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By N. Naude, W. P. Roux

"Traditionally minerals processing equipment, such as jigs, are studied by characterising the feed and products from these processes. With this approach important details on the mechanisms of a process can be overlooked since assumptions have to be made on the internal operations of the equipment. Positron Emission Particle Tracking (PEPT) is a non-invasive technique that can be used to track a particle’s movement inside a closed vessel. PEPT makes it possible to observe the inner workings of a process, providing new information that was unattainable only a few years ago. Jigging has long been considered as one of the most difficult mineral processing techniques to model, due to the complexity of the mechanisms contributing to the separation of minerals during the jigging process. In this investigation PEPT was used to study the particle flow inside a laboratory batch jig. The aim was to determine if the particle trajectories could provide new insight into the jigging and its mechanisms. Three dimensional particle trajectories were observed with spatial and temporal resolution high enough to see details of the individual pulses during jigging. It was found that the pulse height is very dependent on the position in the jig bed. The vertical component from the trajectories showed the rate at which particles move through the jig bed (stratification rate) and it was seen that the density of a particle affects the stratification rate more that the particle’s size and that the shape in the range that was tested had little to no influence. Other phenomena such as a circular flow pattern was observed inside the jig and it was found that smaller lower density particles are affected by this circular flow pattern which tend to disperse these particles throughout the jig bed. Visualising the flow inside a jig by means of PEPT has shown to be instrumental in the deeper understanding of the process."

Jan 1, 2018

By Aubrey Mainza, Malcolm S. Powell

"A hydrocyclone with two vortex finders, named the three-product cyclone, has been successfully tested in the Platinum industry for dealing with the dense chromite found in UG2 ores. This dense component preferentially reports to the cyclone underflow, resulting in an over-ground fine chromite component in the final product. The dense media effect caused by a high chromite concentration in the cyclone feed produces a coarsening of the cyclone overflow, which results in loss of recovery through over-size material in the float feed. The fine barren particles of chromite that report to the overflow are recovered through entrainment in the flotation process, resulting in detrimental contamination of the slag produced from the concentrate.With the three-product cyclone a middlings product has been extracted that has a higher concentration of fine chromite. This volumetric stream flow represents a small percentage of the total cyclone feed and it is thus possible to treat it separately via fine screening to remove the fine chromite from the system and recover coarse silica."

Jan 1, 2003

By R. Els Ellis

Enhanced granulation of UASB granules was tested on pilot scale with two different test reactors (about 5 litres capacity each). Sludge from a local sewage works was used, with peach cannery effluent as carbon source. Cyclic motion of the reactor contents, and a daily replenishment of feed material create the necessary stress conditions for enhanced growth. Sizable granules, bigger than 0.5 mm, were produced within 20 days. Of the two reactors tested, the reactor equipped with a horizontal agitation shaft proved more effective.

Jan 1, 2003

By Kaiwen Liu

Activated carbon is widely used in the removal of organic and/or inorganic contaminants from waste water due to its high surface area, porous structure, and specific surface reactivity. However, in practical applications, it is difficult to recover the activated carbon completely by screening or classification. In this project,we prepared a magnetic form of activated carbon (magnetic activated carbon or M-AC) by precipitation of iron oxides on the surface of activated carbon. The M-AC can be easily separated from effluents by applying an external magnetic field, thus it can be recycled and regenerated for reuse. M-AC was characterized by X-ray diffraction (XRD), specific surface area measurement, and scanning electron microscope (SEM).XRD results show that the major phase of coated iron oxides on activated carbon is magnetite (Fe3O4). The specific surface area of activated carbon was found to be reduced after the impregnation of magnetite particles on the surface. The SEM micrograph shows the aggregation of the iron oxides on the surface of activated carbon. M-ACwas found effective in removing DETA (diethylenetriamine) species and metal ions from solutions. Cu (II) with initial concentrations from 5 ppm to25 ppm in solution is removed by more than 99% with the addition of 0.1 wt.%ofM-AC. For the removal of 25 ppm DETA species from solution, an addition of 0.5 wt.% of M-AC is required due to the larger size of the DETA molecule. Moreover, M-AC showed a good loadingproperty for nickel and gold ions from solutions. M-ACshows a better adsorption capacityover activated carbon and its potential applications in carbon-in-pulp for gold leaching and waste water treatment. Keywords: magnetic activated carbon (M-AC),diethylenetriamine (DETA),metal ion,adsorption

