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By J. E. Murphy

Neodymium was electrowon into a Mg-Cd molten cathode at 650 °C from NdC1,-KC1 electrolyte. With the chloride system, neodymium was deposited into the molten alloy cathode until the neodymium concentration reached 20 wt pct. The alloy was then vacuum melted to remove the Mg and Cd. The current efficiency exceeded 80 pct under optimum conditions and the purity of the metal was 99.9 pct after vacuum melting. As an alternative approach, neodymium was electrowon at 1,030 °C from Nd,O, dissolved in a molten fluoride eleotrolyte. With the oxide-fluoride electrolyte, the metal was electrowon in a molten state with current efficiencies up to 60 pct. The purity of the metal was 99.8 pct with oxygen and carbon as major impurities. A number of problems were encountered including anode effect, low oxide solubility in the electrolyte, high neodymium metal solubility in the electrolyte, and reactivity of the metal with the cell materials. Approaches to improved cell, operation and prospects for commercial adoption of the electrolytic production of neodymium metal are discussed.

Jan 1, 1995

By Daniel Kim, Ari Rantala

Efficient on-line monitoring of electrolytic cell performance in copper electro-refining has been challenging due to the need for complex electrical measurement systems and the management of the enormous volume of data. Based on Kennecott Utah Copper's innovation Outotec has developed a novel and innovative electrolytic cell monitoring system called CellSense™ System. As the system is based on self-powering from bus bars, wireless communication, on-line adaptive modeling and easy to access information and alarming, traditional obstacles of electrolytic cell monitoring are eliminated. With cell voltage and electrolyte temperature measurements, CellSense System enables real-time cell performance discovery and early reaction to critical production or quality disturbances such as short-circuiting, flow blockages, cold cathodes or electrolyte temperature excursions. During the past few years the system has been delivered to over 3500 commercial cells. In this paper the largest CellSense™ System ever delivered and recently adapted by Kennecott Utah Copper with 1412 cells monitored on-line for high tankhouse performance, cathode quality and optimized operator work flow is presented. Early results and benefits are discussed.

Jan 1, 2012

By Ibrahim Yusufoglu, Ahmet Orkun Kalpakli, Cem Kahruman, Sedat Ilhan

"The effects of oxalic acid concentration, temperature, stirring rate and particle size on the dissolution rate of synthetically prepared calcium molybdate were investigated. Dissolution of calcium molybdate in oxalic acid solutions takes place as a series - parallel type reaction. In the first reaction step, which proceeds according to the ""Langmuir - Hinshelwood Mechanism"", calcium aqua oxalato molybdate is formed as a complex chelate intermediate product. In the second reaction step, molybdic acid is formed during the slow hydrolysis of calcium aqua oxalato molybdate, and it reacts rapidly with oxalic acid to form the polymeric hydrogen oxalate dimolybdate chelate as an end product. Activation energies were calculated as 41.4 and 49.9 kJ mol-1 for the first and zero order reactions. The fractional conversion versus time relationship can be given by the following equation.IntroductionMolybdenum is used widely in electric-electronic, metal working, aerospace and aeronautic, nuclear, glass and petrochemical industries because of its high melting temperature and resistance against chemical effects. However, the largest molybdenum consumers are the iron-steel and super alloy industries where molybdenum is used as an alloying element. Industrially important molybdenum minerals are limited to molybdenite (M0S2), powellite (CaMo04) and wulfenite (PbMo04), which are considered as primary molybdenum resources. Secondary molybdenum resources are spent catalysts and scrap [1-4].Molybdenum has been produced by pyrometallurgical processes in the past. Since it is possible to process low grade molybdenum ores and industrial wastes by hydrometallurgical processes, which are more environmentally friendly than pyrometallurgical processes, the importance of the use of hydrometallurgical processes has increased in the molybdenum production industry."

