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By E. D. Gálvez, L. A. Cisternas, R. Acosta-Flores, F. A. Lucay

The optimal design of flotation circuits is a complex task as the mathematical model is nonconvex and includes binary variables, making it difficult to obtain the global optimum solution. Furthermore, there are epistemic uncertainties in the evaluation of the performance of flotation and grinding units. This epistemic uncertainty is generated because semi-empirical models are used with parameters that are a function of the circuit design. Therefore, it is not possible to adjust these models based on experimental data as the experimental conditions are not known at the design stage. This paper analyzed the effect of the uncertainties in flotation units, grinding units, and both units simultaneously. As a result, this paper demonstrated that, for a specific mineral, few structures exist that are optimal for a wide range of values in flotation stage recoveries and liberation fractions in the grinding units. A remarkable aspect of this work is that it introduces grinding, one of the operations that most influences energy consumption in mining and has not been studied in depth in the design of flotation circuits. To demonstrate that there are few optimal structures for a specific mineral when there is high uncertainty in the process units, an a priori approach or first principles was used. Two methods of proof were used: proof by construction and proof by exhaustion. Proof by construction is the construction of a concrete example with a property to demonstrate that something having that property exists. In this work, two examples were considered in the proof by construction. In proof by exhaustion, the conclusion was established by dividing it into a finite number of cases and proving each one separately. Here, 30,000 cases were included for each example. This knowledge can be useful in circuit design including grinding, e.g., after selecting the circuit (or the most promising circuits), and the equipment design parameters and operating conditions can be defined based on simulation and laboratory tests.

Jan 1, 2018

By Sarthak Kaushik

Zeta potential measurements show that the isoelectric point of crandallite, in aqueous solution of 10-2 N sodium chloride is at about pH 5.5. Measurements of turbidity confirm the point of zero charge or crandallite. Calcium ions specifically adsorbed on the surface and thus changed the zeta potential and turbidity. From the measured data, it is confirmed that starch acts as a flocculent for crandallite. Oleic acid, which is a collector used in phosphate ore processing is weakly adsorbed on the surface of crandallite. This results in hydrophobic coagulation of particles resulting in a lower turbidity.

Sep 1, 2012

By C. P. Lowes

"The REFLUX™ Classifier (RC™) consists of a fluidized bed housing, with a system of parallel inclined channels above. This system performs a simultaneous gravity separation and desliming of the feed material, utilising the inclined channels in order to retain the relatively fine dense particles. These particles promote the formation of an autogenous dense medium within the fluidized bed. Relatively large, low density particles are displaced from the fluidized bed and conveyed upwards through the inclined channels reporting to the overflow with other finer particles. Given the hydrodynamic role of both the particle size and density in determining the particle transport through a water based suspension, all gravity separators operate over a limited size range. In the case of the REFLUX™ Classifier, efficient separations can be produced across a very broad size range, from nearly 10 mm down to 10 m, however, for a given application the size range is much more limited. This study was concerned with the processing of dense minerals over a broad size range, and the need for multistage processing. Here the overflow from the first stage cascades to the second stage, incorporating coarse gangue rejection. This approach is shown to deliver remarkably high grades and recovery.INTRODUCTION The performance of the REFLUXTM Classifier (RC™) in beneficiating fine coal is well documented (Galvin, 2012). Although the technology can be applied to relatively fine particles below 0.1 mm, or coarser particles below 2.0 mm or even 8.0 mm (Galvin et al., 2010), in each case the technology is applicable to limited particle size ranges. In coal preparation, the most common size range is 0.25 to 2.0 mm, covering an eight-fold range in the particle diameter. Coal has a relatively low density, typically below 1600 kg/m3, with a significant portion below 1400 kg/m3. In water, the buoyant density difference (~ 400 kg/m3) is therefore low compared to that of gangue minerals (1600 kg/m3) by a factor of 4, enhancing the potential for separation. Thus, in coal preparation, the technology can be applied over a commensurately broader size range, typically up to eight-fold."

