The passivation of chalcopyrite subjected to ferric sulfate leaching and its reactivation with metal sulfides

Research has been undertaken on the passivation of chalcopyrite when subjected to leaching in ferric sulfate medium. The sulfur film which forms on chalcopyrite in the oxidation process is not responsible for the decrease in the rate of copper dissolution observed. The passivating effect created by a reaction product other than sulfur is neutralized to some extent by introduction into the crystal lattice of the passivated solid, metal sulfides such as HgS, As₂S₃, SnS and CoS, so that the metal sulfide nuclei deposited on the passivating layer restore the initial reactivity between the solid and the leaching solution.     

Electrobioleaching of base metal sulfides

Bioleaching of base metal sulfides, such as pyrite, chalcopyrite, and sphalerite, under the influence of applied direct current (DC) potentials is discussed. Contributions toward mineral dissolution from three effects, namely, galvanic, applied potential, and microbiological, are analyzed and compared. Sphalerite could be selectively bioleached in the presence ofThiobacillus ferrooxidans under an applied potential of −500 mV (SCE) from mixed sulfides containing sphalerite, pyrite, and chalcopyrite. Bacterial activity and growth were found to be promoted under electrobioleaching conditions. Probable mechanisms involved in the bioleaching of different sulfides under positive and negative applied potentials are discussed.     

The selective oxidation of mixed metal sulfides with lime in the presence of steam without emitting sulfur-containing pollutants

The selective oxidation of mixed metal sulfides with lime in the presence of steam was studied as a function of the mixing ratio of the constituents, temperature, and steam concentration. Two combinations of samples were used in this study: ZnS/PbS/CaO and ZnS/FeS/CaO. The steam oxidizes one or both of the metal sulfides, and the hydrogen sulfide produced reacts with lime to form calcium sulfide and regenerate steam. There is no net consumption or generation of gaseous species; therefore, this process can be carried out in a closed system. The free energy of the reaction is negative only for certain metal sulfides, and thus selective oxidation for mixed sulfides can be achieved. An overall rate equation developed in this work satisfactorily predicted the experimental data obtained in the temperature range 823 to 1113 K. The potential implications of the results of this work in the treatment of complex sulfide ores are discussed. This paper is based on a presentation made in the T.B. King Memorial Symposium on “Physical Chemistry in Metals Processing” presented at the Annual Meeting of The Metallurgical Society, Denver, CO, February, 1987, under the auspices of the Physical Chemistry Committee and the PTD/ISS.     

Oxygen pressure leaching of white metal

Sulfuric acid–oxygen pressure leaching of white metal was investigated at laboratory scale as an alternative to the pyrometallurgical Peirce–Smith converting to produce metallic copper. The main variables studied were temperature, concentration of sulfuric acid, partial pressure of oxygen, and time of leaching. The results indicated that most of the sulfur in the white metal is oxidized to sulfate in the range 105 °C to 150 °C. The concentration of sulfuric acid over 0.05 M, and oxygen partial pressure over 608 kPa had little effect on the dissolution of copper. The temperature was the most significant variable; below 130 °C copper dissolution was incomplete after 5 h of leaching while at 150 °C the dissolution was complete in 90 min. The dissolution of white metal proceeded in two stages through the formation of CuS as an intermediate compound and the kinetics of copper dissolution was analyzed by considering two consecutive reactions controlled by chemical reaction. The activation energies for the first and second stages were determined as 55 and 88 kJ/mol, respectively.     

Use of X-ray diffraction in a study of ammonia leaching of multimetal sulfides

X-ray diffraction has been used to study the changes in mineralogy that occur during ammonia leaching of sulfide minerals and complex bulk sulfide concentrates. Leaching results in high extraction rates (>90 pct) of copper from chalcopyrite, zinc from sphalerite, and lead from galena. However, under experimental leaching conditions (temperature, 115 °C to 135 °C; par-tial pressure of oxygen, 1.5 kg/cm²; pH ∼ 10.0), the pyrite grains are practically inert. Ap-parently, the amount of pyrite in leach residue is constant in absolute terms. However, its relative percentage changes because the amount of copper and zinc minerals is reduced in the leach residue during progressive leaching. The products formed during the leaching reaction, such as goethite and lead sulfate, tend to increase the weight of the leach residue, and thus the relative weight of pyrite remains nearly unchanged. The ratios of selected line pair intensities of pyrite lines and characteristic (selected) lines of chalcopyrite, sphalerite, and galena are used to establish the oxidative ammonia leaching kinetics of Cu-Zn-Pb bulk concentrates. That is, the variation in the line pair intensity ratios, with time, correlates with the changes in the el-emental concentrations in the leach liquor.     

