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By Rudolf Keller

In the electrolysis of neodymium oxide from a molten fluoride electrolyte, anode effects may occur at the carbon anodes, interfering with smooth cell operation. In laboratory experiments, we attempted to circumvent this problem by selecting electrolytes with a high oxide concentration, possibly at relatively low rare earth content, but cathodic deposition was not satisfactory. A regime at higher cell voltage was discovered to yield good cell performance, but evolution of considerable amounts of fluorocarbon compounds suggested that a reactive treatment of the off-gases would be necessary for environmental acceptability. Subsequent experimentation at low cell voltage revealed conditions for satisfactory operation without occurrence of anode effects and without formation of any CF4 or C2F8.

Jan 1, 1997

By V. I. Lakshmanan

Whilst the prices of metals in nominal terms have largely remained static over the past forty years, in real terms, the primary metals industry receives very much less today for its products than in the past. Yet, it has largely managed to remain competitive, despite the fact that ore reserves are not only diminishing, but are of lower grade and higher complexity, and that there are much greater pressures on companies to be good environmental stewards. This paper examines how hydrometallurgical processing has shown itself to be highly innovative in order to remain viable both economically and environmentally. Aspects of process chemistry are discussed, and the lessons to be learned from having a good understanding of this chemistry are highlighted with reference to a number of case histories such as HPAL for nickel laterites, the Avmin/Chambishi Cosac Project, use of chloride chemistry for titanium extraction, and plant effluent treatment and recycle.

Jan 1, 2003

By Hazoor Singh Sidhu

Materials degradation due to corrosion is the major problem in power generation equipment, gas turbine, fluidized bed combustion, industrial waste incinerators etc. Some super alloys have been developed, but they are unable to have different properties to meet the demand of today?s industry. Therefore, a composite system of a base material providing the necessary mechanical strength with a protective surface layer different in structure and/or chemical composition can be an optimum choice in combining material properties. Thermal spray coating of the components before they put into service by suitable surfacing alloy and with suitable coating method can increase the life of these components several fold. Choice of right coating method and alloy for a particular application is extremely important to get the desired service life. The corrosion of some materials and the role of HVOF thermal spray coatings to counteract the same have been reviewed, with an aim to understand the phenomena along with various applications.

Jan 1, 2006

By M. H. Ghandehari

Sintered (Pr,Sm)Co5 displays a multi-phase microstructure in which closely related intermetallic compounds are formed during the process of fabricating useful magnets from over-stoichiornetric compositions. These compounds have much lower magnetic crystalline anisotropies compared to those of SmCo5 and PrCo5. Despite a careful control of the microstructure in producing "single phase" PrCo5 base magnets, sufficient concentrations of the lower anisotropy phases are formed which act as nucleation centers for domain reversal, resulting in a drop in coercivity. This article describes the use of sintering additives, primarily oxides, to prevent the formation of the magnetically soft phases in the final microstructure.

Jan 1, 1989

By Chia-Fu Chang

We revise the applicability of the theory of self-organized criticality (SOC) to the process of magnetic relaxation in type-II superconductors. It is demonstrated that the driving parameter of self-organization of vortices is the energy barrier for flux creep and not the current density. Power spectrum of the magnetic noise due to vortex avalanches is calculated and is predicted to vary with time during relaxation.

Jan 1, 2006

By Chunlin Chen

Published data on thermodynamics of a number of minor elements (As, Sb, Bi, Pb, Zn, Se, Te, Cr, Sn) in liquid copper, matte and slag have been reviewed, assessed and used in development of thermodynamic solution models of melts. The behavior of antimony in alloys, mattes and slags is used as an example to illustrate the approach taken in assessment of published data and validation of the developed models with respect to the activity of Sb in condensed phases as well as the effects of matte grade, slag chemistry, temperature etc on the equilibrium distribution of Sb between melts and the gas phase. Results obtained from a comparison of different smelting processes with the modeled multi-phase equilibrium are presented and discussed. The predicted effects of slag chemistry and matte grade on the deportment of other minor elements during smelting of copper mattes will be presented and discussed.

Jan 1, 2006

By P. Barrios

The copper refinery of Atlantic Copper was modernised and converted to the Isa permanent cathode system in 1995. The technology installed has proved to be an excellent platform for the development of operational improvements. During the years it has been working, the progressive assimilation of the new technology has been achieved and the level of operator knowledge has allowed design production to be reached and surpassed by more than 10%. At the same time, modifications to the work programmes, using existing equipment, have permitted the incorporation of new cells and the achievement of annual production levels of 250,000 tonnes and a productivity of 0.43 t/man-hour.

Jan 1, 1999

By C. Allen

A series of zinc chloride electrowinning tests was carried out in a laboratory scale cell to evaluate the effect of temperature, current density, electrolyte composition, gas sparging and additives on the performance of the cell with respect to current efficiency, voltage, specific energy consumption and deposit morphology. The anode material was DSA for chlorine evolution and the cathode was made of aluminum. At 400 A/m2 current density, a current efficiency of 90.9%, a voltage of 3.4 V and an energy consumption of 2.78 kWh/kg were observed. Air sparging was found beneficial but was not pursued for health and safety reasons. Various additives in the same chemical family as tetrabutyl ammonium chloride (TBAC1) were tested. Both TBAC1 and tetrabutyl ammonium bromide were found to be equally effective. Attempts to carry out the electrolysis at 1200 A/m2 were not as successful.