Jan 1, 2012

By Michael S. Moats, Daniel Kim, Shijie Wang

"The behavior and deportment of lead, arsenic, antimony and bismuth are critical in producing high quality cathode by copper electrorefining. A critical review of research related to these elements is presented along with a comparison to industrial data, where appropriate. These elements exist predominantly in the anode as complex oxides along die grain boundaries. Upon dissolution, Group 15 elements report both to the electrolyte and slimes while lead essentially enters the slimes. The deportment of the Group 15 elements appears to be influenced by several chemical interactions which are discussed. The effect of these elements on floating slimes and anode passivation is reviewed. Under normal electrorefining conditions, lead, antimony and bismuth are thought to enter the cathode through the encapsulation of slime particles. The literature indicates that arsenic enters the cathode predominately by electrolyte entrainment. Finally, areas for future research regarding these elements are presented.IntroductionControlling lead, arsenic, antimony and bismuth is critically important for the production of high quality cathode in copper electrorefining. The reasons for this are twofold. First, ASTM Grade 1 Cathode specifications [1] for these elements are low, as listed in Table 1. Second, they can affect the efficiency of the electrorefining process (e.g., through passivation, current efficiency, slime processing)."

Jan 1, 2012

By V. Bojarevics, K. Pericleous

"A number of different methods have been developed for noncontact electromagnetic treatment of liquid metal and to investigate the melting/solidification processes. Applying AC magnetic field in terrestrial conditions, along with the buoyancy and thermo-capillary forces, results in turbulent flow. The use of a homogenous DC magnetic field allows damping both of the turbulence and the large scale flow at different rates leading to surprising results at some stages. The dynamic interaction of the turbulent flow with the oscillating interface needs to be accounted if it is required to levitate liquid metal of up to few kilograms without the contact to container walls. At the high values of magnetic field some oscillation modes are damped quickly, while others are modified with a considerable shift of the oscillating droplet frequencies and the damping constants from the non-magnetic case. Numerical models are used to investigate behavior of liquid metal suspended in high DC magnetic fields providing microgravity-like conditions with laminar viscosity and heat transfer to the surroundings.IntroductionSince the early Electro Magnetic (EM) levitation experiments [1] in AC magnetic field it became apparent that the levitated liquid metal is prone to oscillation and instability. The EM and electrostatic levitation experiments with liquid metal droplets show difficulties related to confinement stability and a need for complex correction functions to establish a correlation between the measurements and the droplet material properties [2,3]. Intense internal fluid flow is visually observed, apparently being in the turbulent regime for earthbound conditions."

Jan 1, 2012

By P. M. Pincheira Brown

The widely accepted inverse relationship between copper prices ail stocks, has been commonly used by analysts to explain the behavior of the copper market and to forecast film copper pries. However, empirical data have not shown such a clear relationship between copper prices and stacks. Existing evidence only indicates a weak tong-nut relationship that vanishes in some periods. In this paper a simple comprehensive model is provided which explains both parallel and opposite direction movements between prices and stocks. Former are explained mainly by stocks demand expansions-contractions while the latter are in essence due to increases in the supply curve. Furthermore, econometric estimations are provided, thus giving a powerful tool to forecast and explain price developments of the copper market.

Jan 1, 1999

By John Jiang, Yeonuk Choi, Olivia Wang, Gus Van Weert

"As part of a general review of processing double refractory ores through Barrick Gold's autoclaves/CIL facility at Goldstrike, Nevada, blanking the gold cyanide adsorbing native carbon in the ore with hard (m.p. >55°C) paraffin wax was proposed. To avoid interference from other ore constituents in the exploratory testwork, commercial activated carbon was substituted for native carbon in the ore to establish the best conditions for de-activation of carbon with molten wax.IntroductionDouble refractory gold ores present two barriers to gold extraction. The first is generally a physical barrier: the gold is encapsulated or dispersed in a matrix which is impervious to the gold lixiviant. In most cases, including the Goldstrike deposit, this involves a pyrite or arsenopyrite matrix, although minor gold may also be dispersed in competent silica (quartz) or iron oxides. Gold can be rendered accessible by oxidative destruction of such sulphide matrices. At Goldstrike this is practised by roasting and autoclave oxidation (POX). It is the latter route to which this paper refers.The second barrier refers more correctly to gold recovery. Gold may be extracted from the autoclave oxidized solids with cyanide, forming a gold cyanide complex. One characteristic of this complex is that it adsorbs on graphitic surfaces. This behaviour is used advantageously on a large scale by gold millers, who use man made activated carbon particles to remove the gold from solution during leaching: the Carbon-In-Leach, or CIL process. The gold bearing carbon particles are larger than the ore solids and can be separately recovered by screening. Goldstrike uses the CIL technology to recover gold after autoclave oxidation."

