Ion uptake properties of low-cost inorganic sorption materials in the CaO-Al2O3-SiO2 system prepared from phosphogypsum and kaolin

Phosphogypsum is an acidic by-product generated from the phosphate fertilizer industry. Accumulation of phosphogypsum in large industrial areas has raised an environmental concern due to its negative impact on water, air, and soil. The main aim of this study was to utilize phosphogypsum, in order to reduce its negative impact, for the preparation of sorbents. In this study, low-cost inorganic sorption materials in the CaO-Al2O3-SiO2 system were prepared from phosphogypsum (waste of the Almalyk Chemical Plant, Uzbekistan) and kaolin from Angren deposit, Uzbekistan by thermal activation and their uptake properties for cations and anions were investigated. The starting materials were dry mixed in different ratios using a planetary ball mill and calcined at 500-1000 °C for 2 h. The samples were characterized by X-ray diffraction, scanning electron microscopy, differential thermal analysis, and nitrogen adsorption. The uptake of ammonium, NH4+ (a representative eutrophication-related cation), dihydrophosphate, H2PO4− (a representative harmful oxyanion), and nickel, Ni2+ (a representative heavy metal cation) ions from aqueous solution by the prepared samples was investigated. The experimental results showed that the prepared samples have good ion uptake properties for NH4+ (1.03-2.34 mmol g−1), H2PO4− (0.80-2.48 mmol g−1), and Ni2+ (0.24-0.81 mmol g−1). The NH4+, H2PO4− and Ni2+ uptake of the samples is related to the chemical compositions of the samples prepared from Angren kaolin and Almalyk phosphogypsum in different ratios. From the economic and environmental viewpoints, phosphogypsum can be utilized as a low-cost raw material for preparing sorbents with high uptake ability for ammonium, dihydrophosphate and nickel ions.