Process Of Arsenic Selective Leaching And Its Mechanism In Copper Smelting Soot By Ball Milling

The copper smelting process will produce a large amount of soot rich in copper,zinc,lead,tin,bismuth and other valuable metal elements.The economic recovery value is extremely high,but it is accompanied by harmful metals such as As,which is not conducive to the harmlessness of soot recycling and resource utilization.Therefore,the development of an efficient separation process of arsenic and valuable metals in copper smelting soot is extremely important for eliminating arsenic pollution and solving arsenic cycle accumulation and waste resource utilization.The removal of arsenic technology in soot mainly includes two kinds of hydrometallurgy and pyrometallurgy,but with the increasingly strict environmental protection standards and strict requirements on product quality,the defects of pyrometallurgy for arsenic removal are increasingly obvious.However,hydrometallurgy has low energy consumption and cause low environmental pollution and high arsenic leaching rate,so it is widely used.NaOH and NaOH-Na₂S are alkaline leaching systems that are often used to achieve the selective removal of arsenic in smelting soot.However,using the NaOH leaching system lead to complex composition in the leaching solution,other than that,the treatment is complicated,the consumption of NaOH is large,and the arsenic leaching rate is low.As is known to us,the introduction of the NaOH-Na₂S leaching system could obtain a higher arsenic leaching rate while further precipitating Cu S,Zn S,and Pb S in the leaching solution,thereby achieving the selective leaching of As.However,In terms of traditional systems,it is easy to cause inadequate pharmaceutical reactions,the leaching rate and selectivity of arsenic still need to be improved,and high temperature and high pressure assistance is required,which requires good equipment and cause high energy consumption.Therefore,it’s urgent to explore the energy-saving,environmentally-friendly and efficient pretreatment processes so as to improve the utilization rate of medicaments,strengthen the leaching of arsenic and its efficient separation from valuable metals,and then realize the resource utilization of soot.In recent years,the mechanical activation method can provide more reactive sites and rapid diffusion paths by generating lattice defects,so it is widely used to strengthen the leaching process of hydrometallurgical minerals.Different mineral raw materials have different reactions during mechanical activation.There is no report about the selective leaching of As in copper smelting soot by mechanical activation pretreatment.Based on this,this study tried a new ball milling process,which explored the activation effect bymilling agents with Na₂S or NaOH respectively on copper soot and their strengthening effect on As separation and leaching,and clarified the reaction mechanism.The content and conclusion are as follows:（1）Research on selective separation of arsenic in soot by milling with Na₂S.This section explores the effects of different sulfur-containing co-grinding agents（Na₂S,Na₂S₂O₃,Na₂SO₃）on the selective leaching of As in soot..Except that,we discuss the mass ratio of the co-grinding agent to soot,ball milling time,effects of ball mill speed and ethanol addition on the separation and leaching of As from valuable metals in soot after obtaining the best sulfur-containing co-grinding agent.After determining the optimal pretreatment process parameters,we continue to explore the optimum process parameters for soot leaching after activation under the co-grinding conditions.The results show that the best co-milling reagent is Na₂S;when the mass of Na₂S to ash is0.3:1,the ball mill speed is 600 rpm,and milling time is 30 minutes（that is,after adding milling with Na₂S for 20±5 minutes,0.5 m L ethanol was added in sequence for 10±5 min）,the As and Cu,Zn,Pb and other metals in copper smelting soot can be efficiently separated.At a speed of 600 rpm,the final dosages of NaOH and Na₂S are M_NaOH:Ash=0.5,M_Na2S:Ash=0.4,L/S=25:1,and leaching at a temperature of 328 K for 10 min,As extraction rate can be reached to 85.52%.Under the same conditions,it was increased by 29.51%compared with that without ball milling process.In the temperature range of 298 K～348 K,the leaching process of arsenic in soot tends to be controlled by two processes:chemical reaction control and solid film diffusion.The leaching kinetics equation is in accordance with the unreacted shrinking kernel modeland the Gibbs free energy is△G<0,indicating that the leaching reaction is thermodynamically feasible.