Jan 1, 2012

By Alex Moyano

At present, the Codelco Norte smelter processes in the Teniente Converter and the Flash smelting Furnace 1,420,000 t/y of its Chuquicamata concentrate with an arsenic content of up to 1.5%. In a near future Codelco-Chile is considering different processing options for a new projected concentrates from the Alejandro Hales mine (former Mansa Mina mine with an arsenic content of up to 6%). The main option is the possibility to process 3,000 t/d of mixing concentrates from the Alejandro Hales and the Chuquicamata mines, in the Teniente Converter. The main feature of this smelting unit will be high volatilization of arsenic when processing high arsenic-bearing concentrates. The CN smelter staff carried out a technical feasibility study to evaluate the processing of high arsenic-bearing concentrates directly in the Teniente Converter, thus the low arsenic-bearing concentrates can be processed in the FSF. Accordingly, laboratory scale tests were carried out at the Tohoku University facilities. The lab-scale results allowed an industrial scale test at the Codelco Norte smelter to smelt 2,300 tpd of high arsenic-bearing concentrates in the TC and evaluate the metallurgical impact in the smelting, converting and refining areas of the smelter. The main industrial-scale result confirmed the stabilization of the arsenic content at 0.5% in the 70% Cu produced white metal at the test condition.

Jan 1, 2006

By Pertti Pekkala

Outokumpu has 25 years of experience in the SX area. The development of the solvent extraction plants responds to an ever increasing demand for lower operational costs wd for adaptability to process disturbances with minimized risks. In this paper the features of the VSF ("Vertical Smooth Flow") SX technology are described, such as the separated pumping and mixing, the homogenous gentle mixing, the droplet coalescence and the ultra pure settling. A major advantage of the mixing technology is the high stage efficiency of above 99 per cent. The connection between this and some features of the settler front section is clarified. The present design of VSF plants is based on experience of existing operations at, for example, Zaldivar, Radomiro, Morenci, Kokkola and Harjavalta. These production plants cover a unit capacity range of 60 to 3,600 m3/h expressed as a total flow. It is evident that there are no restrictive factors to increase the total flow up to 5,000-6,000 m3/h by introducing the VSF technology. The copper SX technology has a long history reflecting many individual features of the separate copper SX plants. Still it is necessary to verify all actual running parameters by pilot tests taking into account impurities, chemicals used etc. The design of SX plants is not only about the delivery of equipment but also a process concept, and it is best tailor-made and adapted to specific local requirements.

Jan 1, 1999

By M. S. Moats

A considerable amount of research has been conducted to determine the causes of anode passivation. Chemical and electrochemical reactions that occur after passivation have received little attention. Chronopotentiometry, linear sweep voltammetry, cyclic voltammetry, and impedance spectroscopy have been used to elucidate three reactions that occur after passivation of commercial copper anodes. These involve the dissolution of silver and subsequent cementation and transformation of selenides, the oxidation of lead sulfate to lead oxide, and oxygen evolution. The amount of silver dissolution depends on the silver content of the anode, the time to passivation, and the molar ratio of Ag/(Se+Te). The oxidation of lead from PbSO4 to PbOx explains a potential plateau of oxygen evolution. Silver affects the duration of oxygen evolution on the PbOx. Anodes containing kupferglimmer display a characteristic oxygen evolution potential. It is believed that kupferglimmer provides a lower overpotential for oxygen evolution than the other slime phases or passivated surface.

Jan 1, 1999

By Tracy Morris, Weldon Read, Luis Navarro

"During the leaching of anodic slimes, tellurium dissolves into the leach liquor together with copper and must be removed before the solution is sent to liberator cells for copper recovery. Prior to the installation of autoclaves, tellurium was precipitated using raw slimes that caused a recirculation of tellurium in the leaching circuit. After autoclaves were installed the old leach tanks were converted into tellurium reactors utilizing copper chips, steam and agitation to form a copper telluride precipitate. Tellurium levels of less than 10 rng/L are achieved in a timely manner.IntroductionThe electrolytic refining of copper consists of an electrolytic cell provided with an anode of impure copper, a cathode of substantially pure copper (starter sheet) and an electrolyte made of copper sulfate and sulfuric acid [1]. When a direct electrical current is passed between the anode and cathode inside the cell, the impure copper anode dissolves in the electrolyte and pure copper is plated onto the cathode. During this operation, many of the impurities are deposited on the bottom of the cell as an anodic slime residue composed of insoluble chemical compounds. Slimes are a major source of rare and precious metals in the copper industry [2-5],In the Amarillo Copper Refinery (ACR), the anodic copper slimes are sent to the Precious Metals department in order to extract and then refine the gold, silver, platinum and palladium from them. The remaining impurities, in the form of a soda slag or copper slag are sent to the Hayden smelter for further processing. Copper telluride is sent to the Selenium/Tellurium department inside the plant for selenium and tellurium recovery. During the leaching process of the anodic slimes, copper, tellurium, and other metal species in the slimes are dissolved into leach liquor that cannot be returned to the tankhouse unless the tellurium concentration is below 10 mg/L."