Jan 1, 2018

By Crasta Jeason, T. Sreenivas, M. Narasimha

The subtle nature of the flow inside the hydrocyclone has encouraged development of mathematical models for predicting its performance, which are widely used in simulation of comminution circuits. But most of the models available are based on single average feed density. But the feed to hydrocyclone classifier is generally mixture of particles of different densities. This effect of varying density of feed particles on performance of hydrocyclone has been reported in literature. Further investigation of the effect of multi component feed on the performance of hydrocyclone is the objective of this work. This work involves experimental work to study multicomponent behaviour in various size cyclones. The performance of hydrocyclone for feed mixture of magnetite and quartz has been studied. The effect of presence of magnetite, a high density material on efficiency of separation of quartz has been analysed. It was observed that the effect of component interaction increases with feed solids concentration leading to an increased cut-size for a given optimum cyclone conditions. Based on the multi-component exiperiments available in literature, a concept for modeling the performance of hydrocyclones is proposed. A set of semi-empirical model equations for cut-size, sharpness of separation are presented. An attempt to validate the new hydrocyclone model on multi-component behaviour is made.

Jan 1, 2014

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 D. I. Verrelli

Within the flotation community a belief has developed that some particle shapes are more ?floatable? than others. This is usually attributed to an influence of particle shape or roughness on the induction period required to achieve attachment between the particles and the air bubbles in the pulp. Up to now, such measurements have not been able to readily isolate the effect on individual flotation subprocesses. In contrast, our experimental apparatus, the CSIRO Milli-Timer, enables us to directly observe the process of particle?bubble interaction and attachment by means of a high-speed video recording, thus providing a direct measure of the induction period for attachment. To assess the influence of particle shape on induction time we used two varieties of methylated borosilicate glass particles ? spheres and angular ?frit? ? in a range of tightly-sized fractions. In doing this, we take care to account for the influence of other factors that could affect the induction time, such as the polar angle of sliding commencement, and approach velocity. These parameters are recorded as variables for each interaction, and corrected for using multiple nonlinear regression. Our results illustrate the importance of particle shape on induction period, with angular particles exhibiting induction periods that were an order of magnitude lower than those of spheres. Furthermore, the induction period was seen to decrease with increasing particle velocity, or kinetic energy on approach, but increased as the trajectory approached the limit of just grazing the bubble. Particle shape in mineral processing is a consequence chiefly of the mineral type and the type of grinding employed. The results presented herein indicate that attention should be paid to the shape of particles obtained from the grinding operation, besides particle size. Keywords: attachment, bubbles, flotation, induction period, particles, shape effects, surface roughness

Sep 1, 2012

By T. Suzuki

Acid leach liquors from spent lithium-ion batteries employing lithium cobalt dioxide (LiCoO2) as a cathode active material contain valuable metals such as cobalt and lithium, as well as common metals such as aluminum and copper. The objective of this study was to develop a hydrometallurgical process providing a high selectively between aluminum, cobalt, copper, and lithium from hydrochloric acid solutions. Batch experiment results showed that selective hydroxide precipitation approach was not suitable because a significant amount of cobalt and lithium was co-precipitated with aluminum and copper hydroxides. In contrast, batch experiments and the subsequent data analysis indicated that the sequence of solvent extraction circuits using PC-88A, Acorga M5640, and tri-n-octylamine (TOA) extractants effectively separates four metals of interest. In the first circuit of the proposed process, copper was selectively extracted by Acorga M5640 at the pH 1.0-2.0. Aluminum, cobalt, and lithium remain in the aqueous phase. In the second circuit, aluminium is selectively extracted by PC-88A at pH 2.0-2.5. For the separation of remaining cobalt and lithium, Acorga M5640 provided higher separation efficiency compared to PC-88A single extractant and PC-88A/TOA mixed extractant. However, the stripping efficiency of cobalt from the Acorga M5640 organic phase was found to be low (less than 10 %). Therefore, PC-88A/TOA mixed extractant rather than Acorga M5640 is an advisable choice for the separation of cobalt and lithium. Keywords: spent lithium-ion secondary batteries, solvent extraction, lithium, cobalt

