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By Michael J. Nicol

Growing environmental and occupational safety concerns about the use of cyanide in gold processing has increased the interest in more acceptable alternatives. The most likely of these is thiosulfate. However, the thiosulfate process lacks a proven in-pulp method of recovering the dissolved gold, because activated carbon is not effective for the absorption of the gold thiosulfate complex .. Anion exchange resins do offer a possible route for in-pulp recovery. This paper describes work aimed at the evaluation of the effectiveness of commercially available anion exchange resins for the recovery of gold from thiosulfate leach liquors? and pulps. It has been found that strong-base resins are superior to weak-base resins in that they have a larger capacity, which assists in reducing the competition from other anions within a leach solution. Further studies with a selected commercial strong-base resin have shown that competing polythionateanions (particularly tri-and tetrathionate). Lower the maximum possible gold loading but that gold is selectively recovered over other base metal anions in solution. Kinetic experiments found that while? competilig anibns did not affect the initial rate? of gold loading it was important to minimise the contact time of the resin in solution so to prevent displacement of loaded gold by competing anions over longer times. A small-scale resin-in-pulp plant investigation showed gold can be recovered from a leach pulp by a strong-base resin to yield gold loadings of 3000 mg/L, barren pulp containing less than 0.05 mg/L of dissolved gold and. copper loadings of 500 mg/L. Loaded copper was displaced gold and at a loading of 2000 mg/L gold the copper loading was minimal «500 mg/L). The resin was found to recover gold adsorbed on the solids that would, otherwise have. reported to tails if a solid/liquid separation method were used. A patented two-step elution process in which copper and then gold are separately eluted from the resin is also discussed.

Jan 1, 1998

By C. Geenen

At its Olen site, Union Minière Copper operates a new full-size deposit tank house. A first 200,000 t/y module was commissioned in October 1996, and an additional 130,000 t/y unit started in April 1998. The main objectives of the new tank house project were to produce grade A cathodes starting from anodes with a wide range of compositions and at a minimal operating cost. The tank house uses Isa Process technology. Based on the process parameters agreed upon with MIM, UM Copper developed the basic design and UM Engineering was the in-house contractor for the engineering. The new tank house is equipped with advanced technology polymer concrete cells, automated two-bale cranes and high-capacity machines. The first 200,000 t/y module treats anodes with a more conventional composition at 330 A/m2; the second 130,000 t/y module treats anodes with a high slimes fall (12- 13 kg/t) at current densities up to 285 A/m2. After some teething problems, the new tank house is meeting all set targets. This paper illustrates and comments on the design characteristics and operational results.

Jan 1, 1999

By R. H. Crist

Reactive components of algal cell walls include uronic and alginic acids: In addition, many marine species have half ester sulfate groups which function as fixed anions. Associated metals vary with the media, eg., Ca and Mg in fresh water (FV) and Na, Ca, Mg in seawater. . These metals readily exchange with aqueous phase protons or metal cations. A plot of the total amount of metal cations displaced by protons vs .. pH shows one inflection at pH 4 for FV algae and' in addition a second inflection at pH 2, 3 for marine algae. The first inflection is interpreted as. Indicating the cations associated with carboxyl groups ,and the ,second with half ester ?Sulfate groups. The exchange capacities of various aigal ,species vary widely. When FV algae is placed in a Pb2+ solution,- the amount of Pb2"' deposited on the algae is. Equivalent to the. Total Ca2?, Mg2, and H+ displaced? thereby confirming the ion exchange mechanism. Ion exchange equilibrium constants are reported for the displacement of ca2+ from Vaucheria. With Mg2+, sr2+, Cd2+, Pb2+_ and Na+ as well as the reverse reactions. Cd2+ can .be removed partially from algae by precipitating it as CdS or Cd(OH) 2 Pb2+ and Cu2+ are also partially removed as the hydroxides. Rates of reaction for various alkali hydroxides decrease with increasing .unhydrated cation radius. It is concluded that theory is useful in predicting viable applications for algae in pollution abatement.

