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By P. Raghavan1

Reverse froth flotation experiments were carried out in the laboratory using two different types of kaolins for the separation and removal of coloring titanoferrous impurities from cryo-filtered clay after subjecting to high shear pre-treatment. This high shear pre-treatment consists of high shear agitation of a high solids clay slurry with the dispersant (high shear dispersion, HSD) followed by high shear agitation with the collector (high shear conditioning, HSC). After this pretreatment, the slurry is diluted and reverse flotation is carried out. One sample is from, Gujarat, India (Mamuara clay, ?MC?) while the 2nd sample is from Amberg, Germany (AKW clay, ?AC?). While MC consisted of 89% particles below 2µm and analyzed 1.06% of TiO2 and 0.29% Fe2O3 and measured a brightness of 83.4 %ISO, the corresponding values for AC are 67% below 2µm, 0.3% of TiO2? 0.49% Fe2O3 and 83.4 %ISO. The flotation performance is found to be greatly influenced by the conditions of high shear treatment. Important variables are HSD intensity (rpm), HSD time, HSC intensity (rpm), HSC time, HSD/HSC time ratio, ?HSD+HSC? total time etc. Higher shear intensities favor both the impurity liberation and collection. For both clays, it could be shown that impurity removal increases as total pretreatment time (?HSD +HSC? total time) increases up to a certain limit. For MC, the HSD time was only half or less than that of HSC time, while for AC, HSD time is at least twice (or more) than HSC time which is just an opposite manifestation. This is believed to be due to the striking differences between these two clays. Most importantly, the shear frequency is found more influential than the shear rate for the overall flotation performance for both clays. Interestingly, at high shear frequencies, i.e., when a stirrer with more number of teeth on the rotor is used, the ?HSD+HSC? total time is greatly reduced. Again, increased shear frequency helps to reduce flotation time and significantly improves flotation performance. At optimum conditions, product titania reduced to 0.35% for MC whereas the same reduced to 0.13% for AC. The product of flotation of MC measured 85%ISO brightness while that of AC measured84.6%ISO thus enhancing the value of the final product. It could also be established that the high shear pre-treatment shows better flotation performance than that due to collector dosage. Keywords: high shear dispersion, high shear conditioning, titanoferrous impurities, shear rate, shear frequency, brightness, clay recovery, Mamuara clay, AKW clay

Sep 1, 2012

By S. V. Bogdanov, S. I. Grishaev

"The article presents the materials about the appropriateness of the use of rental indices to assess the effectiveness of the use of deposits of rare earth elements (REE). The authors suggest from the standpoint of rent payments to rate for the owner the possibility of using the anticipated rental income as the indicator for the analysis of preferences and economic significance of enrichment of extracted raw materials in the emerging field of rare earth metals (REE). Usually from ore mined at the fields, for flotation technology to produce concentrates with collective REE, then they are subjected to chemical-metallurgical processing of the received products are divided into pure oxides, chemical compounds or isolated from them pure metals and alloys. This commercial product is shipped to the buyer. REE were a non-renewable natural resources, so the calculations for determining differential and specific rent showed that during the development of the technologies of mineral processing of a specific field it is necessary to consider what the expected rental income depends on the magnitude of differential rent is related to the volume of production of REE for the whole planned period of exploitation of natural resources. This income is determined by the amount of stock field. For long-term exploitation of the deposit is observed in almost direct proportional dependence between the annual differential rent and the rental income. The decrease in rents in the long run is determined by the change in the composition of ores included in the extracted raw materials and the balance between light and heavy REE. The largest 70% reduction of the rent projected for ""cerium"" fields, while for ""yttrium"" these losses are considerably smaller. Tomtor, Chuktukon and Katuginskoye Russian deposits are characterized by a level of rent that is comparable to the mastered foreign sources of REE. Thus, the enrichment of minerals with REM in the domestic deposits is quite competitive at the world level. INTRODUCTION Deposits of rare earth metals (REE) are non-renewable resources that should be developed and used so that it would be possible to provide a reduction due to payment of appropriate resources for future generations. This compensation, due to the reduction of natural resources, can be carried out both in natural and in economic terms (1). When analyzing economic compensation options, particular attention should be paid to rental income in assessing the attractiveness of using different REE deposits. It is known that absolute and differential rents are summands when calculating the value of natural rents. The value of the absolute natural rent is proportional to the unit price of the product obtained from mineral raw materials and sold on the commodity market. Limitations, as well as the use in production processes and business, contribute to the gradual reduction of natural resources, which increases their consumer value and affects the price of commodity products from primary raw materials."

