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By K. Lillkung, O. Forsen, J. Aromaa

"The dissolution rates of Pt, Pd and Rh in 250 g/L NaCl solution were calculated from the current densities determined by polarization curves and potentiostatic measurements measured with wire electrodes at atmospheric pressure. The results achieved with the two methods were similar. The dissolution rates at the corrosion potential were in the order of few nanometers per hour. The polarization curves indicated that to achieve dissolution rates required for economical operation on an industrial scale, the samples need to be polarized to higher potentials. When polarized to higher potentials, the metal dissolution rates were in the order of micrometers per hour. As the Tafel slopes of the metal dissolution region are fairly steep, the potential affects the dissolution rate greatly. Based on the activation energies, the dissolution reactions were controlled by a charge transfer step.IntroductionPlatinum group metals (PGM) have some very unique properties such as their inertness, giving excellent corrosion resistance, and a high melting point. At the same time, these factors make the refining of these metals very challenging. The main applications where PGMs are used are different catalytic converters, mostly in automotive catalysts. The used catalysts are also an attractive secondary source of PGMs. The exact concentrations of PGMs in catalysts vary widely depending on the manufacturer, the age and the capacity of the catalyst. The concentration of Pt in a new catalytic converter range from 300 to 1000 ìg/g, Pd from 200 to 800 ìg/g and Rh from 50 to 100 ìg/g [1]. Precious metal catalysts usually consist of a coat of the metal supported on ã- alumina. The recovery of metals from automotive catalysts has received much attention during the last few years [1-3]. In the near future, the use of PGMs in fuel cells is predicted to increase the amount of secondary PGMs available [4]."

Jan 1, 2012

By M. Maeda, H. Sasaki

Dissolution characteristics of metals vary significantly when they form alloys with other elements. Because hydrometallurgical processes are essential in separation and refining of non-ferrous metals, it is important to study behaviors of alloys in aqueous solutions. The authors have studied dissolution characteristics of precious metals in acid solutions using electrochemical measurement. When precious metals are alloyed with Zn, its dissolution is promoted by an increase in surface area caused by the preferential dissolution of this metal. The electrochemical study also revealed that precious metals dissolved from some alloys at unusually negative potentials; the underpotential dissolutions are explained by activations of these metals in the dealloying.

Jan 1, 2014

By S Jayakumari, E Ringdalen, V Canaguier

Silicomanganese (SiMn), containing approximately 16–30 per cent Si, is produced in submerged arc furnaces using various Mn sources and quartz as the primary raw materials, along with fluxes and reductants. In the high-temperature zone known as the coke bed, a silica-rich slag is formed. SiMn is produced through the reduction of SiO2 from the slag. Dissolution of quartz into slags with different compositions, the primary slag formed from the Mn sources and flux before any MnO reduction occurred, representing conditions at the top of the coke bed, and dissolution of quartz into a partially reduced slag to simulate conditions inside the coke bed has been investigated. Experimental investigations were carried out to study the dissolution of quartz particles of varying sizes, 5 mm and 25 mm in synthetic slags with different compositions at temperatures between 1400°C and 1600°C, with varying holding times. Observed results are compared with liquidus compositions and equilibrium phases for original and formed slags. Particle size has been shown to be of little importance for the dissolution. Quartz dissolved more easily in slag at top of the coke bed than slag in the coke bed. Complete dissolution was observed after 30 mins at 1600°C in all cases, but not after 0 mins.