Sep 1, 2012

"The thiosulfate leaching process developed by Barrick to treat sulfidic high preg-robbing gold ores uses calcium thiosulfate as the leaching reagent for ores pre-treated by pressure oxidation, resin for gold recovery with sulfite/trithionate elution and reverse osmosis as a means of reagent recovery. A large portion of the research that led to the development of the technology was based on previous studies completed by different groups over the years, mainly focused on the ammonium thiosulfate system. Operational limitations in the use of the ammonia-containing recycled water in the pressure oxidation circuit were some of the main drivers for the change from ammonium to calcium thiosulfate for the development of the industrial scale process. One of the main aspects for successful gold extraction and recovery in the thiosulfate system is the pseudo-equilibrium reactions that drive distribution of the different gold species (in solids, solution and on resin) in the system. Previous studies have been focused on the thiosulfate reactions and equilibrium constants for the oxysulfur ions (thiosulfate, trithionate, tetrathionate). However, the literature around the effects of the different metal-oxysulfur complexes (Cu and Hg complexes) that form when the ore is in contact with the leaching reagents, and the related effects on stability of the gold complex is limited. The main changes in the gold complex chemistry and stability in the calcium thiosulfate system as compared to the ammonium and sodium equivalents, as well as related effects on gold recoveries, were investigated in the presence of different types of double refractory ores. INTRODUCTION Barrick has developed a thiosulfate leaching process to treat double refractory gold ores, by combining the use of acidic and alkaline autoclave pre-treatment with thiosulfate resin-in-leach (RIL). The process currently in operation at the Goldstrike mine (the TCM process), uses calcium thiosulfate as the leaching reagent, resin for gold recovery with sulfite/trithionate elution and reverse osmosis as a mean of reagent recycle. The main feed to the process plant is highly preg-robbing sulfidic ore from Goldstrike’s open pit. Prior to feeding the pressure oxidation circuit, the ore is processed through the crushing and grinding circuits and treated in preparation for acid or alkaline autoclave processing (POX)."

Jan 1, 2018

By Alan Bye, Nick Beaton, Wayne Stange, Emmy Manlapig, James Groutsch

"For over 50 years the JKMRC has applied a unique education-based research strategy to develop modelling and simulation tools that are "fit for purpose" for industrial application. These tools are widely used for the analysis and optimisation of mining and mineral processing systems. As the mining industry context evolves to deal with declining head grades, falling commodity prices, professional skill shortages, and an exponential growth in the volume of data, a re-evaluation of what "fit for purpose" means in the future is required. It is contended that future industry needs for simulation-based decision support requires tools and systems that incorporate: • Multi-component modelling, • Models of complex sensor behaviour, • Integration across the physical value-chain e.g. resource to market, • Financial analysis including risk and uncertainty assessment, • Enabling multi-criterion decision making (technical, financial and environmental), • Ore-body knowledge at multiple scales, • The use of fundamental numerical models to provide insight for the development of practically useful models, and • Decision support delivered through remote operations centres. JKMRC and CRC-ORE are collaborating to develop a next-generation simulation-based decision support system that assists in addressing these challenges. The Integrated Extraction Simulator (IES) combines many years of pragmatic and successful work integrated with modern technology trends - in particular the rapid move to cloud-based computing."

