Study of continuous lead removal from aqueous solutions by marble wastes: efficiencies and mechanisms

Lead removal from synthetic solutions and real wastewater by Bianco Gioia marble wastes as abundant, renewable and eco-friendly materials was studied under different experimental conditions in a continuous stirring tank reactor. These marble wastes were found to be very efficient in removing lead for several experimental situations. Indeed, for initial aqueous pH values higher than 3.6, a lead removal efficiency of about 100 % was achieved even for high aqueous concentrations (200 mg L⁻¹), important feeding flow rates (60 mL min⁻¹) and low marble waste dosage (2 g L⁻¹). The best removal capacity (175.7 mg g⁻¹) was obtained for an initial lead concentration of 200 mg L⁻¹, a marble waste dose of 5 g L⁻¹ and an aqueous pH of 5. Even using the real wastewater with low aqueous pH (1.1), lead was also completely removed using 20 g L⁻¹ of the tested marble wastes. According to the energy-dispersive spectroscopy and X-ray diffraction analyses, lead removal seems to be controlled by both precipitation as cerussite (PbCO₃) and hydrocerussite (Pb₃(CO₃)₂(OH)₂), and adsorption onto the surface particles through cation exchange and complexation. The proposed low-cost material efficiently removes lead present in synthetic solutions and real wastewaters and constitutes an interesting environmental management option.