Comparison of the Stabilization/Solidification (S/S) of three galvanic wastes using cement, cement with soluble silicates or magnesium phosphate cements

The galvanic processes used for coating metallic or plastic surfaces generate wastes that should be properly treated before their disposal in a landfill. Stabilization /Solidification (S/S) converts them to solids and reduces the release of heavy metals. In this study, three real wastes (an exhausted electroless nickel plating bath, an exhausted chromium electroplating bath and a zinc plating sludge) were stabilized using different reagents: Portland cement type I, Portland cement mixed with soluble silicates and magnesium phosphate cements prepared with MgO extrapure or hard burned magnesia of about 70 % purity and phosphates like Na3PO4, Na2HPO4 or KH2PO4. In order to analyze the retention of the heavy metals by the matrix the samples were subjected to the leaching test number 2 of the Spanish Order 13/10/89 (similar to the Toxicity Characteristic Leaching Procedure of the U.S. EPA). Heavy metal concentration of the leachate was determined using ICPMS. It was found that magnesium phosphate cements obtained by mixing hard burned magnesia with the different phosphates are appropriate for the Stabilization/Solidification (S/S) of the wastes containing nickel and zinc. The waste containing chromium showed in all cases a Cr(VI) concentration above the limit defined by the U.S.EPA for the disposal of a waste.