Knelson Concentrator Research Articles

Advancing particle forces and motion dynamics in centrifugal concentrator based on flow field simulation

ABSTRACT The forces and motion state of particles within the fluid domain of the Knelson concentrator have long been a focal point for researchers. Presently, Stokes’ flow laws are commonly employed as the basis for theoretical calculations. However, this approach somewhat deviates from reality due to challenges in determining the Reynolds number of particles in the centrifugal force field during practical work. Additionally, the relationship between the Reynolds number and the drag coefficient remains undetermined in certain ranges. This study presents a high predictive relationship curve, obtained using fitting software, to supplement and rectify the limitations in the existing relationship. Leveraging fluid simulation software, this research determines the Reynolds number of particles of different sizes and densities within the fluid, offering a methodological reference for similar flow field problems. A new drag coefficient function is proposed and validated for the Reynolds number range of 1 to 20, addressing a gap in existing theoretical models. The simulation results indicate that under the suitable separation conditions of −0.074 + 0.02 mm particles, the concentrate particles overcome the flushing effect of the reverse washing water and move in the opposite direction to the fluid. This advancement not only improves the theoretical framework but also offers significant academic and practical value by enhancing the efficiency of particle separation in the Knelson concentrator.

Optimizing rare earth element beneficiation using response surface methodology and Knelson concentrator

ABSTRACT The beneficiation of rare earth elements is a crucial process in unlocking the potential of these valuable resources. This study investigates the utilization of response surface methodology in optimizing rare earth beneficiation using a laboratory Knelson concentrator. The experimental design employed response surface methodology to analyze and predict the effects of various parameters, such as feed rate, water pressure, and particle size, on the efficiency of rare earth recovery. Through systematic experimentation and statistical analysis, this research establishes optimal conditions for the Knelson concentrator operation, enhancing the recovery of rare earth elements. The study presents a comprehensive analysis of the impact of individual factors and their interactions on the beneficiation process. The results showed that for −0.5 + 0.074 mm fraction the main influencing factors were in the order of relative centrifugal force > fluidization water flow rate > feeding rate, and the factors acting on −0.074 + 0.02 mm fraction were fluidization water flow rate > relative centrifugal force > feeding rate. The beneficiation performance by Knelson concentrator for −0.074 + 0.02 mm fraction was better than that of −0.5 + 0.074 mm fraction. The findings demonstrate the efficacy of response surface methodology as a tool for optimizing the Knelson concentrator’s performance in rare earth beneficiation. This approach offers insights into process optimization and provides a framework for improving the efficiency of rare earth recovery methods, contributing to the sustainable utilization of these critical elements in various industrial applications.

Optimization of direct smelting for mercury-free gold recovery in artisanal and small-scale gold mining

Artisanal and small-scale gold mining (ASGM) faces challenges in accessing capital, technology, and responsible practices, hindering sustainable operations and contributing to environmental and health impacts from mercury use. This study evaluated optimizing direct smelting of gold concentrates as an alternative to mercury amalgamation for efficient and responsible production. 50 kg of ore from Nholi mine was concentrated using a Knelson concentrator and analyzed (XRF, fire assay with AAS, XRD). Response surface methodology with a face-centered composite design investigated smelting temperature (1100–1400 °C), duration (30–90 min), and concentrates-to-flux ratio (1:1–3:1) effects. The impact of sulfide concentration (pyrite varied 6.7–48%) on gold recovery was explored. Low-sulfide concentrates associated with pyrite and sphalerite yielded best recovery (>80%) at 1250 °C for 90 min with 2:1 concentrates-to-flux ratio. Direct smelting with ≤6.7% sulfide enabled over 87% gold recovery, facilitating responsible ASGM production.

Gold occurrence in the footwall of the Lappberget Deposit, Garpenberg Mine, Sweden: Implications for recovery efficiency

