Permanent storage of chromium in hardened FAU-type zeolite /cement pastes

This chapter presents chromium (Cr) removal from wastewater by ion exchange using FAU-type zeolites and the subsequent stabilization of the resulting sludges in the cement matrix. Amounts of 5 g/l of synthetic faujasite-like zeolite X or 8 g/l of a faujasite- and phillipsite-rich tuff are able to bring the Cr3+ concentration in a wastewater of an electroplating plant, below the law limits allowed for discharge in times of practical significance. The compressive strengths of the compacts containing 10% to 75% of zeolitic materials are much higher than the value of 0.44 megapascal (MPa), suggested by international protocols for handling and landfilling the solidified wastes. Moreover, suitable leaching tests on the hardened pastes result in a Cr 3+ concentration in the leachates lower than the law limits allowed for discharge in water bodies.