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By Douglas W. Fuerstenau

Some historical sketches of the early development of froth flotation are presented. Flotation technology involves several aspects: chemical control of mineral hydrophobicity, selectivity in flotation, flotation kinetics, flotation machines, and process optimization and control. However, only some aspects of the regulation of mineral flotability by the addition of chemical collectors in some selected cases are discussed. The early contributions to flotation science by Langmuir, Gaudin, Wark, and Taggart are briefly outlined. With a firmer understanding of surface chemistry, electrochemistry, and the electrical double layer, progress has been made in understanding the fundamentals of flotation chemistry, although sound theoretical underpinnings still are needed in these very complex systems. Flotation chemistry is related very directly to the type of mineral being floated since the systems depend strongly on the chemical and physical characteristics of the minerals. Full discussion of chemical reagent phenomena would be in terms of the behavior of naturally flotable minerals, sulfides, oxides, silicates and alumino-silicates, and salt-type minerals. At this time, citing a few cases involving salt-type minerals and oxides, the dependence of their flotation surface chemistry will be discussed in terms of the role of adsorption, surface reaction, and the hydrophobic effect.

Sep 1, 2012

By Nicolás Caussade

"The IMPC 2014 slogan "Optimizing Water and Energy Usage for Sustainable Mining" refers to the ever decreasing availability of fresh water and energy, which has turned out to be a crucial aspect in assuring the competitiveness of the mining sector in Chile and the Andes region in general. The concern for sustainability and the supply of water and energy is nowadays part of the top priorities of mining countries and communities. This is also the case for Antofagasta Minerals. Several years ago its mining group implemented an energy policy based on intelligent, strategic and sustainable management, in order to successfully face the challenges imposed by the market. It is called an intelligent policy because it intends to provide energy through a diversified range of sources, which includes the development of in-house alternatives. It is also a policy focused on efficient energy consumption and one that is strategic. Because it is in line with the characteristics of the mining activity, it is developed for the long term. Finally, what makes the policy sustainable is that it gives priority to energy usage from renewable resources and as such, the required capacities have been developed to generate innovative solutions that respond to the restrictions that characterize the industry today."

Jan 1, 2014

By Wu Tao, Lu Shijie, Xia Xiaoou, Zhang Ming

The impeller and stator are the most important components that can significantly influence the performance of flotation cells directly. The performance of the impeller and stator of KYF flotation cell is revealed by CFD (Computational Fluid Dynamic) simulation in this paper. A method of obtaining the circulation volume is proposed. The circulation volume is proportional to third power of impeller diameter. And the circulation volume increases linearly with the increasing of the speed. CFD simulation can draw the conclusions that there is a proportional relationship between power consumption, third power of speed and fifth power of impeller diameter. CFD prediction results agree with the theoretical formula. The difference between the forward and backward impeller is analysed in the paper. The circulation volume of the backward impeller is obviously larger than that of the forward impeller under the same condition, but power consumption of the backward impeller is lower. It is demonstrated that the impeller and stator system of KYF flotation cell is an efficient and reasonable stirring mechanism. CFD simulation could be reliably used in flotation cell design and optimization.

Jan 1, 2014

By Ricardo Duque-Soto, Gonzalo Montes-Atenas

The depletion of water resources has posed an enormous challenge to the continuity of many mine sites, particularly those located in arid zones worldwide. In Chile, the use of seawater has been foreseen as one possibility to solve this problem. Nevertheless, the direct use of high ionic strength solutions such as those present in the sea has been found to have some drawbacks. Specifically, rhe extraction of copper from complex ores using high ionic strength solutions such as that of seawater has become one of the most relevant topics in the field of copper hydrometallurgy. This study aims to determine the effect of the degree of salinity on copper extraction kinetics in mixed oxide-sulfide ores. A leach protocol was implemented to study the extraction kinetics, varying the degree of salinity of the medium and the temperature. A thermodynamic model was developed to explain differences in the metal extraction. It was found that the ionic strength impacted positively the copper extraction, probably due to the reduction of the effective concentration in solution due to ionic interactions enhancing the diffusive mass transport of copper ions. This effect is observed to be enhanced when up to an overall salinity values close to 20gpl.