By-product metals have a significant potential to bring additional economic benefits to mines. However, a detailed characterization of their distribution is generally required to fulfill this potential and should preferably be integrated into a geometallurgical assessment. This contribution presents a detailed mineralogical and textural investigation of gold-bearing phases at the footwall of the Zn–Pb–Ag–(Cu–Au) Lappberget Deposit, Garpenberg Mine, Sweden, using optical microscopy, scanning electron microscope with energy dispersive spectroscopy (SEM-EDS), electron probe microanalysis (EPMA), laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS), and bulk chemical analysis applied to drill core and Knelson concentrator samples. Gold is a by-product at the Garpenberg mine, but it is unclear how the mineralogy, occurrence, and distribution of gold-bearing phases impact on gold recoveries during mineral processing. Our results show that Au-dominant electrum is the most abundant gold-bearing phase in the footwall of the Lappberget deposit, occurring strongly associated to sulfides in a variety of textures and grain sizes. Electrum grains commonly occur within sulfide borders, as inclusions, intergrowth and overgrowths of chalcopyrite, pyrite, galena, sphalerite, and pyrrhotite. Gangue minerals may also contain disseminated electrum and inclusions. Electrum grain sizes range from ∼5 µm to 300 µm, predominantly below 100 µm. The potential of sulfide lattice-bound invisible gold in the form of solid-solution gold and colloidal gold was also investigated, showing Au depletion within the analyzed sulfide carriers. The analysis of the concentrate samples from the Knelson gravity concentrator showed 584 and 431 ppm of gold content. High degree of liberation is observed among the gold-bearing phases in the concentrate, and gold recovery is highest among fractions coarser than 106 µm mesh. Pyrite and galena are the most abundant minerals in the concentrate samples. The gold-bearing phases were categorized based on its mineralogy, texture, grain size, and association and their influence on gold processing, especially textures and grain size, which implicates its liberation in milling and recovery by the gravity separator.

A Preliminary Investigation of the Operating Variables in a Laboratory Knelson Concentrator for Enrichment of Chromite Ore

A Preliminary Investigation of the Operating Variables in a Laboratory Knelson Concentrator for Enrichment of Chromite Ore

Increasing the Added Value of Copper and Silver Metal from Printed Circuit Board Waste Using a Knelson Concentrator with Variations in Size and Centrifugal Force

The use of technology in Indonesia has resulted in an increasing demand for electronic and electrical goods, including printed circuit board (PCB) waste. Currently, PCB waste amounts to 20-50 million tons and continues to grow annually. Given that the composition of PCB waste consists of approximately 40% metals such as Ag, Cu, Fe, Au, Sn, and Mn, recycling PCB FR-2 waste can significantly increase its added value. One effective method is employing a concentration technique to recover these metals. This study aims to investigate the impact of particle size and centrifugal force variations on the content and recovery of Cu and Ag metals in PCB FR-2 waste using a Knelson concentrator. The concentration process involved three size variations: -63+100, -100+150, and-150#, along with three centrifugal force values: 60, 90, and 120 G Force. The results indicate that the size variation-100+150# and a centrifugal force value of 90 G Force exhibited effectiveness in recovering Cu and Ag metals, with a minimal mass loss of 3.9%. The Cu and Ag levels reached 67.49% and 0.18%, respectively, with recovery rates of 53.22% and 39.96%.

Particle Classification in the Enhanced Gravity Field Using the Knelson Concentrator

The particle classification in the enhanced gravity field generated by the Knelson concentrator was studied in this paper. Three main test parameters, namely rotation speed, backwash water pressure, and solid mass percentage, that affected the classification performance of the Knelson concentrator for the classification tests of quartz and synthetic ore, which consisted of quartz and magnetite, were investigated. The yield of quartz concentrate increased with the rotation speed and decreased with the solid mass percentage and backwash water pressure. A lower backwash water pressure and solid mass percentage could improve the classification efficiency. The classification performance of the Knelson concentrator was comparable to that of the traditional hydrocyclone, with a classification efficiency of 76.84% and cut size of 49 μm when the solid mass percentage was 16.67%, the backwash water pressure was 50 kPa, and the rotation speed was 3600 rpm. The classification performance of quartz in synthetic ore tests was inferior to the single quartz tests, and the magnetite showed a better classification efficiency than the quartz with the same combination of test parameters. This study revealed the classification performance in the separation process of the Knelson concentrator in detail, which was beneficial for clarifying the migration rule of fine-grained minerals in the enhanced gravity field.

