Research on Process and Mechanism of Efficient Isolation of Sr/S in Celestite for Srtontium Compounds Preparing

Author:Chen Si Ming

Supervisor:duan dong ping

Database:Doctor

Degree Year:2018

Download:4

Pages:167

Size:5329K

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With development of science and technology,the demands of strontium compounds in many fields,e.g.electronic information,chemical,medicine,ceramics,glass,pyrotechnics,metallurgy,military is acutely increasing.However,at present,the carbothermic reduction method for preparing SrCO3 from celestite,which is the mainly used conversion process in strontium plant,has several defects,as lagging in technology,low reaction efficiency,environmental pollution and so on.It seriously hampers improvement of yield and quality of strontium compounds.In this paper,after analyzing the Sr/S isolation from carbothermic reduction method for preparing SrCO3 by celestite,a novel Sr/S isolation mechanism has been established combining with technology of reduction of carbon containing pellet and pressure oxidation.Therefore,a novel method namely high temperature rapid reduction-pressure oxidation treating for celestite was developed.In addition,the feasibility of preparing Sr(OH)2 from celestite direct was also confirmed.It includes five aspects as follows:A)The effects of conditions of carbothermic reduction on the composition of SrSO4 reduction product were studied by thermodynamics simulation.The results showed that the reaction temperature and C/O molar ratio in the reactant had the most serious influence on the composition of SrSO4 reduction product.Theoretical calculation results showed that only one species as SrS can be found in SrSO4reduction product when the reaction temperature was below 986 oC.And the SrO/SrS molar ratio in SrSO4 reduction product could be varied with different C/O molar ratio in the reactant when the reaction temperature was higher than 986 oC.Further research showed that the reduction mechanism of SrSO4 accorded with disproportionation reaction process.Sr/S isolation cannot be effectively realized in the process of SrSO4 reduction.B)According to the method for manufacturing carbon containing pellet,carbon containing pellet were prepared by mixture of SrSO4 and reducing agent as graphite,anthracite or charcoal.And they were used to research the effects of sort of reducing agent,reaction temperature,C/O molar ratio and reaction time on the reduction ratio of SrSO4.The results showed that anthracite and charcoal have better capabilities for reducing SrSO4 than graphite.With the increasing of reaction temperature and C/O molar,the reducing capabilities of all of reducing agents promoted with increasing of reaction temperature and C/O molar ratio.However,when C/O molar ratio exceeded1.0,the reducing capacities of reducing agent to SrSO4 were nearly saturated.The kinetic parameters of the reduction process of SrSO4 by graphite,anthracite and charcoal were calculated.The results revealed that the reduction process of SrSO4 by these three reducing agents were controlled by the interfacial reaction.The apparent activation energies of the reaction were 105.4 kJ/mol,85.9 kJ/mol and 73.1 kJ/mol,respectively.C)E-pH diagram of S-H2O system was analyzed to confirm the feasibility of isolation of Sr/S in pressure oxidation process of SrS solution.The effects of HCl addition,initial total sulfide concentration,reaction temperature and reaction time on the distribution of S element were investigated.The isolation rules of Sr/S under various conditions were clarified and a novel isolation method of Sr/S was established.It demonstrated that the intermediate x2S-(x=2-5)appeared in oxidation process of S2-in SrS solution.And then the x2S-could be converted into S0,SrSO3 or SrSO4.The mechanisms for forming SrSO4 and SrSO3 in pressure oxidation of SrS were different.SrSO3 was generated by Sx2-,while SrSO4 was generated byS2 O32-which was oxidation by xS2-,or S2-ions which was obtained by decomposing of x2S-in acid solution.D)A process as high temperature rapid reduction–pressure oxidation had been developed for transforming celestite to SrCl2.The effects of added amount of reducing agent,reaction temperature and reaction time on the reduction efficiency of sulfate in celestite were investigated.After optimizing of reaction process parameters,the reduction efficiency of sulfide in celestite could reach 94.3%when the reaction time was only 9 min.The effects of added amount of HCl,initial partial pressure of O2,solid-to-liquid ratio,reaction temperature,reaction time and the number of leachate cycles on the conversion ratio of S0 and H2S and leaching ratio of Sr were investigated.By optimizing the pressure oxidation process conditions,the leaching ratio of Sr could reach over 88%,and the conversion ratio of S0 could reach higher than 76%.After analyzing the result obtained by sixth cycle process of leaching,no obviously decline of conversion ratio of S0 and leaching ratio of Sr could be found.At meanwhile,the conversion ratio of H2S in tail gas was less than 0.6%.The Sr/S molar ratio in leachate could be increased to 10.75.All of the results confirmed that the high temperature rapid reduction–pressure oxidation process for celestite treatment not only ensured the efficient Sr/S isolation,but also effectively inhibited the H2S emissions during the reaction process.E)Aiming at the defects of double decomposition process,the target product was located at soluble Sr(OH)2.Therefore,a novel process for preparing Sr(OH)2 from celestite direct was developed.The effects of initial alkaline concentration,solid-to-liquid ratio,reaction temperature and reaction time on the isolation process of celestite were investigated.The feasibility of direct transformation from celestite to Sr(OH)2 was confirmed.Under optimal conditions,the Sr/S molar ratio of celestite increases from 0.92 to 8.22.And the conversion ratio of Sr(OH)2 was 90.4%at this condition.The mechanism of Sr/S isolation was deducted by analyzing the morphology and composition of reduction process.After alkaline conversion of pre-treated celestite,Sr element was deposited with formation of Sr(OH)2,while SO42-was transferred into leachate.Therefore,Sr/S isolation was carried out in this process.