Jan 1, 2014

By Jorge Menacho

"A typical Chilean producer in the Large Copper Mining Industry today is characterized by high production level with economical results decreasing but still attractive. Operational activities are developed within a low-productivity environment, with high cost and complex relationship between the company and communities, government authorities, providers, clients and their own workers. Decreasing copper grades and limited availability of energy, water and workforce are structural problems which require the State intervention in collaboration with the relevant actors and benefits would be evident in the middle or long term. Main opportunities in the short term are found in the sub optimal conditions we have at many plants today. Robust solutions to control existing operational management system as well as to supply systematic optimization options are needed. These should be oriented toward effective fulfillment of specific operational set points and also to reduce variability in crosscutting tasks. Solutions should include easy connectivity to existing information systems as well as to a suite of simulation and optimization tools settled in a highly interactive communication platform. Relevant issues include minimization of specific energy and fresh water consumption, maximization of the use and performance of critical equipments, minimization of damage to environment and control of effective application of good operational practices. Several specific examples are given."

Jan 1, 2014

By P. Somasundaran

While sustainability itself needs to be redefined in a selfless way, methods of measuring and optimizing it also need to be reformulated. Gone are the days when we had the luxury of abundant resources and the freedom to extract values in self-centered ways. In the past, focus has been mostly on reagent performance, processing operations, and upgrading of tools to maximize rather than optimize value extraction from the earth's crust. Today we as extractors face a new set of challenges that include value separation from low quality resources including wastes, but within the energy, environment, and societal constraints. Development of such technology depends on understanding the role of entities and concepts such as bio-molecular interactions at surfaces, forces involved in inter-granular versus intra-granular fracture in new fragmentation methods, robotic in-situ or extraterrestrial mining, exploiting new membrane and nano technology, use of new sensors and actuators for detection and separation and computation capabilities for faster and economical processing. Equally importantly, we need to communicate with everyone what we foresee and anticipate when we extrapolate the type-performance-cost relationship of ores to the era ahead of us and establish viable schemes for ecological survival. Keywords: sustainable mineral extraction

Sep 1, 2012

By Camilo Uribe, Williams Calderón, Gonzalo Montes-Atenas

In industrial hydrometallurgical operations, the leaching process is often implemented via heap or dump leaching operations. During the pile up of these massive amounts particles a porous material is then formed. The manner it is constructed is crucial since it will define the permeability and other parameters determining the flowrate of leaching solution across the material. This study aims to estimate how the unsaturated permeability of the staked porous structure confined in a column-like geometry varies with and without particle size segregation. The piling up will be modeled using the Rocky® software. Different disposals of particle size distributions across the column will be simulated and their effect onto the overall column unsaturated permeability will be estimated. It was found that when the belt speed increased, the particle segregation in the column also increased. This condition is expected to improve the permeability of the porous structure in the column, probably due to the smaller compaction of larger particles when they are located at the base of the column and maintain a suitable porosity to permit leaching flowrates relatively high, suggesting better extraction results. The opposite was observed when small particles were preferentially located at the bottom of the column. These results are expected to provide an insight towards what is the best way to construct heaps and dumps.

Jan 1, 2014

By Marco Le Roux, Quentin Campbell

"Most coal supply contracts include strict limitations on the moisture content of the products. This limitation exists because of calorific, transport cost, and handling reasons. Managing the retention time on product stockpiles to facilitate drainage commonly controls the moisture content in coarser coal products. A large-scale pilot rig has been commissioned to facilitate research in this regard. A stockpile of about 15 tonnes of a typical washed power station feed coal from the South African Witbank coalfield was loaded onto a 6 x 6 m platform on load cells. The platform was shielded from the elements, like rain and wind, and an artificial rain sprinkler system was installed. A variety of rainfall intensities and durations were simulated and the water accumulation and run-off was measured. The material was also sampled for moisture and particle size before and after the series of tests. At the same time, the drainage characteristics of the same coal were determined in smaller scale drainage columns for comparison. Data is presented in this paper on the drainage rates, maximum accumulated moisture, final moisture, and the effect of evaporation. The results showed that for all rainfall patterns tested, drainage ceased after 2 - 3 days, but evaporation continued for at least the time period under investigation, albeit at a low rate. Evaporation contributed to dewatering at rates that depended on wind, temperature and humidity conditions. This caused a slow reduction in moisture content even after the run-off had ceased. The value of the final moisture depended on the coal PSD. It was also found that the intensity and duration of the more intense rainfall events did not significantly affect the maximum water accumulation, with drainage rates equaling the corresponding water addition rates which suggested that water ran off over the surface of the stockpile with limited penetration. During more intense rainfall scenarios, some penetration was apparent."

