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By Lutz Rolf, Halit Z. Kuyumcu, Salas Cazón. Milton A.

Aim of experimental investigations was the mathematical description of the abrasion process running with a single particle stress. This is on the one hand the basis for the physical interpretation of the process, on the other hand the base for the simulation of abrasion processes carried out in technical scale. With this investigation for the first time the influence of the particle shape changing with increasing abrasion progress was quantitatively described. This influence affects itself particularly strongly on break-fresh particles up to an abrasion degree of approximately 10 to 20%. This is for the description of technical processes the most interesting area.

Jan 1, 2003

By V. Dementiev

Pyrite cinders is a complex raw material, in which the valuable metals are: Au(2.04 g/t), Ag(35.0 g/t), Cu(0.38%), Zn(1.1%) and Fe(56.0%). In this case high costs for mining and ore processing are not required. The hydrometallurgical treatment of pyrite cinders using thiourea, sulfite and cyanide solutions are examined in this paper. It was found that thiourea leaching is ineffective due to high consumption of thiourea and sulfuric acid. The cyanidation on pyrite cinders was conducted. Various options of the preparation of the products for the subsequent cyanidation have been examined. The tests on cyanidation process optimization were conducted. The effectiveness of these cementation methods by metallic iron or extraction for copper recovery from water phase has been shown. Zinc precipitation can be found in the form of carbonate. In order to recover noble metals from cyanide solutions, the cementation onto zinc dust was tested. The developed technology provides for recovery at 49-56%Au, 20-25%Ag, 22.5%Cu and 50%Zn during NaCN (1.4 kg/t) and CaO (6 kg/t) consumption. The results of pilot plant testing are the basis for technical regulations in order to design a pyrite cinders treatment plant. The technology has been examined in pilot-plant conditions. In this case the recovery of 54.5%Au, 45.3%Ag, 30%Cu and 49.9%Zn was achieved to provide saleable products. Keywords: pyrite cinders, thiourea leaching

Sep 1, 2012

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

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

Jan 1, 2003

By A. Sand

Within stamp-charged coke making a large volume of coal is compacted to one single coal cake before entering the coke oven chamber. This is done by means of several falling stampers in a stamping machine having a mold nearly of the oven?s dimensions. Producing a high quality coke also from inferior coals requires a cake density of approximately 80% of the coal density. Besides that the industrial stamp-charging process demands a minimum mechanical strength of the coal cake to move it from the stamping mold into the oven chamber without failure. Densification and the build-up of cake strength were investigated earlier in stamping tests using a micro-stamping device. The quantities derived from these tests (as e.g. cake density or porosity) represent average values for the entire cake. Statements describing the local compaction state at different heights are difficult to achieve without destructing the cake. In order to gain better insight into the densification process and the inner structure of the coal cake a computational model based on the discrete element method (DEM) has been set up using 2 and also 3-dimensional simulation software. The stamper?s position and velocity as well as the force acting on the stamper were monitored and the model?s response was compared against measurement data from laboratory stamping tests. It was possible to reproduce the force and displacement pattern of the stamper in response to the viscoelastic properties of the cake using standard DEM bonding and contact models. Furthermore, the rearrangement of particles in response to the compaction by the stamper was tracked by calculating their displacement at the point the stamper hit the coal surface. The latter can also be used as indicators of particle deformation or breakage. By defining control points at different heights the particle displacement, stress and strain rates, porosity could be studied at different heights. Keywords: coke making, coal stamping, compaction, agglomeration, DEM, simulation

Sep 1, 2012

By C. L. Lin

Previous research on particle damage during high pressure grinding roll (HPGR) crushing was limited by the resolution of point-projection micro CT systems and the extent of damage was described by the percent of particles cracked for different crushing methods as determined at a voxel resolution of 40 microns. With recent advances in X-ray optics, the resolution afforded with point-projection micro CT systems has been improved by at least an order of magnitude using a lens-based X-ray micro CT system. With the use of X-ray lens imaging the resolution is determined by the lens rather than by the spot size of the micro-focus X-ray source. The high resolution X-ray micro CT (HRXMT) system made by Xradia with a voxel resolution of less than 1 micron is now being used for the characterization of particle damage during HPGR crushing. In this way, the direct 3-D determination of the internal damage of crushed ore particles which vary from 40 mm down to 100 microns in size is being studied at a voxel resolution of a few microns. The number, size, and shape of cracks can now be measured at this improved resolution and for the first time the specific crack surface area distributions of the crushed product can be calculated from HRXMT images using specially designed software tools for 3D analysis. Results from selected crushing operations are presented. Copper ore particles from HPGR crushing at high pressure (6 N/mm2) are severely damaged having crack specific surface areas as great as 10 mm2/mm3. Keywords: HPGR, particle damage, X-ray micro tomography, crack surface area

