Effect of Acidic Oxides
It can be seen from Figure S2 (Supporting Information) that as the SiO2 contents increase, the leaching contents of Cd and Cu of the three specimens (1 mg kg−1 Cd, 25 mg kg−1 Cd, and 50 mg kg−1 Cd) increase at the 24th h or on the 30th day; the leaching contents of Cr gradually decrease, while the leaching contents of Pb first decrease and then increase. The binding of trace metals (Cd and Cu) changes significantly as the SiO2 contents increase, meaning that most of the heavy metals become more readily available for leaching. The leaching behavior of Pb in this study indicates that as the SiO2 contents are >27%, Pb may be ejected from the bulk structures of ceramsite during the restructuring process and may be relatively enriched on the surface of the particles, which, therefore, leads to higher leaching contents of Pb. At the 24th h or on the 30th day, the leaching contents of Cd, Cr, Cu, and Pb increase as the Al2O3 contents decrease (as shown in Figure S3, Supporting Information). The reason may be that, during the sintering process, the increasing quantities of Al3+ may substitute for the Si4+ in a network tetrahedron (23) and other unreacted Al2O3 present as oxide acts as an accelerator using the readily available cations (such as Cd, Cr, Cu, and Pb) to increase the pozzolanic reactions, which contribute to the stability of the networks and make heavy metals to enclose in the framework of silicates or aluminosilicates and make them difficult to be leached.
Effect of Acidic OxidesIt can be seen from Figure S2 (Supporting Information) that as the SiO2 contents increase, the leaching contents of Cd and Cu of the three specimens (1 mg kg−1 Cd, 25 mg kg−1 Cd, and 50 mg kg−1 Cd) increase at the 24th h or on the 30th day; the leaching contents of Cr gradually decrease, while the leaching contents of Pb first decrease and then increase. The binding of trace metals (Cd and Cu) changes significantly as the SiO2 contents increase, meaning that most of the heavy metals become more readily available for leaching. The leaching behavior of Pb in this study indicates that as the SiO2 contents are >27%, Pb may be ejected from the bulk structures of ceramsite during the restructuring process and may be relatively enriched on the surface of the particles, which, therefore, leads to higher leaching contents of Pb. At the 24th h or on the 30th day, the leaching contents of Cd, Cr, Cu, and Pb increase as the Al2O3 contents decrease (as shown in Figure S3, Supporting Information). The reason may be that, during the sintering process, the increasing quantities of Al3+ may substitute for the Si4+ in a network tetrahedron (23) and other unreacted Al2O3 present as oxide acts as an accelerator using the readily available cations (such as Cd, Cr, Cu, and Pb) to increase the pozzolanic reactions, which contribute to the stability of the networks and make heavy metals to enclose in the framework of silicates or aluminosilicates and make them difficult to be leached.
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