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By Garren Edwards, van der Westhuizen. Andre

"Due to the depletion of easily treated coarser ores, more mineralogically complex ores with smaller valuable mineral grain sizes are treated, the means to liberate these minerals lies in grinding finer (Partyka & Yan, 2007). Grinding to these fine sizes is energy intensive, and using standard ball mills are energy inefficient at these sizes (P80 < 75µm). Therefore, stirred mills are becoming increasingly prevalent in the mineral processing industry. In order to optimize these mills, the effects and mechanisms of the significant variables need to be understood. This paper investigates a laboratory scale vertical stirred mill (Deswik mill) in an ultra fine grinding application of a South African platinum ore. The operating variables that are considered are stirrer speed, media size, media filling, and slurry density. The resulting grinding efficiencies are considered in two ways. Firstly, a statistical model is fitted to identify the effect of the significant variables on grinding efficiency, and secondly, the grinding efficiencies are also considered in terms of a stress energy model to determine whether this can partly explain the grinding mechanism in this mill. A factorial design of experiments was used on three levels for each variable, such that only linear interactions, second order interactions and two variable interactions are included in the statistical model. The results show that tip speed, media size, percent solids and mill filling are all significant to the grind, at differing energy inputs in the grinding process. The interaction effects of these variables are also dependent on the energy inputs. The results also found that the Kwade stress energy model is applicable to this mill and can be very useful to find the most efficient operating conditions for this system. The most energy efficient operating conditions in terms of mill speed and media size were typically somewhat below the standard operating conditions and it is expected that this is most probably done in order to increase the grinding rate, but at the expense of sacrificing some grinding efficiency."

Jan 1, 2014

By M. C. Harris

"In the flotation process the contact angle is an important indicator of the hydrophobicity of a mineral particle. There is considerable literature showing that the contact angle increases when the chain length of the alkyl group associated with the collector molecule used to render the valuable mineral particle hydrophobic increases. The extent to which an alkyl group interacts with surrounding water molecules is quantified thermodynamically by the excess Gibbs energy. In the present paper it is shown that there exists generally a strong linear relationship between the excess Gibbs energy of the alkyl group associated with the collector and the contact angle. The structure-activity of such alkyl groups is in turn related to the total surface area, molecular volume, the molar volume, molecular weight of the functional groups in the molecule and interaction energies. It is proposed that the demonstrated relationship is indicative of the role which the alkyl group component of the collector, which is attached to the mineral particle, plays in increasing the extent to which water molecules at the surface of the mineral are rejected from the surface thus increasing the contact angle. The relationship between excess Gibbs energy and surface tension is further explored with a view to relating the observations quantitatively to the parameters in the Young equation.INTRODUCTIONThe issue of wettability of materials is of great importance to many industrial applications. Wettability studies usually involve the measurement of contact angles which indicate the degree of wetting when a solid and liquid interact. As is well known the contact angle (O) is the angle between planes tangent to the surfaces of the solid and the liquid at the wetting perimeter which is the zone where the air, water and solid phase merge. When the air bubble attaches to the solid surface there is an increase in the air/solid interface area and a decrease in the solid/water interface area. For attachment to occur the cosine of the contact angle should be less than 1 and this will be promoted if the interfacial surface tension between the air and the solid (? SV) is low. Classically the relationship between these parameters has been expressed through the Young equation (1) for a perfectly flat surface:"

