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By Olgac Kangal, Ali Guney, Gulay Bulut, Guven Onal, Ayhan A. Sirkeci

"This paper presents the results of pilot scale column flotation applications in the two different copper concentrators in Turkey. The Kure Copper Plant is located in the Black Sea Region of Turkey. There are four types of copper ore formations in the Küre region. The so called disseminated ore contains 60-70% siliceous minerals of which Cu content is around 0.5%. The remaining three ore types in the region are generally named “massive ores”. The massive ores may assay up to 15% Cu and the major gangue mineral is pyrite associated with relatively little amount of silica. The main copper mineral in all formations is chalcopyrite that is generally finely disseminated in pyrite therefore satisfactory liberation requires ultrafine grinding especially in the case of the massive ores.A blend of these ores, containing 1.7% Cu on average, is fed to the Küre Copper Concentrator whose capacity is 1.2 million tons of ore annually. Unfortunately, today the plant operates below its designed capacity treating around 550,000 tons of ore per year. The design of Küre Copper Plant was undertaken by the Outokumpu Company of Finland. The operation of the plant is almost automatically controlled and the feed, the concentrate and the tailings are assayed for copper by on-line XRF analysers. The particle size analysers are also connected to the grinding circuit. The feed material is ground almost below 50 µm and the flotation is conducted around pH 11.2 using Hostaflot X-231 (a trade mark of Hoechst) as the collector. Apart from the rougher cells, there are four cleaning stages after which the final concentrate is produced. A very fine grinding requirement for an adequate level of liberation makes successful flotation difficult and consequently the final concentrate can hardly assay above 16% Cu leading to copper losses around 20% in the tailings that contains 0.3% copper."

Jan 1, 2003

By J. Jávor

The response of the air/water interfaces to deformation in presence of surfactants is affected by the adsorption/desorption rate, re-orientation and exchange rate of surfactant. These surface properties can be observed using equilibrium and dynamic surface tension and surface elasticity measurements. However, the effect of these parameters on bubble size in dynamic conditions has not been studied due to the difficulty in capturing freshly formed bubbles in dynamic conditions. The paper presents a new experimental set-up designed and built at the Aalto University, called Shear Force Observation Chamber(SOC). The setupallows the monitoring and analysisof freshly formed air/liquid interfaces in dynamic conditions and facilitates the study of the effect of dynamic surface tension and surface elasticityon freshly formed air bubblesin presence of surfactants. The method helps to establish correlation between bubble size and dynamic interfacial properties and bubble-bubble interaction in turbulent flow. Dowfroth 200, Nasfroth 240 and Dowfroth 250 commercial flotation frothers were tested in this study. The results show a marked difference between results obtained in dynamic conditions compared to the static conditions. The results are presented and the reasons and implication to flotation modelling are discussed in the paper. Keywords: shear force observation chamber, flotation frothers, flotation bubbles, critical coalescence concentration

Sep 1, 2012

By M. R. Robben

Carbonates have gained significant economic importance for the human kind. On one hand over a hundred uses are listed for carbonates. On the other hand, carbonates host base metal deposits. Although the carbonates play a significant part in the development of those deposits, in the mineral processing they consume acid and cause selectivity problems during flotation and leaching. Carbonates also accompany other industrial minerals as waste rock. For all those cases it necessary to find a technique to separate carbonate as early as possible in the processing chain. In this paper, the applicability of near-infrared spectroscopy (NIRS) sorting for the separation of carbonates is discussed. NIRS sorting is a sensor-based sorting technique, in which particles are singularly detected by a sensor and then rejected by an amplified mechanical, hydraulic or pneumatic process. This technique can for example be implemented in the process as a pre-concentration step for coarse particle sizes up to 300 mm. NIRS sorting discriminates among materials based on the difference that exist between their spectral properties in the near-infrared (NIR). Vibrations of molecular bonds in carbonates cause characteristic spectral properties in the NIR, which makes carbonates detectable, possible to identify, distinguish and separate from other rock materials. The spectral properties can also be used to distinguish between different carbonate minerals and mixtures. If the spectral variations are large enough for detection, sorting based on NIRS is possible. Feasibility studies on sensor-based separation of carbonates in the processing of talc, borate, fluorite, marble, zinc-oxides, copper sulphide and iron ore as well as the discrimination of calcite and dolomite mixtures are conducted and indicate the high potential of NIRS sorting in the minerals industry. Keywords: carbonate separation, sensor-based sorting, near infrared spectroscopy, NIRS sorting

