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The New South Wales coal industry is a highly mechanised well organised industry which has developed from an annual production of slightly less than 13 million tons in 1950 to over 33 million tons in 1969. Although continuous miners were not introduced into the mines until 1950, by June 1969 the percentage of coal won by these units was 87.3. The paper describes mining conditions in the various coalfields of the State, their complexities and problems and how these have been dealt with. The introduction of fully mechanised longwall faces has presented a challenge which has been accepted and descriptions of systems in use are discussed. Major expansion of the industry is anticipated to meet the requirements of the growing Australian steel industry, for local power generation and to meet the increasing demands of overseas markets.

Jan 1, 1980

By W. D. Grimsley, R. P. King, J. B. See

Samples (15 to 20 g) of pre-calcined Mamatwan manganese ore or pure Mn 304 smaller than 48 mesh were reacted at temperatures in the range 1000 to 1300°C with samples of spectrographically pure graphite smaller than 325 mesh. Samples (1 g) of ore or pure Mn02 smaller than 48 mesh were reacted at temperatures of 1000 and 1200°C with pure graphite fines in argon, with graphite in carbon, .'1onoxide, and with carbon monoxide alone. In each case, the loss of mass as a function of time was recorded with a hermobalance. The rate and degree of reduction were found to increase with additions of carbon and with increasing temperature up to 1300oC, when they reached their maximum. The shape of the reduction curves, together with the results obtained from examination of the products of reaction by microscopy and X-ray diffraction, were used as the basis for a postulated reduction mechanism. Some details are given of an initial kinetic model that was used to verify the proposed mechanism. It was found that the reduction of Mamatwan ore by graphite at temperatures in the range 1000 to 1300°C occurs in two stages: (i) an initial stage during which the higher oxides of manganese are rapidly reduced to MnO with concurrent formation of CaMn2O4 and (ii) a longer stage during which CaMn2O4 and MnO are reduced to carbides by carbon dissolved in the ferromanganese phase.

Jan 1, 1978

By R. D. Hancock

The complex responsible for the poisoning of anion-exchange resins is identified as the anionic cobaltic penta¬cyanide mono aquo species. It is shown that, at high concentration, this species polymerizes in solutions of pH less than 9. A mechanism for poisoning is presented that involves adsorption of anionic cobalt cyanide by a normal ion-exchange process, followed by polymerization within the resin matrix to form complexes that are too large to diffuse readily through the resin pores. The effects of resin structure and functionality on the extent of cobalt poisoning are examined, and the effect of cobalt poisoning on the kinetics and equilibrium loading of uranium is discussed.

Jan 1, 1979

By Rizo-Pairón Alfonso, A. M. Gaudin

PREVIOUS studies of activation in flotation have directed attention to the action of the activator on the mineral to be floated rather than to the relationship of the activator to the collector The latter phase of the problem, however, seems to have definite scientific, if not also practical, interest In the investigation reported in this paper, experiments were carried out, largely with quartz as subject, barium as activator, and oleate as collector The results obtained indicate that a I I ratio of collector ion to activator ion gives optimum results, and that a 2 I ratio almost fails to achieve activation and flotation Yet, a 2 I ratio would have been expected on stoichiometric grounds, had the coating been a normal salt of the activator ion with the collector ion, since barium is a divalent cation and oleate a monovalent anion To interpret and rationalize the observations, considerations of the crystal chemistry of quartz are helpful The point of view to which these considerations lead may be of general applicability to systems involving suspensions of solids in liquids, they confirm that an adsorbed coating is inescapable APPARATUS AND SUPPLIES The experimental work consisted in barium-ion abstraction tests, hydrogen-ion and hydroxyl-ion abstraction tests, flotation tests, and determinations of the surface of the crushed quartz The flotation machine was built according to the design of D W McGlashan It consists of a drill press in which the bit has been replaced by a stainless-steel impellor surrounding a stainless-steel stator, as in the Fagergren laboratory machine The air intake is controlled by a valve, and the cell consists of a beaker The quartz was obtained from vein quartz stored in large chunks It was first crushed to 20 mesh, then sized on a 28-mesh screen The 20 to 28-mesh size alone was retained for use This size was freed of coarse iron by passage through a Ball-Norton magnetic separator, bleached with boiling hydrochloric acid to remove residual abraded iron, washed with distilled water until the washings were thoroughly free of ferrous, ferric, and excess hydrogen ion, and stored in covered Pyrex beakers under water until used The barium was used as barium chloride, Baker's analyzed C P The oleate was used as sodium oleate It was prepared from sodium hydroxide, Baker's analyzed C P , and oleic acid purified by R R de Arellano3 in the laboratories at the Massachusetts Institute of Technology The purification procedure was elaborated from the recent researches of Brown and Shinowara 2 It consisted in (I) saponification of olive oil with potassium

