| Antimony minerals are the dominant mineral resources in China,but now antimony resources situation is extremely severe due to a prolonged period of intensive exploitation.The development trend of antimony smelting industry will be the comprehensive utilization of complex polymetallic antimony ore with low cost,high efficiency,and environmental friendliness.The traditional pyrometallurgical process requires a high-grade concentrated ore and high energy consumption and causes serious environmental contamination by the lowconcentration SO2,various heavy metals,and arsenic-alkali residue.Obviously,the traditional smelting method is unavailable for processing complex antimony concentrates due to these shortcomings.Slurry electrolysis(SE)can make full use of the anodic oxidation reaction to leach ore,and it has been one of the main directions in the development of complex sulfide mineral comprehensive treatment due to its characteristics of short process,low energy consumption,and environmental friendliness.In this study,a novel technology system has been proposed as selective separation antimony by slurry electrolysis electrooxidation-separation sulfur and arsenic via heating volatilization in the absence of oxygen-cyanide leaching gold.The critical scientific foundations and technologies for the key processes,i.e.,SE electrooxidation selective separation antimony,were investigated systematically in this study.(1)Employing chemical titration analysis,ICP analysis,chemical phase analysis,optical microscopy,XRD,SEM-EDS,and other analytical methods,the process mineralogy of As-Au-Sb ore was studied systematically.The main mineral compositions and their distribution characteristics in the raw materials were determined,the occurrence of antimony,gold,sulfur,and other elements were revealed,and the selective separation and leaching characteristics of antimony were analyzed.The As-Au-Sb ore contains 32.88 g/t Au,31.62%Sb,25.10%S,13.67%Fe,and 4.40%As.Gangue components are mainly SiO2 and Al2O3.Antimony mainly exists in the independent mineral stibnite,occasionally in the yellow antimony,and the proportion of antimony in these two minerals reaches 98.76%.Gold exists mainly as natural gold,and some as invisible gold dispersed or wrapped in stibnite,pyrite,arsenopyrite,and gangue minerals,such as quartz.The difference in oxidation decomposition potential between antimony and gold minerals makes the selective leaching of antimony possible.(2)Through the study on the solubility of antimony chloride,the coupling preparation system of hydrochloric acid and sodium chloride for SE was established:NaCl of 150 g/L and HC1 of 0.6～0.8 mol/L.The addition of Clincreased the solubility of antimony in solution,and also significantly reduced the oxidation decomposition potential of stibnite.E-pH diagram showed,in the Sb2S3H2O system,a high acid concentration was required for the dissolution of stibnite,and the increase of oxidation potential was beneficial to the decomposition and leaching of stibnite with low acid concentration.Besides,maintaining a certain acidity in the solution can promote the dissolution of Sb2S3 and Sb2O3 and facilitate the formation of elemental sulfur in a certain range.Simultaneously,it can also increase the concentration of Sb3+in the solution and prevent the hydrolysis precipitation of antimony ions.In the Sb2S3-Cl-H2O system,the presence of chloride ions significantly reduced the dominant region of stibnite,reduced the oxidation decomposition potential of stibnite,and increased the acidsoluble equilibrium pH value.With an increase in chloride ions,the dominant region of antimony ion was expanded,and its stable pH value was extended to the range that can be realized in practice.Sb2O5 got a large stable region.In the SE process,the potential should be controlled in an appropriate range to prevent the formation of pentavalent antimony compound precipitation.(3)The possible reactions of antimony minerals in the anode region of SE were analyzed.The transformation process of antimony minerals was confirmed by employing E-pH diagram analysis,electrochemical test of the anodic oxidation process,and the characterization of leaching products through optical microscopy,XRD,SEM-EDS,and other methods.Firstly,Fe3+was mainly responsible for the oxidation of stibnite.leading to its reduction to Fe2+.Subsequently,the generated Fe2+would be oxidized to Fe3+at the anode,and the cycle was repeated.With the introduction of iron ions,indirect electrooxidation was achieved,which greatly increased the oxidation decomposition rate of stibnite.The increase in stirring speed,iron ions concentration,and temperature significantly increased the rate of oxidation reaction.Secondly,antimony ions and hydrogen sulfide were generated by acid dissolution of stibnite.but a high concentration of hydrochloric acid was required in this process.Thus,the acid dissolution of stibnite accounted for a low proportion in the SE process.Thirdly,under the SE condition,the reaction speed of direct collision oxidation between stibnite and anode was extremely slow,which also accounted for a very small proportion.The oxidation leaching of stibnite by Fe3+ from high arsenic antimony gold concentrate accorded with the unreacted shrinking core model.The leaching of antimony was controlled by interfacial chemical reactions.(4)In the HCl-NaCl system,the optimized conditions of SE were as follows:electricity of 1.1 times,duration of 6.0 h,temperature of 60℃,HCl of 30 g/L,iron ions of 5 g/L.Sb of 30 g/L,and anode current density of 80 A/m2.Under the optimized conditions,the leaching efficiency of antimony was over 98%,and those of Fe.As.Au were 5.50%.1.14%.and 0.63%,respectively.The content of Sb in cathode antimony was over 98%.moreover,gold and arsenic were basically retained in the residue.The SE samples were characterized by employing optical microscopy.XRD,SEM-EDS.and other analytical methods.The difference of transformation laws in the leaching process of different sulfur-containing minerals was proved.Stibnite was decomposed by oxidation to form elemental sulfur,that is,stibnite contacted with the oxidant Fe3+and the redox reaction occurred,S2was oxidized to zero valence and formed elemental sulfur crystals in situ,antimony ions diffused into the solution,thereby forming porous elemental sulfur structure.The newly emerged elemental sulfur generally embedded around residual stibnite to form a coating layer,which was loose and porous.Due to the low strength,it would collapse and flake under the action of strong stirring of SE.then dispersed in the leaching residue as fine elemental sulfur particles.Meanwhile,pyrite and arsenopyrite were difficult to be oxidized and decomposed and also remained in the leaching residue.The mineral particles were intact and the boundary was smooth with no obvious etching trace.In the SE process,stibnite was oxidized and decomposed,while pyrite and arsenopyrite were not oxidized or leached,which was the basis for the selective oxidation leaching of stibnite by SE.(5)A continuous pilot experiment was carried out with eight electrolytic cells of 50-liter connected in series.The test conditions were:50～60 ℃.,cathode and anode current density of 125 A/m2 and 80 A/m2,electricity of 1.1～1.2 times,liquid-solid ratio of 4:1(mL/g).Continuous slurry electrolysis of As-Au-Sb ore showed that the antimony leaching efficiency was about 98%,and the average leaching efficiencies of Fe,As,Au were 5.50%,1.54%,and 0.64%,respectively.The content of Sb in antimony cathode was over 98%,and the impurities contents were low.As and S can be removed during ingot casting to meet the 2#antimony standard(Sb99.65%). |
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