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By Hector M. Lizama

A new technology, known as the HydroZinc? process, is described for the recovery of zinc from sulphide ores that includes heap leaching, neutralization, solvent extraction and electrowinning. Unit operations were scaled up from bench-scale to a 1-t/d zinc cathode demonstration plant. Bench-scale studies defined the process chemistry and a process flowsheet. Column tests were used to design full-scale heaps for zinc bioleaching, and mini-pilot equipment was used to design a solvent extraction circuit. The characteristics of the process required development of a bleed circuit for water and impurities. The complete integrated process was tested on a demonstration plant scale for two years, with about 10 000 t of zinc sulphide ore being bioleached in two 6-m-tall test heaps. In addition to 1 t/d of zinc cathode, iron hydroxide and gypsum residues were produced. The process also generated a small effluent bleed. Over the course of the two-year demonstration test, a number of technical hurdles were overcome and several improvements were made. Some of the more significant ones are presented along with process descriptions and experimental and demonstration plant data. Some engineering aspects and economic evaluations of the new process are also discussed.

Jan 1, 2003

Testing is in progress to address compatibility issues with regard to long term storage of plutonium in contact with two different intermetallic systems. The two intermetallic systems are: 1. dental amalgam, i.e., mercury plus silver alloy powder, and 2. liquid gallium alloy plus copper powder. Both of these are plasto-metallic materials that undergo a solidification reaction at room temperature. Each system is allowed to react in contact with both high-purity alpha plutonium and a delta stabilized plutonium alloy at varying temperatures in an argon atmosphere. Wetting characteristics and possible interaction will be studied metallographically in the post-mortem condition. Complete results including metallographic examinations will be presented.

Jan 1, 1995

By T. Taniguchi

The existing Mitsubishi Process line at Naoshima Smelter and Refinery has been operating successfully since 1991, and its present production capacity is 270,000tpy of copper. Furnace relining works have been carried out every two years to coincide with the compulsory bi-yearly boiler inspection, but the next target is to extend the furnace refractory life to four years, while still undergoing the mandatory boiler inspection every two years. Although the damage of hearth bricks beneath lances in the Smelting furnace was a matter of concern, it was reduced by controlling gas velocity and evening solid distribution to each lance. The life of bath level bricks in the Converting furnace was also a concern, but four-years continuous use of the bricks was achieved in the course of the last two campaigns. Several other improvements were also carried out to the cooling systems during the shutdown in 2005 to ensure longer campaign life. This paper summarizes recent improvements implemented to enhance the advantages of the Mitsubishi Process.

Jan 1, 2006

By S. H. Amini

The effects of CaF2 and ilmenite on dissolution rate and diffusivity of CaO in calcium alumino-silicate based slag in a temperature range of 1500 ? 1600 ºC were studied by using the rotating disk/cylinder technique. The effect of rotation speed on the rate of dissolution in the base slag indicated that mass transfer in liquid slag played a significant role in controlling the dissolution. At a constant rotation speed, the effect of 5 wt% addition of fluxes tothe slag on the dissolution rate was investigated at various temperatures. While CaF2 had the highest effect, addition of ilmenite increased the rate of dissolution significantly. The diffusivity of lime in these slags was quantified using the dimensionless mass transfer correlations for rotating disk/cylinder in the melt. The diffusivity values were deduced using the data on dissolution rate and solubility of lime in the slags. The measured diffusivity in base slag at 1500 C was found to be about 1.32 10-5 cm2/s and increased to 3.07 10-5 cm2/s at 1600 °C. Addition of 5wt% CaF2 increased the diffusivity by a factor of 3 to 5, while 5wt% ilmenite increased the diffusivity by a factor of 2 to 3 in the temperature range of 1500 to 1600 ºC. The two examined fluxes reduced the activation energy of diffusion.

