Enhanced phosphate removal with fine activated alumina synthesized from a sodium aluminate solution: performance and mechanism

• Published in: RSC advances Vol. 12; no. 8; pp. 4562 - 4571
• Main Authors: Wu, Guoyu, Liu, Guihua, Li, Xiaobin, Peng, Zhihong, Zhou, Qiusheng, Qi, Tiangui
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 03.02.2022; The Royal Society of Chemistry
• Subjects: Adsorption; Aluminum oxide; Chemisorption; Chemistry; Fourier transforms; Infrared analysis; Photoelectrons; Protonation; Sodium aluminate; Specific surface; Surface area; Surface chemistry; Synthesis; Transitional aluminas
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d1ra08474g

Fine activated alumina (FAA) acting as an adsorbent for phosphate was synthesized from an industrial sodium aluminate solution based on phase evolution from Al(OH) 3 and NH 4 Al(OH) 2 CO 3 . This material was obtained in the form of γ-Al 2 O 3 with an open mesoporous structure and a specific surface area of 648.02 m 2 g −1 . The phosphate adsorption capacity of the FAA gradually increased with increases in phosphate concentration or contact time. The maximum adsorption capacity was 261.66 mg g −1 when phosphate was present as H 2 PO 4 − at a pH of 5.0. A removal efficiency of over 96% was achieved in a 50 mg L −1 phosphate solution. The adsorption of phosphate anions could be explained using non-linear Langmuir or Freundlich isotherm models and a pseudo-second-order kinetic model. Tetra-coordinate AlO 4 sites acting as Lewis acids resulted in some chemisorption, while (O) n Al(OH) 2 + ( n = 4, 5, 6) Brønsted acid groups generated by the protonation of AlO 4 or AlO 6 sites in the FAA led to physisorption. Analyses of aluminum-oxygen coordination units using Fourier transform infrared and X-ray photoelectron spectroscopy demonstrated that physisorption was predominant. Minimal chemisorption was also verified by the significant desorption rate observed in dilute NaOH solutions and the high performance of the regenerated FAA. The high specific surface area, many open mesopores and numerous highly active tetra-coordinate AlO 4 sites on the FAA all synergistically contributed to its exceptional adsorption capacity. A fine activated alumina with high specific surface area was prepared by phase evolution from sodium aluminate solution, Al(OH) 3 and NH 4 Al(OH) 2 CO 3 . The maximum adsorption capacity was 261.66 mg g −1 and the regenerated material exhibited high performance phosphate removal.