Sep 1, 2012

By Avishan Atrafi

Frothing behavior of surfactants originate from their preferential adsorption at the gas-solution interface. Different surfactants may demonstrate different adsorption behaviors depending on their molecular structure and surface activity. The quantity and rate of adsorption of surfactants at the gas- solution interface in flotation systems will certainly affect kinetics of reaction and fractionation of surfactant between bulk and foam phase and subsequently their frothing characteristics. In this paper, the frothing characteristics of sodium oleate which is the main constituent of fatty acids used in flotation systems is explained. The adsorption behavior of sodium oleate is then compared to a typical non-ionic frother (Methyl Isobutyl Carbinol, MIBC) in terms of different adsorption behavior at the gas-solution interface. Since long chain fatty acids are weak electrolytes, their behavior is a strong function of pH. Also semi soluble salts including apatite contain considerable amounts of ions like calcium in their lattice, so the effect of presence of ions on the frothing behavior of fatty acids requires an investigation. A mass balance on the surfactant transferred to the foam was solved to estimate the bubble surface area flux in foam, which explained how the adsorbed surfactant at gas-solution interface controls the bubble surface area flux at foam. Since sodium oleate adsorption at foam takes place gradually, frother concentration as a function of time was monitored by the total organic carbon measurement (TOC) to compare the surfactant uptake rate at different concentrations, pH and ionic strength. The surfactant concentration adsorbed within foam together with the value of adsorption density from the Gibbs adsorption, leads to the calculation of the surface area flux and prediction of average bubble size in the foam at a specific time frame. This value was compared at different concentrations of sodium oleate. Dynamic surface tension measurements were accompanied to explain the adsorption behavior, though finally equilibrium surface tension turns out to better explain the foamability characteristics. Keywords: flotation collectors, flotation froths, foams, fatty acids, adsorption behavior

Sep 1, 2012

By Nóra Schreithofer, Kari Heiskanen

"INTRODUCTIONThe knowledge of the adhesion forces between particles and bubbles is of key importance in the improvement of flotation models. The development of the Colloidal Interaction Force Measurement Apparatus (CIFMA) opened the possibility to quantify the adhesion forces between particles and bubbles. The aim of this study was to examine the effect of three main variables: the approach velocity, the loading force and the loading time on the adhesion force between an air bubble and a hydrophobized silica particle."

Jan 1, 2003

By Willis Forsling, Prabhakar Swarna, Hanumantha Rao Kota

"The solubility of wollastonite and its Hallimond flotation behavior as a function of dodecylamine concentration and pH are examined. The flotation response is characterized by adsorption and surface energy in the presence of amine. The methods of UV-Visible and FT-IR spectroscopy for adsorption and sessile-drop contact angle for surface energy estimation are employed.The results of wollastonite dissolution clearly showed its non uniform dissolution. The surfaces are depleted with calcium ions and became rich in silicon within 10 min of flotation time. Maximum flotation of wollastonite corresponds to a half monolayer coverage of amine, which is substantiated by the surface energy parameters as shown in figure 1."

Jan 1, 2003

By Ming’an Wei, Chuanyao Sun, Yangge Zhu, Fayu He, Yanbo Shang, Xingrong Zhang

In order to discuss the separation mechanism of copper-molybdenum ore, surface electronic structures of chalcopyrite and molybdenite were studied in the paper, by using First Principles method of quantum chemistry. So, the separation mechanism of thioglycolic acid (TGA) with chalcopyrite and molybdenite was revealed better. The results showed that differences of the electronic structure of chalcopyrite and molybdenite could directly affect their interactions with TGA, such as band structure, density of states, Mulliken populations, and so on. And the frontier orbitals of chalcopyrite and molybdenite were also calculated by Dmol3 after the optimization by CASTEP, from which the interaction energies between minerals and TGA were obtained and compared. So, the essence of flotation separation of copper and molybdenum were well revealed.

Jan 1, 2014

By Z. Kwela, A. Manhique, W. W. Focke, W. van der Merwe

"The main features of the de Wet improved alkali fusion process for the manufacture of AZST are: Fewer process are steps necessary; radioactivity is removed by leaching rather than by precipitation; fewer waste streams are generated; there is less waste to discard and alkali reagent is recovered in the form of a sodium silicate solution that is essentially free of radioactivity.Here we report on our efforts maximize the alkali recovery in the sodium silicate product stream: Milled zircon, d50 ˜ 9 µm, was fused with caustic soda pearls in open reaction vessels at temperatures between 650°C and 850°C. Fusion times of 1, 2, 4, 24 and 336 hours (with intermittent milling) were investigated. The fusion products were characterized by infrared spectroscopy, X-ray diffraction and by wet chemical analysis.For prolonged fusion times the fusion products approached equilibrium compositions. However, the phases Na2ZrSiO5 and Na4Zr2Si3O12 observed at 850°C did not form at 650°C. Since these compounds do not hydrolyze in water they limit the recovery of alkali in the sodium silicate product stream. For 2-hour fusions a broad spectrum of non-equilibrium reaction-products, that are rich in sodium silicates, is formed."

