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By Williams Calderon, César Arredondo, Gonzalo Montes-Atenas

The quality of final concentrate in froth flotation circuits is largely dictated by the correct implementation of the froth washing operation in flotation cleaning stages, which are commonly installed in column flotation cells. In flotation plants, this aspect has been largely overlooked and the froth washing is restricted to the use of perforated piping through which process water flows producing a similar effect to that observed in "fountains": jet created with low energy crosses the froth phase washing out entrained particles as well as particles weakly attached to bubbles. The aim of this research study is to assess the efficiency of traditional froth washing systems theoretically and experimentally. A theoretical model was implemented using Fluent® software where a jet of variable speed was introduced in a continuous soft matter phase with physical properties similar to those observed in a froth phase in wet and dry conditions. In addition, a simple experimental protocol was designed to validate the model. It was found that the water process jet-like flow influences the behavior of 2 to 3 times the equivalent volume in the froth phase. Such influence zone is dramatically reduced as the froth phase becomes drier. These results were confirmed by the experimental findings indicating that a better froth washing technologies must be assessed and implemented. Some aspects of the ideal froth washing system are derived and discussed in details.

Jan 1, 2014

By William Skinner, Ishmael Quaicoe, Jonas Addai-Mensah, Ataollah Nosrati

To date, intractable ore specific operational challenges such as poor heap geotechnical stability, permeability and high acid consumption rates associated with low grade (~1 wt%) nickel (Ni) laterites still makes the adoption of heap leaching processing unattractive. This paper presents some highlights of drum agglomeration, column leaching and characterization studies undertaken to foster the understanding and knowledge of some of the desirable product attributes of -2 mm and -15 mm, low grade saprolitic (SAP) and goethitic (G) Ni laterite feed ores and their blends (SAP/G). For column leaching, 5-40 mm agglomerate beds were continuously irrigated with 200 g/dm3 H2SO4 solution at 8.5 dm3/m2/h rate over 100 days. Ni, Co, Fe, Al and Mn extraction rates, free acid concentration, agglomerate bed slump and structural changes were determined as a function of time. The results show that at equivalent feed masses, except -15 mm G which displayed slower, pseudo-layering based behaviour, all the feeds (single and blends) displayed coalescence controlled agglomeration behaviour at varying binder dosages. Whilst the agglomerate compressive strength of the G ore was markedly higher than that of SAP ore, those of the blends were substantially similar. At fixed column leaching conditions, the Ni/Co extractions and acid consumption were higher for SAP ore whilst the agglomerate bed slump was lower than those for G ore. The bed of agglomerates produced from -2 mm G/-15 mm SAP blend was more stable than that for the -2 mm G/-2 mm SAP blend agglomerate, the latter experiencing blockage within 24 h of acid irrigation due to agglomerates breakdown. The Ni/Co extractions and acid consumption rates obtained for agglomerates of -15 mm G/-2 mm SAP blend were lower than expected based on the ratios of the SAP and G ores within the blend composition. The findings suggest that judicious saprolitic and limonitic ores’ blending could reduce acid consumption rate, improve the agglomerate bed robustness and enhance bed percolation behaviour under prolonged acid irrigation periods during heap leaching of lateritic ores of variable mineralogy.

