Effect of uniaxially pressing ordinary Portland cement pastes containing metal hydroxides on porosity, density, and leaching

Synthetic metal hydroxide wastes containing Zn and Pb have been mixed with partially hydrated cement and uniaxially pressed. The effect on porosity, pore size distribution, and bulk and skeletal densities has been characterised using mercury intrusion porosimetry. Ca(OH)(2) formation has been determined using differential thermal analysis and metal leaching has been assessed in a series of static leach tests completed on monolithic samples. Pressed solidified materials have increased density, reduced porosity, and reduced Ca(OH)(2). They exhibit increased resistance to acid attack in terms of sample weight loss during leaching due to reduced release of alkalis. Leaching of Zn and Pb is primarily determined by pH. A peak observed in Zn leaching from pressed samples is due to the effect of changing leachate pH on the dominant Zn species present. (C) 1998 Elsevier Science Ltd.