Reactivity of nZVI in the removal of Cu(II) and Zn(II) from synthetic mine drainage

Adsorption properties, including isotherms and kinetics, of nano zero-valent iron (nZVI) for Cu(II) and Zn(II) removal from synthetic mine drainage were evaluated in batch tests. The influence of contact time, nZVI doses, pH, ionic strength, temperature, and concentration on nZVI adsorption properties was assessed. The removal of Cu(II) and Zn(II) increased with pH from 3 to 7 and then stabilized up to pH 10. Moreover, the increased Cu(II) adsorption capacity upon increasing temperature and a positive enthalpy change (ΔH) indicate that the adsorption process is endothermic. The results also showed that the adsorption equilibrium for Cu(II) and Zn(II) was achieved after 50 and 30 min, respectively. Kinetics were best described by a pseudo-nth order model, with the order of sorption of 2.231 and 1.363, and the rate constants of 0.0008 and 0.0679 mg1-n·gn-1/min, for Cu(II) and Zn(II), respectively. The correlation between the amount of metals adsorbed on nZVI surface and the residual amount of metals in water during isothermal tests was best described by the nonlinear Sips model. Using this model, high q maxS were found: 286.6 mg/g and 142.6 mg/g, for Cu(II) and Zn(II), respectively, as indication of their high sorption capacity.