Removal of phosphate in aqueous solutions by the aluminum salt slag derived from the scrap aluminum melting process

Abstract

Aluminum salt slag, a kind of industrial by-product derived from the scrap aluminum melting process, was used to remove phosphate (P) from aqueous solutions in this research. The morphology and microstructure of the sample was characterized by Brunauer–Emmett–Teller (BET) analysis, X-ray photo-electron spectroscopy, scanning electron microscopy, and X-ray diffraction. According to the results, aluminum salt slag exhibited a surface area of 16.73 m²/g and a rough surface with many slit-shaped pores, and its main constituents were determined to be aluminum compounds and salt-flux mixture. The experimental kinetic data were well fitted using both the pseudo-second-order model and Elovich model, which revealed its nature of chemisorption and heterogeneous composites. Furthermore, the isotherm studies showed that it followed Freundlich model better than the Langmuir model, the maximal adsorption capacities calculated by Langmuir model were 2.312–3.467 mg/g. The thermodynamics study demonstrated that the adsorption process was endothermic. Additionally, it was found that a pH of 8.0 was most unfavorable to P removal and ligand exchange may be one of the main adsorption mechanisms. With the advantages of huge production, low costs, and desirable treatment efficiency, the aluminum salt slag is proposed to be another possible adsorbent for P removal from wastewater.

Keywords:

• Aluminum salt slag
• Phosphate
• Adsorption isotherm
• Kinetics
• Ligand exchange

Acknowledgments

The authors thank the support by the National Natural Science Foundation of China (41471433), the National Key Technology R&D Program of China (2012BAC06B03), the support by CRSRI Open Research Program (CKWV2013213/KY), and the Central Public interest Scientific Institution Basal Research Fund (2014-37).