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By Brian Loveday, Sandile Nkwanyana, Indresan Govender

"Recent batch experiments by the authors in a pilot scale ball mill (Ø = 0.6m) have demonstrated that a partial replacement of the ball charge by pebbles (25 % pebbles; 75 % steel balls) optimally reduces the ball and power consumption without altering the rate of production of fine material (passing 75 microns). At higher pebble volumes, the production rate of fines was reduced progressively. With the 25/75 composite charge a saving of 13 % in power consumption was achieved, and a saving of 25 % in steel ball consumption is implied. A partial replacement of steel balls by pebbles reduces the overall density of the grinding media in the charge. Taking into consideration that the production rate of fines is usually proportional to the bulk density of the charge in the mill, it would be expected that a composite charge (e.g. 25/75) would coarsen the grind and consequently reduce the rate of production of fines. Pebble wear contributes a small proportion of fines and it doesn’t provide a full explanation of why the 25/75 composite charge has no (or minimal) adverse effects on the rate of production of fines. Clearly, the production of fines across the mill is directly related to the shear and compressive power dissipation density. Accordingly, we hypothesise that the spatial power dissipation distribution meeting the minimum requirements for fines production— at the so-called active regions—are equivalent, or minimally comparable, for both the 25/75 composite and 100 % ball charge operating conditions. To test the hypothesis, we performed DEM simulations to analyse power dissipation in the active regions. 1. INTRODUCTION Comminution remains to be the most expensive process in mining operations, particularly because the energy consumed in this process accounts for 30-70 % of the total cost of a mining operation (Nadolski et al, 2014). Optimization of comminution circuits has been focussed on reducing capital and operating costs and maximising throughput capacity. For existing operations, it is often a challenge if the optimization process recommends retrofitting new ‘major’ equipment. The challenge arises from new capital cost and the difficulty of retrofitting in an existing circuit, while maintaining production (Major et al, 2001). Thus, for existing mining operations, optimization of comminution (cost and throughput) is often limited to operating conditions and/or addition of auxiliary equipment (such as pebble crushers, additional screens and high pressure grinding rolls (HPGR)) (McIvor and Greenwood, 1996; Hart et al, 2001; Powell et al, 2015b)."

Jan 1, 2018

By U. Dmitrakova, G. Sedelnikova, D. Kim, E. Savari

"The paper presents the results of research on the development of gold and silver extraction technology from refractory gold sulphide flotation concentrate of one deposits of Nord-East of Russia. The concentrate is due to the complex mineral composition. Gold and silver are finely disseminated in sulphide minerals (arsenopyrite and pyrite partially oxidized by 7-11%). These are characterized by high content of silver 219 g/t and sulphide sulfur 32%, the presence of poorly soluble silver minerals (silver sulfosalts, fahlore, finely dispersed hypergenic acanthite in iron hydroxides and jarosite, etc.), and impurity minerals capable of interacting with cyanide (pyrrhotite, marcasite, nonferrous sulphides) and causing higher than normal cyanide consumption. Pretreatment of refractory sulphide concentrate by biooxidation using a mixed association of mesophilic and moderately thermophilic bacteria at a temperature of 36-40 °C for 120 hours oxidized arsenopyrite by 97.5%, pyrite by 93.5%, unlocked refractory gold, and generally oxidized the minerals absorbing cyanide and oxygen before cyanidation. Further oxidation of these minerals-absorbents was facilitated by the aeration in calcareous medium of the solid biooxidation residues of the concentrate. Sorption cyanidation of the solid biooxidation residues with addition of lead (II) of recovered 91.2% of gold and 82.9% silver from biooxidation residue, compared with 80.1% and 46.6%, respectively, for sorption cyanidation without the preceding biooxidation step. Biooxidation of the concentrate prior to cyanidation improves the recovery of precious metals, especially silver, and significantly reduces cyanide consumption from 18.7 kg/t to 3-5 kg/t of concentrate. INTRODUCTION Biooxidation of gold sulphide concentrates using acidophilic microorganisms has been successfully applied worldwide (van Aswegen et al., 2007; Gericke et al., 2009; Sovmen et al., 2007; Sovmen et al., 2009). At least 15 full-scale plants for tank biooxidation of sulphide concentrates are presently in operation, and the construction of new ones is planned (Bulaev et al, 2015)."

