Four stage precipitation for efficient recovery of N, P, and F elements from leachate of waste phosphogypsum

[Display omitted] •Step by step selective recovery of nitrogen, phosphorus and fluorine.•The precipitates can be used as materials especially second precipitates.•The removal efficiency of NH3-N, TP, and F− were above 99%•The emission after treatment can reach the national standard. The leachate from waste phosphogypsum contains substantial amounts of phosphorus, fluorine, ammonia nitrogen (NH3-N), and magnesium ions, which cause soil and water pollution and have great resource utilization value. In this study, quicklime and alkali were used to treat waste phosphogypsum leachate using step-by-step precipitation with precisely controlled pH values and selective recovery of valuable precipitates. The addition of CaO and NaOH in a specific order to adjust the pH value helped recover NH3-N, phosphate (PO43−), and fluoride (F−) in the leachate with a recovery rate above 99%. After the reaction, the residual ion concentration in the post leachate met the first level standard of the “Integrated Wastewater Discharge Standard” (GB8978-1996) (NH3-N