Jan 1, 2014

By S. Kelebek, M. Davidson

"Flotation tests were conducted on a mixed copper ore sample containing bornite and malachite with trace quantity of other secondary copper minerals. The bornite component was very floatable, in sharp contrast to poor flotation characteristics of other copper minerals. A Box-Behnken experimental design methodology was used to study effects of three main reagents, namely potassium amyl xanthate (PAX), hydroxamate (Cytec 6494) and diethylenetriamine (DETA). Pine oil, as a frother, was used at a fixed concentration. Three main models constructed using a statistical software included malachite recovery, overall copper recovery, and copper grade. Bornite recovery was not modelled as its recovery was consistently over 99 % in the presence of hydroxamate and PAX. In each model, the hydroxamate dosage was the dominant parameter (at 95% significance level) determining the recovery of main components including that of gangue, which manifested itself by lowering the copper grade of the concentrate. In comparison, PAX was effective only at 90% significance level. DETA did not affect the overall recovery of copper or malachite significantly, but appeared to cause a significant decline in the concentrate grade, especially when used simultaneously with hydroxamate. Various quadratic models developed for the flotation system investigated are presented."

Jan 1, 2014

By James A. Finch, Xiangzhou Ding, Yue Hua Tan

"The Jameson Cell is one of the choices of flotation machine in coal, base metal processing and other specialist applications. This paper determines the effect on vacuum pressure and bubble size of two design variables, orifice size and downcomer length, and the operating variable air-to-water (AWR) ratio. The main findings are: orifice size and downcomer length impact the vacuum but have limited effect on bubble size; AWR < 1 favours high vacuum, conditions are identified where vacuum is maintained at AWR > 1, and water flowrate has slightly greater impact on bubble size than air flowrate.INTRODUCTIONFroth flotation, the most common technique for mineral separation, has been in use for over a century. The process takes advantage of the difference in wettability of mineral surfaces to achieve the separation of valuable minerals from non-valuable minerals, or gangue. Numerous flotation machines have been invented and patented over the years. The Jameson Cell, invented by Professor Graeme Jameson in the late 1980s, is one successful example. First trialed at Mount Isa Mines (Queensland, Australia), Jameson Cells have been installed at operations around the world for the recovery of fine coal (Mohanty and Honakeri, 1999; Cowburn et al., 2006; Hacifazlioglu and Toroglu, 2007; Uçurum 2009), minerals of copper (Farr 1992; Atkinson et al., 1993; Harbort et al., 1997), lead/zinc (Rohner, 1993; Munro, 2003) and gold (Bennett et al., 2012; Lauder et al., 2003), and in water treatment (Yan and Jameson, 2004), solvent extraction de-oiling (Miller and Readett, 1992; Miller et al., 1997; Harbort et al., 2003; Young et al., 2006), oil sands processing (Neiman et al., 2012), and various food industries (Brenneman, 2014). One of the largest units is the 650 cm diameter separation tank with 24 downcomers installed in an Anglo American operation (Osborne and Euston, 2015). Scale up is relatively straightforward: to increase capacity the number of downcomers is increased with corresponding increase in size of separation tank.The Jameson Cell comprises two main parts: a vertical tube (downcomer) which provides self-aspiration and intense bubble-particles contact, and a (separation) tank where particle-bubble aggregates disengage from the pulp. The intense bubble/slurry mixing in the downcomer with air holdups reaching 60% (Marchese et al., 1992) accelerates particle collection enabling the greatly reduced cell volume compared with mechanical flotation cells and columns. The disengagement of the particle-loaded bubbles from the slurry in the separation tank is usually aided by addition of washwater."

Jan 1, 2018

By G. H. Li

Preparation strontium carbonate with celestite concentrate by flotation is studied by agglomeration-reduction roasting process. It is shown that, the drop strength of green pellet is greater than 4 times?(0.5m) -1 under the balling conditions of moisture of 9% and time of 18~20min. Lignin xanthate obviously improves the ballability of the celestite concentrate due to the increase of surface hydrophilicity, therefore, the balling rate is increased, as well as green ball strength. The drop strength of 7 times?(0.5m) -1 can be obtained when the lignin xanthate dosage is 0.5%~1%. Reduction roasting with anthracite shows that the SrSO4 conversion is 82%~83% for celestite concentrate pellet, under the optimal conditions of roasting temperature of 1100~1150? and time of 30min, and it is 10% higher than conversion of celestite lump under the same conditions. The strontium carbonate are prepared after roasted pellets are leached, purified and carbonated, and the SrCO3 content is higher than 97% , while the content of CaCO3 is less than 0.3%.

