Application of Phosphogypsum as Soil Amendment in Karst Farmlands and Its Environmental Impact Assessment

<p indent="0mm"> The management of phosphogypsum solid waste pollution and resource utilization pose key technical challenges for the sustainable development of the phosphate chemical industry in Southwest China′s karst regions. Investigating methods for using phosphogypsum to improve local soils has significant potential value for the large-scale disposal of phosphogypsum solid waste. Nonetheless, the specific impacts of phosphogypsum addition on soil physical and chemical properties have not been fully elucidated. This study conducted amendment and soil column leaching experiments on the yellow soils of karst farmlands using purified phosphogypsum and crude phosphogypsum. The experimental results show that under the influence of phosphogypsum amendment, the pH value of the yellow soil decreased by 0.59 to 3.09 units on average, the moisture content increased by 4.9% to 30.0%, and the total phosphorus content significantly increased from <sc>190 mg/kg</sc> to <sc>5 768 mg/kg.</sc> Simultaneously, minor declines were observed in the content of total nitrogen and total potassium in the soil. Whether purified phosphogypsum or crude phosphogypsum was added, the contents of potential toxic heavy metals such as Pb (lead), Cr (chromium), Cd (cadmium), and As (arsenic) in the yellow soil remained below the risk control values for soil pollution in agricultural lands. The results of the leaching experiments showed that the addition of a small amount of purified phosphogypsum could increase the phosphorus content in loess while maintaining low phosphorus losses, while the treatment with unpurified phosphogypsum, although more effective in fertilizer enhancement, was accompanied by higher phosphorus losses, thus increasing the risk of ″secondary pollution″. Therefore, the purified phosphogypsum used to improve karst soil has a certain application potential in improving the water retention and nutrient content of the soil and effectively controlling the risk of heavy metal pollution.