Jan 1, 1991

By Li Kaihua, Li Liang, Miao Qingdong, Wang Cong

The current process of production of titanium sponge involves the use of TiCl4 as a feed material and a huge amount of heat is generated during the magnesiothermic reduction process. For this reason, it is possible to agglomerate into a titanium lump with the partial high temperature. And, it is difficult to obtain soft titanium sponge with low content of impurities. In order to solve the current problems in the titanium sponge production process, process optimization experiments study of TiCl4 feeding speed, vacuum distillation temperature, system pressure and time control had been conducted for obtain high quality titanium sponge. Experimental results show that lower feeding speed can improve the output capacity of titanium sponge and softer products can be obtained. The product grade rate of titanium sponge improved significantly.

Jan 1, 2015

By Joseph Bloch

The hydriding of bulk metals and alloys is a gas-solid reaction in which a hydride product layer is initially nucleated adjacent to the gas-solid interface and continues to grow until a complete transformation of the parent (a) phase into the hydride phase. The combination of measurements of the overall hydriding kinetics of samples having defined shapes and dimensions, together with examinations of partially hydrided samples, enables the presentation of the reaction rate in terms of an appropriate reaction model. A common and important type of topochemical development of the hydride in bulk metals and alloys involves a hydride layer formed on the metallic surface. The continuity of the layer can affect the reaction rate. The rate of hydrogen absorption in a sample, in the presence of a hydride layer, is usually analyzed using a model combining several sequential steps in which the hydrogen is transferred from the gas phase into the reaction site. Coupling the flux equations across the layer under proper steady state conditions, results in a complex rate equation in which the steady state rate of hydrogen absorption (proportional to the hydride layer velocity) is expressed in terms of the pressure, temperature, the rate constants of the sequential steps and the critical concentrations of hydrogen in the hydride. Generally, the rate constants of the individual microscopic processes are comparable in magnitude, so that the overall rate is not controlled by any of the specific sequential steps. However, there are two limit cases related to the first stage, the adsorption, for which the general rate equation is much simpler, namely, the fast and the slow adsorption approximations. Using this limit cases, equations are derived for the steady state hydriding rate of a given system. These equations provide means to anticipate the pressure dependence of the steady state absorption rate under low pressures, close to Peq and under very high pressures. At the low pressure regime both the fast and slow absorption cases yield linear pressure dependence. For the very high pressure range, it is found that the rate become independent of the applied pressure. The rate is given then by a combination of the individual rate constants of the system and the critical hydrogen concentrations. The model is shown to apply in several real cases, such as ZrCo, LaNi5 and titanium.

Jan 1, 2002

By Kevin L. Gering

A detection method and apparatus have been developed to perform real-time measurement of aqueous free cyanide, C-. A laboratory prototype can measure cyanide ranging from 5 micrograms ,per liter to 100 milligrams per ?liter for analysis times as short as 2 minutes per measurement. Sample size per measurement is typically only a few mI, thus? minimizing the waste volume produced from spent samples. The basis for this detection device is a quantifiable, stable affinity between the electrode material and free cyanide in the sample; The electrode exhibits piezoelectric behavior, allowing it to be used as a microbalance. This technology 'has experienced two generations of laboratory prototypes, and has been thoroughly tested to determine the operational sensitivity toward process variables such as pH, competing reactions, etc. The speed and ,accuracy of this method make it superior to conventional wet chemistry methods used for quantifying cyanide levels in water. A device based on this technology could be useful in areas involving process monitoring and environmental compliance, .particularly in the cyanide-based leach mining industry. Interest for this detector has been shown by the gold mining industry and others. Patent application is in progress.

