Red mud (RM) is an industrial waste produced in large amounts during alumina extraction from bauxite. Its disposal generates serious environmental pollution due to high alkalinity. Therefore, a strategy for the effective utilization of RM must be developed. For instance, RM may be transformed into useful products, such as adsorbents. Given its high concentrations of aluminum oxides, iron oxides, titanium oxides, silica oxides, and hydroxides, RM may be developed as a cheap adsorbent for the removal of various ions from aqueous solution and soils (e.g., metal and non-metal ions, phenolic compounds, and dyes) and waste gas purification (sulfide and carbide). This review summarizes the background, properties, and applications of RM as an adsorbent. Proper approaches of removing metal and non-metal elements from wastewater are also systematically reviewed and compared. Emphasis is placed on the surface modification of RM to obtain high adsorption. Finally, the scope for future research in this area for RM is discussed in depth.

Cassiterite is the most common and important tin-bearing mineral, and calcite, a primary gangue mineral is generally found in tin deposit. The flotation separation of cassiterite from calcite remains a challenge due to their similar response to traditional reagents. In cassiterite flotation, sodium oleate (NaOL) and sodium silicate (SS) have been widely used as a collector and a depressant, respectively. However, the low selectivity of NaOL and the large amount of SS required (which leads to serious problems in wastewater treatment) remain a difficult issue. In this study, a novel reagent scheme using lead nitrate as the activator, salicylhydroxamic acid (SHA) as the collector and carboxymethyl cellulose as the depressant was employed to improve the separation selectivity of cassiterite from calcite. Results of the flotation experiment using this new reagent scheme showed that compared with the previously reported scheme using benzohydroxamic acid (BHA) as the collector, the separation of cassiterite from calcite exhibited a higher selectivity and selectivity index (SI). The mechanism of the selective separation was investigated by zeta potential measurements, Fourier transform infrared and X-ray photoelectron spectroscopy analysis.