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By John Demol

Monazite, a rare earth and thorium phosphate mineral, is one of the major minerals processed for extraction of rare earths. Industry practice for treating monazite concentrates is to use either a sulfuric acid bake or caustic conversion route. In the sulfuric acid bake, monazite concentrate is mixed with concentrated sulfuric acid and roasted. The rare earth phosphate mineral is converted to rare earth sulfate which dissolves in a subsequent water leach. As the bake temperature increases above 300 °C, thorium becomes less soluble. Although acid baking is practised in industry, the bake reactions are not well understood. A combination of chemical analysis, XRD and SEM-EDS was used to identify reaction processes occurring during sulfuric acid baking of a 93 wt% monazite concentrate between 200 °C and 800 °C. The effects of these reactions on the leachability of the rare earths, thorium and phosphate were also examined.

By Liu Zhonghua

Hydrogen reduction of cobalt sulfide (Co9S8) was experimentally investigated in the temperature range 813-1053 K. The results revealed that the reaction kinetics can be described by the shrinking core mod¬el in chemical control regime at low temperatures, it is of first order with respect to hydrogen concentration, and the reaction activation energy is 67.4 kJ/mol. The SEM second electron images of the samples before and after experiments showed that the swelling of the sample above 973 K is due to the formation of metallic cobalt whiskers.

Jan 1, 1992

By Henrique Ventura Oliveira

Continuous casting is the most important process for solidification of steels. In this process, the fluid flow pattern in the tundish and in the mould have significant effect on the product quality. Problems associated to fluid flow in the tundish include surface turbulence, ?short-circuits?, formation of dead zones and vortexing. During grade changes, mixing in the tundish plays a significant role in determining the length of the intermixed slab. All these flow aspects can be studied by means of mathematical and physical models. In the last years, numerical simulation of fluid flow has become a very popular tool in the analysis of the performance of continuous casting tundishes. In setting-up these numerical simulations, special care should be taken in choosing the appropriate mesh distribution, the interpolation scheme, the adequate location of the inlet boundary and the turbulence model. In the present paper, turbulent fluid flow in different configurations of tundishes was simulated. Different turbulence models were used in the simulations. Residence time distribution (RTD) and mixing curves during grade changes were predicted and compared to results obtained in physical models. The performances of the different turbulence models were evaluated. For the tundishes that have been studied, the performances of the different turbulence models tested in the present work were similar. There is no evidence that any of the models provided sustained improvement when compared to the well-established standard k- model. All turbulence models tested presented limitations in simulating flows under low turbulent Reynolds numbers.

Jan 1, 2006

By Alan J. Hurd

"New insights into the development of microstructure in sol-gel films have recently been revealed by several diagnostic techniques, including imaging ellipsometry, ""chemical imaging"" by fluorescent tracers, light scattering from capillary waves, and finite-element modeling. The evolution of porosity during the continuous transition from dilute sol to porous solid in restricted geometries such as films and fibers is becoming clearer through fundamental understanding of evaporation dynamics and capillarity.IntroductionWith sol-gel processing, the full flexibility of solution chemistry can be exploited to make ceramic films and fibers with well controlled compositional characteristics. No less important is the ability to tune porosity and connectivity for specific applications such as optical and electrical coatings and membranes. Since the chemical and physical factors that determine the microstructure are not entirely understood, new diagnostics applied to sol-gel processing are welcome.Sol-gel films and fibers are distinguished by processing that takes a sol through continuous stages of increasing concentration and connectivity of a solid precursor. The liquid carrier is usually volatile or, at least, volatilizable through heat treatment. During deposition through states of increasing solids concentration, this sol might gel, as in bulk sol-gel processing, however, the gel state may be a fleeting transient that quickly empties of liquid. Nevertheless, the structures formed in solution during this stage influence the structure of the final solid. In particular, porosity is likely to be a remnant of networks formed in the sol-to-gel transition. Here we report on experiments whose goal is to discover the factors involved with porosity development."

Jan 1, 1994

By A. J. Rigby

Current practices employing porous plugs to inject nitrogen into molten copper during primary smelting are described. Nitrogen stirring increases heat transfer to the bath, eliminates temperature stratifications, and improves efficiency during the steps of desulfurization and deoxidation. The opportunity to use porous plugs as the means to introduce reducing gases to deoxidize copper is also discussed. Previously reported laboratory results using porous plugs, which point to very high utilization efficiencies of hydrogen when used as the reducing gas, are again reviewed. Advances in the design of the porous plug, and the introduction of a system enabling external replacement of plugs is also discussed.