Jan 1, 1998

By James A. Voigt

"The efficient separation of metal species from aqueous streams by precipitation techniques requires a fundamental understanding of the various processes that occur during precipitation. These processes include particle nucleation, particle growth by solute deposition, agglomerate formation, and agglomerate break-up. The application of the population balance approach has been used to develop a kinetic model that accounts for these competing kinetic processes. The usefulness of the model is illustrated through its application to the precipitation of yttrium hydroxynitrate, YHN. The kinetic parameters calculated from the model equations and system specific solution chemistry are used to describe several aspects of the effect of pH on the precipitation of the YHN. Implications with respect to the simultaneous precipitation of more than one cation type are also discussed through use of example systems. The effects of solution chemistry, precipitator design, and solvent choice are considered.IntroductionThe application of precipitation technologies to the separation of metals from solution is widely used. Regardless of its application, be it in such diverse areas as the preparation of metal oxide powders for use in commercial products or as a unit operation in the removal of trace metals during wastewater clean up, the fundamental processes involved are the same. These processes include: nucleation from solution, either homogeneous or heterogeneous; growth from solution with chemical reaction either in solution or at the precipitate/solution interface; growth by particle agglomeration; and particle break-up by collisional or shear forces. The effectiveness of the operation and the properties of the precipitate formed, or ""quality"" of the product, are determined by the competing kinetics of the different processes. The kinetics of the processes, in tum, are determined by system-specific solution chemistries and the conditions used to carry out the precipitation operation. For example, generally, when system conditions are such that the supersaturation driving force for precipitation is very high, growth species normally do not have the time to organize themselves with a high degree of crystallographic order and the precipitate is amorphous. In this case nucleation rates are invariably extremely high and the primary mechanism for growth is the agglomeration of nuclei. Conversely, when the supersaturation levels for the same system are reduced, the kinetics of the nucleation and growth processes also are greatly reduced, and a crystalline precipitate can be formed, since the growth species have time to order on particle surfaces."

Jan 1, 1996

By A. J. Paul, K. O. Yu

"Today, foundries are moving towards the use of models and design tools to gain a competitive advantage in producing castings of high desired quality. This leads to a growing alliance between foundries, software developers and researchers seeking to model, visualize and understand the phenomena taking place during the casting process. In addition, there is a need to develop affordable techniques to produce parts in small lot sizes. This leads to the development of a Flexible Manufacturing System consisting of: (1) up-front computer-aided engineering; (2) computer integrated proto typing with solid freeform fabrication; and (3) fabrication of the actual mold and related equipment to cast the part.This paper discusses some of the developments that are taking place today in the areas of modeling the physical phenomena during the casting process as well as towards developing a Flexible Manufacturing System for producing cast parts. Areas that require most work involve prediction of defects and mechanical properties using simplified analyses. In addition, electronic data sharing for collaborative engineering between geographically dispersed team members is also discussed. Case studies are presented showing successes as well as failures.IntroductionCasting, one of the oldest forms of metalworking, has recently seen a flurry of developments in the area of solidification modeling. These developments have come about after the realization that, in order to stay competitive, foundries need to reduce their scrap rate and production costs, and increase casting quality. Even though this is not new knowledge for foundry engineers, the tools to help them achieve this goal are just being developed and put in place for use by foundries. Several state-of-the-art software packages are currently available to analyze the solidification behavior in complex shaped castings. These packages make use of several different approaches for solving the various problems associated with casting processes. The overall architecture of a comprehensive solidification modeling system is shown in Figure 1."

Jan 1, 1994

By Thomas E. Weyand

Prior to 1975, lead-based paints were commonly used in protecting steel structures. Because of the toxic effects of lead on human health and the environment, their use has been significantly reduced. However, problems with these paints persist when they are removed during normal maintenance by pneumatic blasting with mineral abrasives. Technologies are developed to contain the spent abrasive and paint during blasting operations. This paper reports on A study to identify beneficial reuses for the spent blasting material. Nine samples were gathered from different projects within Pennsylvania. The samples were thoroughly characterized with regard to composition, morphology, and EP and TCLP leach test performance. Potential reuse applications will be reviewed with regard to technical adequacy, economics, and environmental constraints.

