Porous alumosilicate aggregate as lead ion sorbent in wastewater treatments

Porous alumosilicate aggregate, namely perlite, was used as an alternative material in wastewater treatments for the selective removal of ionic pollutants such as lead which is present in industrial wastewaters and toxic at relatively low concentrations. Metal retention was investigated by single metals and multispecies equilibrium isotherms (batch system) and by carrying out dynamic (column) experiments. Lead ions were supposedly preferentially retained by ion exchange at the negatively charged silicate functional groups present on the perlite material, and to a minor extent by weak electrostatic (Van der Waals) interactions at non-specific functionalities. In the case of the batch system, the Freundlich isotherm gave a good correlation of the experimental data and lead maximum retention (qmax) in single ion solution was 4.28 mg/gperlite, and in multimetal solution was 1.50 mg/gperlite. In the case of the column system, overall capacity was 3.7 mg/gperlite in single ion solution, and in multimetal solution was 3.0 mg/gperlite. In multimetal solutions, lead ions showed the best interaction at the perlite functional groups because of the lowest free energies of hydration and hydrated radius. After sorption, perlite beads were used as lightweight aggregates for cement mortars after evaluation of the potential release of lead ions from the conglomerates.