Gravity Separation Techniques Research Articles

Pre-concentration of REE values from nepheline syenite rocks of western Odisha, India

ABSTRACT The rare-earth elements (REEs) have gained enormous economic and scientific attention due to their distinct properties and new applications. Nepheline syenite rock is an important primary source of rare earth minerals. The nepheline syenite rocks from the Rairakhol area, western Odisha, have been characterized for their rare earth mineralogical and textural characteristics. Preliminary beneficiation studies of these rocks were carried out to upgrade the REE values using falcon gravity separation and floatation technique. Hornblende, biotite, K-feldspar, albite, and nepheline are the major mineral constituents of the nepheline syenite where REE-bearing minerals occur as accessory minerals. The REE mineral phases present are zircon, sphene, apatite, allanite, britholite, and REE phosphate, with grain sizes ranging from 10 to 50 microns. Allanite and britholite occupy the intergranular spaces of major mineral phases and occur as thin lines or veins whereas sphene and zircon occur as inclusions within major mineral phases. The flotation study shows that the total REE content of the froth product could be enriched to 1696 ppm, which is three times more than the total REE content (563 ppm) of the feed sample.

Characterizing low-grade refractory gold ores using automated mineralogy coupled with LA ICP-MS

Researchers have made notable progress in quantifying refractory components causing gold losses in traditional extraction methods. The potential for improving gold recoveries lies in targeted re-treatment of the 'invisible' gold fraction hosted within various ore minerals, even at low concentrations. This study presents a methodology for analysing the refractory components that cause gold losses in traditional extraction methods. The approach utilizes automated mineralogical techniques in conjunction with in-situ laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) to characterize low-grade refractory ores and assess gold deportment. The methodology combines pre-concentration gravity separation, traditional chemical and mineral techniques, and LA ICP-MS to generate comprehensive datasets. To demonstrate the practical application of the methodology, a case study was conducted on historical tailings material from Witwatersrand's Evander Goldfield in South Africa. The case study aimed to determine the mineralogical distribution of gold that cannot be extracted through cyanidation. The results indicated that invisible gold is primarily hosted in pyrite (with an average concentration of 10.21 ppm representing 32 % of total gold), other sulphides (with an average concentration of 1.29 ppm representing 0.42 % of total gold), and oxides (with an average concentration of 0.50 ppm representing 1 % of total gold). The remaining gold is present in discrete fine cyanide amenable phases (with 28 % deportment) and silicate-hosted phases (with 39 % deportment). Environmental monitoring of the Witwatersrand tailings material revealed a net “acid-producing” nature, with high concentrations of heavy metals (such as As, Cu, Pb, Mn, Hg, and Ni) associated with sulphides (with over 78 % deportment). The deportment information obtained through this approach can optimize ore processing strategies and provide valuable insights for future remediation plans. By characterizing the refractory components causing gold losses and understanding the distribution of gold within the ore, this methodology offers the potential to enhance gold recovery and improve the efficiency of ore processing operations.

Reapplication Potential of Historic Pb–Zn Slag with Regard to Zero Waste Principles

Smelting used to be less efficient; therefore, wastes obtained from historical processing at smelter plants usually contain certain quantities of valuable metals. Upon the extraction of useful metal elements, metallurgical slag can be repurposed as an alternative mineral raw material in the building sector. A case study was conducted, which included an investigation of the physico-chemical, mineralogical, and microstructural properties of Pb–Zn slag found at the historic landfill near the Topilnica Veles smelter in North Macedonia. The slag was sampled using drill holes. The mineralogical and microstructural analysis revealed that Pb–Zn slag is a very complex and inhomogeneous alternative raw material with utilizable levels of metals, specifically Pb (2.3 wt.%), Zn (7.1 wt.%), and Ag (27.5 ppm). Crystalline mineral phases of wurtzite, sphalerite, galena, cerussite, akermanite, wüstite, monticellite, franklinite, and zincite were identified in the analyzed samples. The slag’s matrix consisted of alumino-silicates, amorphous silicates, and mixtures of spinel and silicates. Due to the economic potential of Pb, Zn, and Ag extraction, the first stage of reutilization will be to transform metal concentrates into their collective concentrate, from which the maximum amount of these crucial components can be extracted. This procedure will include combination of gravity concentration and separation techniques. The next step is to assess the Pb–Zn slag’s potential applications in civil engineering, based on its mineralogical and physico-mechanical properties. Alumino-silicates present in Pb–Zn slag, which contain high concentrations of SiO2, Al2O3, CaO, and Fe2O3, are suitable for use in cementitious building composites. The goal of this research is to suggest a solution by which to close the circle of slag’s reutilization in terms of zero waste principles. It is therefore critical to thoroughly investigate the material, the established methods and preparation processes, and the ways of concentrating useful components into commercial products.