Jan 1, 1942

By Alfonso Rizo-Patrón, A. M. Gaudin

PREVIOUS studies of activation in flotation have directed attention to the action of the activator on the mineral to be floated rather than to the relationship of the activator to the collector. The latter phase of the problem, however, seems to have definite scientific, if not also practical, interest. In the investigation reported in this paper, experiments were carried out, largely with quartz as subject, barium as activator, and oleate as collector. The results obtained indicate that a I : I ratio of collector ion to activator ion gives optimum results, and that a 2:I ratio almost fails to achieve activation and flotation. Yet, a 2:I ratio would have been expected on stoichiometric grounds, had the coating been a normal salt of the activator ion with the collector ion, since barium is a divalent cation and oleate a monovalent anion. To interpret and rationalize the observations, considerations of the crystal chemistry of quartz are helpful. The point of view to which these considerations lead may be of general applicability to systems involving suspensions of solids in liquids; they confirm that an adsorbed coating is inescapable. APPARATUS AND SUPPLIES The experimental work consisted in barium-ion abstraction tests, hydrogen-ion and hydroxyl-ion abstraction tests, flotation tests, and determinations of the surface of the crushed quartz. The flotation machine was built according to the design of D. W. McGlashan.* It consists of a drill press in which the bit has been replaced by a stainless-steel impellor surrounding a stainless-steel stator, as in the Fagergren laboratory machine. The air intake is controlled by a valve, and the cell consists of a beaker. The quartz was obtained from vein quartz stored in large chunks. It was first crushed to 20 mesh, then sized on a 28-mesh screen. The 20 to 28-mesh size alone was retained for use. This size was freed of coarse iron by passage through a Ball Norton magnetic separator, bleached with boiling hydrochloric acid to remove residual abraded iron, washed with distilled water until the washings were thoroughly free of ferrous, ferric, and excess hydrogen ion, and stored in covered Pyrex beakers under water until used. The barium was used as barium chloride, Baker's analyzed C. P. The oleate was used as sodium oleate. It was prepared from sodium hydroxide, Baker's analyzed C. P., and oleic acid purified by R. R. de Arellano3 in the laboratories at the Massachusetts Institute of Technology. The purification procedure was elaborated from the recent researches of Brown and Shinowara.2 It consisted in: (I) saponification of olive oil with potassium

Jan 1, 1942

By Feng Shuyu Yang Nianhua

According to the results of high speed photography tests, particle velocity measurement tests and the digital calculation with TP2 software, the shape of shock wave, the declined laws of the shock wave propagation speed and the peak particle velocity are described and analyzed in detail. New viewpoints about the theories of blasting fragmentation based on analysis of the progressive pictures of the fracture region are given. The formula for calculating the depth of fracture regions is established on the basis of the new viewpoints.