Jan 1, 2018

By Garren Edwards, van der Westhuizen. Andre

"Due to the depletion of easily treated coarser ores, more mineralogically complex ores with smaller valuable mineral grain sizes are treated, the means to liberate these minerals lies in grinding finer (Partyka & Yan, 2007). Grinding to these fine sizes is energy intensive, and using standard ball mills are energy inefficient at these sizes (P80 < 75µm). Therefore, stirred mills are becoming increasingly prevalent in the mineral processing industry. In order to optimize these mills, the effects and mechanisms of the significant variables need to be understood. This paper investigates a laboratory scale vertical stirred mill (Deswik mill) in an ultra fine grinding application of a South African platinum ore. The operating variables that are considered are stirrer speed, media size, media filling, and slurry density. The resulting grinding efficiencies are considered in two ways. Firstly, a statistical model is fitted to identify the effect of the significant variables on grinding efficiency, and secondly, the grinding efficiencies are also considered in terms of a stress energy model to determine whether this can partly explain the grinding mechanism in this mill. A factorial design of experiments was used on three levels for each variable, such that only linear interactions, second order interactions and two variable interactions are included in the statistical model. The results show that tip speed, media size, percent solids and mill filling are all significant to the grind, at differing energy inputs in the grinding process. The interaction effects of these variables are also dependent on the energy inputs. The results also found that the Kwade stress energy model is applicable to this mill and can be very useful to find the most efficient operating conditions for this system. The most energy efficient operating conditions in terms of mill speed and media size were typically somewhat below the standard operating conditions and it is expected that this is most probably done in order to increase the grinding rate, but at the expense of sacrificing some grinding efficiency."

Jan 1, 2014

By Francisco Cubillos, Jorge Menacho, Cesar Gomez, Juan Rodríguez

Mineral flotation is the most used process to selectively separate particles of one or more minerals of interest. The process uses natural or induced hydrophobicity to collect particles on the surface of rising bubbles through collisions and formation of bubble-particle aggregates. Flotation machines must keep particles in suspension and well distributed, while at the same time, disperse a mass of air into a population of small bubbles. The efficiency of the separation depends primarily on the characteristics of the bubble population generated in the machine and its distribution and flow throughout its volume. The formation and separation of bubble-particle aggregates create two zones, with strong interactions between them, and with markedly different hydrodynamics conditions. A model describing two-phase hydrodynamics of the continuous and dispersed phases (frother solutions and bubbles, respectively), moving along the whole unit, is proposed. Bubble populations are characterized at the formation stage including the effect of the presence of frothers. Flow through the aggregates formation zone, where bubbles move freely and are closely spherical, is modeled using drift-flux analysis. In the aggregates separation zone, bubbles initially pack maintaining a water layer thick enough to prevent capillary forces to affect their shape. As water drainage proceeds, bubbles deform, capillary channels form, and a network of channels with a diameter size distribution develops; channels become narrower (permeability is reduced) as the distance from the interface increases. Froth hydrodynamics is characterized using models originally developed to describe unsaturated flow through porous solid particle beds. Effects of hydrostatic pressure are considered.

Jan 1, 2014

By G. Sedelnikova

This paper is aimed to elucidate the problem of copper losses in pyrometallurgical slag. Currently, flotation is used to recover copper from the slag and return the metal into the pyrometallurgical process, but the percentage of recovery frequently remains unacceptable. The process of copper leaching from the slag flotation tailings using biologically regenerated ferric sulfate is considered here as an approach to the issue. A sample of the slag flotation tailings containing 0.67% Cu and 4.99% Zn was supplied by the Urals Mining and Metallurgical Company (UGMK, Russia). The Cu and Zn speciation analysis of the sample demonstrated that Cu occurred as 58.1% oxide, 15.4% native Cu, and 18.1% secondary sulfides whereas chalcopyrite proportion was as low as 8.4%. Prevailing Zn species were refractory (58.9% Zn ferrite), and zinc oxide and silicate species made just 37.2% of the total metal content. The silicate generated silica gel that strongly hampered filtration. As demonstrated, Cu recovery is a possibility, which is apparently not the case with Zn. In this work, the stirred tank bioreactor acid leaching employing bacterial Fe3+ sulfate solutions was studied, with ferric sulfate being a product of Fe2+ biological oxidation and not the chemical reactant adding of Fe3+ sulfate. Acidithiobacillus, Sulfobacillus, and Leptospirillum bacilli were employed in Fe2+ biooxidation. Temperature, pH, Eh, S:L ratio, leaching time, and Fe3+ concentration in the source leachate as the process controls were considered. As demonstrated, the process employing biologically regenerated ferric sulfate proved to be more efficient than conventional chemical leaching. Under the optimum conditions, the proportion of Cu extracted into leachate during 2 hours was 79.1%, and that of Zn 27.2%. Precipitation of high-grade Cu sulfide served to extract the metals from the leachate, and Cu extraction was 99.7%. All in all, 23.2% Cu, 0.03% Zn, and 0.02% Fe was returned into the pyrometallurgical process. Keywords: slag flotation tailings, copper leaching

