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By J. D. Miller

Gold adsorption from cyanide solutions by activated carbon has been studied at great length during the past decade. Findings from past research are reviewed and discussed with respect to structural features of various carbons, including carbon black, activated carbon, graphite and diamond.

Jan 1, 1991

By H. Itou, J. M. Toguri, T. Takasu

"Marangoni convection has a large effect on materials processing since it remarkably enhances heat and mass transport near a free interface. To have a better understanding of the behavior of Marangoni convection in molten salts, observation and calculation of the thermal convection in a column held between a pair of Pt disks (2mm in diameter) fixed to hot thermocouples, were carried out.Calculated flow patterns and absolute values of fluid velocity agreed well with the observed results. When the temperatures of both disks were set equal and the height of liquid column was 2.4mm, four vortexes were generated on the longitudinal plane with a typical velocity of 15mm/s . From the calculated isothermal lines, the behavior of the enhanced heat transport was obvious; fluid heated at the disks was conveyed to the free surface and the cooled fluid at the surface was conveyed to the inner region. Increase in the height of column and/or increase in the absolute value of applied temperature difference lead to increase in fluid velocity lineally in this calculation range.IntroductionIn the processing of many materials, fluid flow of melts has a large effect on refining capabilities and on the characteristics of the produced material. Marangoni convection is generated when a spatial gradient of interfacial tension exists on the free interface due to differences in temperature and/or concentration. This promotes heat and mass transfer locally near the interface.For example, Marangoni convection which are created following the dissolution of interfacially active materials, increases the local corrosion rate of refractories (1-3). In absorption and discharge of oxygen and/or nitrogen in a molten metal, the effective reaction rate of the gas components through the gas-liquid interface increases (4-7). Also in crystal growth, the distribution of defects and impurities in the crystal is affected and this can alter its quality (8-11 ). The temperature distribution is also affected and can greatly change the productivity. For these reasons, the effectiveness of Marangoni convection in refining should be quantitatively clarified and its control should be better understood."

Jan 1, 1997

By Donald Voit

"The reaction between zirconia/zircon, coke, and chlorine involves a slow reaction between the coke and the zirconia/zircon and a fast reaction with chlorine. Because of the fast chlorine reaction, the reaction rate for zirconia/zircon is nearly independent of chlorine concentration for most conditions. The reaction between zirconia/zircon and coke is particle size controlled and related to the degree of physical contact between the zirconia/zircon and the coke. Since particle-particle contact is critical, compaction of finely ground coke and zirconia/zircon produces the highest reaction rates. Uncompacted, coarse coke and zirconia/zircon has the slowest reaction behavior with static bed tests.SummaryZirconia reacts with chlorine in the presence of carbon to form zirconium tetrachloride, carbon monoxide, and carbon dioxide. A similar reaction occurs with zirconium silicate with the additional formation of silicon tetrachloride. The reaction rate depends primarily on temperature and the intimacy of contact between the zirconia and the coke. The reaction is multi-stepped with a slow reaction between coke and zirconia to form an intermediate that reacts rapidly with chlorine, causing the order of the reaction for chlorine to be near zero. Chlorination rates in the range of 1 µmole/hr/cm2 are seen for fluid bed reactors. Plug flow, and static bed reactors have reaction rates of the order of 1 mmole/hr/cm2, where the area is based on the zircon surface area in plug flow and fluid bed reactors and the boat cross sectional area in a static bed. Chlorination rates measured in zirconia/coke briquettes are higher with rates as high as 400 mmole/hr/cm2 reported. High chlorine diffusion resistance, not accounted for in the analysis of experimental results, has led to a lot of confusion in the literature interpretation of chlorination data.In general coke and zirconia/zircon particle size, coke and zirconia/zircon intimacy, coke to zirconia/zircon ratio, chlorine concentration, and temperature are important variables for chlorination. Decreasing the coke and zirconia/zircon particle size generally increase the reaction rate. The coke to zirconia/zircon ratio affects the reaction in a more complex way. Increasing the chlorine concentration generally increases the reaction rate, but the effect appears to be more related to the concentration dependency of diffusion than to its role in the kinetics. The reaction rate increases with temperature but the exact behavior is complicated by temperature effects on diffusion."