Jan 1, 2006

By C. G. Anderson, L. G. Twidwell

"Throughout the world, there are many orebodies or materials which have significant value but also contain arsenic, antimony, and mercury. As regulations on the transport, exposure, disposition and emission of these elements have become more stringent; it has become increasingly more difficult to derive the values from the resources. This paper outlines the fundamentals of alkaline sulfide hydrometallurgy and its successful application to arsenic, antimony and mercury bearing ores, concentrates, by-products, and other materials.Fundamental Alkaline Sulfide HydrometallurgyHydrometallurgical methods can be employed for treatment of gold, arsenic, antimony, tin and mercury containing materials, concentrates and ores as well as complex ones containing any number of metals. The alkaline sulfide system is one of these and is essentially a mixture of sodium sulfide and sodium hydroxide. This is a unique hydrometallurgical system as it is a very selective lixiviant for the distinct leaching of tin, gold, antimony, arsenic and mercury [1-7]. Worldwide, it is employed industrially in the CIS, China and the United States for the production of antimony [8-15].As an example, when the system is applied to an arsenic containing material like orpiment, As2S3, a solution of sodium thioarsenite is formed. This is illustrated as:"

Jan 1, 2008

By Funsho K. Ojebuoboh

With several "green" applications in the horizon, bismuth has become an even more important minor metal in the smelting and refining of lead. Smelters with a complex sulfide feed invariably deal with bismuth. Its behavior during the smelting of lead in conventional sinter - blast furnace operation is discussed. Because it readily deports to the lead phase during the refining of lead, its separation from refined lead remained unsatisfactory in early lead production. When commercial requirements of bismuth in lead became more stringent early this century, the procedure whereby calcium and magnesium is used to debismuthise lead was developed. The present conduct of this 1936 process, the Kroll Betterton process, is discussed with emphasis on operational improvements.

Jan 1, 1995

By L. Cifuentes

Electrodialysis (ED), i.e. a technique based on the effects of electrically charged membranes on ions in solution in an electric field, has been applied to Cu-Fe-As-Sb- H2SO4 electrolytes similar to those used in copper electrorefining and electrowinning operations. The effects of current density, time and species concentration have been studied in a batch ED cell. The technique has shown to be effective in concentrating and separating a range of ions and points to possible new methods of treating copper electrometallurgy effluents.

Jan 1, 1999

By V. A. Bryukvin

A characteristic feature of the macrokinetics of the interaction process is the presence of two specifically defined areas of oxidation which had a linear time dependence. The effect of variables, such as residual sulphur content of the melt, temperature and the oxidation potential of the gas phase, on the macrokinetics of oxidation are investigated. Phase composition and structure of products of solidification of partially oxidised melts and thermodynamic properties pentaining to Cu-S-O melts are used to analyze the macrokinetic behaviour and mechanisms of the interaction. The process of interaction of sulfide copper melts with oxygen may be considered as a disproportional absorption process and its mechanism is based on localized interaction on the surface and inside the melt volume. Superficial processes include also the process of primary chemisorption of oxygen by melts at place of metal-metal donor bonds proceeding with formation of oxysulfide liquid solutions and volumetric decomposition of the latter accompanied by evolution of sulfur dioxide and metallization of sulfide melts. It is the degree of dynamic balance of such interaction processes that determines specific individual features of the macro-kinetics and mechanism of oxidation of sulfide copper solutions with oxygen in the gas phase.

Jan 1, 2006

By W. L. Cornell

The processing of lead tailings for removal of the heavy metals produces concentrates upgraded in Co and Ni values. Reflected light microscopy, scanning electron microscopy, image analysis, and Vickers hardness measurements were used to identify mineral species, associations, degree of liberation, and distributions to the test products. Siegenite and bravoite were the most common species encountered, but violarite and enriched pyrite and marcasite phases were also identified. Liberation for the Co and Ni minerals contained in the tailings was 20 micrometers or less.