Jan 1, 2014

By Érica Linhares, Anderson Silveira Lopes, Aline Costa

In the production units of ferromanganese alloys wastewater are generated. They mainly arise from gutters of drainage water from warehouse of raw material (manganese ore, reducing agents and other), product and slag. This wastewater, in general, may contain particles that will suffer difficulty to naturally decant, giving the water turbidity and color characteristics. Thus, this study aims to characterize the effluent, the treated water and the sludge from the sedimentation tank from the one main Brazilian plant. The investigated characteristics were: turbidity, total solids (TS), suspended solids (SS), dissolved solids (DS), pH, Eh, COD (chemical oxygen demand), residue classification and chemical analysis by ICP - OES. The turbidity before treatment was 417 NTU and after passing through the tank, 44 NTU, a figure slightly higher than the emission standards for Class 1 regulated by the Brazilian environmental legislation in force. The values for TS, SS and DS of the effluent were 225, 114.3 and 110 mg/L, respectively. For the treated water the values were 93, 48.3 and 45 mg/L for TS, SS and DS, respectively. The sedimentation process was able to reduce by 21 % of the COD. In the test of loss on ignition (LOI) from the tank bottom sludge were observed losses of 29.35 %, while the volatile analysis found 20.70 % of volatiles in the sample. It was determined that the concentrations of Al, Fe, Mn and S are, respectively, 0.1875 mg.L-1, 0.3071 mg.L-1, 0,789 mg l-1 and 0.00828 mg.L-1, values above the maximum allowed by law. Based on the analysis of X-ray diffraction, the identified minerals in the sludge were quartz, muscovite, kaolinite, calcite and albite.

Jan 1, 2014

By Mahdi Shevrini, Hamed Haghi

"In this research, the operation of screen classifying in silica processing circuits was investigated and modified by replacement of available trommel screens with teetered bed separator (TBS). In addition the effect of the mentioned replacement and addition of attrition scrubber on quality of final product, impurities removal, recovery and production rate were inspected. Considering screen efficiency problems to achieve certain particle size distribution, hydraulic classifying system was selected instead of trommel screens. Application of suggested plan improved quality and particle size distribution of produced silica significantly. Optimization of size classification in process circuit resulted in increase in production rate up to 21% (from 67% to 81%), silica recovery (from 68.35% up to 83.11%) and relative enhancement in removal of impurities such as Fe2O3 and TiO2. After optimization and stabilization of grinding and size classification section, industrial attrition scrubbing tests were carried out and the best solid percent and retention time were determined i.e. 70% and 6 minutes, respectively. Using sodium carbonate during attrition scrubbing, has major effect on removal of surface coating and staining especially sharp increase in clay removal; therefore 2 kg/t of sodium carbonate can be optimistic point of industrial procedure for this silica processing plant. It should be mentioned that application of attrition scrubbing which is followed by screw classifier for de-sliming were useful for better cumulating of particles in the range of appropriate liberation degree (+106-300µm) and efficient removal of metallic (iron and titanium oxides) and non-metallic (clays and feldspars) impurities."

Jan 1, 2014

By Y. H. Hu, X. X. Zhang, Z. F. Dai, H. J. Huang, Q. S. Huang

"In order to get a more comprehensive understanding of the interaction of fine fluorite particles and bubbles, the electro-flotation was conducted, a high speed CCD was used to determine the bubble size distribution, and the results were analyzed using the models of collision and attachment. The electro-flotation was performed in a modified Hallimond tube. The results show that for different fluorite with size of 0 -10µm, 10 -38µm, 38-74um, there is a matching range between the different particle sizes and cathode aperture size (38um, 38um, 74um) to reach highest recovery. In addition, improving the concentration of collector is benefit for the flotation recovery due to the ability of collector to decrease the bubble size and prevent the merger of bubbles. Furthermore, theoretical calculation of collision, adhesion probability and collection probability is in agreement with the experimental data for electro-flotation recovery of fluorite.INTRODUCTIONFluorite is widely distributed, and has been found in more than 40 countries around the world. As fluorite minerals are easy to float, flotation is used as the best method of the current recovery of fluorite (Yang and Ai, 2016; Chen et al., 2017). In the field of mineral processing, the flotation of fine particles is particularly difficult, caused by the small quality and large surface (Sun et al., 2006). Flotation is now considered to contain three subprocesses, including the collision, attachment and detachment between the particles and bubbles (Sun et al., 2011). The collision of particles with bubbles is related to factors such as particle size and density, bubble size, bubble rise rate (Qin et al., 2012). Zongfu Dai et al. (2000) summarized the particle-bubble collisions models in detail and compared the experiment results with the model predictions. However, particle-bubble interactions occur in complex and turbulent flotation environments (Xing et al., 2017). Both thermodynamics and dynamic factors affect the adhesion of particles on bubbles surface (Schulze, 1989; Shahbazi et al., 2010). Scheludko et al. (1976) believes that the necessary condition for successful adhesion of particles on bubbles is that the contact time is greater than the induction time. The probability of adhesion between particles and bubbles increases with the increase of bubble size, but if the particle size is too small, the probability of adhesion decreases instead (Ren, et al. 2014; Norori- McCormac et al., 2017). After the particles adhere to the bubble surface, the particles will slide down to the bottom of the bubble due to gravity. At this point, the gravity, inertial centrifugal force and fluid force promote the desorption of particles from the bubble surface, while the surface tension, surface hydrophobic force maintain the stability of particles-bubble combination (Ralston et al.,2017). In addition, in the process of rising to the foam layer, desorption can also occurs. The purpose of this study is to observe the flotation behavior of fine fluorite with different size and to get a more comprehensive understanding of the interaction of fine fluorite particles and bubbles."

