Eco-efficient treatment of hazardous bauxite liquid-residue using acid-activated clays

The alumina industry requires a material capable of reducing the high levels of iron and alkalinity in bauxite liquid-residue in an eco-efficient manner while producing fewer by-products. This study looked at the efficacy of acid-activated kaolin (AAK) and acid-activated bentonite (AAB) in reducing the high pH value and iron content of bauxite liquid-residue in a single treatment step. The bauxite residue, AAB, and AAK were characterised using XRD, XRF, and FTIR techniques. A batch adsorption study with varying contact times and adsorbent types was conducted, and the results were analysed using adsorption kinetics and isotherm studies. The results showed that AAK and AAB could effectively remove 88% to 94% of the total iron in the bauxite liquid-residue. Similarly, the initial pH value of the bauxite liquid-residue (9.93 ± 0.13) was reduced by about 3.32% with AAK and 4.53% with AAB, respectively. Thus, batch adsorption studies revealed that adsorption capacity was strongly pH dependent, and the type of adsorbent had an effect on the reduction of iron and pH value in the bauxite liquid-residue. The AAB was found to be more effective than AAK in lowering the high pH value and iron content of the bauxite liquid-residue.