Farklı İki Metal Grubun Geri Kazanımı İçin Gravite Ayırıcısı Tasarımı

This study, "Design of a Gravity Separator for the Recovery of Two Different Metal Groups", represents important research aiming to recover metals in a sustainable way and reduce the amount of waste. This study aims to separate metals according to their density differences. It is an effective method, especially for the separation of different metals such as copper and aluminum. Therefore, this study investigates how this technology can be used more efficiently.As a result of the literature review, existing gravity separation techniques were evaluated. This formed the basis for a new and novel gravity separator design based on existing knowledge. This design is designed to have a capacity of one ton per hour. This capacity demonstrates usability on an industrial scale. The designed separator aims to separate mixed copper and aluminum pieces and convert them into pure granule raw material.During the implementation phase, it was tested how this design would perform in the field. As a result of these tests, it is aimed to recover approximately 8760 tons of waste material annually. This makes a positive contribution to the environment by recycling large amounts of waste material. In conclusion, this study highlights an important method for sustainable recovery of metals. The effective use of gravity separation technology is of great importance in reducing the amount of waste and protecting natural resources. This study is an important step in highlighting sustainability and environmentally friendly practices.

Wet gravity separation and froth floatation techniques for rare earth elements beneficiation from monazite ore in Jordan

The demand for extracting Rare Earth Elements (REEs) from their deposits is growing significantly around the world since they are essential in many mature and growing industries. This study investigated the elemental and mineralogical composition of a Bulk sample and its potential for rare earth elements (REEs) beneficiation through Wet Gravity Separation (WGS) and Froth Floatation (FF) processes. Results obtained from WDXRF analysis showed that Si, Hf, Ti, Fe and Zr were the major elements present in the Bulk sample, with SiO2 accounting for 64.79 wt%. The TREOs concentration was around 0.90 wt%, dominated by Ce, La, and Nd, with other REEs present in smaller concentrations. XRD analysis indicated that Quartz was the major mineral present in the Bulk sample. WGS and FF were then used to beneficiate the oxides CeO2, La2O3, Nd2O3, Pr6O11, Y2O3, Gd2O3, and Sm2O3. Results showed significant concentration increases of these elements in the WGS concentrate, with high grade and good recoveries achieved for Ce, La, and Nd. Overall, the study provides insights into the potential of WGS and FF as a beneficiation technique for REEs in monazite ore.

Mineralogical studies and optimization of tabling parameters of low grade chromite ore by box behnken design of experiments

Chromite ore is geologically associated with gangue materials which have lower density compared to pure chromite (FeO.Cr2O3). Gravity separation techniques are very suitable for beneficiation of low grade chromite ore. In the present study mineralogical analysis of the sample has been carried out by using Wavelength dispersive x-ray fluorescence (WDXRF), X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive X-ray (EDX). The beneficiation of low grade (Cr2O3% 26.88) chromite ore has been investigated using wilfley table. Optimization has been carried out using box-behnken statistical design (BBD). The experimental parameters selected are: tilt angle, water flow rate and pre-heat treatment of the chromite ore. It is observed that percentage recovery of Cr2O3 depends upon tilt angle, water flow rate and pre-heat treatment of chromite ore. Pre-heat treatment of chromite ore plays a vital role in gravity separation. The optimized tabling conditions suggested by BBD are 8° tilt angle, 4 L∙min-1 water flow rate and temperature for pre-heat treatment of raw chromite ore at 443.72℃. After tabling under optimized conditions, chromite concentrate contained 1.91 Cr/Fe ratio, 46.02% of Cr2O3 with 65.95% recovery.

