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The extraction of silica from powdered glass cullet with an aqueous solution of sodium hydroxide has been proposed as an alternative to glass recycling aimed to the low temperature production of sodium silicates. The unextracted residue obtained after a counter current two-step extractive process at ≅ 100°C and room pressure is mainly made of calcium and sodium silicate and shows high porosity and a large surface area. We thought that it could be active as an agent for the removal of heavy metals from wastewater. In this paper the capacity of the unextracted residue of removing six metal ions (i.e., Cu2+, Ni2+, Zn2+, Cd2+, Pb2+ e Cr3+) was studied in a stirred batch reactor. The data obtained demonstrate that the removal of metal ions from wastewater is achieved with high capacity in a short time and their concentration is lowered under the legal limits without any appreciable influence from changes of physical and chemical conditions. Sodium and calcium ions take the place of heavy metals in water while pH keeps almost neutral. The exchange mechanism was identified. [ABSTRACT FROM AUTHOR]

Abstract: The unextracted residue obtained after a countercurrent two-step extractive process of silica from pumice lapillus, at 100°C and room pressure, has been found mainly crystallized to the pseudo-cubic form typical of zeolite P. This residue could be active as a low-cost agent for the removal of heavy metals from wastewater. In this paper the removal capacity of six metallic cations (i.e. Cu2+, Ni2+, Zn2+, Cd2+, Pb2+ and Cr3+) was studied in a stirred batch reactor. Results obtained showed that the removal of metal ions (100–500mgg−1) from wastewater is achieved in a short time and the concentration lowered under the legal limits. The adsorption mechanism mainly involves an ionic exchange between sodium ions from the solid phase and heavy metals in solution. However, if wastewater was accompanied by free acidity, it first should be neutralized to pH 4–5 to prevent zeolite destruction. [Copyright &y& Elsevier]