Phosphorus Resource Recovery And Wastewatertreatment Of Circulating Waterin Phosphoric Acid Production

Convert the P₂O₅in the circulating water of phosphoric acid production enterprises into feed-grade calcium hydrogen phosphate products with high added value,make full use of the phosphorus resources,reduce the harm to the environment,reduce production costs and increase profits.The phosphorus-containing wastewater was adsorbed by calcium-magnesium-aluminum hydrotalcite prepared from phosphorus tailings,and the phosphorus-containing wastewater was treated with roasted phosphorus tailings,which reducedthe phosphorus content in the wastewater.The reuse of solid waste phosphorus tailings achieves the purpose of"using waste to treat waste",and also provides sometheoreticalbasis for thecomprehensivetreatment ofphosphorus-containing wastewater.Themain contentsoftheexperiment areas follows:（1）In the defluorination experiment by adding phosphoric acid to increase the acidity of the circulating water,when the initial P₂O₅concentration was adjusted to 34000 mg·L^-1,1.66 g of CaO powderand0.1%Na₂Si O₃·9H₂O wereslowlyadded,and thereaction temperaturewas55℃andthe p Hvalueofthe reaction endpoint was3.36,them（P₂O₅）/m（F）inthe circulatingwaterreached546.28.This result met the requirement that m（P₂O₅）/m（F）≥230 in the reaction solution can prepare feed-grade calcium hydrogen phosphate.Then add lime milk as a neutralizer to prepare feed-grade calcium hydrogen phosphate,and control the p H of the end point to be less than 6.0 to prepare type I feed-grade calcium hydrogen phosphate with a total phosphorus content of more than 16.5%.And the content of citric acid-soluble phosphorus in the product was more than 14%,and the fluorine content wasless than0.18%.Inthe comprehensive defluorination test,without adding phosphoric acid,0.36 g of CaOpowder,0.6times thetheoreticalvalueof Na₂Si O₃·9H₂O andflyashwitha mass fraction of2.5%wereadded,the reaction temperature was 25℃,and the stirring reaction time was 1.5 h.The m（P₂O₅）/m（F）after defluorination reached 305.49,which met the requirement of m（P₂O₅）/m（F）≥230 in the reaction solution to prepare feed-grade calcium hydrogen phosphate.The mixed solution prepared by adding CaCO₃and CaO in different proportions was used as a neutralizer to prepare feed grade calcium hydrogen phosphate.Due to the slow reaction speed of calcium carbonate and phosphoric acid,with the increase of calcium carbonate content,the product quality decreased under the same reaction conditions.The precipitates prepared after defluorination by the two methods were analyzed.The results of XRD and scanning electron microscope（SEM）showed that the two precipitates were mainly calcium hydrogen phosphatedihydrate.（2）Calcium-magnesium-aluminum hydrotalcite was prepared from phosphorus tailings and applied to the treatment of phosphorus-containing wastewater.At the same time,the calcination temperature,adsorbent dosage,p Hvalue,reactiontemperature,coexisting ions and adsorption kinetics were studied.The results showed that the optimal calcination temperature was 400℃,the optimal dosage was 1.5 g·L^-1,the adsorption effect of CLDHs on phosphorus was better under acidic conditions,and the effect of coexisting ions on phosphorus adsorption capacity was CO₃^2->SO₄^2->HCO₃^->NO₃^->Cl^-.When the calcination temperature was 400℃,the dosage of CLDHs was1.5 g·L^-1,the rotating speed in the constant temperature oscillator was 180 r·min^-1,the p H value was6.0,and the reaction temperature was 25℃,the adsorption process was most consistent with the pseudo-second-order kinetics equation,the fitted R²was 0.9980,and the saturated adsorption capacity can reach 21.46 mg·g^-1.The adsorption process was more consistent with Langmuir isothermal adsorptionmodel.The LDHs before and after adsorption of phosphorus were analyzed.XRD and FT-IR results showed that the calcined LDHs could recover part of the layered structure after adsorption of phosphorus,but the degree of crystallinity and regularity decreased.The FT-IR results showed that when LDHs recovered its layered structure,some phosphate ions intercalated into the interlayers of hydrotalcite.（3）Roasting phosphorus tailings can effectively treat phosphorus-containing wastewater,which provides an effective technical path for the resource utilization of phosphorus tailings,which can reduce costs and reduce environmental pollution.For the phosphorus-containing wastewater with aninitial concentrationof44.51 mg·L^-1,2.5 g·L^-1ofhigh-magnesium-phosphorus tailings roasted at950℃were added.After the reaction for 20 min,the phosphorus removal rate of the phosphorus-containing wastewater reached 99.44%.Phosphorus content was reduced to0.25mg·L^-1,reaching the first-class standard of"Integrated Wastewater Discharge Standard（GB 9897-1996）".The effect of phosphorus tailings roasted at 950℃in the treatment of phosphorus-containing wastewater was better than that ofphosphorus tailings roasted at 650℃in the treatment of phosphorus-containing wastewater.The addition of ammonia water can improve the treatment effect of phosphorus-containing wastewater,but it may cause ammonia nitrogen exceeding the standard,resulting in newpollution.