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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Processing and Extractive Metallurgy".

Deadline for manuscript submissions: closed (25 October 2019) | Viewed by 61144

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Dr. Saeed Farrokhpay

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Chemical Engineering, The American University of the Middle East, Kuwait City, Kuwait
Interests: flotation; rheology; clays; nickel laterite; tailings; physical separation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Physical separation is one the main methods of recovering valuable minerals from an ore (in addition to flotation and hydrometallurgy). Physical separation includes gravity concentration, classification techniques such as hydrocyclones and air classifiers, solid–liquid separation (e.g., thickeners and clarifiers), magnetic separation, and electronic sorting. This Special Issue will discuss the latest findings of using physical separation in mineral processing. In particular, it will target the optimisation of physical separation methods to recover strategic metals, including rare earth elements. Papers from both academia and industry are welcome.

Dr. Saeed Farrokhpay
Guest Editor

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Keywords

gravity separation
falcon
hydrocyclone
magnetic separation
flotation

Related Special Issue

Physical Separation and Enrichment, Volume II in Minerals (2 articles)

Published Papers (13 papers)

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Editorial

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3 pages, 184 KiB

Open AccessEditorial

Editorial for the Special Issue: “Physical Separation and Enrichment”

by Saeed Farrokhpay

Minerals 2020, 10(2), 173; https://doi.org/10.3390/min10020173 - 14 Feb 2020

Cited by 1 | Viewed by 1470

Abstract

Physical separation methods have been used in mineral industry for centuries to separate valuable minerals from gangues using differences in their physical properties [...] Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

Research

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13 pages, 5205 KiB

Open AccessArticle

Application of the Discrete Element Method to Study the Effects of Stream Characteristics on Screening Performance

by Ali Davoodi, Gauti Asbjörnsson, Erik Hulthén and Magnus Evertsson

Minerals 2019, 9(12), 788; https://doi.org/10.3390/min9120788 - 14 Dec 2019

Cited by 13 | Viewed by 3081

Abstract

Screening is a key operation in a crushing plant that ensures adequate product quality of aggregates in mineral processing. The screening process can be divided into the two sub-processes of stratification and passage. The stratification process is affected by the relative difference between various properties, such as particle shape, size distribution, and material density. The discrete element method (DEM) is a suitable method for analyzing the interactions between individual particles and between particles and a screen deck in a controlled environment. The main benefit of using the DEM for simulating the screening process is that this method enables the tracking of individual particles in the material flow, and all of the collisions between particles and between particles and boundaries. This paper presents how different particle densities and flowrates affect material stratification and, in turn, the screening performance. The results of this study show that higher density particles have a higher probability of passage because of their higher stratification rate, which increases the probability that a particle will contact the screen deck during the process. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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19 pages, 3453 KiB

Open AccessEditor’s ChoiceArticle

Improving the Quality of Ferruginous Chromite Concentrates Via Physical Separation Methods

by Sunil Kumar Tripathy, Y Rama Murthy, Veerendra Singh, Saeed Farrokhpay and Lev O. Filippov

Minerals 2019, 9(11), 667; https://doi.org/10.3390/min9110667 - 29 Oct 2019

Cited by 8 | Viewed by 5360

Abstract

The low chromium-to-iron ratio of chromite ores is an important issue in some chromite deposits. The value of the chromite ore is indeed dictated in the market by its iron, as well as its chromium content. In the present study, a chromite concentrate was reprocessed by gravity (spiral concentrator) and magnetic separation to enhance the chromium-to-iron ratio. Also, detailed characterization studies including automated mineralogy were carried out to better understand the nature of the samples. Enhancing the chromium-to-iron ratio was achieved by using advanced spiral separators which will be discussed in this paper. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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12 pages, 2870 KiB

Open AccessArticle

Selective Capture of Magnetic Wires to Particles in High Gradient Magnetic Separation

by Jianwu Zeng, Xiong Tong, Fan Yi and Luzheng Chen

Minerals 2019, 9(9), 509; https://doi.org/10.3390/min9090509 - 23 Aug 2019

Cited by 11 | Viewed by 3064

Abstract

High gradient magnetic separation (HGMS) achieves effective separation to fine weakly magnetic minerals using numerous small magnetic wires in matrix, and its separation performance is inherently dependent on the capture characteristics of the wires. In this work, the selective capture of magnetic wire to particles in high gradient magnetic field was theoretically described and simulated using COMSOL Multiphysics. It was found that the capture trajectories of a small amount of particles under the ideal condition was significantly different from those of a large amount of particles under the actual condition, and non-magnetic particles would be much more easily entrained into magnetic deposits captured onto the wire surface under the actual condition than those under the ideal condition. These theoretical and simulated results were basically validated with the experimental magnetic capture to an ilmenite ore, and the wires in slow feed mode have achieved much higher capture selectivity than those in the fast feed mode. For instance, at the magnetic induction of 0.8 T, the TiO₂ grade of magnetic deposits captured by 3 mm diameter wire in the slow feed model reached 36.78%, which is higher than 28.32% in the fast feed model. The selective capture difference between the fast and slow feed models increased with increase in the magnetic induction and with decrease in the pulsating frequency. This investigation contributes to improve HGMS performance in concentrating fine weakly magnetic ores. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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16 pages, 7428 KiB