Sep 1, 2012

By Gauti Asbjörnsson

Material handling is an essential part of the aggregate and mining industries. Mixing and blending of granular material can affect the grading and particle size distribution of the material leaving the system. Segregation and variability can cause problems in the downstream process while insufficient capacity will disturb upstream processes. Process plants utilize surge bins for handling recycle streams of material and act as a buffer for the process. The flow through the surge bin is usually controlled by a simple PID controller or PID controller in combinations with a plant-wide controller. Even though the surge bins play an important role of smoothening out the plant and creating a steady operating condition they are seldom included in plant simulations. This can lead to a number of problems in the form of decreased plant capacity, plant lockdown, and even operation units malfunctioning. The main objective of this study is to investigate the dynamic behavior in surge bins and develop a model more suitable for representing this behavior, which can occur during operation, for dynamic simulations. The proposed model adopts vertical layers which allow for flows between segments depending on the level of neighboring segments. This enables both the representing of segregation within the system and gives an indication on the effects from different inlet- and outlet placements. The proposed model was developed in MATLAB/Simulink and validated against an actual bin with the total capacity of 660 m3 in platinum ore application. With the new bin model significantly higher fidelity and more accurate dynamic, simulation results were achieved. Keywords: dynamic simulation, modeling, segregation, material handling, MATLAB/Simulink

Sep 1, 2012

By Rodrigo Carvalho, Marcelo Tavares

"The accurate prediction of the outcomes in SAG grinding has been a great challenge to researchers and process operators. The use of Discrete Element Methods for modelling charge motion in tumbling mills allowed extraction of not only visual data, such as the position of the charge, but also the energy transfer in terms of the energy dissipated in the collisions. One of the advantages of DEM technique is its scalability to different mill sizes and some operational conditions such as speed and mill filling. Recently the Authors proposed the coupling between DEM outputs and modified Population Balance Models that with proper dedicated ore characterization tests allows the prediction of the outcomes of an energy transfer example. This modelling framework is called the Multi-scale Mechanistic Modelling. This paper shows the application of the Multi-scale Mechanistic Model to a set of pilot plant tests ran at different operational conditions. The prediction of the grinding outcomes and even the stabilization of the charge was achieved by the use of the Multi-scale Mechanistic Modelling framework. This approach has a great potential to become a powerful tool to design and optimize AG and SAG mills."

Jan 1, 2014

By Chao Li, Kym Runge, Saeed Farrokhpay, Dee Bradshaw

"It is well known that froth phase has a controlling influence on the overall flotation performance. Froth recovery is expected to be affected by froth transportation behaviour. The latter has been represented by different volume balance and energy balance based models. In froth transportation models based on a volume balance, the froth phase is divided into different zones. The total froth residence time is the sum of the time spent in each zone and is dependent on the cell geometry, bubble burst rate and the position that bubbles enter into the froth phase. Alternatively, the froth transportation model based on an energy balance treats the froth phase as a block. In this model, froth height above the concentrate lip is being predicted by minimising the energy of the system which is dependent on the froth geometry, froth stability and froth rheology. The froth height can be used to calculate the froth efficiency of delivering mineralized bubbles from the pulp to the concentrate lip. This paper critically analyses the current models of froth transportation in flotation, and examines the limitations of these models. The importance of froth rheology, which is the resistance to the froth flow towards the discharging weir, in determining froth transportation, is also highlighted."

Jan 1, 2014

By Filippov. L. O.

