Search Documents

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

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

Jan 1, 2018

By J. J. Lui

Surfactant plays a critical role in many industrial processes such as petroleum, mining, environment and food processing, and daily life. For ionic surfactant systems, adsorption of surfactant at oil-water interface imposes a net charge to the interface. The nature and magnitude of the charges at the oil-water interface depend on charge characteristics of surfactant molecules, concentration of surfactant and solution pH. In our previous study, zeta potential measurement of hexadecane drop-lets in industrial process water was shown to be a simple, yet powerful method for identifying various types of ionic surfactants present in the aqueous system. In this paper, the site-binding model was applied to prediction of zeta potential of oil droplets in aqueous solutions containing a mixture of cationic and anionic surfactant molecules. The total number of interfacial sites for various types of surfactant involved was determined by applying the Gibbs adsorption equation to the measured interfacial tension-surfactant concentration profiles. The distribution of various types of surfactant molecules at the interfaces was evaluated by Langmuir isotherm constants. With the ionization constant of surfactant taken from the literature, the predicted zeta potentials of oil droplets in surfactant solutions from site binding model were shown in a reasonable agreement with the measured zeta potential values.

Jan 1, 2014

By H. Palza, C. Ihle, S. Contreras

"Processing of minerals, particularly treatment of tailings, has been increasingly challenged by the presence of clays in the feed of thickeners. This occurrence is expected to become increasingly important given the nature of ore deposits currently being exploited and those that have been recently discovered. In sedimentation operations (solid-liquid separation), industrial flocculants often fail to coagulate clay-containing fines, generating supernatants with high levels of turbidity, thus implying operational problems. Recently, it has been reported that graphene oxide (GO), a graphite derivative with high oxygen-containing groups, could enhance the flocculation of clay systems, due to the interaction between clays and GO functional groups. In the present work, we investigated the effect of doping industrial flocculants (commercial polyacrylamide) with GO on the floculation of kaolinite suspensions in a solid-liquid separation stage. Separation performance was evaluated by studying flocculation kinetics using a focused beam reflectance measurement (FBRM) instrument, in a set of batch tests. A statistical analysis of the flocculation kinetics and floc population distribution was further carried out. Our results suggest the existence of a synergistic effect between the studied flocculants and GO. This effect is observed as a decrease of clay fine contents in the supernatant, thus improving solid-liquid separation eficiency for high clay containing tailings. INTRODUCTION Copper, given its mechanical, physical and chemical characteristics, is a critical material for the progress of society and so has been from early stages of mankind. Demand for this metal has increased due to the growth of cities and the technological explosion, leading to increase current mining production and reinforce the efforts in exploration for new deposits (Elshkaki et al. 2016). As copper-rich deposits are being depleted, it has been necessary to develop proper technology to mine deposits of lower grades and more complex mineralogies, keeping in mind that the economic window that allows the exploitation of them is reduced by the increase on operating costs (Crowson 2012 and Northey et al. 2014). High clay bearing minerals are found in many of those low-grade copper deposits, and they induce problems in all stages of the mineral processing route (Taner and Onen 2016). Particularly, in the solid-liquid separation stage, the flocculation process fails to remove the clay fraction from suspension and it leads to operational issues such as filter damage, overconsumption of reagents and the need to add an extra clarifying step for the recovered process water. Those problematics pose an interesting challenge."

Jan 1, 2018

By Marco Le Roux, Martha Van Rensburg, Quentin Campbell

Fluidised bed drying is currently receiving much attention as a dewatering option during the beneficiation of fine (defined here as between 1 mm and 2 mm particles) coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25 - 55°C) within a controlled environment by lowering of the relative humidity of the air. It was firstly proven that fluidization has a major advantage over non-fluidized beds, with regards to drying rate and final moisture content. Hereafter several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. Parameters tested included relative humidity, temperature and coal composition. Energy balances showed a positive nett energy increase in the dried coal during combustion when related to the energy input during drying. In comparison with thermal drying technologies, fluidized bed drying was proven to be less energy intensive. It was therefore shown that this is a viable technology for the dewatering of fine coal.