Sep 1, 2012

By J. Yianatos

The cleaning circuit operation and its effect on the plant metallurgical performance, was characterized at Los Pelambres concentrator, Chile. Experimental data from columns, scavenger and regrinding stages was evaluated. Each stage was characterized by size fractions, and the interaction between stages (columns, scavenger, regrinding) as well as the effect that circulating loads had. The approach for describing the flotation equipment operation (cells and columns) considered the collection and froth zones separately. This methodology allows for the identification of the impact that particle size distribution has on the actual collection and froth transport processes, independently. In this way the effect of regrinding on flotation recovery and grade can be related to the corresponding operating variables, e.g. pulp flowrate, air flowrate, pulp level and pulp density, among others. The effect of gangue entrainment was considered using an empirical dimensionless correlation. The interaction between the circulating load and the overall performance of cleaning circuit was evaluated. The circulating load was defined as the ratio between the solid flowrate of scavenger concentrate over rougher concentrate. It was found that the overall cleaning flotation circuit (column-scavenger) can operate at a relatively high and constant recovery for a wide range of mineral treatment. This is possible when the scavenger has the capacity for compensating the decrease in column recovery at larger circulating loads. Under the condition of high overall cleaning recovery, the rougher stage closely represents the plant recovery. However, at large mineral treatment conditions, the design characteristics (e.g. concentrate transport channel capacity and transfer boxes) as well as instrumentation, control facilities and operation, became bottle-necked. A simulator was developed using empirical models for each stage (column, scavenger and regrinding) in order to evaluate proper operational strategies for cleaning flotation circuits Keywords: flotation, cleaning, regrinding, Vertimill, simulation.

Sep 1, 2012

By F. Xie

Low gold and silver leaching kinetics has been commonly observed in traditional gold-silver cyanidation process, especially in those heap-leaching operations. The reactivity and availability of oxidant was believed to be the critical limitation for gold and silver dissolution. The occurrence of silver sulfide such as acanthite (Ag2S) in the ore may also result in low overall silver extraction. Leaching of gold and silver sulfide in the ferricyanide-cyanide solution has been investigated through rotating disc tests and the assistant effect of ferricyanide on increasing the dissolution rate of gold and silver was noticed. The potential use of ferricyanide as an auxiliary oxidant in gold/silver cyanidation process was proposed based on the results of leaching of gold-silver ores.

Jan 1, 2014

By l. Bokányi

The Tóth adsorption isotherm-model was derived and has been widely used for the inhomogeneous solid surfaces. The three-parameter isotherm incorporates the effect of the interaction between the adsorbed substances as well. All classic isotherms can be clearly derived from this one. Bio sorption is the sequestering of dissolved components, i.e. metals from aqueous environment by living or dead biomass. The mechanism of the bio sorption is rather complex and predominantly refers to the affinity of the chemical functional groups: acetoamido groups of chitin, structural polysaccharides, amino and phosphate groups in nucleic acids, amino, amido sulfhydryl and carboxyl groups in proteins, hydroxyls in polysaccharides, sulphates, etc. towards the soluted substances, i.e. heavy metal ions. The physisorption, as well as the micro precipitation also play a role in the bio sorption mechanism. The description of such a complex process can be done by a model reflecting this complexity. According to our experimental results obtained using algae and immobilised algae for the sorption of heavy metal cations, the most appropriate model for such a description is the Tóth-isotherm, the parameters of which can be interpreted. Flotation process is also a very complex one, the overall result of which depends on the partial results of many micro processes and parameters. The particle interaction which very often takes place in the flotation systems makes the phenomenon even more complex. The flotation kinetic model with particle interaction was already introduced by author in 1994 and further developed in 2000. In this paper based on the experimental results obtained with metallic particles in case of recycling flotation the applicability of the Tóth-equation as an alternative flotation kinetic model for the systems with particle interaction is proved. The applicability of Tóth-model in mineral processing demonstrates again its universal character and the great talent of the late József Tóth, great Hungarian chemist. Keywords : Toth isotherm, biosorption, Langmuir, Freundlich

Sep 1, 2012

By Viswanathan N. Nurni

In metallurgical processes, more and more usage of hydrocarbons is encouragedto bring down the carbon emissions. In this regard, numerous investigations onreduction of oxides by C-O-H-N gas mixture have been reported. Attempts to simulatethese reduction processes using shrinking core model, one of the commonmodels used for such studies, have under predicted the reduction rates. This maybe owing to the fact that the homogeneous reaction in the gas phase is not being considered. If the reaction temperatures are above 1000K, generally so for manyreduction processes, the homogeneous gas reaction rates are expected to be sohigh that one can assume local equilibrium in the gas phase. In the present study,reduction of wustite in a C-O-H-N gas mixture has been modeled using shrinkingcore model considering the water gas shift equilibrium in the gas while it diffusesthrough the product layer.