Jan 1, 2014

By J. Sachweh

The last few years have shown a significant increase in the demands for fine products, which means everything under 10µm. There are more and more applications requesting extremely fine ground powders leading to the development of several milling machines which are better adapted to the new products. Cost saving machinery is important for the worldwide competition. Especially the energy consumption is extremely important for any fine ground product. A worthwhile field for mechanical engineering companies is the dry milling machinery as there are not as many solutions available compared with wet milling applications. In many cases wet mil-ling is the only solution to reach the requested quality, but there are also a lot of applications which can be performed in a dry way on the premise that the right mill and classifier are available. Dry milling permits to save energy and allows to influence the particle size distribution more easily, as a classifier can be used in that case. This will significantly reduce production costs and can enable the production of new products with better properties. The Tower Mill is well-known already in the field of wet grinding. Recent research work and end user reports have shown clearly that this mill has a lot of advantages compared to a ball mill. Up to now this advantage is limited to wet grinding as only few mills have been used for dry grinding. There is no doubt about the efficiency of dry grinding, but new and improved feeding and discharg-ing systems have to be developed in order to enable the full range of its advantages. Especially the high production capacities are a challenge for mill and classifier designers. The Tower Mill with its special grinding mechanism allows to cope with very high feed rates, because machines with more than 1 MW are available. Improved grinding efficiency will decrease the circulation load through the classifier and also lead to smaller classifier sizes. Together with im-proved mills the classifier can work more efficiently because the feed material is finer. Results of a test center plant production will be shown together with a comparison between stan-dard machinery and the MaxxMill®. Preferential applications for each mill will be explained.

Jan 1, 2014

By Erico Tabosa, Meng. Jun, Kym Runge, Matthew Brennan, Weiguo Xie, Dee Bradshaw

Turbulence and its distribution are of great importance in flotation cell design as they affect suspension of particles, air dispersion and particle-bubble collision rates, which in turn determine flotation performance. However, there is no mature technique to measure turbulence in three phase (liquid-solid-gas) systems such as in flotation cells. In this article, the authors present two new approaches that are suitable for measuring turbulence distribution in three phase systems and validate their applicability. The first technique uses a piezoelectric vibration sensor (PVS) to measure fluid kinetic energy standard deviation and the second technique applies electrical resistance tomography (ERT) to measure conductivity variation at a measurement position in a flotation cell. For the PVS technique, calibration of the sensor was performed to determine the values of parameters that were needed to calculate the force applied to the sensor. Then measurement was conducted in a 60L batch flotation cell and the results were compared with LDA measurement. This demonstrated that the piezoelectric sensor signal provides a good representation of fluid kinetic energy standard deviation at the position of measurement. For the ERT technique, conductivity distribution data was processed to give conductivity variations, which were then used to calculate fluid kinetic energy standard deviation at the measurement position. The spatial distribution of turbulence obtained by performing multiple measurements at different positions in the 60 litre batch flotation cell was found to agree with the PVS measurement results. These two techniques are potentially powerful tools for turbulence measurement in flotation environments, enabling a clearer understanding of turbulence’s influence on flotation performance to be determined.

Jan 1, 2014

By G. K. Nimal Subasinghe

The establishment of grind size that optimally liberates the valuable mineral for efficient down-stream processing is of great importance for most mineral processing operations. Reasonably accurate comminution models as well as models of downstream separation processes may be found in the literature but their use in optimizing grind size is limited without an associated liberation model. In this work, an attempt has been made to address the above shortcoming by demonstrating how the effective parameters of the downstream flotation process may be predicted from the liberation characteristics based on the ore texture data for a disseminated nickel ore. In this regard, the liberation model based on linear intercept distributions of mineral and gangue proposed by King (1979) and its application to predict the flotation performance of an industrial plant demonstrated by Schaap (1979) may be considered useful contributions. However, while the model proposed by Schaap is simplistic enough, it is based on several assumptions due to the non-availability of intercept length measurements on the parent rock, in particular, on the extent of mineral exposure on the surface of comminuted particles. In this work, the linear mineral and gangue intercepts on polished specimens of a binary ore, comprising darker pentlandite as the valuable mineral and lighter barren host rock were measured using an image analyser. The resulting intercept distributions followed negative exponential distributions. Using the mean sizes of mineral and gangue intercepts, the proportion of liberated, compo-site and mineral occluded particles of a given size, the extent of mineral exposure on the surface of particles and their mean mineral contents were calculated using principles of renewal theory. The rock was then crushed and ground and different size fractions were floated. It has been shown that the parameters of observed recovery data based on 1st order kinetics such as the associated rate constant and ultimate recovery agrees well with those predicted from the quantities calculated above. This work has important practical implications since it can indicate variations in flotation performance arising from changes in mineralization within a large ore body.