Jan 1, 2014

By Peter J. Scales

The recovery of water for re-use in minerals processing is an important issue in the reduction of water use in mining, as is the dewatering of tailings to reduce the propensity of ?wet? tailings dams. It is common in these dewatering operations to use thickeners whereby polymeric flocculants are combined with the dilute feed to the thickener to aid sedimentation and the subsequent consolidation of particulate materials. Thickeners are the workhorses of water recovery and tailings dewatering and although the basics are well understood, there is still no ability to reliably predict the throughput and underflow density from a thickener based on traditional sedimentation tests and flux analysis. The reasons for the discrepancy between full-scale operations and predictions based on laboratory tests are numerous, including difficulties in mimicking the flocculation conditions experienced in the field and the shear conditions in the thickener. The latter effects are little understood and hard to quantify and include effects due to flocculated aggregate densification, complimentary shear and compressional effects and aggregate break-up. Developing a set of test protocols to quantify the effects of densification, shear in compression effects and aggregate breakup and the subsequent contributions of each to compressional dewatering in a thickening environment has been completed for a simple model polymer flocculated particulate suspension. The data and analysis shows that aggregate densification is a dominant contributor to the difference between observed and predicted behavior based on laboratory tests. A major consideration in the analysis is the fact that common thickener operations are permeability limited and although the various effects are all important, the one that results in the fastest water release is dominant. Of interest also are the shear rate, concentration, and time dependence of the aggregate densification process. A basic model of the process has been developed along with network yielding tests conducted using rheometry. Keywords: compressional dewatering, gravity thickening, rheometry, aggregate densification, raked batch settling

Sep 1, 2012

By L. Y. Feng

The percentage of leached zinc in massive zinc oxide ores (11.7% Zn, >2 mm) is up to 73.3 % in 120 days. Alternatively, crushed to -0.154 mm, mixed with cement 5% (wt), pelletized and solidified. The diameters of the pellets obtained are between 5 mm to 8 mm. When the pellet solidification periods are 3 days, 10 days and 45 days respectively, the alkaline leaching rates of zinc in the pellets are up to 95.8%, 89.1% and 76.4% respectively. Decreasing the solidification time can re-duce reaction time, increase dissolution of zinc in pellets and lower the effect of initial zinc concentration on leaching rate. The experiment results show that the minimum solidification time is three days, and the kinetic study indicates that alkaline leaching of the low grade zinc oxide pellets is controlled by the diffusion of the leach liquor through the gangue layer in the whole leach process, and the apparent rate constants are 3.33×10-2 day-1, 9.18×10-3 day-1, 5.82×10-3 day-1 respectively.

Jan 1, 2014

By K. Hori

In this study, the determination of optimal conditions for jig separation has been investigated with a TACUB jig separator. The TACUB jig, from which a Batac jig originated, is a useful gravity separator that is effective to separate crushed solid wastes as well as coarse ores. A mixture of crushed polyethylene (specific gravity 1.3) and polyvinyl chloride (specific gravity 1.5) was separated by a batch TACUB jig by varying the frequency (wavelength) and the amplitude (pulse stroke length). It was found that the sample particle layer in the separation chamber was fluidized without turbulence by the rising water pulse resulting in the separation. However, a too strong water pulse reduced the efficiency of the separation of the particles. The results indicate that the specific velocity of the rising water is necessary to fluidize the particle layer without turbulence to separate the particles. The expansion ratios of the thickness of the particle layer in rising flows were measured in a cylindrical column. The pressure losses by the particle layer were calculated from the expansion ratios and the velocity of the rising flows by Ergun?s equation. The curve of the pressure loss vs. the velocity of rising flow showed a maximum point corresponded to the point of fluidization. The velocity of a rising flow on the point of fluidization provided the optimal separation condition.

