Electrochemical aspects in some of the hydrometallurgical processes

Hydrometallurgy deals with extraction of metal values from ore minerals through aqueous processing by solubilizing the specific metal value into the aqueous phase and subsequently taking it out of the solution. These steps may be chemical or electrochemical in nature. The electrochemical phenomena depends on the electrical properties of the solid material and the redox characteristics of the solution. The present paper discusses electrochemical aspects of some hydrometallurgical operations involving the following phenomena: (i) corrosion coupling, (ii) galvanic coupling, (iii) dissolution via cyclic action of a redox couple, (iv) displacement or cementation reaction, (v) precipitation under reducing conditions, (vi) dissolution under high pressure, and (vii) dissolution influenced by hole transfer.     

Object-oriented simulation of hydrometallurgical processes: Part II. Application to the bayer process

The steady-state process simulator developed by Kiranoudis et al. has been used for the detailed simulation of the Bayer process flowsheet. It consists of the digestor/flash section as well as the precipitation and washing circuits. Advanced hydrometallurgical process models for the specific unit operations involved were developed and are appropriately described. The simulation studies mainly focus on studying the overall effects of certain design parameters on the entire plant efficiency. The overall performance of the bauxite digestion section is greatly and positively affected by the free-soda concentration of the feed liquor, the corresponding concentration of solid particles, and the operation temperature of the circuit. Precipitation of alumina in crystallizers is greatly affected by the corresponding soda concentration of the washing unit product stream, indicating the importance of this section. Furthermore, ambient temperature is important to the precipitation kinetics, influencing negatively the quantitative precipitation but resulting in particle populations of higher mean diameter.     

Fundamental studies on chlorine behavior as related to zinc electrowinning from aqueous chloride electrolytes

Measurements were made on the transport and equilibrium properties of dissolved chlorine in aqueous HC1, HCl-ZnCl₂, HCl-MgCl₂, and water. These measurements included solubility, absorption rates during bubbling, stripping rates during nitrogen bubbling, and cathodic reduction rates. The solubility of chlorine was found to be affected by speciation into aqueous Cl₂, HC1O, and C1₃ −. With increasing HCl concentration, the solubility of chlorine decreased to a minimum at 0.2 mol dm⁻³, followed by a slow and linear increase. Metal chloride salts depressed the chlorine solubility approximately in proportion to concentration. Mass transfer of aqueous chlorine was found to support a current of about 100 A m⁻² from a chlorine-saturated ZnCl₂-HCl solution under typical zinc electrowinning conditions. Comparisons with published zinc electrowinning papers indicate that air sparging would eliminate dissolved chlorine sufficiently to remove the need for diaphragm cell separation of dissolved chlorine, insofar as current inefficiencies due to cathodic chlorine reduction are concerned.     

铅阳极泥湿法处理工艺述评

本文对近十多年来铅阳极泥湿法处理工艺和进展进行简要述评。湿法工艺有直收率高，生产周期短，劳动条件好，综合回收有价金属等特点，有取代火法工艺的趋势。     

Object-oriented simulation of hydrometallurgical processes Part III. Application to leaching of laterites and pyrites

The steady-state process simulator developed by Kiranoudis et al. has been used for the detailed simulation of sulfuric acid pressure leaching of laterite ores for the extraction of nickel and cobalt, and aqueous pressure oxidation of pyrites for the recovery of gold. Advanced hydrometallurgical process models for the specific unit operations involved were developed and are appropriately described. The simulation mainly focuses on studying the overall effects of certain design parameters on the entire plant efficiency. In the case of pyrites, the autothermal performance of the pressure autoclaves can be maintained by means of the oxidized recycle stream that greatly influences the fundamental heat balances of the reactor. Flashing the reactor pulp at the exit of the autoclaves results in further precipitation of solids related to ionic equilibrium reactions. The effect of grinding is important since most reactions are facilitated by small particle diameters. The ratio of feed pyrites influences the amount of precipitation of solids in the autoclave.     

Application of carbon paste electrodes to elucidate hydrometallurgical dissolution processes with special regard to chalcocite and covellite

Carbon paste electroactive electrodes offer possibilities for the investigation of hydrometallurgical dissolution processes. In this study the oxidation and reduction reactions of copper sulphides are examined by means of such a system. It was established that the anodic oxidation of Cu₂S proceeds in two steps. The first step of oxidation is the Cu₂S-CuS transition, which results in nonstoichiometric intermediate compounds and the reaction rate is controlled by solid state diffusion.     

Applications of solid electrolytes in thermodynamic studies of materials: A review

The use of solid electrolytes for the measurement of the thermodynamic properties of materials is reviewed. A concise history of the development of solid electrolyte galvanic cell techniques is presented, and their advantages and the essential criteria for the satisfactory application of the method are discussed. The principal electrolytes in contemporary use and investigations for which they have been employed are surveyed. Special variations of the cell technique used in thermodynamic and phase equilibria studies are described. A bibliographic review of major investigations up until 1988 is included.     

Applications of solid electrolytes in thermodynamic studies of materials: A review

The use of solid electrolytes for the measurement of the thermodynamic properties of materials is reviewed. A concise history of the development of solid electrolyte galvanic cell techniques is presented, and their advantages and the essential criteria for the satisfactory application of the method are discussed. The principal electrolytes in contemporary use and investigations for which they have been employed are surveyed. Special variations of the cell technique used in thermodynamic and phase equilibria studies are described. A bibliographic review of major investigations up until 1988 is included.     