Jan 1, 2000

By S. S. Chabot, S. E. James

A recent survey of major steel companies worldwide revealed the importance of recycling zinc units from electric arc furnace (EAF) dust, mill scale, blast furnace dust and other zinc containing streams within the steel industry. Many processes have been developed and installed in response to this challenge. The most successful approach involves the production of a crude zinc oxide and its sale to primary zinc producers to recover the metal values. The problem with this process is the high concentration of halides in the crude oxide. This type of material cannot be processed directly in an electrolytic zinc plant because of the corrosion problems it will cause in electrolysis. In 1999, Big River Zinc installed a zinc oxide receiving and washing plant to minimize the impact of halides in its electrolysis circuit. A description of the washing plant and the initial operating results are presented in this paper.

Jan 1, 2000

By Hirokazu Narita

The extractability for Pd(II) using MOTDA and DHS and their durability against a mixed solution of HNO3 and HCl was investigated by solvent extraction and FT-IR measurements. Both MOTDA and DHS selectively extracted Pd(II) over Pt(IV) from 0.75 M HNO32.25 M HCl solutions. The extraction rate of Pd(II) with MOTDA was much greater than that with DHS. In the durability test, the extraction percentage of Pd(II) and the FT-IR spectra were measured using MOTDA and DHS after stirring with 0.75 M HNO32.25 M HCl solutions. The extraction percentage of Pd(II) with MOTDA hardly changed during the two-month stirring; however, that with DHS decreased with an increase in the stirring time. The FT-IR spectra showed the sulfoxide formation by the oxidation of the sulfide in DHS, but not in MOTDA. Consequently, it was found that MOTDA is more durable than DHS.

Jan 1, 2006

By Chen Yongming

In order to eliminate the serious environmental pollution caused by low concentration of sulfur dioxide smoke in antimony smelters, a new smelting process, named as reducing-matting smelting, is proposed in this paper. The effects of technical conditions such as smelting temperature, smelting time, Pyrite cinder addition and the amount of additive on the smelting of stibnite concentrate have been investigated by the method of single-factor experiment. The results show that the optimum conditions are as follow: The amount of pyrite cinder is 1.2 times of its theoretical amount. The addition of soda and sodium sulfate is 15% and 72.6%, respectively, to the amount of stibnite concentrate when the total amount of sodium is 30%. The reducing-matting smelting is conducted at 1100°C for 2h then the smelting temperature is raised to 1200°C for 50min. Under the optimum conditions, the direct and total recovery ratio of antimony can gain 90.99% and 98.87%, respectively, and the fixed ratio of sulfur is higher than 99%.

Jan 1, 2006

By M. Giunti, R. Hampson, S. Gray, P. Kapoulitsas, J. Clark

In 1997 Pasminco's Port Pirie Lead Smelter began a modernisation of its lead and precious metals refinery operations. Driven by the anticipated closure of its Broken Hill mine, the new refining process replaced the locally developed continuous process, which had been in operation since the 1950's. Commissioning of the new plant was staged, beginning in late 1997, and finishing early in 1999. The new plant provides for batch refining of lead, and the use of vacuum induction retorting and bottom blown oxygen cupel technology in the silver refining area. The project has resulted in an increase of lead production capacity of 11% and allows the treatment of a wider range of concentrates than was formerly possible. The most significant change has been to double the smelter's silver capacity to over 400 tonnes per annum. This paper describes the successful implementation and optimisation of the new refinery, which is now consistently meeting design capacity.

Jan 1, 2000

By Vinay Kumar, Jae-Chun Lee, Abhishek Kumar, Manis Kumar Jha

However, India is rich in ores and mineral, but E-waste recycling is necessary due to the report of national and international studies, which cautioned on the generation, treatment and accumulation of e-waste in India. Current data indicate that the total domestic e-waste generation including imports is around 382979 MT, however waste available for recycling and actually recycled are 144143 MT and 19000 MT, respectively. In which recycling by non-formal and formal sector are 95% and 5%, respectively. On the other hand, India has developed expertise in handling verities of metallic wastes in an organized and safe manner. The development of individual process or combined processes for handling the e-waste is underway. Eco- friendly and energy-saving processes are necessary to comply with stringent environmental regulations. The paper includes the recent trend of e-waste generation, recycling process and its future prospects particularly in India.

