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By J. Zou

With the increasing applications of the Chinese metal magnetic liners, the requirement for their technical specifications has become stricter and stricter. It is necessary to deeply analyse the metal magnetic liners in order to improve their reliability and economics. The key issue of metal magnetic liners is magnetic forces: their attractions to mill shell and protection layer. Mathematical models were developed using finite-element analysis software and systematic simulation analyses of the two most critical indexes of magnetic liners were performed to find out the most important parameters and their effect on the liner?s characteristics. The relationships between magnetic forces and installation gaps, thickness of permanent magnets and thickness of protection layer may be used to guide the design of metal magnetic liners for ball mills in order to achieve good economic indexes.

Jan 1, 2014

By Martin Rudolph

"Flotation is without a doubt one of the major processes for the separation of fine minerals and it has been applied for more than a century. A key task of a successful flotation separation is to find the proper chemical treatment to selectively hydrophobize and thus float a certain mineral phase using molecules or ions referred to as collectors, depressants, regulators and frothers. Commonly floatability is determined by microflotation tests using the Hallimond tube with pure mineral phases. This method however requires the pure mineral phase which is very often not even taken from the same deposit which is going to be processed. In this paper we present a new approach to in-situ determine and even map the floatability of finely disseminated mineral phases within cross-sections of an ore. It is based on measuring hydrophobic effects using colloidal probe atomic force microscopy with a hydrophobic polystyrene probe based on force spectroscopy with a lateral resolution of only a few nanometers. Coupled confocal Raman spectroscopy on the same locality enables the identification of the mineral phase. We present the working principles of the method and show which signals in the force spectra characteristic for hydrophobic interactions can be used to define floatability and which can then be mapped as single quantities, e.g. jump-into-contact events due to nanobubble occurrence or parameters of the long range interaction curves most probably due to capillary effects. A finely grained silicate ore containing the valuable rare earth mineral eudialyte from southern Sweden as well as pure samples of magnetite are presented as substrates to demonstrate the capability of this new approach. This method will not only help to find the proper flotation chemistry but it can furthermore help in researching and unravelling problems of floatability within similar mineral phases."

Jan 1, 2014

By Rodolfo Silva, Antonio Peres, Afonso Martins, Gilberto Ramalho, Mario Cabello

The consumption of aggregates in civil construction has increased considerably in Brazil for the last years. The extraction of sand and gravel generates significant environmental impacts. As the quarries and sand deposits are getting exhausted near the big cities, the price of aggregates is increasing. Meanwhile, the extraction of quartzite (dimensional stone) in the state of Minas Gerais has been done mostly in small quarries, with very low recovery, generating approximately six million tons of wastes a year, which causes pollution, increases final prices of products, decreases the life time of quarries and ends up in the closure of enterprises. The government agencies and the quarries’ owners understand that only by finding applications to wastes there will be development to the sector. The aim of this investigation was to study the application to the quartzite wastes as aggregate in the civil construction. Samples of quartzite wastes collected in a quarry were characterized by petrographic analyses. Laboratory tests of crushing and grinding were done to analyze the viability of reducing the size of coarse material to a finer one to be used as raw material in industrialized mortars and concrete pre-molded components.

Jan 1, 2014

Calcium sulfate whiskers are considered to be a prosperous reinforced material in application due to their high mechanical properties. But the hydration occurs easily at moist atmosphere or in aqueous solution. The surface topographies of the calcium sulfate hemihydrate whiskers and the hydrates were analyzed by on-line observation and using XRD. The results indicated the transformation of the crystal type and shape of calcium sulfate hemihydrate whiskers and the reduction of whiskers? aspect ratio. The hydration process of the calcium sulfate hemihydrate whiskers and the effective parameters were further discussed based on FT-IR measurements. The conclusions were obtained that the hydration of calcium sulfate hemihydrate whiskers can be divided into the three phases, namely, initial hemihydration phase, dehydration phase, and coarsening, dissolving and the re-formation of calcium sulfate dehydrate crystal phase. In addition, it was found that in the hydration process of calcium sulfate hemihydrate whiskers the calcium sulfate dihydrate whiskers are formed at first and then converted into the calcium sulfate dihydrate with different crystal shapes, but in the hydration of gypsum hemihydrate the gypsum dihydrate is formed without transition products. The surface active site-calcium ion which has strong trend to react with H2O, the surface ?OH and the inner channels are considered to play important roles in the hydration process of calcium sulfate hemihydrate whiskers.