Jan 1, 2018

By E. R. Bobicki

"Low-grade ultramafic nickel ores, while representing a large potential nickel resource, are difficult to process due to their serpentine content. Microwave treatment is proposed as a technique to improve the beneficiation of ultramafic nickel ores by converting the constituent serpentine to olivine. The present paper reviews the microwave heating response of ultramafic nickel ores and resultant changes in mineralogy, as well as effects on grinding and slurry rheology. Beyond nickel extraction, microwave treatment improves the mineral carbon storage capacity of ultramafic ore tailings, providing a potential source of additional revenue via the sale of carbon credits. The combined positive effects, considered in the context of the whole operation, suggest an economically viable process is possible.INTRODUCTIONAs high-grade deposits become depleted, the processing of low-grade ores has become increasingly important. One such resource is low-grade ultramafic nickel ores. While representing a large source of nickel, these ores are difficult to process due to their serpentine content. Serpentine is a phyllosilicate mineral consisting of 1:1 stacked sheets of silica tetrahedra and magnesium hydroxide octahedra. There are three primary polymorphs: lizardite (platy), antigorite (corrugated) and chrysotile (coiled, fibrous). The anisotropic nature and non-spherical morphology of serpentine particles leads to complex rheology. Suspensions of serpentine minerals, especially those of chrysotile, exhibit high viscosity and yield stress, which can have a negative effect on comminution, flotation and dewatering operations. In flotation, serpentine is known to slime-coat pentlandite, a valuable nickel mineral, and form bubble-fibre aggregates that report to the froth, reducing nickel concentrate grade and recovery. Methods used to counteract the effects of serpentine in processing include desliming, the addition of chemical dispersants, salts or acid, and dilution (Bobicki et al., 2014a). Microwave pre-treatment has been proposed as an alternative way to eliminate the deleterious effects of serpentine in ultramafic nickel ore processing by converting the serpentine to olivine via dehydroxylation, which occurs at 600-700oC (Reaction 1). Olivine is isotropic, consisting of isolated silica tetrahedra linked by octahedrally coordinated magnesium ions, and has the same surface potential as pentlandite at the pH of flotation (~pH 9). Furthermore, since olivine is more reactive to CO2 than serpentine, microwave pre-treatment creates an opportunity to store more CO2 in tailings, an attractive option for mining operations looking to increase their bottom line where carbon pricing exists."

Jan 1, 2018

By Leming Ou, Hongqiang Li, Li Zeng, Qiming Feng, Yiping Lu, Guofan Zhang

"The entrainment of sericite, especially in the presence of hydrophobic microcrystalline graphite, leads to the poor flotation selectivity of microcrystalline graphite ore. In this paper, it was attempted to reduce entrainment of sericite, selective flocculation of microcrystalline graphite using polyethylene oxide (PEO) was studied. For the sake of flocculate microcrystalline graphiteselectively, flocculation tests of microcrystalline graphite and sericite single mineral were conducted.To investigate the effect of selectiveflocculation of graphite on entrainment of sericite in microcrystalline graphite flotation, batch flotation tests of graphite single mineral and artificial mixtures were conducted; theflocculationselectivity of PEO of different molecular weight (M.W.) was alsocompared inartificial mixture flotation. Inthe end, the structure of flocs in different particle size was studied by sieve analysis and microscopic observation. The resultsindicated that PEO of molecular weightone million andtwo million could selectivelyflocculate the microcrystalline graphite and reduce the entrainment of sericite at a lower dosage; further increasingof the dosage of PEO(M.W. ?two million) led to hetero-flocculation between graphite and sericiteandmadethe ash content of concentrate increase again."

Jan 1, 2014

By D. J. Zhao

The reduction of ilmenite pellets was investigated at 950°C and 1000°C under a CO-N2 gas mixture with 10 L/min gas flow rate. All the reducing reactions were conducted in a furnace with a thermogravimetric analysis system. The reduction rate is higher at 1000°C than that at 950°C. At the early stage of the reactions, with the CO concentration increasing in the gas mixture, the reduction rate increased at 1000°C. In addition, at the early stage of the reactions, a rapid temperature increment and a rapid conversion of oxygen were observed on the curves of temperature versus time and conversion of oxygen versus time under different experimental conditions. The solid reaction products obtained in these experiments were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometers (EDS). Metallic Fe with small amount of Ti dissolved in it and oxides of Ti were found in the solid reaction products, but the formation of any nitride phases was not found under the prevailing conditions.