Jan 1, 1997

By D. B. Dreisinger, D. G. Dixon, G. Nazari

"The kinetics of chalcopyrite leaching in acidic ferric/ferrous sulfate media under atmospheric conditions in the presence of pyrite has been investigated. It has been found that pyrite samples from different sources affect the rate of chalcopyrite leaching differently. A strong correlation between the amount of silver associated with the pyrite and its effectiveness has been noted. In this study, improvement of the catalytic properties of pyrite such that all pyrite samples accelerate the rate of copper extraction regardless of their sources is demonstrated, and a detailed discussion of the mechanisms involved in the process of chalcopyrite leaching in the presence of silverenhanced pyrite is presented. INTRODUCTIONIt is well known that chalcopyrite resists leaching in sulfate media. It has been proved that pyrite facilitates the leaching of chalcopyrite (Berry et al., 1978; Dixon et al., 2008; Mehta and Murr, 1983; Muñoz et al., 2008; Nowak et al., 1984, Tshilombo, 2004). Considering the catalytic effects of pyrite on accelerating the kinetics of chalcopyrite leaching, Dixon and Tshilombo (2005) have developed a new process, known as Galvanox™, which has several advantages over other hydrometallurgical processes. Galvanox™ runs under atmospheric conditions, so it requires only low-cost leaching tanks. The sulfur yield at this temperature is high (>95%) which leads to low oxygen consumption and low sulfuric acid generation. The operating temperature is below the melting point of sulfur which eliminates the use of surfactants. This process also does not require fine grinding. Reaction 1 shows the overall leaching reaction in the Galvanox™ process.CuFeS2 + O2 + 2 H2SO4 = CuSO4 + FeSO4 + 2 S0 + 2 H2O (1)Complete copper recovery from the Galvanox™ process can be achieved at a considerably higher rate than other atmospheric ferric sulfate leaching processes (Dixon et al., 2008). Recycling pyrite and recovering copper from tailings with the Galvanox™ process have also been evaluated in continuous pilot leaching campaigns (Dixon et al., 2007)."

Jan 1, 2012

By R. E. Zimmerman, Shiou-Chuan Sun

An evaluation of the mechanism surrounding the froth flotation of coarse coal and mineral particles as a result of experiments conducted at The Pennsylvania State College. Maximum size ranges for both bituminous and anthracite coals were established as well as the factors affecting the floating of coarse particles.

Jan 5, 1950

By Herbert H. Kellogg, Nathaniel Arbiter, Arthur F. Taggart

THE experimental work herein described is presented in support of the following broad hypothesis: Conditioning of metals and metallic sulphides by amine collectors involves metathetic reaction at the solid surface between the collector and an oxidized metallic compound, to produce a coating comprising an amine-bearing compound of low solubility in the system. The type of reaction is different in acid and in basic solutions; both types may occur simultaneously in near-neutral pulps. EXPERIMENTAL The experiments comprise contact-angle tests with a variety of metals and metallic sulphides and extraction tests on ground chalcocite. Contact-angle tests were made principally on metals. Covellite paralleled metallic copper in amine solution at pH 8.8 (Table 3) and in alkaline water, but maintained an angle of about 70° in 10-3 HCl solution, where metallic copper lost its angle. The tests with anionic collectors (Table I) indicate that the behavior of metals in general is parallel to that of their minerals in anionic solutions. It is believed that this is generally true with cationic collectors also, but the covellite test is a warning against a broad assumption to this effect. All test specimens were mounted in Transoptic.* All tests in conditioning solution were preceded by a test in distilled water; cleaning and polishing were continued in every case until the angle in water was zero. Subsequent transfers into and out of solutions and test cells were made in such a way as to prevent exposure of the surface to air.1 The amine used was primary laurylamine, Armour and Co., AM-1120. It was used in the form of the hydrochloride, obtained by precipitation with gaseous hydrochloric acid from an ether solution of the amine, and purified by two recrystallizations from ether-alcohol.2 Inorganic and other test reagents were standard laboratory grades. [ ] Temperatures were not controlled; the probable range of test-solution temperatures is 65° t0 80°F.

