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By M. Lundström, J. Aromaa, S. Seisko

"Gold dissolution was investigated in ferric chloride media, promoted as one of the most promising alternatives for cyanide-free gold leaching. The characteristics of gold open circuit potential (OCP) and its relation to gold dissolution rate was investigated. Furthermore, the reaction mechanism of gold dissolution in ferric chloride leaching was discussed. The effect of solution variables, [Fe3+] = 0.02–1.0 M, [Cl–] = 2–5 M, T = 25–95 °C and pH = 0–1.0, on OCP and dissolution rate were studied electrochemically using rotating disk electrode (RDE) and linear polarization resistance (LPR) method with ?cyc = 1000 RPM. The investigated gold OCPs in ferric chloride solutions were found to vary between 597 and 688 mV vs. saturated calomel electrode (SCE) and gold dissolution rates between 1.2·10–5–5.0·10–4 mol s–1 m–2. Increase in temperature (25–55 °C) and ferric concentration (0.02–1.0 M) changed OCP into more positive values, while increase in chloride concentration (2–5 M) decreased it. The logarithm of gold dissolution rate was shown to increase linearly with increasing OCP at the temperature range 25–95 °C, ferric concentration range 0.02–0.5 M and chloride concentration range 2–4 M. A notable increase in the gold dissolution reaction rate was evident at T > 55 °C. INTRODUCTION Currently cyanide leaching is the predominant method used in gold production from primary raw materials (Marsden and House, 2006). However, since the Baia Mare disaster in Romania in 2000, the use of cyanide has been the subject of international concern due to the toxic nature of the chemical posing a significant health threat if exposed to the ecological entities (Hilson and Monhenius, 2006; UNEP/OCHA, 2000). Therefore, several countries e.g., Costa Rica, Czech Republic, Germany, Hungary, Turkey, many states of the USA and provinces of Argentina, have started to ban or limit cyanidation via legislation (Laitos, 2012). Thus, alternative solutions, such as thiourea, thiosulphate, oil-coal agglomerates as well as halides have been investigated in order to replace cyanide as lixiviant (Adams, 2016; Aromaa et al., 2014; Aylmore, 2005; Hilson and Monhemius, 2006; Lampinen et al., 2015). Ferric and cupric chloride leaching have been reported to have advantage over cyanidation being capable to dissolve refractory gold minerals, without pre-treatment such as pressure oxidation or roasting (Angelidis et al., 1993; Lundström et al., 2014; Marsden and House, 2006; van Meersbergen et al., 1993). According to Aylmore (2005), 4% of publications for alternative lixiviants to cyanide in gold leaching were within category oxidative chloride processes including aqua regia and acid ferric chloride leaching. Further, some patents have been granted for ferric chloride leaching of gold (Abe and Hosaka, 2010; Lundström et al., 2016)"

Jan 1, 2018

There are interactions between different minerals from the same ore, minerals and grinding media, and the electrochemical conditions present in the system. Grinding in steel rod and ball mills is a common practice in minerals processing. It is accepted, that the electrochemical interactions between the grinding media and minerals in a grinding mill, influence the corrosive wear of balls/rods and the surface properties of the ground minerals. A complex massive sulphide, Cu-Zn, TAKNAR, Iran, was used for all the experiments. The aim of this study was to investigate the effect of grinding media (dry or wet) on the pulp chemistry and recovery of Cu and Zn in bulk concentrate. 1100 g of ore samples were milled, and mill products with d80=85 and 75 micron in wet and dry grinding methods were produced. Rougher bulk flotation experiments were performed with 550g ore samples, at 30% solids. SIPX in conjunction with Aero238 in 1:2 ratio (48 g/t), was used as mixed collector system, and copper sulphate (200g/t) and MIBC (20 g/t) were employed as sphalerite activator and frother. Lime and High purity Oxygen gas were used for adjusting pH at 8.5 and aeration. The results showed that, more positive pulp potentials were measured when the feed had been ground in a dry environment, and the difference in pulp potentials between the dry and wet ground feed was approximately 250 mV after the grinding stage. In dry grinding method, the recovery of Cu and Zn increased approximately 5 and 10%, respectively. In addition, in dry ground samples, the volume of middling and coarse particles (+100 micron) were more and Dry ground flotation feed had better agreed with using a mixture of collectors. After using copper sulphate, pulp potential increased about 50 mV in dry and 75 mV in wet grinding methods. Keywords: grinding media, pulp potential, Cu-Zn massive sulphide, bulk flotation