Jan 1, 2014

By Saeed Farrokhpay

It is known that the grinding condition has a major effect on the beneficiation characteristics of the minerals in subsequent processing, in particular, flotation. In the flotation process, particles surface and their condition can significantly influence collector adsorption and flotation performance. For example, particle shape and its surface roughness occurred during grinding may influence flotation characteristics of a specific ore. In fact, adsorption of different cationic and anionic species on mineral surfaces can be varied depending on the selected comminution procedure. The flotation performance of sulphide minerals can be detrimentally affected by the surface oxidation. The amount of surface oxidation may reduce the hydrophobicity of the mineral and makes adsorption of collectors less selective. Improved liberation may generally result in improved flotation recovery. However, this may result in finer grinding and slimes, and consequently, reduce the overall flotation recovery. This paper discusses the effect of wet and dry grinding on copper flotation of a complex Cu-Pb-Zn ore. Industrially, wet grinding is preferred due to its higher energy efficiency and owing to downstream processing requirements. In this study, series of flotation tests were conducted,and surface analysis (XPS and ToFSIMS) were performed after wet or dry grinding at two different P80 values. Mineralogical study was also conducted to investigate the liberation of valuable minerals after grinding. A higher copper flotation recovery was found for wet grinding. However, the copper recovery was increased by further grinding in both conditions (wet and dry). The results showed a higher collector adsorption on copper mineral surfaces after wet grinding. The surface analysis also revealed that the ore is slightly more oxidized after dry grinding probably due to higher temperature during dry grinding.

Sep 1, 2012

By K. Price, G. Wang, L. R. Moore, Y. R. Xiong, J. Gu

"Sand is a naturally occurring granular material that is a result of the physical or chemical breakdown of rocks. Raw/natural sand contains various minerals, and it is this combination of minerals that brings the value to the construction aggregate industry. However, it is the quartz component of sand that is valued in its application as industrial silica in glass, high purity quartz, foundry sand, and oil and gas fracturing. Depending on the industry, the grade requirements can be the concentration of SiO2, particle size or shape, as well as contaminants such as the heavy refractory minerals, clays, fines, and alkali metals. With the ever declining mineral feed grade, processors continue to face challenges making the industry specific concentrate grade. As such, it becomes more important to tailor make the processing reagents to fit the mineral, processing conditions, and desired quality specification. This paper focuses on the application of novel collectors towards the beneficiation of sand for each of the major industrial silica applications. INTRODUCTIONQuartz is a mineral composed of a framework of silicon and oxygen atoms. It is the second most abundant mineral in the Earth’s continental crust. There are many species of quartz, which are defined by the particle size, shape, and color. Silica sand is one of those species, which is the byproduct of the physical or chemical breakdown of quartz containing rocks or crystals. Geologist define silica sand as a silica mineral with a particle size between 0.05 and 2 mm in diameter (Zdunczyk, 2001). Silica sand has significant value to society in recreation (beach sand and toy boxes), construction aggregate (concretes and asphalt), industry (iron & steel casting, fracturing proppants, and glass), as well as specialty products such as semiconductors or silicon wafers used in electronics.The aggregate business is the dominant consumer of silica sand products. Conversely, glass making, foundries (casting material), abrasives, and fracturing proppants are the dominant applications for industrial silica sand. Not much beneficiation is required for sand products going into the construction industry, other than sizing and scrubbing to remove clay. However, the industrial silica sand applications are dependent on particle size, shape, and degree of contaminants, which sets the market value (table 1). Therefore, as the more specialty products are produced, more sophisticated techniques and chemistry need to be applied to ensure the appropriate quality is met."