Metallurgical results for the copper-nickel disseminated ores were improved by using ultrasonic treatment. This has been demonstrated by processing of bubble-pulp flow in the reactor zone of a reactor-separator flotation machine. It can be explained by changes in mineral and size composition of the concentrates. Thus, the selectivity of Cu/Ni flotation for different values of the hydrodynamic parameter increases considerably. Additional effect of the ultrasound treatment has been noticed under conditions when the detachment of the gangue minerals from bubbles can be controlled. Reactor-separator has advantages over other types of flotation cells for this purpose. In fact, the weak diameter of reactors make more efficient the ultrasound effect than in conventional impeller or column flotation machines. A combination of ultrasonic treatment with original organization of gas pulp flux in the reactor-separator allows to obtain significant effects in the flotation attachment/detachment subprocesses, enhancing the process selectivity and/or recovery of substances. Increase of total recovery of copper and nickel into bulk concentrate at constant grade is 8.5% for coarse disseminated ores. For copper ore, copper recovery increased by 10% at unchanged grade of 11.7% and nickel recovery gained 17% at the constant grade of 2%.

Sep 1, 2012

By S. Mitra1

"This study aims to investigate coarse particle detachment mechanisms (particle diameter > 150 ?m) utilising both experimental and numerical technique. Two mechanisms were studied – (i) interactions of bubbleparticle (BP) aggregate with vortices and (ii) coalescence of bubble-particle aggregates. On the first mechanism, interaction behaviour of coherent vortex structures with a BP aggregate (bubble diameter db = 3 mm, particle diameter dp = 0.3 mm) was studied using a CFD model in the Reynolds number range of 100 to 1000. Effect of surface hydrophobicity on the BP stability was examined using a range of contact angle boundary conditions. To address the second mechanism, interactions of bubble-particle aggregate (db ~ 4 mm, dp ~ 0.4 mm) with both free gas-liquid interface and individual bubbles were investigated using high speed imaging. Both rebound and coalescence outcomes were observed to be responsible for BP instability leading to particle detachment.INTRODUCTIONIt is widely known that flotation process performs excellent mineral recovery for base metal ore particles that are typically in the range of ~ 20 to 150 µm in diameter (Jameson, 2010). More specifically, higher recoveries are usually reported for particles in the size range of ~20 to 70 µm while outside this spectrum, generally the recovery diminishes significantly. It would be highly desirable to improve the recovery of particles at the coarse end of the flotation size range spectrum which has significant economic benefit (Jameson, 2010). However, it is essential that insights to particle detachment phenomenon, the primary impediment in coarse particle flotation caused by the underlying hydrodynamic factors are first obtained at a greater depth.In an ideal quiescent liquid medium, due to inertia, coarse particles deviate substantially from the fluid streamlines and collision efficiency with bubbles decreases which can only be augmented by increasing turbulence level in the medium sufficiently to make random physical contacts with bubbles. Nonetheless, even if successful contacts are made, it is difficult for these large particles to remain attached to bubbles in a turbulent shear flow environment. There are two major mechanisms postulated for particle detachment – interaction of turbulent flow structures (eddies) with BP aggregate and coalescence among surrounding aggregates. Earlier work of Schulze (1982) theorised a vortex acceleration component to characterise turbulence effect on BP aggregate instability in flotation machines. Wang et al. (2015) investigated bubble detachment behaviour from a stationary particle in a nearly homogeneous and isotropic flow field. Using PIV (particle image velocimetry), it was shown that the local maximum energy dissipation rate for the case of bubble detachment was significantly higher than the no detachment case, and was also higher than the critical value for bubble detachment calculated using Schulze’ theory (Schulze, 1982). Later, Wang et al. (2017) also visualised the BP aggregate instability in a cavity flow leading to particle detachment which was attributed to bubble coalescence, bubble surface oscillation and particle deceleration phenomena."

