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Transactions of Nonferrous Metals Society of China Available online at 咀-41“ 飞;ScienceDirect DMωs mH回国剧创 -II m---cp -aE 、 Trans. Nonferrous Met. Soc. China 202010 903 -909 ELSEVIER Co-intensification of gold leaching with heavy metals and hydrogen peroxide YANG Yong-bin杨永斌，LI Qian李毒，JIANG Tao姜涛，GUO Yu-feng郭宇峰， LI Guang-hui李光辉，XUBin许斌 School ofMineral Processing and Bioengineering, Central South Universi钞，Changsha410083, China Received 6 July 2009; accepted 19 January 2010 Abstract Co-intensification was researched to accelerate gold leaching with regards to its electrochemical nature by using anodic intensifiers ofheavy metal ions Pb2, Bi3, Tl, Hg2 and Ag丁onthe basis of hydrogen peroxide assistant leaching on three different types of materials which were classified as a re仕actorysulphide gold concentrate, an easily leachable sulphide gold concentrate, and a low grade oxide gold ore according to their leaching characteristics. The results showed that, favorable co-intensification effects on the three materials were obtained and leaching time of gold was effectively shortened to no longer than 12 h from 16 to 24 h for hydrogen peroxide assistant leaching. For the five tested heavy metal ions, Beand Tl presented co-intensifying effect on all the three materials, and Hg2 caused co-intensifying effect on both refractory and easily leachable sulphide gold concentrates, and Pb2 and Ag only had co-intensifying effect on the easily leachable sulphide gold concentrate. Key words gold leaching; co-intensification; cyanidation; heavy metals; hydrogen peroxide Therefore, more effective intensification effect should be obtained by simultaneous promotion of both elec仕odes processes [4] . Some heavy metals such as Pb, Bi, Tl, Hg, and Ag were proved to be effective in intensifying anodic dissolution of gold[5-7]. On this basis, some investigations have been carried out on gold leaching with addition of Tl[4, 8], Bi[町，Pb[坷，Ag[lO], etc. However, few reports have been published on the practical application of these s. The main obstacle may be attributed to the lack of overall recognition on their acting characteristics and on the adaptability of these elements in different materials with different leaching properties. In the previous studies[l1-13], the electrochemical kinetics of gold anodic dissolution intensified by these metals has been systematicaIIy investigated. On this basis, co-intensification of gold leaching has been studied based on mixed potential theory by using heavy metal ions as anodic intensifiers and hydrogen peroxide as cathodic intensifier. In this work, co-intensification has been researched to accelerate gold leaching企omdifferent types of materials with regards to their electrochemical natures by using anodic intensifiers ofheavy metals ions Pb2, Bi3, 1 Introduction Throughout th巳lastcentury, a great deal of concems have been focused upon the problem of low leaching rate of gold cyanidation and a series of intensification techniques have been worked out. Among these techniques, hydrogen peroxide assistant leaching has been proved to be an effective m巳thodto accelerate gold leaching since its appearance in 1987[1-2]. However, it seems ve可difficultfor further progress to be made and few new techniques have been presented ever since. It has been demonstrated that gold leaching is virtuaIIy an electrochemical process incIuding anode dissolution of gold and cathode reduction of oxygen and other oxidants[3]. Intensification of anodic process and cathodic process can both lead to increase of gold leaching rate. When one semi-electrode is intensified to an enough extend, further intensification no longer con仕ibutesto fu口herincrease of gold leaching rate as the leaching process comes to be limited by the counter semi-elec仕odeprocess. Being a cathodic intensifying technique, hydrogen peroxide assistant leaching wiII inevitably come to a limitation and further increase of gold leaching rate wiII depend on anodic intensification. Foundation item Project50725416 supported by the National Natural Science Foundation for Distinguished Young Scholars ofChina Corresponding author LI Qian; Tel 86-731-88830547; Fax 86-731-88830542; E-mail csuliqian DOI IO.lOI6/S1003-63260960234-X illib--Lpj 904 YANG Yong-bin, et a1/Trans. Nonferrous Met. Soc. China 202010 903-909 Tl, Hg2 and Ag丁andcathodic intensifier of hydrogen pH to a given va1ue in the beginning of stirring. After peroxide. 