Evaluation of Efficiency of Using Mechanized Processing Techniques to Recover Tin and Tantalum in Gatsibo, Eastern Province, Rwanda

Rwanda is known to be among the top producers of tin and tantalum, despite having low recovery and grades. This study was carried out to evaluate the efficiency of using mechanized methods to increase the recovery rate and grades of tin and tantalum mined in Gatsibo, Eastern Province, Rwanda, since the general separation techniques used are artisanal. The minerals in those mines include cassiterite (SnO2) and colombite–tantalite ((Fe,Mn)(Ta,Nb)2O5), with impurities such as Al2O3, Fe2O3, MnO, MgO, Cao, Na2O, K2O, TiO2, and P2O5. A combination of gravity separation techniques, including shaking tables and magnetic separation, were used as the mechanized processing techniques. The results were compared to the results obtained by artisanal processing techniques. The proposed mechanized techniques were found to increase the efficiency of tin and tantalum recovery from 60.75% to 81.85% and from 22.9% to 48.57%, respectively, and the grades of the tin and tantalum increased to 63.75% and 35.7%, respectively. Based on these results, the proposed mechanized processing techniques and the recycling of waste from artisanal processing techniques are highly recommended.

Recovery of Metals from Heat-Treated Printed Circuit Boards via an Enhanced Gravity Concentrator and High-Gradient Magnetic Separator.

The recovery and reuse of waste printed circuit boards (PCBs) has attracted more and more attention from global researchers, as recycling of waste PCB metals is of great significance to the rational utilization of metal material resources. This study puts forward a clean and economical method in which enhanced gravity separation and wet high-gradient magnetic separation were combined to recover waste PCBs with heat treatment at a temperature of 240 °C. The heat treatment could improve the metal liberation effect of the PCBs, and the thermal behavior was measured by thermogravimetric analysis (TGA). The pyrolysis of the non-metal fraction (NMF) began around 300 °C, and the glass transition temperature of epoxy resin was 135.17 °C. The enhanced gravity separation technique was used for the separation of metals and NMF under the compound force field. The metals grade of the gravity concentrates fraction (GRF) was 82.97% under the optimal conditions, and the metals recovery reached 90.55%. A wet high-gradient magnetic separator was applied to classify the GRF into magnetic (MA) and non-magnetic (NMA) fractions, which could achieve iron and copper enrichment. After the three stages combined process, the copper and iron grades of the NMA and MA fractions were 70.17% and 73.42%, and the recovery reached 74.02% and 78.11%, respectively.

Physical pre-concentration and ammonium leaching of metal copper from waste printed circuit boards

Waste printed circuit boards (WPCBs) is the most valuable component in electronic waste, which is accompanied by potential environmental threats due to the presence of hazardous substances. In this study, a gradient enrichment approach including physical pre-concentration and leaching deep enrichment was proposed to realize the efficient recovery of copper in WPCBs. Shaking table separation, a typical gravity separation technique, was used to concentrate copper in WPCBs particles with different sizes. The results show that when the particle size is limited, the recovery of copper increases with the decrease of particle size, from 90.06% of 0.5–0.25 mm to 98.07% of −0.045 mm. Subsequently, ammonium leaching system was used to deep recover copper from copper concentrate. The effects of two key parameters, leaching time and leaching temperature, on the leaching rate were studied. Under optimal conditions, the leaching rate of copper increases with the decrease of particle size, from 80.23% of 0.5–0.25 mm to 95.08% of −0.045 mm. The leaching time and temperature (5–45 °C) can promote the leaching. A green and environmentally friendly gradient recovery technical approach was proposed for recover copper from WPCBs to present its maximum utilization value.

