Preparation And Application Of Iron Phosphate From Phosphating Slag

Phosphating slag generated during the surface treatment of iron and steel parts is a hazardous waste.Unreasonable disposal and discharge of phosphating slag cause irreparable damage to the soil and water.For this reason,many scholars have conducted research on the utilization of phosphating slag,but due to economic and practical problems,it is difficult to conform the actual production requirements.This article takes common industrial solid waste phosphating slag as the research object,include preparation of purified iron phosphate by hydrochloric acid environment hydrothermal purification,LiFePO₄/C cathode material for lithium ion battery and three-dimensional electrocatalytic CN/Fe PO₄ particle electrode material,provide different schemes for phosphating residue recycling:（1）A dilute hydrochloric acid solution was used for hydrothermal reaction with phosphating slag to purify iron phosphate with high content in the phosphating slag.The influence of reaction temperature,reaction time and acid concentration on the crystal structure and micro-morphology of the purified iron phosphate was explored.According to the experiment,as the reaction temperature increases,the degree of crystallization of iron phosphate increases synchronously.When the reaction temperature is too high or the reaction time is extended,iron hydroxy phosphate appears in the product;In addition,when the concentration of hydrochloric acid increases,the purity of the product iron phosphate continues to increase,the morphology changes from the initial spherical shape to a plate shape,the particle size（D50）decreases from 18.85μm to 1.53μm;When the concentration of hydrochloric acid is 15wt.%,particles with a uniform shape and an average particle size of 57nm appear in the product.The nanoparticles are amorphous Fe PO₄·2H₂O by thermogravimetry,electron energy spectrum and X-ray diffraction analysis.（2）The application of purified iron phosphate to lithium batteries explored the influence of iron phosphate morphology and crystal water state on the electrochemical performance of synthesized LiFePO₄/C materials.The experimental results show that the removal of the crystallization water has little effect on the micro-morphology of the LiFePO₄/C material,but the degree of crystallization is slightly reduced.Among them,the iron phosphate purified at the concentration of 15wt.%Hydrochloric acid is the precursor,prepared without crystal water.The LiFePO₄/C material has better cell volume and electrical performance data.The specific charge and discharge capacities for the first cycle are 162.3 m Ah·g^-1 and 155.9 m Ah·g^-1,and the coulomb efficiency is 96.1%,the capacity retention rate after the rate cycle is 99.0%.Cyclic Voltammetry（CV）and Electrochemical Impedance Spectroscopy（EIS）tests show that the material has good reversible performance,low charge transfer resistance,and lithium ion diffusion rate D⁺_Li=9.45×10^-12 cm²/s.（3）The purified iron phosphate was used to prepare a three-dimensional electrocatalytic CN/Fe PO₄ particle electrode,design and build the three-dimensional electrocatalytic device,and the response surface method was used to predict the optimal parameters of the experiment.The research shows that the prepared CN/Fe PO₄ particle electrode is composed of C,N,P,Fe and O,the main components are Fe PO₄,Fe₂O₃,Fe⁰ and graphitized C and N.For the three-dimensional electrocatalytic system composed of Ti/Sn O₂-Sb anode,activated carbon fiber felt cathode and CN/Fe PO₄ particle electrode,Design-Expert 11 software obtained the best experimental conditions:current density is 32.6 m A·cm^-2,aeration flow is 1.6 L·min^-1,p H is4.15,CN/Fe PO₄ particle electrode dosage is 2.3 g·L^-1;verification experiments show that the model is true and reliable,reaction kinetic equation is ln（C_o/C_t）=0.190t+0.339,and reaction rate constant is 0.190.