Laboratory Knelson Concentrator Research Articles

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

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.

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.

Computational modelling of water flow inside laboratory Knelson concentrator bowl

ABSTRACTEnhanced gravity concentrators such as Knelson concentrator (KC) are extensively used in the mineral processing industry. The complexities of KC bowl geometry and variation of feed characteristics have forced process engineers to design empirically new units using laboratory and pilot-scale Knelson concentrators. However, numerical modelling methods such as computational fluid dynamics (CFD) and discrete element method (DEM) provide a better insight of flow behaviour of fluid and particulate solid phases inside these processing units. This article reports findings of CFD simulations for single-phase water flow inside the laboratory KC. An available standard 7.5-cm laboratory KC bowl was numerically simulated using realisable k-ε turbulence model to resolve the turbulence dispersion of existing transitional flow regime. The effects of relative centrifugal force (RCF) intensity and bed fluidisation water flow rate on the water velocity and pressure distributions were studied. Simulations confirmed the swirling flow pattern governing inside the bowl. The results revealed that the impact of RCF intensity on the water field values is greater than that of bed fluidisation water flow rate. Both velocity and pressure variations inside the bowl rings followed a linear trend.

Response surface method for modeling of fine coal beneficiation by Knelson concentrator

ABSTRACT In this study, the −1 mm fine coal is treated in a laboratory Knelson concentrator. The influence of various parameters (e.g., feed rate, solid content, centrifugal force, and the fluidization water pressure) on the yield and ash content of clean coal are thoroughly investigated and estimated by statistical polynomial models obtained using the response surface method (RSM). A second order polynomial model is developed to predict the yield and ash content; the models have a correlation coefficient of 0.9902 for yield and of 0.9221 for ash content of clean coal. Three-dimensional plots are presented to show the effects of process variables and their interactions on the response variables. The results show that all the variables affect the yield and ash content of clean coal to some degree. However, the centrifugal force and fluidization water pressure are found to be the most significant factors. Additionally, a numerical optimization process was applied to the developed models to search the factor space for the best trade-offs to achieve the maximum yield and lower ash content in the range of the experimental data. Under optimized working conditions, good separation efficiency is obtained with probability error Ep of 0.09.

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.

An analysis of multiphase flow and solids separation inside Knelson Concentrator based on four-way coupling of CFD and DEM simulation methods

Knelson Concentrator (KC) has been widely used in industrial gravity separation processes. In the present study, the separation process for a multiphase flow in a laboratory Knelson Concentrator (LKC) is numerically simulated using a 4-way coupled CFD-DEM approach. The simulation of the complex multiphase flow is carried out by using a hybrid Eulerian–Lagrangian model, dense discrete phase model (DDPM), as well as DEM collision model to include the solid inter-particle collisions and to compute individual particles trajectories. The particle–fluid interaction is considered by exchanging momentum through the interaction forces such as drag force, virtual mass force and pressure gradient force between the DEM and the CFD computations. The Realizable Mixture k-ε turbulence model is selected to model the turbulence of fluid phase due to its swirling nature. Since coupled simulations are computationally expensive and challenging, the separation process inside the laboratory KC bowl was simulated for a real process time of 20 s under the specific conditions. Coupled CFD-DEM simulation yields valuable information about both particle and fluid flow patterns such as residence time distribution and velocity magnitude of particles inside the rings which are difficult or even impossible to measure experimentally with sufficient accuracy; meanwhile, the simulation results are expressed in terms of performance indices, i.e., concentrate grade and total recovery. To validate the simulation predictions, the authors carried out an experimental test under the same operating conditions used in the simulation. A complete agreement between simulation predictions and laboratory measurements for concentrate grade and total recovery was observed both qualitatively and quantitatively which validates coupled CFD-DEM simulation.

An investigation on laboratory Knelson Concentrator separation performance: Part 3: Multi-component feed separation modelling

In the previous study, mathematical models were proposed to describe the mass of the valuable component and quartz recovered in a Knelson Concentrator bowl based on experiments conducted on two-component synthetic feeds. In continue, a series of experiments were done on multi-component synthetic feeds which were a mixture of five valuable components (i.e., magnetite, zinc, copper, lead and tungsten) and quartz to obtain a general recovery models. In this part, the results of material characterization, details of experimental protocol and finally multi-component recovery models will be presented which are based on material properties and operating condition parameters. The observed results indicate that the best operating condition to obtain maximum recovery of valuable component and highest grade of concentrate is at values higher than 250 for Fd/(Fc-Fb)Q.

Numerical Studies of Separation Performance of Knelson Concentrator for Beneficiation of Fine Coal

ABSTRACT The separation of fine coal in a laboratory Knelson concentrator was studied through experimental and numerical simulation. The flow field characterized of Kenlson concentrator simulated in a three-dimension laboratory Knelson concentrator by using CFD modeling. The results show that the flow regime can be treated as laminar flow, which propitious to layering for particles. In the riffle part, eddies were created by the rotational flow and fluidizing water. The flow of fluids changes from turbulence to laminar, which was propitious to separation for particles. So, the separation processes were realized in riffle part. The CFD-DEM modeling was applied for the first time in the study of the influence of centrifugal force and fluidizing water rates on the separation performance of a laboratory Knelson concentrator. The simulation results indicate that the Ep value was increased with decreasing the centrifugal force at the constant fluidization water rates, and increased with increasing the fluidization water rates at the constant centrifugal force. The simulation results were consistent with the experimental results and the CFE-DEM model was effective and reliable.