采用全湿法从金泥中提金的新工艺

本文针对火法炼金存在的一些问题，通过实验，提出全湿法提金的新工艺流程，实践证明，该新工艺不仅避免了火法炼金的一些问题，金的回收率也很高。     

湿法提纯金工艺的改进

针对火法炼金后的合质金及铅含量较高的合质金在精炼过程中存在的一些问题，通过试验，提出一些改进方法，实践证明，改进后的工艺既保证了金的回收率，同时能效的除掉了金中有害物质－－铅，该工艺提纯的金，品位可达到９９．９５％     

The effects of dietary sodium on the diurnal activity of the renin-angiotensin-aldosterone system and the excretion of urinary electrolytes

Diurnal variations of five normal men were tested over three 24 h consecutive periods. The first experiment began at 0900 h after the subjects had fasted for 12 h and a normal sodium diet of about 70-80 mEq was given at 0900 h, 1200h, and 1630 h (total of about 220 mEq of Na). Significant variations in the plasma renin activity (PRA), in the plasma aldosterone (PA), and in the urinary Na and K outputs were found. The second experiment began at 1200 h with the first feeding time at 2100 h after fasting about 24 h and the subjects were given a normal sodium diet as in the first experiment, but with the meals given at 2100 h, 2400 h, and 0430 h. The diurnal variations in PRA, plasma aldosterone, and urinary electrolytes disappeared. From this study, it appears that the diurnal variation in urinary electrolyte excretion is a factor of the diurnal variation in PRA and plasma aldosterone. The diurnal variation in PRA and plasma aldosterone are related to the timing of sodium ingestion.     

Cell marking in Arabidopsis thaliana and its application to patch-clamp studies

Ion transport processes at the plasma membrane of plant cells are frequently studied by applying membrane-patch voltage-clamp (patch-clamp) electrophysiological techniques to isolated protoplasts. As plants are composed of many tissues and cell types, and each tissue and cell type may be specialized to a particular function and possess a unique complement of transport proteins, it is important to certify the anatomical origin of the protoplasts used for patch-clamp studies. This paper describes a general molecular genetic approach to marking specific cell types for subsequent patch-clamp studies and presents a specific example: a comparison of the K+ currents in protoplasts from cortical and stelar cells of Arabidopsis roots. Transgenic Arabidopsis were generated in which the expression of green fluorescent protein (GFP) from Aequoria victoria was driven by the CaMV 35S promoter (line mGFP3). In roots of the transgenic mGFP3 line, visible fluorescence was restricted to the stele. Protoplasts were generated from roots of the mGFP3 line and K+ currents in non-fluorescent (cortical/epidermal) and fluorescent (stelar) protoplasts were assayed using patch-clamp techniques. It was found that both the frequency of observing inward rectifying K+ channel (IRC) activity and the relative occurrence of IRC compared to outward rectifying K+ channels were significantly lower in protoplasts from cortical/epidermal cells compared to cells of the stele. The presence of GFP did not affect the occurrence or biophysical properties of K+ channels. It is concluded that the generation of transgenic Arabidopsis expressing GFP in a cell-specific fashion is a convenient and reliable way to mark protoplasts derived from contrasting cell types for subsequent patch-clamp studies.     

Studies on the application of copper(I)-ammune sulphate electrolytes in copper electrorefining

The electrolysis of a copper(I)-ammine sulphate electrolyte between copper electrodes has been investigated. A sealed cell and a solution containing 30 g/kg Cu, 95 g/kg NH₃ and 95 g/kg SO₄ were used.Current efficiencies (cathodic and anodic), at current densities over 100 A/m², were higher than 95% and were practically independent of the electrolysis variables (25–55°, 100–500 A/m² and 70–130 g/kg of NH₃ solution).It was shown that at temperatures over 40°C the energy consumption for electrorefining is lower in the copper(I)-ammine electrolyte than in a typical acidic electrolyte.Contributions to the energy consumption from the electrode processes and the resistance of the electrolyte have been determined from the experimental data.     

红土镍矿湿法冶金工艺现状及前景分析

随着硫化镍矿资源的不断消耗以及镍需求量的持续增长,红土镍矿将是未来镍的主要来源。红土镍矿具有储量丰富、易开采、便于运输等特点,成为研究开发的热点。对还原焙烧 氨浸工艺、加压酸浸工艺、常压酸浸工艺等湿法冶金处理红土镍矿的工艺特点及现状进行了阐述,并分析了各工艺的优势与不足,介绍了红土镍矿湿法冶金工艺的研究进展。最后探讨了未来红土镍矿湿法冶金工艺的发展前景,指出加压酸浸工艺将在今后红土镍矿湿法冶金中扮演重要角色。     

Measurement and computation of drag forces in thermogravimetric studies

The upward drag force experienced by a hanging assembly in a thermogravimetric setup due to flowing gas has been measured using an electrobalance for two different gases, viz., argon and carbon dioxide, over a temperature range of 1000 °C to 1250 °C and at a gas flow rate of 1.42×10⁻⁶ to 3.33×10⁻⁶ m³/s (STP). Analytical estimates, assuming the assembly to be a solid sphere of equivalent surface area, predicted drag forces about two orders of magnitude lower than the corresponding experimental values. This discrepancy was resolved by numerical simulation employing the commercial computational fluid-dynamics (CFD) package called “FLUENT” and by employing the exact geometry of the reactor and assembly, with experimental and computed values differing by about 20 pct, on average. The duration of the initial transient flow upon starting the gas flow was very small (less than 5 seconds).