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By L. A. Vaisberg, E. V. Shishkin, S. V. Kazakov

"This research is targeted at finding solution to the problem of reduction of specific energy consumption during disintegration of solid materials with the help of machines, operating in a quasiresonant mode. The objective of the research is the development of an energy-saving method of disintegration of supestrong rock and by-products on the basis of vibrational units with two movable crushing elements, operating in a rigorous synchronous-antiphase mode without stringent kinematic links. In the course of investigations a mathematical analysis of the dynamics of vibrational units was performed to determine required mechanical parameters, allowing for adjustment of the machine actuating elements to high-frequency synchronous-antiphase oscillations in the quasiresonant frequency range. As a result of performed pilot tests, the reliability of desktop studies was confirmed and the dependency of process parameters on the machine regulated parameters in the quasiresonant frequency range was identified. The analysis of obtained data showed that during machine operation with cone-shaped crushing elements in the quasiresonant frequency range, the yield of the high-quality finished product (WFA grits of -3+1 mm grain size class) in one pass reaches 35%, whereas the form of the particles corresponds to the grain form with sharp edge. The quasiresonant operation mode of the vibrational unit with two freely suspended crushing elements (without stringent kinematic links) provided substantial reduction of energy intensity during crushing down to 0.16 kWh/t, which shows reduction of power consumption for crushing by more than 15% compared to conventional equipment.INTRODUCTION The most common and energy-consuming processes in the mining industry are the crushing and grinding of various solid materials. Such large energy costs are due to the fact that the capabilities of the existing crushing and grinding machines are based on traditional methods of destruction, and are limited by their kinematic features, which do not allow to reduce the energy intensity of processes, to lower the irreversible loss of useful components, to improve the quality of marketable products. In connection with the foregoing, the task of energy costs reducing for disintegration is one of the most important issues in the enrichment of both minerals and processing of man-made raw materials. The solution of this problem is possible only through the creation of a fundamentally new highly efficient technique and technology for processing raw materials [1, 2]. It seems that the greatest prospects in this respect are the vibration methods of disintegration, in particular, the vibratory cone crusher based on a two-mass system without rigid kinematic connections between the crushing bodies, with vertical vibrations of the working bodies. In this machine, the principle of rational material destruction is realized – crushing without re-grinding [3-5]."

Jan 1, 2018

By I. N. Babich

"Complex technological problems associated with the processing of mineral raw materials require the search and development of new means and ways of thinking. At present, computer cognitive graphics (CCG) are one of the most actively developing areas of new information technologies. The aim of the study was to optimize the cycle of technological evaluation of ores at all stages of geological exploration of deposits on the basis of analysis of geological sampling data using CCG. A new approach has been developed that facilitates optimization of the whole cycle of subsoil exploration. At the gold ore deposit, the results of the geological sampling data were processed by the method of constructing the CCG in the form of a histogram showing the frequency of gold extraction and the average amount of its content. Significant peaks of the metal content in the ore, exceeding the level of the average content in the ore by tens of times, have been revealed. Graphical interpretation of the parameters of mineralization reflects the uneven nature of its variability, which indicates the presence of large, rarely occurs of gold in the ore and the need to conduct studies on a sample of ore of greater mass than for ores with tiny gold. On a sample of 50 kg gold-quartz ore studies were carried out on gravity enrichment. The maximum size found in the gold concentrate was 0.07 mm. In the course of integrated tests in a gravity concentrate, gold particles up to 3 mm in size were found, which predetermined the need to include the operation of gravity before flotation. A new approach to subsoil research is protected by a patent (RU 2620823).The technological problems that arise before the researcher associated with the processing of resistant ores require the exploration and development of new means and ways of thinking. New problematic situations on complex mineral and raw materials objects are practically not amenable to resolution by existing methods. Integration of industrial and information technologies is necessary. At present, computer graphics (CG) is one of the most rapidly developing areas of new information technologies. For example, in scientific research, including in fundamental research, the accent from the illustrative function of CG (the visualization of what is already known) is increasingly shifting towards the use of computer cognitive graphics (CCG) tools (Bashlykov, 2016). The function of the CCG is to obtain a new knowledge with the help of a graphic representation - a cognitive image or at least to promote the intellectual process of the logical acquisition of this knowledge. In this study, cognitive images are used to graphically represent the distribution of valuable components in the bowels of the deposit, characterizing the state of mineral-raw materials."

