Gao, and 5 co-authors, reported in 2020 that the leaching characteristics of metallurgical slag-based-binders (MSB) solidified/stabilized tailings containing arsenic(As) and antimony(Sb), were investigated via a series of semi-dynamic leaching tests using three kinds of leachant, for the simulation of actual leaching conditions. The effectiveness of solidification/stabilization (S/S) treatment was evaluated by measuring the observed diffusion coefficients (Dobs).
The authors found that MSB efficiently prevented As and Sb leaching, providing Dobs values in the range of 10−15to 10−13cm2/s and 10−11 to 10−9 cm2/s, respectively, with the exception that the leaching mechanism of As was dissolution rather than diffusion under acetic-acid leaching conditions. Physical encapsulation was found to be the dominant mechanism for Sb immobilization,while the dominant mechanism of As immobilization was precipitation in the monolithic MSB S/S treated tailings (MST).
Results showed that the concentrations of leached As, Sb, Ca and Si, were affected by leachant pH and total acidity as well as the MSB constituent ratio. The effect of these parameters may be attributed to the stability of hydration products and their influence on the buffering capacity and structure of matrices, and the leachant pH and total acidity having the greatest influence on leaching characteristics.
The authors concluded that the effect of three types leachant on the leaching characteristics of MST via a series of semi-dynamic leaching tests where the effects of the leachant pH and total acidity and MSB constituents on the leachate pH, leached As, Sb, Ca, and Si concentrations, As and Sb leaching mechanisms, as well as the Dobs values for As and Sb, were investigated. Based on the results obtained from this study, the following conclusions can be drawn:
1) AA leachant conditions (0.17mol/L, pH 2.64) resulted in a substantially lower leachant pH,with increased leached As, Sb, Ca and Si concentrations compared to under DW and SN leachant conditions.
2) The dominant leaching mechanism of As under DW and SN leaching conditions is diffusion, while under AA leaching condition, mineral dissolution was found to be the dominant mechanism. The dominant leaching mechanism for Sb under DW, SN and AA leaching conditions was diffusion.
3) Physical encapsulation was the dominant mechanism for Sb immobilization in monolithic MST, while the dominant mechanism for As immobilization was precipitation.
4)The effects of leachant pH and MSB constituents on the leached As, Sb, Ca and Si concentrations, can be attributed to the stability of hydration products and their influence on the matrices buffering capacity and structure. Leachant pH and total acidity had the greatest influence on the leaching characteristics of MST.
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