Interaction of pentlandite, chalcopyrite, and pyrrhotine with elementary sulfur: II. Sulfidizing of chalcopyrite

The results of the second part of the study into the sulfidizing of the main sulfide minerals of copper-nickel ores, namely, pentlandite, chalcopyrite, and pyrrhotine, by elementary sulfur are presented. The phase compositions of the sulfidizing products are examined by scanning electron microscopy and electronprobe microanalysis, and a mechanism is proposed for the sulfidizing of chalcopyrite under near-equilibrium conditions.     

Interaction of pentlandite,chalcopyrite, and pyrrhotine with elementary sulfur: III. Sulfidizing of nickel-containing pyrrhotine

The sulfidizing of the main sulfide minerals of copper-nickel ores, namely, pentlandite, chalcopyrite, and pyrrhotine, by elementary sulfur is studied. The phase compositions of the sulfidizing products are examined by scanning electron microscopy and electron-probe microanalysis, and a mechanism is proposed for the sulfidizing of nickel-containing pyrrhotine under near-equilibrium conditions.     

Sulfidation of chalcopyrite with elemental sulfur

The sulfidation of chalcopyrite concentrate with elemental sulfur was studied in the temperature range of 325 °C to 500 °C. The effects of temperature, time, and composition of the reactants on the sulfidation were determined. The X-ray diffraction (XRD) and light microscopic analyses showed that the sulfidation of chalcopyrite forms CuS and FeS₂ at temperatures below 400 °C. However, at temperatures above 400 °C, Cu₅FeS₆ and FeS₂ were formed. The sulfidation of chalcopyrite proceeds mainly through the gaseous phase, and temperature has a significant influence on the sulfidation rate in the range of 325 °C to 400 °C. The extraction of copper from the reacted material was determined by leaching in an H₂SO₄-NaCl-O₂ system. Over 90 pct of copper could be extracted by leaching at 100 °C for 60 minutes in the mentioned system.     

Kinetics of the sulfidation of chalcopyrite with gaseous sulfur

The sulfidation of chalcopyrite with gaseous sulfur in the temperature range of 325 °C to 400 °C occurs with the formation of covellite and pyrite as the final products. The rate of sulfidation depends strongly on the temperature, with nearly complete conversion in less than 30 minutes at 400 °C. Microscopic analysis of partially and completely reacted particles showed that the sulfidation proceeded topochemically, with a shrinking core of unreacted chalcopyrite surrounded by successive layers of FeS₂ and CuS. The experimental data exhibited an induction period at the beginning of the reaction. An electrochemical mechanism is proposed for the sulfidation reaction, which involves simultaneous diffusion of Cu⁻ and electrons through the product layers. The rate data showed that the fraction reacted is well represented by a shrinking-core model controlled by the reaction occurring at the chalcopyrite-pyrite interface, resulting in the conversion-vs-time relationship 1−(1−X)^1/3=k(t−t _ind). An activation energy of 98.4 kJ/mol was determined for the temperature range of 325 °C to 400 °C.     

Leaching of chalcopyrite with ferric ion. Part I: General aspects

This paper presents a review of the literature on chalcopyrite leaching with ferric sulphate in acid medium. The effects of several parameters (ferric salt anion, oxidant concentration, pH and temperature) are examined and possible explanations are offered for the passivation of this sulphide during dissolution. The main theories related with chalcopyrite passivation point to the formation of a diffusion layer surrounding the chalcopyrite during dissolution, consisting of: bimetallic sulphide, copper polysulphide with a deficit of iron with respect to chalcopyrite, and elemental sulphur. Recent studies suggest that ferric ion plays two important and opposite roles in this process: as a mineral oxidizing agent and as the agent responsible for chalcopyrite passivation.     

Interaction of oxyfluoride melts of Ca,Si, Mg,Al, and Na with steels: I. Chromium-carbon-containing melts

The interaction of a mixture of Ca, Si, Mg, Al, and Na oxides and fluorides with two chromium-carbon-containing iron-based melts are experimentally studied at 1600°C and p _Ar = 0.1 MPa. The equilibrium concentrations of the components in the slag at a holding time of 500 s are determined. The chromate capacities of the oxyfluoride melts are calculated and related to the composition of the melted slag using its optical basicity.     

Mechanism of action of acetyl kidamycin. I. Interaction with DNA

During the period from November 1972 to February 1975, 39 patients received second renal grafts in our institution. The clinical course of the patients was analyzed and compared with 121 patients who received only one graft during the same period. The graft survival either from living related or cadaveric sources was inferior in the second graft group. However, mortality was not increased by re-transplantation. Major differences were noted in the occurrence of hyperacute or accelerated type rejections. There was a high incidence of this type of rejection in the second graft group, especially in the simultaneous retransplant group.     