Jun 19, 2024

By Kazutoshi Haga, Ariunbolor Narankhuu, Ariuntuya Battsengel, Yasushi Watanabe, Altansukh Batnasan, Akita University

"Rare earth minerals are usually concentrated by flotation, magnetic or gravity separation methods to produce concentrates that are subsequently leached with hydrochloric (HCl), sulfuric acid (H2SO4) or nitric acid (HNO3). About 75 % REEs are lost in gypsum by-product when apatite is dissolved in H2SO4, whereas more than 80% of REE can be extracted from the apatite using HCl and HNO3 leaching processes, respectively. Therefore, the main aim of this study was to find an efficient process of dissolution of rare earth elements (REEs) from apatite ore by sulfuric acid solution due to its lower cost. In order to optimize the dissolution process, effects of different parameters, namely, concentration of H2SO4 (0.05 – 6 M), solid/liquid phase ratio (1:50 – 1:100), temperature (20 – 80 ºC), agitation speed (300 – 900 rpm), and leaching time (0.5 - 6 h) on the dissolution of REEs from apatite ore were examined in various intervals. The contents of main REEs in the apatite ore used in this study were (as % wt): 3 % La, 6 % Ce, 0.6 % Pr, 2.1 % Nd, 0.2 % Sm and 0.3 % Y. X-ray diffraction (XRD) analysis identified fluorapatite and phlogopite as main minerals in the ore. The results obtained from leaching experiments showed that more than 85% of REEs were dissolved from the apatite ore under the optimized conditions, which were: 1 M H2SO4, particle size of -150 + 100 µm, S:L phase ratio of 1:50, agitation speed of 500 rpm at 20 ºC for 1h. The XRD analysis revealed that main mineral compositions of the residues from 1M and 6 M H2SO4 leaching are gypsum (CaSO42H2O) and hemigypsum (CaSO40.5H2O), respectively.INTRODUCTIONThe term rare earth elements (REEs) denote the group of 17 chemically similar metallic elements consisting of the 15 lanthanides, plus yttrium (Y) and scandium (Sc) in the periodic table. These metallic elements are generally divided into two sub-groups; (1) the cerium sub-group, which is called “light rare earth elements” (LREEs), includes the elements from lanthanum (La) to europium (Eu), and (2) the yttrium (Y) sub-group elements, which are known as “heavy rare earth elements” (HREEs), are the remaining lanthanides from gadolinium (Gd) to lutetium (Lu) plus yttrium (Gupta and Krishnamurthy, 2005). The REEs occur together in the minerals due to their chemical and physical similarities, which cause problems of separating them from one another (Abreu and Morais, 2014). Although REEs are relatively abundant in the earth’s crust, they are typically dispersed and rarely occur in concentrated forms, making them economically challenging to obtain. There are a wide variety of rare earth minerals, however economic deposits of REEs in mining are bastnasite (La, Ce) FCO3, monazite (Ce, La, Y, Th) PO4, and xenotime YPO4 (Binnemans, 2013; Xie, et al, 2014). Due to the unique physical, chemical, catalytic, electrical, magnetic and optical properties of REEs, demand of these elements has increased dramatically with the advent of new technologies in electronics, communication, construction, energy and medicine (Jordens, et al, 2013). Since 1990, China has provided about 90 % of REEs worldwide. Japan and United States are the largest consumers of China’s REEs. In 2010, China announced to reduce REEs exports to Japan, as it tended to increase prices of REEs and to reduce a stable supply of REEs in the world market (Humphries, 2013). Therefore, there has been an increase in recent exploration activities intended to reveal new commercial sources of REEs and to bring them into production (Antico, et al, 1996). Apatite is an important host mineral for REEs in igneous and metamorphic rocks and can be used as an ore for those metals (Kanazawa and Kamitani, 2006). Apatite is also the main source of phosphate fertilizers and phosphoric acid (Habashi, 2013; Emsbo, 2015)."

Jan 1, 2016

By Fumito Tanaka

In the Mitsubishi Continuous Copper Smelting & Converting Process, the heat for the dissolution of scraps is effectively supplied from the melts strongly stirred by top injection. Various kinds of shape of scraps not only powder but also lump, sheet, cube and so on can be treated without any emission of dust and fugitive gas, and no additional furnaces for scrap processing is necessary. Therefore, this process is much suitable for recycling. The authors have investigated the melting rate of ice sphere into a water bath equipped with top blowing lances as a basic study for the dissolution of scrap. Hydrodynamic experiments were carried out, and mathematical models were applied to the results. The results show that the melting rate of ice sphere strongly depends on the standing waves at the bath surface.

