The Basic Study Of Element Migration And Control On The Utilization Of Phosphating Sludge

Based on the process of utilizing phosphating sludge to prepare cathode material LiFePO4 for lithium ion battery,the related laws of target element migration and control in each unit process have been explored.So as to provide research support for the construction of the basic theoretical system of multi-element and complex metallurgical solid waste recycling and materialization.According to the properties of composition and amorphous state of phosphating sludge,a selective phase reconstruction method is proposed.By controlling moderate temperature,the iron phosphate component is selectively enriched and purified due to its prior crystallization.Meanwhile,an appropriate amount of impurities can be co-doped in crystalline FePO4,and the excess amorphous impurities will be enriched outside the crystalline phase of FePO4.The impurity metal elements can be replaced leached out by FeCl3 solution,then some of Zn2+ and Mn2+ are coated onto the FePO4 surface through a critical coprecipitation process,thus the hybird coated LiFePO4 is prepared.This route realizes high atomic utilization rate of phosphating sludge.On these grounds,the behavior and regularity of the migration and enrichment of each elements in the process of phase reconstruction are mainly discussed,and obtain the reasonable thermodynamic conditions for the phase reconstruction of phosphating sludge.The?HT,P of crystalline phase translating from amorphous FePO4 and the ST,P and CP of crystalline FePO4 are studied.So that the thermodynamic analysis and the kinetic study of impurity compositions of amorphous and crystallized slag can be carried out.The influence of phase reconstruction on the selective leaching behavior of impurity compositions is comparatively studied.In addition,by hydrochloric acid leaching the impurities of the phosphating sludge,multiple doped LiFePO4 can be prepared in a short process.The feasible temperature range and isothermal crystallization behavior of selective phase reconstitution of phosphating sludge are studied by TG-DSC combine with XRD methods.By means of XRD refinement,qualitative and quantitative analysis of each isothermal crystallization samples can be carried out,so that the rules of selective crystallization and precipitation of FePO4 components can be identified.Some thermodynamic parameters of crystalline FePO4 and its phase transition can be determined by thermal analysis standard sample method.The thermodynamic calculations of the leaching of impurities in amorphous sludge and crystallized sludge are carried out respectively.The studies find that:1)During the heating process of phosphating sludge,FePO4 fraction will take the lead in crystallization.The suitable temperature range of selective crystallization and in-situ doping is 580?590?.2)The crystallinity of FePO4(Xt),can be expressed by temperature(T,853.15K-863.15K)and time(t,min)as:Xt = 1-exp[-exp(216.47-1.88×105/T)t2]3)The relationship between the enrichment rate Er of the target crystallization phase and the temperature T(853.15K-863.15K)is:Er= 111.37-exp(72.42-T/12.37)4)In the process of phase reconstruction,the impurity components are migrated to crystalline FePO4 at a fixed proportion under different temperatures.The controllable upper limit of the solid solution amounts of each components are Zn?10.2%?Mn?0.47%?Ca?1.41%(mol%),respectively.5)Based on the experimental measurements,3 thermodynamic parameters related FePO4 are obtained:The?HT,P of amorphous FePO4 transforms to the crystalline FePO4:?HT,P=-1787.17(J·mol-1)Crystalline FePO4:ST,P = 97.88(J·mol-1·K-1)Crystalline FePO4:CP =-6698.4-27.14T+ 0.007772 + 823.21T1/2(313-373K)6)The phase reconstruction of phosphating sludge can obviously improve the leaching rate of impurities,so that the apparent activation energy can be reduced by about 2-7 kJ·mol-1.7)The routes of preparing two types of LiFePO4 utilizing phosphating sludge are:(i)Through leaching to remove the impurity compositions,followed by lithium conditioning and carbothermal reduction,and then obtain the multi-doped LiFeP04;(ii)After the pretreating of phase reconstruction for phosphating sludge,the impurity metal ions are replacing leached by FeCl3 solution,and the PO43-impurities phosphates is reused as FePO4,and then,through the critical coprecipitation,the Zn and Mn oxides are coated onto the FePO4 with suitable coating amount,finally,by the lithium conditioning and carbothermal reduction,the hybird coating of LiFePO4@MeO-C is obtained.In the above results,the academic idea of the selective crystallization,which realizes the selective crystallization for the target components and the doping migration control for the impurity components,is the theoretical innovation of this paper.A new process developed to prepared lithium iron phosphate utilizing phosphating sludge,which has been authorized invention patent,is the technical innovation of this paper.The measured of ?HT.P of amorphous FePO4 transform to crystalline phase,as well as the ST,P and CP of crystalline FePO4,fill the blank of thermodynamic data.In conclusion,this study provides a new way of utilizing phosphating sludge to prepare LiFePO4.The corresponding basic research provides referable results for the construction of the theoretical system of high efficiency utilization of metallurgical solid waste.