Sep 1, 2012

By Mario Gerards

Maturing populations create an increase in the demand for the type of non-ferrous metals, which are used in the manufacturing of electronic products. The depletion of existing high-grade deposits, make it necessary to boost the efficiency of beneficiation processes and most importantly the yield (recovery rate of the value commodities). Increasing demand now makes it worthwhile to tap into resources, which were previously considered waste, for example secondary deposits such as tailing ponds and electronic waste. In order to achieve increased yields, increasingly finer, or even ultra-fine fractions have to be treated. In most cases, mineral characteristics such as size and density call for non-mechanical, high-capacity technologies to be used. There are various technologies that allow for the separation of fines and ultra-fines. This paper outlines the dynamics and efficiency of pneumatic flotation with emphasis on its application to the recovery of non-ferrous metals, from electronic waste. The conventional agitator flotation technology of an electronic waste processing plant was not able to recover ultra-fine non-ferrous metals satisfactorily, due to losses within the tailings. Because of its adaptability and its inherent suitability for non-ferrous metals, pneumatic flotation has been incorporated to the existing process achieving excellent results. The merit of the process lies in the state of the art technology, which does not utilize compressed air and any rotating parts, which results in a reduction in wear and energy requirement, both features of this innovative technology. In addition, the use of pneumatic flotation resulted in a significant reduction in residence time, when compared to mechanical flotation. Pneumatic technology is able to influence air bubble size in a flotation cell, by changing the speed and pressure of the slurry stream. Higher slurry velocities lead to the formation of smaller air bubbles, which is required for the successful flotation of ultra-fine particles. Conversely, decreasing the slurry velocity leads to bigger air bubbles. The optimum bubble size can be created according to different feed characteristics. This is important in case of feed fluctuations.

Sep 1, 2012

By Roberto Galéry, Braz J. C. Filho, Marcelo M. Stopa, Douglas B. Mazzinghy, Priscila M. Esteves

"The purpose of the research is to monitor ball mill filling by means of signals usually measured in its electrical drive. The method is based on the mill torque estimated from rotor speed and induction motor stator voltage and currents. New signal processing is presented in both time and frequency domain for measurements in a dry laboratory ball mill. Statistical analysis is applied to time series resulting in good correlation to mill filling. Fast Fourier Transform (FFT) and power spectral density (PSD) also resulted in an accurate filling indicator. The proposed method does not need any sensor to be installed directly on the mill and requires only sensors usually available for motor control purposes. The experimental results showed that the method have potential to be used to construct an automatic system for monitoring operational variables in ball mills. The aim of this monitoring is to improve energy efficiency, reliability and productivity.INTRODUCTION Recently, a great number of papers have pointed the importance of ball mill filling monitoring and also of grinding control (Lu, et al., 2014) (Ramasamy, et al., 2005) (Tsamatsoulis, 2014) (Zhou, et al., 2009). Additionally, great amount of control techniques have also been presented with several complexity degrees (Tsamatsoulis, 2014). According to Eremenko (2015) the lack of effective and accurate methods for fill level measurement is the main reason that makes mill optimal control so complicated. It happens because nonlinearity, long time delay and time varying features of the ball mill turns difficult to develop a truly efficient method for monitoring filling. At the same time, fill level has a determining role in charge motion and consequently on particle breakage. For low levels of filling many energy is expended in impacts with very low breakage efficiency. Those impacts can also damage mill liner. In contrast, high levels of filling causes damping effects that reduces breakage and can also affect energy consumption. Based on this it is conclusive that fill level measurement of ball mills is an important issue for grinding efficiency. This fill level information can be used for operators to control ball mills and also for engineers to run simulations and improve confidence levels of circuit designs (Shi, 2016)."

Jan 1, 2018

By Caitlin Rogers

The environmental and economic sustainability of froth flotation is dependent on effective management, which in turn improves the performance of a concentrator. In economic terms this means improved recovery of valuable minerals, in environmental terms this means effective management of acid generating tailings. Three indicators were selected to measure the performance of an integrated flotation system. The system consists of two stages of flotation; valuable mineral flotation followed by environmental desulfurisation by froth flotation. The suitable indicators were selected based on their fulfilment of four attributes. An attribute is a desired aspect of an indicator. The four attributes were: comprehensive, relevant, sensitive and quantitative. Two environmental indicators and one economic indicator were selected. They represent revenue generation from valuable minerals and environmental cost of management. The suitability of the selected indicators was shown using illustrative scenarios.