Jan 1, 2012

By Robert D. Boiler, Bill Wilkie

"There is a wide choice of different types of woven filter media for hundreds of different filtration applications. Factors such as type of fiber, synthetic polymers used, weave style, fabric finishes and fabrication techniques all play an important part in selecting the best choice for a specific type of filter and process application. The purpose of this paper is to offer some basic knowledge of these factors and how they can impact the performance of a filter, the life of the media and the overall cost of operation through case studies of actual plant filtration applications.IntroductionThe use of woven filter cloth in liquid/solid separation applications is generally well known. Woven filter cloth, by the nature of the weaving process, offers unique consistency and repeatability when compared to some other filter media such as needled felts, papers, sintered structures and knitted cloth. This unique consistency and repeatability is particularly applicable to woven filter cloth produced using monofilament fibers. These fibers are consistent in shape and form the basis for a woven cloth with predictable pore size and throughput characteristics. Woven filter cloth can be used in most wet filtration applications. Typical examples are the separation of chemical and pharmaceutical solids from process liquors, waste stream solids capture, liquid foods clarification, mining separations, and polymer filtration.EnvironmentOne of the first considerations is the environmental demand of the given process. Though it is tempting to look immediately at the particles in a filtration process, it is often better to consider some of the more basic needs of the system. There are numerous materials available, both synthetic and wire cloth. Each has its own unique set of properties."

Jan 1, 2012

By J. A. Jensen

In-situ composites were produced in both Ti matrix (Ti-20Y) and Mg matrix (Mg-20Ti, Mg- 20Nb, Mg-20Fe, and Mg-8Li) alloys. In Ti-20Y, a < 1010 > fiber texture formed in both the Ti and Y phases, and UTS increased from 240 MPa, (as-cast) to 950 MPa after deformation processing to a true strain of 7.3. Deformation processing produced smaller UTS increases in the Mg-matrix composites, but they showed exceptional resistance to weakening from exposure to elevated temperatures. The Mg-20Fe, Mg-20Nb. and Mg-20Ti composites tolerated 6-hour exposure to 400°C with no reduction in their 250 to 300 MPa room temperature UTS. All composites studied had excellent ductility and machinability.

Jan 1, 1995

By Hande Cavus, Ibrahim Yusufoglu, Cem Kahruman

"In this study, ammonium tetramolybdate (ATM) was obtained as the intermediate product of ammonium heptamolybdate tetrahydrate (AHM). The thermal decomposition mechanism of ATM was investigated under nonisothermal and isothermal conditions in air and inert gas atmospheres. Nonisothermal experiments were carried out by TGA/DTA/MS while TG was used for isothermal conditions. Characterization of the decomposition products were carried out by XRD and FT-IR. The thermal decomposition of ATM in air proceeds in a single step and forms M0O3 while [(ÍÇ4)2è]ïïï83Ìïè3 and molybdenum suboxide (Ìïè3.÷, ÷=0.025) were obtained in the first and the second steps of thermal decomposition in He, respectively. Activation energies, frequency factors and kinetic model equations were determined for thermal decomposition reactions. Fractional conversion-time diagrams were compared with diagrams drawn according to kinetic model equation.IntroductionM0O3 is usually used as catalyst in industry [1]. AHM is the basic source to produce molybdenum containing catalysts used in petrochemistry [2]. The oxides of Li, V, W, Te, Bi and Sn are doped in M0O3 to produce catalysts, which find commercial applications in the industry. The properties of M0O3 are affected by dissolution, settling, calcination, drying and thermal decomposition processes [1]. There are several studies in the literature about the thermal decomposition of AHM and the characterization of the decomposition products in different gas atmospheres and at various heating rates [3-19]."

