Search Documents

By A. M. Amdur, A. N. Matushkina, G. I. Gazaleeva

"The article highlights results of theoretical and practical studies on the enlargement of fine gold in the process of heat treatment. The object of research is refractory gold silicate-carbonate ores of Vorontsovskoe Deposit (Northern Ural), containing fine gold. For setting up experiments and analyzing the results were used the methods of applied mathematics, mathematical statistics, mathematical and physical modeling. Modeling and calculations were performed using the software package HSC Chemistry 6.0, MatLab, setting up a full factorial experiment and other modern modeling methods. Using a scanning electron microscope, the distribution of fine-dispersed ore gold particles by size was studied. It was found that gold particles smaller than 0,4 µm smoothed the vertices and edges, i.e. they are of globules with an amorphous structure. Amorphous materials are nonequilibrium phases with high thermodynamic activity. The physicochemical properties such as melting temperature, diffusion coefficients, the content of metal impurities differ from the properties of the solid phases. In the course of the research were formulated the following scientific bases of the mechanism of enlargement of the gold particles: - the movement of dispersed droplets of gold in the process of external heat to the surface of the ore particles in the pore occurs under the action of thermocapillary pressure; - after melting of the host rock occurs flotation of molten droplets by the bubbles of gases and coagulation of fine gold; - the conditions of flotation drops of gold in oxide melts; floated drops of radius R = 1-100 µm. Analysis of the equilibrium at the perimeter of wetting a drop of gold-oxide melt-gas showed that the scheme of the tension will not significantly differ from the case of solid gold, while the radius of the gas bubbles should be at least 2 times greater than the radius of drops of gold. The proposed method of predicting the results of the enrichment of the proposed scheme, including heat treatment and gravitational centrifugal concentration of crushed ore. Experimental verification of the proposed scheme in the laboratory showed a satisfactory convergence of experiment and prediction. Gold recovery in the concentrate was 33,84 against 33,7 percent forecast. The increase in overall gold recovery to a gravity concentrate after heat treatment is more than 20 %."

Jan 1, 2018

By Francisca San Martín, Martin Rudolph, Willy Kracht, Tomás Vargas

It has been shown that bacteria Acidithiobacillus ferrooxidans can be used to depress pyrite in seawater flotation at natural pH, which opens the possibility for its use as an alternative to lime to depress pyrite in copper sulfide flotation. In order to have a better understanding of the mechanisms involved in pyrite depression with A. ferrooxidans, an exploratory experimental campaign was carried out, including attachment density and contact angle measurements, and the effect of adding bacteria before or after collector. Biodepression of pyrite improves when increasing pH from 3 to 8, with a decrease in recovery from 92% to 36%. This increase in depressing capability is accompanied by an increase in attachment density, from 2.58×108 bacteria/g to 1.99×109 bacteria/g at pH 3 and 8, respectively, suggesting that the mechanism of depression is related to the attachment of bacteria to the pyrite surface. It was observed that the conditioning sequence with collector and bacteria influences the biodepression capacity of A. ferrooxidans. Having as a reference a value of pyrite recovery equal to 97%, when using only xanthate in seawater flotation at pH 8, the effect of both conditioning with bacteria-followed-by-xanthate and xanthate-followed-by-bacteria were assessed. When bacteria were added before the collector, the recovery of pyrite decreased to 36%. On the other hand, when bacteria were added after collector, the recovery was 64%, showing that biodepression of pyrite with Acidithiobacillus ferrooxidans is more efficient when the conditioning is carried out first with bacteria. The contact angle values show that there is little effect of the second component added to the system, i.e., if pyrite is first conditioned with bacteria, the contact angle does not change significantly once the xanthate is added (bacteria-followed-by-xanthate). The same was observed when the conditioning sequence was xanthate-followed-by-bacteria.