Jan 1, 2011

By I. D. Reznik

Results of thermodynamic computations have been presented for reactions occurring in the process of segregation roasting of oxide nickel ores to describe more accurately the mechanism of the process. Under conditions of laboratory-scale roasting in combination with close-circuit flotation flow-sheets and magnetic separation, a recovery of 80-82% of nickel into 8 to 10% Ni concentrate and a recovery of up to 66% of cobalt was achieved. Process conditions have been selected for processing of both high-iron and high-magnesium ores. The feasibility of conversion of 94-98% of nickel and cobalt into solution by oxidizing pressure leaching with sulfuric acid has been demonstrated. It has been substantiated that it is reasonable to introduce double-stage segregation roasting.

Jan 1, 2003

By S. Neven

The smelting of copper anode slimes, a material which contains mostly lead, silver, copper and selenium, has been practiced for many years with a view to recovering the silver and associated small amounts of gold. However, a theoretical understanding of the process has been lacking and this handicaps efforts to improve and intensify smelting operations. In the past few years work has been done in this area and this work will be reviewed in the paper. The underlying thermodynamics of the oxidation of silver-copper selenide mattes has been developed and used as a basis for the construction of a computational thermodynamics model which attempts to predict the composition of all condensed phases during the course of smelting. The model will be outlined and its successes in matching experimental data, as well as its current deficiencies, will be considered. Supporting work on the thermodynamics of silver solubility in slags, on activity-composition relationships in the Ag-Se system and work in progress on the oxidation state of copper in the slags will be reviewed. These projects are designed to provide further detailed data which will improve the robustness of the thermodynamic model.

Jan 1, 1999

By G. G. Richards

The zinc slag fuming process is used to recover zinc from molten iron-calcium silicate slags by treatment with pulverized coal and air. The rate of zinc fuming is controlled by the complex interaction of several kinetic factors including the rate of entrainment of coal in the slag, the extent of the coal-slag reaction and the rate of ferrous oxide oxidation to ferric oxide. This paper briefly outlines the mechanism of fuming and, on this basis, optimization of process parameters is discussed. Modelling analysis and recent industrial trials at Cominco show that coal entrainment in the slag, bath temperature, and bath depth are critical variables affecting process rate and efficiency. The first step in process optimization is to assess coal bypass of the bath. In general, changes which promote operation at a higher temperature, greater coal entrainment in the slag and extended residence time of the coal in the bath increase fuming performance. Coal entrainment is controlled by injection conditions whereas bath temperature is a function of coal combustion and ferrous oxide oxidation. Residence time of the coal is largely a function of bath depth. The implication of model predictions for continuous fuming is shown.

Jan 1, 1994

By Emil B. Milosavljevic

The photochemical reactions of cyanide ion induced by light were investigated in the presence or absence of a titanium(IV) oxide semiconductor photocatalyst. The light sources employed were the sun and arrays of either mercury or fluorescent (cool white) lamps. The results obtained verify that cyanide decomposes much faster when TiO2 is present in the solution and that it is first oxidized to cyanate. However, contrary to the previous studies, it is established that cyanide is subsequently further oxidized via nitrite all the way to nitrate irrespective of the light source. As expected, the rates of the oxidation processes decrease with the illumination source utilized in the following order: Hg-lamps > sunlight > fluorescent lamps. As nitrate is a significantly less hazardous contaminant than cyanide, complete photocatalytic oxidation of cyanide to nitrate may be a viable method for decontamination of cyanide wastes. Contrary to previous claims, we find that cyanide is slowly photochemically decomposed even in the absence of TiO2. For example, with the mercury lamps as the light source, in two hours, cyanide concentration decreases to essentially zero; up to 7% was converted to cyanate and the remainder to unidentified products.

