH range.
3. The gram-positive bacteria, M.phlei and B.licheniformis JF-2, have higher negative chargein the aqueous solutions, and adsorb calcium and magnesium ions on their cell walls.B.licheniformisJF-2 has a higher zeta potential at very wide pH range thanM.phlei does, and has more affinity tomagnesium than calcium ions, especially at the pH values of 10 to 12. The soluble fraction from
bacterias cell is strongly adsorbed onto the surface of minerals to cause more negative charges on the
minerals.
4. Both M.phlei and B.licheniformis strongly adhere to the surface of dolomite and phosphate,but they seem to have more affinity for dolomite than for phosphate. The differences between
adsorption of calcium and magnesium ions on the cell wall of bacteria, and between adhesion of
bacteria onto the surface of apatite and dolomite may depend upon the chemical composition of the
cell walls and their functions.
5. Both bacteria are poor collectors for phosphate pebble flotation because of their weak
collecting ability. However, they may have some potential in the flotation of fine particles or used with
other collectors or frothers.
6. Both bacteria, soluble fraction or whole cells, can be used for depression of dolomite in
anionic flotation for phosphate when using either sodium oleate or diphosphonic acid as collectors.
7. When the commercial collector, tall oil with kerosene, was used for flotation of the # 1
dolomitic pebble sample at pH 10.6, a concentrate of about 28% P,O, with less than 1% MgO atrecovery of about 60% P,O, can be obtained. When the same reagent system was employed for themore dolomitic pebble sample, the same quality of the concentrate cannot be obtained except at a P,O,recovery of less than 60%. Use of DPA with bacteria improves the P,O, grade of the concentrate at
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about 60% ofP,O, recovery. For the low dolomitic pebble sample, a concentrate with 30%P,O, andless than 1% MgO at a P2O5 recovery of 60-65% can be obtained. For the high dolomitic pebble, a
concentrate with 30% P,O, and less than 1% MgO at P,O, recovery of 55% can be obtained.RECOMMENDATIONS
The mechanisms of adsorption of calcium and magnesium ions onto the selected
microorganisms and the adhesion of bacteria onto the target minerals are still not very clear, even
though there is a direct relationship between the adsorption and adhesion. The better selectivity of
B.licheniformis JF-2 adhesion may be due to its cell wall composition which has fewer fatty acidgroups thanM.phlei. There is still a lack of enough evidence to show that the makeup of the cell wallofB.licheniformis JF-2 is similar to that of the cell wall ofB.sublitis. Further useful work may be totry B.sublitis or otherB.licheniformis strains or to change culture conditions for growth ofM.phlei or
B. licheniformis JF-2. In some instances cultural conditions such as temperature, trace salt or energysources in media, and aerobic or anaerobic growth, can change the composition of the cell wall and
various functions in the cell walls.
Fatty acids as collectors are cheap, but of poor selectivity for phosphate over dolomite. Fatty
acid flotation results using bacteria as dolomite depressant are far from satisfactory because of low
P,05 recovery. A study on pH adjustors may find data of significance. One of the possible adjustingchemicals is Na,CO,. We did not obtain enough results on the effect ofNa,CO, in this study, andfurther work should be done to investigate how it affects the flotation.
A new collector, diphosphonic acid, DPA, is superior for flotation of phosphate from dolomite.
Both bacteria and DPA work well in pure mineral and real sample flotation. The work on study of
DPA as collector should be extended to combine it with work of bacteria as depressants.
For flotation of Florida phosphate rock, including dolomitic phosphate ores, there are several
specific rules in terms of some operation parameters to follow. The operation factors, such as clay
removal, sizing of feed, and high percent solids conditioning, are very critical in some circumstances.
The further work should include searching optimum operating factors and the obtaining the
combination of these parameters.
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