Jan 1, 2018

By V. K. Gupta

Selection of mill size for reducing a feed material of a given size to the desired product size is generally based on the specific energy estimate obtained from Bond test. Over the last thirty years or so, an attempt has been made to develop a more accurate and powerful alternative approach based on the characterization of the particle breakage kinetics and material transport through the mill over a range of operating conditions of interest and correlating the degree of size reduction achieved with the net specific energy input to the mill. Particle breakage kinetics are described in terms of the specific grinding rate and breakage distribution parameters for the individual size fractions. Precise estimates of these parameters and the net energy input to the test ball mill (a laboratory or pilot scale mill) are important for development of desired energy-size correlations. In this context, three tasks are important: (a) preparation of the feed charge, (b) design of batch grinding experiments and (c) computational technique used for estimation of the breakage rate and breakage distribution parameters. This paper highlights several aspects of these three tasks that have been overlooked by researchers working in this field, and describes a more appropriate approach for estimation of model parameters and specific energy input. Several examples are included based on the data available in the literature and those generated in our laboratories to illustrate important points.

Sep 1, 2012

By Sergey Romanenko, Tatyana Aleksandrova, Karen Arustamian

"Current status of question about grinding stage effect to electrochemistry parameters of operation preparation slurry before intermediate selective flotation was assessed in the present scientific work. Needs of more detail study chemical reactions in the slurry preparation and flotation processes were shown. The ores are polymetallic sulphide type and the one are most difficult for mineral processing. The methodology allows increase information base during floatation tests. Ionometric methods and elements of neural network have been used in the study of mineral processing questions.We have also identified the relationship between the received values of the electrochemical parameters and the technological results in selective flotation. The optimal values of the electrochemistry parameters in operation of the preparation slurry before selective flotation has been found. The main effect of using the proposed methodology is to obtain scientifically based solutions to improve the technology parameters of flotation polymetallic sulfide ores. Challenging issue of selectivity of sulphide-polymetallic ores will be considered using case study of sulphidepolymetallic ores. It was shown that several factors are formed in ore grinding: formation of hydroxyl oxides of iron compounds, copper cation leaching, metal-sulphide and metal-sulphite complexes formation. The chemistry was revealed for current processes in slurry preparation operation before selective flotation. Quantitative assessment of interrelations between electrochemical parameters of slurry and process performance was given with using electrochemical control methods. Neuron network-based model was estimated based on data array and was allowed to establish optimum electrochemical conditions of metal-sulphite complex formation to provide maximum efficiency of selective flotation.INTRODUCTIONPhysical and chemical processes that take place in ore grinding have a significant impact on flotation selectivity and can cause low selectivity of the flotation process. Today this issue is given much attention. In the paper [1] it is pointed out that sulphide oxidation products and slurry components, such as sulphide ions, metallic iron and its oxidation products, have effect on flotation performance. So, metallic iron has impact on metal-sulphite complex formation as a result of oxidation-reduction reactions as follows:"