Jan 1, 2018

By David I. Verrelli, Peter T. L. Koh

"Recent experimental measurements of induction time made by direct observation with the ‘Milli-Timer’ indicated that angular particles were able to attach much more rapidly than spherical particles. There was around a tenfold difference in the respective induction periods for particle-bubble attachment. For industrial application, a more holistic comparison is needed, with the induction period for attachment being just one input. Over the years, CSIRO has developed a CFD-flotation model that incorporates both rigorous hydrodynamics, to simulate real industrial cell geometries, and a detailed model of the embedded flotation process, in which the induction period is an important parameter. We conducted transient modelling of batch flotation. First, spherical particles were modelled, as a ‘baseline’, for different particle sizes and levels of hydrophobicity. In the second set of results, the induction period was decreased by a factor of up to ten, simulating flotation of angular particles. Flotation recovery was found to depend upon induction period in a complex manner. For highly hydrophobic or fine particles, the induction period for spheres was already so low that recovery was limited by other factors (e.g. bubble-particle collision frequency). Further decreases in induction period, as for angular particles, did not have a significant effect on recovery in these cases. By contrast, when weakly hydrophobic or coarse particles were modelled, the recovery was predicted to be greatly enhanced for angular particles, in comparison to spheres. For these particles the induction period was limiting recovery, so that the flotation rate constant could be improved directly by reducing the induction period. This is consistent with batch flotation experiments using Ballotini reported earlier. Therefore, when dealing with weakly hydrophobic particles or relatively large particles that are to be floated, an enhancement can be expected for more angular particle shapes. In such cases, judicious specification of the grinding circuit may improve the overall efficiency."

Jan 1, 2014

By X. L. Song

In this paper, ZrSiO4-Cd(S1-xSex) inclusion pigments were synthesized by hydrothermal method. Microstructure, morphology and properties of the powder were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (IR) and CIE chromaticity, respectively. It shows that, precursors obtained at pH is about 6.0 are sol and products with higher crystallinity, red hues (a*=38.23) and inclusion ratio when hydrothermal synthesis temperature is 180? and holding time is 12h. Hydrothermal reaction mechanism was further analyzed as well. In particular, an ideal model of pigment formation was proposed.

Jan 1, 2014

By Brochot. Stephane, Manuel Gonzalez Fernandez

"HPGR (High-Pressure Grinding Rolls) is widely used today for grinding of various kinds of ores such as iron ore or base and precious metal ores. It can be used as first stage of grinding replacing tertiary crusher and SAG mill, but also as regrinding stage to enhance mineral liberation. In addition to better energy efficiency, the advantage of HPGR is to produce much more internal particle fractures allowing faster leaching as it has been demonstrated for some gold ores. This grinding mode of compression and fracture generation also promotes mineral liberation without overgrinding. Mineral processing modelling and simulation associated to detailed ore characterization constitute a powerful tool for plant design and optimization. The mathematical models of the units of operations (grinding and separation) have to reproduce the mineral deportment for which the mineral liberation plays a central role. The present paper is focused on the HPGR modelling with the objective of plant optimization or advanced design from pilot plant tests. The traditional approach of the population balance linked to the energy dissipation and the residence time distribution is generalized in association with a mineral liberation model. The effect of the specific HPGR breakage matrix and grinding function on the mineral liberation rate is discussed and compared to the tumbling mill. The implementation of this mathematical model into a plant simulation tool is illustrated by the example of the optimization of an iron ore concentrator."

