Stabilization of Cr(VI) from fine ferrochrome dust using exfoliated vermiculite

Abstract

It was been reported that untreated wastes from ferrochrome plants release heavy metals including lead, chromium, copper, cadmium, zinc and nickel in the environment. Some of these metals such as hexavalent chromium are potentially toxic and carcinogenic, and can cause a serious threat to human health. The contamination of terrestrial and aquatic ecosystems by hexavalent chromium is worldwide of major environmental concern, especially in South Africa which is the largest producer of chromite and ferrochrome. Therefore, the pre-treatment of these wastes before landfill is of great importance to prevent the contamination of the ecosystems. In the present study, vermiculite, a natural occurring mineral, has been tested for its adsorption effectiveness in removing Cr(VI) from ferrochrome dust leachate. Batch adsorption studies have been carried out to determine the effect of pH, contact time and adsorbent dose on the removal of Cr(VI). The process was found to be highly pH dependent. The optimum conditions for the removal were found to be at pH 1.5, contact time 2 hours and adsorbent dose 10 g.L-1. According to kinetic and isotherm studies, the process is best fitted by the pseudo-second order kinetic model, and to both Langmuir and Freundlich isotherms. The maximum adsorption capacity was found to be 23.25 mg.g-1. Thermodynamic parameters show the spontaneous and endothermic nature of Cr(VI) adsorption onto vermiculite.