Jan 1, 1943

The steam-filtration process for dewatering solids involves the application of slightly superheated steam to a filter cake during filtration. The mechanism by which the technique promotes water removal has been deduced from bench-scale experiments on coal and on granular iron ore concentrates. The mechanism, along with some of the applications and limitations of the process, is presented. Introduction I N the steam-filtration process, slightly super-heated steam is applied to the filter cake during filtration to remove more water than can be extracted by conventional filtration. Although this process was developed by Burton for coal filtration (1), it should have far wider applicability; certainly, it could be used to treat any mineral product, because only low-temperature steam is needed and most conventional filtration equipment can be easily adapted to it. As few restrictions apply to this process, however, it is important that its more obvious advantages and disadvantages be appreciated and, especially, that the criteria on which economic evaluations can be based are understood.

Jan 1, 1965

By C V. Putnis, T Geisler, A Putnis

In nature, ilmenite (FeTiO3) undergoes weathering through oxidation and removal of Fe to form an apparently continuous series of compositions from ilmenite to pseudorutile (ideally Fe2Ti3O9), and with further weathering, to leucoxene. To determine the mechanism of acid-leaching of ilmenite to ultimately form rutile, we have carried out an experimental study of ilmenite alteration in autoclaves at 150¦C in HCl solutions. Resulting products were studied by X-ray diffraction, scanning electron microscopy, electron microprobe and Raman spectroscopy. In some experiments the solution was initially enriched in 18O and the distribution of the isotope in the alteration products mapped from the peak shift in the Raman spectra. The results indicate that the alteration may proceed in two stages, each with a sharp interface between the parent phase and the product. The alteration begins at the original ilmenite crystal surface and along cracks through which the fluid can migrate. The first alteration product is pseudorutile û no phases intermediate between ilmenite and pseudorutile were detected. The textural relationship between ilmenite and pseudorutile suggests a coupled dissolution-reprecipitation mechanism rather than a solid state continuous oxidation and Fe diffusion mechanism. The second stage involves a further dissolution-reprecipitation step to form rutile. Raman spectroscopy shows that the 18O is incorporated in the rutile during the recrystallisation. Throughout the alteration process the original morphology of the ilmenite is preserved although the product is highly porous. The rutile inherits crystallographic information from the parent ilmenite, resulting in a triply-twinned rutile microstructure.

Jan 1, 2008

By R. C. A. Thurston

AT A FATIGUE SESSION organised by the A.S.T.M. in 1949, R. E. Peterson presented a brief introductory paper ( 1) in which lie referred to a discussion on the fatigue of metals which took place in England in 1849, and then proceeded to review some of the subsequent researches concerning the mechanism of fatigue. In the course of the review, he discussed metallograpl1ic studies with single crystals and polycrystalline materials, studies with X-ray methods, and the application of the electron microscope. During that hundred-year period considerable progress was made toward a better under-standing of the nature of fatigue, although it is probable that even greater attention was directed to the more practical aspects of the problem, such as the effects of notches, temperature, corrosion, surface treatment, residual stresses, and so on. Since then there has been an appreciable acceleration in the tempo of the fundamental work, partly influenced by the rapid development of the theory of dislocations, with the result that our knowledge of the mechanism of slip, the initiation of fatigue cracks, and their subsequent propagation, has still further advanced, although it is by no means complete as yet. The present paper is an attempt to out-line the more recent developments in these basic studies, to correlate them when possible, and to draw attention to those directions in which research might profitably be pursued.

Jan 1, 1957

In this paper, uniaxial compression tests were conducted on intact rocks and broken rocks that were reinforced by grouting, and the effects of grouting on the strength of broken rocks were analyzed. The results show that after grouting reinforcement, the bearing capacity of broken rocks with different lithologies increased, and their uniaxial compressive strength recovered by approximately 6%–16%. The results indicated that the stronger the rock, the smaller the strength recovery of the consolidated body formed after grouting. At the same time, using borehole camera observation and deep overburden strata separations, the fracture development characteristics of surrounding rocks of the gob-side retained entry were analyzed and divided into different regions. On this basis, a guided grouting method was proposed; that is, shallow hole grouting was first used in the plastic zone of the broken surrounding rocks to form the isolation layer, and then deep grouting holes were arranged in the elastic-plastic zone of the transition zone to guide the slurry flow to the shallow unfilled zone. Therefore, the broken surrounding rocks were reinforced into an integrated body and selfbearing capacity improved.