Jan 1, 1992

By Richard H. De Voto

The McDonald Gold Project and two satellite gold deposits near Lincoln, Montana, contain at least 9.9 million ounces of gold and 30 million ounces of silver. The McDonald gold deposit alone contains 7.2 million ounces of gold reserves that can be open-pit mined and processed by cyanide heap leaching at a projected cash operating cost of $190 per ounce. The deposit is predominantly oxidized with no chance of acid production, and can be mined, operated, and reclaimed with minimal permanent environmental disturbance other than the creation of an open pit filled with a fresh-water lake which would support trout. The Seven-Up Pete Joint Venture, the owner of the McDonald Gold Project, commenced permitting of an open-pit, heap-leach operation in November 1994. In 1998, Montana citizens passed an anti-cyanide, open-pit mining initiative, 1-137, which banned any new open-pit gold mine which uses cyanide processing, The Venture has conducted extensive studies, including metallurgical testing of the treatability of McDonald ores with alternative lixiviants, and has determined that all other mining and metallurgical treatment systems are vastly uneconomical in the recovery of gold and silver from the McDonald deposit. Therefore, the Venture's proposed open-pit mining and cyanide heap-leach processing is the only technology that can be applied economically to the McDonald deposit. Further, the analyses convincingly demonstrate that the proposed open-pit, cyanide heap leaching technology results in maximum resource conservation of this valuable and unique deposit and poses far less risk to human health and the environment than any of the alternative technologies.

Jan 1, 1998

By Hsing Kuang Lin

Extraction of zinc from chloride solution with dibutyl butylphosphonate (DBBP) in Escaid 110 has been investigated. The distribution coefficient of zinc was found to be independent of equilibrium pH. This independence indicates that the mechanism of the extraction may be solvation. Slope analysis for the system of dilute zinc chloride solution reveals that two moles of DBBP react with one mole of zinc. A series of tests were conducted to bring DBBP to its full loading capacity and the analysis of the results confirms this stoichiometric factor of 2. Extraction isotherms were established by varying either the AIO ratio or the concentration of zinc in the aqueous feed. Both curves were found to be identical.

Jan 1, 1990

By W. K. Tolley

The U.S. Bureau of Mines (USBM) is currently investigating improved technology for mineral flotation. A variable often neglected in flotation control is redox potential. The use of redox control is illustrated by the separation of molybdenite from chalcopyrite. Laboratory testing showed that redox potential had a greater effect on product quality than collector addition. A significant need in froth flotation is greater reliability of the sensors used in measuring and controlling redox potential in mineral slurries. The USBM has developed an automated method for removing scale and reconditioning gold redox-sensing electrodes. Fouled electrodes are anodically polarized to 1.2 V versus the AglAgCI reference potential to remove scale. The electrodes then are conditioned by a brief potentiodynamic treatment to re-establish electrochemical equilibrium. In laboratory tests, this technique removed calcarious deposits from gold electrodes and reconditioned them for useful service in approximately 10 min. In plant practice, this technique would obviate the need for plant operators to manually polish electrodes, and also should result in greater reliability in redox measurements. Inexpensive, automated equipment to condition electrodes in a plant setting is described.

Jan 1, 1995

By Gerardo H. Achurra

During the last years, the Caletones Smelter, like others copper smelters in the world, has evolved from the conventional, inefficient, pollutant and expensive technologies, to modern, environmentally friendly and efficient ones. For this reason' as well as to improve its competitive position this Smelter shut down the reverberatory furnace, started up two big acid plants and has developed some pyrometallurgical technologies. The main facilities of the Caletones Smelting and Converting Process, in the present and the future, are the Teniente Converters, the reactors with a high operational availability that have reached concentrate top process capacities near to 2,400 tpd. These reactors operate in most of Chilean smelters as well as in other smelters in the world such as in Zambia, Peru and Mexico. Since 2000, the Caletones Smelting and Converting Process, has been adapted in two Teniente Converters, four Slag Cleaning Furnaces and four Pierce -Smith Converters. These facilities, together with the operation of two Fluidized Bed Dryers and two Oxygen Plants have allowed to reach concentrate smelting capacities and copper productions of 1,250 ktpy and 380 kfipy, respectively. Associated to EI Teniente Division Expansion Plan, Caletones Smelter, in the first stage, will increase its capacity to 1,440 ktpy in 2004. In the long term, Caletones has different options, such as the processing of 1,600 to 2,000 ktpy of concentrate, producing anodes, white metal or a mixture of them. These options are connected with CODELCO's Smelters & Refineries Strategic Plan, including Mejillones Project. The main challenges of Caletones Smelter are associated to the development and the consolidation of the Continuous and Environmental Friendly Processes, automation and control of different processes and to the improvement of its leadership between other Copper Smelters in the world.