Jan 1, 2001

By VÍCTOR VÁZQUEZ-VÁZQUEZ, GUILLERMO TIBURCIO-MUNIVE, María M. Salazar-Campoy, JESÚS L. VALENZUELA-GARCÍA, OFELIA HERNÁNDEZ-NEGRETE

The present study examined a process for precious metal recovery (silver and gold) from difficult minerals which exhibit refractory characteristics to cyanidation and ammonium thiosulfate leaching (low extraction and high consumption of leaching agent). It is well known that mangano-argentiferous minerals are mainly composed of manganese, silver, gold, and iron. In this research, a mineral sample from Monte del Favor mine, located in Hostotipaquillo, Jalisco, Mexico, was physically and chemically characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), fire assay, and atomic absorption spectroscopy (AAS). Two-stage leaching was carried out: first to eliminate manganese from the sample using sodium sulfite (Na2SO3) as a reductive reagent and sulfuric acid (H2SO4) and a second stage to dissolve silver and gold with sodium hypochlorite (NaClO) and hydrochloric acid (HCl); the results show extraction around 96% for Mn and 98.73% and 83%of Ag and Au, respectively. The usefulness of high acidity and Na2SO3 to obtain good results in Mn and Ag leaching is discussed along with the roles that HCl and NaClO play in the dissolution of Ag and Au values.

Apr 15, 2020

By VÍCTOR VÁZQUEZ-VÁZQUEZ, GUILLERMO TIBURCIO-MUNIVE, María M. Salazar-Campoy, JESÚS L. VALENZUELA-GARCÍA, OFELIA HERNÁNDEZ-NEGRETE

This study examines a process for the recovery of precious metals from difficult minerals that exhibit refractory characteristics to cyanidation: low extraction of metals and high consumption of leaching reagent. A mineral sample from Monte del Favor Mine, located in Hostotipaquillo, Jalisco, Mexico, was physically and chemically characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), fire assay and atomic absorption spectroscopy (AAS). Two stages of leaching were carried out, first to eliminate manganese from the sample using sodium sulfite (Na2SO3) as a reductive reagent along with sulfuric acid (H2SO4), and second to dissolve gold and silver with hydrochloric acid (HCl) and sodium hypochlorite (NaClO). The results show extractions of around 96 percent for manganese (Mn), 98.73 percent for silver (Ag) and 83 percent for gold (Au). The usefulness of high acidity and Na2SO3 to obtain better results in Mn and Ag leaching are discussed along with the roles that HCl and NaClO play in Ag and Au dissolution values.

By Batric Pesic

Silver dissolution with thiourea was studied by using the rotating disk technique. The major parameters studied were: thiourea concentration (0-0.5M), ferric sulfate concentration (0-0.5M), sulfuric acid concentration (0-0.5M), and the effect of many foreign ions (Mn, o.i, Co, Ca, Na, etc.). Temperature effect was studied in the range 5-35 .C. The activation energy was 5.4 Kcal/mole. The dissolution of silver was first order with respect to ferric sulfate, and the secord order with respect to thiourea. Among the additives, copper had a dramatically negative effect. The strong oxidants such as hydrogen peroxide and manganese dioxide were also detrimental for silver dissolution. Silver does not dissolve with thiourea in the absence of ferric ions. Sulfuric acid does not participate in the dissolution reaction either. Chemically, the most important parameter for silver dissolution is the ferric sulfate/thiourea ratio. Thus, in the solutions with excess of ferric sulfate, a solid silver-thiourea complex is formed, which precludes transfer of silver into solution. In the solutions with the excess of thiourea, the free thiourea reacts with formed solid silver-thiourea complex and silver goes into the solution. The solid silver-thiourea complex was characterized according to its chemical composition. The complex contains 6.54%C, 2.49\H, 14.77%N, 16.09%0, 21.62%8, and 37.13% Ag. This composition corresponds to a Ag2so4.3'1U.2ff:i0 compound The soluble silver species are present in the solution as the dimers of AgTU+3 complexes.