Automated Gold Grain Counting. Part 1: Why Counts Matter!

The quantitative and qualitative assessment of gold grains from samples of glacial till is a well-established method for exploring gold deposits hidden under glaciated cover. This method, which is widely used in the industry and has resulted in numerous successes in locating gold deposits in glaciated terrain, is still based on artisanal gravity separation techniques and visual identification. However, being artisanal, it is limited by inconsistent recoveries and difficulties associated with visually identifying the predominantly small gold grains. These limitations hinder its capacity to decipher subtle or complex signals. To improve detection limits through the recovery of small gold grains, a new approach has recently been introduced into the industry, which is commercially referred to as the “ARTGold” procedure. This procedure involves the use of an optimized miniature sluice box coupled with an automated scanning electron microscopy routine. The capabilities of this improved method were highlighted in this study by comparing till surveys conducted around the Borden gold deposit (Ontario, Canada) using the conventional and improved methods at both local and regional scales. Relative to that with the conventional approach, the improved method increased the recovery of gold grains from samples (regional and down-ice mineralization) by almost one order of magnitude. (regional and down-ice mineralization), dominantly in regard of the small size fractions. Increasing the counts in low-abundance regional samples allows for a better discrimination between background signals and significant dispersions. The described method offers an alternative for improving the characterization of gold dispersal in glaciated terrain and related gold deposit footprints.

A study of gold ore for processability by gravity separation techniques

Today’s concentrators deal with a lot of gold deposits comprising smaller ore bodies, having low concentrations of the metal and situated in remote areas. The cost of detailed exploration and a full-fledged processability study considering the time and labour required may appear to exceed the cost of metal recovered from a deposit or a particular ore body. This paper describes some approaches to examining the gold ores mined at such deposits for processability and to developing gravity separation processes, which help save the time and cost of research without affecting the quality of resultant data. This research relied on the GRG test developed by Knelson in Canada, as well as a stage test developed by Institute TOMS in Russia (designed to determine optimum grinding size and number of processing stages). A simulation study was conducted to understand the recovery of gold during the grinding cycle (Stage 1) and to examine the Stage 2 process in a KC-CVD concentrator including concentrate refinement. The authors determined the distribution size of the feed material for each GRG test stage, documented the total percentage of gold recoverable by gravity separation as a function of the ore size, and established how the ore size and the KC-CVD concentrate output influence the gold recovery. This research study resulted in a process flow chart indicating the concentration performance based on gravity separation techniques.

Up-Concentration of Chromium in Stainless Steel Slag and Ferrochromium Slags by Magnetic and Gravity Separation

Slags coming from stainless steel (SS) and ferrochromium (FeCr) production generally contain between 1 and 10% Cr, mostly present in entrapped metallic particles (Fe–Cr alloys) and in spinel structures. To recover Cr from these slags, magnetic and gravity separation techniques were tested for up-concentrating Cr in a fraction for further processing. In case of SS slag and low carbon (LC) FeCr slag a wet high intensity magnetic separation can up-concentrate Cr in the SS slag (fraction <150 µm) from 2.3 wt.% to almost 9 wt.% with a yield of 7 wt.%, and in the LC FeCr slag from 3.1 wt.% to 11 wt.% with a yield of 3 wt.%. Different behavior of Cr-containing spinel’s in the two slag types observed during magnetic separation can be explained by the presence or absence of Fe in the lattice of the Cr-containing spinel’s, which affects their magnetic susceptibility. The Cr content of the concentrates is low compared to chromium ores, indicating that additional processing steps are necessary for a recovery process. In the case of high carbon (HC) FeCr slag, a Cr up-concentration by a factor of more than three (from 9 wt.% to 28 wt.%) can be achieved on the as received slag, after a single dry low intensity magnetic separation step, due to the well-liberated Cr-rich compounds present in this slag. After gravity separation of the HC FeCr slag, a fraction with a Cr content close to high grade Cr ores (≥50% Cr2O3) can be obtained. This fraction represents 12 wt.% of the HC FeCr slag, and can probably be used directly in traditional smelting processes.

