Beidellite and other natural low-cost sorbents to remove chromium and cadmium from water and wastewater

Laboratory experiments were conducted to examine ability of clay minerals and organic matter to remove the cadmium(II) and chromium(III) ions from aqueous effluents. Sample materials for the experiments were taken in Poland and Spain. Their chemical composition, specific surface area, pH in water and potassium chloride, ion exchange capacity and absorption of Cr (III) and Cd (II) have been studied. The clay samples exhibited greater sorption capacity for Cr(III) than for Cd(II) while organic matter, especially brown coal, better sorbed Cd(II) than Cr(III). The Langmuir binding strength parameter (k) was always greater for Cr than for Cd. On the basis of the sequential extraction and microanalysis by SEM it was stated that iron oxides were not involved in the Cd ion binding while their role in Cr(III) binding was essential. Ion binding by Fe oxides and their missing at exchangeable positions yields weak both susceptibility to leaching and mobility of Cr(III) ions. Instead, Cd(II) ions are mainly bound at exchangeable positions, susceptible to leaching. (Author)