Jan 1, 2003

By K. R. Robilliard

Ausmelt Technology has been developed to process copper concentrates containing significant levels of lead, arsenic and antimony. A process was developed aimed at smelting these concentrate materials to remove the contaminants to fume and produce a clean copper product. The production of clean copper and the potential economic benefits of this process step over the sale of impure concentrates is discussed.

Jan 1, 1995

By Carla Lupi

Zinc electrowinning from sulfate solutions is the traditional industrial method to produce SHG zinc. Over the past few years several efforts have been done to improve process efficiency in order to reach high productivity with low energy requirement. The latter aim can be pursued both by means of a hard purification of the electrolyte and reducing the anodic voltage. This work is a comparative study of the results obtained in several previous researches on zinc electrowinning from both sulfate and chloride solutions. Zinc electrowinning tests on industrial sulfate solution have been carried out by using Pb alloy anodes and by adding organic depolarizers such as ethanol, acetic acid or ethylene glycol. Experiments on chloride solutions, obtained by purification of zinc exhausted electrolyte, have been performed by using DSA anodes and by testing the effect of additives such as TEACI and TBAC\. Comparing the best results obtained with the two methods it can be highlighted that a high quality zinc is electrowon in both cases with comparable energy requirements.

Jan 1, 2000

By Gerardo H. Achurra

During the last years, the Caletones Smelter, like others copper smelters in the world, has evolved from the conventional, inefficient, pollutant and expensive technologies, to modern, environmental1y friendly and efficient ones. For this reason as wel1 as to improve its competitive position this Smelter shut down the reverberatory furnace, started up two big acid plants and has developed some pyrometal1urgical technologies. The main facilities of the Caletones Smelting and Converting Process, in the present and the future, are the Teniente Converters, the reactors with a high operational availability that have reached concentrate top process capacities near to 2,400 tpd. These reactors operate in most of Chilean smelters as well as in other smelters in the world such as in Zambia, Peru and Mexico. Since 2000, the Caletones Smelting and Converting Process, has been adapted in two Teniente Converters, four Slag Cleaning Furnaces and four Pierce Smith Converters. These facilities, together with the operation of two Fluidized Bed Dryers and two Oxygen Plants have allowed to reach concentrate smelting capacities and copper productions of 1,250 ktpy and 380 kftpy, respectively. Associated to El Teniente Division Expansion Plan, Caletones Smelter, in the first stage, will increase its capacity to 1,440 ktpy in 2004. In the long term, Caletones has different options, such as the processing of 1,600 to 2,000 ktpy of concentrate, producing anodes, white metal or a mixture of them. These options are connected with CODELCO's Smelters & Refineries Strategic Plan, including Mejillones Project. The main challenges of Caletones Smelter are associated to the development and the consolidation of the Continuous and Environmental Friendly Processes, automation and control of different processes and to the improvement of its leadership between other Copper Smelters in the world.

Jan 1, 2003

By S. P. Mathew

The ISASMELT Lead Process is a continuous two stage process for the production of crude lead from concentrate. It is based on the use of a top entry submerged Sirosmelt lance to produce turbulent baths in which high intensity smelting or reduction reactions can occur. The process involves oxidizing the concentrates in the first stage to produce a high lead slag. This slag is tapped continuously and transferred down a launder to a second furnace where it is reduced with coal. Crude lead and discard slag are tapped continuously from this furnace through a single taphole and separated in a conventional forehearth. Process and engineering design work for a commercial scale Lead ISASKELT plant designed to produce 60000 tpa crude lead has been completed. This plant is planned to be operational in 1991.

Jan 1, 1990

By Oscar Jaime Restrepo, Juan Camilo Restrepo, Jorge Ivan Tóbon

Portland cement is obtained by a conventional synthesis process from a mixture of limestone and clay at high temperature (1450 °C). This work reports the possibility to obtain cement silicates via alternative methods like Solution Combustion Synthesis (SCS), which optimize both time and temperature, and the consequences to energy efficiency and mitigation of CO2 emissions. The production of one ton of cement emits between 0.62 and 0.97 tons of CO2 into the atmosphere. In this process the CO2 emissions are between 21 and 59%. The combustion methods are chemical redox processes in which, at high temperature, a self-sustaining and fast wave is generated from using chemical precursors and organic fuels.