Jan 1, 2014

By P. Prakash

A dual-drive planetary mill, which has a rotating shaft that sweeps a circle of diameter 750 mm, has been designed. The planetary mill is powered by a 5 hp motor to rotate the main shaft and a 3 hp motor to rotate the jars. The charge dynamics inside the horizontal-axis planetary ball mill was established using three-dimensional DEM simulations. The simulation results provided data to determine the impact energy distribution and the effect of process parameters such as mill speed and filling. It has been observed that the mean impact energy per unit time increases with rotation-to-revolution ratio, whereas the average number of inter-particle impacts per unit time decreases. The mill was also used to synthesize a variety of powders. Here three case studies of reaction milling are briefly presented: (i) cementite and silicon carbide, (ii) oxide dispersed strengthened (ODS) steel, and (iii) magnetite from blue dust. In each case, the powder was produced by mixing and then milling the corresponding pure components. The phase evolution, particle size distribution, and morphology of particles during milling were studied for various samples collected at different milling times using laser size analyzer, SEM, TEM, and Mössbauerspectroscopy. The results established a convenient way to produce powders of high technological and commercial value.

Sep 1, 2012

By Martin Rudolph

"Flotation is without a doubt one of the major processes for the separation of fine minerals and it has been applied for more than a century. A key task of a successful flotation separation is to find the proper chemical treatment to selectively hydrophobize and thus float a certain mineral phase using molecules or ions referred to as collectors, depressants, regulators and frothers. Commonly floatability is determined by microflotation tests using the Hallimond tube with pure mineral phases. This method however requires the pure mineral phase which is very often not even taken from the same deposit which is going to be processed. In this paper we present a new approach to in-situ determine and even map the floatability of finely disseminated mineral phases within cross-sections of an ore. It is based on measuring hydrophobic effects using colloidal probe atomic force microscopy with a hydrophobic polystyrene probe based on force spectroscopy with a lateral resolution of only a few nanometers. Coupled confocal Raman spectroscopy on the same locality enables the identification of the mineral phase. We present the working principles of the method and show which signals in the force spectra characteristic for hydrophobic interactions can be used to define floatability and which can then be mapped as single quantities, e.g. jump-into-contact events due to nanobubble occurrence or parameters of the long range interaction curves most probably due to capillary effects. A finely grained silicate ore containing the valuable rare earth mineral eudialyte from southern Sweden as well as pure samples of magnetite are presented as substrates to demonstrate the capability of this new approach. This method will not only help to find the proper flotation chemistry but it can furthermore help in researching and unravelling problems of floatability within similar mineral phases."

Jan 1, 2014

By J. D. Miller

The more efficient production and use of mineral resources is a major objective of our sustainability efforts. Resource characterization is a critical component for optimization of the mine-to-mill process, including innovative processing for sustainable growth. Such characterization is now referred to as geometallurgy, with advanced instrumentation including, for example, particle size analysis, XRF, XRD, NIR, automated SEM/EDAX analysis (QEMSCAN, MLA), and high resolution X-ray micro tomography. Geometallurgical information is important for exploration, deposit evaluation; mine planning, design and analysis of separation processes, etc. Characterization of mineral processing particles in 3D is now possible using high resolution X-ray micro tomography (HRXMT), and such HRXMT systems have been installed at several laboratories around the world. After review of principles, the features of such HRXMT analyses are presented including size/shape, damage state, mineral phase identification, and evaluation/isolation of trace mineral particles. With new algorithms for image analysis, quantitative data treatment is possible for construction of liberation-limited grade/recovery curves, for the determination of specific crack surface area, and for complex texture analysis including grain exposure. Finally, new tomographic characterization possibilities are discussed to provide the foundation for the development of advanced, innovative processing strategies for sustainable growth. Keywords: X-ray tomography, resource characterization, HRXMT, particle size analysis XXVI INTERNATIONAL