Jan 1, 2014

By Tsuyoshi Hirajima, Hideyuki Okamoto, Himawan .. T. B. M. Petrus, Keiko Sasaki

"Flotation of arseno bearing minerals from their copper ore has been an interest due to the increasing awareness on protecting the environment by minimizing the possibility of exposed arsenic compound. Some approaches have been proposed, but the mechanisms of separations have not yet fully understood. In this study, oxidation using oxygen was applied. Instead of the complex copper ore flotation results, pure single mineral of tennantite and chalcopyrite foatability was conducted using Hallimond tube. Resembled with the flotation results of copper concentrate containing tennantite, the separation possessed the best result at alkaline condition (pH 11) at where the arsenic content was reduced from 3300 ppm to 1800 ppm. In order to be able to understand the mechanism of the separation atomic force microscope (AFM) was utilized. AFM images showed changes in morphology and behavior when minerals were treated in both acid and alkaline condition. It was found that the morphological change showed the reaction products representing the rate of reactivity of tennantite and chalcopyrite. From the measured force of adhesion, it can be observed that in alkaline condition the surface of both minerals is more hydrophilic than that in acidic condition possessing higher value. This is in accordance with the X-ray photoelectron spectroscopy (XPS) spectra in which hydroxide moieties occupied the mineral surface in alkaline condition while elemental sulfur is in acidic condition."

Jan 1, 2014

By A. P. Wang

Porous carbon adsorbents derived from inorganic materials templates such as zeolite and mesoporous silicate attracted considerable attention in the last decade and got great progress in re-cent years. However, so far almost all of templates used in the process were artificial porous materials; the porous carbons prepared by this method are very costly, which restricts the synthesis and application of templated porous carbons. In order to reduce the cost of templated porous carbons, natural inorganic porous minerals have been taken into consideration, which maybe possible and promising templates to prepare carbon adsorbents. In this work, we describe template process using tubular halloysite, rich mesoporous zeolite and low bulk density diatomite, as exemplars of the categories of inorganic porous templates which we have studied and discussed the effects of different templating structure on the resultant carbons. Two main carbon precursors, sucrose and furfuryl alcohol, were used respectively. The morphology of minerals and corresponding templated carbons were characterized using electron microscopy. The pore structures of minerals and templated carbons were characterised with nitrogen adsorption. The results showed that the morphology and pore structure of porous carbons are in good pertinence to those of corresponding templates. The morphology and pore structure of templated carbons could reflect those of corresponding templates at nanometer level. The templated carbons with high specific surface areas and rich mesopores can be prepared by using these three kinds of natural porous minerals as templates. The higher the surface area and pore volume of the minerals, the higher those of the corresponding carbons. The template carbons from halloysite possessed higher pore volume and mesoporosities. Based on the large mounts of experiment results, a model for the mechanism of resultant nanopores formation has been proposed. The nanopores of templated carbons are mainly composed of three kinds of pores: templated pores formed by removing mineral, hereditary pores formed by inheriting the pores of templates and nanopores formed during carbonization. These three kinds of pores have a close relationship with corresponding template.