Jan 1, 2018

By J. Ma

Vanadium ore is widely distributed in black rock series (Fan, Zhang and Ye, 2004) in many provinces of China, which accounts for 87% (Zuo, Peng and Dugang, 2001) of vanadium reserves in China. In Cambrian black rock series in south Qinling Mountain, there are large or medium-sized sedimentary deposits such as Zhongcun vanadium deposit, Yinhua vanadium deposit, Qianjiaping vanadium deposit, Xiajiadian gold-vanadium deposit and Lengshuigou vanadium deposit. The vanadium is distributed in other minerals mainly in the form of isomorphic replacement. These types of ore are characterized by no independent vanadium mineral, low grade and vast reserves. Now in China the vanadium extraction technology is backward with low utilization rate of resources. The difficulties of vanadium extraction from black rock series are that the enrichment by means of mechanical beneficiation is difficult; the cost of direct chemical extraction is high and the emission of waste gas from pyrogenic process does not conform to environmental protection standard. Therefore the study of vanadium occurrence, the improvement & optimization of vanadium extraction technology and the realization of pollution-free and low-cost extraction of vanadium from black rock series are of great and realistic importance for environment-friendly exploitation & utilization of vanadium resource in China. The study is based on carbon content in ore of Cambrian black rock series in south Qinling Mountain. Two kinds of ore are selected. Vanadium ore with low carbon content (TC<1%) is taken as Sample 1 while vanadium ore with high carbon content (TC>10%) as Sample 2. Based on analysis of ore?s lithologic features and vanadium?s occurrence, a vanadium extraction technological process characterized by selective grinding, low cost and no pollution is proposed.

Jan 1, 2014

In the present work, the flotation behaviours of zircon, rutile and ilmenite using sodium oleate as collector in absence and presence of depressants were thoroughly investigated. The maximum in the flotation recovery of any of the above minerals falls within similar pH ranges. A range of inorganic and polymer depressants were examined in order to improve the separation of zircon from rutile and ilmenite. Optimum values of conditioning pH and depressant concentration to achieve maximum recovery and best selective floatability of zircon were obtained. Selective flotation of zircon from Ti-bearing minerals was anticipated from single mineral experiments under different pH values, depressant and collector conditions.

Jan 1, 2014

By Alejandro Yañez, Martta Nousiainen, Rodrigo Grau

"Gas dispersion plays a fundamental role in froth flotation. Gas dispersion in flotation is quantified by using four properties: gas velocity, bubble size, gas hold-up and bubble surface area flux. Gas dispersion measurements were conducted in three flotation cells: TankCell 1, TankCell e300 and TankCell e500. The measurements reported in this paper were carried out exclusively in two-phase systems using only water and air at frother dosages exceeding the Critical Coalescence Concentration (CCC) in order to prevent bubbles from coalescing. The measurements conducted in TankCell 1 and TankCell e500 were conducted by Outotec specialists, whereas the characterization of TankCell e300 had been conducted earlier in 2008 by a team from McGill University. When working in two-phase systems and under non-coalescing conditions, gas dispersion characteristics measured in different scales can be compared directly. The measurements conducted in TankCell e300 are taken as a base line in order to compare the performance of TankCell e500, whereas TankCell 1 is a pilot-scale flotation cell which is used in rotor testing. The gas dispersion properties in TankCells were found to be affected by the air flow rate and rotor tip speed. Bubble sizes (d32) measured on the three-size scale seem to be within the same range of 0.6 mm to 1.6 mm. It was noted that the bubble size was influenced by rotor tip speed and gas velocity. In general, as the rotor tip speed increased, the bubble size decreased and as the gas velocity increased, so did the bubble size. The rotor tip speed also has an impact on the hold-up; in general, as the rotor tip speed increased the gas hold-up also increased but the influence of air flow rate on gas hold-up was greater. Bubble surface area flux was found to vary between 40 and 85 1/s. As the gas velocity increased, the bubble surface area flux also increased."