Jan 1, 2018

By P. Gao, J. W. Yu

"Magnetizing roasting-magnetic separation is an important route for the beneficiation of refractory iron ores. In this investigation, a pilot-scale fluidized magnetizing roasting reactor was introduced and used to study the effects of roasting temperature and the flow rates of reducing gas CO and fluidizing gas N2, on the magnetizing roasting performance of an Anshan-type carbonate-bearing fine iron ore. The results showed that the hematite was almost reduced to magnetite by a gas mixture of 4 m3/h CO and 1 m3/h N2 at a roasting temperature of 540 °C. Under the optimized conditions, a high-grade magnetic concentrate assaying 66.1 wt.% Fe with a recovery rate of 91.2% was achieved from an Anshan-type carbonate-bearing fine iron ore assaying 42.0 wt.% Fe. The XRD, VSM, and optical microscopy analyses revealed that the siderite was successfully converted to magnetite by roasting. Some coarse hematite particles were difficult to reduce to magnetite completely; however, these generated magnetite particles with a fine hematite core could also be effectively recovered by magnetic separation after liberation from gangue minerals due to their strong magnetism. INTRODUCTION Magnetizing roasting followed by low-intensity magnetic separation has been considered as an effective solution, both technologically and economically, when upgrading refractory iron ores (Zhang et al., 2012; Peng et al., 2012; Li and Zhu, 2012). According to the type of roasting reactor, the magnetization roasting can be divided into shaft furnace roasting, rotary kiln roasting, and fluidized bed roasting (Zhu and Li, 2014).Shaft furnace magnetization roasting system is mainly composed of heating and reduction processes. The hematite ore is first heated to 700~800 °C in the heating zone, then falls into reduction zone where the weakly magnetic hematite is reduced to magnetite by coke oven gas at 550~600 °C (Yan et al., 2012). However, several years of engineering practices indicate that the shaft furnace can only process the hematite ores with a granularity of 15 ~75 mm, and the shaft furnace roasting is also characterized by heterogeneity of roasted product. Hence, the shaft furnace magnetization roasting technology is gradually replaced by high-gradient magnetic separation with the development of high-gradient magnetic separator. The rotary kiln generally handles the hematite ores with a grain size of less than 30 mm (Zhu and Li, 2014), however the formation of clinker ring in the rotary kiln will affect the yield of iron resource. In the fluidized bed furnace, the hematite ore is shaken up by an upward current of gas which maintains the individual particles in suspension (Yu et al., 2018). The precise adjustment of the gas velocity to the particle size and the specific weight of the hematite ore, make it possible to generate a floating mixture of gas and solids which behaves almost like a liquid (Yu et al., 2017a). The process is reported to have the following advantages over the other roasting techniques: ease of control due to absence of moving parts within the reactor, homogeneity of roasted products, ability to handle fine particles, and high efficiency of heat transfer and mass transfer (Li et al., 2015; Yu et al., 2017b). However, the simultaneous heating and reductive magnetization of hematite ore occur at the same place in the conventional fluidized bed reactor. Therefore, the reductive atmosphere, as well as the safety and stability of anti-explosion are hard to be controlled. Besides, the roasting temperature for conventional fluidized bed furnace is usually up to 950~1150 °C (Liu et al., 2017). Thus, the formation of clinker ring caused by high temperature will affect the operating efficiency."

Jan 1, 2018

By Masakazu Niinae, Kenji Aoki

"Electrokinetic soil remediation by electroosmosis and ionic migration is restricted to soluble substances. At a higher pH, the soil particles sorb more heavy metals than at a lower pH and the precipitation of heavy metals are promoted. Both mechanisms make heavy metals immobile, rendering cleanup more difficult and electrokinetic extraction inefficient.In this study, the effectiveness of introducing a complexing agent to enhance the removal of cadmium from kaolinite in the region of neutral pH by ionic migration is examined. The complexing agent selected was ethylenediaminetetraacetic acid (EDTA). The investigation was carried out in a laboratory-scale column containing kaolinite contaminated with cadmium. As the results of the study, cadmium migrates toward the anode without accumulation of cadmium and is successfully removed at the anode reservoir."