Open AccessArticle

Mineralogy and Pretreatment of a Refractory Gold Deposit in Zambia

by Xu Wang, Wenqing Qin, Fen Jiao, Congren Yang, Yanfang Cui, Wei Li, Zhengquan Zhang and Hao Song

Minerals 2019, 9(7), 406; https://doi.org/10.3390/min9070406 - 01 Jul 2019

Cited by 18 | Viewed by 7723

Abstract

The technological mineralogy of a gold deposit located in North-Western province of Zambia was carried out by using X-ray fluorescence spectroscopy (XRF), X-ray diffraction spectroscopy (XRD), and scanning electron microscope (SEM). The results showed that gold was highly dispersed in gold-bearing minerals such as pyrite, arsenopyrite, and some gangues in the form of natural gold and electrum. The gold grade in the mineral was 15.96 g/t and the particle size distribution of gold was extremely uneven. Most of the gold particles were less than 10 μm and wrapped with gold-bearing minerals, making it difficult to achieve liberation during grinding. According to the characteristics of the refractory gold deposit, the gravity–flotation combined beneficiation process was used to recover the liberated coarse gold and the fine gold in the sulphides. The closed-circuit experiments obtained excellent indicators. The grade and recovery of gold in the gravity separation concentrates reached 91.24 g/t and 57.58%, respectively. The grade and recovery of gold in the flotation concentrates were 49.44 g/t and 33.36%, respectively. The total recovery of gold was 90.94%. The gravity–flotation combined beneficiation pretreatment process provided a feasible method for the refractory gold ore and ensured the effective recovery of gold. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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14 pages, 3470 KiB

Open AccessEditor’s ChoiceArticle

Numerical Simulation of Flow Field Characteristics and Separation Performance Test of Multi-Product Hydrocyclone

by Yuekan Zhang, Peikun Liu, Lanyue Jiang, Xinghua Yang and Junru Yang

Minerals 2019, 9(5), 300; https://doi.org/10.3390/min9050300 - 16 May 2019

Cited by 3 | Viewed by 3173

Abstract

A traditional hydrocyclone can only generate two products with different size fractions after one classification, which does not meet the fine classification requirements for narrow size fractions. In order to achieve the fine classification, a multi-product hydrocyclone with double-overflow-pipe structure was designed in this study. In this work, numerical simulation and experimental test methods were used to study the internal flow field characteristics and distribution characteristics of the product size fraction. The simulation results showed that in contrast with the traditional single overflow pipe, there were two turns in the internal axial velocity direction of the hydrocyclone with the double-overflow-pipe structure. Meanwhile, the influence rule of the diameter of the underflow outlet on the flow field characteristics was obtained through numerical simulation. From the test, five products with different size fractions were obtained after one classification and the influence rule of the diameter of the underflow outlet on the size fraction distribution of multi-products was also obtained. This work provides a feasible research idea for obtaining the fine classification of multiple products. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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18 pages, 5482 KiB

Open AccessArticle

The Effect of the Characteristics of the Partition Plate Unit on the Separating Process of −6 mm Fine Coal in the Compound Dry Separator

by Changshuai Chen, Longlong Wang, Zhenfu Luo, Yuemin Zhao, Bo Lv, Yanhong Fu and Xuan Xu

Minerals 2019, 9(4), 215; https://doi.org/10.3390/min9040215 - 04 Apr 2019

Cited by 7 | Viewed by 2846

Abstract

Although compound dry separation technology has been applied to industrial applications for +6 mm size fraction of coal separation, the technology has not been widely applied in the separation of fine coal (−6 mm). In this study, the effect of the partition plate unit characteristics on both the average density of particles in the bed uniformly and the final separation results in a fine coal separation process were studied. According to the results, the standard deviations of the corresponding density distribution were 0.08, 0.14, and 0.07 when the height of the partition plate was 2.5 cm, the partition plate angle was 35°, and the distance from the apex of partition plate on the backplane, was 12 cm, respectively, which were the lowest values at the same level. These results showed that the average density of particles in the bed was uniformly, and its corresponding density distribution contour map was more regular. When the amplitude was 2.8 mm, the frequency was 29 Hz, the height of the partition plate was 2.5 cm, the partition plate angle was 35°, and the distance from the apex of the partition plate to the backplane was 12 cm; as a result, the E value was 0.115 g/cm³, the yield of the concentrate was 69.24%, the ash content was 12.52%, and the separation effect was better. The characteristics of the partition plate unit have an important effect on the separating process of −6 mm fine coal in the compound dry separator. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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19 pages, 4619 KiB

