Recovery of calcium and sulphur from phosphogypsum with zero by-product generation using a preparative vertical-flow electrophoresis system

Phosphogypsum has been a longstanding issue that poses environmental risks and economic pressure on society. Realizing the recycling of this waste is essential for achieving sustainable phosphorus chemical industry. In order to tackle this problem, this study examined the potential of using a preparative vertical-flow electrophoresis (PVFE) system with supporting media to recover calcium and sulphur from phosphogypsum without producing any by-products. NaOH was used to convert phosphogypsum into slaked lime and Na2SO4, with a maximum leaching efficiency of 98.6 % achieved at a NaOH concentration of 2 mol/L and a molar ratio of sodium to sulfur of 2.1. The slaked lime obtained met the quality standards outlined in the Chinese national standard (HG/T 4120-2009). Electrophoresis separation of the resulting Na2SO4 demonstrated that the NaOH effluent output could reach the desired concentration for reusing in the treatment of phosphogypsum. The addition of a solid supporting media (quartz sands) is the key to achieving the separation of Na2SO4. After considering the economic benefits, the optimal electrophoresis conditions for separating Na2SO4 were determined to be a supply voltage of 10 V and HRT of 240 min. These findings offer a directed and practical solution for the economical and effective recycling of phosphogypsum in phosphorus chemical industry.