Jan 1, 2003

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 M. Evertsson, K. Bhadani, E. Hulthén, M. Bengtsson

"Modelling and simulations for mineral processing plants have been successful in replicating and predicting predefined scenarios of an operating plant. However, there is a need to explore and increase the potential of such simulations to make them attractive for users. One of the tools to increase the attractiveness of the simulations is through applying optimization schemes. Optimization schemes, applied on mineral processing simulations, can identify non-intuitive solutions for a given problem. The problem definition itself is subjective in nature and is dependent on the purpose of the operating plant. The scope of this paper is to demonstrate two optimization schemes: Multi-Objective Optimization (MOO) using a Genetic Algorithm (GA) and Multi-Disciplinary Optimization (MDO) using an Individual Discipline Feasible (IDF) approach. A two stage coarse comminution plant is used as a case plant to demonstrate the applicability of the two optimization schemes. The two schemes are compared based on the problem formulations, types of result and computation time. Results show that the two optimization schemes are suitable in generating solutions to a defined problem and both schemes can be used together to produce complementary results. INTRODUCTION The comminution process for a mineral processing plant consists of multiple crushing and classification stages and aims to produce fine material to liberate ore from the minerals. The modelling and simulation of such processes are well established using static process models (King, 2001; Napier-Munn et al., 1996). A recent development in the dynamic modelling for such processes has shown further increase in fidelity compared to the static process models (Asbjörnsson, 2015). The developed simulations can be utilized to design, operate and control mineral processing plants based on the requirements of users (Bhadani et al., 2017). Typically, the requirements in the operation of the comminution process are conflicting in nature, as for instance, reduction of power draw by process units, maximization of production of fine materials, and increasing utilization of the process units. These conflicting requirements leads to a Multi-Objective Optimization (MOO) problem to operate a mineral processing plant. The MOO problems are normally referred to as non-linear problems and its fundamental understanding with respect to process behaviour is difficult to achieve."

Jan 1, 2018

By S. A. Vorobyev, Yu. L. Mikhlin, Ye. V. Tomashevich, A. A. Karacharov, M. N. Likhatski1, A. S. Romanchenko, S. V. Saikova

"A set of state-of-the-art methods have been applied to study ultrafine particles and nanoscale species arising on mineral surfaces upon milling, interaction with flotation reagents, and leaching of base metal sulfide ores in order to gain insights into interfacial mechanisms. The fine fractions produced by ball milling of a Pb-Zn Gorevsky ore and four Cu-Ni sulfide ores studied with laser diffraction, dynamic light scattering, zeta-potential measurement, Xray photoelectron spectroscopy (XPS), SEM, TEM and other techniques. The particle size distributions had, aside from the peaks at 20-60 ?m, maxima near 1-2 ?m; the flotation was considerably suppressed when the yield of positively charged ultrafine particles approached tenths % (several kg per ton). High-energy XPS and X-ray absorption spectra revealed that sulfide minerals depleted in metal in air and aqueous solutions were composed of outer “polysulfide” layers, strata with disulfide species, and heavily defective underlayers, and “passivation” was explained by stability of the metal-deficit structures. Dixanthogen at pyrite and copper-activated sphalerite, dixanthogen and then cuprous xanthate on chalcopyrite, and chemisorbed xanthate at galena were specified as the main interfacial products using cryo-XPS of fast-frozen flotation slurries. The particle size, zeta-potential and behavior of colloids of Cu and Pb xanthates and dixanthogens were largely determined by the initial ratio of a cation and collector; the properties of copper xanthate nanoparticles were also affected by incorporated dixanthogen (about 15 wt.%). Submicrometer gas domains of 3-8 nm in height and “hydrophobic” forces upon the probe retraction were found on xanthate-treated minerals using atomic force microscopy and spectroscopy; their impact on flotation is briefly discussed.INTRODUCTIONInterfacial phenomena play a key role in flotation, leaching, water purification and related environmental processes. The mineral processing and extraction of metal from sulfide ores commonly involves milling the ore, which produces, along with the particles of 20 µm to 100 µm, mineral entities ranging from micrometer to submicrometer and nanometer scale. Furthermore, ultrafine particles of flotation reagents, products of metal sulfide oxidation, and so on may form spontaneously and accumulate in production water, flotation froth, deposit on mineral surfaces, affecting the flotation performance, and then enter waste waters, mine and natural drainage, polluting soils, surface- and ground waters (Miettinen et al., 2010; Wang et al., 2014). The efficiency of flotation and hydrometallurgical recovery of values, environmental issues are crucially dependent on the state of mineral surfaces. Particularly, it is generally accepted that the surface non-stoichiometry of sulfide minerals induced by oxidation and leaching should affect their hydrophobicity and reactivity, including so-called “passivation”, but the nature of such surface layers are still a matter of controversy (see, for example, Holmes and Crundwell, 2013). Another phenomenon attracting rapidly growing interest in several areas is low-dimensional gas species (“nanobubbles”) at hydrophobic surfaces that may play a decisive role in particle-bubble attachment in flotation but remains scarcely investigated up to now (Xing et al., 2017). Here, we survey our recent results on the abovementioned problems applying a series of rather new methods and approaches; more details can be found in refs. Karacharov et al., 2016; Mikhlin et al., 2015; 2016; 2016a; 2016b; 2016c; 2016d; 2017; 2017a; Vorobyev et al., 2017."