Jan 1, 2014

By Tilak Raj Mankhand, Mudila Dhanunjaya Rao, Kamalesh K. Singh

"Zinc dust is used for the removal of primary impurities by cementation from the zinc sulphate electrolyte before electrowinning of zinc. However, the industrial zinc electrowinning plants has been reported that the zinc dust consumption is in large excess than the stoichiometric requirement. In the present investigation, morphology of the zinc dust has been altered by ball milling and utilized for the cementation of cadmium, which is one of the major impurity and compared the change in the rate of cementation with original zinc dust. Initially, 325 mesh size zinc dust was used for the optimization of the excess quantity of zinc dust to be used at a temperature of 50 °C. The chemical analysis of zinc dust before and after ball milling and morphology were studied by scanning electron microscopy (SEM), and the solution was characterized by Atomic Absorption Spectrophotometer. The rate of cementation increased with increase in ball milling time. The residual precipitate obtained after filtration was also characterized by X-ray diffraction analysis. Finally experiments were conducted to study the effect of temperature and kinetics of cadmium cementation using first order reaction kinetics. Based on the integral method, the calculated activation energy for the cadmium cementation with 4-hours ball milled zinc dust was found to be 3.39 KJ/mole. INTRODUCTION Primary production of zinc in the world is carried out by hydrometallurgical route. The primary impurities in the neutralized zinc sulphate solution that cause negative effect on electrowinning are copper, cadmium, cobalt, and nickel. Copper diminishes the current efficiency and cadmium contaminates the cathode zinc (Morgan, 1977) while electro winning. Nickel and cobalt lead to perforation in the zinc deposit and prevents the electro winning process (Abrasheva et al, 1984). Due to higher electro positivity of these metal impurities than zinc, they can co-deposit with cathode zinc at the time of electrolysis. In addition to that, some possible impurities (including cobalt) in the electrolysis may lower the hydrogen overvoltage, allowing deposition of hydrogen at cathode resulting in fall of current efficiency. The deposition of zinc on the cathode is possible only at higher hydrogen overvoltage which is practicable in the absence of such impurities (Raghavan et al., 1999). Cementation is one of the prominent purification technique, and in that less reactive metal can be replaced by highly reactive metal by allowing them into precipitation. Cementation of cadmium from zinc sulphate electrolyte is being done by the addition of zinc dust."

Jan 1, 2018

By P. Hatefi, O. Rahmani, M. Noor-Mohammadi, A. Tohry

"Depressants play an important role in the selective separation of impurities from iron minerals by direct or inverse flotation. In this paper, sodium co-silicate (SCS) with chemical formula of Na4SiCO6, as a depressant with pH modifier features, has been synthesized and used for phosphorus bearing iron ore in anionic reverse flotation. In this process, phosphorus is floated while the iron oxides are depressed, using fatty acids as collector in an alkaline medium. Batch and pilot flotation tests were carried out to investigate the influence of SCS on the separation selectivity of phosphorus from iron oxides. Also the depression mechanism of SCS on hematite surface was investigated by microflotation tests and FTIR spectroscopy measurements. The flotation results indicated that without using a pH modifier, the pH of pulp could reach up to 10, when SCS was used as depressant. In this condition, a better depression performance was observed compared to sodium silicate (SS). Using the SCS, phosphorus and total iron content in iron concentrate was 0.046% and 66.29%, respectively, compared to SS where these values were 0.06% and 65.75%, respectively. As a result the weight recovery of iron concentrate was increase by around 4%, compare to SS. It was also found that 238 g/t of SCS could be used instead of 3 types of reagents collectively, including 32 g/t of NaOH, 151 g/t of Na2CO3 and 400 g/t of SS gel.INTRODUCTIONThe phosphorous presents in iron ore minerals is mainly in the form apatite mineral. The apatite is separated from iron ore minerals by magnetic and flotation methods (Ma, 2012). The reverse anionic flotation of iron is one of the most common method for removing phosphorus from iron concentrate (Araujo et al., 2005).Usually apatite minerals are readily floated using anionic collectors such as fatty acids (Ma, 2012). In this conditions the iron minerals are depressed and by modifying the pH in alkaline conditions, selective separation of phosphorus from iron concentrate can be achieved. Depressants including; sodium silicate (SS), starch, dextrin, guar gum and humic acids play an important role in the reverse flotation of iron ore (Kar et al., 2013; Ma, 2012; Turrer and Peres, 2010; Araujo et al., 2005). Studies have shown that SS has a better effect on iron recovery and phosphorous reduction, compared with other depressants (Tohry and Dehghani, 2016; Qi et al., 1992, Dho and Iwasaki, 1990). In most flotation processes, modifiers are used to adjust the pH. To achieve alkaline conditions, mainly pH modifiers such as carbon dioxide and sodium carbonate are used."

