Evaluating the removal of Cd(Ⅱ), Pb(Ⅱ) and Cu(Ⅱ) from a wastewater sample of a coating industry by adsorption onto vermiculite

摘要

This work presents an evaluation of vermiculite as a low cost adsorbent for treatment of wastewater from a coatings industry containing Cd(Ⅱ), Pb(Ⅱ) and Cu(Ⅱ). Determination of metal cation concentrations in solution was made by continuous flow anodic stripping voltammetry. Adsorption data was fitted by Freundlich isotherms, as well as by partition constants at pH 4, 5 and 6. In this pH range, a 180 min interaction time was long enough to allow the system to reach apparent equilibrium. It is possible to state that non-expanded vermiculite presents the following affinity orders by the studied ions: pH 4: Cu(Ⅱ) < Cd(Ⅱ) < Pb(Ⅱ); pH 5: Cu(Ⅱ) ≈ Cd (Ⅱ) < Pb(Ⅱ); pH 6: Cd(Ⅱ) < Cu(Ⅱ) < Pb(Ⅱ). For Pb(Ⅱ) and Cd(Ⅱ), the adsorption percentages determined in real wastewaters were around 20% lower than the removal percentage previewed by the Freundlich parameters, a fact that may be explained by competition of the studied cations among themselves, and with Fe(Ⅲ) species, which were present in the water at concentration levels similar to Cd(Ⅱ), Cu(Ⅱ) and Pb(Ⅱ). Additionally, the high content of organic compounds in the wastewater may have decreased the adsorption of Cu(Ⅱ) and Pb(Ⅱ) because of possible formation of soluble complexes between the heavy metal cations and the organic compounds. On the other hand, adsorption of Cd(Ⅱ) from the real wastewater was about 20% higher than previewed by the Freundlich parameters, denoting the complexity of interactions that ions are liable in matrices of wastewaters.