The removal of molybdates and tungstates from aqueous solution by organo-smectites

Abstract

This paper presents the results obtained when studying the removal of molybdate and tungstate anions from aqueous using organically modified montmorillonite. In batch experiments, the influence of pH, reaction time, the initial concentration of Mo and W, and the influence of the amount and type of surfactant was investigated. The modification of smectite with leads to the formation of an organo-mineral complex characterized by a positively-charged surface and a high sorption capacity in the removal of Mo(VI) and W(VI). The pH effect determining the possibility of Mo and W removal from the aqueous solution. In the pH range of 1–5, the sorption of Mo and W efficiency is very high, while at pH>5 sorption is limited or completely inhibited. DDTMA-smectite and DDDDMA-smectite were recognized as the best sorbents. With an increasing amount of surfactant used in modification process, the sorption efficiency increases. Molybdates are removed from solutions compared to tungstates to a much greater extent – maximum sorption capacities were 705 and 390mmol/kg, respectively. Kinetic studies indicated that maximum sorption capacity is achieved faster in the case of Mo than of W, and that the main sorption mechanisms are chemisorption and ion exchange.