Recovery Of Phosphorus And Fluorine In Defluorination Sludge By Leaching

Defluorination sludge is the waste generated from the chemical defluorination process of wet-process phosphoric acid.The sludge contains a lot of fluorine and phosphoric acid.The utilization of phosphorus and fluorine in the defluorination sludge can not only reduce the pollution on the environment,but also produce the economic benefits.In this paper,the components of defluorinated sludge are analyzed and determined,and a process of recovering phosphorus and fluorine in the sludge by leaching is put forward.The leaching liquor is desolvated to obtain concentrated phosphoric acid,which can be used for producing fertilizer or feed.After the leaching residue is ammonolyzed,and the solution is reacted with sodium carbonate to prepare sodium fluoride.The research contents and conclusions are as follows:(1)The composition of the defluorinated sludge is analyzed.The main components of the wet sludge are fluoride,sodium fluorosilicate,phosphoric acid,silica,calcium sulfate and water.The sludge has high phosphorus and fluorine content,and the contents of P2O5,F and SiF62-in the sludge are 20.03%,1 1.15%and 10.90%,respectively.(2)The leaching processes of defluorinated sludge by water and sodium bicarbonate solution are studied,the mass ratio of phosphorus and fluorine(P2O5/F)and the leaching ratio of P2O5 and F are investigated.Under the optimized leaching conditions,the leaching ratio of P2O5 and F are 87.69%and 22.74%respectively,and the P2O5/F of leaching liquor is 6.92 in water system.For the sodium bicarbonate system,the leaching ratio of P2O5,and F are 87.30%and 13.99%respectively,and the P2O5/F is 13.23.After the leaching liquor is concentrated,the P2O5/F of the two leaching systems could not meet the production requirements of the feed-grade calcium hydrogen phosphate.(3)The leaching processes of defluorinated sludge by four organic solvents(methanol,ethanol,acetone and tributyl phosphate)are studied,the mass ratio of phosphorus and fluorine(P2O5/F)and the leaching ratio of P2O5 and F are investigated.The results show that leaching effect of methanol is the best.the leaching ratio of P2O5 and F are 97.72%and 4.15%respectively,and the P2O5/F of leaching liquor is 42.42.After concentration of methanol leaching liquor,the content of P2O5 and P2O5/F of the concentrated solution both meet the production requirements of the feed calcium,and recovery rate of methanol is more than 98%.(4)The process of preparing sodium fluoride by ammoniation of residues is studied.First,sodium fluorosilicate in the residue is decomposed by ammonia,and then sodium fluoride is prepared with sodium carbonate by metathesis reactions.The optimal conditions of ammonia hydrolysis are obtained.The results show that the yield of total F reaches 71.08%,and the purity of sodium fluoride is more than 97%,which meets the national standard requirement of YS/T517-2009.