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By Darryel Boucher, Raymond Langlois, Neil Rowson, Kristian Waters

The Knelson Concentrator is a centrifugal gravity concentrator composed of a high speed rotating bowl into which a mineral slurry is fed. The rotational motion creates a centrifugal acceleration up to an equivalent of 200 G. Under this acceleration, particles enter fluidised riffles along the side of the bowl, with the fluidisation allowing for the substitution of dense material for less dense. The separation mechanism is not fully understood and questions remain on the optimal residence time, slurry feed parameters and bowl surface profile to achieve a better separation. The positron emission particle tracking (PEPT) technique has been applied to record the motion of a -1700+1180 µm particle of a quartz-gold matrix, labelled with 18F radioisotope while it undergoes concentration inside a 3" laboratory scale Knelson Concentrator (KC-MD3) operated at 60 G. The slurry used was composed of quartz and magnetite. Particle trajectories during the first stage of the concentration process where the heavier particles centrifuge through the increasingly dense slurry towards the riffles of the bowl are shown with respect to time. This work reveals new information on particle motion inside the Knelson Concentrator and the results will be used for validation of developed separation model as well as optimisation of a centrifugal concentrator’s performance.

Jan 1, 2014

By Sergio Castro, Janusz Laskowski

In the flotation in highly concentrated electrolyte solutions not only ionic strength but also chemical composition, flotation pH and mineral properties play an important role. As a result an improvement or depression may be observed. A strong improvement in the floatability of hydrophobic bituminous coals and other inherently hydrophobic minerals is characteristic for the "salt flotation process", which is carried out in concentrated electrolyte solutions at natural pH and without addition of any flotation reagents. However, pH is a key factor when saline and hipersaline waters with hydrolyzing metallic ions are used as process water. In the case of flotation of Cu-Mo sulfide ores in seawater, molybdenite is strongly depressed by the Mg2+ hydrolysis products when pH is raised to depress pyrite. Process water with a high content of Mg2+ and Ca2+ ions, and this also includes seawater, have deleterious effect on the anionic flotation of industrial minerals with fatty acids. The flotation of potash ores is carried out in NaCl-KCl saturated brine (6-7 mole/L of NaCl and KCl) with the use of long-chain amines. Such a high electrolyte concentration changes dramatically the amine Krafft point making the collector insoluble in brine; its mode of action entirely differs from that in conventional flotation processes.

Jan 1, 2014

By Lawrence Bbosa, Aubrey Mainza, Indresan Govender

"Positron Emission Particle Tracking (PEPT) and the Discrete Element Method (DEM) are used to develop a probability based model for the power draw of a tumbling mill. Experiments are conducted using dry spherical glass bead charge in a laboratory scale tumbling mill, which is mounted with a torque transducer and tachometer to measure mill power. Particle tracking information from PEPT is used to reconstruct the motion of glass beads and infer the overall charge behavior, while DEM is employed to simulate particle motion and interaction, with collision mechanics calculated using the Hertz-Mindlin contact model. For both sets of data, the product of torque and average angular velocities in discrete cells are accumulated to obtain mill power. This method is found to be within statistical agreement with measured power for all tests. The information from both techniques is then used to develop a model for the power draw as a function of particle size, mill speed and volumetric filling. Predictions of the model match well with measured and calculated values. The model is found to predict mill power within close agreement with measurement and follows trends consistent with existing work on tumbling mill modelling."

Jan 1, 2014

By John Ralston, Jona Addai-Mensah, Patience Mpofu

The flocculation and dewatering behaviour of kaolinite (non swelling) and smectite (swelling) clay dispersions has been investigated using hydrolysable metal ions Mn(II) and Ca(II) and anionic polyacrylamide-acrylate copolymer (PAM) at pH 7.5 and 10.5. A pH-dependent, specific metal ion adsorption behaviour, accompanied by a marked reduction in particle zeta potential and slurry shear yield stress, was observed to have a profound influence on the colloid stability of both types of clays. Due to the differences in the cation exchange capacity, the smectite clay dispersion required a higher amount of metal ions than kaolinite dispersion to produce similar effects. The adsorption density of the anionic PAM at the negatively charged clay particle surfaces correlated well with metal ion hydrolysis and adsorption behaviour, all of which had a strong effect on slurry settling rate and extent of consolidation. At pH 7.5 where Mn(II) ions hydrolyse, metal ion and flocculant adsorption densities were both greater in the presence of Mn(II) than Ca(II) ions. At pH 10.5, however, where Ca(II) ions begins to hydrolyse, higher adsorption densities were observed for Ca(II) ions in comparison with Mn(II) ions, as the latter hydrolysed completely and precipitated. The metal ion mediated flocculant adsorption led to improved hydrogen bond driven particle bridging and facilitated charge neutralisation flocculation mechanisms which significantly enhanced the dewaterability of both clay dispersions.