Jan 1, 1989

By R. K. Paramguru, K. Srinivasa Rao

This paper describes a new approach for examining the kinetics and mechanism of zinc dissolution from sphalerite concentrate in acidic ferric sulfate solution in the presence of manganese dioxide. A literature search was performed to access the possible action of the two oxidizing agents, i.e., ferric ion and manganese dioxide. The possibility of galvanic coupling between ZnS and MnO2 and the cyclic action of the redox couple, Fe2+/Fe3+, on these two minerals were theoretically examined based on corrosion principles. Expressions for the mixed potential (Em) and the mixed current (im) were derived for the relevant corrosion and galvanic couples. Leaching experiments were conducted to establish which of the above phenomena is operative during leaching. The results indicated that the dissolution mostly occurs by the action of ferric ion on ins producing ferrous ions. The presence of MnO2 enables a quick conversion of ferrous to ferric, which maintains the rate of in dissolution. The process has promising features for commercial exploitation.

Jan 1, 1999

Zinc enters into solution on aeration of sphalerite in deionised water. It has been observed that less zinc dissolves in a copper vessel than when the same operation is carried out in a glass vessel of similar shape and size.

Jan 1, 1980

By P. L. Claessens, S. Belisle, C. Bowen

"Use of zinc shot feed is a well-established procedure among North American electro-galvanizers. This form of zinc is easy to handle and relatively inexpensive when compared with zinc oxide. This paper reports results on the kinetics of zinc shot dissolution in traditional pure zinc solutions and in electrolytes used for the plating of nickel/zinc alloys. Despite the cementation of minor amounts of nickel in the latter solution, acceptable dissolution rates of the zinc shot can be achieved through proper adjustment of the solution velocity. Under these conditions, the nickel shell produced by cementation is continuously abraded, exposing the underlying zinc.IntroductionThe use of insoluble, noble metal-containing anodes rather than soluble zinc anodes for the operation of high current density electro-galvanizing lines has gained almost universal acceptance. Two major reasons for this trend are:• improved control of the process by virtue of constant inter-electrode distance; and• increased productivity because the operation of the lines does not require the relatively frequent interruptions for replacement of consumed anodes .The results of the principal anode and cathode reactions are, respectively, depletion of the zinc content of the electrolyte and the increase on its acidity;"

Jan 1, 1991

By Elizaveta Cheremisina

In steelmaking process lime serves as flux. Rapid lime assimilation and slag formation of the desired composition have a significant effect on the refining reactions. It is important to know the rate limiting step of lime dissolution to control and improve the converter process. Kinetics of pure CaO and industrial lime dissolution in model slag has been studied in the range of temperatures 1300 –1600°C. Lime samples were prepared in cylinder form and immersed in the melt for predetermined time. Considering the total mass balance of CaO in the slag and linear dimensions of lime samples, mass transfer coefficients were derived. Diffusion coefficients were calculated under conditions of non-stationary diffusion. The derived activation energy of less than 200 kJ/mol indicates that diffusion is the limiting step in the process of lime-dissolution in slag.

Oct 30, 2017

By M. Seyed Ahmadi

This study investigates the role of nitrogen gas injection in the dissolution rate of Si into liquid Al. A unique revolving liquid metal tank was used, with a capacity of 50 kg of liquid Al. Experiments without gas injection have shown that the dissolution of Si increases as the bath superheat and the tangential velocity of the liquid Al increase. When injecting nitrogen gas at flow rates between 0-5 lit/min in the vicinity of the solid Si, results so far clearly show greater dissolution. In addition, results on the role of the gas flow rate relative to the position of the nozzle are presented and analyzed.