Jan 1, 1999

By Brian R. Green

Resin-in-pulp (RIP) technology has been developed for recovery of gold. It is now time to look forward to the potential for application of the technology to other situations. Some cases have been identified and have merited preliminary testwork. Four examples, which illustrate the potential of RIP, are dealt with in this paper. These include removal of metal-cyanides from pulps, recovery of manganese that is difficult to wash from filter cakes, recovery of nickel from low grade pulps, and recovery of zinc from process residues. The discussion includes descriptions of the problems, factors that affect the choice of resin, and factors that will affect the economics of the process.

Jan 1, 1998

By Tuneo Funahashi

Sumitomo Shisaka Works has been treating EAF(Electric Arc Furnace) dust to recover zinc and lead in the Waelz Kiln process. Since its commencement of operation in 1977, many technical improvements have been successfully made to increase the production capacity and the zinc recovery rate. The EAF dust charge to the Waelz Kiln was increased from 35,000tly to 120,00OtIy, and the production of zinc oxide now amounts to 40,000tly. The zinc content in the clinker was decreased from 5% to less than I%, by the optimization of the kiln heat pattern with no accretion trouble. And the clinker has become more a valuable raw material for steel making. This paper describes the above progress ofthe SMM Waelz Kiln process operation at the Shisaka Works.

Jan 1, 1998

By Richard Hollis

The Mount Isa copper smelter was expanded in 1998 to a capacity of over 250000 t/y anode copper. This tonnage will be produced from a single stream consisting of an Isasmelt smelting furnace, and four Peirce-Smith converters - one of which was installed as part of the expansion project. During the course of the expansion project Mount Isa Mines Limited (MIM) signed an agreement with WMC Fertilizers Ltd (WMCF) to supply sulphur containing smelter gases over the fence to a new sulphuric acid plant to be built by WMCF. This will result in a further increase in copper production by reducing the time when smelting is curtailed by Air Quality Control restrictions. As well as the need to modify the primary gas system to connect to the acid plant, the hoods and crossover ducts and their support structures on the original three converters required replacement, and secondary ventilation was also needed to improve converter aisle hygiene. Each of these areas was addressed by the project. Preliminary ideas for carrying out the modifications were found to have a serious impact on converter aisle operations, and would have led to a production loss of over 50000 tonnes of copper. Following benchmarking in other copper smelters, a suitable construction plan was developed and carried out to minimise this loss. This paper describes the methodology and construction plan adopted.

Jan 1, 1999

By Lucas Lopes da Costa

Bamboo fibers were characterized in terms of diameter distribution and tensile properties. Polyester matrix composites reinforced with these fibers were investigated for their flexural mechanical behavior. Specimens with up to 30% in volume of continuous and aligned bamboo fiber composites were bend-tested until fracture. The results showed an improvement in the composite strength and stiffness with the amount of bamboo fiber. A microstructure analysis by scanning electron microscopy revealed a reasonable adhesion between the fiber and the polyester matrix which justifies the improved mechanical properties of the composites.

Jan 1, 2010

By Rodney T. Jones

Mintek has developed and piloted a novel process for the treatment of nickel-copper and PGM (platinum group metal) sulphide concentrates. The ConRoast process is based on the removal of sulphur by roasting, followed by smelting of the dead-roasted concentrate in a DC arc furnace using an iron-based alloy as a collector for nickel, copper, cobalt, and PGMs. The environmental benefits with respect to sulphur emissions are considerable, in that essentially all of the sulphur is removed from the enclosed roasting equipment in a continuous stream of SO2 of an appropriate strength for feeding to a sulphuric acid plant. This process allows great flexibility with respect to the selection of ore types, and does not impose limits on the minimum quantities of contained base metals or sulphur, and can tolerate very high contents of chromite in the concentrate. The furnace alloy is water-atomized prior to leaching. Iron may be rejected from the alloy hydrometallurgically, by precipitation as hematite for example. The ConRoast process achieves very high metal recoveries, and produces high-purity metals, and a clean high- grade PGM concentrate.