Sep 1, 2012

By Silvia Serranti, Giuseppe Bonifazi, Roberta Palmieri

The possibility to develop an efficient recovery and reuse of concrete materials from Demolition Waste (DW) represents one of the main targets applied to end-of-life constructions dismantling/recycling. The need to recycle end-of life concrete materials is strongly increasing in these last years for several reasons: i) the decrease of steady supplies of good quality natural aggregates, ii) the need to secure ample supplies of concrete aggregates to the construction industry and, finally, iii) the environmental constraints limiting the DW wastes disposal. The fulfilment of these goals produces several benefits, that is: i) a reduction of new resources consumption, ii) a strong reduction of the costs linked to transport and energy production, iii) the possibility to utilize materials, otherwise lost (e.g. land filled), iv) land preservation and, finally, v) the reduction of the environmental impact of new exploitation activities. A lot of efforts have been addressed to develop, set-up and apply innovative technologies to maximize DW conversion into useful secondary raw materials. The possibility to utilize efficient, reliable and low cost analytical tools to perform detection/control actions: i) to assess concrete characteristics, before demolition, and ii) to detect the presence of contaminants in coarse aggregates (e.g. bricks, gypsum, steel, glass, plastics, wood, etc.) represent the key issues to fulfil in order to develop innovative process/control actions/procedures inside the DW sector. In this paper a new technology, based on HyperSpectral Imaging (HSI) sensors is investigated to develop suitable and low cost strategies finalised to define and implement innovative smart detection engines for sorting and/or DW flow stream quality control, addressed to perform recovered materials and/or products certification. The proposed sensing architecture is fast, accurate, affordable and it can strongly contribute to bring down the economic threshold above which recycling is cost efficient.

Jan 1, 2014

By Z. Cheng, Y. Han

"For non-sulphide minerals such as oxidized minerals, fluoride minerals, and oxysalt minerals, there are generality in the molecular structure of their floating collectors, and similarity in crystal structure of the minerals. In the paper, adsorbing mechanism of these collectors on the surface of these mineral particles in different pH pulp was investigated by means of Pauling's rules & valence bond theory, Valence-shell electron pair repulsion theory (VSEPR) theory, Crystal and ligand field theory, and quantum chemistry simulation by DMol3 and CASTEP modules of Material Studio software. Besides, the role and status of hydrogen bond in the floating adsorption mechanism were studied emphatically, and the confirmation and characterization of hydrogen bond were explored also based on the test results. What is more, the conclusion “the effect of hydrogen bond can not be overlooked in adsorbing mechanism of flotation collectors on the minerals” and a new viewpoint of multi-polarity collaboration and hydrogen bond coupling were summarized eventually based on analysis of the measurements. Finally, a novel collector 2-Amino-3-Methyl Heptyloxy-Propylamine (AMHP) was developed based on the new viewpoint of molecular structure design, and its collecting performance was exhibited.INTRODUCTIONWhen it comes to the recovery of flotation, it is necessary for researchers to investigate the flotation mechanism of collectors. In traditional theory, when collectors were used to collect minerals, the attractions between collectors and minerals were divided into chemical, electrostatic and physical attractions (Wills, B.A., 2006). Especially, because of the reaction between sulphide minerals and sulphydryl collectors is complex and various mechanism has been proposed (Yoon and Basilio, 1993), when collectors were used to collect non-sulfide minerals, it can be classified into oxyhydryl anionic collectors and cationic collectors. In traditional theory, the adsorption of oxyhydryl anionic collectors were due to water-repulsion, and the adsorption of cationic collectors were due to electrostatic attraction between the polar head of the collector and the charged electrical double layer on the mineral surface (Wills, B.A., 2006)."