Jan 1, 2018

By Shuji Owada, Mayumi Ito, Takehiko Nishimura, Toru Yamashita, Sadayuki Shinozaki, Takashi Ando, Tomoe Ota

Electrical disintegration (ED) was applied to Nantun coal (China) in order to improve liberation of coal substance for the pretreatment of producing “Hyper Coal” of which the combustion gas was planning to inject directly to turbine for power generation. It has been found that many cracks generated in the ED were existent at phase boundaries with mineral matters and liberation of coal substance became much higher than that in mechanical comminution methods such as roll crusher. Since the ED occurred more easily (with lower voltage applied) for the coals of higher mineral content, it is considered that this method could make a better contribution especially to comminute middling coals. We also found that the ED technique could apply not only single particles but also to coal particles assemblage, keeping almost the same or higher disintegration efficiency. In the mineral matters, Si and Al components were preferentially well liberated by the ED.

Jan 1, 2003

By Christopher Tucker, Marcello Veiga

Social issues are increasingly recognized as significant inhibitors to mineral development projects. Increasingly social risk is being recognized as a key factor determining the success of a mineral investment. Groups opposed to a mine for social or political reasons often use environmental impacts, real or perceived, to prevent mine development. These risk factors depend largely on cultural perceptions of mining activities and must be understood as such in order to be appropriately managed. A first step to addressing social issues is inclusive, transparent and meaningful engagement of stakeholders. This process allows stakeholders to understand what the other parties value in order to collectively establish a common currency for development and the creation of mutual value. Expanding the scope of benefits and values a mine can bring is of increasing importance to mining companies who typically consult outside specialists remote from the mine site and late in the development timeline for this purpose. Training technical staff, engineers and geologists, who make initial and ongoing contact with local interests, in a holistic approach to mine development is crucial to successful and economic mineral development projects. Further extending this conversation to the general public, media governments and non-governmental organizations is a necessary step in developing a meaningful discourse on the benefit of mining activities.

Jan 1, 2014

By M. Wright, A. H. Mwale

This paper examines the combination of unit technologies in a minerals beneficiation train, and explores the inter-relationship between energy input and water consumption for a given mineralogy and product recovery, as these are two critical environmental issues which affect the overall viability of many minerals plants. In particular, we review constitutive relationships for each of the sub-processes of comminution, flotation, and tailings dewatering, and suggest how these might be integrated into a unified hybrid model, with particle size distribution as the key design variable. Such a model can then be used to explore the trade-offs between different performance objectives (be these technical, economic or environmental) as part of a multiple-objectives optimisation exercise. In this way, it may become practical to envision situations in which concentrate grade and recovery are sacrificed, marginally, in order to reduce energy demand in comminution, and improve overall water recovery. This becomes more relevant as the industry commits to advancing the sustainable development agenda in the face of the increasing life -cycle costs and impacts of minerals processing operations, coupled to declining ore body grades, and the desire to maximise recovery of minor and trace elements. Some specific observations for copper are offered.