Jan 1, 2011

By Michael Schindler

Uranyl mineral dissolution appears to be complex, affected by factors such as solution pH and the presence of various cations in solution, and sometimes involving formation of secondary surface precipitates. Such secondary precipitates potentially could armor the underlying uranyl mineral surfaces from further dissolution. A detailed understanding on the formation of secondary precipitate is therefore essential for predictive modeling of radionuclide fate and transport in the subsurface. Several types of secondary precipitates on the surface of uranyl minerals were examined using Atomic Force Microscopy, Scanning Electron Microscopy, and, Xray Photoelectron Spectroscopy.

Aug 1, 2010

By Ismael Nogueira Rabelo de Melo

A adição de Fe-Nb em ligas com alto teor de carbono apresenta baixas taxas de dissolução devido à formação de uma camada carburada na superfície, exigindo longos tempos para dissolução dos carbonetos NbC no banho. Foi avaliada a eficiência da dissolução de Fe-Nb em pó pelo processo de simples adição em uma liga de Ferro Fundido Branco com Alto Teor de Cromo. No processo foram obtidas eficiências de dissolução em torno de 90% e os carbonetos NbC apresentaram em formas finas e em aglomerados.

Oct 30, 2017

By John Ralston, Jinming Duan, David R. E. Snoswell, Daniel Fornasiero, Jingwu Yang

The colloidal stability of synthetic silica spheres with clean, methylated and dehydroxylated sur¬faces was studied at different concentrations of dissolved gas and KCl electrolyte at a fixed pH of 4.2. A classic stability ratio/electrolyte concentration analysis shows that hydrophobic, methy¬lated particles undergo faster rates of aggregation with increasing concentrations of dissolved carbon dioxide. Similar data for hydrophilic particles and dehydroxylated particles show no change as a function of dissolved carbon dioxide concentration. Zeta potential data behave simi¬larly, showing a strong influence of dissolved gas only for methylated particles. The results are interpreted in terms of DLVO theory, with the surface-to-surface interaction dominated by the presence of very small protruding bubbles. Direct evidence for the existence of these very small gas bubbles (or "nanobubbles") was obtained using tapping mode atomic force microscopy. Small bubbles do not form on smooth, hydrophilic, or dehydroxylated silicon oxide water sur¬faces immersed in aqueous solutions under known levels of gas supersaturation. Randomly dis¬tributed small bubbles were observed over the whole surface of observation on methylated surfaces of controlled roughness. Bubbles formed on rough, methylated surfaces were larger and less-densely distributed than those on a smooth surface of similar hydrophobicity. The process of bubble coalescence was observed as a function of time. The macroscopic contact angle, measured with respect to the aqueous or gas phase, is very different from the microscopic contact angle detected by TMAFM and appears to be due to the influence of line tension at the pinned three¬phase contact line. The latter has a value of -3 x 10-10 N and acts to stabilize the small bubbles, flattening them and thereby reducing the Laplace pressure.

Jan 1, 2005

By P. Somasundaran

Beneficiation by froth flotation, which exploits the difference in surface properties of minerals, has been a promising method for coal cleaning. However, dissolved mineral species present in coal flotation systems can interact with particles and other species leading to drastic effects on flotation. Particularly, precipitation or adsorption of such species on the particles can alter their surface properties and thus influence the efficiency of coal cleaning. In this work, the bulk and surface precipitation of the dissolved mineral species present in Pittsburgh No. 8 coal was investigated under controlled experimental conditions. Changes in the surface properties of coal due to the precipitation were monitored by following zeta potential. Solution potential data were used to elucidate the mechanism of the precipitation. The effect of the precipitation of the dissolved species on the floatability of coal was found to be marked.