Jan 1, 1993

By Wei Liu

A new process for extracting cadmium from the electric precipitated dust produced by ISP process was studied. A leaching rate of 89.1% of cadmium was attained by leaching the dust with NH3?H2O-(NH4)2SO4 system under the best leaching conditions: ratio of liquid to solid(l:s)=2.5, c(NH3):c(NH4+)=3:5, total concentration of ammonium and ammonia=8 mol?L-1, leaching time= 1.5h, temperature=35. The most troublesome impurity of lead could be deposited from the leached out solution automatically after put it static more than 15h when the total concentration of zinc and cadmium was up to 45gL-1 , and the final concentration of lead was 0.0047 gL-1, which meant 99% of it was removed. Metallic cadmium which contained cadmium more than 99% was prepared by electrowinning under the conditions: current density=750Am-2, total concentration of Cd2+ and Zn2+>25gL-1. The current efficiency was about 87% and the energy consumption for every ton of cadmium was about 548KWht-1. Main impurities of the metallic cadmium were copper and zinc and all of they could be got rid of in the following pyrometallurgical refining step.

Jan 1, 2006

By M. Huang

A conductivity-based sensor for on-line measurement of free acid was recently built. This sensor is suitable for high ionic strength solutions and its corrosion-free operation is based on induction currents. It has been tested against literature data and measurements made using a previous developed contact-type conductivity cell, with an average difference within 1%. The electrical conductivities of H2SO4?H2O, H2SO4?MgSO4?H2O and NaCl?Laterite-H2Osolutions at temperatures up to 250 °C were discussed. It was found that the solution conductivity depends on various factors, such as the electrolyte concentrations, the type of electrolytes, temperature and the amount of dispersions. A semi-empirical model was developed to account for all the factors discussed. This model was further tested on actual process solutions from the hydrometallurgy of nickel where sulphuric acid solutions containing a variety of metal sulphates and solids. The average difference between the estimated acid concentration from this model and the one from titration was generally less than 5%, which is excellent for industrial applications.

Jan 1, 2006

By Yanxia Lu

Porous silicon carbide (SiC) has been the top selection for diesel particular filters (DPFs) since 2000 because of its high thermal diffusivity and strong body, which help it to survive in the harsh environment of a diesel exhaust system. However, the process to produce SiC DPFs is a costly one. The work presented herein describes more cost effective composite materials for this application, namely Si-SiC and Si₃N₄-SiC. Both composites have shown excellent filtration efficiency, low back pressure and outstanding survivability of regeneration at high soot loadings. Since the composites are batched from silicon metal, they can be prepared by a low temperature process that is impossible in the production of pure SiC PDFs. In fact, fabrication of SiC composites simply involves reactions between nitrogen gas and silicon metal, or silicon metal bonded with SiC, and as such uses a much less costly process when compared to the one employed to make SiC. In addition, the pore structure of the composites can easily be tuned by selecting raw materials and changing the ratio of two components. A typical pore structure consists of well connected pores with a median pore size of 5-20 µm and a porosity of 40-55%. This talk will describe the exothermic behavior as well as the mechanical and thermal properties of SiC composites in comparison to those of SiC filters. It will also show the superior thermal shock resistance of Si₃N₄ bonded SiC which is due to the unique combination of these phases that lowers the thermal expansion and elastic modulus relative to pure SiC.

Jan 1, 2006

By Tiffany Brown

In the thiosulfate gold leaching process, thiosulfate is used to complex gold following electrocatalytic oxidation of the native metal by Cu(II)-ammines. Unfortunately, Cu(II) complexes also catalyse the undesirable conversion of thiosulfate to polythionates. We have been seeking alternatives to ammonia, which fulfil the role of ammonia but minimize thiosulfate decomposition. One aspect of these studies has involved the determination of the rate of thiosulfate oxidation by the Cu(II) complexes from UV-Visible spectral changes. Various ligand classes, including pyridyls, polyamines, aminocarboxylates and picolinates, have been tested and the majority found to inhibit thiosulfate decomposition. Interesting variations in reactivity with the nature and denticity of the ligand and L/M ratio have been observed. In the case of open chain polyamine ligands with 2 to 5 nitrogen donors, the rate of thiosulfate oxidation was generally found to decrease with the denticity and the concentration of each ligand. Saturation of the Cu(II) coordination sphere appears to inhibit the oxidation of thiosulfate when excess thiosulfate is present. The Cu(II) complex of the branched polyamine ligand, tris(2-aminoethyl)amine (tren) exhibits this behaviour in excess thiosulfate. Interestingly, when the [Cu(tren)(OH2)]2+ complex is in excess oxidation of thiosulfate was observed. This unexpected finding prompted a spectrophotometric study of this reaction which has revealed that the oxidation of thiosulfate involves several processes, two of which involve the formation and decay of a tetrathionate radical.

