Determination of Heavy Metals In Wastewaters

Prepared by Aram I. Abdul Rahman Mustafa Hassan

Date 16-Jun-2012

University of sulaimaniSchool of scienceChemistry department

CONTENTS

Waste water Heavy metal Heavy metal toxicity Effect of Heavy Metals on Health and

Environment Methods for Removing Heavy Metals

from Waste Water Methods for the determination of

heavy metals

WASTE WATER

Wastewater is water containing waste, or water that has been in contact with waste material. Waste includes any material that is dissolved, suspended or transported in water. It includes substances such as human waste, food scraps, oils, soaps and chemicals. In homes, this includes water from sinks, showers, bathtubs, toilets, washing machines and dishwashers. Businesses and industries also contribute their share of used water that must be cleaned.

TYPES OF WASTE WATER

Domestic wastewater (includes household waste from washing, bathing, toilets) Biodegradable industrial wastewater (contains a high concentration of organic waste arising from industrial activities and premises . Biodegradable industrial wastewater is generated by activities such as: Manufacturing and bottling of soft drinks and water bottling, Production of alcoholic

beverages in breweries ) Industrial wastewater ( Industrial wastewater is generated by a wide range of activities such as: Chemical industries, Metal plating, Plastics, Leather processing, Pulp and paper manufacture.)

HEAVY METALS

Heavy metals are the non- degradable metals .These metals are toxic and possess high density.

Heavy metals occur in the earth’s crust naturally. Some of the heavy metals are lead, cadmium, mercury, arsenic, chromium and thallium. High concentration of heavy metals causes poisoning.

Heavy metal causes severe water pollution Heavy metals are dangerous because they tend to bio

accumulate. Bioaccumulation means an increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment.

Heavy metals are also common in industrial applications such as in the manufacture of pesticides, batteries, alloys, electroplated metal parts, textile dyes, steel

Heavy metals can enter a water supply by industrial and consumer waste, or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers, and ground water

SOURCES OF HEAVY METALS The main sources of heavy metal are weathering

of rocks and volcanic eruption in which metals are released in water sources.

Other sources are:-* Domestic waste water and urban run-off* Industrial waste water* Agricultural activities* Mining activities

HEAVY METAL TOXICITY

Heavy metals are toxic to human health. Most common heavy metals are lead, mercury, cadmium, arsenic, antimony, bismuth, chromium, iron, manganese, nickel, platinum, silver, thallium, tin, uranium, vanadium, and zinc. Interestingly, small amounts of these elements are common in our environment and diet and are actually necessary for good health, but large amounts of any of them may cause acute or chronic toxicity (poisoning). Heavy metal toxicity can result in damaged or reduced mental and central nervous function, lower energy levels, and damage to blood composition, lungs, kidneys, liver, and other vital organs.

THE MOST COMMONLY ENCOUNTERED TOXIC HEAVY METALS INCLUDE

Arsenic Lead Mercury Cadmium Iron Aluminum  

LEAD

Health effects of lead At high levels, inorganic lead is a general

metabolic poison Lead poisoning effects the neurological and

reproductive systems  Environmental effects of lead Lead accumulates in the bodies of water

organisms and soil organisms  

METHODS FOR REMOVING HEAVY METALS FROM WASTE WATER

Chemical PrecipitationChemical precipitation is the most common technology used to remove dissolved (ionic) metals from water solutions, such as process waste waters containing toxic metals. The ionic metals are converted to an insoluble form (particle) by the chemical reaction between the soluble metal compounds and the precipitating reagent. Typically, the metal precipitated from the solution is in the form of hydroxide. The conceptual mechanism of heavy metal removal by chemical precipitation is represented as

where M(OH)n is insoluble metal hydroxide and Mn+ and OH- represent dissolved metal ions and precipitant, respectively. Therefore, the optimum pH for precipitation of one metal may cause another metal to solubilize, or start to go back into solution.

Most process waste waters contain mixed metals and hence precipitating these different metals as hydroxides can be a tricky process. Chemical precipitation requires large amounts of chemicals to reduce the concentration of metals to an acceptable level for discharging waste waters into the environment.

ION EXCHANGE

  Ion exchange is a reversible chemical reaction wherein an

ion present in solution is exchanged with a similarly charged ion bound to a stationary solid phase (resin). Ion exchange can also be used for recovering valuable heavy metals from inorganic effluents. After separating the loaded resin, metals

Can be recovered in a more concentrated solution by eluting with suitable reagents.

Since the acidic functional groups of the resins consist of sulfonic acid,

It is assumed that the physico-chemical interactions occurring during metal removal can be expressed as follows:

Electrochemical Treatment Techniques Electro-dialysis (ED) is a membrane separation technique in which ionized species in the solution are passed through an ion-exchange membrane by applying an electric potential. The membranes are thin sheets of plastic materials with either anionic or cationic charge. When a solution containing ionic species passes through the cell compartments, the anions migrate toward the anode and the cations migrate toward the cathode, crossing the anion-exchange and cation-exchange membranes. Since ED is a membrane process, it requires clean feed, careful operation, and periodic maintenance to prevent any damage to the membranes. In conclusion,

REMOVAL OF HEAVY METALS FROM INDUSTRIAL WASTEWATERS BY ADSORPTION ONTO ACTIVATED CARBON PREPARED FROM AN AGRICULTURAL SOLID WASTE

Activated carbon was prepared from coir pith by a chemical activation method and characterized. The adsorption of toxic heavy metals, Hg(II), Pb(II), Cd(II), Ni(II), and Cu(II) was studied using synthetic solutions and was reported else

where. In the present work the adsorption of toxic heavy metals from industrial wastewaters onto coir pith carbon was studied. The percent adsorption increased with increase in pH from 2 to 6 and remained constant up to 10. As coir pith is discarded as waste from coir processing industries, the resulting carbon is expected to be an economical product for the removal of toxic heavy metals from industrial wastewaters.

 

METHOD FOR THE DETERMINATION OF HEAVY METALS

Atomic absorption Atomic emission ICP Chromatography Voltammetery

METHODS USING ION CHROMATOGRAPHY

Ion chromatography is known to be a promising method for the analysis of natural water.

It is the best method of determining anions in aqueous solutions. The method is also suitable for determining heavy metals.

Highly sensitive dual—column techniques have been developed to determine metals in different types of water, with the separation according to both the cation— and the anion—exchange mechanism.

  In the first case Cd, Cu, Mn, Ni, Pb, Sr and Zn

have been separated by elution with ethylenediammonium chloride or ethylendiammonium tartrate solutions and determined with a conductometric detector.

When determinations are made by the anion—exchange mechanism, the metals (As, Cr, Mo, Se,Te, V and W) are first converted into oxoanions, and the separation is conducted on columns with "Dionex" low—capacity anion—exchange resin; the elution is performed with sodium carbonate

REFERENCES

http://www.cbc.ca/manitoba/features/lakewinnipeg/wastewater.html

B.V. L’vov (2005), Fifty years of atomic absorption spectrometry; J. Anal. Chem., 60: 382–392.

http://www.cbc.ca/manitoba/features/lakewinnipeg/checkup.html

http://www.tip2000.com/health/waterpollution.asp