Jan 1, 2003

By Ghislain Bournival, Seher Ata, Graeme J. Jameson

A common method to prevent bubbles from coalescing in a flotation cell is by the addition of surfactants, called frothers. The gas dispersion properties in a column were tested for solutions of 1-pentanol, tri(propylene glycol) methyl ether, and poly(propylene glycol) in the presence of sodium chloride. The dependency of surfactant on the gas holdup can be divided into regions. It seemed that for a sufficiently low concentration of surfactant, even a stronger surfactant could show a transition in gas holdup from constant/decreasing to increasing with concentration. This region, however, was not marked by a decrease in the average bubble size. In addition, PPG gave higher gas holdup values while averaging larger bubbles. On the other hand, sodium chloride mostly affected the gas holdup when the concentration was high enough to prevent bubble coalescence. Another parameter affecting the gas holdup was the superficial gas velocity. A linear dependency was found between the two under a bubbly flow regime. The current study showed that both surfactants and salt could slightly affect the influence of the superficial gas velocity on the gas holdup.

Jan 1, 2014

By William Skinner, Jennifer MacCarthy, Jonas Addai-Mensah, Ataollah Nosrati

"Acid leaching in agitated tanks is central to hydrometallurgical processing for valuable metals’ (e.g., copper, gold, nickel and cobalt) recovery from low grade (e.g., < 2 wt.%) ores. In this study, atmospheric leaching behaviour of Australian saprolitic nickel (Ni) laterite ore using sulfuric acid was investigated under isothermal, batch conditions at pH 1. The effect of primary process variables comprising time (4 h) and temperature (70 and 95 oC) on the leaching mechanisms and kinetics was established for -2 mm, low grade (~1 % Ni) saprolitic ore dispersions at 40 wt.% solid loading. Leaching proceeded incongruently, reflecting the proliferation of gangue minerals’ constituent elements (e.g., Mg, Al, Fe) alongside Ni and Co in the pregnant leach solutions (PLS). Subsequent analysis showed that 89% Ni and 78% Co were extracted after 4 h at 95 oC whilst at 70 oC the recoveries of these metals were markedly low (< 25 %). Overall, 177 and 644 kg H2SO4 /t dry ore were consumed at 70 and 95 oC, respectively. Activation energy of 79.0 ±1.0 kJ/mol was estimated for the mechanism of Ni and Co leaching and associated kinetics. Particles size analyses indicated that when the breakage of frail laterite particles due to shear is taken into consideration, differences in feed and leached product particle size distributions were insignificant , despite a remarkable increase in BET specific surface area of the product. Mineralogical analyses of the feed ore and leached solid products revealed a sub-crystalline silica phase enrichment of the latter. The overall results suggest that the mechanism of acid leaching of saprolitic Ni laterite may be described by a chemical reaction-controlled, shrinking core model."