Jan 1, 2014

By Rong Fan, Roger Smart, Ning Xu

As part of an Australian Research Council project with Newmont and Newcrest mining companies studying the influence of clay minerals on rheology, hydrodynamics and flotation response, the cryo-SEM technique has been used to capture and image the clay (low crystallinity kaolinite Q38) aggregate structures in the flotation pulp immediately after collector and before frother addition. Samples were also collected from the earliest froth phase and the froth overflow corresponding to early and later concentrates. In this technique, a copper tube is filled with the sample during operation of the cell. The tube is immediately plunged into liquid nitrogen vitrifying the water phase before it can crystallise as ice thereby retaining the structures without volume or other physical change. After sublimation of the vitrified water surface, the aggregate structures are revealed and can be compared between pulp and froth phases from clays in different feeds and flotation conditions. The images from both low-clay ore and ore with clay content reveal various levels of aggregation as predominantly edge-edge connected aggregates similar to those found in our previous studies of high-clay tailings. For the samples from the ore with clay content, more extensive edge-edge clay strings are found in the early froth phase as compared to exiting froth overflow and the pulp phase with short edge-edge connected strings. It is suggested that the strings of clay particles result from edge-edge aggregation in the Plateau borders of the bubbles before breakage during sampling and the more extensive edge-edge aggregation in early froth phase is induced by crowding in the bubble borders. The clay strings collected into the overflow concentrate are almost all broken up compared with the Froth before drop-back. The implications for entrainment and entrapment mechanisms of gangue capture in froth will be discussed.

Jan 1, 2014

By G. Bulut, Ü. Yenial

"Heavy metals contamination in aqueous systems can be found in a variety of industries, in particularly mining, metal processing, finishing and plating. Water containing more than 0.5 ppm heavy metal considered as a toxic due to harmful effects on health. The major techniques employed for heavy metal removal from industrial wastewaters include precipitation, reduction, ion-exchange, and adsorption. Adsorption is a heavy metal removal method for aqueous systems. As a common adsorbent, activated carbon has been used in treatment but it is ineffective on some elements. Thus, there has been a research for developing highly effective and selective adsorbents. In this study the adsorption of lead and arsenic ions on to coal waste and red mud waste was studied. The experimental parameters were determined as pH, equilibrium time and the initial concentrations, activation by heat treatment and the blend of adsorbents. According to their adsorption capabilities, red mud was found to adsorb lead and arsenic ion with high efficiency but coal waste did not adsorb arsenic ion. However the binary adsorptions of these ions were enhanced the adsorption efficiencies. In addition the blend of coal waste and red mud affected the adsorption efficiency. INTRODUCTION As a result of rapidly developing industry and excessive use of water resources, the need of clean water and wastewater management appear as a problem. Wastewater recycling activities and researches come to the fore for an effective use of wastewater. Recycling of wastewater, which contains heavy metals harmful to the environment and human, is a difficult process. Heavy metals are generally divided into three categories: toxic metals, precious metals, radionuclides. Wastewaters from various industries, containing heavy metals, are the main polluters of water and soil. Although their toxic structures, heavy metals are used extensively in industry as they have technological significance. Usually mining industry, metal industry and industrial organizations produce heavy metal containing wastewaters (Volesky 1990, Ting and Lawson 1991, Bishop 2002)."

Jan 1, 2018

By Katarina Theander, Robert J. Pugh

The generation of froth with a critical degree of stability and height is an important aspect of the froth flotation. In this paper we have studied the synergism and anti-synergism in frothing behaviour in a mixed flotation collector/frother mixture (a model fatty acid; sodium oleate and a model frother; nonionic (polyethyleneoxide alkyl C14E6). Values of the collector / frother molecular interaction parameters (the ß-parameters) were determined from the surface tension data using regular solution theory. The frothing characteristics of the system were evaluated using a glass column equipped with a series of conductivity electrodes, which enabled the water content of the froth to be determined. From these measurements, the dynamic frothability and static froth stability were determined. It was concluded that the synergism/anti-synergism in frothability was depended on the molecular composition of the surfactant system, the diffusion of monomer to the thin film interface and on the breakdown of the mixed nonionic/anionic micelles.