Jan 1, 2003

By Braulio Fernández, Gonzalo Montes-Atenas

The mechanisms taking place during the leaching of chalcopyrite when it is in contact with other sulphide minerals, particularly pyrite, is still a matter not fully solved. The GalvanoxTM process has been suggested as a technical solution to extract copper from chalcopyrite at commercial level inhibiting passivation phenomena widely reported in the field of hydrometallurgy. Although there are some rules of thumb to implement the process in fully flooded stirred conditions such as the optimum pyrite/chalcopyrite mass ratio should range between 2 and 4, among others; not many research studies have been focused on studying the effect of the surface contact area between chalcopyrite and pyrite to reach best copper extraction conditions. The aim of this research work is to determine the effect of the mass and surface area ratio between the minerals and the surface area of each of the mineral species effectively exposed to the leaching solution. Different particle size distributions of pure pyrite and chalcopyrite were contacted in a small column and subjected to leach tests using sulphuric acid in concentrations close those used in industrial leaching processes. The mass and surface area ratios which optimize the extraction of copper were obtained. It was found the best leaching conditions were attained when reducing the particle size distribution of pyrite regardless the particle size distribution of chalcopyrite. Further analysis concerning the impact of this conclusions on large scale operations is presented and discussed.

Jan 1, 2014

By Kobus (J. J. ) Rossouw, P. Chris Pistorius, Johannes Sono

"Different coal properties are important in SL/RN (coal-based rotary kiln) direct reduction of iron ore, and in electrical smelting of prereduced iron ore. Laboratory simulation was used to evaluate two candidate coals, which were similar in volatile content and rank, but differed in reactive maceral content. The tests served to evaluate both the reduction rate (during direct reduction) and the dissolution rate of carbon from the coal into an iron bath.Reduction rates of mixtures of magnetite and devolatilised coal were assessed isothermally, using samples of 55 grams. The off-gas analysis was used to follow the extent of reduction. Results are shown in Figure 1 a). Coal B was expected to be more reactive, based on its higher content of reactive macerals (77%, compared with 61% for Coal A). In line with this, Figure 1 a) does show a higher reduction rate with this coal. However, increasing the reduction temperature increases the reduction rate substantially,especially for the less-reactive Coal A.For the dissolution experiments, samples (mass: 250 g) were melted in an alumina crucible (under a nitrogen atmosphere), to give a starting composition around 1%C. When the desired temperature was reached, 25 g of char was added on top of the melt, through a feeding port. Results are shown in Figure 1 b). The more-reactive Coal B was less crystalline (the graphite crystallite size estimated from X-ray diffraction was 4.6Å, compared with 11.4Å for Coal A). This is associated with a lower dissolution rate in iron."

Jan 1, 2003

By John A. Herbst, Ming Song, Xiangjun Qiu

"It has been known for sometime that as wear occurs in tumbling mills there is an associated change in mill throughput. These changes have traditionally been simplistically, attributed to “mill volume effects”. New high fidelity simulation (HFS) tools (involving DEM, CFD and Breakage models) are now giving new “microscale” insights into the complex interactions that occur between evolving lifter/liner profiles and breakage. An illustration of this analysis is shown in Figure 1 below.Here we see that after a new lining is installed (Region I) the wearing process reduces the liner thickness resulting in a larger power draw and an associated higher throughput until Region II is reached. By this point the lifter height is reduced significantly changing charge motion (less cataracting) the power begins to decline, but the comminution efficiency increases with this type of “calmer” breakage environment therefore the throughput continues to increase. In Region III the lifter is no longer providing the minimum required charge lifting action, the power and the throughput both drop off significantly. In the last two stages the behavior is especially complex because throughput is not linearly related to power since grinding efficiency is changing.The study described here shows that these new HFS tools allow the design of wear part profiles which will maximize mill productivity over the entire life of liner/lifter systems. A simple example of such a design procedure is shown involving the selection of a sinusoidal profile for a 34 ft diameter SAG mill.The paper discusses how the principles exposed in this simple example can be applied to search for an optimal profile in which non-standard modifications are allowed to compensate for throughput or wear shortcomings of standard profiles."