Jan 1, 2003

By Ersin Yazici, Ahmet Bas, Haci Deveci

Pregnant leach solutions from waste of printed circuit boards (WPCB) leaching contain many impurity metals (Fe in particular) at significant levels. These impurities should be reduced to acceptable levels to avoid problems in downstream recovery processes e.g., low current efficiencies in electro-winning of copper from sulfate solutions in the presence of ferric. In this study, removal of iron in the form of goethite from synthetic (30 g/L Cu2+ and 1 M SO42-) and real leach solutions of WPCB was studied in some detail. The influences of initial concentration of iron (1-4.5 g/L Fe3+), pH (2.5-4.0), temperature (80-90°C) and seeding (23.5 g/L) were investigated over a period of 4 h. A significant increase in the iron precipitation was observed (i.e., from 68% to 96% over 4 h) with rising the pH from 2.5 to 4.0. The addition of seeds had also increased the removal rate over 4 h albeit to a limited extent i.e., from 96% to 99%. For the real leach solutions of sulfate (H2SO4-H2O2) and sulfate/chloride leaching (H2SO4-CuSO4-NaCl), precipitation of iron was found to be 63-73% (pH 2.5) and 93-98% (pH 4.0), respectively. The precipitates were further characterised by SEM-EDS analysis which showed the presence of copper (1-25%) in the precipitates indicating significant copper co-precipitation from the solution. These copper losses can be attributed to the formation of copper compounds such as anthlerite and brochantite within the range of pH (2.5-4.0) tested. This study showed that iron can be readily removed from synthetic/real leach solutions of WPCBs to a large extent (=93%) at the expense of high copper losses particularly at pH 4.0.

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 V. A. Feofanov

Technogenic water of ore mining enterprises, nonferrous metals operations, the enterprises of electroplating and instrument making, containing copper in the form of those or other connections can serve as perspective sources on receiving the copper-bearing raw material. Extraction of copper from the given water also solves a problem of water treating from a toxic component that reduces environmental load at evacuation of water in an open basin. The method of case hardening allows extracting copper selectively with reception of a deposit with the content of copper up to 70%. Weakness of the method is its efficiency basically in acid reduction, and also its low degree of copper extraction. On the basis of case hardening the method of galvanic coagulation is devised. It is based on the work of a short-circuited galvanic cell of iron-coke at variable contact of coupled metals components among themselves, cleared by the oxygen of air. The following processes of galvanic coagulation are considered: ? Extraction of copper; ? Formation ferrites of copper; ? Copper sorption on just-aggregated oxide forms of iron. Establishing conditions for passing the given stages provides an opportunity of copper extraction from technogenic water at any value of ??, content of salt and concentration of copper with reception of a compact deposit from which it is possible to extract copper by the known ways of enrichment and metallurgy. Investigations on optimization and intensification of galvanic coagulation with the purpose of reception the maximum rich deposit on copper have shown that the average contents of copper in a solution of 100~200 mg/dm3 the contents of copper in a deposit is 6%~10% at extraction 85%~90%, depending on characteristics of treated technogenic water. Using methods of scanning microscopy it is determined structures, composition and mechanism of phase formation in investigated electro-chemical process. The second stage of galvanic coagulation increases a degree of copper extraction up to 98%~99% that allows returning the cleared waters in circulation for waste recycling or evacuation in an open basin. Nowadays the method of galvanic coagulation is the most acceptable for copper extraction from technogenic water both from the point of view of efficiency and instrument setting that allows applying the method in conditions of the working enterprises.