Jan 1, 2016

By Ma Lijuan, Zhang Yubing, Wang Bo, Sun Huilan

The effect of lime ratio on phase composition and alumina leaching property of MgO-contained calcium aluminate clinker were investigated by analytical reagent, the XRD analysis of its mechanism was discussed. The results showed that: when the sintering temperature was 1350 ℃, C/A was 1.4, A/S was 1.3 and the content of MgO was 4%, the increase of the C/A promoted the formation of C12A7 and restrained the formation of Q-phase. The alumina-leaching ratio of the clinker (A/S was 1.3) was increased from 74.33% to 91.34% when the content of CaO was 5.21%.

Jan 1, 2015

By Robert H. Hsu

Palladium finely dispersed in a substrate of kieselguhr, Pd/k for short, has been successfully used for hydrogen storage, separation and pumping for a number of years at the Savannah River Site (SRS). Recently SRS has developed a new pd/k flow through bed (FTB) prototype for separating hydrogen from other gases and simultaneously storing the hydrogen on palladium. The FTB uses single-pass liquid nitrogen cooling during hydrogen absorption/separation/storage and electrical heating for desorption/unloading of hydrogen. Fourteen absorption-desorption or loading/unloading cycles using hydrogen have been conducted with the new FTB prototype. Test results show that all design performance objectives have been successfully achieved: recover 295% of hydrogen gas from feed gas, produce 99.9% hydrogen product gas and < 5% hydrogen in discharge gas. This paper will discuss characteristics of the palladium-coated kieselguhr or diatomaceous earth, design and operation of the FTB, and results of performance tests such as separation efficiency, hydrogen storage capacity and system heat transfer characteristics.

Jan 1, 2002

By W. F. Ranson, R. C. Progelhof

"I. THE PROBLEM: MANUFACTURING PRODUCTIVITYThe 1985 President's Commission [I] on Industrial Competitiveness found compelling evidence of the declining economic position of the United States in world markets. The annual rate of increase in the United States productivity is approximately one-seventh that of our major trading partners over the last decade: profit levels in manufacturing investments are below those of the mid-1960's; an increasingly negative trade balance since 1971; and a sharp decline in the United States share of world trade in manufactured goods for more than two decades. A particularly dramatic example of the shifting economic balance is the fact that Japanese productivity growth has been five times greater than that of this country since 1960. In face, Japan's productivity now exceeds that of the United States in such critical industries as steel, transportation equipment, electronics and electrical machinery.American employees have experienced the competitive consequences of this nation's lagging industrial performance. Between 1980 and 1984 alone, the population of non-farm employees engaged in manufacturing dropped from 22.4% to 20.6%. This reduction in manufacturing must be arrested.Commissions RecommendationsThe comprehensive set of recommendations offered by the President's Commission recognized the nation's ""key competitive advantages"", technology and human resources, and calls for their strengthening. Particular emphasis is placed on manufacturing technology and the fact that this country does not translate research into new technologies rapidly and fully.""Perhaps the most glaring deficiency in America's technological capabilities has been our failure to devote enough attention to manufacturing or 'process' technology. It does us little good to design state-of-the-art products if within a short time our foreign competitors can manufacture them more cheaply. The United States has failed to apply its own technologies to manufacturing. Robotics automation and statistical quality control were all first developed in the United States but in recent years they have been more effectively applied elsewhere""."

Jan 1, 1988

By Andrzej Warczok

Intensive smelting of copper concentrate in Teniente Converter (CT) leads to the production of high grade matte and highly oxidized slag. Smelting slag is processed in Teniente vascular slag cleaning furnace. The slag composition and forms of copper affect the slag cleaning process and final copper content. Converting of high grade matte in Pierce-Smith converter faces some difficulties in proper slagging of iron oxides. Overblowing in copper making stage allows for slag liquidation but leads to high content of copper oxide in converter slag. Converter slag recycling into CT results in the increase of the participation of oxidic copper. Separate treatment of converter slag and its impact on the forms of copper in CT slag has been analyzed. Thermodynamic properties of a system and kinetic limitations pointed out the negative effect of converter slag recycling on the forms of copper and copper recovery in slag cleaning stage. Experimental results of slag cleaning tests in a crucible scale as well as microscopic examination of laboratory and industrial slag samples supported the above analysis and permitted to formulate recommendations of separate processing of converter slag. Keywords: copper, losses, slag, recycling

Jan 1, 2001