Jan 1, 2018

By S. Narra, M. Nelles, I. Eickhoff, S. Teitge

"The aim of the research is to develop a holistic process flow for the recycling of glass fibres from glass reinforced plastics (GRP) and carbon fibres from carbon fibre reinforced plastics (CFRP), wherein the dissolution of the fibre epoxy resin matrix, separation of fibre fractions and their renewed material use is intended. In clear distinction to the previous research and development projects, the aim here is to recycle complex composite structures such as dismantled/disused wind turbine rotor blades and end-of-life composite wastes. In the course of the study, mechanical, hydrothermal and thermal processes and their combined procedures will be developed. As the fibre length is a decisive quality criterion in the recycling of composite materials, the further focus of the study will be the development of upstream and downstream material processing, in which the fibres are retained in their original form. The evaluation of the recycled fibres obtained is based on the elemental composition, measurement and morphological evaluation of individual filaments by scanning electron microscope (SEM), micro tensile tests on single fibres and their comparison to virgin fibres. The resulting process water is analysed by gas chromatography and mass spectroscopy (GC-MS) and a potential recirculation is determined. In cooperation with companies from the composite processing industry as well as recycling companies, a return of the recycled fibres to the known manufacturing process will be examined and an energetic and economic evaluation of the overall process will be carried out. Ambitious aim of the study is to achieve an actual recycling instead of the present downcycling or the energetic utilization. INTRODUCTION As global warming increases, so does the awareness of consumption and production of energy. To counteract the effects of global warming, renewable energy has been increasingly used during the last two decades, not only in Germany, but worldwide. Both, hydropower and wind energy, hereby play a fundamental role. After the end of their useful life of 20 to 30 years, the wind turbines (WTs) are being dismantled. Due to their foundations and tower segments, their recycling rate hereby exceeds 90% by mass. So far, the resulting rotor blade waste played a minor role accounting for only 2 - 3 weight-% of the total plant. Rotor blades of modern wind turbines are made of glass and carbon fibers, which are embedded in an epoxy or polyester resin matrix, balsa wood, PU or PET foams as fillers as well as various paints and coatings. These wastes currently end up in waste incineration or are sold to non-European countries."

Jan 1, 2018

By M. Ito

Cobalt-rich ferromanganese crust and nodule ores from seamount areas contain volcanic and sedimentary rocks as substrate or nuclei and these ores require mineral processing to remove the substrate/nuclei rock before smelting. This paper reviews the results of jig separation and air table treatment for the coarse fraction and flotation and hybrid jigging for the fine fraction. Using these techniques substrate/nuclei rock was removed from the cobalt-rich ferromanganese oxide components. The mineralogical properties and metallurgical treatment methods including hydrometallurgical treatment of low grade ore is also reviewed.

Sep 1, 2012

By M. Mirnezami

Pentlandite samples were obtained as Ni concentrate from three Canadian plants and one specimen sample from Ward?s Scientific Establishment. The samples were upgraded using gravity and magnetic separation techniques. Nickel concentration was determined by atomic absorption spectroscopy. Microprobe analysis identified a range in Co and Cu lattice substitutions. All samples exhibited similar zeta potential-pH trend with isoelectric points from 2 to 3, and similar responses to copper activation and addition of xanthate. The similar trends indicate that the variations in lattice substitution identified have no significant effect on electrokinetic properties; that is, samples from any source likely yield results that can be generalized.

Sep 1, 2012

By Massimiliano Zanin, William Skinner, Owusu Clement, Jonas Addai-Mensah, Daniel Fornasiero

This paper highlights the importance of pulp aeration in the selective separation of chalcopyrite from chalcopyrite/pyrite mixtures of varying pyrite content (20-80 wt.%). Laboratory batch flotation studies and oxygen demand tests were performed to predict the optimum amount of air required for the selective separation of chalcopyrite from pyrite. The pulp oxygen demand was shown to increase with increasing pyrite content but decrease with time as more air is introduced into the system. Complementary batch flotation tests showed significant improvement in chalcopyrite flotation under moderate pre-aeration of the pulp. However, a continuous decrease of chalcopyrite flotation was observed under highly aerated conditions. The amount of air required to achieve maximum chalcopyrite flotation recovery correlated positively with the mass fraction of pyrite in the pulps. The greater the wt.% of pyrite in the chalcopyrite/pyrite pulp, the longer the aeration time required. The optimum aeration time was established as the time before which the oxygen consumption rate constant reaches a bottom plateau. Surface analysis (XPS) indicated that the continuous decrease in pyrite recovery observed with increasing aeration time was due to the formation of more iron oxy/hydroxide on its surfaces, the same species accounting for the decrease in Cp recovery after prolonged aeration.