（2）The optimal technological conditions for NaOH ball mill pretreatment and leaching were determined.The single-factor test results of NaOH ball mill pretreatment showed that:the mass of NaOH to ash is 0.5:1,the rotation speed is 600rpm,and the milling activation time is 60 min（milling for 50±5 min and thengrind for10±5 min after add a certain amount of ethanol）,the As leaching rate can be increased to 78.92%,as compared to without ball milling,the As leaching rate is increased by22.91%.The best leaching process conditions are the final dosage of NaOH and Na₂S are M_NaOH:Ash=0.5,M_Na2S:Ash=0.4,liquid-solid ratio L/S=25:1,and the temperature is 328 K for 10 minutes（arsenic leaching rate increased to 81.11%）.Comparing the apparent activation energy Ea before and after ball milling,it can be seen that the apparent activation energy after ball milling is reduced from 35.93 k J·mol^-1 to 16.27k J·mol^-1.This shows that ball milling pretreatment can reduce the activation energy of the reaction,improve the chemical reaction process,and enhance the mass transfer rate of the leaching process.At the same time,ball milling pretreatment can reduce the sensitivity of the leaching reaction to temperature,so that the reaction can be carried out at a lower temperature,which can reduce the energy consumption and cost of the reaction to a certain extent.A comparative study of the change of arsenic leaching efficiency of soot under different treatment conditions shows that the arsenic leaching efficiency is only 56.01%without ball milling.Ball milling alone（without co-grinding agent）may promote the combination of arsenic and other metal ions in soot While inhibiting the leaching of As,and the addition of co-grinding agent can change the leaching behavior of As,under the conditions of Na₂S ball mill pretreatment and NaOH ball mill pretreatment,the leaching rate of As in the soot increased by 29.51%and 25.11%respectively compared with that without ball mill And Cu,Pb,Zn and other metals in the soot are basically not leached,and the As content in the leached residual solids can be reduced from 5.74%to 0.13%and 0.07%,respectively,which has created harmless and resource utilization of copper smelting soot Favorable conditions.In order to further prove the strengthening effect of ball mill pretreatment on As leaching,the leaching efficiency of arsenic in soot was compared between dry milling and wet milling conditions.The results show that the leaching rate of As during wet grinding is better than that of arsenic without ball milling under the same conditions,but it is reduced by about 14.41%compared with the Na₂S dry grinding pretreatment.That because more disordered structure,lattice defects and increase the proportion of amorphous material when ball milling with Na₂S,which can more effectively promote the reactivity of soot particles and further enhance the leaching effect of As.（3）The chemical activation mechanism of defect activation and sulfidation separation of As leaching enhanced by ball mill pretreatment was revealed.Particle morphology and particle size analysis results show that:during high-speed ball milling,high temperature and pressure are locally generated,which can induce the solid-solid reaction to a certain extent;and during mechanical ball milling,high-speed friction and collision will generate huge impact energy,destroy the internal structure of the particles,and promote more crystals.At the same time,the continuous effect of mechanical force will cause the particle size to decrease significantly,the active interface area between the reaction components will increase,and the apparent activation energy will decrease,which will provide a faster diffusion path for the subsequent leaching process.XRD and XPS results show that after co-grinding Na₂S with soot,metals such as Cu,Pb,Zn in soot will chemically react with them to form insoluble sulfide metals in alkaline media,and some pentavalent arsenic in soot can transfer to more mobile trivalent arsenic.After co-milling pretreatment with NaOH and soot,local high temperature and high pressure are generated to promote the reaction between Pb SO₄ and NaOH to form Pb（OH）₂,and finally decompose into Pb O and part Pb O react with Na₂S under the leaching system to generate insoluble sulfide,which can improve the recovery efficiency of Pb to a certain extent,and oxidation state arsenic can be converted into soluble arsenate after ball pretreatment in alkaline medium.Both of two pretreatment processes achieved the efficient separation of As from valuable metals in copper smelting soot.