Jan 1, 2003

By G. M. Wolfaardt, B. C. Qi

"From a lifecycle point of view, biologically digested sludge is a valuable product that should be reused if possible. Sludge may be applied to agricultural land for further sludge treatment and improvement of the characteristics of the soil. The characteristics of sludge that affect its applicability for soil conditioning include moisture content, pathogens, nutrients and metals. In this paper, the use of solid anaerobic digestion sludge of the lignocellulosic residues to condition soil was investigated in regards to nutrient composition, water content/retention capacity, hygienic quality (contamination of pathogenic bacteria) and heavy metal adsorbing/releasing characteristics of the sludge.It was found that the digested sludge had approximately 44.5% free and immobilized water and 46.9% bound water. The water-holding capacity of the sludge was high. This was a merit to apply the sludge to agriculture in dry areas. Anaerobic digestion under thermophilic conditions showed a promising disinfecting effect to the sludge, in contrast to the landfill digestion. The anaerobic digestion sludge could be considered as a humus-rich hygienic product that improves soil fertility and water holding capacity, nourishes plants and immobilizes heavy metals in the environment"

Jan 1, 2003

By N. D. Ilankoon

"The use of thiosulfate as an alternative lixiviant for cyanide to treat complex refractory ores followed by the use of ion exchange resins (IX resins) for gold recovery has become an industrial reality. In this study, polyethylenimine (PEI) coated iron oxide magnetic nanoparticles (MNPs) were used to recover gold from the leaching solutions that consist of calcium thiosulfate, copper and gold. The gold loaded MNPs were easily separated from the solution using an external magnetic field. Proposing a novel adsorbent with characteristically easy solid-liquid separation, to recover gold from synthetic thiosulfate leaching solutions and gold elution and reuse of MNPs were the main objectives of this study. Adsorption isotherm studies revealed that the data fitted both Langmuir and Freundlich isotherm models equally well. The maximum adsorption capacity was 18.5 mg/g at pH 8 and 50?C. According to thermodynamic studies the physisorption process was exothermic and spontaneous. Gold and copper elution, and the regeneration and reuse of the nanoparticles were investigated and promising results were obtained. Different elution systems comprising sulfites, chlorides, glycine, EDTA (ethylenediaminetetraacetic acid) and sodium hydroxide were considered. Among them, EDTA for copper elution and NaOH for gold elution were the most efficient eluants. Regeneration and reuse studies revealed that the MNPs can be used for several cycles without significant performance loss. INTRODUCTION Although cyanidation has been used for gold leaching for more than 100 years, some major drawbacks associated with cyanidation have led to a quest for alternative lixiviants for gold leaching. Cyanide is ineffective in treating carbonaceous refractory ores as gold cyanide complex is adsorbed onto the native carbon in the ore itself known as preg-robbing. On the other hand environmental concerns associated with cyanidation drives the need for environmental friendly alternatives for cyanide. As of today, thiosulfate is known to be the most extensively studied and most promising alternative lixiviant for cyanide in both technical and environmental perspectives (Aylmore and Muir 2001, Oraby 2009)."