Jan 1, 2011

By Daojin Cao

Aiming at many controversial reports on Raman spectral pattern of octamolybdate ion in aqueous solution appearing in the literature, a new method for the establishment of corresponding relation between Raman spectral pattern and chemical components of aqueous molybdate solution was put forward using spectroscopy measure and component analyses of saturated solution of ammonium octamolybdate hydrate known structure. It was found that the main characteristic of Raman spectral pattern of the saturated solution was described as the same ?double-peaks, hereinto a weak peak at the boundary? as some literature, but chemical components of the saturated solution were affirmed to be octamolybdate ion (Mo8O264-) and double protonated heptamolybdate ion (H2Mo7O244-), which were in equilibrium in aqueous solution each other. The authors propose that the pattern of the saturated solution can be regarded as the standard pattern of primiparous octamolybdate ion during acidified molybdate solution. It is satisfying that the standard pattern is applied to the identification of primiparous octamolybdate ion during acidified molybdate solution.

Jan 1, 2006

By A. A. Shook

The off gas from the #5 converter at BHP Copper's San Manuel smelter was analyzed continuously over a period of several weeks using an online sulfur dioxide analyzer. These data have shown that the oxygen utilization efficiency of this copper converter was somewhat lower than anticipated, and that oxygen efficiency declines significantly during the copper blow. A sharp reduction in sulfur dioxide generation was consistently observed at the end of the copper blow, which could be used by converter operators to prevent over-blowing and minimize rolling out of stack.

Jan 1, 1999

Iron(II), sulphur dioxide and sugars such as lactose are potential reducing agents for manganese dioxide to produce manganese(II) for subsequent hydrometallurgical treatment. The leaching of limonitic laterite and manganiferrous ores with sulphur dioxide produces iron(II) which in turn can catalyse the leaching of manganese dioxide in acid media. This paper presents a critical analysis of the kinetics of reductive dissolution of synthetic manganese dioxide and manganese ore to compare and contrast the effect of sulphur dioxide and iron(II) in acid media containing sulphate or perchlorate anions. Both one-electron and two-electron mechanisms are considered in the case of sulphur dioxide. The current knowledge on chemical speciation is used to construct an Eh-pH diagram to show the effect of complexation of Mn(II), Fe(II) and Fe(III) with sulphate. Heterogeneous and electrochemical reaction kinetic models are combined to propose reaction mechanisms which rationalize the dissolution kinetics.

Jan 1, 2003

By C. K. Gupta

The paper reports on the experimental work and results obtained in processing a xenotime concentrate. The rare earth resource concentrate has been treated by three different methods namely, hydrothermal leaching, alkali roasting and alkali pugging or baking. The recovery in hydrothermal leaching with caustic soda at 150-160°C has been 89%. En comparison, processes involving alkali roastings with soda ash at 850°C and with caustic soda at 500°C, and alkali pugging or baking with caustic soda at 200°C have given recovery values close to 100%

Jan 1, 1992

By Takeshi Yoshikawa

For the sake of effective control of titanium-compound inclusions in the steel-making processes, especially for stainless steel production, the influences of alloying elements of chromium, nickel, manganese, molybdenum, copper and oxygen on the thermodynamic property of titanium in molten iron were investigated at 1873K. At a certain titanium potential controlled by the coexistence of Ti3O5 and Ti2O3 doubly saturation of steels, the interaction parameters between alloying elements and titanium in molten iron were determined as follows. [ ] From the investigations on the equilibrium of titanium deoxidation in molten iron, the activity coefficient of titanium and the first order interaction parameter between oxygen and titanium were determined as follows. [ ] Also, deoxidation equilibrium for titanium in molten 304 stainless steel was measured and compared with the calculated results using the determined interaction parameters.

Jan 1, 2006

By Wantae Kim

In order to establish the optimized recovery process for heavy minerals from Korean beach sand, we investigated the several physical separation methods such as gravity and magnetic separation followed by mineralogical characterization. There was clear relationship between the particle size and heavy mineral content that heavy minerals were mostly concentrated in the particles below 100mesh. Gravity separation using the spiral and shaking table separators made it possible to concentrate heavy minerals by rejecting the light and coarse particles consist mainly of quartz and other non-valuable minerals. The high-intensity magnetic roll separator and subsequent induced magnetic separator were applied to fractionate magnetic particles according to their magnetic susceptibility. The content of TiO2 of high susceptible ilmenite-rich fraction was 43.98wt.% while those of ZrO2 of non-magnetic and magnetic residue were 6.78wt.% and 3.11wt.%, respectively.

Jan 1, 2006

By Nobuaki Sato

For decontamination of SO2 containing waste gases from industries such as ferrous and non-ferrous metal companies, desulfurization with hydrogen production by the reaction of Br2 and SO2 was proposed as bromine-sulfur (BS) process. In this process, SO2 is fixed as H2SO4 in the presence of Br2 and H2O forming H2SO4 and HBr. Then hydrogen is produced by the decomposition of HBr and Br2 as byproduct is recycled. The reaction of Br2, SO2 and H2O was found not to occur in liquid phase but to occur in vapor one. The production ratios of H2SO4 and HBr showed a maximum at temperatures around 60 oC. The highest production ratio was obtained at 70 oC with a mixing ratio of Br2:SO2:H2O=1:1:10. The experimental results were discussed with thermodynamic consideration.

Jan 1, 2006