An investigation into the dry processing of low specific gravity ores using a laboratory Knelson concentrator

ABSTRACT The Knelson concentrator (KC) was originally invented and developed for treating gold ores, and due to its high efficiency, low cost and minor environmental impact, it has become an active research area for processing low specific gravity (SG) deposits. The laboratory scale KC has shown its potential for processing high-density ores on a dry basis. This work investigated the feasibility and the optimum operating conditions when processing a dry low SG feed with a modified KC. A synthetic mixture of magnetite (SG 5.2) and quartz (SG 2.65) with a grade of 1% magnetite and three synthetic mixtures of magnetite and quartz with a grade of 5% magnetite in different sizes were used to mimic a low-density ratio ore. Central composite design (CCD) and response surface method (RSM) were used to design the experiments and optimise each process. The effects of each individual factors and their interactions on concentrate grade and magnetite recovery were evaluated for each feed. Optimum operating conditions were obtained at a bowl speed, solids feed rate and air fluidising pressure of 20G, 100 g/min and 12 psi, for 1% grade feed; 14, 300 g/min and 13 psi, for 5% coarse feed; 18 G, 300 g/min and 13 psi, for 5% intermediate feed; and 10 G, 100 g/min and 14 psi for 5% full-size feed.

A preliminary investigation of dry gravity separation with low specific gravity ores using a laboratory Knelson Concentrator

It has become an active research area for treating low specific gravity (SG) deposits by centrifugal separation due to its high efficiency, low cost and minor environmental impact. Laboratory Knelson Concentrator has shown its potential for processing high density ores on a dry basis. This study investigated the feasibility and the optimum operating conditions when processing a dry low SG feed with a modified Knelson Concentrator. A synthetic mixture of magnetite and quartz with a grade of 1% magnetite was used to mimic a low-density ratio ore. Bowl speed (G), air fluidizing pressure (psi) and solids feed rate (g/min) were chosen as the operating variables. Box-Behnken design was used to design the experiments and response surface method was used for optimization. The effects of each individual factors and their interactions on concentrate grade and magnetite recovery were evaluated. The dry process achieved up to 60 % magnetite recovery with an upgrade ratio of 5. The optimized values for the concentration with the highest recovery and grade of bowl speed, solids feed rate and air fluidizing pressure are 27 G, 200 g/min and 12 psi, respectively.

Modeling of Knelson Concentrator Operating Parameters by Using Application of Box–Behnken Experimental Design for Chromite Ore

Modeling of Knelson Concentrator Operating Parameters by Using Application of Box–Behnken Experimental Design for Chromite Ore

Asbestos Waste Treatment—An Effective Process to Selectively Recover Gold and Other Nonferrous Metals

We investigated the potential of tailings generated from chrysotile asbestos fiber production as a source of iron, nonferrous metals, and gold. We proposed the use of granulometric separation and systematically examined different enrichment processes, namely magnetic separation, gravity concentration, and enrichment using a Knelson concentrator, to extract the valuable components. The characterization of the initial tailing samples revealed that it comprises primarily of serpentine, brucite, antigorite, hematite, vustite, sillimanite, and magnesium oxide. Using the suggested enrichment process, we isolated gold, chromite, and nickel-cobalt concentrates as valuable products in addition to magnetite. The new approach exhibited high separation efficiency for iron, nonferrous metals, and gold, allowing their satisfactory extraction.

Optimizing Gold Recovery of Artisanal Mining: A Lesson Learned from Kenya

The metallurgical testings to treat the Kenyan artisanal gold mining samples were performed with several processes such as gravity concentration (i.e., Knelson Concentrator and panning), flotation, and cyanidation or leaching. These tests were conducted to find the best processing stages to improve the Kenyan artisanal mining recovery. From the three categories of samples treated, sample A, which was processed through gravity concentration and flotation, produced 95.64% of gold recovery. Meanwhile, sample B could produce 98.74% of gold recovery with the cyanidation test. The results from sample A and sample B confirmed that the combination of the Knelson concentrator and flotation, which the Processing Center should handle, was the perfect combination to reduce the use of cyanide during the leaching process. On the other hand, the study also showed that the tailing sample (sample C) could still be recovered through flotation. With the results obtained, the best scenario was proposed. The government played a critical role in facilitating both the artisanal miners and the Processing Center for both cases, in Kenya or Aceh.