Jan 1, 2003

By Bohumír Cech, Jirí Hanika, Václav Veselý

"PET bottles are separated and subsequently crushed into flakes. Except for PET, these flakes contain PE, PVC, paper, adhesives, beverages remainders and mineral impurities. PET itself usually is a glycol and terephthalic and isophthalic acid polymer.The suggested method consists in PET flakes crystallization at 255°C. In the meantime, volatile substances evaporate and PVC disintegrates. Formed crystalline PET is crushed into small particles and then is subject to the basic hydrolysis at an atmospheric pressure. In addition to lye solution, glycol is added in the hydrolysis. Water is eliminated by boiling, which gives rise to suspension of sodium salt of terephthalic acid and glycol. The suspension is skimmed and the filtered glycol is vacuum distilled. Pure glycol is then the distillation product.Crystals are dissolved in water and the solution is filtered, which eliminates PE and impurities. Electrodialysis removes pure terephthalic acid salt from the solution. Glycol solution is returned to the hydrolysis. Terephthalic acid is precipitated by a mineral acid. Subsequently, it is washed and dried. The filtrate is separated through electrodialysis to lye and acid. The lye gets back to the hydrolysis and the acid is used for precipitation. Terephthalic acid and glycol are products in a “polymer grade” quality. The waste is a part of washing waters, distillation residues after glycol regeneration and a filter cake after the terephthalate solution filtration."

Jan 1, 2008

By Ennio Bonetti

The technological applications of MgH2 hydrides for hydrogen storage demand the overcoming of some critical issues: an improvement of the reaction kinetics and a reduction of the desorption temperature. The synthesis of nanocrystalline MgH2 by reactive milling and inert gas condensation and a proper metal catalyst addition, constitute recently employed strategies. In the investigation of the hydrogen short and long-range dynamics, sorption kinetics and nanostructure stability, the mechanical spectroscopy offers some specific advantages. In the present research this technique was employed with other experimental approaches (XRD DSC) to investigate relaxational and structural damping processes in nanocrystalline MgH2 with added catalysts (Fe). Time/temperature variation of the dynamic elasticity moduli and mechanical quality factor are correlated to hydrogen anelastic relaxation processes and concomitant structural transformation of MgH2 to Mg associated to long range H diffusion. Results are discussed with reference to microstructural modification strategies able to assist hydrogen release.

Jan 1, 2006

By Ashish Kumar

Comminution is an essential mineral processing operation to liberate the minerals from the ore. This however, is an energy intensive step in mineral processing industries. This work highlights the possibility of saving in grinding energy for ore comminution reducing work index of the ore by effective utilization of microwave energy. This reduced work index results in increased throughput of the grinding circuit in mineral beneficiation plant in order not to shift the product size. The fundamental principle behind this application remains the ability of microwave to heat individual phases within the ore matrix. The constituents of the ore typically having different thermal and mechanical properties develop stress of sufficient magnitude to create intergranular and transgranular fractures during heating and subsequent quenching of the ore. The experiments conducted with the ore samples of Zawar Mines and Rampura Agucha Mine of Hindustan Zinc Limited, India (A member of Vedanta Resources Plc) reflect a substantial up-shift in cumulative weight percentage passing in finer sieve fractions under quenched conditions. Further, the experiments carried out on Rampura Agucha ore reveal 20-30% reduction in work index, which result in decreased milling time or saving in grinding energy. The simulation studies estimates a 2-4% increase in plant throughput. Moreover, preliminary flotation studies indicated a significant increment in total metal recovery and concentrate grade for the desired grade and recovery values respectively. This paper is a technical note on the laboratory investigations carried out at Central Research & Development Laboratory of Hindustan Zinc Limited. Results have been encouraging to progress the work further. It is also proposed to carry out modeling work for simulation so as to predict the changes in minerals.

