Lime-enhanced reduction of sulfide concentrates: A thermodynamic discussion

The need to control or eliminate sulfur dioxide emissions from sulfide smelters has increased the drive to develop new processes for the extraction of metal from sulfide minerals. One such process currently gaining interest is the lime-enhanced reduction of metal sulfides. This paper discusses the thermodynamic aspects relevant to chalcopyrite, chalcocite, and pyrrhotite reduction with hydrogen, carbon monoxide, or carbon in the presence of lime. The effects of temperature and gas composition on sulfide reduction are also discussed. ΔG°vs T diagrams for lime-enhanced sulfide reductions with hydrogen, carbon monoxide, and carbon are constructed and discussed together with some experimental results produced by the authors.     

Lime-enhanced hydrogen reduction of molybdenite

Kinetics of the direct hydrogen reduction of a high-grade (59 pct Mo) molybdenite (MoS₂) concentrate was investigated in the presence of lime as a function of the quantity of lime in the charge, hydrogen flow rate, temperature, and time of reduction. Lime was found to enhance tremendously the reduction rate of MoS₂ and drastically reduce H₂S emission into the off gas to negligible levels. Successful application of the lime-hydrogen reduction technique was found to depend on the employment of low hydrogen flow rate and moderate temperatures of reduction. In these laboratory studies, best results were obtained with a lime addition ≥ three times the theoretical requirement and at 1173 K in 3.6 ks employing a hydrogen flow rate of 3.33 cm³s^-1. The results were tested for the treatment of a low-grade (41 pct Mo) molybdenite concentrate. In this latter case, the procedure consisted of upgrading the concentrate by acid leaching (with dil HC1+HF) followed by lime-hydrogen reduction. The influence of quantity of acids, temperature, and time of leaching were investigated to optimize the conditions required for upgrading the MoS2 concentrate. The molybdenum powders obtained from the highgrade as well as upgraded molybdenite concentrates had 96 to 97 pct purity and could be further refined to 99.9 pct by electron-beam melting. Based on this lime-enhanced hydrogen reduction concept, a new ‘Leach-Reduction-Melting’ approach has been suggested as an alternative to the traditional methods of molybdenum extraction.     

Kinetics of manganese ore reduction by carbon monoxide

A step has been made in the direction of understanding the fundamental chemical processes taking place inside electric are furnaces producing manganese alloys. The reduction of higher manganese oxides to MnO by carbon monoxide has been studied in the temperature range 700 °C to 1100 °C. A topochemical pattern with a single shrinking core inside the ore particles has been observed in most cases. It has been found that the reduction of some manganese silicates (braunite minerals) is influenced by reaction interface kinetics, whereas the reduction rate of manganese oxides (bixbyite and hausmannite) is mostly determined by product shell pore diffusion. Sintering kinetics and the extent of natural porosity determine the product shell pore diffusivity. As the melting point of the reaction product is approached, rapid sintering leads to a decrease in diffusivity.     

Kinetics of zinc oxide reduction with carbon monoxide

Reduction of ZnO single particles with CO was investigated at atmospheric pressure from 1000° to 1500°C. Weight loss data up to about 90 pct reduction were easily reproducible for the dense photoconductive grade ZnO particles but not for the American grade samples, whose scatter was attributed to the 13 pct residual internal porosity and to impurities. The data agreed closely with a mixed regime model, which pictures external diffusion acting in series with an irreversible first order kinetic process at the surface. After the diffusional contribution was subtracted, activation energies of 37,900 (±2040) cal per mole and 20,600 (±10,200) cal per mole were obtained for the photoconductive and American grades, respectively. For the photoconductive grade the mixed regime model gave a good fit over the entire temperature range. Diffusional limitations were approached at 1500°C.     

Successive gas-solid reaction model for the hydrogen reduction of cuprous sulfide in the presence of lime

As an alternative to conventional smelting processes for producing metals from sulfide ores, which suffer from SO₂ emission problems, direct reduction in the presence of lime has in recent years attracted much attention. In this work, a mathematical model of successive gas-solid reactions in a porous pellet has been applied to the hydrogen reduction of cuprous sulfide (Cu₂S) in the presence of lime. The model has been formulated by incorporating the intrinsic kinetics of the individual reactions obtained from separate experiments, and compared with the experimental results on the hydrogen reduction of chalcocite mixed with lime particles. The model predictions were in good agreement with experimental measurements of the overall rate of reaction and the degree of sulfur fixation over a wide range of experimental conditions. The mathematical model not only can predict the performance of a given system but also enables one to design the optimum pellet properties and reaction conditions in terms of the reaction rate and sulfur fixation. Formerly Graduate Student in the Department of Metallurgy and Metallurgical Engineering, University of Utah.     

CO还原烧结矿过程中的析碳行为

高炉中CO 还原烧结矿过程中会发生析碳反应,对高炉操作产生不利的影响。采用 CS-8800型高频红外碳硫分析仪分析CO 还原烧结矿过程中的析碳行为,并采用 Nova400NanoSEM型场发射扫描电子显微镜分析还原后烧结矿微观结构。研究结果表明：随着温度的升高,析碳反应 CO 的平衡浓度越高,反应越难发生。在低温下析出的碳较多,析出的碳主要分布在烧结矿表面和气孔中,而在温度较高时只有微量碳析出;体系中 CO2对析碳反应有明显的抑制作用;析碳量随着还原时间的增加而增加。     

Fuzzy logic model of lime enhanced hydrogen reduction of cuprous sulphide

Traditional methods for metal extraction from sulphide minerals cause environmental pollutions. In recent decades, direct hydrogen reduction in the presence of lime has attracted an increasing attention among metal-sulphide separation methods. This study aimed to represent an alternative technique for the modelling lime enhanced direct hydrogen reduction process with a fuzzy logic model. The focus of this paper is to find a well defined relationship among the vital variables including bulk temperature, ratio of molar quantities of the solid reactants, pellet diameter, porosity, sulphide particle size, weight loss of the pellet, sulphur fixation in the pellet, and reaction completion time using a fuzzy logic model scheme. Finally, the results predicted by the fuzzy logic model were evaluated and validated against a mathematical model and experimental data.