Jan 1, 2014

By Paolo Bevilacqua, Paolo Antonini, Lorenzo De Lorenzi

"Ceramic production requires large quantities of K-feldspar, which is commonly sourced from granites, alkali-granites, and feldspathic sands. These rocks contain other minerals, such as quartz and plagioclase, which are undesirable for ceramic production. Due to the coarse mineral grains that constitute these rocks, a reasonable liberation is achieved at a relatively coarse particle size.The feasibility of feldspar-quartz separation using a dynamic dense medium separation system has been investigated as an alternative to flotation techniques. The use of a two stages cylindrical vessel (Tri-Flo) was preferred to a conical vessel, due to the improved separation efficiency.In a full-scale processing plant, a dense medium separation process can be used as a K-feldspar preconcentration step. This reduces the amount of material to be treated in the more expensive processes, such as finer comminution, flotation or magnetic separation.A comparison between commercial raw materials for the ceramic industry and the “rich in feldspar” products of the Tri-Flo process is reported, and the validity of the process is demonstrated."

Jan 1, 2003

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

By P. Knüpfer, B. Babel, M. Rudolph, F. Perez Maldonado, U. A. Peuker, L. Ditscherlein

"In heterocoagulation processes for the separation of mineral particles, the most famous being froth flotation, the main characteristic of separation is a differing wettability of the constituents to be separated. This most crucial property in the economically important process of flotation is often only and incompletely, quantitatively described in terms of contact angles against water. A water contact angle larger than 90° is referred to as hydrophobic and hydrophilic vice versa. Looking at Young’s equation shows that it is actually the surface energy of the solid in interaction with the surrounding phases and their surface energies (or surface tensions for liquids) which describes whether there will be hydrophobic/hydrophilic hydration interactions leading to attraction or repulsion. This, we have previously published for various more or less hydrophobic minerals in correlation to their flotation response, i.e. flotability (c.f. Rudolph & Hartmann, Coll.Surf.A 513, 380-388). In the same paper we also discussed the heterogeneity of wettabilities as assessed with the novel method of inverse gas chromatography. Furthermore we have also reported on hydrophobic force distributions as assessed with atomic force microscopy which are as well due to wettability heterogeneities (c.f. Fritzsche et al., Coll.Surf.A 459, 166-171).In this paper we present wettability distributions of different substrates and particles with various surface roughnesses/shapes and degrees of hydrophobization as assessed with iGC, AFM and dynamic sessile drop analyses. We are putting the results in context in unifying models and present methodologies helpful to make use of the fundamental information and their impact on the actual industrial separation process in fundamental process models. Besides froth flotation we also emphasize the impact on selective hydrophobic flocculation process."

Jan 1, 2018

By C. Dorfling, S. Bradshaw, J. Eksteen, M. Khesa, C. A. Snyders

Titaniferous ores serve as a major feedstock for the production of a white titanium dioxide pigment, a titanium metal and several other titanium-based products. Such ores exist mainly as heavy mineral sands. Ilmenite is upgraded to intermediate products namely synthetic rutile and titania slag through the synthetic rutile route and the reductive smelting route respectively. Tronox KwaZulu Natal Sands (Pty) Ltd recovers high titania slag via the reductive smelting process while slag is used as a feedstock to the pigment industry and furnace dust from the gas cleaning plant is disposed as waste. Previous investigations have shown that such furnace dust can contain significant amount of titanium-bearing minerals. This study looks at the characteristics of the furnace dust obtained from Tronox KwaZulu Natal Sands and investigates a possible high temperature recovery route in detail. The furnace dust was examined by using x-ray fluorescence, x-ray diffraction, microscopy and laser-diffraction size analyses. The characterization work showed that the furnace dust was rich in titanium and iron, containing 49.4 wt% ??????2 and 29.5 wt% ????2??3. These oxides were associated with Si, Mn, K, and Al oxides as impurities. A Carbolite® vertical tube furnace was used to investigate the extent of formation of titania slag and metallic iron on a laboratory scale at 1500°C, 1600°C and 1650°C. The laboratory reduction tests revealed that the slag samples with an equivalent titanium dioxide content ranging from 70.9 -76.9 wt% at 1600°C and 1650°C could be obtained. The Fe content of the metallic iron samples produced ranged between 93.0 and 97.1 wt%. The experimental results were found to be in relatively good agreement with the FactSage simulations, both of which demonstrated the potential of producing a titania slag and a metallic iron from the furnace dust.