Sep 1, 2012

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 T. B. M. Himawan

In this study, effect of thiosulphate and oxidation using oxygen were studied in arseno copper ore flotation. Single mineral study of chalcopyrite and tennantite in regard to the aforementioned techniques was also studied. Zeta potential, XPS, contact angle and floatability of single minerals were conducted for each treatment to understand the mechanism. It was revealed that the separation is best conducted in alkaline condition at where there will be interaction between thiosulphate and the mineral surface as well as the formation of hydroxide species in the oxidation using oxygen. From zeta potential of both thiosulphate and oxidation conditioning, it can be found that the reactivity of tennantite is much higher rather than chalcopyrite resulting higher rate of depression on both techniques as shown from contact angle and floatability of each mineral after treatment. XPS spectra confirmed qualitatively and quantitatively the existence of species responsible for the depression of each conditioning techniques. As for the copper ore flotation test, it is the oxidation using oxygen provides best performance after 60 minutes of oxidation. Keywords: tennantite, chalcopyrite, arseno copper ore A, thiosulphate, oxidation using oxygen

Sep 1, 2012

By Shankar Narasimhan

Data Reconciliation is a technique that has been developed more than fifty years ago and has been refined over the past few decades and is now being deployed routinely in several process industries such as refining, petrochemicals, mineral processing and hydro-metallurgy. The main aim of data reconciliation is to obtain accurate estimates of all process variables and parameters using plant measurements that are invariably corrupted by random errors and may also contain biases and other gross errors. These reconciled estimates are subsequently used either in offline exercises such as simulation, retrofitting, and de-bottlenecking or in online optimization and control applications. In this presentation, a brief history of data reconciliation, its assumptions, and uses are reviewed. New developments in this area are highlighted such as robust data reconciliation to handle model uncertainties, and reconciliation using identified models derived purely from operating data. Several case studies in the mineral processing industries reported in the literature are also highlighted to indicate the potential benefits of this technique.

Sep 1, 2012

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 Dilip Kumar Mohanty

In today?s world, Sustainability is the key issue before the mankind. With the ever-increasing population & unimaginable boost in industrial growth to cope up with a steady increase in demand and fast change in life style of a human being, the natural resources are exploited to such an extent that the very existence of living beings in this earth planet is threatened. In such devastating situation, the concept of Sustainability emerges out as a great savior. This concept focuses on minimum/ judicious use of natural resources, thereby preserving the resources for future generation while meeting the bare minimum requirement of the present generation. For an emerging economy like India, Mining and Mineral based industries form the back bone of our economic development. Thus, sustainability of mining and mineral processing industry has a far reaching impact on sustainable economic development of our nation. While at a macro-economic level, we have to strike a balance between economic development vis-à-vis socio-economic & environmental impacts, Industries have to ensure judicious and frugal use of natural resources by making use of energy efficient plants & machineries and adopting befitting technology for reduction & recycling of waste. In the context of the above, it would be interesting to look into the sustainability measures taken up by National Aluminium company (Nalco) at its Crushing & conveying plant at Panchpatmali Bauxite Mine, which is incidentally Asia?s largest Bauxite Mine. In the backdrop of the above stated facts, in this paper the authors make an attempt to bring out the sustainability issues in areas of energy conservation, environmental impact/pollution vis-a-vis mitigation measures adopted in crusher & conveyor plant of Panchpatmali Bauxite Mine & CSR / peripheral developmental activities undertaken by Nalco to mitigate the socio- economic impacts. Keywords: sustainability, energy efficiency, recycle, csr, peripheral development