1eaching for a given time, the slurry was filtered and the 2 Experimental Three kinds of gold containing materia1s were used in this study two concentrates with su1phides as gold-bearing minera1s and one raw ore with oxides as gold-bearing minera1s. The er two were 1abe1ed as su1phide gold concentrate A and su1phide gold concentrate B, respective1y, and the third was named as oxide gold ore. Their chemica1 compositions are 1isted in Tab1e 1. From Tab1e 1, two concentrates are high gold cont巳ntmateria1s and the oxide gold ore has on1y a 10w gold content of 3.9 g/t. In addition, the two su1phide concentrates have high S and Fe contents and noticeab1e Cu content, which may cause negative effects on gold 1eaching, whi1e the oxide ore has 1itt1e contents of these components. It was indicated by chemica1 phase ana1ysis that pyrit巳wasthe main su1phide minera1 of these two concentrates. Concentrate A a1so contained some chalcopyrite, pyrrhotite and marcasite as minor su1phide minera1s, whi1e concentrate B on1y contained some chalcopyrite as minor su1phide minera1s; and neither pyrrhotite nor marcasite was found. The intensifying reagents used in this study include hydrogen peroxide in the of aqueous solution with 30 H202, and heavy meta1s in the of ana1ytically pure nitrate or su1phf注tesuch as PbN03h BiN03h T1N03, HgS04, and AgN03. Hydrogen peroxide was used as cathodic process intensifier and heavy meta1 sa1ts were used as anodic process intensifiers. Besides, analytically pure sodium cyanide was used as 1ixiviant and chemically pure CaO was used to a司justpH va1ue. Heavy meta1 sa1ts and cyanide had been prepared in solutions before addition and CaO was added in the of fine1y ground powder. For each test, 50 g samp1e was frrst ground in a d160 mmX 50 mm wet ball mil1 with mass fraction of 40 in grinding slurry, and then put in a 500 mL beaker. Cyanide, intensifiers, and water were added into the beaker to prepare a slurry of 20 and given concentrations of cyanide and intensifiers. The slurry was stirred with a EUROSTAR step1ess speed regu1ation stirrer and CaO powder was added in the slurry to a司just residue was dried in a e1ectric drying oven. The residue and pregnant solution were both ana1yzed by atomic absorption spectrome位Yto determine gold content. 3 Results and discussion 3.1 Fundamental cyanide leaching characteristics Fundamenta1 1eaching characteristics of these three kinds of gold containing materia1s were studied though conventiona1 cyanide 1eaching in terms of gold 1eaching recovery as a function of 1eaching time. It was clearly found企omFig.1 that conventiona1 gold 1eaching characteristics were quite different among three materia1s. For su1phide gold concen仕ateA, gold 1eaching rate tumed up ve可slow1y.Go1d 1eaching recove可increased slow1y with increasing time especially after 36 h, and it was on1y 54.89 for a 1eaching time as 10ng as 48 h. Therefore, su1phide gold concen位ateA was a typica1 re企actorygold concentrate which is di旺cultto be effective1y 1eached by conventiona1 cyanide 1eaching. In con仕ast，su1phide gold concentrate B exhibited a much more favourab1e 1eachabi1ity with much 1arger 1eaching rate and higher gold 1eaching recovery. Go1d 1eaching recove巧rapproached 60 within on1y 4 h and reached 94.23 after 24 h. For the oxide gold ore, there was a1so a re1ative1y 1arge gold 1eaching rate. Go1d 1eaching recovery reached 68.8 within on1y 2 h and approached 80 after 8 h. However, further 1eaching was very difficu1t after 12 h and fina1 recovery was on1y 84.55 after 24 h because ofthe 10w origina1 gold content in the raw ore. The reason for the s仕ikingdifference between two kinds of concentrates might 1ie in their su1phide components. Concentrate A contained some amount of pyrrhotite and marcasite whi1e oncentrate B did contain either of them. As we lrnow, pyrrhotite and marcasite were prone to be oxidized du由19gold cyanidation and dep1eted in oxygen and cyanide which were essentia1 for gold 1eaching[14-15]. Herefore, gold 1eaching企Om concentrat巳Awas serious1y impeded. On the oth巳rhand, according to mixed potentia1 theory illustrated in Fig.2, the oxidizing reaction of pyrrhotite and marcasite may act as simultaneous1y occurring anodic reactions which Table 1 Chemical compositions of gold containing materials Sample wAu/g.C1 wAg/g.C1 wCu/ wPb/ wZn/ wFe/ wS/ Sulphide gold concentrat巳A57.8 1020 1.05 0.47 1.37 31.10 38.20 Sulphide gold concentrate B 79.4 229.7 1.17 1.26 0.99 25.27 24.48 Oxide gold ore 3.9 0.72 0.02 0.069 0.03 2.42 0.18 f YANG Yong-bin, et aVTrans. Nonferrous Met. Soc. China 202010 903-909 905 王C啤qJ J 6O -a 50 O O 40 30 O -Slphide gold concentrate A .. -Sulphide gold concentrate B 圃Oxidegold ore 40 50 Leaching time/h Fig.l Gold leaching recoveries for three kinds of gold containing ores Grinding grade 0.074 mm 99.50, slurry density 20, NaCN 0.2, pH 11, and stirring speed 1 000 r/min J JM“ JM, J G JE---41 伊M，口M“ ψ Fig.2 Diagram for illus仕ationof decrease in current density 企omeasi1y oxidizing components J ao current density curve for anodic dissolution of pur巳gold;J a, current density curve for anodic dissolution of imaginary easi1y oxidizing compon巳nts;Jc current density curve for cathodic reduction of oxygen raise anodic curve企ompure gold anodic process to total of coexisting anodic process. This wi1l negatively shift mixed potential仕omMo to M] and result in the reduction of gold dissolution current density from J Mo to J Mj . On the basis of above mentioned leaching characteristics, concentrate A was c1assified as re仕actory sulphide gold concentrate; concentrate B was c1assified as easily leachable sulphide gold concen位ate;and the oxide ore was named as low grade oxide gold ore because of its low gold content characterized leaching effect. 