Jan 1, 2018

"The effect of operational conditions, such as air flow rate, impeller speed and solid concentration, as well as the effect of solids concentration and frother dosage, on the bubble size distribution produced in a lab scale flotation cell, were investigated. The cell was operated under batch conditions. The measurement of bubble size was accomplished using an automated photographic technique. The technique enabled fine and coarse bubble distributions to be measured in two-phase (liquid-gas) and three-phase systems (solid-liquid-gas). In each experiment, around ten thousand bubbles were characterized.This paper discusses the main results obtained using the new photographic technique and compares these with previous findings available in the literature. The results indicate that photographic techniques combined with digital imaging processing might become a standard technique for measuring bubble size distribution in flotation machines.HUT BUBBLE SIZE ANALYSERThe importance of having precise and reliable equipment for measuring bubble size distribution in industrial flotation machines has been widely recognized. The measurement of bubble size, particularly in three-phase systems, is rather complex due to the opaque nature of the pulp. However photographic techniques combined with ingenious sampling techniques are utilized for overcoming this difficulty. The technique named HUT, combines previously developed visualization methods with digital image processing procedures. In this technique bubbles and aggregates are exposed to a monochrome progressive scan camera. The acquired images are directly stored in a computer connected to the camera for post-processing. The sampling apparatus consists essentially of a vertical tube for collecting bubbles, a viewing chamber and a collection chamber, where particles carried by the bubbles are released. The function of the collection chamber is to maintain the viewing chamber clear for imaging purposes. Each image is automatically processed off-line, using digital image tools. In this paper the advantages and limitations of this new technique are described."

Jan 1, 2003

By Luís Marcelo Tavares, Juliana Segura

Comminution is one of the most energy consuming stages in a mineral processing plant. This consumption is not only related to the power supplied to equipment, but also to the indirect or embodied energy, mainly associated to materials that are worn during operation, including grinding media and liners. Until recently, preparation of iron ores in Brazil did not use comminution intensively, given that plants mainly produced sinter feed, natural pellet fines, besides lump ore. However, with decreasing ore grades, size reduction now occupies a centre stage in nearly all new plants. Technologies used up to date for processing low-grade iron ores in Brazil, in particular itabirites, have consisted of three or four stages of crushing followed by ball milling. A number of new plants are either being built or are currently being designed that will process the same type of ore, so that engineers are investigating alternative comminution routes. The paper analyses comparatively four comminution routes for processing a particular itabirite ore, many of which using technologies and layouts that have not yet been used in such application. Using data from bench scale and/or pilot-plant tests, the different routes are compared on the basis of sustainability principles in accordance to the Brazilian energy matrix, which is quite particular. It is concluded that if the sustainability criterion is used, then the optimal route would correspond to a circuit that uses HPGR technology with truncated feed followed by ball milling. Given the particular case of itabirite iron ores and specially to the one in the present work and the source of Brazilian energy, it is evident that indirect energy expenditure in comminution plays a significant role in greenhouse gas emissions when compared to direct energy, being the reason for the great attractiveness of HPGR technology. Evidently that these will have to be balanced against CAPEX, OPEX, NPV and other qualitative criteria, which can certainly lead to a different optimal circuit.

Jan 1, 2014

By C. Raghu Kumar

Hydraulic or teetered bed separators (TBS) are finding new avenues for application in the field of mineral processing. Floatex Density Separator (FDS) is a hydraulic/teetered bed separator capable of operating at high tonnage due to its advanced instrumentation. FDS/TBS is being used in Indian mineral sand industry for classification and segregation of different minerals. The purpose of this paper is to provide details on the performance of the plant scale FDS in recovering the chromite from feed (below 1mm size). Historically this feed has been processed using hydrocyclones and spiral classifiers; however, there is a strong trend now to employ teetered bed separators, thus allowing significant changes to be made in the plant for improving process efficiency. In the present work, the performance of the plant scale FDS is described in terms of partition curve (yield, cut size, classification efficiency/Ep) for different combination of process variables and also in terms of metallurgical grade and recovery. It is found that, efficient classification can be achieved at a maximum cut size of 380 µm with and the imperfection is also reported as low as 0.16. The grade of the underflow product is enriched as maximum as 52.2% Cr2O3 from a feed assaying 40.4% Cr2O3.