Jan 1, 2014

By R. D. van der Weijden, W. F. C. van Wageningen

"Copper(II) can be recovered or removed from acidic copper sulfate solutions as cuprite or metallic copper powder by reduction with carbohydrates (van der Weijden et al., 2001, 2002). In order to make this process suitable for a commercial scale pipe reactor, process conditions and reactor configuration need to guarantee proper throughput of the dilute suspension. This is where crystal engineering also comes into view. Copper powder characteristics, such as size and shape of particles, influence the tendency to adhere to reactor walls and to agglomerate, which in turn influence the throughput. Furthermore, separation, drying, packaging and product quality, are dependent on the powder characteristics.In this paper the effect of both chemical and physical parameters on the shape and size of particles were systematically studied in a number of autoclave experiments. These parameters include mixing, Cu(II) concentration, pH, temperature, seeding, use of additives and reactor materials. Additionally, Monte Carlo simulations of copper growth inside a Kenics static mixer were made. Results show that the use of additives, and the use of static mixers influence particle characteristics the most."

Jan 1, 2003

By Gaurav Soni, Roe-Hoan Yoon

A first principle flotation model has been derived from the basic mechanisms involved in flotation. The model consists of a series of analytical equations for bubble generation, bubble-particle collision, attachment, detachment, and froth phase recovery. The model can predict flotation from both hydrodynamic and surface chemistry parameters such as bubble size, particle size, energy dissipation rate, ?-potentials, contact angles (?), etc. The model predictions have been compared with the results of a series of laboratory flotation tests conducted using mono-sized glass beads of different particle sizes and contact angles under different operating conditions. Some of the experiments were conducted using a 1:9 mixtures if hydrophobic silica and hydrophilic magnetite, so that the product graded could be readily determined by simple magnetic separation. The model predictions are in good agreement with the experimental results both in recovery and grade. A computer simulator developed on the basis of the model is capable of designing a preliminary flotation circuit on the basis of feed characteristics, e.g., size-by-liberation data, and the hydrodynamic information on the flotation cells to be incorporated in the circuit.

Jan 1, 2014

By Brian Lindner, Lidia Auret, Niel Knoblauch

In this paper, a fault detection and identification framework based on feature extraction and topology extraction methods is proposed, and evaluated on a simulated base metals refinery high pressure leaching process. Feature extraction methods included linear and kernel principal component analysis, while process topology information was extracted with linear cross-correlation, partial cross-correlation and transfer entropy. Connectivity maps were constructed to identify possible fault propagation paths to aid root cause analysis. The results indicate that process topology can enhance the fault identification capability of data-based process monitoring methods. The study of the considered base metals refinery pressure leaching process is ongoing, with future work including the creation of a fault library which would lead to further critical evaluation of the proposed fault detection and identification framework.

Jan 1, 2014

By M. Brozek

The particle settling velocity is the argument of separation in such processes as classification and enrichment in jigs. It characterizes material forwarded to the separation process and belongs to the so-called complex arguments because it is the function of particle density and size. i.e. the function of two simple arguments. The affiliation to a given subset is determined by the values of two mag-nitudes and the distribution of such argument in a sample is the function of distributions of particle density and size. The paper will present a method of determining the distribution of settling velocity in the sample of spherical particles for the turbulent particle motion in which the settling velocity is expressed by the Newton formula. Because it depends on density and size of particle which are random variable of certain distributions, the settling velocity is a random variable. Applying theorems of probability, concerning distributions of function of random variables, the authors will present general formula of probability density function of settling velocity for the turbulent motion and particularly calculate probability density function for Weibull?s forms of frequency functions of particle size and density. Distribution of settling velocity will calculate numerically and perform in graphical form.