Mineralogical characterization and physical upgrading of radioactive and rare metal minerals from Wadi Al-Baroud granitic pegmatite at the Central Eastern Desert of Egypt

Granitic pegmatites of Wadi Al-Baroud area in the Central Eastern Desert of Egypt have appreciated amounts of radioactive (U, Th) and rare metal- (Nb, Ta, Y, Zr, Hf, and rare earth elements—REEs) bearing minerals. A combination of both geochemical and physical methods has been used for investigation of Wadi Al-Baroud granitic pegmatites. The identification, imaging, and chemistry of rare metal-bearing minerals were conducted using the optical microscope, X-ray diffraction (XRD), scanning electron microscope (SEM), and electron microprobe analyzer (EMPA). The pegmatites host Nb-Ta oxides (euxenite-Y, fergusonite-Y, and yttrocolumbite-Y), REE minerals (xenotime-Y, monazite-Ce and allanite-Ce), U-Th minerals (thorite and uranothorite), and Hf-rich zircon. In addition, muscovite, quartz, feldspars, and some iron oxide minerals such as magnetite, goethite, and lepidocrocite represent the essential, gangue, and associated minerals. Physical upgrading of Wadi Al-Baroud-mineralized pegmatites was carried out using gravity and magnetic separation techniques. Applying the optimum conditions for both separation techniques, it is possible to attain a good concentrate with an acceptable recovery. Accordingly, the final concentrate contains ~ 0.25% U, 0.46% Th, and 0.31% REE with recovery of 91.17% U, 96.56% Th, and 86.19% REE in a weight of 6.58% out of the original sample assays 0.02% U, 0.04% Th, and 0.03% REE. Therefore, it is well-recommended that the final concentrate should subject to proper hydrometallurgical treatment to extract their valuable metal contents.

Monazite chemistry and its distribution along the coast of Neendakara–Kayamkulam belt, Kerala, India

The beach sands along the coasts of India contain large reserves of strategic minerals like ilmenite, monazite, zircon, etc. Monazite mineral is primarily used as an ore for extracting rare earths particularly cerium and lanthanum. In the present study, the chemistry and distribution of monazite found in the beach sands of Neendakara–Kayamkulam belt in Kerala, south India, is studied using advanced techniques and standardized methods. Beach sediments were collected and analyzed for the texture, and mineralogy reveals that the study area contains characteristically fine sand with maximum 98.9% total heavy minerals (THM) content with ilmenite as predominant mineral species. The content of monazite ranges from 0.1 to 1.4%. A combination of unit operations like gravity separation, magnetic separation and electrostatic separation techniques were applied to the beach sand to recover monazite mineral. The data indicate that samples show a maximum yield of about 81% for THM and 0.5% for monazite. The ED-XRF, XRD and SEM–EDS analysis gives reliable results on the chemistry of monazite. The major chemical constituents of monazite mineral like Ce2O3, La2O3, P2O5 corresponds to 26.658, 13.421 and 23.649%, respectively. The SEM reveals the weathering mechanism, both mechanical and chemical, occurred in monazite mineral. Advanced characterization of monazite mineral will influence positively the efficiency of determining their potential applications.

