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By P. K. Fedotov

Annually at least 5% percent of world power consumption is involved in the process of ore dressing while ore processing technology. Such rate of energy consumption demonstrates the importance of a given process study in the human life-sustaining activity. Examining of interparticle destruction being under external stress pressure in ore responses this problem solution at the greatest degree. The technology of destruction in the roll press is of great interest. The use of the given equipment allows to save a significant amount of energy by means of the built-in ore destruction mechanism. Examination of stress-strain fields which determine the level of interparticle destruction between the rolls in the ore layer enables to specify both level of ore destruction and power consumption. The mathematical computer modeling for the deformable environment use based on the finite-element method (FEM) allows to carry out the given research. We use FEM solution for elastic contact problem for the most complete study of power consumption employed in ore and interparticle destruction. This problem solution allows also to examine energy consumption expenses spent for ore crushing in the roll press. Also we have identified the mechanism of ore in a layer of the particles under pressure roller press. It is established that high level of performance and reduction of energy consumption in interparticle destruction of ore in the layer due to the appearance of the gradient of normal stresses in contact of particles of mineral raw materials. The algorithm has been developed determining crushing product particle size distribution of fractured particles in the layer, using the Bond’s theory of crushing. The use of our FEM model reduces the time of equipment selection for new plant and at the design stage to reduce the risks of errors in the choice of roller presses.

Jan 1, 2018

By G. H. Li

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

Jan 1, 2014

By 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

By Manuel Diaz

"In these difficult times for the mining world, mainly due to the global uncertainty about metal prices and the increased activity of opponents to the mining industry, it is essential that mining companies focus on efforts and strategies that will give them the most flexibility to succeed under the fury of these phenomena. The careful management of systems to control costs, and indicators to measure with great precision actual variations in costs and cash flows, are essential to adequately manage the uncertainty. Similarly, clear corporate and regional strategies designed to maximize cash flow and operating margin will allow the company to be better prepared to face any negative situations caused by declining metals prices, stricter government regulations and increasing social pressure. Gold Fields Limited, a corporation of South African origin and with more than 100 years in the gold mining business, has developed the ability to adapt to large changes generated by different global crisis throughout its history. This occasion will be no different. Given the critical situation of the mining industry in the world today, Gold Fields has embarked on a re-structuring plan at global level that will allow much closer control and real efficiency of production costs. This plan includes the creation of regional business units that allow greater independence for each region while still preserving the standards and cultural values of the Corporation. This presentation will explain why we believe that this approach combines the best aspects of the two styles of business, and what are the expected results. In the Americas Region, Gold Fields currently operates Cerro Corona, in Peru. In addition, the company is considering opportunities for growth in Chile, Brazil, Mexico and Canada."

Jan 1, 2014

By B. McFadzean, J. Taguta

The enthalpy of immersion is the heat change arising from the replacement of the solid-gas interface with the solid-liquid interface when a solid surface is immersed in a liquid. Although immersion calorimetry has been established as a valuable and reliable means of determining solid surface properties such as wettability, it has seldom been applied in mineral processing research. In this study, precision solution calorimetry was employed to measure the enthalpies of immersion of different minerals in water. The enthalpies of immersion were then related to the first-order flotation rate constant as determined by the microflotation technique. The same measurements were also made on sulphide minerals whose surfaces were modified to different degrees of hydrophobicity using different percentage coverages of amyl xanthate collector. The enthalpy of immersion technique was capable of distinguishing and ranking minerals according to their wettability. All mineral types and collector-treated minerals conformed to the same relationship that was found between the enthalpy of immersion and the flotation rate constant. This conformed, empirically, to a power law equation. As the enthalpy of immersion decreased, there were large increases in flotation response for very small changes in hydrophobicity. In addition, a critical enthalpy of immersion (CEI) was found, above which no flotation could occur. The scatter in the data points could be corrected for by adjusting the rate constant using the density of the minerals to produce a robust relationship between the rate constant and enthalpy of immersion. These results have shown that the enthalpy of immersion is able to indicate both the natural mineral hydrophobicity and the extent to which collectors can render a mineral hydrophobic. This technique has considerable potential to be used as a sensitive and accurate measure of mineral surface wettability in order to predict flotation performance.