Jan 1, 2012

By Ting Luo, Hongmin Zhu, Kai Huang, Shuanglong Du, Tao Gui, Yifan Xiu

"Poplar cotton, a cellulosic material, was found to adsorb metals ions effectively. In the present study, the biosorption characteristics of Pb(II) onto poplar cotton, were evaluated as a function of pH, contact time, biomass dosage, initial concentration and temperature. Within the pH range investigated (1.0-6.0), the optimal pH value suitable for the uptake of Pb(II) was determined. The maximum adsorption capacity obtained from the Langmuir model is around 0.52mol kg for the poplar cotton sorbent. Equilibration is achieved in 60min for the studied concentrations. Results suggest that the poplar cotton can be directly used as an effective and low-cost biosorbent for removal of Pb(II) from aqueous solution.IntroductionHigh value utilization of various biowastes produced in agricultural, forestry, fishing industries, etc. have attracted great interest from many researchers [1], Biomass, due to its easy availability, great abundance, low cost, easy processing, eco-friendliness and biodegradability, has exhibited exciting potential for being used as raw materials for the preparation of many new hi-tech functional products [2]. For example, using biowastes to synthesize sorbents for application in the removal of toxic substances such as dyes [3], heavy metals from the waste water [4] or in the recovery of valuable metals [5] from the ore tailings and secondary metals resources has made great progress in last decade. In present study, poplar cotton, a kind of white light fluff of poplar trees, like that of dandelion, usually flying in the air each spring was tested as a biosorbent for the remove lead ions from the water. It may also provide some good ideas for new sorbent design. Lead, as one of the typical poisonous heavy metals, for its typical toxicity and extensive pollution, was chosen to test the adsorption behavior of poplar cotton in aqueous solutions."

Jan 1, 2012

By Kurt Svens

"As zinc consumption is gradually increasing all the time in the world, many zinc plants are looking for possible expansions. As the sulphuric acid market as well as the fertilizer market in many areas is saturated, the costs for the roasting-acid plant section of the zinc plant will create problems when making feasibility calculations for possible expansions. For solving the customers' situation, two proven zinc concentrate direct leaching technologies are available. A third one, which is possible, does not have any industrially proven applications in the zinc area.IntroductionTime to time, the zinc plants in the world scrutinize their operations with respect to their cost efficiency, the total zinc recovery and the near-by or far-away consumer markets, especially the for zinc and sulphuric acid. Their preliminary profitability calculations can show that a possible total expansion is not economical, when they are looking to expand the whole roasting/acid plant - leaching - solution purification - electrowinning - casting route, as the possible market price for the sulphuric acid is low or the sulphuric acid market is too far away. Based on these facts, their economical study often indicates that implementing a zinc concentrate direct leaching option could be more favourable. Regarding this situation, several aspects concerning three alternative direct leaching methods will be discussed, of which pressure leaching and the atmospheric leaching processes have several industrial applications in the zinc industry, as the ultrafine grinding - conventional leaching process at present has none. As iron is also dissolved during zinc concentrate direct leaching, iron removal processes generally used in the zinc industry are additionally discussed below."

Jan 1, 2012

By John A. Clark, Danylo Oryshchyn, Casey Carney, Stephen Gerdemann, Cathy Summers, Thomas Ochs

"Limited analysis of combustion gas streams where carbon capture is not of interest is done mainly to ascertain operation parameters. Stringent regulations on acid gases and particulates promote careful flue gas analysis. Unregulated components are typically not analyzed. Typically not more than four points (two in the boiler, and one each in the flue and the stack) are sampled. A successful oxy-fuel process with carbon capture and compression is anticipated to require as many as 12 sample points with analysis for water, nitrogen, oxygen, argon, NOx, SOx, and carbon monoxide. Carbon dioxide captured for beverages produces a high value product and the cost associated with analysis is warranted. However, carbon capture for disposal must keep all costs to a minimum. This paper will compare alternative approaches for cost-effective sampling and analysis of the carbon dioxide product streams from oxy-fuel combustion, through all stages of production through compression and pipeline/vessel delivery.IntroductionAnalysis of gases in an oxy-combustion process with carbon capture is essential to the operations of the oxy-fired boiler and the subsequent collection, compression, and purification of carbon dioxide. The process is charged with pure oxygen and not-so-pure carbon in the form of coal at the front end, generating a product of mainly carbon dioxide with traces of argon, nitrogen, sulfur compounds, nitrogen compounds, oxygen, hydrogen, and mercury. It is possible that hydrogen chloride and hydrogen sulfide may also be present in trace amounts [1]. The trace components primarily come from impurities contained in coal such as water, sulfur, nitrogen, and volatile organic compounds. Coal also contains a good deal of mineral matter that is transformed into ash during combustion, becoming particulates that can complicate the analysis regimes utilizing standard analytical equipment."