Jan 1, 2018

By E. V. Zelinskaya, A. E. Burdonov

"In the raw aluminum production processon electrolyzers with self-baking anodes, during technological operations, flow-regulated treatment and adjustment of the electrolyte chemical composition produced by diesel and floor-rail technology, alumina and fluoride salts are spilled through the ventilation grilles of the electrolysis body aeration channels, leakage in the equipment, machinery and motorized machinery construction elements. As a result of this, a part of the bus station and the level of ± 0 (the basement room with supporting curbstones and columns, on which electrolyzers are installed) are covered with technological raw material. This leads to an increase in the conductor (bus) resistance, contact connections deterioration, cell insulation failure and raw materials loss. For example, at the enterprise ""Rusal-Bratsk"", as a result of the activity, up to 420 tons per month of alumina-containing wastes that are unfit for use in the electrolysis process are formed due to the alumina substantial contamination with salts of iron and silicon, which significantly reduces the technical and economic parameters of the electrolysis process. The main scientific problem is the processing (cleaning) of alumina-containing waste having a complex mineralogical composition of the material, its contrast and structure, from oxides of iron and silicon, using ""dry"" separation methods. In the performing the work process, qualitative indicators of the influence of external factors (air humidity, precipitation, sunlight, temperature difference) on the physicochemical processes components interaction during the raw materials storage are established. On the basis of laboratory tests, it is established that alumina-containing raw materials can be separated and photometric and gravitational separation methods used. A mathematical model of the motion of particles of primary and prepared alumina-containing raw materials in a cascade-gravity classifier was developed. The criteria and factors characterizing the alumina-containing material, as well as influencing and determining the maximum material enrichment, are established."

Jan 1, 2018

By A. Akcil, O. Celep, C. Erust, E. Y. Yazici1, H. Deveci1

"Recycling of WEEE has already gain prime importance from both environmental and economic point of view. For the recovery of metals from e-waste, many conventional physical, bio/hydrometallurgical and pyrometallurgical processes are proposed. Economic potential of e-waste is mainly driven by its precious metal content. Physical separation methods (e.g. electrostatic, magnetic, eddy current and gravity separation) exploit the differences in the physical properties of metals and non-metals. Physical separation methods are simple and economically sound but they suffer from metal losses and ineffectiveness at fine sizes. Hydrometallurgical processes are promising owing to their relatively low cost, reduced environmental impact, potential for high metal recoveries and suitability for small scale applications. Hydrometallurgical processes can be developed for selective extraction of base/precious metals using suitable reagent systems. Sulphate-based leaching with a suitable oxidant (e.g. H2O2, O2, Fe3+) is effective for copper and other base metals. After removal/recovery of base metals, precious metals can be easily extracted using various lixiviants including thiosulphate, thiourea, cyanide and chloride. However, further research is required to develop new, cost effective and environmentally friendly processes and/or refine existing ones for leaching and, in particular, downstream processes. INTRODUCTION Electrical and electronic equipments are indispensable to modern societies with numerous applications in the field of medicine, transport, communication, education, security and environmental protection. With technological developments and innovations, the replacement of old equipment leads to ever fast accumulation of waste materials such as waste electrical and electronic equipment (WEEE or e-waste). People are upgrading their mobile phones, computers, televisions, audio equipment and printers more frequently than ever before (Babu et al., 2007; Lee et al., 2007). With the rapid growth in technology today, the life span and utilisation period of most electronic and electrical equipment has been reduced considerably with concomitant generation of huge amounts of WEEE over the past several decades. According to statistics presented by Balde et al. (2015), total WEEE produced around the world was 41.8 million tonnes in 2014 and expected to rise to approximately 50 million tonnes by 2018. Kumar et al. (2017) estimated that annual growth rate for the WEEE stream is 3–5% (Singh et al., 2016). The aim of this paper is to provide an overview of physical separation and hydrometallurgical methods available for the treatment of WEEE."

Jan 1, 2018

By Ataollah Nosrati

Agglomeration of fine mineral particles is an important step in heap leaching processes employed for a cost-effective hydrometallurgical extraction of value metals from low-grade ores. In this study, the effect of acidic binder composition and feed ore particle size on binder dosage requirement and isothermal, batch agglomeration behavior of siliceous goethite nickel laterite has been investigated. Agglomeration tests performed with tap water and 30, 44 and 98% w/w H2SO4 solutions as binders revealed the key role of binder formulation in controlling ore particle wettability, nucleation and granule growth behavior. Both lower binder acid content and higher dosage led to greater wetting, nucleation and granule growth rates. Variation of feed ore fine/coarse particles? mass ratio dramatically impacted on binder dosage requirement for effective particle wetting, nucleation, and growth agglomeration behavior. Increasing fine (-150 µm) fraction mass content in a -2 mm feed ore, led to higher binder dosage requirement and enhanced nucleation, however the overall agglomeration rate/granule size growth decreased. In contrast, the presence of coarse (5 ? 15 mm) particles in feed ore led to (i) lower binder dosage requirement, (ii) enhanced initial agglomerate size growth rate, and (iii) reduced coalescence. For dry agglomerates of similar sizes, competent coarser feed particles led to remarkably higher compressive strength than did finer feed particles. Microstructure analyses indicated that the granules containing coarser particles exhibited a distinctive, competent core/shell (fines) structure which led to their structural reinforcement. The appropriation of the findings for optimizing agglomeration behavior for enhanced heap leaching of complex, low grade laterite ores are discussed in this context.