Jan 1, 2014

By Kwang Soon Moon

Liquid ? liquid reactions such as solvent extraction in hydrometallurgy and BTX extraction in petrochemical industry has long suffered from the long retention time mainly due to the limited interfacial area caused by the immiscibility between water and oil phase, requiring typically very large perfect mixer type reactors and tall adsorption towers. A novel spray reactor for immiscible liquids; that is the KISEI Nozzle Reactor (KNR) was introduced, enabling the drastic increase in the interfacial area between the reacting immiscible liquids. Various spray mechanisms were applied in materials processing, e.g. spray drying, powder metallurgy, and aerosol industry, but not in hydrometallurgy. The KISEI Nozzle Reactor(KNR) was fully developed and used in production of biodiesel from the immiscible triglycerides and methanol. An experience with a full production plant facility is briefly discussed in the current paper. With the fog-like methanol spray in oil medium, the trans esterification reaction was almost instantaneous, and transformed the traditional batch trans esterification process into a continuous production process. And above all, with no moving parts in the KISEI Nozzle Reactor (KNR), the process requires minimal operation and maintenance costs. Keywords: immiscible liquids reaction, nozzle spray reactor, continuous biodiesel reactor, hydrometallurgy, organic extraction, micro emulsion

Sep 1, 2012

By V. Panayotov

Flotation practice usually uses the Sheridan-Grizvold selection method, where zinc minerals are activated by addition of copper sulphate and depressed by addition of sodium cyanide, ferrous sulphate, zinc sulphate or various mixtures of these reagents. The method is suitable for the flotation of sulphide ores, which, do not bear precious metals, such as silver and gold. When classical technology with cyanide is applied to depress zinc minerals, the precious metals, which are contained mainly into lead minerals, are dissolved into the solution, which represents a technological loss. In order to avoid this process, we have made use from the knowledge on the semiconducting properties of lead and zinc sulphide minerals. We have changed the surface charge of minerals by means of an electrochemical impact realized by direct current application and specially designed set of insoluble or semi-soluble electrodes. Thus, flotation separation of lead and zinc sulphide minerals was achieved, at increased recovery of lead, zinc and silver. The technology proposed was implemented in a Bulgarian flotation factory; it worked over 5 years providing significant, positive economic, technological and environmental impact. Silver recovery was increased by 0.8-1.0 %, and lead and zinc recovery was increased by 0.8-1.0 %. The technology is easily controllable and adaptable to raw materials and parameters of the technological process. It can be paid back for 6-8 months after the implementation. Keywords: lead-zinc flotation separation, electrochemical impact

Sep 1, 2012

By M. E. Taranenko, V. A. Krivonosov, S. A. Nemykin

"In concentrating production energy-consuming power installations are wide used, the most powerful of them are the wet autogenous grinding mill operating in closed circuit with a spiral classifier. The analysis of the current state of the automation of the grinding process shows that the reserves for maximizing productivity and minimizing electricity consumption have not yet been exhausted on the existing process equipment. Usage of the achievements of the modern management theory reveals an opportunity for further optimizing of the grinding process. The purpose of the research is to develop an automated control system of complex ""the mill-classifier"" to conduct the grinding process in the most operating efficiency, ensuring the maximization of productivity and minimization of specific electricity consumption. The main idea of this work is to study the specific features of the ore grinding process and creation on this basis of automated control system complex ""mill-classifier"" which allows to find and to maintain the optimal mode of grinding based on identification of the current object parameters, observance and regulating of the object state coordinates. Research methods. We used the methods of system analysis, mathematical statistics, modern automated control theory, theory of systems identification, optimal control, modelling of dynamic processes. Developed scientific provisions: - identification algorithm of the loading sub-system management object of complex ""mill - classifier"" allowing to obtain the unbiased estimators of its parameters according to the data of normal object exploitation; - observing device, which differs from the classic version of the observer Luenberger with possibility of estimating not only the state coordinates of the control object, but also the low-frequency perturbation component; - automated system stabilizing the active power of the grinding mode on the basis of a states controller with Luenberger observer; - structure of the software and hardware that implements the developed models, algorithms, methods of control, management and optimization in the framework of the automation of grinding."

