Stabilization/solidification of hexavalent chromium containing tailings using low-carbon binders for cemented paste backfill

Abstract

This study investigates the stabilization/solidification (S/S) capacity of Cr(VI)-containing tailings using the low-carbon, cement-free binders. The isothermal calorimeter test indicated that the addition of Cr(VI) delayed the binder hydration in the initial stage. X-ray diffraction and thermogravimetric analysis showed phase modifications with the formation of U-phase and Cr-containing hydrotalcite (Ht) like phase. Transformation of Cr(VI) to Cr(III) was noticed from the X-ray photoelectron spectroscopy, which reduced toxicity and favored the immobilization of Cr(VI). Toxicity characteristic leaching procedure (TCLP) indicated that Cr(VI) could be immobilized in S/S tailings using all the four binders in this work, but binders using calcined quarry dust as an activator presented better immobilization effect. Adding CaSO4 further in-creased the immobilization capacity due to more ettringite (AFt) generation. Partial replacement of slag by metakaolin did not significantly contribute to the hydration gels formation, but the best S/S tailings capacity was found. This was attributed to the better physical encapsulation effect due to lower porosity and water permeability. These findings have clear practical implications for S/S of hexavalent chromium containing tailings using low-carbon binders for cemented paste backfill.