Fundamental studies related to the development of the smelting reduction of iron oxide and carbon-constant volume studies

Abstract

Today, most of the iron-making capacity of the world is still dependent upon the blast furnace process, although the production of sponge iron by direct reduction processes is gaining acceptance in many areas. Another method of making iron, known as smelting reduction, is receiving attention, and pilot-plant scale operations are being developed in Europe and possibly elsewhere. In this method, iron oxide is reduced with carbon (coal) by a fast reaction such that liquid iron is the product, heat being provided to the reaction by the exothermic oxidation of carbon monoxide by oxygen within the reaction vessel.

In the present investigation, an attempt has been made to study the behaviour of composite pellets of wüstite and carbon in the region of 1500°C in various gas atmospheres at constant volume. Reaction rates were followed within the constant-volume system by measuring the increase in pressure with time using a pressure transducer. Composite pellets containing slightly more than the stoichiometrically required amount of carbon were reacted to form liquid iron in an argon atmosphere; to achieve melting, good mixing of the pellets was a critical requirement. Melting conditions were also obtained in carbon monoxide-carbon dioxide mixtures between 100 per cent CO and 100 per cent CO₂ When composite pellets, surrounded by a protective layer of carbon, were introduced into an atmosphere containing free oxygen, it was again possible to obtain melting and reduction to liquid iron. The activation energy for the reaction was approximately 15 kcal/mole. Possible reaction mechanisms are discussed.

Résumé

De nos jours, la réduction des oxydes de fer s'accomplit en grande partie au haut foumeau. On note toutefois une implantation graduelle des procédés de réduction directe des oxydes en fer éponge. Une autre méthode de production du fer, connue sous Ie nom de smeltage réducteur, est actuellement à l'étude. Des essais à l'échelle de l'usine pilote se font actuellement en Europe et possiblement ailleurs. La méthode consiste à produire du fer liquide en réduisant rapidement l'oxyde de fer par du carbone. L'énergie requise pour la réaction vient de l'oxydation exothermique du monoxyde de carbone par l'oxygène présént dans l'enceinte réactionnelle.

Les auteurs ont étudié le comportement de boulet1es composées de wüstite et de carbone en présence de diverses atmosphères gazeuses dans une enceinte fermée à 1,500°C. Les vitesses de réaction ont été détérminées en mesurant l'augmentation de la pression dans l'enceinte au moyen d'un transducteur de pression. Des boule1tes composées comportant un peu plus que la quantité stoechiométrique de carbone ont été réduites en fer liquide dans une atmosphère d'argon. La fusion n'avait lieu que si les constituants des boulet1es étaient intimement mélangés. La fusion de boulet1es a été réalisée dans des atmosphères constituées de melanges CO-CO₂, les proportions variant entre 100% CO et 100% CO₂. Le fer liquide a aussi été obtenu en faisant réagir des boulettes d'oxyde et de carbone entourées d'une couche protectrice de carbone, dans une atmosphère contenant de l'oxygène libre. L' énergie d'activation de la réaction était d'environ 15 kcal/mole. En fin, les auteurs discutent des mécanismes de la réaction.     

Speciation and reduction potentials of metal ions in concentrated chloride and sulfate solutions relevant to processing base metal sulfides

The speciation, Eh-pH and Eh-log a_Cl- dependence of Fe(III), Fe(II), Cu(II), Cu(I), Ag(I), Pb(II), Zn(II), Ni(II), As(III), Sb(III), and Bi(III) ions in practical (high ionic strength) sulfate and chloride solutions are discussed. The emphasis is placed on those ions which form strong sulfato-, chloro-, and hydroxo-complex species. Measured potentials are compared with potentials calculated from reported association and stability constants to test the applicability of these constants in nonideal solutions and to characterize predominant species. Formerly Postgraduate Student, Murdoch University, Perth, Western Australia     

Acid leaching studies of neutron-irradiated chyrsotile asbestos

Samples of chrysotile from Quebec (UICC B and Jeffrey 4T-30) and from the Coalinga region of California (Calidria RG-144) were irradiated with thermal neutrons in a reactor. The main activation products induced were 46Sc, 51Cr, 59Fe and 60Co. Accurately weighed samples of the irradiated materials were dispersed in N HCl by hand shaking for 10 s. After leaching for predetermined periods at 25 degrees C, the samples were filtered and the concentrations of Mg determined in the filtrates by inductively-coupled plasma atomic emission spectrometry (IPC-AES) and the activities of the four radionuclides by high resolution gamma-ray spectrometry. Similar measurements were made on solutions obtained by refluxing samples of irradiated chrysotile with 2N HCl for 2 h. The specific activities of each of the four activation products were calculated in arbitrary units and, as the concentrations of Sc, Cr, Fe and Co in the UICC B sample had already been determined, it was possible to estimate the concentrations of these elements in the other two samples. Similarities in the leaching patterns of magnesium and of the activation products showed that with all samples, high proportions of the parent trace elements were present in the form of isomorphous substitutes for magnesium in structural brucite. Agreement was closest with the Calidria chrysotile in which all the radionuclides had a similar pattern. With the Jeffrey and UICC B samples, the presence of a high proportion of the iron as relatively insoluble magnetite accounted for the observed discrepancy in behaviour between 59Fe and Mg. More detailed calculation of leaching rates over specific time intervals showed that, initially, 51Cr and 60Co dissolved more rapidly than Mg but that this was followed by a period in which the opposite was the case. It was concluded that the Calidria RG-144 sample is an ideal candidate for studies of magnesium dissolution in vivo.     