Sep 1, 2012

By Susanna A. C. Stadler, Chris Aldrich, Jacques J. Eksteen

Slag foaming occurs in several pyrometallurgical processes. These processes include steelmaking in basic oxygen steelmaking furnaces and electric arc furnaces as well as various non-ferrous operations like sulphide smelting/converting and base metal slag cleaning. Although slag foaming in steelmaking processes has been extensively researched, little attention has been given to slag foaming in non-ferrous operations. Slag foaming phenomena are complex because often the system consists of three or more phases. With this in mind, factors previously identified as influencing slag foaming were investigated. These include the slag basicity, physical properties of the slag, namely viscosity, surface tension and density, the formation of particles due to undercooling of the slag and the FexO concentration in the slag. The effect of increasing FexO concentration was found to decrease the foam index due to lower viscosities, but higher surface tension depression appears to have led to increased foam index values at high FexO concentrations. The foaming index decreases with increasing basicity, until precipitation of solids occurs. After this point, the foaming index was found to increase with increasing basicity due to increased solids precipitation. In general, increasing amounts of slag-wettable solids led to higher foam indices, but the precise nature of the effect on slag foaming was dependant on the nature of the solid precipitate.

Jan 1, 2003

By Barun Gorain, Aparup Chattopadhyay

"Many double refractory gold deposits are characterized by the dominance of ""invisible gold"" (sub-microscopic gold) as solid solution or as colloidal-sized particles in different sulfides and other phases. These deposits are mainly composed of silicates and carbonates with moderate clay and mica content and with minor amount of sulfides and organic carbonaceous matters. The presence of highly preg-robbing and finely disseminated carbonaceous matter adversely affects gold recovery in leach circuits. Characterization of carbonaceous matters, commonly known as TCM and quantification of gold associated within these carbonaceous matters along with different sulfide and oxide phases is highly complex and challenging. Studies were initiated on various complex ore deposits and also on samples representing various process streams. This paper presents the development of a systematic approach to gold deportment studies using state-of-the-art mineralogy characterization techniques for quantification of invisible and visible metal contents in various species. The relevance of this mineralogy characterization to metallurgy will also be discussed in this paper."

Jan 1, 2014

By F. v. d. Meer, G. Kretschmar, T. Mütze, T. Leißner

"Dynamic air classifiers separate particles in a gas flow due to different particle trajectories utilizing differences in the settling velocity of particles as characteristic property for separation. The present contribution takes a close look at the separation of heterogeneous mixtures, in which valuables and gangue minerals show significant differences in density. The focus was on a moist iron ore sample, which was characterized in terms of mineralogy, grain size distribution, and particle size distribution. The material was classified at a cut size of 45 µm and at feed moistures between 0 and 6 wt.-%. Additionally to standard characterization techniques, the moisture of both products was measured as well as the yield of fines as product fraction in a corresponding processing plant. In addition, an automated mineral liberation analysis (MLA) provided information of the enrichment and segregation of individual mineral phases in the products. The MLA of the classification products reveals a selective comminution of the mineral phases and especially on overmilling of the valuables. For the first time, the separation of individual mineral phases has been assessed and compared to the classic assessment of classification processes by means of particle size analyses. KEYWORDS Dynamic classifier, segregation, MLA, selective comminution INTRODUCTION Dynamic air classifiers separate particles in a gas flow due to the different trajectories of the particles. The result of such a separation process depends on the gas throughput of the classifier, the dimensions, design and rotational speed of the deflector wheel, as well as the state of dispersion and thus the geometry of as well as the turbulence and interparticle interactions in the separation zone. Air classification of moist feed materials can be divided into several sub-process (Leschonski, 1977; Mütze et al., 2016): - dosage of the feed material, - dispersing the solid feed material into a gas stream, - feeding the dispersed material into the classification zone by pneumatic conveying, - drying of moist particles during pneumatic conveying, - separation of coarse and fine particles, and - separation of fine particles from gas."