Centrifugal Concentration of Mandailing Natal North Sumatera Gold Ores Using Knelson Concentrator

Gravity concentration is the type of separation process of minerals based upon the difference in density. This technique has been known for centuries. It has the ability to separate the valuable minerals with relatively low production cost and little environmental impact, such as gold ores. Separation of gold from gangue minerals by using gravity concentration has been used for decades. In fact, it has the limitation to process fine particles. In attempt to recover fine particles using gravity concentration methods, the technique has been developed by combining centrifugal force. One of wellknown devices, Knelson Concentrator, was used to separate gravity recoverable golds (GRG) from the gangue minerals of Mandailing Natal (North Sumatera) sulfide complex gold ores with -200# of particle size. The head grade of ores was 5 g/t of gold. The ores were separated by using Knelson Concentrator with variation of pulp density, feeding rate, and water fluidization pressure. The results have proved that these three variables have particular impacts on gold recovery. The recovery of gold was increased by the increasing of pulp density until it reached the optimum level in 25% of solid with 86.9% of gold recovered, and then decresed by increasing of pulp density into 84.88% of gold with 30% of solid in pulp. It has the same trends in variation of feeding rate and water fluidization pressure. The highest point with 87.08% of recovery and 17.88 g/t of concentrate grade was anchieved at 25% of solid, 0.7 kg/minutes of feeding rate, and 2.7 kg/cm2 of water fluidization pressure.

Experience in Retrofitting the Mineral Processing Equipment to Intensify the Gravity Recovery of Gold

The experience of replacing a Knelson concentrator with MOD 2 and MOD 3 jigs at the gold recovery plant of the Karalveem deposit is described. Due to the change in the source product quality (an increase in the amount of finely disseminated gold from 17 to 75 % of the total gold obtained), the Knelson concentrator performance at stages 4 and 5 was unsatisfactory. It was decided to retrofit the equipment and replace the Knelson concentrator with the MOD 2 and MOD 3 jigs. The gold in the Karalveem deposit ore was briefly characterized by size as fine, dust, and medium-round gold, and the mineral composition of the Karalveem deposit ore samples considered. Statistically significant results of testing before and after retrofitting (replacing the Knelson concentrator with MOD 2 and MOD 3 jigs) have been represented. The efficiency of the MOD type jig installation has been evaluated. The authors have concluded that industrial testing the recovery of fine, dust, and medium-round gold on the MOD type jigs can be performed at any mine to process this type of ores, and these jigs may compete with Knelson concentrators that have already gained popularity.

Application of Enhanced Gravity Separators for Fine Particle Processing: An Overview

Beneficiation of low-grade ore is of critical importance in order to meet the growing demand for coal and mineral industries. But, low-grade ores require fine grinding to obtain the desired liberation of valuable minerals. As a result, production of fine particles makes the beneficiation process difficult through conventional gravity separators. Hence, alternative beneficiation techniques are being investigated for upgradation of metal values from low-grade ores. The gravitational force effecting the separation is replaced by the centrifugal force to usher in enhanced gravity separators. The objective of the present paper is to summarize the applicability aspect of enhanced gravity separators for different mineral systems including non-ferrous, precious, ferrous, and industrial minerals. These mineral systems include run off mine ore, secondary products like tailings and plant slags, etc. For this purpose, the design, operational features, types, and separation mechanism of enhanced gravity separators, such as Falcon concentrator, Knelson concentrator, multi-gravity separator (MGS), and Kelsey Jig, are discussed. Based on our review, research scope and future possibilities of enhanced gravity separators are also proposed.

The Effects of Pulp Rheology on Gravity Gold Recovery in Free Milling Gold Ore of the Tarkwaian Systems of Ghana

ABSTRACT Gravity gold characterization provides a comprehensive understanding on the effect of mineralogy, particle size, and liberation on gravity concentrator performance. This is of significant economic importance for gold ores with a high amount of coarse gold particles. In this study, the effect of pulp rheology on gravity recoverable gold (GRG) was investigated using a single-stage GRG test on paleoplacer gold deposits of the Tarkwaian system of Ghana. The elemental and mineralogical composition of the gold ore was characterized using ICP-MS, XRD, and QEMSCAN analyses. Bench-scale gravity concentration was performed on the gold ore at varying clay contents (in the range of 5–30 wt.%) using Lab Knelson concentrator in the absence and presence of NaOH (2.5 kg/t) and CaO (2.5 kg/t). The mineralogical analysis showed the ore is oxidized and comprised 88% Quartz, 8% muscovite mica, 2% hematite, and 2% kaolinite. Liberation and association analyses showed 58% of the gold particles were liberated, 1% formed binary with quartz, and 41% formed complex aggregates with other mineral phases. The gravity concentration of the ore without clay material yielded 51% Au recovery (11.2 g/t) at the grind size of 80% passing 106 µm. Partial replacement of the ore with clay material at 5%, 10%, 15%, 20%, and 30% decreased gold recovery from 51% to 25.7%, 12.7%, 8.8%, 5.1%, and 1.5%, respectively. Subsequent conditioning of the slurry with NaOH improved gold recovery due to possible improvement in slurry rheology. However, the addition of CaO decreased gold recovery due to an increase in slurry viscosity.