Sep 1, 2012

By E. Lee

Cone crushers are widely used within the mining and aggregate industries for the size reduction of minerals, ores, and rock materials. In mining applications for example, the product from cone crushers is often fed to HPGRs or directly to mills in the subsequent grinding circuit. An improved cone crusher performance can therefore result in an overall improved and more efficient comminution process. The objective of this paper is to systematically study a number of different ways of applying compressive crushing. By mathematically modelling these different crushing concepts and then theoretically optimizing crushing sequences accordingly, each concept can be studied and evaluated. In addition, aspects concerning whether or not the results are mechanically or practically achievable are considered. This study thus explores the advantages and disadvantages of different crushing concepts. In this paper, four different theoretical crushing concepts are presented and studied. The results show that in terms of interparticle crushing, optimal crushing sequences with varying compression ratios can be replaced by easier implemented series of constant compressions without significant deterioration. It is also shown that that considerably better performance is obtained for crushing sequences with both breakage modes. The subsequent comparison between such concepts indicates that different approaches can achieve the same results, and that the different concepts are comparable. It is further concluded that interparticle crushing should be kept to a minimum if fines generation or energy consumption is to be minimized, and that each of the studied concepts presents different challenges for implementation. Keywords: compressive crushing, cone crusher, optimization, modeling, crushing concept

Sep 1, 2012

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

By A. Sand

Within stamp-charged coke making a large volume of coal is compacted to one single coal cake before entering the coke oven chamber. This is done by means of several falling stampers in a stamping machine having a mold nearly of the oven?s dimensions. Producing a high quality coke also from inferior coals requires a cake density of approximately 80% of the coal density. Besides that the industrial stamp-charging process demands a minimum mechanical strength of the coal cake to move it from the stamping mold into the oven chamber without failure. Densification and the build-up of cake strength were investigated earlier in stamping tests using a micro-stamping device. The quantities derived from these tests (as e.g. cake density or porosity) represent average values for the entire cake. Statements describing the local compaction state at different heights are difficult to achieve without destructing the cake. In order to gain better insight into the densification process and the inner structure of the coal cake a computational model based on the discrete element method (DEM) has been set up using 2 and also 3-dimensional simulation software. The stamper?s position and velocity as well as the force acting on the stamper were monitored and the model?s response was compared against measurement data from laboratory stamping tests. It was possible to reproduce the force and displacement pattern of the stamper in response to the viscoelastic properties of the cake using standard DEM bonding and contact models. Furthermore, the rearrangement of particles in response to the compaction by the stamper was tracked by calculating their displacement at the point the stamper hit the coal surface. The latter can also be used as indicators of particle deformation or breakage. By defining control points at different heights the particle displacement, stress and strain rates, porosity could be studied at different heights. Keywords: coke making, coal stamping, compaction, agglomeration, DEM, simulation

Sep 1, 2012

By Anatoly Usov

The detailed researches of a broad circle of problems connected to development of the electric pulse method destruction materials (EPD) of a various nature and area of use are executed. The electrical and power characteristics of process, physical fundamentals of selectivity of a breakdown and destruction are investigated, the device of electric pulse (EP) disaggregation and ?omminution of materials are developed, the technological efficiency of disintegration of industrial minerals estimated. Due to its technological advantages, the EPD could have a great potential in minerals mining and processing technologies. Low specific power and weight-and-size characteristics of EP installations based on the existing out-of-date electric equipment are at present the main reasons hindering the effective application of the method in mining and processing technologies. The main studies carried out in Russia in the field of electro technical equipment development for EP technology are presented. The pulse capacitors service life affects greatly the economic efficiency of the process because the capacitors cost accounts for a considerable, and in some cases, the most part of the operational costs. Determined and analyzed in the study are the ways which could significantly improve the specific characteristics of high voltage pulse generators (VPG), such as to use of high-frequency voltage transformation to develop a charger; to use pulse transformers (PT) with iron magnetic circuits made of materials characterized by high magnetic permeability, in pulse generating circuits; as well as to use special ways which could produce voltage pulses with a short front. The experiments have proved the possibility to adapt these technological solutions for EP devices, and a further strategy of the EP technologies development and application has been suggested on this base. Keywords: electric pulse disaggregation, electric pulse installation, charger battery, high voltage pulse generator

Sep 1, 2012

By P. Huang

Chitosan was tested as a depressant in the differential flotation separation of chalcopyrite and galena. The micro-flotation results showed that chitosan selectively depressed chalcopyrite while galena was floated by potassium ethyl xanthate in acidic solutions. With the addition of 0.67 mg/L chitosan (CT) in the slurry of chalcopyrite-galena mixtures at pH 4, the recovery of galena was 95% while that of chalcopyrite was 30%, indicating that chitosan could potentially be used in differential Cu-Pb sulfide separation. Furthermore, the study of chitosan with either low (LCT) or high molecular weight (HCT) in the differential flotation indicated that better separation was achieved by the chitosan with lower molecular weight (LCT). ToF-SIMS was employed to study the distribution of CT on the surface of chalcopyrite-galena mixtures by ion mass spectra analysis and surface imaging, which showed that CT adsorbed heavily on chalcopyrite but barely adsorbed on galena. The positive ion ToF-SIMS spectra provided information on the surface composition of chalcopyrite-galena mixtures after CT treatment. It appears that the selective adsorption of CT on chalcopyrite was originated from the strong interaction between NH3+ and Cu. Keywords: differential flotation, micro-flotation