Jan 1, 2018

By R. A. Kleiv, H. Havskjold, N. Church, T. Malvik, M. Tro, E. Larsen

Liberation is one of the major purposes of comminution in mineral processing. In the simplest form, two or more minerals are present in a particle and have to be reduced such that the individual particles contain only one mineral. The complexity of the mineral intergrowth varies from ore to ore. Poor magnetic separation of iron ore may have many causes. In this paper, the emphasis is given to the problem of fine magnetite inclusions in quartz or other gangue minerals. This is highlighted by two Norwegian cases: one on a magnetite ore and the other on a hematite/magnetite ore. The inclusions in question are so small that they are not liberated by reasonable grinding. In both cases, the result has been either poor recovery or lower grade concentrates than desired. The first example concerns production of direct reduction concentrates from magnetite. Magnetic inclusions in gangue particles will be magnetized enough for the particles to pass into the concentrate. The second example is given a more detailed study, where the problem is caused by silicates with small inclusions of magnetite in a combined LIMS and WHIMS separation. This study included microscopy, Davies tube testing, and magnetization measurements. In particular, large gangue particles with magnetite inclusions were shown to have a tendency to bypass the LIMS separators as drag forces in presence of hematite are large. Such particles will then be picked up by the WHIMS as their magnetization is higher than for hematite. This was demonstrated by Davies tube tests, which indicated that such particles were picked up in preference to hematite particles. However, the Davies results did not give a good quantification. Magnetization measurements of gangue particles with magnetite inclusions was shown to be a better tool to quantify the magnitude of the effect of magnetite inclusions in magnetic separation.

Jan 1, 2018

By Paul W. Weiblen, Louis J. Cabri, Rolando Lastra

"Preliminary tests were done to determine whether comminution by electric-pulse disaggregation, or E-PD (cf. Rudashevsky et al; 1995), was more effective than using conventional crushing for Merensky Reef ore. A hand sample of the Merensky Reef was sawn in two: then one sub-sample was comminuted to .2 mm using E-PD at the University of Minnesota, and the other sub-sample was crushed to .2 mm using a conventional jaw crusher at CANMET.The products of the electric-pulse disaggregation and jaw crusher were fractionated by sieving and by a separation using a heavy liquid with a specific gravity of 3.3, because the proportion of platinum-group minerals (PGM) and sulphides to silicate minerals is very low. Thus, four mineral separates were produced: .2000 + 833 µm, -833 +208 µm, -208-µm float and -208-µm sink. All the mineral separates were studied by image analysis (Lastra et al; 1998). The main objective was to determine the liberation of gangue (silicate minerals), chromite, pyrrhotite, chalcopyrite, pentlandite and PGM. In the case of the PGM, a specific image analysis program was written to search and measure these minerals.The results show that the liberation obtained for gangue was similar (~99%) using either method of comminution. However, the liberation obtained for chromite (~89% vs. ~38%), pentlandite (~50% vs. 1%), pyrrhotite (~56% vs. ~38%), and PGM (~56% vs. ~1%) by E-PD was higher than that obtained by conventional jaw crusher, whereas the liberation obtained for chalcopyrite (~20% vs. ~71%) by E-PD was lower. Nevertheless, the image analysis of the products also showed that the PGM are strongly associated with pentlandite. Thus, for the Merensky Reef, liberation of pentlandite from the gangue minerals and chromite is important to recover more of the PGM. This maybe be significant because, in addition to increased recovery of platinum-group minerals (PGM), Merensky Reef pentlandite also contains significant quantities of valuable platinum-group elements like Pd and Rh (Cabri, 1981; Cabri 1988, Kinloch 1982, Peyerl 1983). Hence, the results indicate that for the Merensky Reef, electric-pulse disaggregation would represent a better comminution operation than a conventional jaw crusher would. In addition, the greatly improved liberation for chromite may find application for the PGM-rich UG2 chromitite."