Jan 1, 1992

By M. L. Apel

A conceptual approach to the bioremediation of uranium mill tailings (UMT) is presented., This approach focuses on, biosorption to remediate the. effluent solution and bioleaching remediate the. solid fraction. Comparative biosorption studies were performed with synthetic single metal solutions using a commercially available biopolymer. The maximum rate of metal sorption by calcium alginate was found to be 5.43, 6,39, 6.48, and 9.74 mg dm-3 min-1 for U022*, Ba2+, Cd2+ and Zn2+, respectively. Activation energy (AEa) for barium uptake by calcium alginate beads was determined to be 11.5 kJ, indicating a diffusion controlled reaction mechanism. Thermodynamic values (AG+ AH+ and ASt) of the metal-alginate activated complex, as reported in the literature, were found to be in agreement with those calculated from this research. Results show that this biopolymer can be effectively applied in the removal of select metals prevalent in uranium mill tailing effluents and associated waste streams.

Jan 1, 1991

By Roy J. M. van Lier

In industrial aqueous solutions, germanium generally occurs in trace amounts amid high concentrations of other metals, such as zinc, copper and iron. Separation of germanium from these metals as well as its isolation from gallium and indium pose a real challenge to the hydrometallurgist. After a brief discussion of the aqueous chemistry of germanium, this paper reviews the flowsheet of the Apex Mine in Utah. The Apex property was the only mine in the world to be operated primarily for production of gallium and germanium, but apparently closed due to great operating difficulties. Several process variants proposed for the treatment of the Apex ore, including bioleaching methods, are addressed. Following a more general description of the behavior of germanium in hydrometallurgical zinc processing streams, available technology for its recovery from aqueous solutions is summarized. Precipitation, solvent extraction, ion exchange, electrowinning, ion flotation and liquid-membrane separation are all outlined in terms of the aqueous chemistry of germanium. Finally, the production of high purity germanium dioxide and metal is briefly discussed

Jan 1, 1995

By C. O. Bounds

Management of emission control dust from electric? arc furnace (EAF) steelmaking as an RCRA-EPA listed hazardous waste places economic and environmental pressures on the steelmaking industry. Horsehead Resource Development Company, Inc. (HRD) serves the industry by recovering nonferrous metals from the dust in rotary kiln plants in Palmerton, PA and Chicago, IL, and has demonstrated the commercial viability of its patented coal-fired FLAME REACTOR Process. However, because of location and/or regulation, many steelmakers could be more economically served via on-site processing of its dust. Therefore, in 198-7, through a contract with the Gas Research Institute, HRD embarked on a program to develop a gas-fired reactor and test a prototype unit. The development program has successfully proven the environmental, technical and economic performance of the concept. Consistently high zinc, lead and cadmium recovery to an oxide concentrate as well as production of a nonhazardous, delistable slag have routinely been achieved. The gas-fired FLAME REACTOR field experiment results and the economic performance of on-site or smaller regional plants will be highlighted.