Scale Transition in Steel-Concrete Interaction. I: Model

This paper deals with the analysis of reinforced concrete (RC) structures with special emphasis on modeling of the interaction between concrete and reinforcement. A new mode for consideration of the response of the composite material at the member (structural) scale is proposed. It is obtained from extension of the fracture energy concept, originally developed for the simulation of cracking of plain concrete, to reinforced concrete. Hereby, the fracture energy related to the opening of primary cracks is increased in order to account for bond slip between steel and concrete. This increase is determined from the distribution of bond slip by means of a one-dimensional composite model introduced at the bar scale. The model consists of steel bars and the surrounding concrete. Between these two components, a nonlinear bond stress–bond slip relation is considered. The obtained results at the bar scale, such as the average crack spacing between adjacent cracks and the load-displacement response of the composite material, form the basis for determination of the increase of the fracture energy at the member scale. The performance of the proposed transition of the steel-concrete interaction from the bar scale to the member scale is assessed by means of reanalysis of experiments performed on RC bars. The application of the respective material model for reinforced concrete to real-life engineering structures is reported in Part II of this series.     

Cuprous hydrometallurgy Party VI. Activation of chalcopyrite by reduction with copper and solutions of copper(I) salts

Chalcopyrite is reduced by solutions of copper(I) sulfate and copper(I) chloride to chalcocite (Cu₂S) and bornite (Cu₅FeS₄) whilst the iron reports to the solution. Factors which affect the rate and efficiency of reduction are examined. The reaction is rapid on fresh surfaces of chalcopyrite but slows markedly as a film of chalcocite or bornite forms. The reduction in the presence of copper metal goes to completion and gives a material which is more readily leached by oxidising agents than is chalcopyrite. Thus 99% of the copper in the reduced chalcopyrite is leached when copper(II) sulfate in aqueous acetonitrile is the oxidising agent, whereas only 30% of the copper is leached from pure chalcopyrite under similar conditions. Concentrated solutions of copper(I) salts are less effective in reducing CuFeS₂ in a heterogeneous solid-liquid reaction than is copper metal in a “galvanic” solid-solid reaction. Solutions of copper(II) sulfate plus concentrated copper(I) sulfate in dilute acetonitrile (4 M) containing copper sheets are an effective reductant for chalcopyrite.     

Pressure oxidation leaching of chalcopyrite. Part I. Comparison of high and low temperature reaction kinetics and products

The kinetics and products from the pressure oxidation of a chalcopyrite concentrate are compared under a range of reaction conditions promoted by various companies. The reaction conditions compared in this article, Part I, are referred to as the Phelps Dodge-Placer Dome and Activox® processes. The medium temperature processing of the concentrate will be reported in Part II.Experiments were conducted with the same concentrate over a temperature range of 108–220 °C with different salt and acid additions to compare the kinetics and recovery of copper, the speciation of sulfur and the deportment of iron-containing and other phases in the leach residues. The aim was to improve understanding of the mechanism and practical issues for the competing processes and to provide background knowledge often not available in the public domain.The chalcopyrite concentrate was found by Quantitative X-ray Diffraction (QXRD) analysis to contain about 80% chalcopyrite, 10% quartz, 6% pyrite and 2.5% talc and 1.5% clinochlore. It was demonstrated that greater than 94% of the copper could be extracted from the concentrate using either the Phelps Dodge-Placer Dome or Activox® process within 30 min. The extraction of the residual copper was strongly influenced by the presence of elemental sulfur.About 80–90% oxidation of sulfide to elemental sulfur occurred at 108 °C and was enhanced by the presence of the chloride ion. Above 180 °C there was complete oxidation to sulfate. However, in the presence of added chloride ion the rate of sulfate formation decreased.QXRD was employed to examine the leach residues. Iron was leached and re-precipitated forming a number of different phases depending upon the process temperature, acidity and salinity. At low temperature, in the presence of chloride, akaganéite was formed together with an uncharacterised amorphous hydrated iron oxide. Hematite formation was favoured at temperatures ≥ 150 °C, low acidity and low salinity; basic ferric sulfate formed at high temperature (220 °C), high acidity and low salinity. Goethite formation was favoured at ≤ 150 °C by low acidity and low salinity. Jarosite was formed at all temperatures under conditions of moderate to high acidity and its formation was enhanced in the presence of sodium ions.Several basic copper salts including atacamite (Cu₂(OH)₃Cl) and antlerite (CuSO₄·2Cu(OH)₂) were precipitated at 108 °C at low acidity, typically at pH > 2.8. Atacamite formed initially when the sulfate concentration was low but dissolved and the copper was re-precipitated to form antlerite as the sulfate (and copper) concentrations increased.     