Jan 1, 2002

By J. E. Klein

Bench scale tests using a stack of ten whole SAES St909 pellets, 6 grams, to crack methane have been completed with pure methane feed. Test conditions ranged from 600 to 800°C at 101 kPa (760 ton) with a methane feed rate of ten sccm. Methane reformation tests, test where hydrogen was passed through a St909 bed after cracking methane, were performed to determine if and how much methane can be generated under "reformation" conditions. Phase structure determinations of St909, composed of a ZrMnFe alloy with aluminum used as a pellet binder, after methane cracking were complicated by the number of materials that can be formed by the elements in the St909 and the carbon from methane cracking. It was determined that the aluminum not only alloys with the Zr, Mn, and Fe in the St909 alloy, but also forms aluminum transition metal carbides in addition to ZrC as the carbon content and the temperature of the St909 increases. Some A14C3 was also found in some pellets. Passing hydrogen over St909 pellets after methane cracking formed methane at various rates in the temperature range of 600 to 800°C. Temperatures of 800°C gave the best methane cracking performance and efficiencies decreased rapidly with temperature.

Jan 1, 2002

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 H. Dijkman

The PAQUES Bio Systems' core technology, marketed under the name THIOPAQ®, consists of various high-rate biological processes for metal-sulfur-water systems, complemented with common solid/liquid and gas separation steps. Sulfur species are converted to sulfide, which is a valuable component as it can be used for metals reduction and precipitation. Selective recovery of valuable metals can be employed, leading to revenue from metal values. In this paper, biotechnological systems for the treatment of metal sulfate solutions and dilute SO, gases are described. These installations can be designed to either produce predominantly aqueous (NaHS) or gaseous (H2S) sulfide. The emphasis here is on hydrogen sulfide gas. The main case history discussed is the demonstration plant that ran on hydrogen gas at Kennecott Utah Copper. Three years of operating experience clearly show that sulfate reduction with hydrogen gas is a viable option. Furthermore, the selective recovery of copper from leach water with the hydrogen sulfide produced was shown to be very effective.

Jan 1, 1999

By L. H. Lewis

The relationships that link microstructural properties of advanced permanent magnet materials with magnetic properties such as the coercivity are often difficult to quantify, especially in materials with nano-scale structures. Recent work on RE2Fe14B-based powders fabricated with rapid- solidification techniques such as inert gas atomization (IGA) and melt-spinning provide insight into the nanostructural features which affect the acquisition and stability of coercivity. In all cases the coercivity is found to be a function of both the scale of the constituent microstructure and of the presence and distribution of minor phases.

Jan 1, 1997

By Nexhmedin Lohja

Macro management of metallurgical industries becomes an important issue in certain situations especially when some government owned metallurgical industries are on the verge or have stopped being feasible. In these cases a government lead macro management in collaboration with domestic institutions and foreign scientific and management expert companies is decisive in order to steer them to a profitable path. This process is not necessary an easy one and incorporates many unknowns and various alternatives. In this paper the macromanagement of the metallurgical industries in Albania will be described as a particular case along with a survey of its mineral deposits, metallurgical facilities and various perspectives for future development. As a country with many mineral resources, the exploration, research, exploitation and processing work of mineral ores before 1990 constituted an important activity of its economy, especially in the exportation of various products of this industry. Since 1990 this activity slowed downs considerably for various reasons and this prompted the necessity of a government lead macromanagement in collaboration with domestic institution and foreign expert companies. This process aims at improving and renewing the technologies in the metallurgical industry in order to transform it into a feasible branch of economy. This goal is being implemented among others through proper geological surveys, rehabilitating and renewing the existing facilities through domestic and foreign investments, the transformation of the ownership or the management from state-owned to local or foreign private companies, etc. Priority is given to the raising of the processing range of the traditional minerals such as chromium, copper, nickel-iron etc. as well as developing new perspective technologies to treat new mineral deposits.