Jan 1, 2014

By Skinner. W.

"Introducing cutting-edge development work, which aims to simplify mineral processing flow-sheets, reduce costs and address environmental issues. Over the past four years Innovative Mineral Processing Technologies Pty. Ltd (IMPTEC) Australia have developed a Super-fine Crusher and a Planar Magnetic Separator which offer low cost, wet or dry alternatives to conventional grinding and conventional magnetic separation. Each of these machines has been successfully trialed at pilot scale and are now in the process of transitioning to commercial scale. This paper reports on the progress made in each of these fields. The potential scope for application of super-fine crushing technology as an alternative to grinding is potentially expansive and could include beneficiation of metalliferous ores, precious metal ore processing, hydrometallurgical processing, industrial minerals and coal processing, plastic fillers and ceramics processing as well as processing of cementitious slags and fly-ash. IMPTEC have recently achieved outstanding results at pilot scale with a dry combination of super-fine crushing and planar magnetic separation, which offers an alternative to the wet processing of magnetic iron ores. The dry combination has set new laboratory performance benchmarks when compared with the industry standard wet Davis Tube Tester. The test results have also established a strong evidence base showing that super-fine crushing achieves liberation of value minerals at coarser sizes when compared with grinding. The dry combination of super-fine crushing and planar magnetic separation also addresses environmental issues and completely eliminates grinding. An IMPTEC super-fine crusher is currently undergoing commercial trials, generating ultra-fine products from granulated lead blast furnace slag for use as cement substitutes. The performance of the super-fine crusher on this extreme duty highlights the potential benefits of super-fine crushing over the wide range of industries and applications where conventional grinding is employed.INTRODUCTION Present day mineral processing practices can become anchored in convention, where, inefficient methodologies are recognized and accepted as “best practice” or “industry standard”. Motivated by this challenge, IMPTEC has undertaken the development of radically different and improved methodologies in the fields of fine comminution and magnetic separation. Whilst, crushing is much less energy intensive and generally less capital and maintenance intensive than grinding, the technology has stalled due to the lack of crushing devices, which have the capacity to adapt to fine and ultra-fine duties. Grinding practice advances have been achieved through major increases in machine size and power. However, these advances are also accompanied by major escalations in capital, operating and maintenance costs. The economics of this strategy has become increasingly questionable. A typical example is the viability of low-grade magnetite beneficiation, which can hinge largely on the cost of grinding to fine and ultra-fine liberation sizes."

Jan 1, 2018

By W. H. Cheung

Nickel and cobalt production relies heavily on the processing of nickel laterite ores; these ores contain the majority of known Ni and Co reserves, 80% and 90% ~ 95%, respectively. The Caron process is used to extract Ni and Co metals from low-grade nickel laterite ores (1% Ni and 0.1% Co). It involves selective reduction of NiO and CoO minerals followed by ammoniacal leaching. Despite low metal recoveries, this process continues to be technically and economically reliable and thus commercially important globally. However, keeping the Caron process cost-effective has been a challenge for industries because of increasing economic and environmental pressures. Although studies of the Caron process have been extensive, significant improvements in recoveries of industrial processes have not been forthcoming. Reported industrial metal recovery from high iron content ore is only 80% ~ 85% for Ni and only 40% ~ 45% for Co; recovery is even lower for ores rich in magnesium. The real difficulty here is that there is no complete understanding of and control over the complex series of reactions in the ore and in the leaching solution during processing. Achieving effective metal recoveries from the Caron will require control of the mineral transformations, which affect the activation of minerals by reduction. In this study, the effect of over-reduction was investigated, which superseded the effect of activation by lowering the activity of the minerals and thus metal dissolution. Reduction was carried out in a batch reduction apparatus with 1:1 and 1:2.5 CO/CO2 gas mixtures from temperatures of 500 ~ 700°C and residence times up to 60 minutes. The pre-reduced ores were leached using a standard ammoniacal leaching test. Thermodynamic analysis and possible effects of stable phase field on leaching was examined. The results suggest that control of over reduction effects are directly related to the mineral transformation and reduction conditions.