Jan 1, 2014

By L. A. Cisternas, R. I. Jeldres, C. Cruz, P. A. Robles

"Previous studies have shown that the floatability of chalcopyrite in seawater at highly alkaline conditions is significantly affected by the presence of clays. The reason is that the species of calcium and magnesium present in seawater under those conditions may act as a bridge between the surfaces of clay and chalcopyrite, generating massive aggregates that then depress. In this context, the objective of this work is to analyze the impact of pretreated seawater with low amount of calcium and magnesium ions on the recovery of a sulphide copper mineral with high kaolinite content as clay. The seawater pre-treatment is done by the addition of sodium hydroxide in a high carbon dioxide environment. The chemical reactions realized under these conditions lead to the formation and precipitation of calcium and magnesium species that are subsequently removed by vacuum filtration. The pre-treated seawater is then used in flotation tests at pH 11 for copper sulphide, where the mineral is synthetically prepared by mixtures of chalcopyrite, kaolinite, and quartz. When comparing the flotation results for different types of water, including seawater and pre-treated seawater, a significant effect is observed: as the seawater hardness decreases, which comprises the calcium and magnesium ions, the recovery of chalcopyrite is increased. However, the effect is markedly enhanced in the presence of kaolinite. Therefore, the results indicate that sodium hydroxide and carbon dioxide are able to remove different species of calcium and magnesium from seawater and could improve the chalcopyrite recovery with high kaolinite content. INTRODUCTIONIn many cases, mineral deposits are found in arid areas with little access to water resources. Water is a fundamental element to carry out the unit operations that achieved the separation of valuable minerals (especially in concentration operations). Seawater has acquired an interesting role in recent years (Cisternas and Moreno, 2014); in fact, it seems to be one of the few viable options to ensure the sustainability of the mining industry in arid zones. At present, there are numerous experiences of industries that use or have used this resource, either by submitting the seawater to a desalination treatment by reverse osmosis or by applying it directly, without desalting. The latter case may involve significant economic benefits (for example, by avoiding the investment of building a desalination plant) and in some cases some operational benefits. A positive aspect is that in general terms the foaming in the saline medium is much more efficient compared to fresh water (Quinn et al., 2014; Castro et al., 2010). Some reports show that the foaming doses required to achieve a certain quality of bubbles are remarkably reduced, reaching exceptional cases such as Xstrata's Raglan concentrator, where it did not even include foaming to carry out the operation. This fact is quite promising, considering that some researchers have stated that controlling the quality of bubbles and foam could float minerals through coarse particles. This would lead to multiple benefits, such as energy savings by avoiding excessive grinding and a lower presence of fine ore that causes major problems in water recovery operations by gravitation (such as thickening) and in tailings management. However, seawater also causes significant challenges in multiple operations (Jeldres et al., 2017, 2016; Castro et al., 2010), as for example in minerals with high clay content (Uribe et al., 2017). In fresh water, the presence of clays minerals in ores is already a major problem in the flotation stages since the operation becomes difficult to be controlled, and operators are commonly forced to increase the consumption of reagents because the collectors are deposited on the clays' surfaces reducing froth stability (Farrokhpay and Bradshaw, 2012). Sometimes the use of rheology-modifying reagents should also be incorporated since the pulps become more visc"

Jan 1, 2018

By M. Rudolph, D. H. Hoang, N. Kupka

"Froth flotation has been subjected to modelling since the 1930s and there is a large variety of approaches that intend to portray the entire process. Among these, three fundamental models could be considered exhaustive: the Pyke model [1], the Yoon model [2] and the Schwarz and Koh model [3]. The first model makes use of the generalized Sutherland equation collision model, the Dobby-Finch attachment model and its own stability model, the second model considers an extended DLVO approach for the attachment and stability whereas the third model makes use of computational fluid dynamics. Using a scheelite ore as a test case, a specific batch flotation test was repeated ten times and analyzed for chemical assays, mineralogical studies and froth properties. The detailed data are used to feed the three flotation models aforementioned in order to compare the outcomes of the three approaches, their capacity to reflect reality and to predict it. This article intends to pave the path towards reliable process models incorporating in depth mineralogy information, e.g. surface liberation, particle size and particle shape. KEYWORDS Froth flotation fundamental models, scheelite, automated mineralogy, critical assessment. INTRODUCTION In mineral processing, only three approaches aiming at describing froth flotation fundamentally could be considered exhaustive: Pyke’s collision and sliding approach [1], Yoon’s kinetic approach [2] and Schwarz and Koh’s approach [3]. The models will hereafter be referred to as Pyke model, Yoon model and Schwarz and Koh model. The first model makes use of the generalized Sutherland equation collision model, the Dobby-Finch attachment model and its own stability model, the second model considers an extended DLVO approach for the attachment and stability whereas the third model makes use of computational fluid dynamics. All three approaches rely on the widely accepted idea that flotation is a kinetic reaction dependent on a flotation rate constant kp, as expressed in Eq. [4]:"

