Abstract
This study defines the optimal parameters that allow the use of waste mollusk shells (WS) to remove heavy metals from three mining and metallurgical leachates. First, the influence of parameters such as pH, contact time, initial metal concentration, adsorbent dose and the presence of co-ions in Cu(2+), Cd(2+), Zn(2+) and Ni(2+) adsorption was investigated in synthetic solutions. Metal uptake was found to be dependent on the initial pH of the solution, the removal rate increasing with the increase in pH, showing the highest affinity at pH 5-6. The removal efficiency at lower concentrations was greater than at higher values. The competitive adsorption results on bimetallic solutions showed that the adsorption capacity of the sorbent was restricted by the presence of other ions and suppressed the uptake of heavy metals compared to the single adsorption. Cu(2+) was the metal that most inhibited the removal of Cd(2+), Zn(2+) and Ni(2+). The Langmuir isotherm provided the best fit to the experimental data for Cu(2+), Cd(2+) and Zn(2+) and the Freundlich isotherm, for Ni(2+). The data showed that the maximum adsorption capacity a(max) for Zn(2+), Cd(2+) and Cu(2+), was 526.32 mg g(-1), 555.56 mg g(-1) and 769.23 mg g(-1), respectively. Sorption kinetics data best fit the pseudo-second-order kinetic model. The results obtained in the tests with three mining and metallurgical leachates showed that WS were effective in simultaneously removing several heavy metals ions such as Cu, Ni, Zn, Cd, Ni, As and Se.