Jan 1, 2018

By A. Boulton

Low molecular weight synthetic polymers substituted with hydroxyl, carboxyl or sulfonate functional groups were used to improve the flotation separation of zinc or copper sulfide minerals from iron sulfide gangue minerals in three massive sulfide ores of different mineral composition. These polymers produced significant improvements in zinc or copper grades as a result of a selective depression of iron sulfide minerals. These results are significant considering the differences in ore type, proportion and type of iron sulfide minerals present, and grinding medium used in this study.

Jan 1, 2003

By J. Kwon, D. Lee, H. Cho

"The use of the combined grinding and liberation model to predict liberation characteristics of iron ore comminuted by a ball mill was studied. Comminution characteristics were obtained using the one-size fraction method. The iron ore samples were crushed and separated into a number of narrow size fractions by screening. The size fractions were further divided by magnetic separation into three classes: concentrate, middling, and tailings. Subsequently, various size-grade classes were subjected to ball milling, and the results were analyzed in terms of the kinetic grinding model. The mineralogical textures of the grinding products were analyzed using mineral liberation analysis. The distribution of iron content within the size fractions was characterized by the beta distribution combined with the Andrew–Mica diagram. It was found that the grinding characteristics of the iron ore samples varied slightly with the iron content. However, the liberation characteristics were well described by the same set of liberation model parameters, regardless of composition. The variation in grinding kinetics with composition and the liberation model parameters was used in the combined comminution–liberation model to predict the evolution of the size-composition matrix as grinding proceeded. The predicted results agreed well with the experimental results. The developed model can be used to construct the yield–recovery graph and to calculate the liberation efficiency to determine the size reduction threshold for efficient separation. INTRODUCTION In mineral processing, comminution is usually the first step that ores undergo to liberate valuable minerals from gangue minerals. Generally, as the particle size decreases, higher liberation can be achieved. However, excessively small particles are unfavorable to subsequent processes, such as separation. Moreover, comminution is a highly energy-consuming process itself that accounts for approximately 60% of all energy used for processing. Therefore, there is a definite need to increase energy efficiency by applying adequate stress so that a high degree of liberation can be acquired at the coarsest size without overgrinding. To this end, it is essential to develop a model to predict the liberation of minerals as a function of size reduction."

Jan 1, 2018

By Scott C. Brown, Brij M. Moudgil, Ivan U. Vakarelski

The manipulation of the apparent hydrophobicity of particlute surfaces is necessary to achieve optimal selectivity in flotation processes. Previously a number of works have investigated the role of microscale surface and particulate morphologies on chemically modified substrates. These works have suggested that microscale surface asperities lead to an increase in flotation efficiency by assisting in the rupture of wetting films. Yet, in mineral processing the presence of surface asperities may lead to a reduction in flotation. The reason for this may-in part-be due to the presence of nanoscale irregularities at the interface. In this work, it is proposed that the presence of roughness at the nanoscale may have a dominant impact on the apparent hydrophobicity of mineral surfaces during flotation. It is suggested that as inter-asperity seperation distances are reduced capillary effects are enhanced for high energy mineral surfaces leading to the formation of liquid domains, which adversely impact hydrophobicity. In addition, as these distances approach the surfactant headgroup size obstruction of surfactant self-assembly process may occur, thereby further limiting flotation.