Sep 1, 2012

By R. Bugueño, W. Calderón, G. Montes-Atenas

From the point of view of industrial performance of metal extraction, the efficiency of a column leaching operation depends strongly on the leaching agent and the ore properties such as mineral composition, mineral liberation and particle size distribution. One aspect that has become particularly important is how the leaching solution flows through the porous structure which contains the valuable minerals. It is known that the output flow rate of leaching solution depends mainly on factors of the input flow, environmental condition and porous bed properties. The latter factor is often evaluated and reported under saturated conditions but in practical leaching systems unsaturated conditions are dominant. This investigation has the purpose of determining the residence time of the leaching solution in columns with different diameters under unsaturated conditions by using experimental data and numerical simulations. Laboratory leach test were performed using isothermal jacketed columns with top cap to reduce the evaporation. The simulations were performed using the software SVFlux® which incorporates material properties such as Soil Water Characteristic Curve (SWCC) and Unsaturated Hydraulic Conductivity. Preliminary results indicate a non-linear asymptotic behavior of the saturation rate with respect to the operation time. Results from numerical simulations show the same non-linear behavior and a considerable delay between input and output flows. Further analysis concerning with the effect of transpiration and evaporation mechanisms is discussed.

Jan 1, 2014

By Daniela Campos, Aldo Casali, Gonzalo Montes-Atenas

The understanding of the effect of the major variables influencing the froth flotation performance may allow both to predict and to identify best operating conditions towards optimizing the process efficiency. The aim of this research work is to model the effect of dissolved oxygen onto froth flotation performance. Experimental pilot plant results were obtained from a continuous circuit consisting of a ball mill and a rougher bank of four flotation cells. A series of flotation experiments were run with different conditions of dissolved oxygen keeping constant most of other operating conditions. Variables difficult to control were measured or estimated. A set of mathematical models suggested in the published literature were tested. It was found that the copper recovery results were highly sensitive to the concentration of dissolved oxygen. The latter confirmed the reactions mechanisms associated to the collecting capabilities of current flotation reagents used in the flotation of copper sulfide ores. On the contrary, the results of molybdenum recovery varied non-linearly with changes in dissolved oxygen which could not be explained directly in terms of the computed specific rate constants. The error analysis confirmed that Klimpel continuous model exhibited the best specific rate constant correlation with molybdenum recovery data. Lastly, the classic particle force balance equations indicated that the adjustments of estimated mineral liberation with experimental data exhibited a turning point when passing from highly liberated to low liberated particles. The values of recovery for such turning point correlated well with the concentration of dissolved oxygen. The results indicated corrections due to changes in the dissolved oxygen must be incorporated in future froth flotation descriptions.

Jan 1, 2014

By Francisco Vicuña, Miguel Becerra, Gonzalo Montes-Atenas

"The optimization of the copper recovery from smelting slag by a process of comminution / flotation has been a widely discussed topic during the last few decades. Several studies covering the characterization of different types of slag, the impact of the slag cooling rate and of different flotation operating conditions on the flotation performance have been widely published. Currently, at El Soldado mine site (Angloamerican), there are large copper bearing slag deposits that can be a profitable alternative for the concentrator with capacity to treat this material. Under this process schema, the optimization of the flotation process to obtain better copper recoveries is a relevant topic of study. The aim of this study is to assess the efficiency of a sulfidation stage of a slag and to correlate that process with copper recoveries results in a flotation circuit. This article presents a detailed examination at both laboratory and plant scales of the slag sulfidation on the recovery of copper in the flotation process. The experimental methodology involves studying the effect of the sulfidation agent dosage, the pH, the particle size distribution of the flotation feed and the conditioning time. Furthermore, the performance of the sulfidation stage was analysed through the XPS analytical technique. It was observed that the sulfidation of particles in floatable size fractions correlated well with the increase in copper recovery. The results indicated that it is possible to increase between 2 to 4 points the total copper recovery with a sulfidation process implemented appropriately."

