Solution chemistry during cement hydration in the presence of metal hydroxide wastes

Experiments were completed to compare the effects of 10% additions of Pb, Zn, and Cd hydroxide synthetic wastes on the early hydration of ordinary Portland cement, by analysing changes in the composition of solutions extracted during hydration, and using conduction calorimetry, and differential thermal analysis. Pb2+ was initially present at high concentrations, although this rapidly falls when the rate of heat evolution increases, despite the high pH environment. The Pb waste also delayed SO42- removal from solution compared to OPC control data. Zn2+ was present in extracts at low concentrations but suppressed the heat evolution associated with normal cement hydration. SO42- was rapidly removed from solution suggesting CaZn2(OH)(6).H2O precipitates coat the surfaces of gypsum as well as cement clinker particles. Cd was present in the waste as crystalline Cd(OH)2 and was not detected in solutions extracted from hydrating cement/Cd waste. (C) 1997 Elsevier Science Ltd.