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The waste red mud, remaining in remarkable quantities after the digestion of bauxite ores following the Bayer process, contains number of voluble minerals with excellent sorption properties towards aqueous heavy metals. Heating at 600 degrees C was found to be a favorable treatment for revalorization of rinsed red mud into an efficient Ni2+ sorbent (RBRM600). As potential practical application of RBRM600 for Ni2+ accumulation greatly depends on the solution composition and pH, the influence of these vital process variables was considered in this study. The initial pH rise from 2 to 3.5 caused the most evident increase in the amounts of Ni2+ removed: furthermore, the effect was more obvious for lower initial sorbate concentrations. Conversely, changes of the solution pH between 3.5 and 8 did not have a significant influence on the sorption. The increase of initial cation concentration caused the increase of the sorbed amount. following Langmuir isotherm model. The calculated maximum sorption capacity of 27.54 mg/g demonstrated capacity increase of approximately 20% in respect to inactivated rinsed red mud. Coexisting cations inhibited Ni2+ removal in the following order: Cu2+ GT Pb2+ GT = Zn2+ GT Cd2+ GT GT Ca2+, whereas the presence of Na+ and K+ did not affect the process. The investigated anions caused decrease of Ni2+ removal efficiency in the order: EDTA GT chromate GT acetate GT sulphate, however, fluoride slightly improved sorption. Low desorption of Ni2+ in various media showed that the heavy metal cations are tightly bound to RBRM600 surface, thus disposal or reuse of spent sorbent should be considered. (C) 2011 Elsevier B.V. All rights reserved.

The waste red mud, remaining in remarkable quantities after the digestion of bauxite ores following the Bayer process, contains number of voluble minerals with excellent sorption properties towards aqueous heavy metals. Heating at 600 degrees C was found to be a favorable treatment for revalorization of rinsed red mud into an efficient Ni2+ sorbent (RBRM600). As potential practical application of RBRM600 for Ni2+ accumulation greatly depends on the solution composition and pH, the influence of these vital process variables was considered in this study. The initial pH rise from 2 to 3.5 caused the most evident increase in the amounts of Ni2+ removed: furthermore, the effect was more obvious for lower initial sorbate concentrations. Conversely, changes of the solution pH between 3.5 and 8 did not have a significant influence on the sorption. The increase of initial cation concentration caused the increase of the sorbed amount. following Langmuir isotherm model. The calculated maximum sorption capacity of 27.54 mg/g demonstrated capacity increase of approximately 20% in respect to inactivated rinsed red mud. Coexisting cations inhibited Ni2+ removal in the following order: Cu2+ GT Pb2+ GT = Zn2+ GT Cd2+ GT GT Ca2+, whereas the presence of Na+ and K+ did not affect the process. The investigated anions caused decrease of Ni2+ removal efficiency in the order: EDTA GT chromate GT acetate GT sulphate, however, fluoride slightly improved sorption. Low desorption of Ni2+ in various media showed that the heavy metal cations are tightly bound to RBRM600 surface, thus disposal or reuse of spent sorbent should be considered. (C) 2011 Elsevier B.V. All rights reserved.

Red mud, an abundant industrial waste from alumina industry, represents a rich source of various metal oxides, mainly of Fe2O3 Al2O3 and SiO2. In this study, the rinsed Bosnian red mud (RBRM) was evaluated as an economical, composite sorbent for aqueous Ni2+ ions. The process was investigated as a function of pH, contact time and initial metal concentration. The investigated mineral mixture exhibited a high acid neutralising capacity, and its most important role in cation immobilization was observed in the initial pH range 2-8. The initial metal ion concentration strongly influenced the sorption kinetics and equilibrium times. Addition of 5 g/L of RBRM caused 100% removal from the solutions of 10(-4) to 5 x 10(-4) mol/L, whereas with the further increase of Ni2+ concentration to 8 x 10(-3) mol/L, the removal efficiency decreased to 26%. The maximum sorption capacity of 0.372 mmol/g, at initial pH 5, was determined using Langmuir theoretical model. The possibility of sorption efficiency improvement by annealing RBRM powder was investigated in the range 200-900 degrees C and the relationships between temperature, red mud physicochemical and sorption properties were established. The optimum heating temperature was found to be 600 degrees C, due to water exclusion from gibbsite and bayerite phases, leading to improved porosity and surface area, as well as increased pH value and sorption efficiency. The stability of the sorbed cation was assessed by leaching experiments in distilled water and acidic TCLP2 solution. (C) 2010 Elsevier BM. All rights reserved.

Red mud, an abundant industrial waste from alumina industry, represents a rich source of various metal oxides, mainly of Fe2O3 Al2O3 and SiO2. In this study, the rinsed Bosnian red mud (RBRM) was evaluated as an economical, composite sorbent for aqueous Ni2+ ions. The process was investigated as a function of pH, contact time and initial metal concentration. The investigated mineral mixture exhibited a high acid neutralising capacity, and its most important role in cation immobilization was observed in the initial pH range 2-8. The initial metal ion concentration strongly influenced the sorption kinetics and equilibrium times. Addition of 5 g/L of RBRM caused 100% removal from the solutions of 10(-4) to 5 x 10(-4) mol/L, whereas with the further increase of Ni2+ concentration to 8 x 10(-3) mol/L, the removal efficiency decreased to 26%. The maximum sorption capacity of 0.372 mmol/g, at initial pH 5, was determined using Langmuir theoretical model. The possibility of sorption efficiency improvement by annealing RBRM powder was investigated in the range 200-900 degrees C and the relationships between temperature, red mud physicochemical and sorption properties were established. The optimum heating temperature was found to be 600 degrees C, due to water exclusion from gibbsite and bayerite phases, leading to improved porosity and surface area, as well as increased pH value and sorption efficiency. The stability of the sorbed cation was assessed by leaching experiments in distilled water and acidic TCLP2 solution. (C) 2010 Elsevier BM. All rights reserved.