Jan 1, 2018

By M. Mezzetti, E. Anders, O. Popov, P. Hoske, H. Lieberwirth, M. Voigt

"The material breakage induced by high energy electric discharges is known in general as electric impulse technology. This technology can be used for processing solid materials, such as rocks and ores. The electric impulse technology has been around for about 60 years, originally developed and intensively investigated by Russian researchers. However, the application fields have been limited to research and laboratory scale projects. Currently, there are new attempts to transfer this technology into practical industrial applications. Practical examples include drilling of deep geothermal wells with an electric impulse driven drill-head. Traditional comminution implies high energy consumption, hence, high costs. The Electric Impulse Technology is interesting for comminution of mineral and complex ores since it could allow improved recovery and energy reduction, thus resulting in significant savings. Another advantage is the dust free processing, which contributes to make minerals processing environmentally friendly. The use of electrical comminution for processing complex ores is investigated within the ELIZE research project funded by the BMBF (project No. 033R161 A) and industrial partners. The main objective is the development of an industrial scale electrical comminution machine. The first development stages include the investigation and characterization of the electric impulse induced weakening on rocks and ores. The characterization results of the preliminary trials at the microstructural scale on granite, skarn and greisen will be presented and discussed in this article. INTRODUCTION The pioneer work in the area of electric impulse technology was conducted by Russian researchers about 60 years ago [1]. While there have been some successful attempts to transfer this technology into practical applications, such as rock processing [2], laboratory processing of mineral ores [3–5], recycling [5] and geothermal drilling [6–9], the jump into practical industrial large scale application has not been accomplished yet. The Institute of Mineral Processing Machines of the TU Bergakademie Freiberg currently leads a project which can be seen as the next logical step for the technology transfer to industrial applications, namely, the development of continuously operating complex ore processing machines based on the electric impulse technology."

Jan 1, 2018

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 K. Bru, D. B. Parvaz

"Electric pulse fragmentation (EPF) is an innovative technology that uses high-voltage pulsed power (HVPP) for the selective comminution of the treated material. Highly energetic electrical pulses are used to fracture rocks at mineral grain boundaries, resulting in extensive micro-cracks and/or complete fragmentation of the processed particles depending on the applied energy. In this study, the EPF technology was applied to a low-grade schist ore containing cassiterite, in order to investigate its influence on the selectivity of the fragmentation. The impact of EPF on subsequent comminution steps was studied by combining either the EPF technology or jaw crushing (used here as conventional crushing) with subsequent impact crushing. The results confirmed the potential of the EPF treatment for a selective fragmentation of the schist ore. This gave the potential advantages of reducing the total energy consumption in the comminution circuit and of improving the recovery of cassiterite during concentration processes. INTRODUCTION The rise in the world consumption of metals combined with the depletion of most of the high-grade ore reserves leads to an increased need to process ores of lower grade, with a more complex mineralogy. To recover the valuable minerals contained in such ores, fine grinding is required, but this process has high energy requirements and leads to the production of a large amounts of fines, which can impede the performance of later concentration processes such as gravimetric separation and flotation. Addressing this issue is a major challenge for the mining industry. Selective comminution methods have the potential to significantly contribute to the profitable exploitation of these low-grade ores by generating cracks specifically at mineral grain boundaries rather than randomly as in a conventional mechanical comminution system. This allows the liberation of valuable components from the feed material without overgrinding, i.e. this prevents unnecessary size reduction of already liberated grains, which leads to a reduction in production of fines and in energy consumption. In addition, rock not fragmented by the process are usually weakened by the dense fracture network generated, which increases grindability of the rock (Wang et al., 2011)."

