Research On Key Technology Of Leachate Treatment In Phosphorus Chemical Industry Slag Field Based On Full Component Recycling

The wet phosphoric acid process will produce the type II general industrial solid waste-phosphogypsum（PG）.With the rapid development of the phosphorus chemical industry,the emissions of industrial by-product phosphogypsum are increasing rapidly.However,the comprehensive utilization of phosphogypsum resources in China cannot be complete,and pile storage is still the main method of processing industrial solid waste phosphogypsum.The phosphogypsum in the storage yard is washed and leached by rainwater,and the leachate produced has the characteristics of low p H,strong corrosiveness,high total phosphorus,and high ammonia nitrogen concentration.The soluble phosphorus,ammonia nitrogen,fluorine,heavy metals and other impurities in the leachate can easily migrate to the surrounding soil,water,and atmosphere,which would lead to environmental pollution.Therefore,treatment of the leachate produced by the phosphogypsum storage yard is an urgent problem that needs to be solved for phosphate compound fertilizer production enterprises.In this dissertation,the leachate from a phosphogypsum pile of a phosphate compound fertilizer plant in Hubei Province is selected as our research object.The leachate from the pile is treated by a chemical precipitation method,and the leachate is adjusted to a specific p H using lime and flake caustic so as to achieve the purpose of removing ammonia nitrogen,phosphate and fluoride,and recover the precipitates in each stage to achieve resource utilization of N,P,and F.In addition,based on this treatment method,it is applied to the actual phosphogypsum leachate treatment engineering case.1.A new treatment method of phosphogypsum leachate was developed:Quicklime and flake caustic soda were used to treat the leachate of the phosphogypsum storage yard,under control the p H value,recovery of N、P and F was realized.The results show that adjusting p H with the addition of Ca O and Na OH can recover ammonia nitrogen（NH₃-N）,phosphate(PO₄^3-)and fluoride（F^-）in the leachate,and the recovery efficiency is above 99%.When the reaction is completed,the residual ion concentration in the post leachate meets the first level standard of"Integrated Wastewater Discharge Standard"（GB8978-1996）（Among them NH₃-N<5 mg/L,TP<0.5 mg/L,F^-<5 mg/L）;X-ray diffraction（XRD）and scanning electron microscopy（SEM）characterization showing the composition of the precipitates produced at p H 3,6,8.5,and 12provided basic data for further experimental research.2.Integrated phosphogypsum leachate resource treatment device:Based on the phosphogypsum leachate treatment method,X-ray diffraction（XRD）and XRF（X-ray fluorescence spectroscopy）are used to analyze the precipitates produced at different p H stages.The results showed that at p H=3.02,the precipitate is mainly composed of Ca F₂,Ca SO₄·2H₂O,Al PO₄ and other substances;at p H=6.23,the precipitate is mainly composed of Ca F₂,Ca HPO₄·2H₂O,Mg KPO₄·6H₂O and other substances;at p H=8.51,the precipitates are mainly composed of Mg NH₄PO₄·6H₂O,KMg PO₄·6H₂O and other substances;at p H=12.50,precipitate is mainly composed of Ca₅（PO₄）₃F,Ca₁₀（PO₄）₆（OH）₂,Mg（OH）₂ and other substances,the preciptates at different p H stages can be recycled and reused through the device designed in this paper.The resource recovery phosphogypsum leachate treatment device in this article includes:water inlet and outlet,automatic control dosing system,mixed sedimentation system and product discharge system.The water inlet and outlet and automatic dosing system are connected with the mixed settling system for adding leachate and chemicals as well as discharge the treated leachate;the product discharge system is connected with the mixed settling system to collect the solid precipitation generated by the mixed settling system.3.A demonstration project of phosphogypsum leachate was established:Based on the above-mentioned resource recovery phosphogypsum leachate treatment device and treatment method,this article analyzed the water balance and water quality of each production unit of a chemical group company in Hubei,adjusted the p H value of different nodes of the phosphogypsum leachate treatment method and the control unit of the treatment device,designed the group’s sewage treatment system,so that the ammonia nitrogen,total phosphorus,and fluoride of the effluent water reached the"Integrated Wastewater Discharge Standard"（GB8978-1996）Level 1 standard.