Jan 1, 2018

By Masakazu Niinae, Kenji Aoki

"Electrokinetic soil remediation by electroosmosis and ionic migration is restricted to soluble substances. At a higher pH, the soil particles sorb more heavy metals than at a lower pH and the precipitation of heavy metals are promoted. Both mechanisms make heavy metals immobile, rendering cleanup more difficult and electrokinetic extraction inefficient.In this study, the effectiveness of introducing a complexing agent to enhance the removal of cadmium from kaolinite in the region of neutral pH by ionic migration is examined. The complexing agent selected was ethylenediaminetetraacetic acid (EDTA). The investigation was carried out in a laboratory-scale column containing kaolinite contaminated with cadmium. As the results of the study, cadmium migrates toward the anode without accumulation of cadmium and is successfully removed at the anode reservoir."

Jan 1, 2003

By Thomas Mütze, Anja Hirte, Ursx Peuker, Thomas Kuhn

"The comminution behavior of two ferromanganese nodules samples of the equatorial northeast Pacific has been examined as a basis for the separation of two kinds of metal-rich layers. Those layers were finely grown together during nodule formation and are one reason that the exploration of deep-sea minerals calls for the development of new mineral processing concepts. Therefore fundamental analyses of the fracture behavior have been made under compressive and impact stress. Further experiments took focus on the crushing behavior in a jaw crusher and a small scale impact crusher as well as the milling behavior in a dry vibrating mill, a wet planetary ball mill, and a wet agitated ball mill. The comminuted products were characterized by PSD, particle shape, particle density, and porosity. The experiments show a low stress resistance of the ferromanganese nodules. Compared to compressive stress, impact stress turned out to be the more effective for crushing. Both samples showed no significant difference in the comminution behaviour which makes differing mechanical treatments unnecessary. In both cases particle sizes below 1 µm were achieved by wet grinding. This particle size is necessary to separate the two kinds of metal-rich layers which is part of continuative studies."

Jan 1, 2014

By V. A. Feofanov

Technogenic water of ore mining enterprises, nonferrous metals operations, the enterprises of electroplating and instrument making, containing copper in the form of those or other connections can serve as perspective sources on receiving the copper-bearing raw material. Extraction of copper from the given water also solves a problem of water treating from a toxic component that reduces environmental load at evacuation of water in an open basin. The method of case hardening allows extracting copper selectively with reception of a deposit with the content of copper up to 70%. Weakness of the method is its efficiency basically in acid reduction, and also its low degree of copper extraction. On the basis of case hardening the method of galvanic coagulation is devised. It is based on the work of a short-circuited galvanic cell of iron-coke at variable contact of coupled metals components among themselves, cleared by the oxygen of air. The following processes of galvanic coagulation are considered: ? Extraction of copper; ? Formation ferrites of copper; ? Copper sorption on just-aggregated oxide forms of iron. Establishing conditions for passing the given stages provides an opportunity of copper extraction from technogenic water at any value of ??, content of salt and concentration of copper with reception of a compact deposit from which it is possible to extract copper by the known ways of enrichment and metallurgy. Investigations on optimization and intensification of galvanic coagulation with the purpose of reception the maximum rich deposit on copper have shown that the average contents of copper in a solution of 100~200 mg/dm3 the contents of copper in a deposit is 6%~10% at extraction 85%~90%, depending on characteristics of treated technogenic water. Using methods of scanning microscopy it is determined structures, composition and mechanism of phase formation in investigated electro-chemical process. The second stage of galvanic coagulation increases a degree of copper extraction up to 98%~99% that allows returning the cleared waters in circulation for waste recycling or evacuation in an open basin. Nowadays the method of galvanic coagulation is the most acceptable for copper extraction from technogenic water both from the point of view of efficiency and instrument setting that allows applying the method in conditions of the working enterprises.

Jan 1, 2014

By G. P. Wong

"In the Inco matte separation process, a slow-cooled converter matte is separated into three main discrete mineral phases: chalcocite (Cc), heazlewoodite (Hz) and a Cu-Ni-Fe alloy. After magnetic removal of the alloy, Cc and Hz are separated by flotation at pH>12 with diphenyl guanidine (DPG) as both collector and frother. High selectivity is achieved in rougher flotation. However, in later flotation stages such as in the middlings circuit, as oxidation takes place, Hz becomes highly floatable, resulting in a very poor separation between Cc and Hz.Starch and dextrin as Hz depressants were evaluated on the middlings circuit feed and showed no positive impact on Cc/Hz separation selectivity. Ethylene diamine tetra-acetic acid (EDTA) extraction showed the existence of abundant surface Cu and Ni ions. The use of triethylene triamine (TETA) or EDTA in flotation did not improve Cc/Hz separation selectivity. Microflotation tests were carried out on pure synthetic Cc and Hz minerals. It was found that Hz did not float in the presence of DPG. However, Hz conditioned with either copper sulfate solution or in contact with Cc floated readily in the presence of DPG. It is concluded that the major reason for Hz flotation in the middlings circuit is due to Cc oxidation releasing Cu ions that adsorb on the Hz surface making it reactive with DPG thus rendering the Hz floatable."