Interaction of exogenous zirconium oxide nanophases with sulfur and tin in nickel melts

The interaction of exogenous refractory compound (ZrO₂) nanoparticles with sulfur and tin, which are present as surfactants in model nickel melts, is studied. Thermodynamic calculations are performed to consider the versions of removal of sulfur and tin from a melt in the form of S₂, SO₂, H₂S, Sn, and SnO. It is shown that the probability of their removal under melting conditions is low. Their contents is found to decrease when ZrO₂ nanoparticles are introduced: the degree of removal is α = 12–18% S in a model Ni–S alloy and 14–20% Sn in a model Ni–Sn alloy.     

Interaction of alumina and alumomagnesium spinel nanoparticles with sulfur in model iron melts

The interaction of exogenous nanoparticles of refractory compounds Al₂O₃ and MgAl₂O₄ with model iron melts containing sulfur as a surfactant is studied. The choice of these nanoparticles and possible variants of sulfur removal from the melt in the form of S₂, SO₂, and H₂S are confirmed by thermodynamic calculations. The dependences of the degree of sulfur removal in the course of the heterophase interaction on the size factors (duration of isothermal storage after the addition of nanoparticles), the type of added nanoparticles, and the sulfur concentration in the model melts are studied. The degree of sulfur removal is 17–32 and 16–35 rel. % upon the introduction of Al₂O₃ and MgAl₂O₄ nanoparticles, respectively.     

Mathematical modeling of sulfide flash smelting process: Part I. Model development and verification with laboratory and pilot plant measurements for chalcopyrite concentrate smelting

A mathematical model has been developed to describe the various processes occurring in a flash furnace shaft. The model incorporates turbulent fluid dynamics, chemical reaction kinetics, and heat and mass transfer. The key features include the use of thek-ε turbulence model, incorporating the effect of particles on the turbulence, and the four-flux model for radiative heat transfer. The model predictions were compared with measurements obtained in a laboratory flash furnace and a pilot plant flash furnace. Good agreement was obtained between the predicted and measured data in terms of the SO₂ and O₂ concentrations, the amount of sulfur remaining in the particles, and the gas temperature. Model predictions show that the reactions of sulfide particles are mostly completed within about 1 m of the burner, and the double-entry burner system with radial feeding of the concentrate particles gives better performance than the singleentry burner system. The model thus verified was used to further predict various aspects of industrial flash furnace operation. The results indicate that from the viewpoint of sulfide oxidation, smelting rate can be substantially increased in most existing industrial flash furnaces. Formerly Graduate Student, Department of Metallurgical Engineering, University of Utah.     

Leaching of chalcopyrite with ferric ion. Part II: Effect of redox potential

This paper reports the effect of redox potential (or Fe³⁺/Fe²⁺ ratio) on chalcopyrite leaching. The relationship between redox potential and other variables (iron concentration and temperature) is also evaluated. Leaching tests were performed in stirred Erlenmeyer flasks with 0.5 g of pure chalcopyrite and 100 mL of a Fe³⁺/Fe²⁺ sulphate solution. The redox potential ranged between 300 and 600 mV Ag/AgCl for the solution at a pH 1.8, 180 rpm, with temperatures at 35 °C or 68 °C. The results show that although ferric ion is responsible for the oxidation of chalcopyrite, ferrous ion has an important role in that it controls precipitation and nucleation of jarosites, which ultimately causes passivation of this sulphide. Chalcopyrite dissolves through the formation of an intermediary product (covellite, CuS) that is later oxidized by ferric ion, releasing Cu²⁺ ions.     

Conducting psychotherapy with psychotherapists: I. Prevalence, patients, and problems.

Examines responses from 349 psychologists of the American Psychological Association (APA) Division of Psychotherapy who completed a questionnaire regarding the prevalence of treating fellow psychotherapists, the type of psychotherapist-patients they treated, and the stressors and satisfactions of conducting such work. Three fourths of respondents related that they had treated mental health professionals and professionals-in-training over the past 3 years, and that this population constituted 3% to 796 of their caseloads. Nearly all of the therapist-patients were self-referred, and 85% received individual therapy. The psychotherapist-patients tended to be psychologists (37%) or social workers (29%) of diverse theoretical traditions, with the exception of biologically oriented clinicians. Satisfactions clustered around pleasures inherent in doing meaningful work, acknowledgment by peers, and the opportunity to help therapist-patients enhance their own clinical effectiveness. Predominant stressors concerned evaluation anxieties in treating colleagues and in the related belief that colleagues are more challenging and resistant to change. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction of refractory compound nanoparticles with a surfactant in a nickel melt: I. Heterophase interaction

The interaction of nanoparticles of refractory compounds Al₂O₃ and TiN with a model nickel melt containing a surfactant (sulfur) is studied. The choice of the type of nanoparticles for their interaction with the metal at 1873 K and possible versions of sulfur removal from the melt in the form of S₂, SO₂, and H₂S are grounded. A technique for the preparation of an Ni-Al₂O₃ (TiN) compact and its introduction into the melt is developed. The character of the change in the sulfur content in the metal after introducing the compact is determined, and the effect of the isothermal holding time of the melt on sulfur removal is revealed.