Jan 1, 2018

By Erico Tabosa, Kym Runge, Peter Holtham

"The distribution of turbulence in an industrial scale mechanical flotation cell and its effect on flotation kinetics was studied using a fully instrumented 3m³ cell. The cell was operated at a copper concentrator in Australia with different combinations of airflow rates, impeller speeds and sizes and cell aspect ratio providing a wide range of hydrodynamic conditions. An analysis of the overall flotation cell performance showed that the overall copper recoveries were very similar for the conditions tested. However, by decoupling pulp effects from froth effects it was possible to evaluate whether the changes made affected the pulp zone and/or froth zone responses. The analysis showed that the overall recovery has the potential to be up to 7% higher, if not limited by froth recovery. The cell hydrodynamics were characterised by the overall energy dissipation rate and, to understand the distribution of turbulence within the cell, localised measurements were made using a piezoelectric vibration sensor. By comparing the metallurgical performance of the cell with the different hydrodynamic conditions it was found that the collection zone flotation rate constant was not directly related to overall energy dissipation, as is commonly observed at laboratory scale, where energy is usually only changed by varying impeller speed. In this study, energy dissipation rate was varied using not only impeller speed, but also the size of the impeller and the cell aspect ratio. In these circumstances, the best correlation was found to be between the collection zone flotation rate constant and the distribution of turbulence, i.e. the size of the turbulent zone."

Jan 1, 2014

By Lala Zhao, Yuemin Zhao, Guangyuan Xie, Chusheng Liu, Chenlong Duan

"Screening is an important means of size classification used on granular or particulate materials. The vibrating modes of screen separator have a great effect on the screening process. Elliptical vibration mode is a complex motion mode which gets the common characteristics of both linear and circular vibration modes. However, the fundamental motion and screen penetration of the particles on the elliptically vibrating screen deck are still poorly understood. A numerical study of the motion of particulates flow along an elliptically vibrating screen deck is presented by means of a three dimensional Discrete Element Method (3D-DEM). The motion characteristic of the particle flow is analyzed at a particle scale. The effects of vibration amplitude, throwing index, vibration direction angle and screen deck inclination angle on the screening process are discussed. The results show that the particles average velocity increases linearly with the increase of vibration amplitude, throwing index and screen deck inclination angle, but decreases linearly with the increase of vibration direction angle. The screening efficiency is highest when the vibration amplitude, throwing index, vibration direction angle and screen deck inclination angle are 4.5 mm, 3.3, 40° and 6°, respectively. This work is helpful for developing a deep understanding of particle motion on the elliptically vibrating screen and for optimizing screen separator designs."