Sep 1, 2012

By Cagri Emer

In conventional mechanical flotation cells, when the size of particles exceed a particular value, that is of the order of 100 µm for metal sulphides, the recovery of particles decline rapidly. It appears that the turbulence in the agitated vessel is sufficiently intense to rupture the forces of attraction between the particles and the bubbles, so the large particles are flung off the bubbles in the turbulent field. It has recently been suggested, that a fluidized bed would be a very favorable environment in which to contact bubbles and the particles. In a fluidized bed, particles are supported by rising flow of fluid, which separates them from each other and allows them to move freely while remaining close together. In this novel method, bubbles injected into the fluidized bed are able to rise through it, colliding with hydrophobic particles, transporting them to the top of the column where they can form a froth layer that overflows into a launder. The flow in a fluidized bed is generally slow and nonturbulent, and preliminary experiments have shown, that it is possible to collect mineral particles as large as 1 mm and coal particles as large as 5.5 mm. If the upper particle size limit can be extended, there could be significant reductions in the overall energy consumption in concentrators. Calculations show for example that if the top size for flotation could be increased from 100 µm to 400 µm, there would be a reduction in grinding energy of the order of 40%. It is therefore, important to study the mechanism of coarse particle capture in fluidized beds. In this work, the factors governing the capture rate of particles, particularly the particle and bubble size, the fluidization velocity and the superficial gas velocity have been investigated, and the results will be presented.

Sep 1, 2012

By M. A. Hampton

The surface oxidation of sulfide minerals in aqueous solutions is an important sub-process in sulfide flotation and hydrometallurgy, but a full understanding of the oxidation process and products is still lacking. Many oxidation pathways and products involving elemental sulfur, metal polysulfide, metal-deficient sulfide and sulfate have been proposed, confirmed and argued. In this paper we provide further insight into the surface electrochemical behaviour of galena in aqueous solutions. For this research we have developed a novel experimental system, that combines chronoamperometry and AC-mode AFM surface imaging, which allows for in-situ, synchronized electrochemical control and examination of oxidative surface morphology. At pH4, the morphology of elemental sulfur (detected by ex-situ Cryo-XPS) formed on the oxidizing galena surface depends on the electrochemical potential pathway. In multi-step chronoamperometry (i.e. four potential steps from 0 mV to + 350 mV) the sulfur forms as nanoscopic domains, whereas in single-step chronoamperometry (i.e. one potential step from 0 mV to + 350 mV) sulfur forms as a heterogeneous layer. In each case the oxidation is controlled so that the number of electrons (coulombs) passed per unit area is the same, therefore the amount of sulfur produced is also the same. The differences in morphology with electrochemical potential pathway are explained using a nucleation and growth model. The formation of sulfur on the surface increased both advancing and receding contact angle of galena, but the morphological changes induced by different electrochemical potential pathways did not significantly alter the hydrophobicity of the surface. Keywords: galena, lead sulfide, oxidation, Atomic Force Microscopy, electrochemistry, collectorless flotation, hydrophobic

Sep 1, 2012

By C. Eswaraiah

A drop weight tester (DWT) is designed and fabricated for the purpose of analyzing single particle impact breakage characteristics of different ores. The test results were evaluated through the breakage distributions of different size fractions at five different input energy levels. The breakage parameter, t10 (Narayanan, 1986) is used to represent the degree of size reduction, which is assumed to be representative of the breakage product size distribution obtained from single particle breakage. Representation of breakage distribution with this method consist one more breakage dependent parameter (a). To evaluate the impact breakage characteristic of different ores, a mathematical relationship was established to analyze the dependency of breakage parameters, t10 and a on specific input energy (EIS) or fracture energy (Tavares et al, 1998, Fandrich, 1998), specimen size (?) and Bond?s operating work index (WI0). Mathematical results developed gives adequate model for all ball mill modeling. It can be concluded that the drop weight test method is a useful and practical way of evaluating the impact strengths of various ores and results of which can be used in modeling mills.

Sep 1, 2012