Jan 1, 2018

By Trevor Saldanha, Stephen Grano

A key uncertainty in flotation modelling is determining, a priori, the proportion of each mineral which will develop a certain rate constant for different feeds of variable liberation and hydrophobicity. First and foremost is the ability to predict the proportion of minerals that will not be recovered, even at very long flotation times, and which therefore report to the tailing stream as the non-floatable fraction (i.e., having a zero rate constant). Recent empirical evidence has shown there are at least two factors which contribute to heterogeneity in flotation rates and, in particular, the appearance of a non-floatable fraction - heterogeneity in the distribution of adsorbed collector amount on a particle-by-particle basis, even for the same liberated mineral in the same size fraction, and the existence of a critical contact angle below which the bubble-particle union is unstable. In this paper, inferred measures of the critical contact angle for liberated particles are compared with stability model calculations. This has demonstrated that the dependency of the critical contact angle with particle size and mineral specific gravity are explicable by bubble-particle stability considerations. This argument is further extended to the flotation behaviour of composite particles, as a function of liberation class, in which the wetting perimeter of the attached bubble on the composite particle surface is constrained by the presence of a surrounding hydrophilic domain for the case of simple binary composites. Reasons for the different flotation behaviour of composite particles having different textures, as noted in the literature, are also discussed in terms of the stability of the bubble-particle union.

Jan 1, 2014

By E. V. Manlapig

"Some researchers postulate that the floatability of a particle in the streams of an industrial flotation circuit is a function of only its size and liberation properties. They do not discount the importance of reagent or surface contamination on particle floatability but assume that the reagent coverage or surface contamination of the particle surfaces is essentially uniform for particles of similar size and mineralogical properties when subjected to a particular chemical regime.In this paper, samples collected from batch tests performed on different streams of the Red Dog lead cleaning circuit have been characterised with respect to their size, mineral association and mineral surface exposure. An analysis of this data set indicates that particle recovery rate is significantly affected by mineralogical properties - in particular the degree of valuable mineral surface exposure.However, through the use of a nodal analysis technique developed by the authors, it can be concluded that particles with the same size and mineral composition do not all float with the same rate, but with a distribution of rates. The characteristics of this floatability distribution do not change during the flotation process. It is suspected that the particles within a size mineralogical class in this study have varying degrees of surface oxidation and that this results in varying particle flotation rates. Thus basing particle floatability on size and mineralogical effects, alone, in a flotation model is not always valid."

Jan 1, 2003

By Kazutoshi Haga, Atsushi Shibayama, Altansukh Batnasan

The objectives of this study were to propose a viable alternative method for recovery of precious metals such as gold (Au), silver (Ag) and palladium (Pd) from waste printed circuit boards (WPCBs) and to regenerate the spent lixiviant solution for reuse. The proposed method generally consists of several steps as follows: 1). iodine-iodide leaching for metals extraction; 2). separation and recovery of precious metals and metal impurities from a pregnant leach solution; 3). regeneration of the spent iodine-iodide solution/lixiviant. In this method, more than 99% of Au leaching was achieved in the iodine-iodide solution from the solid residue of WPCBs that was obtained via sequential processes including incineration at 800 ?C and high pressure oxidative leaching with a diluted sulfuric acid at 120 ?C, while the leaching of Ag and Pd was less than 1%, respectively. Besides Ca, Cu, Ni, Co and Zn as main metal impurities, leaching efficiency of other metals did not exceed 1%. The precious metals and base metals as metal impurities present in the pregnant leach solution were separated and recovered by precipitation using L-AA and NaOH solutions. About 99.8% Au, 81.7% Ag and 72.8% Pd were recovered from the pregnant solution at pH of 2 with the addition of 0.1 M L-AA as precipitating agent. The remained small amounts of precious metals and metal impurities were precipitated at pH 13 using 1 M NaOH. The spent lixiviant after sequential precipitation was regenerated in the presence of hydrogen peroxide, hydrochloric acid and potassium iodide. It was revealed that over 90% of gold could be extracted from the residue of WPCBs with the regenerated lixiviant solution.