Jan 1, 2018

By R. A. Kleiv, H. Havskjold, N. Church, T. Malvik, M. Tro, E. Larsen

Liberation is one of the major purposes of comminution in mineral processing. In the simplest form, two or more minerals are present in a particle and have to be reduced such that the individual particles contain only one mineral. The complexity of the mineral intergrowth varies from ore to ore. Poor magnetic separation of iron ore may have many causes. In this paper, the emphasis is given to the problem of fine magnetite inclusions in quartz or other gangue minerals. This is highlighted by two Norwegian cases: one on a magnetite ore and the other on a hematite/magnetite ore. The inclusions in question are so small that they are not liberated by reasonable grinding. In both cases, the result has been either poor recovery or lower grade concentrates than desired. The first example concerns production of direct reduction concentrates from magnetite. Magnetic inclusions in gangue particles will be magnetized enough for the particles to pass into the concentrate. The second example is given a more detailed study, where the problem is caused by silicates with small inclusions of magnetite in a combined LIMS and WHIMS separation. This study included microscopy, Davies tube testing, and magnetization measurements. In particular, large gangue particles with magnetite inclusions were shown to have a tendency to bypass the LIMS separators as drag forces in presence of hematite are large. Such particles will then be picked up by the WHIMS as their magnetization is higher than for hematite. This was demonstrated by Davies tube tests, which indicated that such particles were picked up in preference to hematite particles. However, the Davies results did not give a good quantification. Magnetization measurements of gangue particles with magnetite inclusions was shown to be a better tool to quantify the magnitude of the effect of magnetite inclusions in magnetic separation.

Jan 1, 2018

By Qingming Feng, Dongbo An, Jinhong Zhang

The application of the geopolymerization of mine tailings as construction materials is hindered by the fact that conventional geopolymerization of mine tailings usually involves a large consumption of alkali, i.e., sodium hydroxide (NaOH), and a long curing time, because of the relatively low reactivity and the high Si/Al ratio of mine tailings when compared to other active resources such as fly ash and clay minerals. The present study is focused on efficiently activating mine tailings, reducing alkali consumption, decreasing curing time and improving compressive strength. We firstly investigate the temperature effect on the alkali activation of mine tailings during geopolymerization. Secondly, the impact of additives, i.e., calcium hydroxide and aluminium oxide, on the compressive strength of samples is studied. Thirdly, different forming pressures have been applied to remove excessive alkali and its impact on samples&apos; strength has been investigated. The results show that a 40 MPa unconfined compressive strength (UCS) can be achieved with the geopolymerization samples after mine tailings are activated by sodium hydroxide at 170°C for 1 hour with the addition of calcium hydroxide and alkali dissolved aluminium oxide, further compressed with a 10 MPa forming pressure and finally cured at 90°C for 3 days. The findings of the present work provide a novel method for the geopolymerization of mine tailings as construction materials.

Jan 1, 2014

By Ray Everson, Henry Kasaini

"We carried out adsorption experiments in chloride media to study the adsorption characteristics of Pd (II) anions on the surface of activated carbon. Throughout the experiments, we used commercial activated carbon pellets (0.8 Norit). The adsorption process was interpreted by using the ionisation and adsorption model. This implies that palladium anions were adsorbed physically on a protonated surface of activated carbon either as anionic complex species (PdCl4 -2) or aqua chloro-complex species [PdCl3(H2O)-] in acidic media. Furthermore, we established that adsorption of Pd (II) species was reversible at high chloride [Cl-1] concentration. The maximum adsorption capacity (Qsat) of Pd (II) anions averaged 27 mg/g. The Toth adsorption isotherms fairly predicted the equilibrium adsorption of Pd (II) species and the associated surface coverage.The effect of temperature and acid strength of the feed solution on the adsorption of Pd (II) ions were quantified. The adsorption kinetics was limited by external mass transfer since the effect of pore diffusion on the overall rate constant was negligibly small. A pseudo first-order kinetics model was used to describe the adsorption kinetics."

