Migration and Transformation of Phosphorus from Phosphogypsum Leachate with High Fluorine Concentration in Soils with Different pH Values

Abstract

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.