简介概要

Chemical leaching mechanism of chalcopyrite with difference mineralization

来源期刊：Rare Metals2013年第1期

论文作者：Jing Bai Jian-Kang Wen Song-Tao Huang Biao Wu

文章页码：63 - 66

摘要：This paper presents the effect of mineralization on chalcopyrite chemical leaching in very simple H2SO4 solution systems at pH 1.0, with 5 % chalcopyrite concentrate at 65℃. The copper extractions after 12 days leaching of marine volcanic and porphyry chalcopyrite were 85.7 and 66.6 %, respectively. It was found that sulphur element formed on the surface of two samples as a result of XRD and SEM-EDAX, which was very porous that did not inhibit chemical leaching reaction. Meanwhile, （Cu, Fe）12As4S13 formed on the surface of porphyry type chalcopyrite, which may cause low leaching ratio of porphyry type chalcopyrite as passivation. （Cu, Fe）12As4S13 may be one kind of the polysulphide compounds.

Rare Metals 2013,32(01),63-66+2

Chemical leaching mechanism of chalcopyrite with difference mineralization

Jing Bai Jian-Kang Wen Song-Tao Huang Biao Wu

National Engineering Laboratory of Biohydrometallury, General Research Institute for Nonferrous Metals

作者简介：Jing Bai,e-mail:baijing0214@gmail.com;

收稿日期：22 February 2012

基金：financially supported by the National Natural Science Foundation of China(No.50934002);the National Basic Research Program of China(No.2010CB630905);the National High Technology Research and Development Program of China(No.2012AA061502);

Chemical leaching mechanism of chalcopyrite with difference mineralization

Abstract：

This paper presents the effect of mineralization on chalcopyrite chemical leaching in very simple H2SO4 solution systems at pH 1.0, with 5 % chalcopyrite concentrate at 65℃. The copper extractions after 12 days leaching of marine volcanic and porphyry chalcopyrite were 85.7 and 66.6 %, respectively. It was found that sulphur element formed on the surface of two samples as a result of XRD and SEM-EDAX, which was very porous that did not inhibit chemical leaching reaction. Meanwhile, (Cu, Fe)12As4S13 formed on the surface of porphyry type chalcopyrite, which may cause low leaching ratio of porphyry type chalcopyrite as passivation. (Cu, Fe)12As4S13 may be one kind of the polysulphide compounds.

Keyword：

Chalcopyrite; Chemical leaching; Passivation; Mineralization;

Received： 22 February 2012

1 Introduction

Chalcopyrite is the most abundant copper mineral in the world[1].Many attempts were made by researchers to solve low dissolution rates,but they were not successful because of the refractory nature of chalcopyrite[2–4].It is widely accepted that the low dissolution rate is caused by the formation of a passivating layer on the mineral surface,whether by bioleaching or chemical leaching.The following equation is commonly accepted as a possible mechanism of chalcopyrite leaching[5–8].

In Eqs.(1)and(2),the oxidants are ferric ion and dissolved oxygen,respectively,and sulphur is made as reaction product.In Eq.(2),hydrogen ion is only an indicator for the reaction when the oxidant O₂reacts with chalcopyrite;simultaneously H?is also consumed.Hiroyoshi et al.[9–11]discovered that the copper dissolution rate from chalcopyrite is higher in a ferrous sulphate medium than in a ferric sulphate medium.Ferrous plays a significant role on chalcopyrite leaching in sulphate media.The copper dissolution rate increased as the initial ferrous ion concentration increased,but passivation phenomena were still in ferrous sulphate medium.Cordoba et al.[12–16]supported this theory on the redox potential of chalcopyrite leaching experimentally with tests having a high redox potential.Therefore,the role of Fe^3?as an oxidant on chalcopyrite leaching is open to question.

Most of the known copper deposits in the world,belong to four types of geology as follows:(1)porphyry type and vein-metasomatic type copper deposit with the intermediate-acid intrusive magma,the amount of which is 2/3 of total copper resource in the world,(2)strata-bound deposit in sedimentary rocks,(3)pyrite-type massive sulphide deposit,natural copper deposit and exhalation-sedimentary polymetallic deposit with volcanic activity,and(4)Cu–Ni sulphide deposit related to maficigneous rock.These types of copper deposits are distributed unevenly in the world[17,18].It is found that porphyry type chalcopyrite is more difficult to be leached than other types at the same conditions.However,the mechanism still needs to be further investigated.

In this study,the different leaching of chalcopyrites with two types of mineralization in very simple H₂SO₄solution system was investigated,and the leaching mechanisms of different mineralization on chalcopyrite were studied.

2 Experimental

2.1 Chalcopyrite samples

The leaching tests were performed with two chalcopyrite minerals from Dahongshan(approximately 94.10%CuFeS₂)Yunnan Province and Dexing(approximately88.81%CuFeS₂)Jiangxi Province in China,respectively.The chalcopyrite sample from Dahongshan belongs to marine volcanic type,and the sample from Dexing is porphyry type[18].Table 1 shows the chemical composition of these minerals.The main impurity of Dexing mineral was copper arsenate(Cu₃(AsO₄)₂),as determined by X-ray analysis.There were no impurities in the mineral from Dahongshan.The minerals were wet-ground using a ceramic ball mill.The average particle size of these minerals was around 45 lm.