Jul 28, 2020

By Arthur F. Taggart

RECENT jig practice has shown such marked departures from the pronouncements of the textbooks, particularly as to particle size recovered and size range of feed, as to make it desirable to reexamine the mechanism of jig action. This paper presents the results of such a study. The general conclusions of the paper are: I. A jig bed is a bi-functioned as well as bi-parted body. The upper layer comprises a plastic stream moving slowly in a substantially horizontal direction from feed lip to tail board. It serves to rough out tailing and light middling and to pick up heavy middling and lift it out of the jig box. The lower layer acts as the ultimate separating means by absorbing concentrate and rejecting heavy middling. 2. The separating function of the lower layer is performed in three definitely different ways, depending upon the relative sizes of the grains presented to it and those composing it. EXPERIMENTAL The experimental work consisted of close and long-continued visual observations of operating beds in a plunger jig, eccentric driven, and in determinations of the settling rates of various metal spheres through a quartz bed under various conditions of operation. Falling velocities were measured by an ingenious method devised by A. C. Dorenfeld, a student in the Mining Department at Columbia. Spheres of different metallic alloys, Y8-in. diameter, were cast with a short piece of fine copper wire frozen in to serve for suspension. A short piece of black cotton thread was looped to the top of the wire to serve as an indicator. The set-up for a test is shown in Fig. I. The thread should be boiled, if necessary, to make it freely water absorbent. The piece of clean plate glass D is supported rigidly at the proper height in a vertical position. The white scale E is similarly supported behind the glass. At the beginning of a test, D is filmed with water by holding it (best with clean rubber finger cots) under running tap water. It is then clamped in approximate position and C, already wet, is laid across it and drawn straight and vertical with the upper end at or near the top of D, and the ball A slightly above the top of the expanded bed. The water film holds the string to the glass. For a test the string is released, its upper end position noted just after the top of the ball becomes submerged, when the corresponding time is read, and thereafter simultaneous readings of position and time are taken as desired. Results of the visual studies of the bed are given at the pertinent places in the following discussion. Results of the settling tests are summarized in Figs. 2 and 3. DEFINITIONS The name bed as used herein refers to the entire mixture of solids and water filling the jig box. A layer is a stratum of a bed composed of particles of substantially the same specific gravities. A granular product is long-range when it approximates a crushed or ground product limited as to upper size only; a shorlrange product is one closely sized. A bed is loaded when operating with continuous feed

Jan 1, 1943

By J. B. Reed, T. A. Read, H. Rosenthal

Although the season cracking of brass has been a subject of experimental investigation for more than thirty years, the mechanism that is responsible for this phenomenon is still obscure. While at- tempts to elucidate the stress-corrosion cracking of some alloys have been relatively successful, the principal accomplishments made in the studies of the season cracking of brass have consisted of improved techniques for the fabrication of articles of alpha brass, which reduce the danger of season-cracking failure in service. The primary purpose of the present paper is to collect the published experimental data which appear to be of importance to the development of an adequate theory of the mechanism of the season cracking of brass. Some of the possible mechanisms which have been proposed will also be discussed, together with some promising avenues of future attack on the problems. Several excellent survey papers on season cracking are available, including the recent ones by Croft and Sachs(1)2 and by Gibbs(2). The principal facts concerning season cracking, as presented in these papers, may be summarized as follows. The season cracking of alpha brass is a special type of stress-corrosion failure, which may occur in atmospheres containing ammonia, air, and water vapor. The stress causing failure may be either the