Jan 1, 2014

By G. P. Karmakar, K. K. Chandan

"The drilling mud is an essential part of the drilling process, which plays a major role in keeping safe and efficient oil and gas well drilling. In the oil industry, bentonite clay dissolved in water produces the simplest type of drilling muds. Bentonite clay contains montmorillonite particles. These particles are dispersed uniformly in water and such dispersions are used in various industrial products like paints, ceramics, pesticides and drilling muds. The bentonite clay easily dissolves in water and increases the viscosity of the water, which is one of the most important properties of a drilling mud. Bentonite has the highest swelling capacity, which is responsible for building up of the viscosity of the clay-water system. The flocculation behavior of bentonite is one of the major concerns for the performance of the water-based drilling mud in the oil and gas well drilling process. The behavior of drilling mud greatly depends upon the quality and quantity of bentonite clay, as well as the additives that are used in their formulations. In this work, a comprehensive study has been carried out to find out the effect of added polyacrylamide (PAM) polymer, surfactant, pH and salt concentrations on the dispersion/ flocculation characteristics of bentonite clay-water system. It has been observed that the increase in PAM dosage reduces the residual turbidity and improves the settling rate of the bentonite particles. The flocculation rate has also been found to be better under higher pH conditions. The combined effect of salt concentration and PAM dosage improved the overall flocculation efficiency of the system.INTRODUCTIONIn the oil industry, bentonite clay dissolved in water produces simplest type of drilling muds. Bentonite clay containes montmorillonite particles. These particles are dispersed uniformly in water. Such dispersions are used in various industrial products like paints, ceramics, pesticides and drilling muds (Akther et al., 2007). The bentonite clay easily hydrates in water and increases the viscosity of the mud system (Razi et al., 2013; Meng et al., 2012). Bentonite clay in the drilling mud increases the viscosity which is one of the most important prop erties of a drilling mud. Bentonite has the highest swelling capacity, which is responsible for the building up viscosity of the clay-water system (Sonmez et al., 2013). The drilling mud is an essential part of the drilling process, which plays a major role in keeping a safe and efficient oil or gas well drilling (ASME, S. S. C., 2005). The flocculation behavior of bentonite is one of the major concerns for the performance of the water-based drilling mud in the oil or gas well drilling process. This behavior of drilling muds greatly depend upon the quality and quantity of bentonite clay, as well as the additives that are used in their formulations (Yu and Amanullah, 2005; Akther et al., 2007). Bentonite particles form aggregate under certain conditions including high temperature, and high concentration (Luckham and Rossi, 1999). If the quality of bentonite is not sufficient to accomplish intended viscosity of the muds, it is essential to add certain additives to increase the viscosity and prevent aggregation of the system (Razi et al., 2013). The anionic polymer bearing sample can build up inter-particle bonds between the polymer and clay particles. The addition of various additives like, polymers control the dispersion and enhance the viscosity of the mud by controlling the flocculation of montmorillonite particles in bentonite dispersion (Heller and Keren, 2002; Mahto and Sharma, 2004)."

Jan 1, 2018

By M. Saghaeian, R. Hejazi, H. Abedini, M. Zare

Water recovery in mineral processing plants is one of the most important subjects because water supply is a critical matter economically and environmentally, especially in desert areas. In this paper, the filtration behaviour of two iron ore tailing sample has been investigated using laboratory scale vacuum and pressure filtration units. These samples including tailing from Sirjan and Zarand concentrate production plants with the d80 of 94 and 41 micron, respectively. The results show that by using vacuum filtration the cake moisture content of Sirjan sample would be about 24%. But the filtration time is too long and vacuum belt filter cannot be used in industrial scale. Adding about 40 g/ton of flocculant would decrease the filtration time by about 30% and make the vacuum belt filter appropriate for dewatering of this sample. For Zarand tailing sample, the vacuum filtration would produce a wet cake by about 31% moisture content. Filtration time is too long and adding flocculant would not improve the results very much. So pressure filtration must be used for dewatering of this sample. The results of laboratory tests show that using pressure filter would reduce the cake moisture content to 21%. The filtration time is logical, so this process can be used for Zarand tailing dewatering.

Jan 1, 2014

By B. Vasanthakumar, H. Ravishankar, S. Subramanian, J. Braun

The flotation of sphalerite and galena in the presence of intra- and extra-cellular components isolated from Bacillus circulans before and after adaptation to the chosen minerals has been studied. Based on various biochemical treatments, the key biomolecule primarily responsible for the flotation of sphalerite has been identified as DNA, which functions as a bio-collector. A noteworthy finding is the considerably higher flotation recovery of sphalerite obtained in the presence of single stranded DNA (79.8%) vis-à-vis double stranded DNA (50.2%). Selective flotation tests using the soluble fraction obtained after thermolysis treatment highlight that sphalerite-adapted cells yield a higher selectivity index (S. I.) of 31.2 compared to galena-adapted (S.I. 4.3) or unadapted (S.I. 12.2) cells. During bacterial adaptation to the above chosen minerals, the quantitative and qualitative changes in the surface potential, surface morphology and cell wall components have been monitored. The prior adaptation of the bacteria to sphalerite results in the secretion of a higher amount of proteins, eDNA and phosphate, whereas adaptation to galena leads to a higher amount of polysaccharide, uronic acid and acetylated sugar, vis-à-vis the unadapted bacteria. A significant observation is that the bacteria undergo a change in morphology from rod to sphere as a strategy to resist metal toxicity during adaptation to galena. Interestingly, this phenomenon is not observed during bacterial adaptation to sphalerite. This morphological transition has been shown to involve changes in crucial cell wall components as well as changes in the levels of expression of bacterial cytoskeleton element mreB gene involved in the maintenance of the rod shape. The sequence of B.circulans mreB gene has been identified using Polymerase Chain Reaction (PCR) followed by DNA sequencing.