Jan 1, 2014

By T. Ueda, T. Oki, S. Koyanaka

"Accurate assessment of the liberation state of crushed ore particles is important for efficient mineral processing. In general, the liberation state is assessed by two-dimensional (2D) measurement of polished ore sample sections. However, this 2D measurement inevitably suffers from overestimation of the degree of liberation, known as stereological bias. This arises from the fact that biphase particle sections of which only one phase happens to have been cut are indistinguishable from liberated particles. To date, several stereological correction methods have been proposed, but their applicability for various types of particles has not yet been sufficiently examined, and this tends to undermine their practicality. We have addressed this problem using a numerical-analytical approach in which various types of biphase particles are modeled, and the 2D sectional information is compared with actual three-dimensional (3D) information. Through simulations, we revealed a general relationship between the internal mineral structure of particles and the stereological bias. Finally, we have developed a unique stereological correction method in which the texture (a 2D pattern characteristic) of particle sections is used to estimate the internal structure of particles, and thereby the stereological bias. KEYWORDS Mineral liberation, stereological bias, texture analysis INTRODUCTION Mineral liberation assessment of 2D particle sections inevitably suffers from stereological bias; that is, overestimation of the degree of liberation. Stereological bias is caused by the fact that a composite particle can be misidentified as a liberated particle when only one phase happens to have been cut in sectional measurement. Stereological bias has attracted attention since Gaudin pointed out its importance in 1939 (Gaudin, 1939). Several attempts have been made to measure the 3D liberation state directly, avoiding the bias, using X-ray computed tomography (Gay and Morrison, 2006; Lin and Miller, 1996; Miller et al., 2003; Miller et al., 2009; Reyes et al., 2017; Videla et al., 2007). These have provided useful information through laboratory testing, but further technical refinement is necessary for practical usage, to overcome the technique’s limitations in terms of resolution, assessment of minerals of similar density, and speed. Therefore, for practical purposes, detailed information regarding mineral phase geometry is obtained by sectional analysis, using automated scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX)-based analysis (e.g., with a mineral liberation analyzer (MLA) (Fandrich et al., 2007; Sandmann, 2015)); and the development of an effective method of stereological correction, which predicts the relevant bias and transforms the measurable 2D degree of liberation into its 3D counterpart, is an important research aim."

Jan 1, 2018

By P. Yu, L. X. Liu

"A mechanistic model for tumbling mills was developed during PhD studies at the JKMRC. The concept was presented at the IMPC of 2014, followed by progress in a sub-process of the model presented at the IMPC of 2016. Additionally, a number of papers on the sub-models and breakage function have been published. This paper provides a consolidated summary of the outcomes and status of the model. The overall model structure is presented along with the sub-models such as appearance functions, breakage rate functions, energy distribution, transport, and multicomponent grinding interaction model. The strengths and capabilities of the model structure as achieved to date are presented. The gaps in knowledge and sub-processes are also presented, providing a guide to the areas that require further research and development. It is proposed that the approach developed in this paper provides a structure that can accommodate future mechanistic, dynamic mill model evolution that can incorporate the latest research outcomes and provide a platform to test modelling improvements. This can assist in substantially improving the predictive mill modelling capability in the industry, the importance of which should not be underestimated for this workhorse of mineral processing.INTRODUCTION Grinding is almost the largest single energy-consuming process in the mineral processing industry, which was estimated that about 0.2% of global, and 1.3% of Australia’s electricity is consumed by comminution of gold and copper ores (Ballantyne and Powell, 2014). Although there are some relatively new grinding mills, such as stirred mills, vibrating mills and HPGRs (High-Pressure Grinding Rolls), etc., tumbling mills, as the traditional grinding facilities, are more extensively used."

Jan 1, 2018

By P. Saha, D. M. Chakrabarti, J. P. Srivastavam, P. Bhattacharyya, B. R. Sarkhel, Banerjeem B.

The phosphatic soil deposit at the Sukulu hills region of Uganda contains 10-12% P2O5. The ore occurs as a naturally degraded soil deposit containing a very sticky slime composed of earthy lateritic minerals. Desliming of the ore, which is imperative for its further beneficiation, is an extremely difficult hurdle to overcome for its commercial utilisation. Earlier studies on samples of the same ore at the National Metallurgical Laboratory (NML) and abroad established that it was necessary to pass the ore through a series of three stages of desliming, each consisting of a step of vigorous attrition scrubbing followed by hydrocycloning, for effective elimination of the sticky slime. In the present paper an innovative use of the very strong shear-fields created inside a hydrocyclone has been discussed, that could effectively eliminate the stubborn slime from the ore. The standard design of the hydrocyclone was suitably modified to increase the shearing effect on the slurry. It was possible, through the application of this modified hydrocyclone, to not only totally eliminate all the stages of attrition scrubbing, but also to reduce the subsequent stages of hydrocycloning. The modified technique yielded a concentrate of grade comparable to that obtained by employing the earlier more complex flow sheet, with about 25% higher P2O5 recovery.

