Preparation of activated red mud particle adsorbent and its adsorption mechanism for phosphate ions

• Published in: Desalination and water treatment Vol. 188; pp. 169 - 184
• Main Authors: Li, Longjiang, Zhang, Qin, Li, Xianbo, Cheng, Wei, Ban, Lan
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-06-2020
• Subjects: Adsorption mechanism; Non thermally activated red mud particle adsorbent (ARMFA); Phosphate flotation tailwater; Phosphate ion; Non thermally activated red mud particle adsorbent (ARMFA); Phosphate ion; Phosphate flotation tailwater; Adsorption mechanism
• ISSN: 1944-3986; 1944-3986
• DOI: 10.5004/dwt.2020.25342

Herein, granulation molding was conducted using a disc granulator via a two-step rolling granulation method. Red mud (RM), which has good absorption efficiency on phosphate ions in wastewater, was used as the raw material, and some amount of fly ash was doped as a pore-assisting modifier. High belite cement and hydroxypropyl methyl cellulose were used as binders; HCl was the active modifier, and H2O2 and MnO2 were the pore regulators. A non-thermally activated red mud particle adsorbent (ARMFA) was prepared via an optimal formulation of the above additives, and the adsorbent had 9.25 pH, 40.54 m2 g-1 specific surface area, 2.10 cm3 g-1 pore volume, 1.31 KPa compressive strength, and 3.72% pulverization rate at 24 h. This adsorbent can be used to adsorb phosphate ions (P) in phosphate ore dressing plant discharge wastewater. For 156.7 mg L–1 total initial P concentration, 25 g L–1 ARMFA amount, 14 h adsorption time, and 38.46 mg g–1 adsorption and 98.17% removal rate of the total P were achieved. Particularly, the toxicity of ARMFA was below the standard limit. When the pH was 8–9, P mainly existed in the form of HPO42- and PO43-. These ions reacted with Ca2+, Na+, Al3+, Mg2+, etc., and formed strong chemical bonds through surface deposition and ion exchange, which were then distributed on the inner surface of the ARMFA channels. The adsorption of P by the ARMFA is per the pseudo-second-order dynamics model, and the Langmuir model can best describe the adsorption process. Phosphorus, fluorine, and other toxicity indicators in the tailwater after adsorption reached the standard requirements. After adsorbing P, the alkalinity of the ARMFA decreased, and the metal ions and toxic substances were consolidated. These results provide a foundation for the use of RM in building materials.