Jan 1, 2018

By Sami Makni, Ahmed Bouajila

"To remain competitive in an open market, mining companies are more and more requested to optimise their complex and highly multivariate processes. The increasing amount of process data, brought about by intensive use of instrumentation and the progress in computer data acquisition, enhances the need for more and more powerful and robust tools for the analysis and modelling of the process data. Now, with the emergence of multivariate data analysis (MDA) techniques, on-line clustering of mineral process behaviour is possible and could help in the extraction of valuable process operation indicators. MDA can be used in different mineral processes such as flotation, grinding, smelting etc.In this paper, we focus on grinding process considered as the most costly and power consuming node of the mineral processing scheme. Different objective-oriented levels of data clustering will be addressed.First, the evaluation of grinding operation taking into account data and constraints from all processes before (e.g. blasting, crushing) and after (e.g. flotation, leaching, etc.) the grinding node. The second level deals with process diagnosis by differentiating operation level and identifying behaviour drifts. Control and optimisation are two other levels concerned here with the selection of optimum trajectories in the drift correct.Industrial plant data are processed in order to illustrate the feasibility and the potentiality of MDA applications in addressing the clustering and interpretation of grinding mill behaviour."

Jan 1, 2003

By Rainer M. Lotzien, Michael J. G. Battersby, Jan Kleefeld, Julian V. Brown, Rainer M. Imhof

A new flotation system has been developed to improve the generally slow separating differentials of fine bubbles and fine particle suspensions. The new technology is based on established pneumatic flotation designs called Imhoflot which use intensive in-line pre-aeration to aerate the flotation pulp prior to its introduction to the separating cell. In the new system (see figure 1) this separation is speeded up dramatically by the introduction of centrifugal motivation in the separating vessel, without the use of internal moving parts. The design focuses on providing increased differential forces on buoyant mineralised bubbles and hydrophilic fines. The commercial benefit to industry is much reduced residence time, less than 30 seconds, which offers considerable cost savings in equipment and infrastructure.

Jan 1, 2003

By Tsvetan Damyanov, Nikolay Hristov, Evgeni Kostadinov, Lubomir Kuzev

"The process of grinding in drum mills is directly dependent on the dynamic forces occuring in the free movement of the grinding bodies in the volume. The subject of discussion are the potential impacts between grinding bodies having different shape and equal weight in a drum mill that has a diameter of 1200 mm. The study utilised ball grinding bodies having a diameter of 120 mm and tetraballpebs having a conditional diameter of 120 mm. The study was carried out using the Solid Works Simulation software. The following cases were examined: • Impact between two identical grinding bodies; • Impact between a grinding body and the shell surface. The study provided numerical values for impact force, kinetic energy of impact, linear speed of impact, linear displacment of the center of gravity and duration of impact deformation. The impact force of the balls is approximately 179000 N. The impact force of the tetraballpebs with typical vertices, edges and spherical surfaces depending on the area of impact is 177000 to 185000 N. Upon impact between two spherical surfaces of tetraballpebs, the contact area is 263.55 mm2, which is more than twice the contact area upon impact between two balls, which is 114.39 mm2. This determines better conditions for the transmission of kinetic energy by reducing opportunities for overgrinding."

