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Soil pH can effectively regulate phosphorus (P) transport. In this study, phosphogypsum (PG) leachate, with a high concentration of fluoride ions (F−) and low pH, was applied to soils for the control of P release under different soil pH conditions. P transport in soil columns was investigated by monitoring tracer molecules in acidic, alkaline, and neutral soils. Saturated P-soil column experiments were conducted to determine the influence of soil pH on the release and retention of P derived from PG leachate in the soil. The results were compared with those obtained using phosphate fertilizer solution and a blank control, which showed that PG leachate with a high F− concentration and low pH significantly reduced the P retention capacity of all three types of soil. The high F− concentration and low pH level of PG leachate did not affect the conversion direction of P in the acidic soil environment (S01), which was dominated by iron (Fe) and aluminum (Al) elements. In contrast, the high F− concentration and low pH level promoted the conversion of dicalcium phosphate (Ca2-P) and octacalcium phosphate (Ca8-P) to iron phosphate (Fe-P) and aluminum phosphate (Al-P) in alkaline soil (S02), which was dominated by calcium (Ca) systems. Varying pH conditions were found to change the fractions of various P forms in soil by affecting microbial biomass and activity related to soil P cycling, thus inhibiting the mutual conversion of PG leachate P between inorganic and organic forms in different types of soil. The findings of this study provide support for the effective control of soil and groundwater pollution caused by P contamination derived from PG leachate. [ABSTRACT FROM AUTHOR]

The stacking of phosphogypsum has caused considerable phosphorus pollution in water bodies near phosphogypsum yards through surface runoff and underground infiltration. The phosphate oxygen isotope (δ18O p) tracing method has served as a valuable tool for tracing phosphorus pollution in water. However, the existing δ18O p enrichment and purification methods are complex, costly, and inefficient for phosphate recovery, particularly for phosphogypsum leachate with complex compositions. Herein, a simplified and optimized pretreatment method for δ18O p measurement in phosphogypsum leachate was developed. Zirconium/polyvinyl alcohol (Zr/PVA) gel beads showed good selectivity for phosphate enrichment from water at different initial phosphate concentrations with appropriate Zr/PVA dosage. The optimal enrichment pH value was <7, and the concentrated phosphate on the Zr/PVA gel beads could be effectively eluted in an alkaline environment. Compared with the traditional Fe or Mg coprecipitation enrichment methods, impurities in the solution showed no obvious adverse effects on the phosphate enrichment process. Further, the phosphate solution eluted from the Zr/PVA gel beads was purified by a simple adjustment of the pH instead of cation exchange in the traditional purification process. Magnesium ions in the solution could be completely removed when the pH ranged from 3.17 to 6.15, and the phosphate recovery rate could reach 98.66% when the eluent pH was 5.02. Fourier-transform infrared spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy revealed that similar to traditional pretreatment method, the proposed method can obtain high-purity Ag 3 PO 4 solids for δ18O P measurement and no isotope fractionation of δ18O P was observed. Therefore, this study provides a promising and reliable pretreatment method for δ18O P measurement, especially in complex phosphogypsum leachate. [Display omitted] • Zr/PVA gel beads show strongly selective enrichment effect on phosphate from water. • The enriched phosphate by Zr/PVA gel beads can be easily eluted under alkaline conditions. • The Ag 3 PO 4 generated by the optimized purification method has a high purity enough to support δ18O P measurement. • The optimized purification method greatly simplifies the pretreatment for δ18O P measurement. [ABSTRACT FROM AUTHOR]