Jan 1, 2003

By L. Muhr, Y. -T. Tang, M. -O. Simonnot, B. Laubie, R. -L. Qui, Z. Chour

"Agromining aims at recovering metals from different secondary resources with hyperaccumulating plants. These natural plants can selectively concentrate metals at very high level and can be transformed to produce commercial compounds. The classical strategy to recover metals from hyperaccumulator plants is based on hydrometallurgy. It consists of: i) burning the plant to obtain ash, which is a very rich bio-ore without organic matter, ii) transferring the target element(s) into aqueous solution by acid leaching and iii) purifying the leach liquor to obtain the target element(s) in the desired form. This method has enabled us to obtain nickel salts, nickel oxide, zinc and cadmium from different plants. However, it is not possible to apply this approach to recover rare earth elements (REEs) from the fern D. dichotoma, growing on mine tailings in South China. Actually, this plant is very rich in silicon: plant burning gives an amorphous ash, very stable despite severe leaching conditions. Therefore, the strategy has been changed and processes are currently developed to extract REEs by direct leaching of the biomass, without burning the plant. Several conditions (i.e. leaching solutions) have been investigated, showing that a good extraction yield was obtained with HNO3 0.5 N (around 84%). This yield was increased to 99% by adding a complexing resin into the leaching solution. After two-steps of elution, results have shown that is possible to recover 75% of the REEs at 81% purity.INTRODUCTION The demand of rare earth elements (REEs) (including 15 lanthanides, yttrium and scandium) has been growing sharply over the past years, because of their industrial applications. REEs are essential elements for emerging technologies, and are used for example in permanent magnets, lamp phosphors or rechargeable batteries. China is the main producer, and the market supply became tense in 2010 when this country decided to limit exports of these elements. Exploitable mineral resources, as well as REE separation capacity are concentrated in a few countries (e.g. USA, Australia, Malaysia, France), which increases the supply risk. Therefore, these elements are considered as critical raw materials (CRM) for many countries and especially for EU (Fortier and Gambogi, 2017)."

Jan 1, 2018

By A. F. Usov

A potential of electric pulse disintegration in benification used for primary deposits ores containing precious metals is shown. Of special significance is that PGM and gold grains, being highly plastic, are easily liberated and are not smeared on the disintegrated rock fragments surface. It al-lows gravity separation, which is less expensive and more efficient, to be used instead of chemical processing, which is expensive and environmentally faulty.

Jan 1, 2014

By Douglas Fuerstenau

"Comminution not only is the major energy cost in mineral processing but it also can limit the grade of ores that can economically be processed. Rittinger first postulated that the energy for comminution is proportional to the new surface produced. Because most of the strain energy needed to initiate and propagate cracks in particles cannot be recovered, researchers reported woefully low comminution efficiencies. Recognizing this, Schoenert proposed that the baseline for assessing comminution efficiency should be the mechanical energy needed to break single particles. After extensive single-particle studies, Schoenert turned to comminuting beds of particle in piston dies. Finding particle-bed comminution to be energy efficient, he had the brilliant conception of making the process continuous, namely his invention of the choke-fed high-pressure roll mill (HPGR). Practical comminution involves masses of particles, which can lead to energy efficiencies far less than that of single-particle breakage. A three-way classification of grinding modes in terms of the mobility of the particle mass provides the necessary insight into the low efficiency of different comminution machines: namely, single-particle breakage, confined particle-bed grinding (HPGR), and loose-bed grinding (ball mill). Examples are given for determining and comparing comminution efficiencies. The size distribution of comminuted products become self-similar, and a single parameter, the median size, can be used to quantify the extent of comminution. The reduction ratio, expressed in terms of the mean size of the feed and product, varies linearly with expended energy and the slope of such plots is a measure of the grindability of the mineral. This approach clearly gives the order of energy efficiency as single-particle > particle-bed > loose-bed comminution. HPGRs are more efficient at low reduction ratios but lose that advantage at higher reduction ratios. Extensive hybrid grinding experiments carried out with our instrumented ball mill and HPGR showed significant energy savings by first comminuting the material in the HPGR and followed by the ball mill. At Cerro Verde an industrial-scale hybrid HPGR/ball mill system is reported to have a 13 percent energy savings over a SAG mill/ball mill system."