Jan 1, 2014

By Takaaki Wajima

The slag was attempted to be converted into the adsorbent for phosphate removal from aqueous solution using the alkali fusion method. The slag was mixed with NaOH powder (NaOH / Slag = 1.6), and then the mixture was heated at 600 ? for 6 h to prepare the precursor. The precursor was stirred at room temperature in distilled water to synthesize the adsorbent, and the removal ability of the obtained adsorbent for phosphate from aqueous solution was investigated. The products, including hydrocalumite and calcite, were synthesized, and the removal efficiencies of the adsorbent for F- and PO43- showed higher than those of raw BF slag, especially removal of PO43- are excellent (99 %), while the removal of Cl- , SO42-, NO3- and Br- was minor. The adsorbent could remove PO43- selectively in the co-existing solution of Cl-, NO3-, F-, SO42- and Br-.The equilibrium adsorption capacity of the adsorbent for PO43- was extrapolated using Langmuir and Freundlich models, and experimental data are found to fit Langmuir than Freundlich. The calculated maximum adsorption capacity of the adsorbent for PO43- is higher than other adsorbent reported previously. The high affinity of the adsorbent for PO43- in aqueous solution was caused by the formation of hydroxyapatite [Ca5(PO4)3(OH)] and brushite [CaHPO4?2H2O]. The prepared adsorbent is expected to be anew inorganic adsorbent for the removal of phosphate ion from wastewater. Keywords: Blast furnace slag, Alkali fusion, Phosphate removal, High selectivity

Sep 1, 2012

By J. Gebhardt, D. McBride, M. Cross, S. Gilbert

Heap leaching of ores containing chalcopyrite offers a low cost option to treat low grade complex copper sulfide ore bodies. However, the slow leach kinetics of chalcopyrite at ambient conditions typically results in unacceptably low recoveries. As the mineralogy of new ore deposits becomes more complex and the effects of gangue chemistry exert a greater influence on copper sulfide leach behavior, the control of leach reaction chemistry becomes more critical. Computational fluid dynamics (CFD) technology has been useful in the capture of multi-phase interactions and provides a path to simulate complex fluid flow, gas and liquid phases, through the heap, along with species transport. Coupling the flow models with the reactive mineral dissolution, and the sometimes competing aqueous chemical and solid-liquid reactions, yields a comprehensive model of the heap leach process. The leach kinetics of chalcopyrite dissolution in heap conditions is examined, and the incorporation of chalcopyrite leach kinetics in the CFD model is described. The application of the model to investigate optimization of the heap is discussed.

Jan 1, 2014

By Wei Sun, Xue-feng Cao, Lei Sun, Run-qing Liu

The flotation performance of kaolinite in laboratory micro-flotation was investigated with 3- (dodecyloxy) propan-1-amine (ON12) as the collector. Compared with dode cylamine (DDA), which is commonly used as the bauxite reverse flotation collector, ON12 shows stronger collecting ability for kaolinite than using the same amounts of DDA, when experimental pH value reaches more than 6. With the addition of ON12, the isoelectric point of kaolinite shifts to 6.1 from 3.6, which suggests a strong adsorption between kaolinite and ON12. Infrared spectra analysis indicates that the type of ON12 adsorbed on the kaolinite surface is mainly of electrostatic adsorption. Molecular dynamics simulation further indicate that electrostatic adsorption of ON12 cation on kaolinite (001) surface based on electrostatic interaction between NH4+ and O atoms. ON12 will be suitable for bauxite reverse flotation with the efficiency depressors of the diaspora.

Jan 1, 2014

By H. Pearce, A. E. Lewis, A. Ochieng

Hydrodynamics and mixing are fundamental to the operation of mineral process systems such as flotation cells and metal precipitation reactors. The computational fluid dynamics (CFD) technique has been employed in the present work to study the hydrodynamics in a mixing vessel stirred with either a Rushton turbine or a pitched blade impeller. The multiple frame of reference (MFR) approach has been used to model both impellers. A draft tube was used only in the Rushton turbine stirred vessel. The flow profiles for the pitched blade impeller have been studied in three regions; below the impeller tip, at the middle of the tank, and near the liquid surface. The simulation results were compared with literature data obtained using a laser Doppler velocimetry in the three regions of the vessel, and it was found that the model predictions were better in the impeller region. There was a poor prediction of the experimental results in the region closer to the liquid surface; however, this was improved when the turbulence parameter (C2) in the k-e model was set to a higher value. The value of the impeller clearance at which the Rushton turbine generates an axial impeller type flow has been determined and it has been shown that, at this clearance, a draft tube can be used to enhance axial flow in a Rushton turbine stirred reactor.

