Solidification of chloride ion in alkali-activated slag-red mud

As an industrial solid waste discharged during the extraction of alumina in the aluminium industry, red mud (RM) causes serious environmental pollution. Consequently, it has become imperative to utilize red mud efficiently and environmentally. This study investigated the influence of various slag/red mud ratio and alkali binder ratio on both the chloride ion solidification capacity and mechanical strength of alkali-activated slag-red mud (AASR). The physical adsorption and chemical binding of chloride ion by AASR are quantitatively evaluated. The results imply that the bound chloride content and compressive strength of AASR decreased significantly with the increase in red mud content. The increase in red mud content inhibits Friedel's salt production, resulting in a decrease in the percentage of chemically bound chloride in the total chloride binding from 26.6 % to 14.4 %. The binding chloride amount of AASR decreases with the increase in alkali binder ratio, which is related to the reduction in the quantity of hydration products per unit volume of AASR. While ensuring that the chloride ion solidification capacity and strength of the alkali-activated slag-red mud meet practical production needs, the study provides new reference data for the reapplication of red mud in marine environment. •The chloride ion solidification in AASR involves physical adsorption and chemical binding.•A moderate content of red mud promotes the formation of hydration products in alkali-activated slag.•Further increase of red mud content decrease chloride solidification capacity especially the chemical binding capacity.