Jan 1, 2014

By Peter Scales, Ricardo Jeldres, Fernando Concha, Pedro Toledo, Shane Usher, Anthony Stickland

The impact of several electrolytes present in seawater on the rheological properties of flocculated mineral suspensions was assessed using the creep test. Flocculated suspensions were obtained by adding polymer flocculant to a cylinder of mineral suspension and aggregating the suspension using the plunger method. The suspension was allowed to sediment and the supernatant liquid decanted prior to tests for the viscoelastic properties of the resulting sediment. The solid used was alumina AKP-30 both, below and above the isoelectric point. The polymer used was AN934SH, an anionic flocculant with high molecular weight. Salts analyzed were MgCl2, CaCl2 and NaCl, known as water structure makers, and KI and KCl, known as water structure breakers. A high salt concentration of 0.5 M was used to approach the ionic strength of seawater. For both pH’s studied, the sediments demonstrated a viscoelastic non-linear behavior observed as a non-linear relationship between yield strain and applied stress. In the absence of flocculant, it was observed that the viscosity and yield stress of a suspension increase in the presence of structure maker salts for the case of both silica suspensions and alumina suspensions. These results were explained using hypernetted chain statistical mechanics models describing the interaction of ions with solvated surfaces. In contrast, with the presence of flocculant, the shear yield strain of alumina suspensions increases with the breaker character of the salts, however, this result has been explained by an extension of the results from the models. The work has significant implications for the flocculation of mineral suspensions in the presence of seawater.

Jan 1, 2014

By Knut L. Sandvik, Erik Larsen

Crystalline silicon solar cells are the most important solar cells manufactured today. This will most probably remain the situation the next decade. The future silicon feedstock is most likely not reject from the production of electronic-grade silicon. There will probably be a more direct solar-grade silicon route, excluding the electronic-grade silicon "detour". Estimated global solar energy demand in 2001 required approximately 5,500 tons of silicon feedstock. This required 65,000 tons of quartz. If the trend continues, the solar energy demand in 2010 would require approximately 30,000 tons of silicon feedstock and 350,000 tons of quartz, although the need for quartz probably will be lower than this. Quartzite has been regarded as the most suitable primary raw material used in the silicon solar cell production chain. This may change as the raw material requirements for the production of metallurgical-grade silicon are most likely to change. In addition, quartz or other silica-containing minerals from other rocks may be of a higher purity or contain lesser amounts of the most harmful elements. This favours increased beneficiation of primary raw materials in the future solar silicon feedstock production chain.

Jan 1, 2003

By Xianjun Lyu, Junxiang Wang, Peng Wu, Minjie Lian

"In recent years, the efficient cementation of mine tailings is a new way to manage mine solid wastes. The traditional cement materials have a slow setting time, large dosage and poor cementation strength for fine aggregate such as mine tailings. Therefore, the preparation of new type cementitious materials for the cementation of fine tailings has great potential in the treatment of mine waste solids. The paper mainly focuses on exploring the critical factors affecting the cementing performance of granulated blast furnace slag and its performance in the cementation of fine aggregate. Results indicate that the fineness of slag has a significant effect on its cementitious activity and Portland cement clinker has a better stimulation effect on the cementitious properties of slag than lime. And, anhydrite has a better early stimulation effect on the cementitious properties of alkali-activated slag compared to semi-hydrated gypsum and dihydrate gypsum. According to a series of tests on the cementation of fine iron tailings, the optimal ratio of slag, Portland cement clinker and anhydrite is determined as 60:30:10. Compared with P.O 42.5 ordinary Portland cement, the new slag based cementitious material shows much better cementing performance on fine tailings sample. Under the dosage of 12%, the compressive strength of fine tailings mortar using slag-based cementitious material in 3 curing days is increased to 168% that of using P.O 42.5 ordinary Portland cement, while the compressive strength in 28 days curing period is increased to 194%."