Jan 1, 2014

By Graeme J. Jameson

In conventional flotation machines, the recovery is strongly related to particle size. As particle size increases, the recovery also increases, reaching a maximum in the range 20 to 120µm. Beyond this range however, the recovery declines quite quickly. The reason for the decline in recovery observed with coarse particles can be traced to the effect of turbulence. Bubbles trapped in turbulent eddies rotate rapidly, and when the centrifugal force on a particle exceeds the retaining forces due to surface tension, the particle detaches. Since the centrifugal force varies as the cube of the diameter of the particle, and the attachment force varies simply as the diameter, being proportional to the length of the contact line, it is clear that detachment forces will predominate as the particle size increases. The corollary is that the recovery of coarse particles can be improved if the level of the turbulence in the cell can be reduced to a minimum. In this paper, a new type of flotation machine will be described, in which the particles to be floated are suspended in a fluidized bed. An up flow of fluidizing water is provided, by recycling liquid from the top of the cell. The recycle stream is aerated in a high-energy device that disperses the air into fine bubbles that capture the fines and ultrafines. Results are presented for several minerals and coarse coal. Keyword: fluidized bed flotation

Sep 1, 2012

By C. Suazo, N. Mora

"The bubble size distribution plays a fundamental role in flotation kinetics. Nowadays it is possible to measure the bubble size distribution, gas holdup and superficial gas velocity by using specialized equipment developed for this purpose. In this article a methodology is presented for estimating the kinetic rate constant using a known particle and bubble size distributions. The attachment and detachment probabilities were modelled from three matrixes. The first matrix represents particle size distribution, the second was named the probability matrix, and the third is the bubble size distribution. Using laboratory data, it has been possible to estimate the flotation rate constant as a function of operating conditions and both the bubble and particle size distributions. The model tested at laboratory scale achieved a quadratic correlation coefficient equal to 0.97. This methodology could be used in the operation and control of the flotation, when in the near future we have industrial equipment that allows in-line measurement, in real time, of gas dispersion and bubble size distribution. knowing particle size distribution, it will be possible to manipulate the operating flotation cell conditions, in order to modify the bubble size distribution and find the bubble distribution that maximizes flotation kinetics. Furthermore, knowing the bubble size distribution, the grinding operator will be able to look for the particle size distribution that produces the maximum flotation kinetics. In order to do this, the operator will have to modify the solids percentage fed to the hydrocyclone cluster, modify the apex/vortex ratio, etc. Finally, this article shows that the maximum flotation speed is reached when the particle size distibution slope is equal to the bubble size distribution slope."

Jan 1, 2014

By Ronald Díaz

"Cerro Corona is a porphyry ore with different geometallurgical units and alterations produced by an extensive family of geological failures that have determined a special type of mineralization. With the increasing depth of the mine, it is estimated that the host rock will be less altered. Consequently, the ore will have a higher resistance to breakage accompanied by associated problems such as lower throughput. In light of this reality, various projects have been carried out with the objective to optimize mineral processing of ore with low clay content and high hardness, including reducing the blasting grid, increasing the load factor, using adequate mixtures of hard ore, reducing crusher settings, installing air guns in the transfer chutes, increasing ball charge, and changes in the lifter design, wear control in the hydrocyclones, syntonization of control logics, supervisor control of the SAG mil, characterization of feed ore, etc. However the most important factor was the teamwork between mine and plant personnel, aiming at common objectives for the company. These projects started in 2011, including characterization of mineralogical domains, breakage and blasting characteristics, and also a revision of the actual operating conditions in the crushing and grinding circuit. The development of different designs of the SAG mill lifters and the unloading grates, a 16% ball charge increase, improvements in the blasting process, reduction of the primary crusher setting, weight reduction on the feed lid, and variation of operational parameters, all allowed the company to achieve its objectives of maintaining impact control and steel recharge within the expected operational parameters. The achieved throughput is above design capacity, sustainable, and not without new challenges for maintaining and optimizing this production level."