Jan 1, 2003

By Ashton M. Swartbooi, Robert van Hille, Alison E. Lewis

"Nickel production by precipitation using hydrogen reduction generates an ammonium sulphate solution containing approximately 2g/L of nickel, and 1g/L of cobalt as an impurity of the process. Sulphide precipitation is an effective method for heavy metal removal, especially when compared to hydroxide processes: metals can be removed from solution at relatively low pH levels, small quantities of sludge are formed, and due to the high reactivity of sulphides the reactor retention time is reduced. However, the low solubility of sulphide species can lead to spontaneous nucleation of fines (due to higher supersaturation levels which are difficult to separate from solution, leading to reduced process efficiency. Using a fluidised bed reactor, fines formation can be minimised as the pellets provide a large surface area and promote heterogeneous nucleation.A synthetic nickel-cobalt ammonium sulphate solution was reacted with two forms of sulphide reagent: (a) a liquid sulphide solution and (b) gaseous hydrogen sulphide. A range of factors (including pH, reagent concentrations, metal to sulphide molar ratio, flow rates and recirculation rates) influencing the efficiency of the precipitation reaction have been studied. The efficiency of the precipitation reaction was measured using both metal recovery and fines formation as indicators.Figure 1 shows the effect of decreasing the metal:sulphide ratio (at constant SS = 2.725e+17), on the metal removal for liquid sulphide. By decreasing the metal:sulphide ratio, up to 99% removal of both nickel and cobalt could be achieved.These results also indicate that the precipitates that formed were polysulphides, since no sulphide was present in solution after the experiment. This would also indicate that a lower metal:sulphide ratio would be more favourable. However, decreasing this ratio (at constant metal concentrations) would lead to an increase in the fines concentration, because of increased supersaturation levels induced by the higher sulphide concentrations. To decrease the supersaturation, dilute solutions of either reagent would be employed."

Jan 1, 2003

By Remmerswaal, U. Boin, M. B. G. Castro

"To design sustainable products that can be recycled with high resource efficiency, low environmental impact and economic feasibility, the choice of materials and materials combinations, made in the design stage, is fundamental. The products we design, manufacture and use now will be the resources of the future. Designers are able to select materials for a product according to the many functional requirements they must fulfil. But they have a limited knowledge of the recycling processes and its requirements regarding quality of the secondary material streams. Resource Engineers have to manage the processing of these streams, that are becoming more complex with the increasing variety of materials and decreasing size of components. After mechanical separation of the materials streams resulting from shredding of EOL (endof- life) products, there is always a degree of contamination, from two possible causes:Incomplete liberation: the bonds between different materials combined in a component are not completely destroyed by shredding, resulting in some particles containing two or more materials attached;Separation efficiency: the mechanical separation processes are not able to separate perfectly the many material particles; there are always a number of foreign particles in the recovered streams.Sometimes, those contaminants cannot be removed by the industrial metallurgic recycling processes, and a more serious problem occurs when the contamination levels compromise the recycling of the material stream by lowering its quality (i.e. the properties of the recycled material will be lower due to the contamination). As a consequence, the material must be diluted in virgin raw material and/or used in a less demanding application (downgrading), causing resource depletion and increased energy use, waste production and recycling costs. In order to make the best choice of materials combinations for a product, a systematic approach is necessary, that can close the gap between the knowledge areas of Product Design and Recycling Technology."

Jan 1, 2003

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 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 Olga D. Khmelnitskaya

The paper presents the results of research on the development of gold recovery technology from oxidized gold-copper ore of one of deposits in Russian Federation. Gold and copper grades in the ore are 9.5 g/t and 0.4%, respectively. Various options of flowsheets, such as direct cyanidation, thiourea leaching, flotation and gravity concentration followed by subsequent cyanidation of con-centration products, were tested. It was established that gravity-cyanidation technology with filtra-tion leaching tails and the use of solutions in the recirculation is the optimal option for ore treatment. The proposed flowsheet provides gold recovery for 91.0% at NaCN consumption 2.5 kg/t ac-cording to the results of pilot testing. Ammonia-cyanide gold leaching was also examined. In comparison with cyanidation, gold leaching solution in system NaCN-NH4OH-(NH4)2CO3 allows NaCN consumption to be reduced three times from 4.5 kg to 1.5 kg per 1 ton of the ore and provides the same gold recovery. Based on the laboratory and pilot plant tests results of gravity-cyanidation technology of gold dissolution, process design criteria were developed.

Jan 1, 2014

By T. C. Sun

Two wasted activated sludges (WAS), from an industrial wastewater treatment and a sewage treatment plant respectively, and 7 collectors are used to investigate the feasibility of air flotation thickening of WAS by adding the collectors used in mineral processing. The collectors experimented include straight chain fat acids with different chain length, sodium oleate, alkyl sodium sulphonate, sodium dedecylsulfonate, and dodecylamine. The results show that the thickening efficiency varied depending on different collectors. Of the collectors experimented, dodecanoic acid and dodecylamine are best collector for thickening both sludges.

Jan 1, 2014

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

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

Jan 1, 2018