Investigation On Reduction Of Low And Medium Phosphorite By Kiln

Kiln phosphoric acid(KPA)is a new mothod synthnesis of furnace-process and blast furnace process.It is using directly low-grade or phosphorite tailing without sulphuric acid and large power.However,there are many critical problems for kiln phosphoric acid,such as: immaturity process,the problem of disposing of byproduct waste,burning loss of carbon,etc.This study was used two kinds of pellets,pellet with reaction-layer and composite pellet with double reaction-layer,reduction of low-phosphorite with KPA.The optimum reduction temperature was determined though thermogravimetric and differential thermal analysis of reducing phosphate rock with coke or carbon monoxide,and the thermodynamic functions illustrate the effects of parameters,such as: calcium to silica ratio(C/S),calcination temperature,on oxidation-reduction reactions.We explored the influences of factors--structure of pellet,C/S,calcination temperature,air velocity,etc--on reduction ratio of phosophorite and performance of residual pellets.Eventually,the best reduction technology is determined,and the residual pellets can be used as lightweight aggregate.The results appear as shown blew.The reduction of phosphorite by reductants such as coke and carbon monoxide at high temperature.The equilibrium constant of the reactions,reducer is coke and CO,is proportional to the temperature and in inverse proportion to C/S.But,the Gibbis free energy is inversely proportional to temperature and in proportion to C/S.Addition,the enthaipy change of the first reaction is inversely proportional to temperature,and the second reaction,reducing the endotherm by approximately half compared with the former under the same conditions,does not change with temperature,the enthaipy change of the two is proportional to C/S.Therefore,the higher temperature and lower C/S is favorable to the reactions.For common pellet: as C/S=0.4,reduction temperature of 1300?,holding of 3 hours,the maximum of reduction ratio is only 49.76% in air.But,as C/S=0.4,reduction temperature of 1275?,holding of 3 hours,the maximum of reduction rate is 96.4% in nitrogen.This shows the ball have serious problem of burning loss of carbon in air,but the problem is resolved in nitrogen.For pellet with reaction-layer: the reduction rate increased firstly and then decreased with a rise of air velocity or pore forming substance content,when rate is 500ml/min,the content is 8%,coefficient of excess coal of 1.4,temperature is 1300?,holding time of 3 hours,reaching peak is 84.14%.And residual particales with hollow structure have been prepared via kiln phosphoric acid process at 1250? for 3 hours that the bulk density is 671kg/m3,compressive strength is 2.3MPa.For composite pellet with double reaction-layer: the residual particales with porous structure have been prepared by KPA process at 1275? for 3 hours that the bulk density is 794kg/m3,compressive strength is 1.24 MPa.Under this same condition,the reduction ratio of phosphorite is 86.74%,and the reduction of first reaction-layer is 95.44%,but second reaction-layer is only 78.03%.