Batch experiments were carried out to investigate the kinetics of adsorption of lead ions by steel slag on the basis of the external diffusion, intraparticle diffusion and adsorption reaction model (pseudo-first-order, pseudo-second-order). The results showed that the controlling step for the adsorption kinetics changed with experimental parameters varied. When the particle size of steel slag was larger than 120 mesh, intraparticle diffusion of Pb²⁺ was the controlling step; when the initial concentration of Pb²⁺ was less than 150 mg L^—1 or the shaking rate was lower than 150 rpm, external diffusion of Pb²⁺ was promoted. Contrary to the former experimental conditions, the adsorption reaction was the controlling step, and the adsorption followed second-order kinetics, with an adsorption rate constant of 13.26 g mg^—1 min^{— 1}. The adsorption isotherm of Pb²⁺ with steel slag followed the Langmuir model, with a correlation coefficient of 0.99.

Direct application of aerobic biodegradation for leachate treatment is not feasible due to high concentrations of nitrogen and chemical oxygen demand. Several potential leachate treatment schemes incorporating struvite precipitation as pretreatment and two types of activated sludge processes (conventional activated sludge and batch decant reactor (intermittent cycle extended aeration system [ICEAS process]) with and without addition of powdered activated carbon (PAC) were evaluated in this study. The hydraulic retention times (HRT) of 6 h and 12 h were applied in the biological stages of each process. Treatment schemes incorporating PAC addition showed acceptable results. In the conventional activated sludge process, total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), NH₃, and P removal rates were 87, 84, 98.3, and 94%, respectively, with HRT of 6 h and 95.8, 95.1, 99.1, and 98.7% with HRT of 12 h. For the ICEAS process, removal rates were 89.3, 87.9, 98.2, and 94% with HRT of 6 h and 95.8, 95, 99.2, and 98.7% with HRT of 12 h. On the basis of these results, it can be concluded that struvite precipitation, followed by activated sludge process with PAC addition, can be a strong alternative leachate treatment, achieving the standards set for effluent discharges to receiving waters.

This study investigated the pozzolanic reactions and engineering properties of waste brick-blended cements in relation to various replacement ratios (0—50%). The waste brick consisted of SiO₂ (63.21%), Al₂O₃ (16.41%), Fe₂O₃ (6.05%), Na₂O (1.19%), K₂O (2.83%) and MgO (1.11%), and had a pozzolanic activity index of 107%. The toxic characteristic leaching procedure (TCLP) results demonstrate that the heavy-metal content in waste bricks met the Environmental Protection Agency regulatory limits. Experimental results indicate that 10, 20, 30, 40 and 50% of cement can be replaced by waste brick, which causes the initial and final setting times to increase. Compressive strength development was slower in waste brick-blended cement (WBBC) pastes in the early ages; however, strength at the later ages increased significantly. Species analyses demonstrate that the hydrates in WBBC pastes primarily consisted of Ca(OH)₂ and calcium silicate hydrate (C—S—H) gel, like those found in ordinary Portland cement (OPC) paste. Pozzolanic reaction products formed in the WBBC pastes, in particular, various reaction products, including hydrates of calcium silicates (CSH), aluminates (CAH) and aluminosilicates (CASH), formed as expected, resulting in consumption of Ca(OH)₂ during the late ages of curing. The changes in the properties of WBBC pastes were significant as blend ratio increased, due to the pores of C—S—H gels and CAH filling via pozzolanic reactions. This filling of gel pores resulted in densification and subsequently enhanced the gel/space ratio and degree of hydration. Experimental results demonstrate waste brick can be supplementary cementitious material.