Jan 1, 2014

By K. A. Natarajan

Involvement of various indigenous microorganisms in extracellular and intracellular iron oxide formation is a convincing index for iron ore biogenesis. Biomineralization of various iron oxides such as hematite, magnetite, goethite and limonite with the participation of aerobic and anaerobic microorganisms is well established. Various aerobic and anaerobic bacteria such as Gallionella, Leptothrix, Acidithiobacillus, Thermoplasmales, Pseudomonas, Bacillus spp and Shewanella putrefaciens, which are implicated in the formation of higher and lower oxides of iron have been isolated from different iron ore deposits. Diversity of microbial life in iron ore deposits can be put to beneficial use such as selective removal of undesirable constituents such as silica, alumina, clays, phosphorous and calcite and also to bring about environmental detoxification. Role of microorganisms such as Paenibacillus polymyxa, Bacillus subtilis, Yeasts and a sulfate reducing anaerobe in the biobeneficiation of hematite is illustrated. Surface chemical changes brought about by bacteria - iron ore mineral interactions are discussed with respect to hydrophobcity, adsorption isotherms, zeta potential data and bioreagents generation. Bacterial adaptation to minerals such as hematite, quartz, alumina, calcite, apatite and clays results in secretion of mineral ? specific biosurfactants such as proteins and polysaccharides. Such bioreagents can be used as selective collectors, dispersants and flocculants in iron ore beneficiation. Research results are highlighted to demonstrate silica, alumina, phosphate, calcite and clay removal from hematite. Environmental friendliness of such biobeneficiation processes is demonstrated with respect to biodegradation of toxic amine collectors, utility of ?in situ? organisms in enhancing settlement of fines in tailing dams and water harvesting. Keywords: bio-mineralization, bio-beneficiation, bio-remediation, Gallionella, Leptothrix

Sep 1, 2012

By S. Mohanta

The air dense medium fluidized bed separator which has been developed for the dry beneficiation of coal is recognized as a low cost and high efficiency process. The success of this separator for beneficiating any specific coal, alone or in combination with other processing methods, mostly depends on the characteristics of run-of-mine coal. Therefore, a thorough knowledge of the mineralogical composition and washability characteristics of representative coal sample is highly essential for correctly and effectively assess the suitability of this process. Available literature conforms that although the characteristics of Indian non-coking coals are well known, the correlations between the particle compositions with its density are entirely lacking. In the present study the washability, proximate, ultimate and elemental analysis was conducted for four typical Indian high-ash non-coking coals and their elemental compositions were well correlated with the specific gravity of coal. The results obtained in this study provide some essential information to the coal-processing engineer for efficiently operate and control the process. Furthermore, the beneficiation potential of air dense medium fluidized bed was experimentally evaluated and compared with the results obtained from an operating wet beneficiation plant. Based on this comparative study the air dense medium fluidized bed is established to be a possible alternative to the conventional wet beneficiation method for beneficiating Indian coals with Ep values in the range of 0.03 to 0.06

Sep 1, 2012

By Verónica Fernández, Jaime Solari

"The Chilean Environmental Impact Assessment System (EIAS) of investment projects was created in 1994, date in which the General Environmental Law was enacted. The compulsory environmental approval of projects began in 1997 when the Regulation (S.D. 30/97) was officially issued. By beginning late to regulate the environmental effect of investment projects, Chile could take advantage of the international experience in the matter and therefore, the EIAS has many of the attributes of successful environmental assessment systems elsewhere. Thus, the main characteristics of the Chilean EIAS are: preventive, single-window, specific to certain projects, multi-agency assessment at the regional scale, 3 kind of applications, deadlines, citizen and native communities participation, link to relevant permits, definite conditions of approval/rejection, review of applications by an ad hoc institution. The Chilean EIAS has allowed during the period 1997-2013, the review of 21,110 projects for a total investment value of US$ 408 billion, of which a 76% have been approved. In the case of the mining projects, the corresponding figures for the similar period are 1,257 projects for a total investment value of US$ 119 billion, of which 78% projects were approved. The experience derived from the environmental impact assessment of mining projects indicates that Chile has been successful in linking together mining development with environmental protection. There is still little prejudice against mining and this is a still a largely welcome economic activity at all levels in the relevant regions of the country. The challenge that mining companies face today in Chile is to improve the sustainability of projects and operations, by learning to share scarce and valuable resources (water, glaciers, renewable energy) with the local and native communities, through a process of dialogue whereby mining development also generates benefits for these communities."

Jan 1, 2014