Jan 1, 2014

By R. Singh

The paper presents the results of characterization and beneficiation studies carried out on a lean grade tungsten ore sample from Degana, India. Basically, three different routes, involving gravity separation, magnetic separation, and froth flotation were studied for concentration of the sample by physical and physico-chemical methods. Considering the low recovery by physical methods, efforts were put in to produce a tungsten concentrate by physical methods suitable for subsequent hydrometallurgical recovery of tungsten as ammonium para-tungstate. This strategy proved quite helpful in minimizing the losses of tungsten in tailings. Based upon these studies a novel integrated technological process flow-sheet was developed for the exploitation of lean grade tungsten ore deposit of Degana, India. Keywords: lean tungsten ore, characterization, beneficiation, gravity and magnetic separation, hydrometallurgical extraction, integrated process route

Sep 1, 2012

By Mohammad Mainul Hoque, Linhan Ge, Ai Wang, Geoffrey Evans, Subhasish Mitra

"Dispersed phase interactions involving bubbles and particles in the turbulent environment play a significant role in the flotation process. The conventional collision models only account for the deterministic rather than the stochastic behavior of turbulenct flow. What the bubble-particle collisions would be like remains an open problem due to the complex nature of turbulent flow. To address this research question, the present study aims to quantify the bubble-particle collision efficiency incorporating turbulence using the computational method. Multiple solid particles were released to interact with a single stationary rigid bubble (non-deformable interface). Effect of particles Stokes number, turbulent intensity (TI) and integral length scale on the bubble-particle collision efficiency (Pc) was examined. Large Eddy Simulation method (LES) was used to compute the continuous phase. Fluctuating velocity required at the inlet boundary condition was derived from Gaussian energy spectrum to generate the upstream turbulence. Discrete Phase Model (DPM) is used to simulate particle trajectory. The characteristics of turbulent flow were analyzed through Energy spectrum and energy dissipation rate. The critical initial releasing radius of the annulus, where Pc equals zero, reaches up to 1.5(Rb+Rp) under high turbulent intensity (TI) 20.48% compared to 0.23(Rb+Rp) calculated from the traditional Pc model. Pc decreases as the distance of initial releasing annulus between bubble centre increases. Pc increases as particle Stokes number increase up to 0.66. The collision efficiency for particles of St less than 0.38 is higher under TI 11.78% compared to TI 4%.INTRODUCTION To increase mineral recovery, interactions between bubbles and particles are essential. All flotation devices achieve it through introducing some level of turbulence into the system by increasing specific energy dissipation rate. Figure 1 shows three different flotation equipment, traditional floatation cell, Concorde cell and cyclonic-static micro-bubble flotation column (FCSMC), with different turbulence generation mechanisms – impeller, down-flow liquid jet and pump recirculation, respectively."

Jan 1, 2018

By E. Emelyanenko, P. Solozhenkin, J. Yagudina, O. Ibragimova

To recover tetrahedrite-tennantite series minerals from porphyry copper-pyrite ores by the froth flotation method, further research on thiol collectors is launched to promote the utilization efficiency of copper ores. In the present paper the adsorption mechanism of the collectors on tennantite surface has been investigated by computational modeling and FTIR-spectroscopic analysis, which have revealed that the decrease in prognosis of collector activity evaluation (PCAE) for tennantite is in the following order: BX (-0.34318), AEROPHINE 3418A (- 0.61756), AERO 5100 (-14.18857). The lower PCAE the stronger the ability of the collector to interact with the mineral surface of tennantite and form the stable complex. More kinetic reliable conditions to form suitable adsorption layer and rupture of the liquid interlayer with AERO 5100 have been observed by FTIR spectra due to decrease of the intensity and stretching and bending vibrations of water (less than 20 and 65%, respectively). In order to verify the feasibility of AERO 5100 as a collector the industrial flotation tests have been conducted. Flotation performance has improved significantly with the stadially grinding and preflotation of tennantite in intercycle copper flotation that allows to avoid desliming of the fragile mineral and minimize loss of Cu and As in tailings. The recovery of copper in copper concentrate increases by 3.9% with the grade maintained.

