Sulfuric acid pressure leaching of nickeliferous limonites

This laboratory study examines the sulfuric acid pressure leaching characteristics of nickeliferous limonite samples from South New Caledonia. The effect of temperature (225°C to 300°C), acid-to-ore ratio (0.21 to 0.30), pct solids (10 to 45), particle size (-20 to -270 mesh), and agitation (50 to 600 rpm) on nickel extraction and selectivity are discussed. For overall improvement of the leach response, leaching is best conducted at temperatures higher than 250°C and at solids less than 33 pct. Variation of goethite, hematite, and basic aluminum sulfate content of the leach residue was determined semiquantitatively as a function of leaching time. Sulfate content of the residue rises sharply during the first several minutes of leaching, then falls, and finally equilibrates at five to six percent. This change in sulfate analysis can be explained by assuming a series of consecutive iron and aluminum hydrolysis reactions.     

Control of autoclave scaling during acid pressure leaching of nickeliferous laterite ore

An operating problem encountered at the Moa Bay operation in Cuba, where nickeliferous laterite ore is processed by sulfuric acid pressure leaching, is the formation of alunite and hematite deposits on the autoclave walls. The AMAX Extractive Research & Development, Inc., metallurgical laboratory (Golden, Colorado) has made substantial improvements in the Moa Bay process in the area of metal recovery, energy consumption, and feed versatility. One of the advantages of AMAX's process is its ability to treat substantial portions of nickel-and magnesium-rich serpentine while maintaining acid utilization efficiency. Scale formation is minimized by combining staged acid addition with vigorous agitation and 270 °C operation. This paper describes how advantage can be taken of MgSO₄· XH₂O precipitation both to inhibit alunite scaling and to disperse hematite scale within the MgSO₄ · XH₂O matrix. Cooling the autoclave from its 270 ·C operating temperature down to 180 ·C takes advantage of the reverse solubility of magnesium sulfate. The magnesium dissolves, liberating entrained hematite, thus providing a means for control of autoclave scale with minimum process disruption. P. B. QUENEAU, Formerly with AMAX Extractive Research and Development, Inc., Golden, CO, P. REY, Formerly with COFREMMI, Paris, France,     

Sulfuric acid leaching of polymetallic Abu Zeneima gibbsite-shale

The gibbsite shales belonging to the Paleozoic sequence of sedimentary rocks occurring at the Abu Zeneima area in SW Sinai Egypt has been found to host several economic metal values. These include Al, Cu, Zn, Co, Ni, REE, and U beside several Mn minerals. In this work, the ore was subjected to sulfuric acid leaching to maximize extraction of these metal values. The optimum leaching conditions were 800 g/L acid with a Solid/Liquid ratio of 1/2 at 100 °C for 4 h and using an ore size of − 60 mesh. Under these conditions, it was possible to achieve high leaching efficiencies with complete leaching of Al together with 93.0% Cu, 58.6% Zn, 69.0% Co, 92.6% Ni and 84.4% U. Extension of the leaching time to 8 and 12 h significantly improved the leaching efficiencies of Co and Zn to 91.0% and 84.0% respectively.     

Reduction roasting/ammonia leaching of nickeliferous laterites

A well characterized ore sample from Sukinda (India) consisting of nickeliferous limonite has been used to study the extractibility of nickel by the reduction roast/ammonia leach process. Techniques such as X-ray diffraction, surface area measurement and electron spectroscopy for chemical analysis (ESCA) have been used to investigate the ore after various treatments. It has been observed that the process is very sensitive to the roasting conditions, particularly subsequent cooling. Reoxidation during cooling occurs unless special precautions are taken to prevent it and is often limited to surface regions, where it is not detected by X-ray diffraction. ESCA has been used to identify constituents in surface regions of the ore particles. It is shown that careful control of the reduction process is a prerequisite for high recovery of nickel. Under the experimental conditions it was observed that for high Ni recovery it is necessary for iron to be present in a soluble state. It is not necessary to reduce the iron constituent to the metallic state as wustite d dissolves rapidly.     