Jan 1, 1945

By Dan Wang, Qiuju Li, Xiao Guo

The chemical states and ions interaction were significant interest to understanding columbite mineral/acid solution interface dissolution and reaction. The present research work was focus to explore the specific cations ( Nb5+, Fe2+, Fe3+) distribution near the ferrocolumbite mineral/acid solution interface, and determine these cations leaching sequence in sulfuric acid solution. X-ray photoelectron spectroscopy had the potential to provide detailed dissolution information by resolving chemical state and ion distribution of ferrocolumbite during sulfuric acid leaching process. The binding energy decreased in sequence as Nb5+- O < Fe2+- O < Fe3+- O, and increased in sequence as Fe3+- SO4 < Fe2+- SO4 < Nb5+- SO4 which revealed Nb in ferrocolumbite mineral more easily leached comparing to Fe. The ratio of Fe2+- O/Fe3+-O on leaching residue decreased, and Fe2+- SO4/Fe3+-SO4 ratio increased as sulfuric acid contraction increasing suggested that the Fe2+ oxidized to Fe3+ and released Nb from mineral and dissolved into leaching solution. The ratio of Nb/Fe was lower 0.07 with sulfuric acid contraction increasing which meant Nb dissolution promoted by oxidation of iron. The dissolution mechanism of Fe element in ferrocolumbite mineral was Fe2+- O broken and generated Fe2+. Fe2+ was oxidized to Fe3+ in concentrated sulfuric acid leaching solution. The dissolution mechanism of Nb in ferrocolumbite was that Nb5+- O was directly digested by H+, and the released Nb5+ complex with SO4 2− ion formed cation − anion pairs. The coordination of formation Nb5+- SO4 pairs and oxidation Fe2+ in mineral could promote ferrocolumbite dissolution.

Aug 5, 2023

By Shiou-Chuan Sun

THERE are several postulations for the mechanism of slime-coating. Ince1 proposed the electrostatic hypothesis, del Giudice2 suggested the chemical theory; Bankoff3 reported that slime-coating is inhibited whenever the surfaces of the slime particles are ionized sufficiently for Brownian movement to occur, and is facilitated when they are not. These postulations were examined by experiments involving the Burton tube, the cataphoretic cell, and slime-coating. The techniques involved will be described elsewhere in this paper. The electrostatic hypothesis, supported by migration experiments in a Burton tube, was abandoned by del Giudice.2 Experiments of mineral migration in a Burton tube, after the idea of Ince with modification, indicated that this apparatus was inefficient for accurate observation. A cataphoretic cell was constructed. The experimental data, as shown in this paper, enable the correlation and advancing of this hypothesis. Del Giudice&apos;s chemical hypothesis considered that slime particles are attached to the galena surfaces by a cement formed as the result of a metathetical reaction between the sulphide and the slime particles. Applying this hypothesis, the calcite slime particles were cemented to the galena surface by the formation of a cementing lead carbonate. In a similar way, lead silicate was considered as the cement of quartz slime coating on galena. Experiments verifying this hypothesis were carried out according to the following procedure: Fresh mineral particles selected from the central part of the broken lumps and examined first under a microscope for ascertaining a clean surface were placed in a small beaker (1.5-in. dia. by 2.5 in. deep) half filled with one kind of slime pulp. The dilution of all slime pulp was 4: 1 and the particle size of slime was minus 400-mesh. After agitation for 5 min. the specimen was removed by a sharp-end tong and washed gently three times in three separate distilled water baths. It was dried before a small electrical fan and examined immediately under a microscope. A photograph was made of the observation. With reference to the published solubilities,4 several of these experiments, which contradict the chemical hypothesis, are listed as following: I. The coating of fluorite slime on the galena surface was light but the coating of galena slime on the fluorite surface was heavy. In a similar way, the coating of quartz slime on the galena was fairly light, but the coating of galena slime on the quartz particle was heavy. According to the chemical hypothesis, using the same constituents and regardless of which is the slime, the density of the coating should be expected to be the same. This, however, as shown above, is not true. Moreover, fluorite (CaF2), having a solubility of 16 mg.[4a] per liter of water, should not be