Advanced Recovery Techniques for Waste Materials from IT and Telecommunication Equipment Printed Circuit Boards

Waste from information technology (IT) and telecommunication equipment (WITTE) constitutes a significant fraction of waste from electrical and electronic equipment (WEEE). The presence of rare metals and hazardous materials (e.g., heavy metals or flame retardants) makes the necessary recycling procedures difficult and expensive. Important efforts are being made for Waste Printed Circuit Board (WPCB) recycling because, even if they only amount to 5–10% of the WITTE weight, they constitute up to 80% of the recovered value. This paper summarizes the recycling techniques applicable to WPCBs. In the first part, dismantling and mechanical recycling techniques are presented. Within the frame of electro-mechanical separation technology, the chain process of shredding, washing, and sieving, followed by one or a combination of magnetic, eddy current, corona electrostatic, triboelectrostatic, or gravity separation techniques, is presented. The chemical and electrochemical processes are of utmost importance for the fine separation of metals coming from complex equipment such as WPCBs. Thermal recycling techniques such as pyrolysis and thermal treatment are presented as complementary solutions for achieving both an extra separation stage and thermal energy. As the recycling processes of WPCBs require adequate, efficient, and ecological recycling techniques, the aim of this survey is to identify and highlight the most important ones. Due to the high economic value of the resulting raw materials relative to the WPCBs’ weight and composition, their recycling represents both a necessary environmental protection action, as well as an economic opportunity.

Promising Options for Solving the Dolomite Problem of the Florida Phosphate Resources—a Brief Review

Separation of dolomite from phosphate is the most challenging problem in phosphate mineral processing. Over 50% of the future phosphate reserve in Florida contains too much dolomite to process using the current industry practice. The current phosphoric acid production practice requires less than 1% MgO in the phosphate concentrate as the feed material. The Florida Industrial and Phosphate (FIPR) Institute has collaborated with worldwide experts in the field to address this issue. As a result, the industry is now offered three feasible options. Option 1 offers three methods for reducing MgO content in the concentrate from the Crago process, including adding a dolomite depressant in the rougher flotation step, dolomite flotation of the cleaner concentrate, and scrubbing the cleaner concentrate in quartz sand. These methods could reduce MgO content in the final concentrate by 20–40%. Option 2 involves crushing and grinding of high-dolomite phosphate pebbles followed by dolomite flotation at slightly acidic pH using a new collector that does not require phosphoric acid as a phosphate depressant, achieving a final concentrate analyzing less than 0.9% MgO at about 87% P2O5 recovery. Option 3 is a gravity separation technique using an innovative separation jig, and its full potential remains to be demonstrated.

A study of the feasibility of upgrading rare earth elements minerals from iron-oxide-silicate rich tailings using Knelson concentrator and Wilfley shaking table

A number of gravity separation techniques for rare earth elements (REE) minerals have been investigated and reported in the literature. These include the use of dense/heavy media, Falcon concentrators, Knelson concentrators, spiral concentrators, laboratory scale jigs, and shaking tables. Most of these methods have provided considerable REE minerals recovery and upgrade; but remain at the laboratory testing stage. There are vast quantities of iron-oxide-silicate rich tailings (IST) containing low grade REE in Australia. This work is part of research and development studies currently underway at the University of South Australia to develop economically viable methods to exploit selected IST for their REE contents. In this investigation, the feasibility of exploiting the differences in specific gravity to concentrate REE minerals from a typical IST sample was studied using two gravity separation units, a Knelson concentrator (KC) and Wilfley shaking table. The feed sample and gravity separation products were characterised using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN) to study and compare the performance of the KC and shaking table as gravity preconcentration methods. The results indicated that the performance of both the KC and shaking table are significantly dependent on the mineralogical and particle size characteristics of the feed, however, the tabling was found to be the preferred choice over the KC, due to its greater selectivity. Tabling of >38 μm feed samples produced the desired split between the iron oxides and silicate minerals. The results suggest that desliming of the feed to remove fine/ultrafine particles (<38 μm) prior to tabling is key to attaining the desired results with the shaking table. Overall, tabling produced appreciable REE minerals upgrade, with iron oxides occupying the bulk of the concentrates. The test results confirm the complex mineralogy of the IST, which compromised REE minerals upgrade. A modified concentration criterion expression which considers the liberation characteristics of minerals is proposed, which provides a better idea on the feasibility of gravity separation.