Jan 1, 2006

The presence of clay adversely affects the floatability of copper and molybdenum during processing porphyry copper/molybdenum ores. In addition, reagent consumptions are much higher than when treating clay-free ores. Ores containing kaoline, brammollite, illite and montmorillonite were examined in the laboratory to determine how clay minerals affect the floatability of copper and molybdenum, and to find a possible solution to alleviate the harmful effect of clay slimes. It was demonstrated that the presence of clay mostly affects floatability of coarse and middling particles, and reduces selectivity. The results of the research work showed that there may be several possible ways of reducing the detrimental affects of clay slimes on flotation, some of which include a) use of alternative flowsheets, b) flotation at reduced pulp density, and c) the use of special frothers. The applicability of the findings in plant practice are discussed.

Jan 1, 1999

By G. Achurra

The products of the smelting of copper concentrates in an El Teniente Converter (CT) are a high grade matte, analyzing 74-76% Cu; and a highly oxidized slag, typically containing 15-20% Fe3O4 and 4-10% Cu. The El Teniente Division of CODELCO¬CHILE has developed a slag reduction-cleaning process, that is practised in a tilting, horizontal furnace, to recover copper from these slags. The El Teniente slag cleaning process has been successfully implemented at the El Teniente Caletones smelter and various other smelters in Chile: Today, eight such slag cleaning furnaces, each with a capacity of 800-1000 tonnes/day, are in operation in Chile. This paper discusses basic laboratory research and industrial tests that led to substantial reductions in the slag cleaning cycle time and the specific consumption of fuel and reductants. Simultaneously, the slag cleaning off-gas quality was improved. Based on the experimental results, recommendations were made to improve the practice of the El Teniente slag cleaning process. The recommended modifications have been fully implemented at the Caletones smelter.

Jan 1, 1999

By A. F. Otero

During the electrowinning (EW) of copper significant quantities of highly toxic vapors (acid mist) are produced due to the liberation of oxygen at the cathodes. Acid mist affects the health of operators, the environment and plant infrastructure. Acid mist can be decreased to acceptable levels by a combination of physical means (e.g. ventilation, plastic spheres over electrolyte) and chemical surfactants that decrease the surface tension of the electrolyte, modifying the way oxygen bubbles burst at the surface of the electrolyte. However, only few chemical surfactants are compatible with electrolytic applications, and they are not always used due to their high costs. This paper describes the application of a novel surfactant of natural origin (commercial name Mistop®) to suppress acid mist in copper EW process. Mistop® contains triterpenic saponins derived from the Chilean quillaja tree Quillaja saponaria Molina. The product is non-toxic, and poses no risks to the environment or to EW operators. Mistop® was tested at a laboratory, pilot plant and industrial scale in the world?s largest copper EW production plant at Radomiro Tomic (RT), CODELCO, Chile. At a Mistop® dosage of 8-9 ppm, acid mist decreased below the value accepted by Chilean regulations (< 0.5 mg/m3). At this dosage, Mistop® represents and economical alternative to chemical surfactants, and it is currently industrially used at RT.

Jan 1, 2003

By Clodualdo C. Conde

In order for Philippines Associated Smelting and Refining Corporation (PASAR) Corporation to remain a leader in the copper smelting and refining industry, continuous improvements in plant technology are required. Reliable performance of plant equipment is essential for a competitive smelting operation. PASAR is constantly searching for the best equipment and technology to allow us to manufacture products more efficiently. When the Smelter was commissioned in 1993, the Flash Furnace off-gas treatment system was a constant source of problems. There were frequent shut-downs of the electrostatic precipitator due to material buildups on the discharge electrodes and collecting plates. In 1998, the precipitator was successfully upgraded to eliminate the buildup problems and to increase the collection efficiency. The upgrade greatly reduced down time and maintenance, and the enhanced collection efficiency also eliminated pluggage problems and material losses in the Acid Plant. This extensive precipitator upgrade was accomplished during a 30-day Smelter turnaround.

Jan 1, 1999