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 9.5) favored the removal of As(III), whereas the pH range from 1.1 to 3.2 was e€ective for As(V) removal. The process of arsenic adsorption follows a ®rst-order rate expression and obeys the Langmuirs model. It was found that the adsorption of As(III) was exothermic, whereas As(V) adsorption was endothermic. ...
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Arsenic removal from aqueous solutions by adsorption on red mud Waste Management 20 (2000) 761±767 www.elsevier.nl/locate/wasman Arsenic removal from aqueous solutions by adsorption on red mud H. Soner Altundogan *, Sema Altundogan, Fikret Tumen, Memnune Bildik Æ Æ È Fõrat University, Department of Chemical Engineering, 23279 Elazõg Turkey Æ, Received 26 June 1999; received in revised form 6 March 2000; accepted 21 March 2000Abstract Use of red mud, which is a waste product from bauxite processing, has been explored as an alternate adsorbent for arsenic in thisstudy. The tests showed that the alkaline aqueous medium (pH 9.5) favored the removal of As(III), whereas the pH range from 1.1to 3.2 was e€ective for As(V) removal. The process of arsenic adsorption follows a ®rst-order rate expression and obeys the Lang-muirs model. It was found that the adsorption of As(III) was exothermic, whereas As(V) adsorption was endothermic. It would beadvantageous to use this residue as an adsorbent replacing polyvalent metal salts. # 2000 Elsevier Science Ltd. All rights reserved.Keywords: Arsenic adsorption; Red mud; Langmuir isotherm1. Introduction been reported to be more toxic than pentavalent and organic arsenicals [2]. Although environmental restrictions and regulations The wastewaters from some industrial source such ashave limited the production and uses of arsenic and gold, copper and zinc ore extraction, acid mine drainage and wood product preservation contain up to 130 mg 1À1its compounds, they are still extensively used in metal-lurgy, agriculture, forestry, electronics, pharmaceuticals soluble arsenic [3,4]. Also, potable waters in some parts of the world have been found to contain 0.1±2 mg lÀ1and glass and ceramic industry, etc. Arsenic, being oneof the more toxic pollutants, is introduced into the arsenic [5,6]. The presence of arsenic in drinking water has been restricted to 0.05 mg lÀ1 [2].environment through weathering of rocks and minetailings, industrial wastes discharges, fertilizers, agri- Arsenic is commonly removed from aqueous solutionscultural employments of pesticides, smelting of metals by coprecipitation with polyvalent metal hydroxideand burning of fossil fuels. ¯ocs such as iron(III) [7] and aluminum hydroxides Arsenic occurs in À3, 0, +3 and +5 oxidation states in [8,9].aquatic systems. The elemental state is extremely rare The use of solid adsorbents in removing such pollu-whereas À3 oxidation state is found only at extremely tants from wastewater compares favorably with con-reducing conditions. Arsenate species (pentavalent state) ventional precipitation or ¯occulation methods. Forare stable in oxygenated waters. Under mildly reducing example, in some ¯occulation treatments, a largeconditions, arsenites (trivalent state) predominate [1]. amount of salt must be added which introduces pollu-Arsenic combines strongly with carbon in arsenical tants such as sulfate ions into the water. Moreover, theorganic compounds which are used as pesticides, chemo- cost of the chemical reagents used in such treatmentsterapeutic agents and chemical warfare agents. can limit their commercial application. Activated carbon The presence of arsenic in water causes toxic and [10], activated bauxite [10], activated alumina [10,11],carcinogenic e€ects on human beings. It has been amorphous aluminum hydroxide [12], amorphous ironreported that long-term uptake of arsenic contaminated (III) hydroxide [13], iron(III) hydroxide loaded coraldrinking water has produced gastrointestinal, skin, liver limestone [14] and hematite [15] can be mentionedand nerve tissue injuries. The toxicity of arsenic ®rmly among the adsorbents studied for arsenic removal fromdepends on its oxidation state and trivalent arsenic has aqueous solution. Red mud is formed during the digestion in the Bayer Process which is practised for alumina production from * Corresponding author. Fax: +90-424-212-2717. bauxite. Mineralogically, red mud consists mainly of E-mail address: saltundogan@®rat.edu.tr (H.S. Altundogan). Æ0956-053X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.PII: S0956-053X(00)00031-3762 H.S. Altundog et al. / Waste Management 20 (2000) 761±767 Æan solutions ...