Fundamental aspects of creep in metal matrix composites

The primary characteristics of the creep of metal matrix composites (MMCs) are reviewed, including the shapes of the creep curves, the origin of the threshold stresses, and the nature of the rate-controlling processes. A detailed analysis of two representative MMCs provides no support for the concept of a constant substructure model for creep with a stress exponent (n) of 8. Analysis of the data demonstrates that creep is controlled by deformation in the matrix alloys and, as in solid solution alloys, there is a division into control by viscous glide (class A) and climb (class M), respectively. This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee.     

Echophonocardiographic studies of the contribution of the atrioventricular valves to the first heart sound

The movements of the mitral, tricuspid and aortic valves have been recorded echocardiographically and related to the first heart sound (S1) in patients with various hemodynamic and conduction abnormalities. Closure of the mitral and tricuspid valves has been studied with respect to the corresponding atrioventricular pressure crossover and it is clear that both valves finish closing about 50 msec after pressure crossover. In order to clarify the relative contribution of tricuspid valve closure and aortic root events to the second high frequency component of S1, a new simultaneous dual echophonocardiographic technique was employed. This permitted the simultaneous registration of tricuspid and aortic valve movements and demonstrated that in certain circumstances the second high frequency component of S1, could be attributed to tricuspid closure, aortic root events being excluded from the genesis of this sound. These observations suggest that the two high frequency components of S1 are related to closure of the mitral and tricuspid valves. The results do not however, exclude a contribution to S1 of aortic root events, which may be of lower frequency vibrations.     

Oxidation of heavy nonferrous metal and iron sulfides via a chain mechanism

Gaseous sulfur monoxide (SO) is experimentally found to be a primary intermediate product in the oxidation of nonferrous metal and iron monosulfides. This finding is used to develop a theory for the chain oxidation of metal sulfides to form oxysulfide complexes MSO _x and gaseous SO. The main steps of the metal sulfide oxidation via a chain mechanism are thermodynamically characterized. The Gibbs energies of the oxidation reactions are shown to decrease in the absolute value relative to the type of sulfide as follows: FeS, Ni₃S₂, CoS, NiS, ZnS, PbS, CdS, CuS, and Cu₂S. The thermodynamic probability of all steps of the chain oxidation of the monosulfides with the evolution of gaseous atomic oxygen and sulfur is estimated.     

Methodology of kinetic interaction studies in clinical pharmacology: an experimental contribution on diftalone and acetylsalicylic acid

The possible interaction of acetylsalicylic acid (ASA) and diftalone (DIF), a new anti-inflammatory drug, was studied in 6 volunteers. All subjects received each of the following three treatments: ASA 1 g, DIF 0.5 g, ASA 1 g plus DIF 0.5 g at 4-day intervals (stage 1 of the study). In stage II of the same study, each subject received ASA 1 g plus DIF 0.5 g in three different occasions 1 week apart; after a 7-day pre-treatment with either DIF 0.25 g b.i.d., or ASA 0.5 g b.i.d., or DIF 0.25 g b.i.d. plus ASA 0.5 g b.i.d. A total of four different comparisons were made. After pre-treatment with DIF, but not after pre-treatment with DIF plus ASA, the peak level of salicylate was significantly reduced by about 15%. No other evidence of interaction was found.     

含铜难处理金矿石混合氯浸试验研究

某难处理金矿石中含有大量铜,如果直接氰化浸出,除了消耗大量氰化物外,还会在金表面形成一层薄膜,减慢金的溶解速度,金回收率低于30%;如果预氧化处理后再氰化提金,操作复杂、过程冗长、有污染、成本高,而且回收率并无实质性提高。为提高金回收率,降低生产成本,试验将该难处理金矿石破碎细磨后采用低浓度的NH4Cl和氨水混合浸出,利用氯离子与金形成稳定的配合物进行提金,矿石中的铜离子起氧化作用,促进金的反应,金浸出率可达87%以上。该方法无需进行预氧化处理,避免添加有毒有害药剂,消除对环境的污染。