Jan 1, 2003

By Aldo Cipriano, Fernando Estrada

The mining industry is in search of control strategies that allow considering a global optimization of their processes, ensuring their stability. This has led to the application of recently developed control techniques on large-scale systems in the mining processes. One of the most important process of the mining industry is the mineral grinding, as the product particle size impacts, in a significant manner, the recovery rate of the valuable mineral in the separation stages. As a solution, a centralized hybrid model predictive control (HMPC) is presented; this control approach maintains the product particle size on a defined range and minimizes energy consumption, maintaining the grinding plant in a stable operation. As a comparison, a conventional model predictive control with an expert system to handle discrete events was developed, showing HMPC is a suitable solution that can used in the grinding process, with the benefit that it handles in the same controller both discrete and continuous dynamics and events.

Jan 1, 2014

By Jiongtian Liu, Jianjun Wu, Yongzhou Wan, Li Feng

"Mechanical Thermal Expression (MTE) is a developing non-evaporative lignite dewatering technology. It has been shown to effectively dewater high moisture content in low rank coals via the application of mechanical force and thermal energy at elevated temperatures. In this paper, the dewatering behavior of Yunnan Xiaolongtang lignite during the MTE-process was studied. Furthermore, how variations in temperature and pressure during the MTE process affect the surface oxygen functional groups and pore structure were also discussed using Fourier transform infrared spectrometer (FTIR) and mercury intrusion porosimetry (MIP). Increases in MTE temperature and pressure resulted in significant reductions in residual moisture content and moisture holding capacity, along with the increase of fixed carbon content and reductions of other elements content, especially oxygen content, which have been largely attributed to the destruction of the surface oxygen functional groups and porosity in lignite. The optimized technology conditions are temperature 150~220°C and pressure 7~10MPa. The residual moisture content of the lignite treated by MTE under the conditions of 200°C and 10MPa is decreased to 8%, while the dewatering rate exceeds 76 % and the calorific value approaches 22 MJ/kg. The experimental results offer a deeper understanding of the influence of process parameters on the lignite stuctures and properties. The reduction in residual moisture content, surface oxygen functional groups and pore volume under increasingly severe MTE conditions are suggestive of the structure changes that accompany increased coalification (rank) within the lignitic range."

Jan 1, 2014

By P. Somasundaran, G. Anastassakis, Z. Pan, D. R. Nagaraj

Gums are often used as depressants for talceous gangue minerals in the flotation of nickel and platinum bearing ores. However, the mechanisms of gum adsorption on talc are not clearly established. In this work, adsorption of guar gum at the talc-solution interface is investigated using spectroscopic and allied techniques. Guar gum adsorption on talc is not affected significantly by changes in solution conditions such as pH and ionic strength. Electrokinetic studies showed that guar gum decreased the negative zeta potential of talc but did not reverse the charge. Fluorescence spectroscopy studies conducted to investigate the role of hydrophobic bonding using pyrene and dansyl probes showed no evidence of the formation of hydrophobic domains at talc-aqueous interface. Urea, a hydrogen bond breaker, reduced the adsorption of guar on talc to the same extent as that for guar/alumina system, in which hydrogen bond plays an important role. All of the above results suggest that one of the main driving forces for guar adsorption on talc is hydrogen bonding rather than electrostatic or hydrophobic force.

