Study On Comprehensive Utilization Of Electrolytic Manganese Anode Slime

Electrolytic manganese anode slime(EMAS)is a kind of hazardous waste in the production of electrolytic manganese metal(EMM).However,the EMAS stored in the storeroom will seriously threaten the local ecological environment.Moreover,EMAS contains a large number of Mn,Pb and other valuable elements,which also cause a huge waste of metal resources.Therefore,the utilization of EMAS is becoming more and more urgent.The EMAS used this study is randomly sampled from an EMM industry factory in Guangxi,China.This study focuses on the comprehensive utilization of EMAS.Firstly,the basic physical and chemical properties of EMAS are analyzed by different analytical methods.Subsequently,studies are carried out on the reduction leaching of EMAS strengthened by an electric field,the removal of lead in EMAS and the preparation of chemical manganese dioxide.The conclusions are as follows:The XRF analysis shows that the EMAS is mainly composed of Mn,Pb,Ca,Fe,Se,Sn,O,S,Si.The content of Mn and Pb in the EMAS reached 54.2 wt.%and 6.22%wt.%respectively.The XRD analysis shows that the major composition phases of EMAS are MnO₂(?????),MnOOH,MnO_1.88,Mn SO₄,(NH₄)₂SO₄,Pb SO₄,Pb_2-xMn₆O₈,etc.The surface morphology of the EMAS is analyzed and the results show that the particles of EMAS have an irregular shape and an uneven size,there is a large amount of agglomeration between particles.The main particles present a relatively dense state.The results show that the Mn of EMAS can be effectively extracted in the existence of an electric field and a certain concentration of Fe²⁺.The manganese leaching efficiency is 97.5%under the optimal conditions of leaching time of 150 min,0.8 mol/L Fe²⁺,liquid–solid ratio of 8 m L/g,1.6 mol/L H₂SO₄,current density of 120 m A/cm²,temperature of333 K.Moreover,lead concentrations in leaching residue reach up to 45.24 wt.%,which make the leaching residues can be recycled as lead concentrate.The analysis of kinetics shows that the rate of the leaching process is controlled by diffusion of the product layer,whose activation energy E_a=38.38 k J/mol.The kinetic equation of the leaching process can be expressed as 1-2/3X-(1-X)^2/3=A·exp(?38.38/RT).The cycle production of Fe³⁺and Fe²⁺become the medium of electronic transmission of electrochemical reaction which make the manganese of EMAS is continuously leached out into solution.At the same time,the manganese of EMAS can directly extracted by an electric field.The removal of lead from EMAS by vacuum carbonthermal reduction is studied.The effects of reduction temperature,holding time and C/EMAS mass ratio on lead removal are investigated.The results show that the removal rate of lead reach up to 99.85%under the conditions of 950?for 100 min and 10%C/EMAS mass ratio.XRD and SEM analysis results show that during the process of vacuum carbothermal reduction,the main phase of EMAS is gradually reduced to MnO,and its dense structure is destroyed,forming many multi-dimensional channels and cracks.The lead compounds in EMAS are reduced to lead.Under a high-temperature vacuum environment,the lead is continuously volatilizing and releasing.The recovery rate of chemical MnO₂(CMD)up to 36.6%by roasting-pickling.The crystal of CMD is basically the same as the electrolytic manganese dioxide(EMD),also the specific surface area and the micropore volume are higher than that of EMD.The discharge capacity of CMD is higher than EMD.At the discharge current of 0.1 A/g,the specific capacity of CMD is 240.84 m Ah/g.