Applied Basic Research On Separation And Enrichment Of Valuable Metals In High Bismuth Lead Anode Slime

Lead anode slime is a kind of byproduct produced in lead bullion electrolytic refining process.Lead anode slime is a complex polymetallic material and its yield is about 1.2%¹.8%weight of the lead bullion.According to the statistics released by International Lead and Zinc Study Group,11.451 million tons of lead was produced in the world in 2017.The amount of lead anode slime produced by lead bullion electrolysis refining is approximately 27500⁴1200tons.Valuable elements comprehensive recovery from lead anode slime is one of the effective methods to realize the effective utilization of this kind of metallurgical complex material.Lead anode slime provided by a copper smelting enterprise in Yunnan Province is rich in bismuth?48.58%?,arsenic?12.97%?,antimony?12.55%?,lead?11.98%?,silver?3595g/t?and gold?22g/t?.According to its characteristics,a novelty technological process of“hydrothermal oxidation alkaline leaching arsenic,antimony,lead-crude bismuth alloy casting-bismuth electrolysis”was proposed in order to realize the removal of arsenic,antimony and lead,the extraction of bismuth and enrichment of gold and silver.Firstly,?-pH diagrams of As-N-Na-H₂O?Sb-N-Na-H₂O?Bi-N-Na-H₂O?Pb-N-Na-H₂O at298K,373K,423K,473K were constructed according to thermodynamic calculation and the thermodynamic behaviors of arsenic,antimony,lead and bismuth in the aqueous solution were discussed.When NaNO₃ was adopted in the NaOH system as oxidant,majority of arsenic can dissolve in the solution in the form of Na₃AsO₄.Antimony can be oxidized into Sb₂O₃ then forming soluble NaSbO₂,lead can be oxidized into PbO and PbO₂ then react with dissociative OH^-ions in the solution and dissolve into the solution in the complex form of soluble PbO₃^2-or HPbO₂^-.There is no obvious stable reagion of soluble bismuth species in alkaline system.The oxidation order of As?Sb?Pb?Bi were indentified in pure NaOH and NaOH-NaNO₃ system from easy to difficult.Compared with pure NaOH system,NaNO₃ can promote the oxidative dissolution from As???to As?V?at 423K.Meanwhlie NaNO₃ can change the oxidation order of Pb and Bi;partial Bi can be oxidized into insoluble Bi₂O₃ in NaOH system;lead dissolution can not be affected.Therefore,it is feasible to remove arsenic,antimony and lead from bismuth-rich lead anode slimes to enrich bismuth,gold and sliver by using NaOH-NaNO₃ system from a thermodynamic point of view.Secondly,the oxidative dissolution principles of lead and antimony in NaOH-NaNO₃solution were investigated by using electrochemical methods and the mechanisms of antimony and lead oxide dissolution was proposed.When the NaOH concentration is controlled at 4mol/L it is beneficial to the oxidation of lead and antiomoy in the NaOH solution;when the NaNO₃ concentration is inferior to 0.24 mol/L,increasing NaNO₃concentration is beneficial to the formation of PbO,which can promote the dissolution of lead.It is is not beneficial to the formation of PbO when the NaNO₃ concentration excesses 0.24mol/L,which can inhibit the dissolution of lead.Appropriate NaNO₃ concentration is advantageous to the oxidative dissolution of metal antimony,excessive NaNO₃ can oxidze low valence oxides into insoluble NaSbO_3,thereby suppressing the dissolution of antimony.Thirdly,the principles of arsenic,antimony,lead and bismuth saparation,phase transformation,reaction pathway,reaction limitation and the lixivium regeneration and cyclic utilization were investigated.Optimized experimental parameters were obtained.Under the optimized condition the leaching ratio of arsenic,antimony and lead excesses 95%?75%?60%,respectively;In the leaching lixivium,arsenic exists in the form of Na₃AsO₄,all antimony and lead exist in the form of Pb₂Sb₂O₇;in the leaching residues,antimony and lead exist in the form of Pb₂Sb₂O₇,partial Pb₂Sb₂O₇ can dissolve into alkaline lixivium;some part of antimony remained in the residues in the form of NaSb?OH?₆.Bismuth remained in the leaching residues in the form of Bi and Bi₂O₃.Kilogram-scale hydrothermal leaching experiments were carried out under the small-scale experiments.The results show that the average leaching ratios of arsenic,antimony,lead are 95.52%,75.85%,64.72%,respectively.The average content of bismuth,gold,silver in leaching leaching residues were 77.24%,5773.26g/t,35.33g/t,respectively.Compared with the raw lead anode slime the content of gold and silver were enriched about 1.6 times;A novelty method was proposed for effectively separating antimony,lead and arsenic from leaching lixivium through adding Pb₂Sb₂O₇ seed crystal.Lead and antimony can be removed in the form of Pb₂Sb₂O₇ through adding Pb₂Sb₂O₇ seed crystal when Sb?III?was oxidized into Sb?V?by NaNO₃ in leaching lixivium.Then CaO was employed to remove arsenic in the solution.The purified lixivium was returned to hydrothermal oxidation alkaline leaching process to leach lead anode slime,showing good recycling effect.Fourthly,the thermodynamics behaviors of the leaching residues were investigated during the reductive melting and casting of crude bismuth alloy process,it can be found that the initial temperature of metal oxides carbon reduction from low to high are Cu?Bi?Pb?Sb?Sn.Bismuth oxides can obtain enough reduction thermodynamic driving force when the temperature excesses 800?.The optimized technical condition was obtained,the obtained crude bismuth alloy provide a favorable condition for the bismuth electrolysis.Compared with the raw lead anode slime,the content of gold and silver were enriched about 1.68 times and 1.77times,respectively.Finally,the optimized technical condition of bismuth electrolysis process was determined in HCl-NaCl-BiCl₃ system,the average purity of cathode bismuth can achieve 98.89%,the average electrolysis current efficiency is 96.59%,the average power consumption is 148.88 kW·h/t?Bi?.Potentiodynamic polarization method was employed to investigate the effect of sodium lignosulphonate on the kinetic parameters of cathode bismuth deposition and cathodic deposition behavior,it can be found that Tafel slope,exchange current density and microstructure of cathodic bismuth surface were significantly influenced by the addition of sodium lignosulphonate during the cathodic electrodeposition of Bi³⁺.Kilogram-scale experiment indicates that the electrolysis current efficiency exceeds 96%,the purity of cathode bismuth exceeds 98%and the power consumption is 181.48¹93.56kW·h/t?Bi?when the crude bismuth alloy was electrolyzed for 24h?48h?72h?112h.Compared with the raw lead anode slimes the content of gold and silver in anode slime were enriched about 9.54times and 10.13 times respectively after bismuth electrolysis.