Determining the Separation Performance of the Knelson Concentrator

This study was aimed at determining the separation performance of the Knelson concentrator in Zonguldak fine coal (-1+0.15 mm). The experiments were carried out in the Knelson concentrator under the following optimal parameters determined in previous studies; water flow rate of 3.14 L/min., bowl speed of 459 rpm, solids ratio of 23.87%, and feed flow rate of 1.50 L/min. A series of tests were conducted at optimal test parameters to obtain enough samples for float and sink analysis. Clean coal and tailing products were subjected to float and sink analysis. Based on this analysis, partition curve for coal cleaning process was generated. The cut-point of the separation was obtained at the specific gravity of 1.72 [g/cm3]. The probable error (Ep) value, which signifies the efficiency of the process, was calculated as 0.11 These results indicated that Knelson concentrator is very effective in separating fine coal.

Analysis of the operating mechanism of a Knelson concentrator

In this study, the operating mechanism of a Knelson concentrator (KC) is analyzed by considering the concentration mechanisms of dense minerals obtained based on the feed properties, operating parameters, and design parameters of the KC bowl. The efficiency of the KC is affected by all the studied factors, i.e., the structural parameters of the ring, water flow rate, rotating speed, and gangue size distribution, which further restrict each other and act together. A concentration criterion (Xi), which is the ratio of the settling velocity to the fluidized water flow velocity, is defined to obtain the correlation between these four key factors. Based on the mechanistic linkage provided by the aforementioned criterion, these factors affect the KC performance because they influence the concentration mechanism. This determination was obtained as follows: as the magnitude of Xi increased, the concentration mechanism of the dense mineral transformed from surface plating to substitution and then to elutriation, followed by overload. In case of surface plating, the size distribution of the dense mineral in each ring was similar to that of the feed, and recovery increased gradually from ring R1 to ring R5. In case of substitution, the coarse and dense particles replaced the light particles and formed a thick concentrate layer, with high concentrate grade and tungsten recovery. In case of elutriation, the tungsten particles completely replaced the quartz particles and preferential enrichment could be observed at the bottom of the ring; in this case, the concentrate grade and recovery were the highest and the tungsten particle size was the coarsest. Further, some fine and dense particles were carried into the tailings because of the large water flow velocity.

Performance evaluation of processing clay-containing ore in Knelson concentrator

Performance of some mineral processing operations is known to be impeded due to the presence of even a small amount of clays. The study was conducted to evaluate the influence of commonly encountered clay types, bentonite and kaolin, on the performance of Knelson concentrator. Artificially mixed slurries of magnetite, quartz and clay were used for the experiments. The results indicated that the influence of both clay types on the operation of Knelson concentrator was insignificant; the reason is probably that clay particles are transported to the tailing without entering the concentrated bed inside the concentrate bowl of Knelson concentrator. Both magnetite and gangue recovery were analysed by plotting performance curves using size distribution.

Ring-by-ring analysis and models of retained mass of quartz in a laboratory Knelson Concentrator

The basic principle of a Knelson Concentrator (KC) is the differential settling velocities of particles in a medium under a centrifugal field. Whether the ore particles remain in the KC bowl depends on the terminal settling velocity (v) of the particles and the fluidization water flow velocity (V). Both variables are functions of the material properties and the operating parameters. This study reports the relations between the retained mass of quartz in each ring of the KC bowl (obtained by measuring the quartz mass ring by ring) and the rotational speed, fluidization water flow rate, and particle size. The retained mass of quartz in each ring was then modeled by approximating the fluidization water velocity and defining a new ratiov/V. Based on the experimental data, the functional relation between the quartz mass in each ring of the KC bowl and the feed particle properties/operating conditions was fitted by a Weibull model. The model established by the ring-by-ring approach gives more accurate predictions than a previous model, and a model based on the quartz mass in the entire bowl.