Jan 1, 2003

By Di Liu, Yongjun Peng

"It was identified that clay minerals adversely affect fine coal flotation through slime coatings. In the study, it was interesting to find that an anionic polymer dispersant, lignosulfonate, successfully mitigated the negative effect of clay minerals in coal flotation using fresh water, but in saline water, it exacerbated coal flotation.In order to understand the mechanisms underpinning the different behaviour of lignosulfonate in coal flotation using fresh and saline water, the adsorption isotherm, and dynamic light scattering (DLS) measurements were conducted in this study. While DLS monitored the molecular conformation change (swelling or shrinking) of the polymer in fresh and saline water, adsorption isotherms enabled polymer adsorbed amount on clay and coal mineral surfaces to be determined. It was found that lignosulfonate adsorbed on the coal and clay mineral surfaces providing effective electrostatic repulsions and resulting in a mitigation of clay minerals from coal surfaces in deionised water. In the presence of saline water, however, polymer molecular conformation changed. Polymer molecules were compressed and adsorbed in form of aggregates. The adsorption amount of lignosulfonate on clay minerals increased in saline water. A low dosage of lignosulfonate could not provide sufficient electrosteric repulsion to disperse clay minerals. Moreover, the high adsorption amount of the polymer on coal and clay surfaces led to a more hydrophilic coal surface, and coal flotation was therefore depressed in saline water. This study provides a new insight into understanding the role of anionic polymeric dispersants in mineral flotation using different quality water."

Jan 1, 2014

By Heinrich Hutchison, Thomas von Moltke, Roelof F. Sandenbergh, Katarina P. Cerovic

In the leaching of gold in aqueous cyanide solutions the rate of gold leaching may be decreased by the passivation of the gold, that may however be prevented or reversed in the presence of lead species in solution. In the present study potentiostatic, potentiodyanamic and XPS (X-ray photoelectron spectroscopy) analysis were used to further clarify the action of lead ions on the anodic activity of gold in alkaline cyanide solutions. It was found that lead increased the gold dissolution rate as it deposited on the gold surface at potentials more positive than its reversible Nernst potential for bulk metal deposition, i.e. by underpotential deposition mechanism, but that it decreased gold activity if present as bulk plated lead on the gold.

Jan 1, 2003

In this study, the effect of different regrinding conditions on the depression of fine pyrite at the cleaner stage was investigated. The regrinding condition was manipulated by different grinding media (stainless steel and mild steel). It was found that, after regrinding with mild steel grinding media, the flotation recovery of pyrite is much lower than with stainless steel grinding media, and it is more difficult to restore by adding more collector. This means, regrinding with mild steel grinding media may depress the pyrite flotation more strongly. The copper activation of pyrite during regrinding was also studied. It was found, that the mild steel grinding media is more beneficial to copper activation than stainless steel media. Additionally, the analysis of pyrite recovery based on the particle size indicated, that the fine particles are more susceptible to different grinding environments than intermediate and coarse particles and therefore are more easily depressed with a much lower flotation recovery.

Sep 1, 2012

By Sanja Miskovic, Manjunath Basavarajappa

Numerical investigation of fluid flow characteristics and mixing efficiency of different impeller designs, based on the mixing characteristics of a passive scalar/tracer, is conducted using CFD for lab scale flotation cells of diameter D and height H equal to 300 mm. Fine computational mesh containing close to 1.6 million cells is used to obtain fully resolved steady state flow field close to the impeller. Unsteady scalar mixing simulations are performed on a relative coarse grid consisting of approximately 450,000 cells. Based on detailed numerical simulations, flows are fully characterized for four impeller designs at two off-bottom clearances C of 50 and 25 mm (D/6 and D/12). Passive scalar is injected from the cell bottom and the time required to attain uniform concentration distribution inside the cell volume is taken as the mixing time by monitoring scalar concentration at four discrete locations. The effect of varying agitation speed and off-bottom clearance on mean flow characteristics is also investigated. The scalar mixing results reveal regions of low mixing efficiency and are used to understand mixing process in greater detail. Through the previous research work, it was found that the main flow pattern undergoes transition from double-loop to single-loop configuration with decrease in off-bottom clearance below a certain critical height for stirred tanks using flotation impellers in the absence of stator. The inclusion of stator is found to alter the mean flow behaviour by preventing the jet from transitioning to axial type flow for lower clearance. Power numbers for different impeller designs are calculated based on the torque generated on impeller blades, and also from the total turbulent kinetic energy dissipation in the overall fluid volume. Power number is found to exhibit a significant dependence on off-bottom clearance based on the CFD results.

Jan 1, 2014