Study On Solidification Of Fluorine And Soluble Phosphorus And Control Method Of Water Content In Phosphogypsum

Phosphogypsum is a kind of industrial waste with high moisture content produced by acid hydrolysis of phosphate ore in the production process of wet process phosphoric acid.At present,more than 250 million tons of phosphogypsum are piled up in China.Moreover,phosphogypsum contains much soluble phosphorus,fluorine and harmful substances which are easy to migrate.Once they enter the environment,they will bring serious pollution to the surrounding areas of enterprises.Therefore,harmless treatment of phosphogypsum has become one of the issues that concern the academia,society and industry.This thesis is based on the principle of precipitation-dissolution equilibrium,the principle of surfactant compounding and the principle of interfacial chemistry.Centre on the moisture content control technology and the harmless treatment method of phosphogypsum are systematically studied.The main conclusions are as follows:1 The physicochemical properties of phosphate ore and phosphogypsum were analyzed by XRF,XRD,DTA-TGA,SEM-EDS and laser particle size analysis.The results shown that the main components of phosphogypsum are CaSO₄·2H₂O and SiO₂.The main impurities are soluble phosphorus,F^-and other substances.The size distribution of phosphogypsum crystal is not uniform,and its morphology is thin plate and rod.2 Based on the interfacial chemical behavior of wet-process phosphoric acid leaching system,the study on the control of water content of phosphogypsum by surfactant was carried out.The results shown that among PDMS,D-G,PVA,PEG and TW80 non-ionic surfactant,PDMS non-ionic surfactant has the best effect on reducing the water content of phosphogypsum,which the water content of phosphogypsum is reduced by 4.35%.Among SDBS,SDS,ALS,SC,CTAC ionic surfactant,SDBS and CTAC ionic surfactant have better effect on reducing the water content of phosphogypsum,respectively.The moisture content of phosphogypsum was decreased by 6.76%and 5.8%.3 According to the principle of surfactant mixing,the study on the control of water content in phosphogypsum by binary surfactant mixing was carried out.The results shown that binary surfactant PDMS+SDBS,D-G+SDBS,PDMS+SDS,D-G+SDS,SDS,SDS+SDS,CTAC+SDS,CTAC+SDBS,PDMS+CTAC,D-G+CTAC,PDMS+D-G can reduce the water content of phosphogypsum.Among them,PDMS+SDBS has the best effect in reducing the water content of phosphogypsum,making the phosphogypsum crystal change from short rod shape,thin plate shape to coarse rod shape.When the mass ratio of PDMS and SDBS is 4:6,the water content of phosphogypsum was decreased by 15.7%.4 The stabilization of soluble phosphorus and fluorine in phosphogypsum was studied using by calcium carbonate,magnesium carbonate and calcium hydroxide as curing agents.The results shown that CaCO₃,Ca?OH?₂,MgCO₃ and CaCO₃+Ca?OH?₂+MgCO₃ can effectively stabilize the soluble phosphorus and fluorine in phosphogypsum.Soluble phosphorus and fluorine in phosphogypsum cured by CaCO₃+Ca?OH?₂+MgCO₃ mixture are better than CaCO₃,Ca?OH?₂ and MgCO₃ curing agent.When the mass ratio of phosphogypsum to curing agent is 25:1,the curing rates of soluble phosphorus and fluorine in phosphogypsum by CaCO₃+Ca?OH?₂+MgCO₃mixture are 70.11%and 96.79%respectively.The stabilized phosphogypsum meets the national phosphogypsum emission standard.In summary,the technology of controlling water content of phosphogypsum by surfactant and stabilizing phosphogypsum by curing agent can effectively reduce moisture content of phosphogypsum and its soluble phosphorus and fluorine.This thesis will provide reference for the industrialization of harmless treatment and resource utilization of phosphogypsum.