Jan 1, 2006

By Guo-Sen Zhu

Research on the formation mechanism and control of corner transverse cracks was carried out. The optical microscope and SEM were applied to analyze the characteristics of cracks. It is found that the cracks occur at the relatively lower temperature due to unbending strain and have almost nothing to do with the mold cooling and powder. The keys to prevent corner transverse cracks are to optimize the corner temperature of slab and maintain the good state of casting machine. Increasing casting speed and decreasing the cooling water flux at the corner in the unbending segments, resulting in mild cooling, were applied during investigation to control corner temperature above the upper limit temperature of the No.3 brittle zone of Nb-contained steel tested by Gleeble-1500 system. As a result, corner transverse cracks were minimized, but centerline segregation got worse. And then increasing the cooling water flux at the corner (intensive cooling) was applied to make corner temperature below the lower limit temperature of the No.3 brittle zone. Great diminution of both corner transverse cracks and centerline segregation was achieved finally.

Jan 1, 2006

By Matthew Jeffrey

Leaching, cementation, electroplating and flotation are all electrochemical phenomenon. They are also key processes in the hydrometallurgical treatment of metals. Unfortunately electrochemical methods tend to be under-utilized when studying these processes and one possible reason for this is the confusion surrounding the large number of electrochemical techniques available. In this paper four former PhD students of Professor Ian Ritchie present an insight into how one electrochemical technique can be used to compliment rate/kinetic studies. The paper details how to perform the experiments, interpret data, and recognize complications with the results. Examples where this approach has been highly successful are presented, and include: cementation of zinc by aluminium, cementation of copper by nickel, cyanide leaching of gold and the cementation of gold thiourea by mild steel. The examples illustrate that this universal approach adopted by Ian Ritchie provides the key to understanding the mechanism of many hydrometallurgical reactions.

Jan 1, 2003

By Stephen M. Testa

Several methodologies are available for the remediation of contaminated soils including bioremediation, vapor extraction, chemical fixation, incineration and direct disposal. A proven innovative and cost effective alternative for the fixation of contaminated soils is via cold-mix Environmentally Processed Asphaltm (EPA"'). EPAm methodology utilizes contaminated soil as an ingredient in an industrial process to produce a commercially viable product. Petroleum hydrocarbon and metal affected soil is incorporated with a water-based asphalt emulsion and varying amounts of aggregate to produce a range of cold-mix asphaltic products that fulfills the requirements of a variety of end uses. This viable and creative use which is within the intent and spirit of current regulations in producing, in lieu of a landfill waste, an end product for use as a berm, road base, liner, or other site specific application. Consideration of certain engineering and environmental factors including durability, stability, chemical resistance and ageing, biological resistance, permeability, leachability and geochemical aspects suggests that cold-mix asphalt incorporation of affected soil will perform more than adequately under normal conditions for a long period of time.

Jan 1, 1994

By C. Lupi

Zinc chloride electrowinning presents difficulties in obtaining smooth, compact and dendrite free deposits with a high current efficiency due to the presence of undesirable metal ions. However, it is hard to define a level of impurities tolerable in zinc deposition, and despite a lot of research in this field, the reaction mechanisms of the undesired metal ions are still not clearly understood. In this study, the influence of Fe, Cd, Co, Ni and Cu additions were investigated, as well as their synergic effect on the zinc electrodeposition process from chloride electrolytes and on the obtained deposit morphology. The tests were all performed in presence of TBACl which reduces the harmful effect of such impurities on the zinc reduction.

Jan 1, 2003

By Keizo Uematsu, Kumiko Sanda, Nozomu Uchida

"Full understanding of mechanical properties is the most important assignment in ceramics. Establishment of defects-property relationship is crucial for fulfilling the assignment. This study reports detailed characteristics of defects and their relevance to the mechanical properties for alumina ceramics made through a typical industrial processing. Novel characterization methods were applied to evaluate their defects. A very simple direct correlation was successfully found between defects and properties in ceramics. This result is a great epoch in the field of ceramics. IntroductionThe ceramic materials are used in refractoriness, corrosion resistant materials and structural materials. The low fracture toughness and scatter of strength are very important problems in ceramics. The toughness of ceramics is lower than metal and polymer materials, and the allowed defect size is small. Very small internal defects (pore, crack, huge particle) can be a fracture origin in the brittle fracture. The characteristics of defects such as size, distribution and shape change markedly by process condition, which cause the scatter of strength. This study conducts quantitative evaluation and direct observation of the sizes, shape and a number of internal defects with a light microscope, and discusses the relationship for mechanical properties and defect sizes"

Jan 1, 2000