Simultaneous removal of metal species from acidic aqueous solutions using cryptocrystalline magnesite/bentonite clay composite: an experimental and modelling approach

The overall aim of the present study was to fabricate cryptocrystalline magnesite and bentonite clay composite and evaluate its application for simultaneous removal of Co(II), Cu(II), Ni(II), Pb(II) and Zn(II) from wastewater in a single step. Batch laboratory experiments were employed to optimize metals removal conditions. Parameters optimized included: effect of shaking time, dosage and species concentration. Optimization experiments revealed that 15 min of equilibration, 1 g of dosage, 500 mg L-1 of concentration and 1 g:100 mL S/L ratios were the optimum conditions for removal of metal ions from wastewater. The pH of the solution increased from pH < 3 to pH > 11. Removal of Co(II), Cu(II), Ni(II), Pb(II) and Zn(II) was 100%. The data fitted well to pseudo-second-order than pseudo-first-order and intra-particle diffusion model hence confirming chemisorption as the rate limiting the reaction. The adsorption data fitted well to Langmuir adsorption isotherm as compared to the Freundlich adsorption isotherm hence implying monolayer adsorption. The PH REdox EQuilibrium (in C language) (PHREEQC) geochemical model predicted that the metal ions exist as divalent species in aqueous solution at pH < 3. It also predicted that metal ions precipitate as metal hydroxides from aqueous solution at pH > 11. As such, it was concluded that the mechanochemical synthesized composite has the potential to remove divalent metals species from contaminated waterbodies. (C) 2015 Elsevier Ltd. All rights reserved.