The removal of phosphate by thermally treated red mud from water: The effect of surface chemistry on phosphate immobilization

• Published in: Chemosphere (Oxford) 2020-05, Vol.247, p.125867-125867, Article 125867
• Main Authors: Lin, Jui-Yen, Kim, Minsoo, Li, Dan, Kim, Hyunook, Huang, Chin-pao
• Format: Article
• Language: English
• Subjects: Adsorption; Bauxite residue; Electric double layer; Hot Temperature; Industrial Waste; Phosphates - analysis; Sorption; Surface acidity; Surface precipitation; Surface Properties; Water Pollutants, Chemical - analysis; Water Purification - methods
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2020.125867

This study investigated thermal treatment of red mud (RM) and its effect on phase composition, surface property, and sorption capacity exemplified by phosphate. Dehydration (∼600 °C), decomposition of carbonate minerals (700 °C–800 °C), and silicate/aluminate formation (900 °C–1000 °C) occurred upon thermal treatment of RM. Grain growth and vitrification that rendered initial morphology changes and decreased the specific surface area of RM from 26.5 to 4.1 m2/g when treated from 600 to 1000 °C, respectively. Surface acidity, i.e., intrinsic acidity constant and surface acidity density, decreased as well after thermal treatment at 600 °C due to burnouts of organics then increased upon further elevated-temperature treatment because of phase transformation. Thermal activation enhanced phosphate adsorption density (μmol/m2). Multilayer sorption aided by leached metal ions was responsible for phosphate immobilization. [Display omitted] •Dehydration, decarbonatization, and formation of new silicate/aluminate phases occurred.•Surface acidity increased after phase transformation at high temperature.•Thermal activation increased phosphorus adsorption density.•Multilayer adsorption model better describe phosphorus uptake by thermally treated red mud.