Jan 1, 2003

By Hong Zhong, Shuai Wang, Xin Ma

"In this paper, we report a simple and effective process for producing a surfactant mixture of O-isopropyl-N-ethyl thionocarbamate (IPETC) and 4-(tert-butyl)benzyl mercaptan (BBSH). The composite collector was synthesized via one-pot reaction of sodium isopropyl xanthate, 4-tert-butylbenzylchloride and ethylamine using tert-butyl alcohol as solvent. The whole process for the synthesis of composite collector involves neither foul smelling reagents or intermediates, nor any by-products requires special treatment for disposal, and thus can be scaled up to an industrial level. The flotation response of chalcopyrite and pyrite independently with IPETC and BBSH collectors and with their mixture (the mole ratio of IPETC and BBSH is 1:1) was assessed. The microflotation results showed that the collecting ability of BBSH was slightly stronger than that of IPETC and that IPETC was more selective collector than BBSH against pyrite, and that the composite collector displayed a stronger collecting ability toward chalcopyrite than IPETC, and superior selectivity for chalcopyrite against pyrite than BBSH. The batch flotation results showed that composite collector exhibited better performance than IPETC and BBSH. It was demonstrated that the mixing of IPETC and BBSH would give rise to a synergistic effect significantly enhancing overall flotation performance. In addition, the adsorption mechanism of BBSH on the surface of chalcopyrite was conducted by adsorption test and infrared spectrum measurement, and the results showed that the interaction of BBSH on the chalcopyrite surface was dominated by the chemical adsorption, and the formation of a strong S-M bond plays a key role in the adsorption of mercaptans on minerals surfaces. The developed flotation reagents with special preparation method is the author’s original design, patented (patent of the People’s Republic of China) and have no analogues in the world of mineral processing. (Application number 201810100107.1, ""Alkyl thioether alcohol compounds, methods for their preparation and applications thereof "", China).1. INTRODUCTION Froth flotation is an essential method widely used in the mineral processing industry to selectively separate valuable minerals from gangues[1]. Worldwide, more than 109 tons of materials are treated annually by this method with the majority being metal sulfides and oxides[2]. Nowadays, the judicious utilization of complex sulfides to meet the ever-growing demand of mineral resources gains more attention, due to the gradual depletion of deposits with high grade, making imperative the development of new high-efficiency collectors and mixtures of collectors to process complex minerals. In comparison to individual collectors, the use of mixtures has several notable benefits including lower dosage requirements, improved selectivity, rates and recovery and an increase in the recovery of coarse particles[3-9]. Moreover, in terms of cost and environmental issues, using collector mixtures can reduce the total amount of agents used, thus reducing the overall effect on the environment and economic costs without affecting the flotation performance. Therefore, the search for high-efficiency mixtures of collectors is still interesting and relevant."

Jan 1, 2018

By Paul W. Weiblen, Louis J. Cabri, Rolando Lastra

"Preliminary tests were done to determine whether comminution by electric-pulse disaggregation, or E-PD (cf. Rudashevsky et al; 1995), was more effective than using conventional crushing for Merensky Reef ore. A hand sample of the Merensky Reef was sawn in two: then one sub-sample was comminuted to .2 mm using E-PD at the University of Minnesota, and the other sub-sample was crushed to .2 mm using a conventional jaw crusher at CANMET.The products of the electric-pulse disaggregation and jaw crusher were fractionated by sieving and by a separation using a heavy liquid with a specific gravity of 3.3, because the proportion of platinum-group minerals (PGM) and sulphides to silicate minerals is very low. Thus, four mineral separates were produced: .2000 + 833 µm, -833 +208 µm, -208-µm float and -208-µm sink. All the mineral separates were studied by image analysis (Lastra et al; 1998). The main objective was to determine the liberation of gangue (silicate minerals), chromite, pyrrhotite, chalcopyrite, pentlandite and PGM. In the case of the PGM, a specific image analysis program was written to search and measure these minerals.The results show that the liberation obtained for gangue was similar (~99%) using either method of comminution. However, the liberation obtained for chromite (~89% vs. ~38%), pentlandite (~50% vs. 1%), pyrrhotite (~56% vs. ~38%), and PGM (~56% vs. ~1%) by E-PD was higher than that obtained by conventional jaw crusher, whereas the liberation obtained for chalcopyrite (~20% vs. ~71%) by E-PD was lower. Nevertheless, the image analysis of the products also showed that the PGM are strongly associated with pentlandite. Thus, for the Merensky Reef, liberation of pentlandite from the gangue minerals and chromite is important to recover more of the PGM. This maybe be significant because, in addition to increased recovery of platinum-group minerals (PGM), Merensky Reef pentlandite also contains significant quantities of valuable platinum-group elements like Pd and Rh (Cabri, 1981; Cabri 1988, Kinloch 1982, Peyerl 1983). Hence, the results indicate that for the Merensky Reef, electric-pulse disaggregation would represent a better comminution operation than a conventional jaw crusher would. In addition, the greatly improved liberation for chromite may find application for the PGM-rich UG2 chromitite."

