tailieunhanh - Arsenic removal from aqueous solutions by adsorption on red mud

Abstract Use of red mud, which is a waste product from bauxite processing, has been explored as an alternate adsorbent for arsenic in this study. The tests showed that the alkaline aqueous medium (pH ) favored the removal of As(III), whereas the pH range from to was e ective for As(V) removal. The process of arsenic adsorption follows a ®rst-order rate expression and obeys the Langmuir's model. It was found that the adsorption of As(III) was exothermic, whereas As(V) adsorption was endothermic. . | WASTE MANAGEMENT PERGAMON Waste Management 20 2000 761-767 locate wasman Arsenic removal from aqueous solutions by adsorption on red mud H. Soner Altundogan Sema Altundogan Fikret Tumen Memnune Bildik Firat University Department of Chemical Engineering 23279 Elazig Turkey Received 26 June 1999 received in revised form 6 March 2000 accepted 21 March 2000 Abstract Use of red mud which is a waste product from bauxite processing has been explored as an alternate adsorbent for arsenic in this study. The tests showed that the alkaline aqueous medium pH favored the removal of As III whereas the pH range from to was effective for As V removal. The process of arsenic adsorption follows a first-order rate expression and obeys the Langmuir s model. It was found that the adsorption of As III was exothermic whereas As V adsorption was endothermic. It would be advantageous to use this residue as an adsorbent replacing polyvalent metal salts. 2000 Elsevier Science Ltd. All rights reserved. Keywords Arsenic adsorption Red mud Langmuir isotherm 1. Introduction Although environmental restrictions and regulations have limited the production and uses of arsenic and its compounds they are still extensively used in metallurgy agriculture forestry electronics pharmaceuticals and glass and ceramic industry etc. Arsenic being one of the more toxic pollutants is introduced into the environment through weathering of rocks and mine tailings industrial wastes discharges fertilizers agricultural employments of pesticides smelting of metals and burning of fossil fuels. Arsenic occurs in -3 0 3 and 5 oxidation states in aquatic systems. The elemental state is extremely rare whereas -3 oxidation state is found only at extremely reducing conditions. Arsenate species pentavalent state are stable in oxygenated waters. Under mildly reducing conditions arsenites trivalent state predominate 1 . Arsenic combines strongly with carbon in arsenical organic compounds which are .