Jan 1, 1990

By James M. Fragomeni

"The mechanical behavior of an Al-Li alloy was studied and related to the extrusion processing parameters, the plastic metal flow during defonnation, the anisotropy, and the microstructure. The extrusion temperatures, strain rates, extrusion ratios, billet temperatures, and extrusion geometries were varied during processing and correlated with the microstructure and properties. The extrusion processing variables were related to the mechariicar behavior, anisotropy, and microstructure through the ZenerHollomon parameter i.e., the temperature compensated strain rate. Based on optical and electron microscopy studies it was found that regardless of the extrusion conditions, the various microstructures for the most part were unrecrystallized for both the as-extruded and the solution heat-treated conditions. Smaller grain sizes were correlated to larger Zener-Hollomon parameters. The extrusion temperature and ratio did not significantly affect the strength or ductility as did the section geometry, which had a large affect on these mechanical properties. The anisotropy of the properties varied substantially when comparing the extruded longitudinal versus transverse grain orientations.IntroductionThe extrusion process also has a substantial influence on: the microsfructure and mechanical properties of a material that is Athens, Ohio, 45701 fonned The plastic defonnation that occurs during the extrusion process alters the grain size, crystallographic texture, anisotropy, subgrain size, dislocation density and various other microstructural features. Often the material being extruded is not homogeneous, therefore variations in the microstructure and properties occur across the cross-section of the final extruded product. The mechanical properties and microstructure can also vary with length since it is hard to maintain a constant temperature throughout the extrusion process. The extrusion temperature often varies from the heat generated during the extrusion process. The demonstration material that was extruded for this .study was an aluminum alloy containing 2.6wt, % lithium and 0.09wt.% zirconium. This alloy was strengthened by heat treatment causing nucleation, growth, and coarsening of coherent metastable o' (Al3Li) precipitates in the microstructure. The ? precipitates which are a consequence 9f artificially aging the AlLi alloy, are spherical, ordered, and coherent with the aluminum matrix and impede the dislocation glide inotion during plastic defonnation. Theo particles grow homogeneously in the matrix, and have the Cu3Au (L 12)"" superlattice crystal structure. Aluminum-lithium alloys are used primarily for aerospace structural applications since they have attractive properties such as a lower density and higher elastic modulus than conventional 2XXX and 7XXX alloys."

Jan 1, 2000

By Takashi Nakamura

Dismantling and detachment of parts from e-scrap are essential and involve higher cost techniques in pretreatment processes for physical separation. New techniques are desired for effective recycling of minor rare metals, therefore, we are trying to develop new detachment processes such as a new break down process. The principal of this new process is an electrical disintegration by electric pulse. E-scrap is broken down by high voltage electric pulses in water. IC chips and LSI can be detached from printed circuit boards under proper conditions. Ta- capacitors are also broken down to plastic parts and Ta sinter with lead wire. This is very useful in terms of pretreatment for e-scrap recycling. Also in the case of metallurgical production, with its intrinsic potential of smelting, extraction, enrichment and separation methods, play an important role in the context of minor rare metals.

Jan 1, 2015

By Abbas H. Mirza

Arsenic and selenium are found in low quantities together with other metals in several nonferrous metallurgical process streams such as scrubber blowdown solution, acid plant wastewater, gas cleaning plant water, etc. Normally, the other metals in these streams are present as cations and can be precipitated by conventional lime treatment and sulfide polishing. However, arsenic and selenium are invariably present as anions, AsO33-and AsO43 in the case of arsenic and SeO32 and SeO42 for selenium. Conventional lime treatment removes most of the arsenic, but it does not remove selenium. The present paper reviews the processes and technologies developed to date on the removal of arsenic and selenium from metallurgical process streams.

Jan 1, 1996

By Agnes Y. Lee

he U.S. Bureau of Mines developed a method to treat lead-contaminated soil and ebonite battery casing wastes to produce a nonhazardous material. The cleanup procedure involves wet screening to separate a minus 18-mesh soil fraction; removal of metal1ic lead, rocks, wood, etc. ; carbonation to change lead sulfate to acid-soluble lead carbonate; size reduction; acid leaching; and rinsing. The casing wastes undergo size reduction and washing to remove the lead sulfate sludge before carbonation. Similarly, the minus 18-mesh soil is carbonated, then acid leached and rinsed. In leaching, fluosilicic acid (H SiF,) and hydrogen peroxide (H20,) are used to dissolve lead compounds. An electrowinning method is employed to strip lead from the lead-rich leachate. The acid content in the leachate is replenished with fresh H,SiF, acid prior to recycling. Treated casing wastes and soils pass the Toxicity Characteristic Leaching Procedure (TCLP) test and can be reclassified as nonhazardous materia1s. Based on this process, a conceptual pilot plant has been designed which will be demonstrated on wastes from two Superfund sites.