An investigation on laboratory Knelson Concentrator separation performance: Part 2: Two-component feed separation modelling

In the previous study, a mathematical model was proposed to predict retained mass inside a laboratory Knelson Concentrator bowl. In this part, a model is proposed to describe the particle separation performance of the laboratory Knelson Concentrator. The separation model considers the main forces (fluid drag force, Fd, centrifugal force, Fc, and buoyancy force, Fb) acting on particles inside the concentrating bowl, which are functions of material properties as well as the operating condition parameters. Several materials with different densities including magnetite, zinc, ferromolybdenum, lead, and tungsten were used as valuable components to simulate minerals with the same densities in two-component synthetic feeds with various size fractions. The modelling of component separation in the Knelson Concentrator was performed based on the ratio of Fd/(Fc-Fb). Based on an extensive experimental database, practical and simple models were proposed as predictors of recovered mass of valuable components from tailings and the mass of quartz (as gangue) in the Knelson Concentrator versus the ratio of Fd/(Fc-Fb) for quartz.

An investigation on laboratory Knelson Concentrator separation performance: Part 1: Retained mass modelling

The retained mass of material in the Knelson Concentrator (KC) bowl depends on the main forces—the fluid drag force (Fd), the centrifugal force (Fc), and the buoyancy force (Fb)—which act on the particles in the concentrating bowl. They are functions of the material properties, as well as the operating condition parameters. In this experimental study, the fluid drag force (Fd) experienced by a solid particle in the rotating bowl was estimated by the fluidization water pressure (Pw) multiplied by the projected area (Ap) of a spherical particle hydraulically equivalent to the solid particle, and used in the model fitting. Quartz, magnetite, zinc, copper, and lead powders were used in different sizes as minerals with the same density to investigate and model the retained mass of material in the KC bowl. By defining the new ratio of Fd/(Fc-Fb), the retained volume of the different materials in the KC bowl was modelled, and it was shown to be the same for a given value of Fd/(Fc-Fb) ratio. Based on the developed experimental database consisting of 284 tests, a Weibull model was proposed. It can accurately model the retained mass of material in the KC bowl for particles with various sizes and densities under a given operating condition.

DEM simulation of laboratory Knelson concentrator to study the effects of feed properties and operating parameters

Understanding of the separation mechanism of Knelson concentrators at particle scale and investigation of the effects of different feed properties and operating parameters helps process engineers to design, control and optimize these particulate solids processing units. This article reports findings of an investigation on separation performance of laboratory Knelson concentrator using an open-source Discrete Element Method (DEM) solver ‘LIGGGHTS’. An available standard 7.5-cm (3″) laboratory Knelson concentrator with five collecting rings was numerically simulated. The effects of feed properties including feed mass, feed type, feed grade, feed particles size, feed particle population and operating parameters including centrifugal force intensity, feeding rate and concentration cycle time on separation performance of laboratory Knelson concentrator were studied. Results of DEM simulations are expressed qualitatively and quantitatively in terms of performance indices, i.e., concentrate grade and total recovery. For validation of simulation predictions, the authors carried out several experimental tests on synthetic samples of pure quartz and magnetite mixtures under the same conditions used in simulation environment. A close agreement between simulation predictions and laboratory measurements for concentrate grade and total recovery was observed which validates DEM simulations.

Understanding the discrepancy between prediction and plant GRG recovery for improving the gold gravity performance

Gravity recoverable gold (GRG) content in a sample is typically determined using the standard three-stage test developed at McGill University ( Laplante et al., 2000). A comparison of GRG recovery in laboratory with its actual recovery in plants shows that plants recover between one-third and two-thirds of the predicted GRG from laboratory test. Research conducted at COREM seeking the identification and the understanding of potential causes of this discrepancy reveals that particle shape transformation during grinding is a major contributor among other causes such as bleed percent processed, quality of cyclone classification and gravity concentrator operating conditions. To analyze the gold particle shapes and their deportment, samples were collected from different streams of a grinding–gravity (Knelson) circuit in a gold plant and compared to a concentrate sample from a laboratory Knelson concentrator (KC MD3). A particle characterization based on gold morphology was developed to diagnose typical shapes generated in the gold grinding–gravity circuit. The study revealed that the GRG particles reporting to the plant cyclone overflow are the most flattened particles among the samples analyzed and that on the other hand gold particles recovered in the laboratory Knelson concentrator are the least flattened, highlighting the potential cause of discrepancy between the two recoveries. In this paper, the GRG mapping in a conventional grinding–gravity circuit and the transformation of GRG to non-GRG, as mainly explained by gold particle reshaping will be discussed.

Quantifying the content of gravity recoverable platinum group minerals in ore samples

A protocol for predicting recovery of platinum group minerals (GRPGM) is adapted from the protocol for gravity recoverable gold. This paper introduces the methodology to characterize the content of GRPGM in samples using the 3-in. (7.5 cm) laboratory Knelson concentrator. Results for two ore samples are presented, as well as some mineralogical analysis of the gravity concentrates. The methodology can also be used for sample preconcentration to aid mineralogical analysis.