Thermal Analysis And Kinetics Studies For Carbothermal Reduction Process Of Low Grade Phosphate Ore

As an important chemical raw material,phosphorus products are widely used in medicine,chemical industry,agriculture,national defense technology and other fields.The raw material for the preparation of phosphorus products is phosphate ore.With the exploration and development of phosphate rock,the resources of high-grade phosphate rock are becoming less and less,medium-low grade phosphate is dominating the main market.At present,there are three main methods to produce phosphoric acid:wet process phosphoric acid,hot process phosphoric acid and kiln process phosphoric acid.The process of wet process phosphoric acid needs to meet the requirements of high-grade phosphoric ore,and the subsequent separation process is complex.Kiln process phosphoric acid is still in the research stage at present.Hot process phosphoric acid can directly use medium and low grade phosphoric ore and can be applied to the present phosphate resource situation.Medium-low grade phosphate ore was reduced by carbothermal reduction process under 1250?.Reaction time,carbon excess coefficient?CEC?and mole ratio of silicon and calcium oxide?Si/Ca?were selected as independent variables and response surface method?RSM?was employed to obtain maximum phosphorus reduction ratio.The results showed that there was a significant interaction between reaction time and CEC.Under1250?,the optimal condition for phosphorus reduction ratio was obtained at the reaction time of 144 min,Si/Ca of 2.7,CEC of 2.28,confirmation runs gave 95.22%of phosphorus reduction ratio as compared to 96.91%of the predicted ratio.In addition,four different kinds of medium-low grade phosphate ore were tested under the same condition and the reduction ratio were 95.50%,96.04%,96.40%and 98.30%,respectively.Those results were close to or better than the predicted value.The XRD and XRF analyses verified the reduction of fluorapatite.The obtained optimal parameters of carbothermal reduction of phosphate rock is helpful to reduce energy cost.The effect of different kinds of silica source?diatomite and silica?in apatite carbothermal reduction reaction was studied.The optimal condition for apatite reduction ratio was obtained at the temperature of 1300?,CEC of 1.5,Si/Ca of 1.8,the reaction time of 80 min,diatomite system apatite reduction ratio reached 91%,silica powder system apatite reduction ratio only reached 54%.Melting point of diatomite system reached at1300?,the reaction converted from solid-solid reaction to solid-liquid reaction,showing that the diatomite apatite carbon thermal reduction system does play a role.When diatomite and silica were used as silicon sources in the carbothermal reduction reaction of phosphate ore,the results were 90.93%and 88.15%,respectively.The melting effect of various metal oxides in phosphate ore covered the melting effect of diatomite.Non-isothermal kinetics studies of phosphate ore carbothermal reduction in the response surface optimization conditions?calcium silicon molar ratio of 2.7,the excess carbon coefficient 2.28?was investigated.The results shown that the apparent activation energy E is 419.12 k J/mol.The most probable mechanism functions are G???=1-?1-??^1/4and f???=4?1-??^3/4,the reaction is controlled by shrinking core model.