The leaching of nickeliferous laterite with ferric chloride

Several experiments were conducted to investigate the extraction of nickel from nickeliferous laterite by ferric chloride solutions as a function of pulp density, solution composition, and temperature. Solubility relationships for goethite and nickel laterite in aqueous solution were reviewed in terms of leaching rates and reaction mechanisms. Generally, the amount of nickel extracted increased with temperature, the amount of “free acid,” and ferric chloride concentration; however, the amount was inhibited by ferrous chloride. In this investigation, as much as 96 pct of the available nickel was extracted by ferric chloride solution. Nickel extraction was found to be more dependent on ferric chloride concentration than on the concentration of hydrochloric acid. Mechanistically, nickel extraction occurred by the formation of an intermediate ferric chloride complex, which was then hydrolyzed to hematite.     

Sulfuric acid oxygen-pressure leaching of Ni3S2 prepared by a wet process

Ni₃S₂ prepared by a wet process was easily leached as nickel sulfate at 383 K, p_o2 1 MPa, and sulfuric acid concentration of 0.1–0.15 mol L⁻¹. The leaching reaction proceeds through the intermediate formation of NiS prior to complete dissolution. A constant leaching rate was observed for most of the duration of the reaction, and this has been attributed to an increase in the specific surface area of the sulfide particles. A thin sulfur layer was formed on the sulfide; the diffusion of oxygen through the sulfur layer was found to be rate-determining.     

Extraction of vanadium from black shale using pressure acid leaching

The extraction of vanadium from black shale was attempted using pressure acid leaching. The effects of the several parameters which included reaction time, concentration of sulfuric acid, leaching temperature, liquid to solid ratio and concentration of additive (FeSO₄) upon leaching efficiency of vanadium were investigated and a two-step counter-current leaching approach was developed. The results showed that the leaching efficiency of vanadium in the two-step process could reach above 90%. Vanadium was effectively separated and enriched by solvent extraction after leachate pretreatments, including the reduction of Fe³⁺ and adjustment of pH value. The extraction and stripping yields of vanadium were both > 98%. Ammonia was added to a stripping liquor to precipitate vanadium and then the ammonium poly-vanadate produced was calcined at 550 °C for 3 h to produce the high purity V₂O₅ powder. The overall yield of vanadium through all process stages was about 85%.     

Kinetics of vanadium dissolution from black shale in pressure acid leaching

The leaching kinetics of vanadium from black shale in the sulphuric acid-oxygen system is presented. The effects of agitation speed, leaching temperature in the range of 110-150 °C, sulphuric acid concentration, oxygen partial pressure and particle size on the rate of vanadium leaching were determined. The results indicate that the rate is nearly independent of agitation above 200 rpm and increases with increasing temperature, sulphuric acid concentration and oxygen partial pressure. As leaching occurs, there is a progressive dissolution of a vanadium-bearing alumino-silicate phase, while the inert quartz phase assembles onto the mineral surface and remains as an “ash” layer. The leaching kinetics was analyzed by using a new variant of the shrinking core model (SCM) in which both the interfacial transfer and diffusion across the product layer affect the leaching rate. The determined activation energy was found to be 40.14 kJ/mol and the reaction orders with respect to sulphuric acid concentration and oxygen partial pressure were 0.61 and 1.67, respectively. A semi-empirical rate equation was derived to describe the process.     

二段加压酸浸中铁的行为研究

为了降低一浸终液残酸量和便于处理高铁闪锌矿,冶金工作者开发出了二段加压浸出工艺.但新工艺的完善需要理论的跟进.铁在加压浸出中的行为,一直是加压酸浸理论的重难点.而二段加压酸浸中铁的行为,国内外尚没相关正式研究报告.本文通过设计试验,对铁在二段加压酸浸中的行为进行了浅析,特别是研究了第二段加压浸出中铁的浸出行为.     

锌精矿常压浸出与加压浸出工艺比较

比较了常压浸出与加压浸出两种工艺的机理、流程、技术经济指标、投资以及存在的问题。试验和生产数据表明,加压浸出在技术上和工艺上都更具有吸引力。     

锌精矿常压浸出与加压浸出工艺比较

比较了常压浸出与加压浸出两种工艺的机理、流程、技术经济指标、投资以及存在的问题。试验和生产数据表明,加压浸出在技术上和工艺上都更具有吸引力。     

高压酸浸钢结构厂房结构设计优化

某海外红土镍矿冶炼厂高压酸浸钢结构厂房的楼层结构复杂,且有重型设备支承于楼层上,工程所在地抗震设防烈度较高,这给工程设计带来比较大的难度.本文通过不同方案的对比分析进行结构设计优化,综合考虑工艺要求与结构受力性能,确定了结构方案、支撑系统及节点形式.采用空间结构计算程序SATWE与ETABS软件对结构进行对比计算分析,考察结构在正常使用及地震作用情况下的性能,校核了方案的合理程度.通过采用多重次梁与钢结构井字梁的布置方法,使得框架柱的截面尺寸得以按照轴力而非弯矩进行控制,截面尺寸优化为最合理的尺寸.     