Jan 1, 2014

By P. Basarova

The attachment of bubbles onto a collecting surface is an ubiquitous natural phenomenon, playing a critical role in numerous practical processes. The goal of the project is to broaden the knowledge about hydrodynamic interactions between small bubbles and large solids that occur in nature and industrial processes. Focusing on collision processes between a single rising bubble (Db<1 mm) and a larger falling spherical particle in stagnant liquid, the theoretical model describing the bubble trajectory is given here. The model is based on analysis of forces acting on the bubble, and utilizes equation for the bubble motion. Mobile and immobile type of bubble surface mobility are considered. The calculated results are compared with the experimental data; here a high-speed video camera was used to capture the bubble motion and bubble-particle interaction. Very good agreement between experimental and calculated data was found. For both types of surface mobilities, the bubble deviation in the horizontal direction is nearly linear. The proportion constant is bigger for immobile bubble surface and increases with the bubble size. Furthermore, particular forces acting on bubble were studied. A similar course of relative bubble velocity and force impact was observed for identical bubble position. For cases when the bubble centre is close to the particle axis, only deflection in one direction is observed. When the bubble is reaching the maximum trajectory, the force ratio is changed. The bubble is firstly pushed away from the particle, but when it is within close distance from the particle, the bubble is pushed towards the particle.

Sep 1, 2012

By Svetlana Krashenina, Nebojsa Petrovic, Oscar Lopez

"As easily mined gold deposits are becoming increasingly rare, gold producers are turning to the processing of ores with polymetallic and copper mineralization. These base metals can create metallurgical and waste handling/disposal challenges, which can render the project uneconomic. Base metals such as copper compete for the cyanide reagent used to extract gold, necessitating the need to increase cyanide volumes and consequently, cyanide consumption costs. Copper will also stabilize in tailings water as weak acid dissociable cyanide, a form that is both difficult and costly to destruct. SART (sulphidization-acidification-recycling-thickening) process technology can be applied to remove base metal interferences in gold projects. SART breaks the copper-cyanide complex and precipitates the copper as a saleable copper sulphide concentrate. With the copper removed, the cyanide can be regenerated as free cyanide for recycle to the gold recovery process. This improves cyanide utilization efficiency and mitigates copper presence in tailings. Additionally, copper recovery generates an incremental revenue source to further improve project economics. Engineering Dobersek GmbH together with BioteQ developed a SART and AVR testing program to recover cyanide and maximize operational efficiencies at a gold processing plant in Kazakhstan with high cyanide consumption in the leach circuit. Results from on-site testing demonstrated that up to 99.98% of copper can be removed and precipitated as copper sulphide and 60-90% of cyanide can be recovered from the AVR and recycled for leaching, reducing total overall cyanide use. This paper provides an overview of the testing methodology and results together with a discussion on the potential of SART to improve gold production operations to deliver both environmental and economic benefits."

Jan 1, 2014

By Bulelwa Ndlovu, Saeed Farrokhpay, Dee Bradshaw

The effects of phyllosilicate minerals on the flotation performance and froth stability of a copper ore was investigated. It was found that various phyllosilicate minerals affect the copper recovery differently however they all caused the flotation grade to be reduced. The effect of different phyllosilicate minerals on the froth stability followed the order of talc >> montmorillonite > muscovite > kaolinite > illite. The results demonstrated that there could be a relationship between the deleterious effect of phyllosilicate minerals on the flotation and froth stability. Talc and montmorillonite have both shown the highest effect on the flotation recovery and grade as well as froth stability. On the other hand, illite has the least effect on the both flotation performance and froth stability. Kaolinite and muscovite also affected the copper flotation grade (but not the recovery) while they also affected the froth stability. Therefore it is possible to control the flotation performance when phyllosilicate minerals are present via monitoring and controlling froth stability which needs to be investigated further.