Jan 1, 2003

By M. Naymanbayev

The characteristics of the mineral composition of ores and valuable set of components: the technology of processing depending on the type of mineralization, the nature of the impregnation of ore minerals and their composition have been considered. There have been given technological schemes for processing concrete objects. The analysis of fitness fields for industrial development (degree of scrutiny, the effectiveness of developed enrichment and hydrometallurgy technology) has been provided.

Sep 1, 2012

By L. Y. Zhang

The metallic sulphides in Jinchuan Mine are relative friable and the gangue minerals suffer of wide secondary change, the overgrinding of metallic sulphides and sliming of gangue minerals are the main cause that makes the mineral separation indexes difficult to improve. So changing the process of grinding, and classification, and optimizing the particle size distribution of grinding product is the key improving the separation performance of Jinchuan nickel and copper ore.

Jan 1, 2014

By Kyle P. Flynn, Frank J. Hrach, James D. Bittner

ST Equipment & Technology, LLC (STET) has developed a processing system based on tribo-electrostatic belt separation that provides the mineral processing industry a means to beneficiate fine materials with an entirely dry technology. In contrast to other electrostatic separation processes that are typically limited to particles greater than 75µm in size, the triboelectric belt separator is ideally suited for separation of very fine (<1µm) to moderately coarse (300µm) particles with very high throughput. The high efficiency multi-stage separation through internal charging/recharging and recycle results in far superior separations that can be achieved with a conventional single-stage free-fall tribo-electrostatic separator. The triboelectric belt separator technology has been used to separate a wide range of materials including mixtures of glassy aluminosilicates/carbon, calcite/quartz, talc/magnesite, and barite/quartz. An economic comparison of using the tribo-electrostatic belt separation versus conventional flotation for barite / quartz separation illustrates the advantages of dry processing for minerals.

Jan 1, 2014

By T. Sreenivas

This paper describes results of laboratory studies on recovery of dissolved uranium values from alkaline leach slurries of a medium-grade uranium ore from Gogi (Karnataka, India) using the resin-in-pulp (RIP) process. Besides anionic carbonate complex of uranium, the other major ionic constituents of the leach solution are CO32-, HCO3-, SO42- and MoO42-. The total dissolved solutes (TDS) are about 45 g/L. Various commercially available strong bases anionic resin-in-pulp (RIP) grade resins ? both macroporous and gel type, were studied with respect to their loading capacity. Parametric variation studies were then carried out with the short-listed resins. Results of the semi-continuous counter-current extraction and elution tests indicated extraction efficiency of about 98% and practically complete elution of the loaded uranium values with NaCl eluant using a gel type polystyrene based resin grafted with quaternary ammonium ion. Keywords: uranium, hydrometallurgy, ion exchange, resin-in-pulp

Sep 1, 2012

By John Ralston, Stephen Grano, Yongjun Peng, Daniel Fornasiero

"A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of grinding conditions on galena flotation and galena separation from pyrite. The changes occurring on the mineral surface during grinding were investigated by EDTA extraction and ToF-SIMS measurements.Galena flotation and galena separation from pyrite were strongly dependent on the type and amount of oxidation species produced on galena and pyrite surfaces under different grinding conditions. Iron oxidation species depressed both galena and pyrite flotation, whilst lead oxidation species activated pyrite flotation but had little effect on galena flotation. Optimum galena flotation and galena selectivity against pyrite were achieved by selecting grinding conditions that enabled lead and iron oxidation production to be controlled.Grinding conditions had a large effect on the flotation of the galena particles of different sizes. Flotation of fine galena particles (-10 µm) was depressed by iron oxidation species derived from the grinding media. Chromium grinding medium decreased the production of iron oxidation species and therefore increased the flotation of fine galena particles."

Jan 1, 2003