Intensification of sulphation and pressure acid leaching of nickel laterite by microwave radiation

The microwave is a clean and environmentally acceptable energy and various microwave-assisted metal extraction processes have been developed. The novel application of microwave irradiation for sulphation of the nickel laterite ore prior to pressure sulphuric acid leaching has been investigated. Under optimum conditions, about 92% of nickel can be extracted from the ore and above 90% of the iron precipitates as hematite with the residual acid content in the leachate lower than 31 g/L. The microwave sulphation proceeds rapidly and a relatively low leaching temperature and low mass ratio of sulphuric acid to ore can be used in the subsequent pressure leaching to achieve a satisfactory nickel extraction. This may potentially reduce the subsequent heavy capital and operation cost of the pressure acid leaching process.     

Lead leaching from pressure cookers

Leachability of lead by tap water and tamarind solution from Indian pressure cookers while cooking with and without a safety valve is studied. Lead contamination of food by cookers is not very high when compared to the daily intake of lead from various food items consumed by the Indian community. However, looking at the very wide range of lead levels leached from various brands of pressure cookers, it certainly seems possible to keep the lead contamination to the minimum by proper choice of the materials used in the manufacture of these pressure cookers. The rubber gasket, which is a very important component of any pressure cooker, contains the maximum lead concentration; the safety valve is another important source leading to lead contamination of cooked food.     

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.     

Scale formation in a batch reactor under pressure acid leaching of a limonitic laterite

The formation of scale under sulphuric acid pressure leaching conditions of a limonitic laterite ore was investigated. Experiments were conducted using a batch titanium autoclave in order to study the effects of acidity (0.15–0.40 M), and temperature (250–270°C) on scale formation. It was found that scale increases with acidity reaching a maximum at 0.22 M free sulphuric acid. Further increase of acidity causes reduction of scale, but scale is not affected by temperature. The scale mainly consists of hematite with traces of hydronium alunite as revealed by SEM photographs and EDX analyses. Anionic surfactants were tested as a means of scale reduction with some success. A reduction of 37% in scale formation was achieved at an acidity of 0.22 M and 270°C.     

Sulfation of a nickeliferous laterite

The sulfur trioxide roasting of a ferruginous, nickeliferous laterite was investigated at temperatures from 500° to 800°C. The kinetics of the fixed bed sulfation appeared to be logarithmic and this was interpreted to indicate a transport controlled process. Reaction rate constants were evaluated and it was found that the time for equivalent sulfation of nickel was more than 5 orders of magnitude greater at 800°C than at 600°C. The composition of the products appeared to dominate the reaction kinetics through changes in their physical nature. Nickel and cobalt sulfated quite rapidly at temperatures from 600° to 700°C but favorable selectivity over iron could be obtained only at temperatures >750°C where the nickel sulfation rate falls off rapidly. A two-step sulfation process was investigated that takes advantage of the rate characteristics of the low temperature process and attains selectivity by reversing the iron reaction at a higher temperature. Approximately 87 pct of the nickel, 97 pct of the cobalt, and 2 pct of the iron were extracted in a two-step process without additives.     

Enrichment of valuable metals from the sulfuric acid leach liquors of nickeliferous oxide ores

The enrichment of valuable metals from sulfuric acid leach liquors of various nickeliferous oxide ores has been investigated. Suitable enrichment processes based on sulfide precipitation and the Na-jarosite process have been tested and proved to be effective for recovering Ni, Co, and Cu from high-magnesium and high-iron pregnant liquors. Once the major impurities of magnesium and iron had been separated from the valuable metals, the resulting concentrated sulfate solutions mainly containing valuable metals (Ni, Co, and Cu) could be used for further metal separations by solvent extraction methods. It is hoped that such sequences may also be applied for the recovery and enrichment of valuable metals from dilute pregnant leaching liquors.