Jan 1, 2003

By F. S. Hoseinian, K. Filho, D. Deglon, T. Souza, M. Safari

"This paper investigates the reverse flotation of hematite in three laboratory flotation cells with very different contacting environments. The main objectives are to investigate the recovery of coarse quartz by flotation and fine hematite by entrainment. The laboratory flotation cells used were the mechanical, oscillating grid and pneumatic cells. The effect of froth height and solid concentration were investigated in the mechanical and pneumatic cells. The effect of impeller speed and energy input were investigated in the mechanical and oscillating grid cells. Froth height results show that coarse quartz particle recovery decreases almost linearly with increasing froth height due to increased detachment of coarse quartz particles in the froth. Fine hematite particle recovery also decreases almost linearly with increasing froth height due to decreased water recovery and associated entrainment. Agitation/energy input results show that coarse quartz particle recovery increases with increasing impeller speed to an optimum, after which this decreases dramatically. The increase is due to improved gas dispersion, generation of smaller bubbles and increased bubble-particle collision and attachment. The decrease is due to significantly increased bubble-particle detachment at higher impeller speeds. The recovery of coarse quartz particles in the OGC is higher than that in the mechanical cell with an optimum at a much lower energy input. Solids concentration results show that both mass recovery and water recovery increase with increasing solid concentrations. The pneumatic cell achieves higher mass recoveries and lower water recoveries than those in the mechanical cell at equivalent solids concentrations and operating conditions. INTRODUCTIONFlotation is a selective process for separating different minerals from each other. The flotation separation efficiency depends on the recoveries of the mineral species by both true flotation and entrainment (Neethling and Cilliers 2009; Wang et al. 2015). Both chemical variables and hydrodynamic conditions within the flotation cell affect the recovery and selectivity of the flotation process. Cationic reverse flotation of hematite is a common method for selective separation of quartz from iron ores to produce pellet feed. The presence of coarse quartz particles in the tailings and fine hematite particles in the concentrate are two major challenges in the reverse flotation of hematite (Vieira and Peres 2007)."

Jan 1, 2018

By T. Kalliomäki, B. P. Wilson, M. Lundström, J. Aromaa

"The diffusion rate of cupric ions and limiting current density are important factors that determine the rate of copper mass transport in electrolytes proximal to the electrodes used in electrorefining. As a result, diffusion can critically affect both the rate and morphology of cathodic copper deposition thus it is crucial that it be optimized to improve production. The diffusion coefficient of cupric ion (DCu(II)) in copper electrolytes has been previously researched but the values detailed in the literature show significant variations and moreover arsenic - a common impurity - is generally excluded. Furthermore, in previous studies the models have only been validated with model solutions rather than real industrial electrolytes. In this study, the limiting current density and diffusion coefficient of cupric ion were defined for synthetic electrolytes containing copper (40–60 g/dm3), nickel (0–20 g/dm3), sulfuric acid (130–220 g/dm3) and arsenic (0–45 g/dm3). The cathodic limiting current densities were measured at three temperatures (50, 60, 70 °C) with linear sweep voltammetry using the rotating disc electrode (RDE) as the cathode. By utilizing the limiting current density, models for the DCu(II) were constructed using Levich equation. The validity of the DCu(II) model for technical use was confirmed through their application to industrial electrorefining electrolytes with known element concentrations. Consequently, this study provides improved models for limiting current density and diffusion coefficient of cupric ion that can be utilized for industrial process optimization.INTRODUCTION For an efficient copper electrolysis process, the mass transport of copper ions has to be effective. The main mass transport types of copper ions in copper electrorefining are diffusion and convection while the effect of migration is negligible. In order to maintain good mass transport, it is beneficial to keep both diffusion and convection high to maximize the limiting current density (jlim) (Bard and Faulkner, 2001). jlim is the highest current density that can flow in the cell, thus by maximizing jlim the deposition time can be minimized and the good quality of cathodic copper can be ensured. Thus, it is important to research possibilities that increase and optimize diffusion since slow diffusion in the electrolyte limits the rate of the process (Levich, 1947; Moats et al., 2000; Subbaiah and Das, 1989)."

Jan 1, 2018