Jan 1, 2018

By S. A. Kubyshkin, A. A. Agafonov, A. L. Shakhnin, S. M. Sukharzhevsky, A. A. Komlev, N. V. Vorob’ev-Desyatovskii, A. Pichugina

Cyanidation of gold ore results in formation not only of Na[Au(CN)2], but also cyanometallate complexes of some transition metals. During subsequent gold extraction from such solutions and pulps, using activated carbons (??), a number of problems arise. An effective solution of the problem is not possible without detailed knowledge of the interaction mechanism of transition metals cyanide complexes with AC particles. The chemical properties of AC particles and graphene, saturated with [?u(CN)n](n-1)- (n=2, 3), were studied by XPS, ESR, SQUID, and DFT. The obtained results were compared with the data on AC adsorption of anionic form of Ag(I), Au(I), Cd(II), Hg(II), Cr(III), Fe(II), Fe(III), Co(III), Rh(III), Ni(II), Pd(II), Pt(II) and Pt(IV) cyanide complexes. The adsorption of [?u(CN)n](n-1)- (n=2, 3) on AC from aqueous solutions in air is accompanied with oxidation of ?u(I) atoms. Besides, Cu(II) and Cu(III) compounds were found on AC surface. Quantum-chemical calculations confirmed the possibility of formation of Cu(I) complex with carbene-like sites of AC. The reactions of [?u(CN)n](n-1)- (n=2, 3) complexes and aromatic carbenes and their cation-radical were theoretically studied at DFT PBE level to obtain the information on adsorption of cyanometallate complexes on AC. Carbenes with different fragments were regarded as a model of activated carbons, which have free edge sites with paired o and n electrons. It was shown that [Cu(CN)2]- bounds firmly with triplet carbene, if one Cu-CN bond breaks. The dissociation process occurs through a multi-step spin-crossing mechanism to reduce total spin multiplicity of the metal-carbene complex. The behavior of transition element complexes in contact with AC in aqueous solutions is determined by the following characteristics: geometrical structure of ionic complexes; nature of ligands bonded to the central atom; concentration of reactive oxygen species in solution and its pH; nature of binding sites of AC.

Jan 1, 2018

By M. Saba

In cyanide leaching procedure, achieving an acceptable efficiency for silver and gold is very time-consuming, thus, enough studies have not been performed for optimization and modeling of this process. The kinetics of cyanide leaching includes two steps: first step comprises a sharp slope while the other has a slight increasing trend. In the present study, in order to reduce the time and cost, the cyanide leaching process of a sulfide silver/gold ore was optimized in the first period. The applied parameters and their ranges are: temperature 20-40 (°C); time 1-8 (hrs); cyanide concentration 1-2 (mole cyanide / mole Cu); the percentage of solid to liquid 1-2 (%) and pH 10-12. For design of experiments fractional factorial 2(5-1) was used. Also four center points were applied to increase the accuracy of the model. In addition, by analysis of variance (ANOVA) the most effective parameters were identified and the optimized condition was determined. A regression model was proposed to describe the effects of independent variables and their interacting role on silver recovery. Results showed that the model was linear for silver and nonlinear for gold. In the gold recovery process, the two important parameters are time and pH with the former being more effective. Due to the existence of cyanide ions in the medium, temperature and cyanide concentration have less influence in the gold recovery process. Solid to liquid ratio, in addition, comprises a slight negative impact on the procedure. This emphasizes the different kinetics of silver/ gold cyanide leaching. Finally, using the optimum condition the amount of silver and gold obtained were 61% and 67% in 8 hours, respectively. While in general conditions, the results were 37% and 54% in 24 hours, respectively. Keywords: cyanide leaching, refractory gold/silver ore, modeling, optimization

Sep 1, 2012

By V. A. Luganov

Methods of treatment of pyrite concentrates differ, depending on the content of pyrite and non-ferrous metals: oxidation roasting, sulphatization roasting, smelting, direct hydrometallurgical treatment and so on. Existing technologies do not provide for high recovery of metals, expenses associated with existing technologies are high, and environmental issues, associated with the existing technologies need serious attention. We have developed universal technology of the activating-dissociating autogenous roasting of pyrite concentrates using air based, or air, enriched with oxygen, blow. The basic process is taking place in accordance with the following reaction: (1-x)FeS2 + (1-2x)O2 = Fe1-xS + (1-2x)SO2 +Q The products of this reaction are pyrrhotinized cinder and roasting gases, rich in SO2 (up to 18 % in case of air blow) and poor in SO3, that contain up to 1 % of elemental sulphur. Cinder contains different forms of pyrrhotite. These forms of pyrrhotite differ by its content (from Fe0.843S to Fe0.945S), thermodynamic, magnetic (from 4.10-1 to 3.6 SI units), flotation properties (with pyrite dissociation the ?-potential of the product is moving towards more electrically positive charge, from 0.95 for pyrite to 0.2 for dissociation products) and other properties that depend on the conditions of roasting. The combination of pyrrhotizing roasting with different methods of cinder treatment allows to increase the level of sulphatization of non-ferrous metals during the roasting; reduce the amount of blow used during the processing; reduce dust losses to the gas phase; reduce the capacity of gas cleaning system and increase resistance to corrosion of the gas-treatment system, used for the production of sulfuric acid from pyrites. This combination of treatments also allows to use magnetic separation and flotation for separation of ferrous and non-ferrous metal compounds during cinder treatment; perform de-arsenation of arsenic containing concentrates and by-products. Pyrrhotinized cinder may be treated by oxidizing and non-oxidizing hydrometallurgical methods. Keywords: Pyrite, polymetallic ores, sulphidization roasting, pyrrhotite, magnetic separation, arsenic sulphide

