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Ind. Eng. Chem. Res. 1998, 37, 4816-4822
Removal of Arsenic(V) from Aqueous Solution Using Industrial Solid Waste: Adsorption Rates and Equilibrium Studies Chinnaiya Namasivayam* and Sadasivam Senthilkumar Environmental Chemistry Division, Department of Environmental Sciences, Bharathiar University, Coimbatore 641 046, Tamil Nadu, India
Industrial solid wastes can be recycled as nonconventional adsorbents, if they are nontoxic, to reduce the cost of wastewater treatments. “Waste” Fe(III)/Cr(III) hydroxide, generated electrolytically in the treatment of Cr(VI) containing wastewaters in a fertilizer industry was used for the adsorption of arsenic(V) from aqueous solution. Parameters studied include arsenic(V) concentration, agitation time, adsorbent dosage, adsorbent particle size, temperature, and pH. The adsorption capacity was evaluated by using both Langmuir and Freundlich isotherm models. The adsorption followed a first-order rate expression. Adsorption of As(V) was independent of the initial pH (3-10) of the aqueous solution. Temperature studies showed that the adsorption process was endothermic in nature. Desorption of As(V) from spent adsorbent was also investigated using NaOH solutions. 1. Introduction Arsenic has detrimental effects on human, plants, and animals. The source of arsenic pollution is from the discharge of various industries such as smelting, petroleum-refining, and pesticide, herbicide, glass, and ceramic manufacturing industries (Huang and Fu, 1984). According to the Indian Standards Institution, the tolerance limit for arsenic for the discharge of the effluents into inland surface waters is 0.2 mg/L (Indian Standards Institution, 1974). The chemistry of arsenic is complex and interesting. The oxyanions of arsenic(V) exist in four different arsenate species as H3AsO4, H2AsO4-, HAsO42-, and AsO43- in the pH range 12, respectively (Sadiq et al., 1983). Conventional methods of arsenic removal such as coagulation-precipitation with lime, alum, and ferric sulfate produce a wet bulky material and the safe disposal of the materials has not yet been solved and is not cost-effective in the Indian context. Hence low-cost nonconventional methods and materials have been sought for a long time. Industrial waste such as fly ash (Diamadopoulos et al., 1993), bauxite, alumina, activated carbon (Gupta and Chen, 1978), pyrite fines (Zouboulis et al., 1993a), hematite, kaolin, quartz (Xu et al., 1988), and basic yttrium carbonate (Wasay et al., 1996a) have been studied for the removal of arsenic. In most of the separation methods, the removal of arsenic was found to be greatly dependent on pH, so that the optimum pH range is very limited. Fe(III)/Cr(III) hydroxide is a waste byproduct resulting from the treatment of Cr(VI) containing wastewaters using Fe(II) in industries. A huge amount of this waste is being accumulated in several industries in India. This waste can be effectively used as a substitute to alum and ferric chloride in water/wastewater treatment processes. “Waste” Fe(III)/Cr(III) hydroxide has been employed for the treatment of wastewaters from industries such as fertilizer (Namasivayam, 1989), dairy (Namasivayam * To whom all correspondence should be addressed. E-mail:
[email protected]. Phone: 91-422-422 222. Fax: 91422-422 387.
and Ranganathan, 1992), distillery (Namasivayam and Kanagarathinum, 1992), chrome plating (Namasivayam and Ranganathan, 1993 & 1994a), and tannery (Namasivayam and Senthilkumar, 1994), dyeing (Namasivayam et al., 1994a), nickel plating (Namasivayam and Ranganathan, 1994b), pesticide (Namasivayam et al., 1994b), radiator (Namasivayam and Ranganathan, 1995a; Namasivayam and Senthilkumar, 1998) and for the removal of toxic ions, dyes (Namasivayam and Senthilkumar, 1995), cadmium (Namasivayam and Ranganathan, 1995b), mixtures of metal ions (Namasivayam and Ranganathan, 1995c), and mercury (Namasivayam and Senthilkumar, 1997). A massive outbreak of arsenical dermatosis, observed in some parts of West Bengal state of India, is linked with high levels of arsenic in tube well waters (0.2-2.0 mg/L) (Chakrabarty and Saha, 1987). Several people have been afflicted with ulcers and internal cancers. Hence there is an urgent need to clean the tube well waters of arsenic with low-cost and efficient adsorbents. The objective of the present study was to develop an effective treatment method to remove arsenic(V) using “waste” Fe(III)/Cr(III) hydroxide. Both Fe(III) and Cr(III) are capable of forming polymeric hydroxides and adsorption of arsenic(V) is due to both. Removal of anions such as nitrate, phosphate, and sulfate by adsorption at the ferric and chromic oxide/water interfaces has been reported (Yates and Healy, 1975). Adsorption of organics by aluminum, chromium, and iron hydroxides has also been reported (Levina and Ermolenko, 1955). 2. Materials and Methods 2.1. Adsorbent. Dry waste Fe(III)/Cr(III) hydroxide was obtained from Southern Petrochemical Industries Corporation (SPIC) Ltd., Tuticorin, Tamil Nadu, India. It was ground, washed with distilled water to remove the finest particles,