Jan 1, 1943

By J. E. Dutrizac

Fracture-exposed surfaces of sphalerite samples having five different solid solution iron contents ranging from 0.0 wt% to 14.8 wt% Fe were leached for 15 to 120 s at 100°C in 0.3 M Fe(S04)1.5 -0.3 M H2S04 media. The reacted samples were examined using X-ray photoelectron spectroscopy (XPS) which provides chemical state information on the first few nanometers of the solid surface. Surface compositions show that the leaching rate increases with increasing solid solution iron content of the sphalerite. Detailed evaluation of high resolution S2p spectra show that the leaching progresses via the formation of polysulphide species. Disulphide species were not detected in any of the experiments. Examination of the Zn2p and Fe2p spectra indicate little change in the chemical states of these elements over the duration of the experiments. Longer leaching times resulted in the generation of elemental sulphur. The ratios of elemental sulphur to dissolved ferrous ions and zinc suggest that less than 5% of the sulphide is oxidized to sulphate. Morphological studies showed that the elemental sulphur commonly formed at a few isolated sites, such as the grain boundaries. Furthermore, euhedral sulphur crystals were often identified. These observations suggest that at least part of the elemental sulphur forms via dissolved sulphide species which are oxidized in solution by ferric sulphate.

Jan 1, 2003

By A. B. Van Cleave

It was first pointed out in 1934 by Gaudin (1) that the "oily" oxidation product of the alkyl xanthate ion-dialkyl dixanthogen, might be the "active flotation agent" on sulphide minerals and there have been a number of studies supporting this hypothesis (2,3,4). However, all of these studies have relied largely on electrochemical evidence. Galena, being a semiconductor, may be used as an electrode in aqueous solution and it was shown that ethyl xanthate ion does not adsorb with charge transfer in the absence of oxygen unless the potential of the galena surface is above -100 mv versus the hydrogen electrode (H2 E). At this potential the galena surface is slightly hydrophobic but does not become strongly hydrophobic unless the potential is raised to 210 mv (versus H2 E). It is suggested that, at potentials of 210 mv or above, ethyl xanthate ions are oxidised to diethyl dixanthogen and that chemisorption of oxygen raises the galena surface to this potential. On the other hand, examination of xanthated galena surfaces by chemical or physical methods (5,6,7) has failed to detect dixanthogen and it has been shown that dixanthogen may be reduced to lead xanthate at a lead sulphide surface. (5,8)*. It was suggested by Leja and Poling (5) that, as dixanthogen is a neutral molecule it would not be repelled by the negatively charged galena surface so that the adsorption was envisaged as taking place through homogeneous oxidation of the xanthate ion to dixanthogen, adsorption and reduction of the dixanthogen to a chemisorbed lead xanthate species. In paper I of this series (11) it was shown that the thiosulphate ion, which forms on galena surfaces in slurries at the pH normally used for flotation, will reduce dixanthogen. There is, therefore, the impasse that the electrochemical evidence requires that xanthate ion be oxidised to dixanthogen at the galena surface while the chemical evidence shows that the reverse reaction takes place.

Jan 1, 1973

By Stephen R. La Brooy, Tong Deng, Pritam Singh, David M. Muir, A. J. Monhemius, G. W. Warren, E. Peters

The controlled addition of ammonia to cyanide solutions inhibits the leaching of copper minerals but extracts up to 80% Au using as little as 10% of the cyanide compared with conventional cyanidation of copper-gold ores. The solubility of copper minerals and copper speciation in solution is dependent on NH3, CN-, pH and Eh. Rotating disc and electrochemical studies show that gold is leached by a mixed Cu-CN--NH3 complex with either Cu(II) or O2 as oxidant. This complex is slowly oxidised to CuCN and Cu(OH)2 by air.

Jan 1, 1993