Jan 1, 2003

Froth flotation is an industrial process commonly used for the separation of mineral particles. Bubbles sparged in a pulp collect and carry hydrophobic particles to the top layer of a flotation cell, the froth zone. There is a strong correlation between the stability of the froth phase and the flux of solids. However, flotation units placed in series operate, as a whole, in a non-steady state regime with the concentration of particle decreasing from one cell to the next resulting in a decrease in froth stability, which can compromise the recovery of valuables. Organic chemical reagents, frothers, are generally added to prevent fine bubbles from coalescing and to increase the stability of the froth phase. Frothers represent the second largest group of mining chemicals. It is crucial to understand the resulting properties of the frother on the froth phase in order to select the most suitable reagent for a particular operation. The bubble coalescence dynamic of three different surfactants, 1-pentanol, poly (propylene glycol), and tri (propylene glycol) methyl ether, were investigated in this study. In the first stage, the stabilisation mechanism of bubbles in a solution of surfactant was investigated using a specifically designed experimental setup. The coalescence behaviour of bubble pairs was recorded using high-speed video imaging in which information such as the coalescence time and the deformation of the resultant bubble upon coalescence could be extracted. The results were then compared between the different surfactants for several concentrations. It is shown in a study that the coalescence time increases with surfactant concentration until the Gibbs-Marangoni effect is suppressed by bulk diffusion. Conversely, the oscillation of the resultant bubble was found to be affected only at concentrations at which the film is saturated. The implications of the effects of surfactant type and concentration on the coalescence time and bubble oscillation in froth flotation are discussed. Keywords: froth flotation, frother, bubble coalescence

Sep 1, 2012

By P. V. Ramesh Babu

India has sizeable number of small deposits of rare metal bearing minerals namely columbite-tantalite, pyrochlore, beryl, lepidolite, spodumene and rare-earth element bearing minerals monazite and xenotime in different parts of India. Pegmatites, alkali granites, syenites, and the derived gravel and soils are the main source for rare metal and rare earth (RMRE) minerals. The RMRE minerals are classified as prescribed substances under Atomic Energy act of 1962 keeping in view the uses in the nuclear industry. Atomic Minerals Directorate for Exploration and Research (AMD) of Department of Atomic Energy (DAE) is the sole agency responsible for exploration and exploitation of RMRE minerals in India since 1962. The latest technological advancements and applications in the field of space, electronics, communication and nuclear industry using these metals and their products have necessitated to augment the production and resources of RMRE minerals. These minerals play a significant role in the technological and economic development of the country. The light rare earth element bearing mineral monazite is abundant in beach sands and is being commercially exploited by Indian Rare Earths Limited (IREL). Columbite-tantalite, the chief source for niobium and tantalum (Nb-Ta) metals present in the pegmatitic gravel are recovered by small mobile beneficiation plants. The cut and fill method of mining adapted is eco-friendly. The processing flow-sheet consists of wet sizing at ½ in and 1mm followed by gravity concentration of sized products utilizing the methods of jigging and wet tabling. The sizing equipment include revolving and vibratory screens and the gravity concentration equipments used are fixed sieve jigs and movable screen jigs for final upgradation. The gravity concentrates are further upgraded by magnetic separation to remove magnetite and ilmenite. The mine areas are reclaimed by filling with coarse size tailings and new plantations. These mobile pilot plants were earlier operated in Bihar mica belt, Jharkhand, pegmatitic areas of Karnataka and Nellore mica belt of Andhra Pradesh and are currently being operated in Bastar-Malkangiri pegmatite belt of Chhattisgarh and pegmatites of Jharsuguda district of Orissa. Beryl, lepidolite, spodumene and cassiterite minerals are the by-products from the pegmatite ores. Fergusonite, samarskite and microlite are the other niobium and tantalum bearing minerals which are also found in pegmatites. Xenotime, the chief mineral of yttirium generally occurs in granites and pegmatites. The rare earth minerals monazite and xenotime get concentrated in the placer sands of rivers and beaches. The occurrence of xenotime in the sands of Siri River and Deo River in Chhotanagpur granitic terrain in parts of Chhattisgarh and Jharkhand are an example. These sands containing 1-2.5% heavy minerals were processed by a mobile plant consisting of sizing equipments like trommel and vibratory screen followed by separation of heavy minerals from -1mm sands with the help of gravity concentration equipments like spirals/shaking tables/sluices. Xenotime and monazite from the pre-concentrate are further separated by magnetic and electro-static methods. The present paper illustrates the pilot plant set up for the recovery of rare metal as well as rare earth minerals. Keywords: small deposits, rare earths, rare metals, pegmatite, Nb-Ta, xenotime, India

Sep 1, 2012