Jan 1, 2018

By A. V. Nguye, P. A. Harvey

Previous studies have reported that inorganic electrolytes can enhance floatability of coal. The research has shown that the enhancement, if any, is highly dependent on changes in solution pH, type of electrolyte, and electrolyte concentration. The reasons for this are still not clear. In this study the floatability of coal particles in mono and divalent salt solutions was investigated. The zeta potential and hydrophobicity of the coal was measured experimentally, and a modified Hallimond tube was used to determine the floatability of coal particles by single bubbles, where the collision efficiency was equal to unity. The experimental information was used in conjunction with the Hogg-Healy-Fuerstenau equation to quantify the electrical double layer interaction. It was found that for low electrolyte concentration (less than 0.1 M) solutions the flotation recovery of coal particles was less than that for distilled water, and decreased with increase in concentration. Conversely, at electrolyte concentrations above 0.1 M, flotation recovery increased with increasing concentration. Both of these results are consistent with previous observations, but are inconsistent with expectations when considering the possible influence of electrical double layer interaction. A possible mechanism, based on the existence of the pre-existing submicron-sized gas bubbles, known as bubstons (i.e. bubbles stabilized by ions), present in water in close proximity to the hydrophobic coal surfaces is discussed in line with the early observation of flotation improvements by microbubbles “nucleating” on hydrophobic surfaces. In particular, the dependence of the bubble-particle attachment efficiency on electrolyte concentrations supports hypothesis on the salt-dependent and ion-specific existence of bubstons. However, a theoretical explanation of the transition salt concentration (at about 0.1M) is deficient at present. The existence of these submicrobubbles in close proximity to hydrophobic surfaces is not trivial. They can (as can individual gas molecules or other solutes) mediate and extend the range and magnitude of the attraction between hydrophobic macroscopic surfaces. These bubbstons may explain the curious phenomena of the socalled long-ranged hydrophobic attraction measured with the Surface Force Apparatus and Atomic Force Microscopy, and the slippage at hydrophobic surfaces. Finally, the coalescence of bubbstons affects the rupture of liquid films at a very large thickness (over 100 nm), observed, but unexpected, by flotation chemists.

Jan 1, 2003

By F. C. Araújo, T. Tavares, J. Leite

"This work presents the small-scale mining cluster of kaolin in Rio Grande do Norte (RN) and Paraiba (PB), both Brazilian states, including the following information: number of companies, process flowcharts, production numbers, mineralogical (XRD) and chemical (XRF) composition, granulometric distribution (screen and laser granulometer) and image analysis (SEM). Some social indicators in the region of the RN and PB States are presented in association with these data. The number of companies and their flowsheet were obtained through in situ visits and sample collection for technological characterization. The comparative study of the different flowsheets for kaolin production in the world was done using the databases and presenting the state of the art of kaolin processing. The results indicated that the mean feed typically contains 35-39% kaolin with quartz, muscovite and kaolinite as main mineralogical components and SiO2 (65.83%), Al2O3 (21.19%), K2O (3.9%), and Fe2O3 (0,63%) as main chemical constituents. The products of mineral processing are twofold, one between 74 µm and 37 µm, and the other smaller than 37 µm. The wastes of operation had major quantities of kaolin. The average Human Development Index (HDI) of the cluster region is approximately of 0.61, which shows an association between mineral processing plant and social indicators. The kaolin recovery, however, is between 30-55% for the three most common types of flowsheets that are currently used in the small kaolin mining cluster, indicating a need for technological improvement to achieve regional development. These data could be used incrementally to adapt the process plant currently used in the small-scale mining cluster of kaolin."

Jan 1, 2014

By Jonas Addai-Mensah

In this paper, the results emerging from the several basic and applied studies performed to provide fundamental understanding of the interplay between clay pulp chemistry, orthokinetic flocculation performance, particle interactions, applied shear and dewaterability of fine clay mineral dispersions are presented, reconciled, and discussed. Modification of pulp chemistry and behaviour was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and high molecular weight, anionic polyacrylamide copolymers: carboxylate substituted (PAM A) and 2-amido 2-methyl propane sulphonate (PAM S) (PAM S), non-ionic polyacrylamide homopolymer (PAM N) and non-conventional, non-ionic polyethylene oxide (PEO) as flocculants. Clear links between pulp interfacial chemistry, particle interactions and dewatering behaviour, resulting from the influence of hydrolyzable metal ion, pH, temperature, polymer structure type and shear, are established. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs (>10 m/h) comprised: (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time and (iv) anionic rather than non-ionic PAM. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20 ? 25 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5 - 15 wt % solid. Application of the findings and new knowledge gained to real plant tails? case studies for marked improvement in dewaterability through thickening is demonstrated.