3.2 Co-intensification of gold leaching from refractory sulphide gold concentrate Intensification of gold leaching企omre企actory sulphide gold concentrate by heavy metals was conducted by separately adding 10-5 mollL Pb2, Bi3, Tl, Hg2, Ag; and the results are shown in Table 2. Table 2 Gold leaching re∞very in th而presenceof heavy metal ions for re企actorysulphide gold concentrate Conventional Leaching in th巳presenceof heavy metal ions leaching Pb2 Bi3 Tl Hg2 Ag 44.15 43.52 46.23 45.05 45.82 44.08 Grindin咀grade0.074 mm 99.50, aqueo咀sphase-to-solid ratio 5 1, NaCN 0.2, pH 11, stiπing speed 1 000 r/min, leaching time 24 h, heavy metal ∞ncentratio但10→moVL For the refractory sulphide gold concen仕ate，heavy metals did not show substantial promoting effect on gold leaching. Among these five kinds of metal ions, B户，Tl, Hg2 just slight1y increased gold leaching recovery and Pb2, Ag did not take effect at all. This indicated that the intensifying effect of heavy metal on gold anodic dissolution could not promote the gold leaching rate for the re企actorysulphide gold concentrate because easily oxidizing components depleted oxygen and cyanide needed for gold leaching and reduced mixed potential. With the negative shi位ofmixed potential, th巳difference between anodic currents with and without anodic intensifiers might decrease, which would undermine the effect of anodic intensification. Therefore, anodic intensifiers should not be suitable for gold ores contammg oxygen consummg components. In order to acquire expectant accelerating effect on gold leaching, cathodic process must be intensified in priority to diminish oxygen consuming matters and to increase anodic current. This would not only direct1y promote gold‘leaching but also help heavy metals to take effect by increasing mixed potential to the value at which the differences between the anodic cu凹eswith and without heavy metal ions b巳comeremarkable. Hydrogen peroxide was used as cathodic intensifier for gold leaching alone and together with heavy metal ions B户，Tl, Hg2. From Fig.3, hydrogen peroxide significant1y raised gold leaching rate and gold leaching recovery, which indicated great promoting effect by cathodic intensification. Gold leaching recovery a丘er8 h was sharply increased企om31.88 to 60.20. In addition, gold leaching process was further intensified by hydrogen peroxide together with heavy metal ions, exhibiting pronounced co-intensifying effect. Gold leaching recovery after 8 h was further increased to around 70, which meant about 10 increment according to single intensification with hydrogen peroxide. This evidential1y demons位atedthe inducing function of cathodic intensification on effectiveness of anodic intensification and co-intensification. As for three kinds of tested metal ions, the contribution of Bi3 to YANG Yong-bin, et al/Trans. Nonferrous Met. Soc. China 202010 903-909 3.3 Co-intensification of gold leaching from easily leachable sulphide gold concentrate Experiments were conducted to study the effect of co-intensification on gold leaching from easily leachable sulphide gold concentrate by simultaneously using hydrogen peroxide and heavy metal ions in comparison with single intensification of semi-electrode process by singly using hydrogen peroxide or heavy metal ions. The results are shown in Fig.5. Three main aspects of inforrnation could be found from Fig.5. Firstly, gold leaching was effectively promoted by using cathodic intensifier of hydrogen peroxide. Gold leaching recovery was increased from 94.23 to more than 97 after leaching for 24 h. Secondly, anodic intensifiers of heavy metal ions presented stronger intensifyi吨effectsthan hydrogen peroxide, as they not only further increased gold recove巧，in contrast with hydrogen peroxide but also made it possible to shorten leaching time from 24 h to 16 h. Thirdly, simultaneous use of hydrogen peroxide and heavy metal ions presented favourable co-intensifying effect which was more effective than that obtained by single intensifying with only one of the intensifiers. Gold leaching rate was further increased on the basis of intensified leaching by heavy metal ions, resulting in higher gold leaching recove可andshorter leaching time. Although there existed some differences among effects of these five kinds of heavy metal ions mainly on leaching rate in the earlier leaching period, it is common for them that co-intensification increased gold leaching recovery to near 96 or even above 97 within 12 h and shortened leaching time to 12一16h. In a word, for the easily leach
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