Solidification of lead ions in portland cement matrix

Solidification/stabilization is world-wide accepted treatment for immobilization of wastes such as heavy metals and represents mixing of materials with binders and reagents in order to reduce the leaching of contaminants. The most commonly used medium in solidification/stabilization process is Portland cement, pozzolana such as fly ash from coal and solvent silicates. The purpose of this paper is to investigate the use of pure Portland cement and Portland cement with addition of 30% fly ash as binders for immobilization Pb2+ ions. Samples (1×1×6 cm) were prepared by mixing cement with water containing 10 000 mg/dm3 Pb2+ and 30 000 mg/dm3 Pb2+. These samples were immersed in an aggressive acid solution (pH=4) and deionized water as reference. The temperature of acid solution and deionized water was 20°C and 50°C. Flexural strength of samples was measured. After 1, 3, 7, 14, 28, 35, 42, 49 and 56 days the concentration of toxic metal ions and Ca2+ ions in leachate solutions was determined by atomic absorption spectrometry. The end product of treatment, usually after sufficient curing, is solid monolithic material which, depending on characteristics of leaching, can be usefully applied or disposed of in a safe way. © 2000 Elsevier Ltd. All rights reserved