Sep 1, 2012

By T. A. Penzov

As a result of recent scientific and experimental studies new technical devices have been developed for monitoring and control the process of grinding. The description of microprocessor module MILLCONT 1 for control of the loading of the mill and microprocessor density control module DENSIMETER is given in the paper. The improved variant of the automatic system for ore grinding control in single-stage ball mill working in close cycle with a classifier with above mentioned technical means is shown in the paper. The loops for measuring and stabilization of the basic technological parameters (density of the ready pulp ? and fineness of grinding of the pulp ß) are described in the paper. The nowadays economic results in ore grinding process automation are given as well.

Jan 1, 2014

By Vladko Panayotov, Marinela Panayotova

"Recently, in order to extract metals, the industry is trying to process old metallurgical slag. The material requires very fine grinding that results in enhanced slime-formation. This in turn leads to problems in the course of the flotation process and to a loss of metal. In addition, it causes difficulties in the wastewater treatment aimed at water reuse. The aggregation and separation of the fine particles and their further subjecting to mineral processing would result in more efficient use of raw materials. Closing the water cycle also would be facilitated. The paper presents results from studying sixteen flocculation reagents, commercially available for treating municipal wastewater, including products based on nanotechnology, for their ability to rend the production wastewater in suitable for reuse in the flotation. It turned out that, from all studied reagents, the cationic C-587 is suitable for the purpose. Some of reagents were studied for their ability to flocculate selectively, in presence of coke fines, rich in copper fines which are produced at grinding of a slag from lead-zinc metallurgy. Most promising reagents are chosen, based on the chemical analysis of the flocculated materials. Open-cycle rough copper flotation experiments with the flocculated fines and recycled wastewater gave encouraging results."

Jan 1, 2014

By A. Singh, M. Ntlhane, V. Ross, M. Dlame

"Fine valuable particles are often lost to flotation tailings streams due to inefficient collection by air bubbles as well as passivation of surfaces by oxidation and slimes. The application of high-shear hydrodynamic cavitation devices (HCDs) to overcome this problem has already proven to be a considerable success in the industry. This paper details the results of further investigations that were undertaken at Mintek to better understand the mechanisms involved when preconditioning feed slurries in an HCD. By promoting inter-particle attrition and conditions of high shear within the reactor, cleaning of particle surfaces is enhanced as well as the formation of superfine (nano) bubbles which are believed to aid their agglomeration and subsequent collection by normal sized bubbles. In order to broaden the envelope of understanding with regard to application of the technology, rather than tailings material as investigated earlier, a Platinum Group Mineral (PGM) UG2 ore from the Bushveld Complex in South Africa was used in this study. The results of a series of batch flotation tests in a 10L Denver cell are presented, being conducted after the feed has been subjected to different methods of preconditioning. It was demonstrated that the preconditioning significantly improved the flotation kinetics of the PGMs, the optimum being obtained after around 20 passes through the reactor. This was accompanied by a much enhanced recovery-mass pull relationship and a significant improvement in the grade-recovery response. Significantly, the selectivity between the PGM and the deleterious chromite (expressed as Cr2O3) gangue more than doubled under these conditions. Modelling of the PGM data by means of the modified Kelsall model indicated that both the fast and slow floating rate constants were improved.INTRODUCTIONIt is well known that the flotation recovery of fine and ultrafine particles, typically less than 10 micron in size, is a challenge (Yoon et al., 1989; Miettenin et al., 2010). Although these particles are typically well liberated, due to their very low mass and inertia, the collision efficiency with air bubbles is low as a result of the inability of particles to penetrate the liquid streamlines around bubbles. Hence the probability of contact is often regarded as the ratedetermining step in flotation of ultrafine particles. Introducing more power into conventional flotation machines is likely to solve only part of the problem, as conventional mechanisms are effective only to a point in terms of shear and micro-turbulence. Further challenges are posed by the treatment of low-grade or oxidised tailings dump material, where valuables are passivated due to prolonged exposure to the atmosphere or slimes. Over the years, various mitigating strategies have been investigated, including the use of dissolved air flotation (Martinez-Gomez et al., 2013; Calgaroto et al., 2015), shear flocculation (Subrahmanyam and Forssberg, 1990), seed or carrier flotation (Tabosa and Rubio, 2010), sonication to clean particle surfaces (Aldrich and Feng, 1999; Newell et al., 2006), high intensity conditioning (Bulatovic and Salter, 1989; Chen et al., 1999; Tabosa and Rubio, 2010), and various electrochemical approaches such as changing Eh in order to promote formation of dixanthogen, dissolution of oxidation products by lowering the pH, activation by sulphidisation (Newell et al., 2006; Becker et al., 2014), and the use of alternative collectors."