Sep 1, 2012

By S. H. Morar

Froth stability is widely recognized as a key driver of flotation selectivity. It is well known that froth stability is affected by the type and quantity of surface active reagents present (frothers), and the concentration and hydrophobicity of solid particles present. While some studies have been performed on the effect of frothers on froth stability in three-phase systems and the hydrophobicity of particles present, very little work has been performed on the effect of solids loading on froth stability. This may be due to insufficiently robust measurement techniques. This paper investigates the use of a new machine vision measurement to measure solids loading, and the relationship between this measurement, bubble size, and bubble burst rate on the froth surface. Keywords: froth flotation, machine vision, solids loading

Sep 1, 2012

By T. S. Qiu

In view of the bad effect that Na-bentonite direct adsorb Pb2+-containing wastewater, this article has carried out two kinds modification treatment on Na-bentonite: the direct microwave radiation modification and microwave radiation organic modification by adding quaternary ammonium salt?cetyltrimethylammonium bromide,and analysis the main influencing factors of the modification effect. In static conditions, preparing Pb2+-containing wastewater as the research object, it has respectively studied the effects of Na-bentonite, microwave soil of direct microwave modification and microwave soil of organic modification on the process of adsorption Pb2+, and discusses the effects of pH value, temperature, adsorbent dosage, stirring time on the adsorption Pb2+ in wastewater by modified bentonite, at the same time it does a verification test to the practical Pb2+-containing wastewater. Comparison the effects of adsorption Pb2+ in wastewater, the results show that organic modified microwave bentonite is obviously better than direct microwave modified bentonite and Na-bentonite, and can make 6 mg/L Pb2+-containing wastewater meet the national discharge standards. Through scanning electron microscope, the result of test is that organic modified microwave bentonite is the cause of improving adsorption Pb2+ in wastewater. Preparing modified bentonite by microwave heating will not only shorten the response time, reduce energy consumption and work-load, but also modified effect is good.

Jan 1, 2014

By P. Braga, A. Chaves, S. França, A. Luz

"In Brazil, there are no official reserves of molybdenum, and the unofficial reserves are modest. Therefore, the molybdenum ore (molybdenite) produced as a co-product or by-product of emerald mining in the region of Campo Formoso, BA, has arisen as the only economic option. The flotation process is commonly used in Brazil for the recovery of molybdenite from emerald mining tailings, but it produces low-content molybdenite concentrates, thereby resulting in a product with low economic value. The molybdenite concentrate produced in Campo Formoso contains 83.5% MoS2 (50% Mo), which is less than the international standard product that contains > 90% MoS2 (54% Mo).This low value is due to the presence of talc, which is a naturally hydrophobic mineral that is also floated with the molybdenite during the flotation process. Separability studies were done in a Partridge-Smith cell using dextrin and quebracho as a molybdenite depressor in solution at different concentrations and pH values to produce a technical-grade concentrate (i.e., 90% MoS2). These basic studies were accompanied by measurements of the zeta potential and contact angle, which was determined by the capillary rise method. The results of these floatability studies were used in bench flotation tests, which were performed in a Denver laboratory flotation cell. A molybdenite concentrate of 93.4% MoS2 was obtained when dextrin was used at a concentration of 100 g/t."