Jan 1, 2014

By David De Klerk, Maximilian Richter, Thirunavukkarasu Pathmathas, Indresan Govender

We consider the average power dissipation distribution for dense granular flows of an idealised mono-sized charge (5 mm glass beads) in a 300 mm diameter tumbling mill operated in the cascading-to-cataracting Froude regime. By combining the inherent frictional nature of particles within a dense flow regime and noting that tumbling mills are typically characterised by collisional and turbulent stresses, we derive the power dissipation distribution for athermal boundary conditions. The input data to the model (velocity, solids concentration, pressure and flow depth) are obtained directly from non-invasive measurement using a nuclear imaging technique: Positron Emission Particle tracking (PEPT). The power dissipation due shear stresses is shown to be the dominant mode of dissipation in the tumbling mill with up to two orders of magnitude difference between pressure induced dissipation and shear.

Jan 1, 2014

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 Ghislain Bournival, Seher Ata, Yesenia Saavedra Moreno

"In froth flotation, frothers are commonly added to the pulp to modify the interfacial properties of bubbles. These properties may be modelled using commercial software packages. The volume of fluid (VOF) method was used to track the interface motion during the post-rupture oscillation of the newly formed bubble. The aim of this research was to provide an insight into the modelling of viscoelastic phenomena through the coalescence dynamics of two bubbles in solutions of various surface tensions using a three-dimensional computational study. Different surface tensions were used to simulate changes in methyl isobutyl carbinol (MIBC) concentration. The computational results were evaluated by comparing the oscillatory motion of the newly formed bubble for the different MIBC concentrations. For known MIBC concentrations, the deviations of the computational damping constants from the experiments were quantified, revealing possible deviations in the VOF surface tension model. In addition, the analysis provided insight into the flow patterns of the fluids and the effect of frother concentration on the velocity magnitude in the liquid and air phases. This analysis provided a further understanding of coalescence dynamic and post-rupture oscillation in froth flotation. Such a process is believed to affect the stability of particles at the interface due to the release of surface energy when the bubble surface is reduced.INTRODUCTIONIn froth flotation, bubble coalescence is an important phenomenon that is highly dependent on the interfacial properties of the liquid film between bubbles. It is known that the frother adsorption at the liquid-air interface changes the interfacial properties, resulting in an increase of surface elasticity and reduction of surface energy (Pugh, 2016). However, in a two-phase system, it is the frother type, concentration, frother molecule conformation at the interface and viscoelasticity properties that dictate film stability (Pugh, 2016). The viscoelasticity phenomena can be explained in terms of surface viscosity, which quantifies the energy dissipation at the interface and surface elasticity that represents the energy absorbed at the interface as result of bubble oscillation (Pugh, 2016). In the case of systems stabilized by nonionic frothers, it has been shown that surface forces alone do not account for film stability, but the viscoelasticity represents the ability to damp external disturbances in the thin film separating the bubbles and prevent coalescence (Santini et al., 2007)."

Jan 1, 2018

By Bern Klein, Givemore Sakuhuni

Flotation is the dominant base metal extraction technique and it requires ore to be ground below the liberation size for effective recovery due to its dependence on mineral surface properties. For a poly-metallic ore, differential hardness of constituent minerals leads to over grinding of softer minerals before the harder minerals are fully liberated, which makes selection of a target grind size complex, and the complexity increases when treating leaner ores. Flotation recovery deteriorates above 100 and below 10 microns causing significant loses of valuable minerals in most flotation circuits. Although enhanced gravity concentration is known to be effective at recovering particles above 100 microns, which are difficult to hydro-dynamically transport, exploiting differential specific gravity for base metal separation was not an option in the past. This was partly due to the absence of high mass yield gravity techniques. The advent of continuous gravity concentrators with flexible mass yields, in the past two decades, has necessitated investigation of possible base metal applications. The Knelson CVD, one of the continuous discharge centrifugal concentrators, has an established application niche for sulphides associated with gold. However, its base metal applications have never been rigorously tested. Considering the dependence of flotation recovery on particle size, continuous discharge centrifugal concentration can be integrated in flotation circuits to capture flotation non-recoverable coarse particles. This paper explores how particle size, liberation and mineral hardness influence application of continuous centrifugal technology to regulate galena deportment in a polymetallic base metal plant. The results show that particle size affects galena recovery more than liberation. In view of these results, the CVD can be integrated in the primary grinding circuit to pre-concentrate the heavy sulphides at a coarser grind size with potential grinding energy savings.