Jan 1, 2018

There are some problems in the beneficiation of fine-grained oxidized iron mineral such as high cost, severe sliming, poor results and low recovery due to the fine disseminated size of the mineral. Taking several representative types of finely-disseminated oxidized iron minerals as examples, the author analyzed the main difficulties in the beneficiation of such kind of ores and discussed the existing problems in grinding-classification, technological process, flotation reagents and separation equipments and the resolvents of these problems.

Jan 1, 2014

By Juan Estrada, Mirtha Frómeta, Rubén Alcalá, Emilio Montejo, José Castellanos, Juan Berto, María Rivas

"The oxidized nickel ores from San Felipe deposit are composed mainly Smectites which gives to the pulps very unfavorable rheological .properties (cinematic viscosity and high shearing strength) for transportation processes (pumping), very low settling velocities and very low thickened pulps. These properties do not allow the preparation of high % solids, which affects the economic efficiency if a high pressure acid leach (HPAL) process is used. Pulps of close to 30% solids have very high BYS making pumping impossible. CIPIMM developed three technologies to solve these problems and to substantially increase the % solids in the pulps to be leached without a thickening step. These technologies are: • CIPIMM 2. At Preparation of pulps using additives. This method is based on the effect of some additives (inorganic salts) to improve the pulp’s properties. The use of this method allows increasing the % solids in the pulp up to 40% with good rheological properties • CIPIMM 2B. Preparation of pulps by thermal treatment of the ore previous to the preparation of the pulps. This method is based on the thermal destruction of the clays structure. Its use allows to obtain pulps with 50 - 60 % solids with excellent rheological characteristics. As a collateral effect, the Ni and Co grades increases by 10 - 15%. • CIPIMM 2C. Pulp preparation by chemical treatment. This method is based on the chemical transformation of clays, to obtain without thickening, pulps with 43- 45% solids and excellent rheological properties. The use of one of the three technologies depends on the chemical and mineralogical composition of the ores and the results of technical-economical evaluations to determine which one is the best alternative before running higher scale tests."

Jan 1, 2014

By D. Whittles, S. Kingman, S. Bradshaw, N. Miles

The influence of microwave energy at high electric field strength on ore strength has been investigated. Two ores of varying mineralogy were treated in both multimode and single mode microwave cavities. After treatment, any change in strength relative to untreated ore was established. It was shown that in the multimode cavity reduction in strength was related to the applied power level. Results of tests carried out in the single mode cavities showed that, for both ores, reductions in ore strength > 50% could be achieved in very short periods (<1 second). Thermal stress analysis showed that the mechanism of microwave induced failure was the development of tangential stresses at the grain boundaries. It was concluded that operation at 915 MHz with high power and short residence times gives feasible scale-up possibilities.

