ADSORPTION OF HEAVY METAL (ARSENIC ,COPPER, LEAD CADMIUM) USING ACTIVATED COMPLEXES (BAMBOO CHIPS, PALM KERNEL CHIPS AND SNAIL SHELL) CLAY

ABSTRACT

Adsorption and desorption studies on different types of adsorbents, including natural materials such as teak tree bark powder, rice husk, natural bentonite, different algae like Ecklonia maxima, Escherichia coli, Ascophyllum nodasum, Rhizopus nigricans, Cladophora fascicularis, goethite and soils of three nuclear power plant and artificial materials such as Fe oxide-coated sand, goethite pretreated with phosphate, dithizone-modified sodium trititanate whisker, modified nano-metre sized TiO₂, Chromosorb 102 resins and poly(m-phenylenediamine) are summarized. The kinet-ics, thermodynamics, sorption/desorption mechanism of different metal ions on different adsorbents under different experimental conditions are discussed. It is found that desorbing agent is greatly dependent on the adsorbate used. All the metal ions are desorbed using acids like HCl, HNO₃ and H₂SO₄ in most of the cases, except Cr(VI). EDTA can be used to remove Pb²⁺ and Zn ²⁺ in addition to acids. Since Cr(VI) is present in anionic form; it can be eliminated from the loaded adsorbents using bases like NaOH, Na₂CO ₃ or NaHCO₃.

CHAPTER ONE

1.1            BACKGROUND OF THE STUDY

THE heavy metals present in the aquatic environment are considered to be the major inorganic contaminant due to their mobility in the aqueous ecosystem, toxicity to higher life forms and non-biodegradable nature. The heavy metals hazardous to human health include Pb, Hg, Cd, As, Cu, Zn and Cr. As and Cd cause cancer, Hg can cause mutations and genetic damage, while Cu, Pb and Hg can cause brain and bone damage. The problem of heavy metal pollution in water and aquatic organisms, including fish needs continuous monitoring and surveil-lance as these elements do not degrade and tend to bio-magnify in man through food chain. Hence, there is a need to remove heavy metals from the aquatic ecosystem. Several methods have been devised for the treatment and removal of heavy metals. The commonly adopted proce-dure for removing the heavy metal ions from aqueous streams includes chemical precipitation, lime coagula-tion, ion exchange, reverse osmosis and solvent extrac-tion¹. These so-called conventional methods are not so effective when the metal concentration in the effluent is low. These methods are also non-selective. Adsorption

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process may be an alternative technology for the removal of heavy metals, which are present in very low concentra-tion in the aquatic environment. In the adsorption proc-ess, both biosorbents and chemical sorbents can be used for metal removal and recovery. Biosorbents include Earth’s forests and plants, ocean and freshwater plankton, algae, fish and all living creatures. Similarly, in chemi-sorption process, several adsorbents like zeolite, activated carbon, fly ash, clay and red mud can be used.

The process of biosorption can only be economical if a suitable eluant is used for the recovery of metals from the loaded adsorbent. In a complete metal removal and re-covery process, the adsorbents are to be used in a con-tinuous sorption–desorption cycle. For this purpose, the adsorbents should fulfill the following criteria²: (i) They should be cheap and reusable. (ii) Both uptake and release of metal ions should be efficient and rapid. (iii) Desorption of metal ions from the sorbents should be metal-selective and economically feasible.

Although U uptake capacity of Penicillium and Actin-omycetes is the same, Penicillium sp. is considered as a better biosorbent as metals can be eluted from it more ef-ficiently³. Therefore, selection of specific eluants is more important. Sodium carbonate⁴, potassium cyanide⁵, EDTA⁶, nitric acid⁷, sulphuric acid and hydrochloric acid⁸ are some of the common eluants used for the recov-ery of metal ions from the loaded adsorbents. The main objective of the present article is to review adsorption– desorption characteristics of different heavy metals from their respective adsorbents.