Jan 1, 2018

By Matveyeva Tamara

The main deposits of gold-sulfide ores of Russia are characterized as refractory raw material with the non-uniform finely-interspersed sulfide mineralization, submicron gold, the low gold content (3-5 ppm) and non-uniform distribution of the gold associated with pyrite and arsenopyrite. These ores show low indicators of extraction of gold and silver at cyanidation. Flotation is one of the basic technological procedures of processing of gold sulfide ores however simultaneous presence of pyrite and arsenopyrite and lack of effective methods of their selection constrains application possibility of flotation schemes because of rigid requirements to flotation concentrates under the arsenic content and practically excludes smelting of pyrite concentrate. The main losses of precious metals at flotation technologically are concentrated in thin classes (up to 15 %) demonstrating an inefficiency of standard reagent modes. For an estimation of expediency and possibility of application of selective flotation of pyrite and arsenopyrite a scientific substantiation of the mechanism and criteria of selection of gold-bearing ferrous sulfides of various material structure is developed and for difficultly divided pairs of sulfides with close technological properties the new selective reagents providing effective extraction of gold from hard-to-beneficiate ores are designed. The original technique for modifying surface composition of natural sulfides by nano-sized Au is worked out and the mechanism of selective adsorption of new reagents ? oxypropyl ester of diethyl-dithiocarbamatic acid (OPDTC) and oak bark extract (OBE) on Au-bearing sulfide minerals is revealed. Formation of almost insoluble OPDTC-Au compounds is defined by methods of scanning electronic microscopy (SEM) and UV-spectroscopy. Application of developed reagent modes using new reagents have been tested in laboratory conditions at flotation gold-sulfide ores samples and collective concentrate probes providing high extraction of gold and improved quality of the concentrate (less than 2 % As). Keywords: pyrite, arsenopyrite, selective flotation, flotation reagents adsorption, complex-forming, gold recovery.

Sep 1, 2012

Goethite ore are the third most abundant source of iron. The overwhelming part of these ore is represented by low-grade varieties which cannot be used in iron and steel industry without preliminary beneficiation. Biomass is a renewable solid fuel, which is feasible for the substitution of coke and coal in the manufacturing due to its lower contents of harmful elements and abundant raw material sources. Utilization of biomass in iron ore sintering process as heating agent and reducing agent contributes to energy conservation and emission reduction. The biomass was mixed together with goethite ore for roasting process to investigate the effects of reduction roasting. The results show that the goethite ore is dramatically reduced and magnetized into maghemite by biomass with the biomass dosage less than 20% and the roasting temperature below 650 oC. When the goethite ore roasted with biomass, the magnetization values could be enhanced more than two orders of magnitude, meets the standard of magnetic separation, which could significantly reduce the iron beneficiation cost. Keywords: biomass, goethite, reduction, magnetization, roasting