Jan 1, 2003

By K. Trybalski

Facing the optimization activities, which purpose is to minimize the copper processing costs, the main sources of their occurring were presented. In this purpose, the costs analysis was performed, divided to individual standings, for one of the polish copper beneficiation plants. It was proved, that the main component of the copper beneficiation costs is energy consumption, generated mainly in grinding and classification node, particularly by operating mills. The technological system ? grinding and classification node ? in KGHM Polska Miedz S.A., ZWR region Lubin was then selected to investigation. To evaluate the grinding and classification node, the energetic factors W were proposed, calculated on the basis of the energetic-technological data of process, given by node monitoring system. The correctness of the energetic factors selection to evaluate the work of this node and their practical application in industrial conditions was experimentally proved in other technological object. The selected technological object ? grinding and classification node ? was then mathematically modeled and optimized. The calculated energetic factors were the basis to build mathematical models, identifying industrial copper grinding and classification process. The models described correlation and character of dependency between factors and energetic-technical data of the process. These were regressive and neural networks models. On the basis of factors models, the optimization tasks were determined, which purpose was to select the optimal points of grinding and classification node work. Also, the estimated economical effect, possible to achieve after introduction of given monitoring values to grinding and classification node optimization system, was presented.

Jan 1, 2014

By I. Silin, H. Wotruba, J. Huben, A. Ognyanova

"With increasing shortage of raw materials, the beneficiation of ultra-fine ores will play a larger role in the near future. Many established process technologies do not yield satisfactory separation results for ultra-fine materials. Without selectivity, high-grade concentrates cannot be produced. The material at hand is a taconite which had to be ground to d(90) = 25 µm to guarantee liberation of the iron oxides. The comminution was done by High Pressure Grinding Roll (HPGR) and resulted in smooth surfaces and clear grain boundaries. This is an indication of selective grinding and mineral liberation. Further processing steps included selective desliming, magnetic separation as well as reverse flotation. INTRODUCTION During the last centuries, the processing of iron ores became increasingly important. The coarse-grained, so-called lump ores that are ready for direct usage in blast furnaces without further processing are becoming gradually less abundant. The processing of ultra-fine-grained ores, which in addition require a complex ore beneficiation due to the composition of the material, will progressively gain relevance with increasing resource shortages in the future (Arvidson, 2013). The term “ultra-fine” does not hold a precise definition in mineral processing. In this paper, “ultra-fine-grained” ores are defined by the required grind size for full liberation smaller than 20 µm. Many established mineral processing technologies do not yield satisfactory separation results for ultra-fine materials. Thus, they are limited in their application to produce high-grade concentrates suitable for sintering and pelletizing for direct reduction processes. The production of a high-grade iron concentrate (over 68% Fe) with low silica content (under 2.5% SiO2) is possible from both magnetite and hematite containing ore. In addition to the mineral processing technologies (magnetic and gravity separation, flotation), technologies for the liberation of fine-grained iron ores need to be developed and improved. In contrast to the conventional wet grinding circuit by means of tumbling mills, several future trends in dry and wet grinding and regrinding are already in use. These include technologies such as vibration mills (Palla®Mill), stirred media mills (Vertimill®), vertical roller mills (Loesche) and high-pressure grinding rolls (HPGR) (Jankovic, 2015). This study preliminary investigated the mineral processing of a low-grade, ultra-fine-grained, complex iron ore in a laboratory scale after dry grinding by HPGR to 90% < 25 µm without consideration of the grinding, milling, energy and classification cost."

