铂钯精矿中砷碲的碱性湿法选择性分离研究

Selective Separation of As and Te from Pt-Pd Concentrate Using Alkaline Leaching

以铜阳极泥分铜后液高效还原所得铂钯精矿为研究对象,采用常压碱浸工艺高效分离As和Te等杂质,碱浸液用H_(2)SO_(4)中和沉碲、实现As和Te的高效分离。试验考察了H_(2)O_(2)用量、NaOH浓度、液固比、反应时间和温度等参数对As和Te浸出率的影响,及碱浸液中和pH值和反应时间对As和Te分离效果的影响。结果表明:在NaOH浓度2.5 mol·L^(-1)、液固比5:1、不添加H_(2)O_(2)常温搅拌浸出1 h优化条件下,碱浸渣率为41.53%,Te和As的浸出率分别达到97.46%和99.17%;碱浸液采用H_(2)SO_(4)中和至pH=5后反应1.5 h,沉碲后液中Te含量仅为0.1416 g·L^(-1),所得TeO_(2)沉淀中Te含量为71.77%、As含量为0.919%,粗TeO_(2)沉淀经一次提纯后Te和As含量分别为77.55%和0.050%,X射线衍射(XRD)显示主要物相为TeO_(2),扫描电镜(SEM)表明微观形貌为大小不均的非规则鳞片状。铂钯精矿常压碱浸可有效浸出杂质元素As和Te,碱浸液硫酸中和实现As和Te的高效分离,该工艺的成功开发可为铂钯精矿的清洁富集和碲的高效分离提供一定的工艺参数和理论依据。

Platinum group metals(PGMs)are important strategic and critical resource.The mineral resources of PGMs are predominately localized in South Africa and Russia,and others are mainly in a few countries,such as Zimbabwe and the United States.China's PGMs mineral resources are extremely deficient,the prospective reserves is only about 350 tons,which is no more than 0.5%of the world's total reserves.However,China is the largest PGMs consumer in the world,how to efficiently separate and enrich PGMs from a variety of resources has become an important way to solve the contradiction between supply and demand in China.Copper anode slime is an important raw material which is rich in many rare and precious metals,it has become a hot spot in the treatment of how to efficiently and greenly recover Au,Ag,Pt and Pd.According to the configuration characteristics of Au,Ag,Pt,Pd and Te in the copper-rich solution from copper anode slime,the research group established a new online in-situ high-efficiency reduction rare and precious metals novel approach to obtain high-grade platinum palladium concentrate,the main impurities of the concentrate were As and Te.Nonferrous smelting dust was usually used to separate As through acid leaching,alkali leaching and water leaching methods.The main processes of separating tellurium by hydrometallurgy were acid leaching and alkali leaching,the raw material was Pt-Pd concentrate obtained by zinc replacement and smelting slag from Kaldor furnace.However,the composition and impurities of Pt-Pd concentrate were complex and changeable,and the experimental raw materials had unique secondary mineral characteristics,so it was necessary to systematically explore the leaching behavior of As and Te in order to obtain the optimum leaching conditions.The soluble metal salts in Pt-Pd concentrate were removed through washing,obtained residue was light yellow powder.The micro morphology,phase composition and valance of elements in the samples were systematically characterized by the means of chemical analysis,X-ray fluorescence(XRF),X-ray diffraction(XRD),scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).The arsenic and tellurium were separated from Pt-Pd concentrate by atmospheric alkaline leaching process,alkaline leaching solution was neutralized by H_(2)SO_(4)for selectively separating tellurium.The effects of H_(2)O_(2) dosage,NaOH concentration,leaching liquid to solid ratio,leaching duration and temperature on leaching efficiency of arsenic and tellurium were explored,and neutralizing acidity and reacting duration on separating tellurium were investigated.The results showed that the main components of the Pt-Pd concentrate sample were As,Te,Fe and Bi,the total mass fraction accounted for about 75%,the content of As and Te were 31.43%and 16.77%,Au,Ag,Pt and Pd were 129,3920,600 and 2340 g·t^(-1),respectively.The microscopy analysis showed that the particle size of Pt-Pd concentrate was fine and uneven,with occasional crystalline particles less than 2μm.The main phases was identified as AgCl,characteristic diffraction peaks of Au,Pt and Pd were no detailed because of the low content,As,Fe,Bi and Te also had no characteristic diffraction peaks,it might exist as amorphous phase.The results of XPS showed that the electron binding energy of As 3d in Pt-Pd concentrate was 45.6 and 44.8 eV,which were the characteristic peaks of As(V)and As(III),and As in the concentrate mainly existed in the form of amorphous arsenate and arsenite,the electron binding energy of Te 3d5/2 in platinum palladium concentrate was 576.3 eV,which might be in the form of amorphous TeO_(2)or tellurite.The reaching results showed that tellurite in Pt-Pd concentrate could be oxidized to insoluble tellurate by hydrogen peroxide solution,led to the decrease leaching rate of Te and the increase of leaching residue rate with the increase of H_(2)O_(2) dosage.At the same time,arsenite could be oxidized to arsenate by H_(2)O_(2),both of which were soluble in alkaline solution,therefore,the amount of H_(2)O_(2) had little effect on the leaching rate of As.The leaching rate of As and Te increased with the increase of NaOH concentration and liquid-solid mass ratio,while leaching temperature and duration had little effect on the leaching rate.The optimum conditions of alkaline leaching were determined as follows:NaOH concentration of 2.5 mol·L^(-1),liquid to solid ratio of 5∶1,without H_(2)O_(2) stirring leaching for 1 h at room temperature.Under these conditions,the leaching residue efficiency reached 41.53%,the contents of As and Te decreased from 31.43%,16.77%to 0.518%and 0.988%,the reaching rate were 99.17%,97.46%,respectively.Alkaline leaching solution was neutralized by H_(2)SO_(4)for selectively separating tellurium.The content of tellurium in precipitation liquid only reached 0.1416 g·L^(-1) under pH=5,reacting duration 1.5 h,and the content of Te and As in TeO_(2)slag reached 71.77%and 0.919%respectively,and the content of Te and As in the purified TeO_(2)slag reached 77.55%and 0.050%,respectively.XRD pattern of purified TeO_(2)was a single TeO_(2)phase,whose microscopic appearance was irregular scaly superposition with uneven size.The normal pressure alkaline leaching process of Pt-Pd concentrate could effectively separate As and Te,while the sulfuric acid neutralization process of alkaline leaching solution realized high-efficiency separation of arsenic and tellurium.