Jan 1, 2003

By Roberto Galery, Priscila Esteves, Braz Cardoso, Marcelo Stopa

"It was developed in this work a computational tool to aid in anomaly detection present in the operation of ball mills. The tool uses a torque estimator that is based on measurements taken exclusively in the drive motor. The ball mill equipment widely used in the mining industry has, inherent to its principle of operation, high energy consumption and low efficiency. These characteristics are accentuated when the mill operates outside the ideal conditions of velocity and loading. Direct measurement of these variables is extremely difficult because it requires the installation of sensors in moving parts of the mill. Thus, systems that can help monitoring the operating conditions and predict anomalies are useful because they contribute to improving the performance of the process, help to reduce the energetic consumption, wear on the mill surface and frequency of maintenance shutdowns. The detection strategy implemented in this work is based on the fact that operational anomalies such as an inadequate percentage of balls and incorrect angular velocity manifest itself as a change in spectral components of the torque signal in the mill driven by an electric motor. The mill torque was estimated by processing motor variables measured by sensors commonly used for control purpose and installed exclusively in the motor. The mill was operated at various fault operating conditions and signals from electric motor and vibration on the mill shaft were measured. The spectral components present in the estimated torque signal were then compared with signals from a vibration sensor in order to establishing a correlation with anomalous operation condition of the mill. The experimental results showed that the signals obtained has an excellent correlation with other variables obtained by direct measurement and have potential to be used to construct a system for automatic fault detection in the operation of ball mills."

Jan 1, 2014

By A. Collings, A. Farmer

Power ultrasound may be used in the processing of mineral suspensions to clean the particle surfaces of oxidation products and fine coatings, mainly through the large, but very localised forces, produced by cavitation. This effect may be utilised in lowering the level of iron contamination in silica sand used for glass making, in improving the sharpness of electrostatic separation of heavy mineral concentrates, in shortening the time of leaching of minerals and in improving the selectivity and recovery of flotation processes. Parameters affecting the efficiency of these processes, such as input power and levels of reagent addition, are discussed. In particular, we present data showing the relationship between power input and the particle size of surface coatings removed, which can be explained by the Derjaguin approximation for the energy of interaction between a sphere and a flat surface. Pilot scale studies, using commercially available components, are currently being used to assess process viability and will be compared with laboratory scale results.

Jan 1, 2003

By A. L. Hinde

The steady-state and dynamic behaviour of semi-autogenous grinding (SAG) mills are arguably best described using a population model that caters for the breakage kinetics and the material trans-port of rock and pulp inside the mill. Breakage kinetics are usually expressed in terms of a specific breakage rate function and a separate primary breakage distribution function. Material transport usually invokes the concept of a specific discharge rate function. Unfortunately, the breakage rate and breakage distribution functions for SAG mills are very difficult to estimate uniquely from plant data alone. Simplifying assumptions must be made to over-come this problem, which leads to many unresolved dilemmas with regard to whether or not the de-rived functions are accurate, precise, and reflect reality. For example, it is sometimes assumed that the breakage distribution function for a SAG mill treating run-of-mine ore can be derived from laboratory dropweight and tumbling tests on small rocks in narrow size ranges. Such tests hardly reflect the environmental conditions likely to be encountered in a pilot or production SAG mill where there is a wide spectrum of particle sizes. It is shown that the dilemmas associated with standard population balance models (models that utilise separate breakage rate and breakage distribution functions) can be overcome by expressing breakage behaviour inside a SAG mill in terms of a single function. This function is an energy-based cumulative breakage rate function defined as the fractional rate at which particles and rocks coarser than a given size break to below that size per unit specific energy input. A model for SAG milling is formulated, which invokes the concept of a cumulative breakage rate function. Comparisons are made between the mathematical structure of this ?simple model? and standard population balance models. Perhaps the most attractive feature of the ?simple model? is that the cumulative breakage rate function can be uniquely estimated from measurements of size distributions and mass flows of the feed and discharge streams together with the size distribution and holdup mass of the mill charge. Such measurement can easily be made at pilot scale. It is concluded that this simplified approach to SAG milling may turn out to be the quickest way to fully describe and quantify the performance of these very complex mills.