Jan 1, 2018

By Alan Bax, John D. Lewins

"Platinum Australia Limited (“PLA”) is currently undertaking a Feasibility Study into the development of the Panton Platinum Palladium Project located in the Kimberley region of Western Australia. The Panton Intrusive is a layered, differentiated mafic to ultramafic structurally complex body that has undergone numerous folding and faulting events. This has resulted in a southwesterly plunging synclinal structure some 10 kilometres in length and 3 kilometres wide.High grade PGM mineralisation is hosted within a number of stratiform chromitite reefs within the ultramafic sequence. The focus of the Feasibility Study is on the Top Reef which is situated approximately 150 metres below the mafic/ultramafic interface. The average true width of this reef is approximately 1.2 metres and the reef has a defined resource is 10.1 million tonnes at an average grade of 6.1 g/t PGM + Au.The Palladium to Platinum ratio of the Top Reef is approximately 1.15:1 and the reef also contains an average of 0.4 g/t Au and 0.3 g/t other PGM’s. The Panton ore is considered refractory in nature and standard flotation techniques achieve a PGM + Au recovery of less than 65% with a concentrate grade of less than 100 g/t PGM + Au. As part of the Feasibility Study Platinum Australia in conjunction with their major shareholder Lonmin Plc developed a new metallurgical process which has achieved an overall PGM + Au recovery of approximately 80% into a high grade PGM concentrate which is suitable for feeding direct to a PGM refinery.THE PANTON PROCESSThe Panton Process incorporates a two-stage Milling and Flotation circuit with no cleaning stages to produce a low grade, high recovery flotation concentrate. Typically the concentrate mass constitutes 25% of the feed and has a PGM + Au grade of 25 g/t.This low-grade concentrate is subjected to calcination in a rotary kiln or fluid bed at a temperature of approximately 400 0C for a period of 60 minutes. This step is designed to render the platinum minerals soluble in cyanide and both the temperature and the duration of calcination are critical to the efficiency of the leaching process."

Jan 1, 2003

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 Ghislain Bournival, Cagri Emer, Seher Ata

"It is well known among flotation practitioners that the contact angle can be correlated with the amount of material recovered from feed by flotation. The contact angle of solids can easily be modified by the addition of a collector. However, some collectors also have frothing properties thus altering the solid and bubble surface properties simultaneously. To avoid this problem, a technique has previously been used in which silanol groups are attached to the surfaces of the particles, but this method has its own problems. In this work, silica particles with various surface hydrophobicities were prepared using an esterification process. By using alcohols with different hydrocarbon chain lengths, from 4 to 12 carbon atoms, surfaces with a wide range of contact angles could be prepared. The technique was used in the modification of silica particles that were tested in a fluidized bed flotation column, and a laboratory mechanical flotation cell. In parallel experiments, dodecylamine (DDA) was used as a collector. It was found that irrespective of the type of flotation machine and surface preparation method, there was a close correspondence between flotation recovery and the contact angle of the particles. The silanation process has known drawbacks relating to the presence of moisture during the reaction, and the stability of the silane coating after it is been prepared. Esterification does not suffer from these disadvantages. This work has shown that the esterification technique is a robust alternative method for preparing hydrophobic quartz surfaces."

Jan 1, 2014

By C. Abbruzzese, F. Vegliò, S. Ubaldini, R. Massidda

The aim of this paper was to study the influence of different water/organic solvent mixtures (isopropyl alcohol, ethanol and ethylene glycol) on the gold desorption process. The experimental work was carried out on laboratory scale, using activated coconut carbon with different temperatures and extraction times, without adding cyanide. Best results have been obtained in this order: isopropyl alcohol > ethylene glycol > ethanol. Starting from gold concentration of about 5 g Au per kg of carbon, best kinetics resulted in 97-100% of gold extraction, after 8 hours of desorption, at a temperature of 80ºC.

Jan 1, 2003

By Seungwoo Park, Gaurav Soni, Roe-Hoan Yoon, Hyunsun Do, Kaiwu Huang

In a flotation froth (and foam), air bubbles become larger due to coalescence, causing bubble size to increase, bubble surface area to decrease, and hence casing less hydrophobic particles to drop off to the pulp phase below. Thus, bubble coarsening provides an important mechanism by which product grades are increased. On the other hand, excessive bubble coarsening results in low recoveries. In the present work, a model describing the process of bubbles becoming coarser in a foam as they rise to the top by deriving a mathematical relation between the Plateau border area, which controls film drainage rate, and the lamella film thickness, which controls bubble-coalescence rate. The model has been derived by assuming that liquid drainage rate increases due to slip at the air/water interface, and that the critical rupture thickness is determined by the capillary waves created by thermal motion. The model developed in the present work can predict the bubble size ratio between the top and bottom of a foam as functions of aeration rate, foam height, and surface tension (frother dosage). The model predictions are in good agreement with the changes in bubble sizes measured using a high-speed camera.

Jan 1, 2014