Jan 1, 2014

By Bulelwa Ndlovu, Saeed Farrokhpay, Dee Bradshaw

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

Jan 1, 2014

By 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 William Conger, Greg Schick

Grinding media consumption is a major cost variable in industrial mineral comminution circuits. Specifically, industrial SAG media consumption results from a combination of surface abrasion wear, media breakage, surface spalling and rejection size from the mill. Three main consumption rates; weight of media consumed per time, per kWh and per weight of ore ground are defined and compared. Recent industrial data has provided an opportunity to relate consumption in terms of weight of media consumed to weight of ore ground (g/tonne) and weight of media consumed per kWh of energy consumed (g/kWh) with SAG specific grinding energy consumed (kWh/tonne). Using relationships developed from this data it is possible to project SAG media consumption in future mineral comminution circuits.

Jan 1, 2014

By A. Morrison, D. Mesa, P. R. Brito-Parada

"Froth flotation is the most widely used mineral separation technique. It is based on the relative hydrophobicity of valuable and gangue particles. In a flotation tank, two distinct zones can be identified: the pulp and the froth. The pulp is a turbulent region in which hydrophobic valuable particles attach to air bubbles while hydrophilic gangue particles remain in the slurry. As the particle-laden bubbles rise, a mineralised froth zone is formed that overflows as a concentrate. Although the process is more than a hundred years old, there remain many aspects that are not completely understood, particularly for the froth zone. Thus, the rules governing the design of flotation tanks tend to focus on pulp zone parameters, which are largely based on operating data. An example of this is the design and operation of impellers. These tend to be designed paying attention to hydrodynamic phenomena in the pulp zone, but their effect on the froth zone has not been completely addressed. The role of impellers in a flotation tank is to break the air bubbles in order to generate smaller ones and to provide an environment that enables the collision between those bubbles and the particles in the slurry. This usually creates turbulent regimes that can affect the pulp-froth interface, destabilising the lower regions of the froth and affecting the overall performance of the process. Different impeller designs and retrofit modifications have been proposed in the past, addressing some of those issues. However, there is no systematic study of the effect of different impeller designs on the bubble size in the pulp and its links to the stability of the froth. This work tested the impact of an impeller designs combined with the use of a stator on the performance of an 87 litres continuously operated laboratory-scale flotation tank, with a focus on bubble size in the pulp and froth stability. The results showed that the implementation of a stator system decreased bubble size and increased froth stability. That resulted in an increase of mass pull, measured as a proxy of metallurgical recovery."

Jan 1, 2018

By Paulo Castillo, Cesar Gomez, Jaime Alvarez

Operations using flotation to produce mineral concentrates require testing of frothers to characterize their ability to preserve bubble formation size and to build a stable froth. Many techniques have been proposed to measure parameters associated with these two roles. These techniques focus, in general, on only one of these roles and are based on special equipment operated at conditions quite different from those existing in industrial cells and columns. Both roles have been simultaneously characterized in a laboratory flotation column, but the requirements associated with the installation and operation of one of these units, are a serious limitation for its use on-site. A technique based on the use of a laboratory mechanical cell, a common piece of equipment in operations, will have wider application. Establishing the ability of a frother to control coalescence by preserving bubble formation size is done through bubble size measurements as a function of frother concentration. Froth build-up and stabilization is associated with the amount of water carried by bubbles into the froth layer, which has been demonstrated to correlate with the gas holdup in the collection zone. Procedures devised for determining the critical coalescence concentration (CCC) from measurements of bubble size as a function of frother concentration, and the gas holdup by collection of water displaced from the cell by the presence of bubbles at different frother concentrations, were tested. Three analytical-grade frothers were utilized: a straight-chain (1-heptanol) and a branched (MIBC) alcohol and a polyglycol (PPG425). The results obtained at a standard set of conditions, demonstrated consistent differences between these frothers, and the ranking from least to most effective for reducing bubble size or decreasing water drainage followed the same sequences found when more complex frother characterization techniques are used.

Jan 1, 2014