Jan 1, 2014

By Yimin Zhu

This paper introduces the sixteen mappings and rules of mineral flotation and the subgroup, period etc in periodic table of chemical element to provide mineral flotation workers to refer in theory and practice research. the nine mappings and rules of mineral flotation and the subgroup, period are Saline minerals including the first main groups and collectors of aliphatic acid and aliphatic amines, Minerals including the second main group elements and collector of aliphatic acid, Hydrated ion of the second main group elements and quartz flotation, The floatability of oxidized minerals including the four main group elements, Organic acid including the fifth main group elements and wolframe, tin flotation collectors, The floatability of sulfide minerals including the fifth main group elements, Inorganic compounds including the seventh main group elements and mineral flotation regulator, Oxidized minerals including the forth Subgroup elements and organic flotation agents with phosphorus and arsenic, Oxidized minerals including the fifth subgroup elements and organic floating agents including the fifth main group elements, Minerals including the first subgroup elements and CN-, Sulfide minerals including the second subgroup elements and CN-, The effect of the highest N-valency inorganic acids or salts including p area elements of the third period in mineral flotation, Oxidized minerals including transition elements of the forth period and 3# flocculating agent, The floatability of minerals including elements of the sixth period, Element area of generating compositions and the collecting theory of mineral flotation and so and. Keywords: mineral flotation, periodic table of chemical element, subgroup, period, regulator, coordination chemistry

Sep 1, 2012

By Janusz S. Laskowski

The flotation-related properties of hexanol derivatives and mono-alkyl ethers of propylene oxide, which include many important flotation frothers (e.g. MIBC, DF-200, DF-250, DF-1012, etc.) have been studied. The obtained results show that the DFI (Dynamic Foamability Index) - CCC (Critical Coalescence Concentration) plot can be used to classify flotation frothers. The frothers characterized by low CCC and high DFI values have properties of strong flotation frothers, while those with high CCC and low DFI values are more selective. The proposed frother classification system, based on simple CCC and DFI measurements, provides, for the first time, a solid ground-work for characterization of the flotation frothers.

Jan 1, 2003

By J. Lindström, J. Hamuyuni, M. Lundström, J. Aromaa

"The rising demand for metals today, coupled with the scarcity of primary sources for raw materials threatens both technological advancements and industrial manufacturing. In order to meet the demand, metals and other resources trapped in waste streams, have to be harnessed. This philosophy supports circular economy, where metals and other resources are kept in a closed loop. The pickling acid recovery system of most stainless steel production is one such example where the dissolved metals such as iron, nickel and chromium are currently not completely recovered due to the limitations of the current technologies. The aim of this study was to assess the available metals recovery methods from extremely concentrated acids. The main aim is to simultaneously recover metals and keep sulphuric acid reusable in acid circulation process. From the available literature, the most promising methods were chosen for laboratory experiments. Based on experimental work, the results and observations of electrodeposition, solvent extraction, and freeze crystallization are provided. KEYWORDS Pickling acid, metal recovery, solvent extraction, cathodic polarization, Freeze crystallization. INTRODUCTION Pickling in stainless steel production is an essential surface treatment process (Regel-Rosocka, M. (2010); Agrawal and Sahu, 2009). It is applied for removing surface films such as oxides and chromium-depleted layers to improve the corrosion resistance and surface finish of steel (Regel-Rosocka, 2010). Whilst the process greatly improves the surface finish of the stainless steel, it generates large amount of used acid, containing dissolved metals including chromium, iron, and nickel (Agrawal and Sahu, 2009). Recovery of acid is common practice for most steel producing industries (Nyman and Koivunen, 1986). In this work, acid regeneration process is investigated so as to simultaneously reusing sulfuric acid and recovering the dissolved metals. Recovery of valuable metals even in very small amounts would also bring additional revenue to the steel production industry. At a time when metal production has also been challenged by lack of natural resources for raw materials, secondary sources for metals such as the acid pickling process therefore, have greater potential as supplements. From earlier studies, electrodeposition (Giovanardi and Orlando, 2011; Kuznetsov et al., 200; Rögener et al., 2012; Surviliene et al., 2006), solvent extraction (Alguacil and López 1996; Haghshenas et al., 2009; Kesieme et al., 2013) and freeze crystallization (Beyer et al.,2003; Hasan et al.,2017; Van der Ham et al., 1999) are some of the most established potential methods. Earlier studies have also shown that simultaneous recovery of acid and metals would require combination of different methods. This is primarily due to the nature of very stable metal containing complex compounds formed during pickling. These complexes must be broken down to free the metals for further recovery processes."