Jan 1, 2014

By Alexander E. Sobolev

The kinetics of oxidative dissolution of lead sulfide in solutions of nitric acid and sodium hypochlorite was studied using the rotating disk method and the factor experiment design. The dependences of the PbS dissolution rate on concentration of oxidant (HNO3 or NaOCl), temperature, disk rotation frequency, and duration of interaction were determined. The adequate kinetic models allowing calculating the specific dissolution rate at any combination of values of the influencing factors were obtained. As a result of the complex analysis of kinetic parameters, the modes of the each process proceeding were established, their macromechanisms were determined, and the limiting stages of the oxidative dissolution processes were revealed. The dissolution kinetics of lead sulfide in solutions of nitric acid was found to have several regimes. At HNO3 concentrations below 0.5 mol/L, the process proceeds in a mixed mode close to a diffusion-controlled. It is caused by low oxidative activity of HNO3 and considerable diffusional diffuculties at this acid concentration range. At the nitric acid concentrations more than 0.5 mol/L and less than 6.0 mol/L, the process was found to be kinetically controlled. The limiting stage of the interaction is the surface chemical reaction. The observed relatively high order of the dissolution rate with respect to the concentration of HNO3 was explained by the autocatalytic action of the acid reduction products. At nitric acid concentrations exceeding 6 mol/L, the process proceeds in a mixed mode close to a diffusion-controlled, and the dissolution rate sharply decreased that was explained by a decrease in the solubility of reaction products. When lead sulfide is dissolved in sodium hypochlorite solutions, at first time the amount of PbS transferred into solution remains close to zero. Gradually, as time goes, this amount begins to increase sharply. The dissolution rate rises and reaches the maximum value, further remaining constant. At the steady-state regime, the dissolution rate is independent of the duration of interaction and disk rotation frequency. The process was found to be kinetically controlled. The limiting stage is likely to be chemical reaction on the surface of solid lead sulfide. The obtained kinetic characteristics enlarge the database on hydrochemical oxidation kinetics of sulfides and can be used for the elaboration of the recommendations for the effective comprehensive exploitation of lead-bearing ores and concentrates. Keywords: lead sulfide, nitric acid, sodium hypochlorite, hydrochemical oxidation, dissolution kinetics

Sep 1, 2012

By Masakazu Niinae, Tasuma Suzuki, Mai Moribe, Yohhei Okabe

Bench-scale electrokinetic experiments were performed to elucidate the electrokinetic remediation mechanisms of arsenate from artificially contaminated kaolinite. The electrokinetic experiments in which a constant voltage was applied demonstrated that high soil pH favored arsenate remediation with respect to both the remediation time and electricity consumption. It was also demonstrated that applying a pulse voltage (1 hour ON, 1 hour OFF) significantly improved the electricity consumption efficiency when the soil pH was maintained at the initial value during the experiments; this trend was not observed when the soil pH was gradually increased from the cathode side. These electrokinetic experimental results indicate that the remediation rate-limiting step varied with soil pH. When the soil pH was maintained at the initial value of 7.2 during the experiments, arsenate desorption was the remediation rate-limiting step rather than the migration of dissolved arsenate toward the anode. Conversely, when the cathode pH was not controlled and the soil pH was correspondingly increased gradually from the cathode side, the migration of hydroxyl and desorbed arsenate ions toward the anode played a more important role in the control of the overall remediation efficiency.

Jan 1, 2014

By Graeme J. Jameson

"When mineral particles are floated in a mechanical flotation cell, it is found that the rate constant, after reaching a maximum value, starts to decline as particle size increases. It had been thought that the reduction in rate constant had been due to the increased prevalence of composite particles in natural ores, for larger particles. However, Jameson (2012) showed that the rate constant for composites is certainly a function of the surface liberation, but the reduction in flotation rate is independent of particle size. Thus all particles are equally affected by reduced surface liberation, independently of their size. He further argued that the classical peak observed in the rate constant with increasing particle size, is a function of machine hydrodynamics. Thus in mechanical cells, the peak may be due to the high energy dissipation rate and its effects on the detachment of particles from bubbles (Goel and Jameson, 2012). Consequently, in a different flotation environment, it may be possible to float large composite particles that cannot be floated in mechanical cells. This paper describes the flotation of large composite particles in a fluidized bed flotation cell. The particles to be floated are fed to a column in which there is a continuous upflow of liquid. A conventional froth layer of controlled depth is formed at the top of the vessel. A fluidized bed of particles is established which provides a gentle environment for the contacting of large particles with bubbles. An example is given where a porphyry copper ore was prepared at a top size of 710 µm, and floated with conventional collector (PAX) and frother (MIBC). The concentrate was separated into size fractions and examined by photography. Composites were observed at all size fractions, but above 400 µm, all particles were composites. The implications for future flotation circuits will be described."

Jan 1, 2014