Jan 1, 1995

Distal air-fall ashes are widespread deposits that may record volcanism many hundreds of kilometres from their source. They are characteristically thin, fine-grained and have a low preservation potential usually being either eroded, or reworked and incorporated in overlying sediments following deposition. The most likely sites of accumulation are deep sea, lake and swamp environments where low energy conditions favour preservation. Post-depositional alteration of predominantly glassy volcanic ash is commonly extensive hampering identification of such layers in the geological record. As a result air-fall tuffs are poorly represented in the rock record and furthermore are commonly misinterpreted. Southeast Queensland during the late Triassic hosted active silicic volcanism and a number of fault-controlled basins in which coal-bearing sediments were accumulating. Silicic volcanics of late Triassic age are represented by the Brisbane Tuff in the Brisbane city area, the Chillingham Volcanics to the south of Brisbane and extending into New South Wales, the North Arm and Mount Byron Volcanics to the north of Brisbane, the Aranbanga Beds exposed around Gayndah and the Agnes Waters and Muncon Volcanics which occur northwest of Bundaberg. Stephens (1986) interprets these Volcanics as the remnants of a major silicic igneous 'province which he likens to modern continental orogenic margins. The Ipswich, Tarong and Callide Basins of southeast Queensland all contain coal measure sequences of late Triassic age that accumulated in alluvial plain environments. A Dicroidium flora is common to all and palynol.ogical evidence indicates a late Triassic (Carnian) age (de Jersey, 1975; Stevens, 1981). The coal seams of the three basins are characterised by their thickness (up to 25 m) and the presence of abundant thin, laterally persistent, kaolinite claystones (tonsteins) that show a marked similarity of morphology, texture and mineralogy. Detailed studies of the Ipswich Coal Measures (Falkner, 1986) suggest a volcanic air-fall origin for the tonsteins of the Ipswich Basin. Similar.tonsteins from the Tarong and Callide Basins provide evidence for widespread silicic volcanism during the late Triassic in southeast Queensland.

Jan 1, 1987

By Evgeny G. Gurvich

While direct study of high temperature hydrothermal activity and the associated mineral formation as well as study of their scales are possible in the modern ocean, researchers are deprived of such opportunity for past geologic time. Even in cases where hydrothermal deposits that formed in the geological past are preserved they have been covered by sediments or overlain by lava and have become inaccessible after a time for obser-vation and sampling. Rarely are these buried hydrothermal deposits found during deep-sea drilling or coring operations, and their direct study on an ocean scale is impossible at present. Even within hydrothermal fields, without special preliminary detailed surveys, the probability of intersecting hydrothermal edifices that are covered by sediments becomes a rare event.

Aug 24, 2006

After the war that was nearing an end In early 1945, regular consulting work for Bralorne, the Bradleys, Pennsalt Chemical Co., and a directorship and occasional consulting for Homestake Mining Co. made it almost certain that in spite of my 61 years I would have enough work to feed my family. But this routine work would not provide enough income to lay up funds for the inevitable future when I could no longer do arduous work. And it would not give me the adventure that had first lured me into mining. Therefore I was greatly relieved as well as pleased when, in the 18 months from April 1945 to November 1946, I was asked to make three of the most adventurous as well as profitable examinations that ever came my way. Pati[n]o Mines, Bolivia The first of the exciting jobs was an examination of the Pati[n]o tin mines in Bolivia. After I had unsuccessfully tried to induce Anaconda to purchase these mines In 1915, the World War I crisis that had forced the half-Indian accountant to try to sell the mines had come to an end. The European market for tin improved dramatically, and "Don Simon" was able to borrow money for expenses while the concentrates were still In Bolivia. He took advantage of the favorable conditions by buying adjacent properties and increasing development work until his Bolivian tin mines were the greatest in the world. And his daughter had marled the French Count de Boisrouvain and was cutting a swath In high International society. Pati[n]o wanted to get rid of the drudgery of running a complicated mining Industry in a remote area In Bolivia when the fleshpots of Paris were much more seductive. An added incentive was the fact that his miners had become unruly and had even threatened his 11fe.

Jan 1, 1976