Jan 1, 2018

By G. K. Nimal Subasinghe

The performance of Knelson Concentrators (KC) used in gravity gold circuits often rely on manufacturers recommendations for selecting operating parameters such as, fluidising water flow rate and cycle time. These parameters are not only dependent on the machine parameters but also on the feed characteristics such as, size distribution of the gold and gangue particles and the composition of its constituent minerals. Particles entering a KC experience a centrifugal acceleration due to the high bowl rotational speeds. The required centripetal force to maintain a circular orbit is provided by the fluid drag force created by inwardly moving fluidising water and the Bagnold?s force arising from the particle/particle collisions. When the fluidising water flow rate is low particles move towards the outer rim of the bowl forming a packed bed within the grooves. On the other hand, if the fluidizing water flowrate is high the bed expands and some particles would move towards the centre of the bowl and gets carried to the tailings stream, thereby reducing the amount of material retained within the grooves of the bowl. Based on a force balance on a particle captured within the KC, a criterion which can be used to predict the amount of material recovered in the bowl has been derived and validated by experimental data. It has been shown that this criterion may be used to demarcate the transition of the bed from a packed-bed state to a fluidised state depending on the fluidizing water flowrate. By identifying the conditions for the optimal expansion of the bed comprising different constituent mineral particles, it is possible to estimate the optimal fluidising water flow rate that would maximise gold recovery while minimising gangue recovery. It was also observed that the accumulation of valuable mineral in the bowl takes place by the displacement of the gangue particles in the bed by the incoming heavy mineral particles. The kinetics of this segregation process was also studied using synthetic mineral mixtures. The experimental data suggests that this process follows first order kinetics and that the build up of heavy mineral reaches a maximum which could be used to identify the optimal cycle time. In this work, the suitability of the above model in optimizing the performance of a KC have been reviewed. Also the necessity and merits of testing an unaltered

Jan 1, 2014

By Chris A. Fleming

"The ability to recover cyanide from gold plant tailings has been known almost as long as the cyanidation process has been practiced, but there has been little incentive to process tailings in this way in the past. With the development of technologies that make it possible to recover and recycle free or complexed cyanide directly from gold plant slurry tailings, which indicates, on paper at least, significant cost savings compared to cyanide destruction, coupled with the introduction of legislation to seriously limit the discharge of cyanide to the environment in most gold-producing regions of the world, many companies are evaluating the cyanide-recovery alternative.There is arguably an even more compelling reason for mining companies to consider cyanide recycling. With the growing storm of negative public opinion that the use of cyanide in the mining industry is attracting - following several highly publicized spills over the last couple of years - the time has come for the gold industry to demonstrate environmental diligence and stewardship in the use of this commodity that is so vital for their industry. There is no doubt that the widespread implementation of cyanide recycling will reduce the impact of the cyanidation process on the environment, both by reducing the risk of spills (with less cyanide being transported from manufacturing plants to gold mines), and by reducing the loading of toxic and nontoxic metals and ions in the tailings.This paper briefly discusses the pros and cons of the different processes that are available for the treatment of gold plant tailings to regenerate and recovery cyanide for recycling, and presents a techno-economic argument for the incorporation of this technology into many gold plant flowsheets today."

Jan 1, 2003