Jan 1, 2018

By Mingxia Liu, Qi Liu, Tao Jiang

"In addition to physical parameters such as small mass and high specific surface area of fine and ultrafine minerals, chemical parameters such as the adsorption affinity of collectors on the minerals also plays an important role in fine particle flotation. In this study, we have examined collectors with two different ionized groups, carboxylate and hydroxamate, on the flotation of fine niobium oxide (pyrochlore). To facilitate comparison, two hydrocarbon radicals were tested: octyl and oleoyl, which led to four collectors that were studied: octyl hydroxamic acid (OHA), sodium octanoate (C8OONa), oleoyl hydroxamic acid (C18HA), and sodium oleate (NaOl). Small-scale flotation and isothermal microcalorimetric titration measurements were performed to determine the flotation recoveries of different sized pyrochlore and the enthalpic behavior after adsorption of the collectors on pyrochlore. It was found that the flotation performance of the carboxylate-based collectors was generally inferior to hydroxamate-based collectors. Sodium octanoate could not float pyrochlore irrespective of the particle size of the pyrochlore tested. With a longer hydrocarbon chain, sodium oleate was effective to float the relatively coarse pyrochlore (>20 µm) but its collection efficiency dropped sharply for particles smaller than 20 µm. On the other hand, the two hydroxamate-based collectors, octyl hydroxamic acid and oleoyl hydroxamic acid, showed good collecting ability to both the coarse and fine pyrochlore. The isothermal microcalorimetric titration studies indicated a consistent correlation of chain length with floatability of collectors for relatively coarse pyrochlore, as well as a positive relationship between the adsorption affinity and fine pyrochlore flotation recoveries. The key finding of this study was that efficient fine particle flotation could be achieved when strongly chemisorbing collectors were used.INTRODUCTION The first detailed study of the effect of particle size on flotation was made by Gaudin (1931) with sulphide ores. In 1942, Gaudin again demonstrated that (Gaudin et al., 1942) fine particles possess different flotation properties from larger particles. Since then the effect of particle size on froth flotation has been an important research topic by many researchers, e.g., Gaudin (1957), Miettinen et al. (2010), Warren (1976) Jameson (2010), summarizing the behavior of fine particles in terms of their low particle momentum, leading to low rate of collision with bubbles which reduces the chance of adhesion. The suggested remediation methods are mainly based on two approaches: increasing particle size or decreasing bubble size (Warren, 1976). Sand-fine splitting followed by separate flotation treatment of the sand and fines, using deep flotation cells, using starvation quantities of collectors, and using long flotation times, are also strategies to address the problems of fine particle flotation."

Jan 1, 2018

By Fedotov Pavel

"Today the main objective of improving the process of ore dressing is to reduce energy consumption and performance of the basic rule of auxiliary enrichment processes. One of the modern means of ore destruction with a minimum of energy consumption is the interparticle fracturing, for example in the roller press. There still remain the unsolved problems of the energy consumption determination and the particle size distribution of the crushing product .Existing methods for determining these parameters are empirical and require considerable expenses and time. The improved finite element was developed to solve these problems using finite element contact interaction of the rock. Also it was developed to clarify the stress-strain and the rock fracture energy in a layer. These elements are used to study ore destruction in the layer and allows to create a model taking into account the interaction of crushing particles surfaces. The same algorithm was developed determining crushing product particle size distribution in the layer on the base of the Bond’s theory of crushing. The presented finite element model allows to determine the quantity of strain energy and particle size distribution of crushed product during the destruction processes of the material in the roller press with fair accuracy."

Jan 1, 2014