Sep 1, 2012

By Andrew T. McBride, Malcolm S. Powell, Indresan Govender

"Current empirical Semi Autogneous Grinding (SAG) mill models contain assumptions concerning the amount of energy available for particle breakage, how this energy is distributed in the mill media and the rate at which the energy is transferred. Despite these assumptions the JK SAG model is highly functional with a proven track record. DEM provides a numerical framework to greatly improve on these assumptions that were necessary due to a lack of available input data.This paper identifies key outputs of the Discrete Element Method (DEM), such as energy spectra and impact probability distribution. It describes how they can be incorporated into current mill models utilising practical rock breakage data. The rate at which energy is transferred is shown to be dependent on particle position and mill rotational speed and not once per cycle as previously assumed. Based upon this an improved energy transfer methodology is presented. The fundamental outputs of the DEM are validated against experimental three-dimensional particle tracking data, so as to establish whether the DEM produces correct energy transfer predictions on the inter-particle level, which is crucial to this work."

Jan 1, 2003

By S. Gaydardzhiev

Initial experiments towards preparation of hollow ceramic microtubes by dip-coating of fibrous plants with water based alumina gel-casting slurries using hemp and coconut fibres as templates have been done. It has been found that the wettability of fibres and accordingly the stability of the developed ceramic layer on their surface during slurry gelation varied significantly within the different fibre types. Good correlation between the diameters of the template fibres and the resulting channels has been found at the level of solids loadings used, 31 %. Hemp fibres used as bundles have led to formation of multi channel patterns while the coconut fibres-templated process resulted in uniform monochannel materials. The micro tubes have show good mechanical handling.

Jan 1, 2014

By A. V. Rasskazova

"The oxidized and mixed ores are processed by heap leaching. Primary ores with high gold content are floated. In recent years mining of primary ores with the low gold content (up to 4 ppm) has increased. Extraction of gold from these ores by floatation is technologically ineffective. Gravity concentration is ineffective for fine gold particles because of their floatability. The research objective was assessment of the viability of processing gold-bearing ore with combined gravitational and hydrometallurgical methods and testing of recovery of metals from a gold-copper oxidized ore chloride-hypochlorite leaching solution. The advantage of chloride-hypochlorite lixiviant is the low cost of reagents which is produced by the electrochemical synthesis of NaCl solution with the addition of HCl. The adsorption of chlorine compounds by a mineral matrix and its ability to oxidize the refractory ore components and allows for the application of chloride-hypochlorite systems for gold recovery for both oxidized and primary ores. The complexity and problem in using a gold–chloride system is the strong adsorption of gold–chloride complexes onto mineral surfaces, such as goethite, quartz, and alumina. In preliminary testing, gold recovery from gravity circuit gold bearing concentrates processed by agitation leaching in chloride-hypochlorite solution, gold recovery has reached up 82% after 4 hours of leaching. Chloride-hypochlorite leaching of copper-gold oxidized ore with preliminary processing by sulfuric acid provided for 94 % gold recovery to solution. Understanding of ecological hazard of cyanides is the motive power of researches in the field of search non-cyanic chemistries to provide for technologically and economically effective solvents of gold. Soluble compounds of chlorine with a suitable oxidizer are one of the alternatives to cyanides. Basic researches of gold extraction by chloride-hypochlorite solution have shown high rates of gold recovery.INTRODUCTION Because of the continued and growing environmental concern for the use of cyanide for gold processing, interest for the use of non-cyanide lixiviants, especially with halides has renewed recently (Tran et al., 2001; Ferron et al., 2003; Bhaghalha, 2007). Leaching solutions based on halides (chloride, bromide and iodide) are viable alternative to cyanide (Kwang et al., 2008). The major disadvantage of the chlorine–chloride system is the high reactivity of chlorine in reaction with sulfide and gangue carbonate minerals. It is believed that only high grade materials may be treated by chlorine–chloride systems economically (Baghalha, 2007). Another important problem of the application of gold–chloride complex is that it tends to be rather unstable and may re-precipitate upon contact with a reductant, such as sulfidic minerals of ore. It is well known that Au(III)–chloride hydrolysis species are strongly adsorbed by goethite, quartz, and alumina (Machfsky et al., 1991). To minimize adsorption of gold–chloro complexes, it works best to minimize the adsorption time."

