Enhancing arsenic solidification/stabilisation efficiency of metallurgical slag-based green mining fill and its structure analysis

Abstract

To dispose of arsenic-containing tailings with low carbon and high efficiency, sodium sulphate (Na2 SO4), sodium hydroxide (NaOH), calcium nitrate Ca(NO3)2 and calcium hydroxide Ca(OH)2 were independently added to metallurgical slag-based binder (MSB) solidification/stabilisation (S/S)-treated tailings (MSTs) to enhance the MST arsenic S/S performance. Results showed that only Ca(OH)2 could increase the unconfined compressive strength of MST from 16.3 to 20.49 MPa and decrease the leachate As concentration from 31 µg/L to below 10 µg/L. Na3 AsO4·12H2 O and NaAsO2 were used to prepare pure MSB paste for mechanism analysis. The results of microstructure analyses showed the high specific surface area and amorphous properties of calcium–sodium aluminosilicate hydrate facilitated the adsorption or solid-solution formation of As(V) and As(III). As(V) formed an inner-sphere complex in ettringite, whereas As(III) formed an outer-sphere complex, and the relatively larger size and charge of As(V) compared with SO42− restrict substitution inside channels without affecting the ettringite structure under high loading of As(V). The added Ca(OH)2 promoted the hydration reaction of MSBs and facilitated the formation of a Ca–As(V) precipitate with low solubility, from Ca4 (OH)2 (AsO4)2·4H2 O (Ksp = 10−27.49) to Ca5 (AsO4)3 (OH) (Ksp = 10−40.12). This work is beneficial for the application of cement-free MSB in the S/S process.