Basic Research On The Influence Of Dopants On The Carbothermal Reduction Reaction Of Phosphate Rock

As a basic chemical raw material,phosphoric acid is used in many industries and plays an important role in national life.At present,the domestic methods for producing phosphoric acid mainly include wet method and thermal method.Although the relative cost of wet-process phosphoric acid is lower,the quality of phosphoric acid is poor,the impurity content is high er,and it can’t be directly used as high-quality phosphoric acid.The thermal method produces better quality of phosphoric acid,the energy consumption are higher,and the economy is lower.The kiln method,as an environmentally-friendly and energy-saving high-quality phosphoric acid production method.It cannot be industrialized due to problems such as the ring in the rotary kiln and the low uti lization rate of phosphate rock.Therefore,based on the above problems,it is a new way to solve the problem of kiln process from the point of view of phosphate rock reaction itself,through the way of adding admixture,to improve the utilization rate of phospha te rock without causing residual slag to melt circle at high temperature.In this paper,the self-made fluoroapatite,analytical pure silica,and deashing anthracite are used as raw materials to analyze the material changes,kinetic parameters,and residue morphology of pure materials.Furthermore,the idea of adding dopants to improve coke activity to solve the kiln process phosphoric acid problem is proposed.The phosphorus reduction rates,kinetic parameters and residue flow temperature of dopants（K₂CO₃,Na₂CO₃,NiSO₄,K₂CO₃ and NiSO₄composite）and undoped system were analyzed.The XRD analysis of the residue was used to investigate the material changes of different systems and t he effect of the dopant on the reaction process was analyzed.The appearance of the residue was analyzed by combining the SEM spectra of the residue to determine the effect of the dopant on the morphology of the residue.Firstly,the analysis of the pure material system shows that the change course of the carbothermal reduction reaction material of phosphate rock is:first ly,fluoroapatite defluorination reaction with silica to form Ca₃（PO₄）₂,which is then reduced by coal to produce CaO and combined with Silica forms calcium silicate,and fluorine excludes the system in the form of SiF₄ gas.The reaction is a metamorphic chemical reaction and t he reaction order decreases with increasing temperature.The activation energy of the reaction is 273.76 kJ·mol^-1.As the temperature increases,the system produces more liquid phase,which acts as a medium to promote the diffusion of the substance and accelerates the reaction,so the reaction rate is increased and the conversion rate is increased.In the tube furnace,the effects of acidity value,carbon excess coefficient were investigated.The analysis results show that the phosphorus reduction rate increases with the increase of the ratio of silicon to calci um,and then decreases slightly.The phosphorus reduction rate increases with the increase of the coke excess coefficient and tends to be stable.For different dopant systems,the optimal addition amount in the experimental range is:K ₂CO₃,Na₂CO₃ addition amount is6%of coke addition amount,NiSO₄ addition amount is 8%of coke addition amount,adding 7%The composite dopant has a ratio of K₂CO₃/NiSO₄=6/4.On this basis,the relationship between the phosphorus reduction rate of the five systems was investigated,and the activation energy of the reaction was calculated and compared.The phosphorus reduction rate of the four dopant systems increased with the increase of temperature and time.At the same temperature and time,the phosphorus reduction rate of the dopant system was significantly higher than that of the undoped system.At low temperature,the alkali metal carbonate has a gerat effect,while the promotion effect of NiSO₄ is superior,and the composite system has the common effect of alkali metal and NiSO ₄,so the promoting effect is optimal.Comparing the kinetics of the five systems,the activation energy of the undoped system is 255.65 kJ·mol^-1,and the activation energy of the dopant system is respectively 233.62kJ·mol^-1,240.11kJ·mol^-1,230.96 kJ·mol^-1,219.24 kJ·mol^-1.It can be seen that the addition of dopants can effectively reduce the activation energy of the carbothermal reduction reaction of phosphate rock.Comparing the phosphorus conversion rate and the activation energy of different systems,the composite system has a better promoting effect.Comparing the XRD patterns of different system residues,the material chang e process is basically the same as that of the pure material system for the non-addition system,and the phosphate rock itself carries SiO ₂ more reactive than the added silica;and the comparative dopant system and undoped The XRD patterns of the various temperatures of the system show that the dopants only strengthen the progress of the reaction,and no new substances are produced.Comparing the flow temperatures of the five systems,it can be seen that the flow temperature of the residue decreases with th e increase of the reaction temperature;it decreases with the increase of the conversion rate.Analysis of the SEM spectrum of the residue at 1300°C shows that the appearance of the residue with the dopant system is basically the same as that of the undope d system,indicating that the addition of the dopant does not change the appearance of the residue,which is a solid residue,in line with the kiln process phosphoric acid.Solid waste slag requirements.