Jan 1, 2010

A novel, low-pressure adaptation of Praxair?s coherent jet technology utilizing CoJet lances was developed for application at Inco&apos;s Copper Cliff Smelter where oxygen is available in large tonnage quantities but only at relatively low supply pressures (< 193 kPa header pressure). The project objectives were to evaluate the effect of coherent jet technology on controlling oxygen lance accretion (?horn?) formation and to increase oxygen efficiency in the Inco Oxygen Top-Blowing Nitrogen Bottom Stirring (TBBS) MK Reactor used for converting nickel- contaminated chalcocite to semi-blister copper. This paper describes the development and subsequent implementation and testing of two CoJet lances in this application.

Jan 1, 2005

The reported values of the standard reduction potentials of the Au(NH3)2+/Au(0) and Au(S2O3)23-/Au(0) couples are reviewed to emphasise the experimental difficulties associated with the measurement of reliable values for these quantities. The standard reduction potential for Ag(I)/Ag(0) in ammonia and thiosulphate solutions measured at ionic strength 0.1 and 25oCis used to predict the following relevant stability constants () for gold complexes based on the linear free energy correlations: Au(NH3)2+2 = 1013, Au(S2O3)23-2 = 1024 and Au(NH3)43+4 = 1033. The equilibrium constant ( 10-11) for the reaction Au(S2O3)23- + 2NH3 = Au(NH3)2+ + 2S2O32- based on these stability constants is in reasonable agreement with the measured value (10-9) based on potentiometric and spectroscopic data when excess ammonia was added to a solution of Na3Au(S2O3)2. This also indicates that the stability constant of Au(NH3)2+ is 9 to11 orders of magnitude less than that of Au(S2O3)23-. Relevant species distribution and Eh-pH diagrams based on the revised data are presented.

Jan 1, 2003

By Hai-Xing Fang, Bing Xie, Hong-Yi Li

"In the duplex melting process, chromium forms chromium spinels, the study of which will help to exploit the Hongge ores (rich in chromium) in the Panzhihua-Xichang area in China. Mimicked chromium slag was synthesized. The oxidation and decomposition mechanism of the Fe-Cr spinels contained was studied in a sodium roasting process. The effects of temperature, roasting time, amount of soda added and filling reagents were investigated. The leaching-reduction-precipitation-calcination procedure to extract Cr2CO3 was optimized. The results showed that the optimized roasting temperature was 1000~1020°C with a stoichiometric Na2CO3 addition and without any filling reagents. Roasted materials were leached with distilled water and were filtered to obtain a chromium-containing solution, which was adjusted to pH 1.60-1.80. A reducing reagent, NaHSO3, was added in a stoichiometric ratio and the solution was then adjusted to pH 7.25~8.25. Maximum Cr2O3 precipitation was obtained and the precipitate was calcined at 1050°C for 2h to obtain Cr2Ü3 with recovery rate over 96%.IntroductionChromium is widely applied in the metallurgical industry, in refractory materials and in the chemical industry with its particular properties of hardness, wear-resistance, high temperature resistance and corrosion resistance [1]. There is no free state of chromium in nature and chromite is the main chromium containing mineral [2], China is poor in chromium resources, despite its large demand, and there are few deposits of high grade of chromite ores except in some regions in Tibet and Xinjiang province [1, 4]. Hongge, one of largest titanomagnetite mines in Panzhihua-Xichang area, is a polymetallic deposit mainly containing iron and titanium; it is also associated with various beneficial elements such as chromium, copper, nickel, etc. [3]. As investigated in Reference 3, the chromium reserves of Hongge ores are so large that it is of great importance to study how to extract the chromium from them."

Jan 1, 2012