Jan 1, 2014

By Achilles Dutra, Everton Santos, José Oliveira

The beneficiation of phosphate ores by froth flotation is the most efficient process used to separate apatite from gangue minerals like calcite, dolomite and quartz. However, the similarity of surface properties between apatite and calcite generally lead to non-selective adsorption of reagents, rendering the selective separation of these minerals a worldwide problem. The phosphate deposit of Itataia, State of Ceará, Brazil, studied in the present work, presents a complex mineralogical composition having uranium associated with the apatite mineral. The main gangue minerals are calcite and quartz. The bulk flotation of apatite and calcite with anionic collectors in an alkaline medium followed by the selective flotation of calcite at pH 5.5 using phosphoric acid as well as citric acid as depressant have been suggested for this ore. This paper presents the results of contact angle measurements obtained using jojoba oil, a natural reagent composed mainly of gadoleic acid (C20:1) and long-chain fatty alcohols (eicosenol and docosenol), as an alternative collector for the selective separation of apatite and calcite minerals. The hydrophobicity studies were carried out using a computer controlled contact angle goniometer. Additionally, the collector adsorption was evaluated via electrophoretic mobility and FTIR measurements. The results indicated that a high selectivity can be obtained by using jojoba oil as collector in a slightly acid pH range, without the use of depressant. The best results were achieved with a jojoba oil concentration of 200 mg.L-1 at pH 6.5, where the apatite was fully hydrophilic and calcite showed a high hydrophobicity (? > 60 º).

Jan 1, 2014

By A. Buchanan, M. Mirnezami, A. L. Restrepo, J. A. Finch, M. S. Hashemi

Settling rate studies on slurries from Cu/Zn flotation plants occasionally revealed two aggregation maxima at pH 8-10 and 10-12. From measurements on sphalerite and silica suspensions the double maxima were replicated by Zn ions (pH 8-10) and Mg ions (pH 10-12) corresponding to the presence of zinc hydroxide and magnesium hydroxide, respectively. A combination of chemical and electrostatic bridging by the hydroxides is considered to be the aggregation mechanism.

Jan 1, 2003

By Charlene Gokhale

Geopolymerisation has emerged during the last few years as an industrial and ecological approach to construction and waste management. By utilizing waste materials and their reactive properties, it is now possible to create geopolymers systems that not only mechanically durable enough to be used as construction materials but are also potential stable immobilisation systems for toxic waste. Previous studies by Van Jaarsveld et al. (1997) and Van Jaarsveld et al. (1998) have reported on the numerous applications of geopolymers in the immobilisation of toxic metals. Research into the possible utilisation of geopolymers as an encapsulation media for organic waste has however been rare. This paper therefore provides an insight into the possible utilisation of geopolymers as a binder for hazardous organic materials.

Jan 1, 2003

By Gjergj Dodbiba, Toyohisa Fujita, Li Pang Wang, Masashi Yamane

"The platinum-group metals (PGMs), are currently receiving worldwide attention as they have major industrial uses. PGMs, i.e. ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt), are widely used as catalysts in petroleum and chemical processes. In addition, they find wide applications in automotive exhaust-gas control converters and are of immense importance to the electronic industry. Broadly speaking, PGMs are extracted in minute quantities from a limited number of ores, found mainly in South Africa and Russia. As the PGMs are both costly and almost indestructible, they are usually recycled from various forms of scrap. In other words, the recycling of the PGMs is an essential factor in the overall management of the PGM economy. In addition, the ever-increasing user areas have created renewed interest in the search for new sources or deposits of PGM, which in turn requires an in-depth knowledge of its characteristics. In this work, the emphasis is placed on the need to analyze the composition and microstructure of blast-furnace slag for recovering PGM metals. In other words, chemical composition, surface analysis and microstructure analysis of the DC arc furnace slag have been carries out. The aim is to provide a detailed analysis of this material for anyone with an interest in gaining further knowledge of its specific content for recovering PGMs."

Jan 1, 2014