Les méthodes traditionnelles d’extraction du métal à partir de minéraux sulfureux engendrent une pollution environnementale. Dans les dernières décennies, on a porté une plus grande attention à la réduction directe de l’hydrogène en présence de chaux, parmi les méthodes de séparation du métal-sulfure. Cette étude avait pour but de représenter une technique de rechange pour la modélisation du procédé de réduction directe de l’hydrogène, augmentée par la chaux, au moyen d’un modèle de logique floue. Le point central de cet article est de trouver une relation bien définie parmi les variables vitales, incluant la température globale, le rapport des quantités molaires des réactants solides, le diamètre des boulettes, la porosité, la taille de particule du sulfure, la perte de poids de la boulette, la fixation du soufre dans la boulette et le temps d’exécution de la réaction en utilisant un schéma de modèle de logique floue. Finalement, on a évalué et validé les résultats prédits par le modèle de logique floue contre un modèle mathématique et des données expérimentales.     

Open air carbon monoxide poisoning

The J = 1-0 to 4-3 spectral lines of SD+3 were measured in the 152-610 GHz region using a source-modulated microwave spectrometer. The SD+3 ion was generated in a free space absorption cell by a hollow-cathode discharge in a gas mixture of D2S and D2. The rotational constant B0 and the centrifugal distortion constants DJ and DJK were determined from the measured frequencies. A vibration-rotation analysis was carried out and the rz structures of SH+3 and SD+3 were derived from their zero point averaged rotational constants, expressed as SH+3: rz = 1.36512(22) ? and thetaz = 94.098(26) degrees, and SD+3: rz = 1.36086(16) ? and thetaz = 94.1211(195) degrees, where the difference between thetaz(HSH) and thetaz(DSD) was assumed to be the same as that between thetaz(HPH) of PH3 and thetaz(DPD) of PD3. From the shift between the rz structures of SH+3 and SD+3, the re structure of SH+3 was estimated to be re = 1.35001(113) ?, thetae = 94.181(135) degrees. Copyright 1998 Academic Press.     

The use of exhaled carbon monoxide for the diagnosis of carbon monoxide poisoning. A case report

Antigliadin antibodies (AGA) mark celiac disease, but AGA are also encountered in IgA-nephritis, psoriasis, sickle-cell anemia, hepatic disorders, juvenile rheumatoid arthritis, autoimmune thyroidism and in persons who occupationally contact great amounts of wheat. AGA IgA and/or IgG were registered in 19 of 60 subjects (51 adults and 9 children) with various immunomediated diseases without symptoms of celiac disease: in 4 cases of chronic active hepatitis, in 2 of 4 cases of chronic persistent hepatitis, in 4 of 16 cases of rheumatoid arthritis, in 3 of 19 cases of IgA-deficiency, in 1 of 8 cases of SLE, in 2 cases of postvaccine reaction, in all the single cases of juvenile rheumatoid arthritis, focal scleroderma, macroglobulinemia. IgA only occurred in in 6 patients, IgG- in 6 patients, both IgA and IgG in 7 patients. The most pronounced positive reaction to AGA was recorded in 8-year-old girl with juvenile rheumatoid arthritis. The emergence of AGA in immunomediated diseases may be attributed to the response to food protein in pathological conditions and is often unrelated closely with celiac disease.     

Screening for carbon monoxide in children

We present the use of risperidone as a potentiation strategy of the serotonergic antidepressants in four patients suffering from refractory obsessive-compulsive disorder. There were an important improvement in three patients. Adding risperidone to serotonergic antidepressants causes complex interactions between serotonergic, dopaminergic and noradrenergic systems, that could lay to the clinical improvement. These and other similar cases make necessary controlled studies. Adding risperidone to serotonergic antidepressants in patients suffering from refractory obsessive-compulsive disorder might be an effective strategy with low risk for secondary effects and without the presence of tics or psychotic symptoms.     

Copper deoxidation kinetics utilizing carbon monoxide

Gaseous deoxidation of liquid copper with carbon monoxide as the reducing gas has been examined. The reducing gas was introduced at a submerged orifice so that well characterized, single bubbles were formed. The deoxidation kinetics are determined primarily by the mass transport of oxygen in liquid copper. No effect of sulfur over the range of 10 to 200 ppm was observed. Increasing the temperature from 1113 to 1173°C slightly inhibit the kinetics of oxygen removal. R. J. ANDREINI and R. B. PHILLIPS, Formerly Graduate Students, Michigan Technological University, Houghton, MI 49931, This paper is based on a portion of the dissertation submitted by R. J. Andreini in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Michigan Technological University.     

Copper deoxidation kinetics utilizing carbon monoxide

Gaseous deoxidation of liquid copper with carbon monoxide as the reducing gas has been examined. The reducing gas was introduced at a submerged orifice so that well characterized, single bubbles were formed. The deoxidation kinetics are determined primarily by the mass transport of oxygen in liquid copper. No effect of sulfur over the range of 10 to 200 ppm was observed. Increasing the temperature from 1113 to 1173°C slightly inhibit the kinetics of oxygen removal. Formerly Graduate Students, Michigan Technological University, Houghton, MI 49931 This paper is based on a portion of the dissertation submitted by R. J. Andreini in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Michigan Technological University.