Evaluation of the leaching properties of solidified heavy metal wastes

Abstract

The effects of three inorganic materials on the leaching properties of Type I Portland cement solidification matrix were studied. Also, possible effects on the cement chemistry were suggested. Cadnium nitrate and hydroxide sludges of cadmium and lead were used as the inorganic materials. Cure times of i, 7, and 28 days were studied. Leachability effects were determined by the Toxicity Characteristic Leaching Procedure (TCLP). Hydroxide sludges were added in hydroxide to cement weight percentages of 10% and 30%. A control group containing no additives were also prepared. A control group containing only hydroxide sludges was also tested by the TCLP to determine the amount of metal leached from the sludges alone.

Cadmium (Cd⁺²), in hydroxide or nitrate form, was found by leaching results to be well contained in the cement matrix. All of the TCLP leaching results for Cd⁺² were well below the 1.0 mg/L guideline established in the procedure. Lead (Pb⁺²) was found not to be readily contained as was seen by the high amounts of Pb⁺² leached. Approximately ali of the Cd was immobilized by the addition of cement after a 1 day cure time, whereas a considerable amount of Pb⁺² was still left in a leachable form after 28 days.