Mineralogical characterization of the typical coarse iron ore particles and the potential to discharge waste gangue using a dry density-based gravity separation

ABSTRACT Discharging waste gangue from coarse iron ore prior to subsequent upgrading and purification is beneficial to decrease the energy consumption in the grinding stage. In this study, a dry density-based gravity separation technique was used to improve the quality of iron ore by discharging waste gangue. Mineralogical analysis results indicated that the major component of raw iron ore is hematite with small amounts of magnesioferrite and magnetite, and the elements included in the iron ore sample were Fe, Si, S, Mg, Al, and Ca, and the specific iron–compounds (Fe3O4, Fe2O3, and FeS2) were determined. High-density gas-atomized iron powder and low-density zircon sand with specific size fractions were validated for appropriateness for mixing in proportion as a binary dense media for the dry separation of coarse iron ore. A regulatory model of the bed density based on the composition of the binary dense media was proven efficient in predicting and adjusting the bed density for separating the coarse iron ore. The actual separation experiments of −31.5 + 6 mm iron ore indicated that the concentrate yield and grade of 83.4% and 52.4%, respectively, were achieved with the highest Fe-recovery of 96.1% at a gas velocity of 6.37 cm/s. The concentrate yield and grade of 63.7% and 52.7%, respectively, with the highest Fe-recovery of 73.0% were achieved at a static bed height of 80 mm. Both the results suggested the satisfied separation performance. The fundamental investigation indicated that discharging waste gangue using the dry gravity separation prior to further upgrading coarse iron ore has substantial potential in industry.

A design of experiments investigation into the processing of fine low specific gravity minerals using a laboratory Knelson Concentrator

Fine grinding, required to liberate valuable minerals in finely disseminated deposits, creates significant challenges for beneficiation. For these deposits, traditional gravity separation techniques are often ineffective, and centrifugal separators, such as the Knelson Concentrator, are required. The Knelson Concentrator is well established for treating gold ores, and due to its relatively low cost and small environmental impact when compared to other separation techniques, it has become an active area of research for the processing of lower specific gravity (SG) minerals. This work investigates the optimum operating conditions when processing fine (−53 μm) low SG material using a laboratory Knelson Concentrator. A synthetic feed comprised of magnetite (SG 5.2) and quartz (SG 2.65), with grades of 5%, 10% and 15% magnetite, was used to mimic a low-density ore. Central composite design was used to design the experiments and response surface method was used for optimization, with the experimental variables being bowl speed (G), fluidizing water rate (L/min) and solids feed rate (g/min). The results indicate, for 5% and 10% magnetite feeds, that bowl speed impacts concentrate grade negatively and heavy mineral recovery positively, while the fluidizing water rate has an opposite effect on separation. A trade off between grade and recovery must therefore be made when processing this material. When processing the 15% feed, maximum concentrate grade and magnetite recovery were achieved at high bowl speeds and low fluidizing water rates.

Development of dry coal gravity separation techniques

Dry separation method was used at the beginning of 20th century to separate coal separation process. First industrial applications of dry separation took place in the middle of 1930s. At that time air separator Frazer-Yankey, based on aero suspension was used in in Pittsburgh and Lundale, West Wirginia coal preparation plants. Later, some more constructions like RAW air jig, air table “V” type Birtley, air jig type Kirkup, air table “V” type Peale-Davis or air jig type Bruay-Soulary were constructed. Fast development of wet technologies of processes, especially jigging and heavy dense medium separation caused the discontinuation of the further development of dry separation methods and replacement of dry preparation plants with plants based on wet methods of enrichment. At the end of 20th century and beginning of 21st century dry separation method started once again to be widely used in the world. New types of equipment like FGX vibrating air table, TFX air jig or KAT process technology were introduced to wide applications in Asian countries. The paper describes few constructions of old air separators and new ones, used nowadays. It contains comparison of the separation results obtained by means of various equipment and shows possibility to separate coal in laboratory scale air jig.