1.2 STATEMENT OF THE PROBLEM

Heavy metal pollution occurs in many industrial waste-waters such as those produced by metal plating facilities, mining operations, battery manufacturing processes, the production of paints and pigments, ammunition, ceramic and glass industries. This wastewater commonly includes Cd, Pb, Cu, Ni, and Cr. These heavy metals are not biode-gradable and their presence in streams and lakes leads to bioaccumulation in living organisms, causing health prob-lems in animals, plants, and human beings. Excessive human intake of Cd leads to damage of kidney and renal system, skeletal deformation (Itai-itai), cardiovascular dis-eases and hypertension (Oliver, 1997). Severe gastrointesti-nal irritation, muscular pain, anemia, teeth discoloration, loss of smell and possible necrotic changes in the liver and kidney can also occur. Cadmium is also known carcin-ogen. Therefore, the removal of excess heavy metal ions from wastewater is essential to protect human and environ-mental health. As a result, the removal of toxic heavy metal ions from sewage and from industrial and mining effluents has been widely studied in recent years.

The most widely used methods for removing heavy met-als are chemical or electrochemical precipitation (Lai and Lin, 2003; Ozdemir et al., 2005) and ion exchange treat-ment (Cardoso et al., 2004). It has been reported that some aquatic plants (Axtell et al., 2003), agricultural by-products (Argun et al., 2005, 2007; Chuah et al., 2005), clay (Ma´r-quez et al., 2004), zeolite (Erdem et al., 2004), turba (Ho et al., 1995) and microorganisms (Li et al., 2004) have the capacity to adsorb and accumulate heavy metals.

Hydrogen peroxide (H₂O₂) is a strong oxidant (standard potential 1.80 and 0.87 V at pH 0 and 14, respectively) (Neyens and Baeyens, 2003) and its application in the treat-ment of various organic and inorganic pollutants is well established. However, oxidation by H₂O₂ alone is not effec-tive for high concentrations of complex organic and inor-ganic compounds, because of low rates of reaction at reasonable H₂O₂ concentrations. Transition metal salts

(e.g., iron salts), ozone and UV-light can activate H₂O₂ to form hydroxyl radicals. Among these materials ferrous iron and hydrogen peroxide commonly known as Fenton’s reagent. Hydrogen peroxide and ferrous ions are usually more stable in a strong acid. However, if hydrogen perox-ide is added to an aqueous system containing an organic substrate and excess ferrous ions in a strong acid, a com-plex redox reaction (Ahn et al., 1999) will occur as in

Hydroxyl radicals (oxidation potential: 2.8 V) are stronger oxidants than ozone and H₂O₂. The Fenton reaction causes the dissociation of the oxidant and the formation of highly reactive hydroxyl radicals that attack and destroy the or-ganic components (Neyens and Baeyens, 2003). The Fen-ton reaction has also several important advantages such as a short reaction time among all advanced oxidation pro-cesses, iron and H₂O₂ are cheap and non-toxic, there is no mass transfer limitations due to its homogenous catalytic nature, there is no energy involved as catalyst and the pro-cess is easily to run and control. It has been widely used for treatment of highly polluted industrial wastewaters (San Sebastian et al., 2003; Lopez et al., 2004) and remediation of polluted soils (Li et al., 1997).

Tree barks are produced in large quantities at sawmills as a solid waste. It basically contains lignin, cellulose and tannin. Some components of barks, such as phenolic groups of lignin, polysaccharides and tannins, have stained the treated water and greatly increased COD. Several mod-ification techniques have been studied to reduce organic components of natural adsorbent and to increase adsorp-tion capacity (Horsfall et al., 2006; Argun and Dursun, 2006; Taty-Costodes et al., 2003). However, effect of Fen-ton on modification of the natural adsorbents did not exist. For this purpose in this study, we extensively studied the modification of a natural adsorbent (pine bark) with Fen-ton’s reagent (hydrogen peroxide and ferrous ions) for cad-mium removal which was intended to benefit of the Fenton destroy of organic components in barks.

1.2            SIGNIFICANCE OF THE STUDY

The main significance is to carry out a research on the adsorption of heavy metal (arsenic ,copper, lead cadmium) using activated complexes (bamboo chips, palm kernel chips and snail shell) clay and its composite treated and untreated.