Evaluation of heavy metal removal from aqueous solution onto scolecite

Scolecite is a zeolite associated to basalts of the Parana Continental Igneous Province (PCIP, South America). The potential of scolecite as a new material for heavy metal removal (Pb2+, Cu2+, Zn2+, Ni2+, Co2+ and Cd2+) from aqueous solutions is evaluated. The experiments were carried out by immersion of 0.5 g of sample in solutions containing the metal ions, and kept under constant agitation for 24 h, at ambient temperature. The meq of cations retained per mass of scolecite was evaluated as a function of: initial concentration (5–60 mg L−1), pH (4–6), liquid/solid ratio (200, 1000 and 2000) and particle size. The results indicated a great affinity of scolecite for Cu2+ with a retention value of 130 μeq g−1 at pH 6, Ci=30 mg L−1 and liquid/solid ratio of 200. In the same conditions, the maximum retention measured for the other ions were 64 μeq g−1 (Zn2+), 56 μeq g−1 (Pb2+), 31 μeq g−1 (Ni2+), 7.8 μeq g−1 (Co2+) and 3.2 μeq g−1 (Cd2+). These values increase substantially when the L/S ratio is increased. The affinity of copper and lead for scolecite is discussed based on their free ionic forms (i.e., their hydrated bivalent ions) and their hydrolysis products. The remaining ions are retained as free ions.