2.2 Leaching tests

All leaching tests were performed in a shaker at 150 rpm and65°C using 300 ml Erlenmeyer flasks covered with hydrophobic cotton to admit oxygen while reducing water loss through evaporation.A pulp density of 5%(100 ml of leaching solution and 5 g of mineral)and p H 1.0 was chosen.The water evaporation was compensated with distilled water,pH was adjusted when above the initial value.

2.3 Analysis

A solution sample of 1 ml was periodically taken from the leaching solution to obtain kinetic information on metal dissolution.Copper and total iron concentrations were determined by atomic absorption spectroscopy analysis.Ferrous ion concentration was tested using photocolorimetric method based on the formation of a reddish colored complex of Fe^2?with orthophenanthroline in a UV–vis spectrophotometer at a wavelength of 510 nm.Finally,solid residues were characterized by XRD and SEM-EDAX analysis.

Table 1 Chemical composition of the minerals tested 下载原图

Table 1 Chemical composition of the minerals tested

3 Results and discussion

The copper extraction of chalcopyrite from Dahongshan(Dhs)was 85.7%,which was only 66.6%for Dexing(Dx)after 12 days leaching(Fig.1a).The copper extraction of Dhs was higher than that of Dx initially,and the gap of leaching ratio between them was increased.In addition,considering that the extraction ratio did not decline during the leaching process,it seems that there was no passivation formed in the leaching of Dhs.Figure 1b shows the changes in total iron and the ferrous ions as a function of the experimental time.The behaviour of the iron dissolution was similar with that of the copper dissolution.Iron ion was initially dissolved as ferrous ion,and with the leaching going on,ferrous ion continued to be oxidized to ferric ion by dissolved oxygen,seen Eq.(3).

It should be noted that the iron ions are dissolved from both Dhs and Dx minerals as ferrous ion initially,and ferrous ion is slowly oxidized to ferric in contact with dissolved oxygen in the medium.The drop of ferrous ions in the final stage of Dhs and Dx was due to an increase of the values of pH in the leaching medium.Moreover,it is found that the increasing of Fe^3?in the solution has no relationship with the copper dissolution.These results suggest that the copper extraction in this solution is conducted as Eq.(2).The ORP is consistent with the result of Fe^3?/Fe^2?ratio(Fig.1c).Potential in the leaching process,both Dhs and Dx,had always been below 410 mV.

The SEM images of leaching residues are shown in Fig.2.Because pH is maintained at 1.0,there is no presence of jarosite in both Dhs and Dx.Figure 2a shows the SEM image of Dhs residue,the letters‘A’and‘B’represent sulphur and chalcopyrite,respectively.There is no apparent passivating layer formed in Dhs,and the sulphur film is so porous on the surface that it must not inhibit chemical leaching reaction.Figure 2b shows the SEM image of Dx residue,and the materials at‘A’,‘B’and‘C’in the graph are chalcopyrite,sulphur and(Cu,Fe)₁₂As₄S₁₃.(Cu,Fe)₁₂As₄S₁₃is very dense on the mineral surface,which was responsible for passivation and causes the low leaching ratio of Dx chalcopyrite.

The results of SEM-EDAX are confirmed by the X-ray analysis of leaching residue samples of Dhs and Dx,which is shown in Fig.3.From Fig.3a,it is found that the sulphur element is the only reaction production of Dhs,which confirmed that there is no passivation layer formed in the leaching process.However,in addition to the sulphur element,(Cu,Fe)₁₂As₄S₁₃is also formed(Fig.3b),which may be one of the polysulphide compounds and inhibits the leaching of Dx as passivating layer.(Cu,Fe)₁₂As₄S₁₃may be the reaction production of Cu₃(AsO₄)₂which is the main impurity of Dx mineral.

Fig.1 Cu extraction(a),iron ion extraction(b),and Fe(III)/Fe(II)and ORP(c)of two chalcopyrites from Dhs and Dx

Fig.2 SEM images of residues of Dhs(a)and Dx(b);Letters of‘A’and‘B’in the graph of Dhs(a)representing sulphur and chalcopyrite,respectively;Letters of‘A’,‘B’and‘C’in the graph of Dx(b)representing sulphur,chalcopyrite and(Cu,Fe)12As4S13

4 Conclusion

The chalcopyrite sample of Dhs belongs to marine volcanic type,and the sample of Dx is porphyry type[18].Copper extractions of Dhs and Dx after 12 days leaching are 85.7and 66.6%,respectively.The gap of leaching ratio between them increases with time.These results imply that the chemical leaching behaviour of these two types of mineralization of chalcopyrites are different.

Fig.3 X-ray diffraction(XRD)patterns of the leaching residues from Dhs(a)and Dx(b)

It is found that sulphur element formed on the surface of two samples as the result of XRD and SEM-EDAX analysis,which is so porous that it does not inhibit chemical leaching reaction.On the surface of porphyry type chalcopyrite,(Cu,Fe)₁₂As₄S₁₃formed a passivating layer,which may be one kind of polysulphide compound.In addition,the research shows that the difference of leaching behaviour between two samples is attributed to impurity.

Moreover,it is found that the increasing of Fe^3?in the solution has no relationship with the copper dissolution,which indicates that the copper extraction from chalcopyrite in H₂SO₄solution occurs directly by dissolved oxygen.