Sep 1, 2012

By William Skinner, Jennifer MacCarthy, Jonas Addai-Mensah, Ataollah Nosrati

"Acid leaching in agitated tanks is central to hydrometallurgical processing for valuable metals’ (e.g., copper, gold, nickel and cobalt) recovery from low grade (e.g., < 2 wt.%) ores. In this study, atmospheric leaching behaviour of Australian saprolitic nickel (Ni) laterite ore using sulfuric acid was investigated under isothermal, batch conditions at pH 1. The effect of primary process variables comprising time (4 h) and temperature (70 and 95 oC) on the leaching mechanisms and kinetics was established for -2 mm, low grade (~1 % Ni) saprolitic ore dispersions at 40 wt.% solid loading. Leaching proceeded incongruently, reflecting the proliferation of gangue minerals’ constituent elements (e.g., Mg, Al, Fe) alongside Ni and Co in the pregnant leach solutions (PLS). Subsequent analysis showed that 89% Ni and 78% Co were extracted after 4 h at 95 oC whilst at 70 oC the recoveries of these metals were markedly low (< 25 %). Overall, 177 and 644 kg H2SO4 /t dry ore were consumed at 70 and 95 oC, respectively. Activation energy of 79.0 ±1.0 kJ/mol was estimated for the mechanism of Ni and Co leaching and associated kinetics. Particles size analyses indicated that when the breakage of frail laterite particles due to shear is taken into consideration, differences in feed and leached product particle size distributions were insignificant , despite a remarkable increase in BET specific surface area of the product. Mineralogical analyses of the feed ore and leached solid products revealed a sub-crystalline silica phase enrichment of the latter. The overall results suggest that the mechanism of acid leaching of saprolitic Ni laterite may be described by a chemical reaction-controlled, shrinking core model."

Jan 1, 2014

By Chiharu Tokoro

Acid Mine Drainage (AMD), high acid water containing heavy metals discharged from mines, has been recognized as major cause of mine pollution. In Japan, the government spends billions of yen every year to prevent pollution caused by AMD in about 80 abandoned mines. It is widely recognized that the treatment could continue for long decades or an even century. However, costs and environmental loads are uncertain during the treatment because a predictive model for the quality of AMD, the dosage of neutralizer, and the amount of sludge that is applicable for abandoned mines with limited data has not yet been established. In this study, a two-steps predictive model for solution composition and neutralization chemical requirements of AMD in future was constructed based on the geochemical modeling. Requisite input data of the model was the past historical water quality data from AMD monitoring, such as metal concentration and pH in the solution, instead of the sample rocks as other conventional prediction methods. In the first step, solution composition of AMD in the future was extrapolated from the available historical data using geochemical simulation considering the first order kinetics for the mineral dissolution. In the second step, neutralizer dosage and sludge generation in the future was predicted based on the geochemical simulation supposing the chemical equilibrium and oxidation state for all of elements in the solution. Based on case studies of two abandoned mines in Japan, solution composition, neutralizer dosage and sludge generation were estimated. The results of this study demonstrate the effectiveness of our model for the prediction of AMD quality and chemical requirements of neutralization treatment after mine closing. The model is useful for the estimation of the neutralizer dosage and the sludge volume in abandoned mines with limited data. Keywords: acid mine drainage, predictive model, geochemical modeling, first order kinetics, water monitoring

Sep 1, 2012

By Aziza A. Yousef, Suzan S. Ibrahim, Mahmoud A. Arafa, Mohamed A. Abdel Khalek

In view of the shortage of soft water all over the Middle East countries, seawater may be used to replace the fresh water in flotation beneficiation. The flotation process required about 7 m3 of fresh water/ ton ore. This article aimed to study the effect of seawater cations and anions on the flotation process of four important mineral commodities. The adsorption of collector, zeta-potential, zero point of charge and floatability of pure minerals were studied. The individual effects of different cations and anions that are predominant in seawater, within their more or less actual concentrations were studied on individual mineral and on groups of them. The troublesome Ca2+ and Mg2+ ions, in the anionic circuit could be controlled by soda ash addition to the pulp before the anionic collector. The addition of sodium silicate improved the floatation selectivity of mineral mixtures and natural ore. At the optimum conditions the calcareous phosphate ore yielded a concentrate recovery of 83% with a grade of 34% P2O5, with 0.61%MgO, which from an ore assaying (25.3% P2O5 and 9.4% MgO).