Jan 1, 2014

By Peter Ay, Vincenz Mehlstaubl, Satyanarayana Narra

"This study gives an insight into non-destructive testing methods suitable for porosity analysis at a small scale, firstly summarizing relevant state-of-the-art technology and pending patents, secondly realizing and documenting the start-up of the VHX-2000 digital microscope by the manufacturer Keyence and thirdly demonstrating practical application with the extended analysis of three fundamentally different agglomerates for which important application-related parameters are determined. Various analysis procedures on the different agglomerates the efficient and timesaving operational features of the digital microscope are outlined. Firstly an analysis of flax fibre agglomerates determines the process conditions best suited to produce agglomerates with specific properties by determining sphericity, cubicity, density and porosity as well as fibre damage and alteration. Secondly the production of iron-hydroxide - hemp-fibre agglomerates serves to obtain information on porosity values as a result of a cauterization of the fibres. The third analysis provides estimations of porosity values for acid-treated lignin agglomerates. Measurements were carried out with compact dry agglomerates and with soaked, expanded agglomerates, determining factors for total water carrying capacity. Practicability of non-destructive testing by digital microscopy is demonstrated and explained concerning the applications in this study by obtaining definite structural findings about the analysed agglomerates. Information on its operation is made available by a practice-oriented manual for the VHX-2000 digital microscope. Further suggestions for more in-detail analysis results with different instruments are given."

Jan 1, 2014

By Steven Bradshaw, Edson Charikinya

The application of high power microwave energy to secondary crusher products has been shown to induce micro fractures and cracks in the ore. This suggests that heap leaching could benefit from microwave-induced fractures, as the extent and kinetics of heap leaching processes depend on the accessibility of grains to lixiviants, which can potentially be improved through microwave treatment. The density and pattern of microwave induced cracks and how these cracks subsequently affect heap leaching recovery has not yet been investigated. The objective of this study was to apply X-ray micro computed tomography (X-ray CT) to investigate microwave induced cracks in large cone and HPGR crushed sphalerite particles within 3D space. The ore particles were microwave treated in a single mode microwave applicator coupled to a switched mode power supply and a water cooled microwave transmission sub system operating at 2.45 GHz. The ore particles were treated at specific absorbed microwave heating energies of between 2 and 3kWh/t by treating at 6 kW of forward power for treatment times of 1 s. X-ray tomography analysis was conducted on fine (-5+4.75) mm, medium (-16+9.5) mm, and large (-25+19) mm sphalerite particles before and after microwave treatment at voxel resolutions of 5 µm, 15 µm and 25 µm respectively. Image segmentation, thresholding and spatial registration techniques were used to study crack patterns in 3D images of HPGR and cone crushed particles. Analysis of the X-ray CT images after microwave treatment shows considerable micro crack formation within the Cone and HPGR crushed particles. The cracks pattern showed interphase cracks propagating across all phases, with no evidence of preferential cracking. A greater density of microwave induced cracks was observed on fine (-5+4.75) mm particles compared to the medium (-16+9.5) mm and (-25+19) mm large particles. The results showed overall increased particle porosity following microwave treatment.

Jan 1, 2014

By N. N. Ngoepe

Positron Emission particle tracking (PEPT), which makes use of a radioactively labeled tracer particle, a positron camera and a tracking algorithm has been shown to be a viable method for studying flow properties in both the pulp and froth phases of flotation cells. Detailed velocity measurements of 300-400 µm glass beads were extracted to assess turbulence from velocity fluctuations in a micro flotation cell. The effects of particle speed and orientation at the instant of attachment events were studied. A minimum speed of 0.16 m/s was needed for a collision to lead to attachment. The most attachment events happen when the particle is directly in line with the inlet tube at 90o.

Sep 1, 2012

By F. Concha

A robust theory of sedimentation-consolidation evolved and was accepted by researchers world-wide in the last two decades of the 20th century. This theory provides a reliable method of thickener design and simulation. However, a process model, simple or sophisticated, empirical or phenomenological, is useful only if it is possible to determine, in an objective way, its experimental parameters. Research workers at the University of Concepción, together with Cettem Mineral Technology Center, created an integrated system of thickener design, simulation and control, including instrumentation, algorithm and software, which can be used by personnel in industry without specialized knowledge of thickening theory. In the paper, the development of three instruments for the measurement of pulp concentration, solid flux density and sediment compressibility is described. Each instrument uses software for data input, parameter calculation and results display. The paper also describes software for the optimization of the experimental parameter and for the design and simulation of industrial thickeners. Finally, mathematical algorithm and control strategies based on the phenomenological model are presented and compared with classical feedback control.

Jan 1, 2014