Jan 1, 1993

By R. W. Bartlett

The extensive central Idaho black sand placer deposits are a potential source of rare earth elements, particularly the heavy rare earth elements that are not prevalent in commercial bastnasite deposits. These placers derive from the Idaho batholith. The geology, occurrence, and extent of these deposits are reviewed and the diverse mineral assemblages and complex mineral chemical compositions of these sands are described. Niobium, yttrium and thorium are also present in significant concentrations. The results of prior mining practice, including concentration and separation of the heavy minerals are reviewed. Technical approaches to extraction of rare earths from Idaho black sand concentrates are discussed.

Jan 1, 1992

By Joel A. Huffinan

"This presentation is being given to better inform the audience of the dependability of precious metal analysis by fire assay. A brief explanation, however, of standard fire assay exploration procedures will be given. An overview of other types of analyses by fire assay will be discussed as well, and the operation of a modern day assay laboratory.IntroductionThe use of lead oxide for the fire assay process dates back to the finds in Troy II and the Cappadocian Tablets about 3,000 B.C. Some advances have been made in the basic procedures due to instrumentation and electronics, but the fusion and cupellation procedures used in fire assay remain much the same as during this period.In 1600 AD. Agricola was the first to take a scientific approach to fire assay recording methods and procedures used (Hillerbrand and Allen, 1905) [1]. Since this period, much of the recognized research into the analysis of ores and metals was carried out in the late 1800's and early 1900's prior to World War II, and again after the deregulation of precious metals. The renewed interest in precious metals mining and metallurgy are due much to advances in precious metals heap leaching in late 1970's."

Jan 1, 1999

By M. K. Mohan

Lead recovery from process solutions contributes not only to the conservation of resources but also clean environment. Zeolites are natural aluminosilicates, which finds applications as catalysts and in wastewater treatment. In the present investigation, studies were taken up on the processing of Pb from process solutions by zeolites. Effects of pH of the solution, time and type of zeolite viz. chabazite, mordenite, erionite and clinoptilolite on the removal of Pb from solutions was investigated. Rate of sorption was found to depend on the pH of the solution and about 99 pct. recovery was observed at pH 6. Optimal conditions were established for the maximum recovery of lead from process solutions. Possible sorption mechanisms were proposed. The calculated adsorption constants calculated from Langmuir and Freundlich equations showed that the adsorption of lead on chabazite was strong.

Jan 1, 1999

By Robert Hanson, Mayur K. Patel

"Pneumatic conveying pipelines are used throughout a variety of industries, from food processing/packing to power generation plants, as an efficient means of transporting materials between storage and processing points. In general, different phases of pneumatic conveying exist when material is conveyed from point A to point B in a pipeline. This depends on the operating pressure and the material conveyed. Lean phase conveying exists when pipelines are operated at high airflow rates, relatively low pressures, inducing sufficient turbulence for particles to become entrained in the air stream. Thus, particles are conveyed along the pipelines at velocities in the range of IS-2Sm/s. Generally, the initial capital costs for lean phase system is low, however the running costs are high. The opposite is true for dense phase, high-pressure systems. In considering either conveying system, it is important that the rate of erosion of the pipeline be considered when designing such a system, since it is the rate of erosion that dictates the lifetime of components. In general, the high level of erosion occurs for lean phase flows, where high impact velocity contribute substantially to the rate of erosion as well as other processes such as particle breaking, if the particles are friable. This would lead to poor quality of material, not normally desirable. On a positive note, the process of erosion is used in other applications, which benefits from this process, e.g. abrasive guns.The failure, by puncture, of pneumatic conveyor bends in industry causes several major problems. Two of these are: (a) escape of the conveyed product causing health and dust hazard and (b) repairing and cleaning up after punctures necessitates shutting down conveyors, which will affect the operation ofthe plant, thus reducing profitability.The paper reports on modelling strategy used in the development of a modelling framework and the initial validation phases of the models incorporated within. The modelling framework encompasses Computational Fluid Dynamics (CFD) related engineering tools, based on Eulerian (gas) and Lagrangian (particle) approaches, to represent the two distinct conveyed phases, to represent the erosion process which is used to ascertain the lifetime of conveyor bends."

Jan 1, 2001