Jan 1, 2018

By Y. M. Zhu, G. C. Gong

"The influences of citric acid (CA) on the flotation behavior of cassiterite using styrene phosphonic acid (SPA) as the collector were studied via single mineral flotation tests, contact angle measurements, zeta potential determinations and solution chemistry calculations in this paper. The results of single mineral flotation tests revealed under the conditions that pH=4 and the dosage of SPA 100 mg/L, the recovery of cassiterite reached 76.78%. The addition of 20 mg/L AC decreased the recovery by 12.42% at pH=4. Contact angle measurements demonstrated the adsorption of CA prior to SPA made the cassiterite more hydrophilic. The results of zeta potential determinations and solution chemistry calculations indicated the chemisorption of C6H7O7- and C6H6O72- filled parts of the Sn site on cassiterite surface and prevented the SPA from getting adsorbed. The hydrophilic effect of AC was stronger than the hydrophobic effect of SPA and the flotation of cassiterite was crippled. INTRODUCTION Tin is an important metal which is widely used in medical instruments, marine engineering materials, electronic and electrical devices, welding, weapon manufacturing and organotin compounds industries (Angadi et al., 2015). Cassiterite is the only mineral from which the tin can be extracted, thus it is of great importance to efficiently exploit the cassiterite mineral. Flotation is an indispensable method for the recovery of cassiterite (Li et al., 2015). However, cassiterite is usually in association with many other gangue minerals which are of similar floatability, such as quartz, calcite, fluorite, iron oxide, wolframite, scheelite and tourmaline (Sreevinas, 1997). So some modifiers are necessary in the cassiterite flotation process. The amounts of the modifiers used in the flotation must be judicious and the overmuch modifiers may cripple the recovery of cassiterite (Parsonage et al., 1987). Nevertheless, the research about the effects of the modifiers on the flotation behavior of cassiterite has been rarely reported. In this paper, the influences of citric acid (CA) on the flotation of cassiterite using styrene phosphonic acid (SPA) as the collector were investigated by flotation tests, contact angle measurements, zeta potential determinations and solution chemistry calculations."

Jan 1, 2018

By A. G. Bulaev

Biohydrometallurgical technologies based on activity of acidophilic microorganisms oxidizing ferrous iron, sulfur, and sulfide minerals are widely used to extract base and noble metals from sulfide ores and concentrates. As sulfide minerals oxidation is exothermic, industrial processes are usually preformed at 40–50°C. Moderate thermophiles predominate under these conditions. Most of moderately thermophilic acidophilic microorganisms that oxidize metal sulfide are mixotrophic, i.e., they use both organic nutrients and CO2 as carbon sources. Carbon availability is crucial for microbial activity and affects efficiency of biohydrometallurgical processes. Aeration with CO2-enriched air is often used to increase microbial activity in biooxidation reactors. Organic nutrients can be used as alternative carbon source for moderately thermophiles performing biooxidation of sulfide concentrates. We performed several experiments with different sulfide concentrates to study effects of organic carbon sources on biooxidation efficiency and demonstrated that application of such organic nutrients as yeast extract (YE) and molasses made it possible to increase biooxidation efficiency. For example, addition of 0.02% YE in the nutrient medium increased biooxidation rate of pyrite–arsenopyrite gold bearing and chalcopyrite concentrates in batch mode at 45°C. YE addition increased oxidation rate of sulfide sulfur and gold recovery level from 65 to 87% and from 73 to 81%, respectively. Similarly, YE addition increased copper extraction from 47 to 54%. At the same time, YE addition increased efficiency of biooxidation of pyrite–arsenopyrite gold bearing concentrate in continuous mode. Without YE addition, oxidation rates of pyrite and arsenopyrite were 65.7% and 94%, while gold extraction was 71%. YE addition (0.02%) made it possible to oxidize 74% and 95 % of pyrite and arsenopyrite and extract 78% of gold. Addition of molasses (0.02%) similarly affected biooxidation efficiency. Thus, addition of organic nutrients in nutrient media is a promising strategy for improvement of biohydrometallurgical processes.

Jan 1, 2018