Jan 1, 2003

By G. Venkateswara Rao

The jigging of ferrous ore to produce higher-grade products has been practiced for many decades. This is due to easy separation, a beneficial trade- off between operating cost and reduced yield relative to Dense Media Separation (DMS). Jigging becomes prominent for beneficiation of iron ores in the coarser size range. At present drive is towards the use of under bed air pulsed jigs for the beneficiation of ferrous ores. The main advantage is that the under bed air pulsed jigs are capable of generating the large pulse of amplitudes required to fluidize a deep bed of heavy ores particularly lump iron ore up to 40mm size. The major jig parameters effecting the jigging operation are bed height, shape of the pulse, residence time, operating pressure, valve cycle time and water flow rate. With the pulse shape set correctly for optimum stratification rate, even it is still necessary to provide enough residence time, to ensure the difficult material will take time to migrate to the expected layer in the bed. In order to find the Jig Stratification Index (JIS) parameters like bed height, operating pressure, water flow rate, cycle valve time and shape of the pulse were optimized first by conducting various tests. Typical Iron ore samples from Odisha (both lump and fines) were subjected to stratification studies at residence time of 1, 5 and 15 minutes. Jig Stratification Index (JSI) for both lump (0.30) and fines (0.20) were determined by using APIC Jig. The maximum possible JSI was calculated by using heavy liquid separation test (0.42 for lump and 0.24 for fines). It is found that the jig bed JSI is less than the Heavy liquid JSI for both lump and fines. The ratio of Jig bed JSI to the heavy liquid JSI is 0.83 for lump and 0.71 for fines. The JSI and ratio of Jig bed JSI to Heavy liquid JSI are low for fines due to fluid turbulences causing some degree of remixing in the jig bed. The fluid turbulences are more for fines than lump, hence jigging of fines is difficult and challenging. Keywords: sub grade iron ore, gravity separation, jigging, apic jig, stratification, residence time, jig stratification index

Sep 1, 2012

By Eberhard Gock

The worldwide implementation of corrosion protection of low alloyed automotive metal sheets by zinc coating has led to supply shortages of zinc free non-alloyed steel scrap in the foundry industry. In a collaboration project, partly financed by the German government, with partners from the automotive industry, zinc metallurgy, scrap trading, foundry industry, and plant construction, a new acid-based pre-dezincification process has been developed, and a pilot plant with throughput of about 100 t/d has been put into operation at the Clausthal Umwelt-Institut GmbH (CUTEC) together with the Clausthal University of Technology in Germany. During the treatment process, acid from a zinc metallurgical plant will be supplied, which can be recycled to the primary zinc extraction process after raising the zinc concentration to more than 130 g/L zinc. This way, the separation of small amounts of iron by precipitation and the electrolytic zinc winning are outsourced and, as a result, the pre-dezincification process runs waste-free. In Germany, the amount of zinc coated ?new scrap? is approx. 3 million t per year with a zinc content of approximately 60,000 t per year. The possible additional incomes for the dezincified steel scrap are in the order of ?40 to ?50 per ton of scrap, the gained zinc content during the acid dezincification defrays the costs of the process, if the throughput is more than 700 t/d. In comparison to conventional dezincification during the electro arc furnace process followed by upgrading in a rotary kiln (Waelz process), the acid dezincification process running at a maximum of 50°C will cut the energy costs by up to 74% and the CO2 emission by up to 88%. In fact, a demonstration plant is being designed right now and will be installed for processing a part of the zinc coated metal scrap from the Volkswagen AG in Wolfsburg, Germany. Keywords: steel scrap, zinc-coated steel, dezincification methods, acid

Sep 1, 2012

By S. Castro

Molybdenite flotation is strongly depressed at pH higher than 9.5 in the flotation of Cu-Mo ores in sea water. Chemically sea water contains mainly Na+ and Cl- ions, but also some secondary ions, such as SO42-, Mg2+; Ca2+, HCO3-; etc., which are not necessarily indifferent for the flotation of molybdenite. The natural floatability of molybdenite in sea water and in NaCl solutions containing different secondary ions is investigated by micro-flotation tests. The tests indicate that the floatability of molybdenite in alkaline media in 0.6 M NaCl solutions is not affected by the presence of anions, such as, SO42- and HCO3-, at concentrations similar to those occurring in sea water. However, a strong depression of molybdenite at pH ranging from 9.5-10.0, is produced by the alkaline earth metal cations (Ca2+ and Mg2+ ions), dissolved in distilled water or in 0.6M NaCl solutions. It was found that effect of Mg2+ions is significantly stronger than Ca2+ ions. Effect of both ions is attributed to hydrolysis and adsorption of MOH+ hydroxy-complexes. This is followed by subsequent precipitation of hydrophilic colloidal hydroxides at the molybdenite/solution interface, and in bulk solution.

Sep 1, 2012