Stabilization/solidification of sludges containing heavy metals by using cement and waste pozzolans

The experiments were carried out with 16 mixtures of cement, fly ash, slag, and shell-lime; each of these mixtures was blended with water. The research also evaluated an optimal S/S process designed to encapsulate inorganic hazardous wastes (heavy metals) within cement, pozzolanic materials, and the accelerators which are Na₂S, NH₄Cl, FeSO₄, and water glass, thereby creating a non-hazardous product. Characteristics of the stabilized/solidified product, including compressive strength and metal concentration in the leachate, were evaluated. The compressive strength of 146 kg/cm² is attainable for solidification additives alone cured at 23°C for 28 days. Optimal mixtures are those which contain 14% of slag, 55% of fly ash, 14% of shell-lime, and 17% of cement. The optimal mixtures with the accelerator formulations are effective in solidifying electroplating and tanning waste sludges, alone with respect to reducing leachability. Consequently, the formulations are effective both with respect to the achievement of acceptable compressive strength and the reducing leachability after the increase of cement and the decrease of water-cement ratio. Appropriately blended mixture of the pozzolanic materials can serve as binding agents for solidifying wastes.