Open AccessArticle

The Effect of Inlet Velocity on the Separation Performance of a Two-Stage Hydrocyclone

by Lanyue Jiang, Peikun Liu, Yuekan Zhang, Xinghua Yang and Hui Wang

Minerals 2019, 9(4), 209; https://doi.org/10.3390/min9040209 - 30 Mar 2019

Cited by 19 | Viewed by 6216

Abstract

The “entrainment of coarse particles in overflow” and the “entrainment of fine particles in underflow” are two inevitable phenomena in the hydrocyclone separation process, which can result in a wide product size distribution that does not meet the requirement of a precise classification. Hence, this study proposed a two-stage (TS) hydrocyclone, and the effects of the inlet velocity on the TS hydrocyclone were investigated using computational fluid dynamics (CFD). More specifically, the influences of the first-stage inlet velocity on the second-stage swirling flow field and the separation performance were studied. In addition, the particle size distribution of the product was analyzed. It was found that the first-stage overflow contained few coarse particles above 40 μm and that the second-stage underflow contained few fine particles. The second-stage underflow was free of particles smaller than 10 μm and almost free of particles smaller than 20 μm. The underflow product contained few fine particles. Moreover, the median particle size of the second-stage overflow product was similar to that of the feed. Inspired by this observation, we propose to recycle the second-stage overflow to the feed for re-classification and to use only the first-stage overflow and the second-stage underflow as products. In this way, fine particle products free of coarse particle entrainment, and coarse particle products free of fine particle entrainment can be obtained, achieving the goal of precise classification. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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14 pages, 3783 KiB

Open AccessArticle

Scrubbing and Inhibiting Coagulation Effect on the Purification of Natural Powder Quartz

by Xin Du, Chao Liang, Donglai Hou, Zhiming Sun and Shuilin Zheng

Minerals 2019, 9(3), 140; https://doi.org/10.3390/min9030140 - 26 Feb 2019

Cited by 8 | Viewed by 2766

Abstract

The low removal efficiency of fine clay impurities in natural powder quartz (NPQ) is the main problem that affects the practical utilization of this natural resource. In this work, detailed characterizations of NPQ and clay impurities in NPQ were analyzed by SEM-EDS, mineral liberation analysis (MLA) and impurities distribution analysis. A combined physical purification process, including sieving, scrubbing and centrifugation, was applied to remove the clay impurities. It was observed that the fine clay impurities adhering on quartz surface were effectively liberated by scrubbing, and the content of Fe₂O₃ and Al₂O₃ in the concentrate decreased from 0.48% and 0.40% to less than 0.01% and 0.02% at pH 9.3 or when the dosage of sodium hexametaphosphate (SHMP) was 1 × 10³ g/t. The coagulation interaction between quartz and impurities including hematite and orthoclase were analyzed based on the classical Deyaguin-Landau-Verwey-Overbeek (DLVO) theory. The results indicated that the main coagulation affecting the separation efficiency was the heterocoagulation between quartz and impurities and homocoagulation among hematite particles. Furthermore, adding regulators such as sodium hydroxide (NaOH) or SHMP could significantly decrease the zeta potential of minerals and thus increase the total interaction energy (V_T), which could effectively improve the dispersion of these fine impurity particles, and consequently improve the removal efficiency of impurities. Reverse increase of the zeta potential of minerals in strongly alkaline solutions or excessive SHMP were detected, which was likely the main factor limiting the further improvement of the purification efficiency. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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17 pages, 5657 KiB

Open AccessArticle

The Study on Numerical Simulation and Experiments of Four Product Hydrocyclone with Double Vortex Finders

by Yuekan Zhang, Peikun Liu, Lanyue Jiang and Xinghua Yang

Minerals 2019, 9(1), 23; https://doi.org/10.3390/min9010023 - 30 Dec 2018

Cited by 12 | Viewed by 3207

Abstract

A hydrocyclone is an instrument that can effectively separate multi-phase mixtures of particles with different densities or sizes based on centrifugal sedimentation principles. However, conventional hydrocyclones lead to two products only, resulting in an over-wide particle size range that does not meet the requirements of subsequent operations. In this article, a two-stage series, a four product hydrocyclone is proposed. The first stage hydrocyclone is designed to be a coaxial double overflow pipe: under the effect of separation, fine particles are discharged from the internal overflow pipe, while medium-size particles are discharged from external overflow pipe before entering the second stage hydrocyclone for fine sedimentation. In other words, one-stage grading leads to four products, including the first stage underflow, the first stage overflow, the second stage underflow, and the second stage overflow. The effects of structural parameters and operational parameters on flow field distribution in hydrocyclone were investigated via a study of flow field distribution in multi-product hydrocyclones using numerical simulations. The application of four product hydrocyclone in iron recovery shows that the grade and recovery of iron concentrate exceed 65.08% and 86.14%, respectively. This study provides references for understanding the flow field distribution in hydrocyclones and development of multi-product grading instrument in terms of both theory and industrial applications. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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14 pages, 4022 KiB

Open AccessArticle

The Process of the Intensification of Coal Fly Ash Flotation Using a Stirred Tank

by Lu Yang, Zhenna Zhu, Xin Qi, Xiaokang Yan and Haijun Zhang

Minerals 2018, 8(12), 597; https://doi.org/10.3390/min8120597 - 17 Dec 2018

Cited by 20 | Viewed by 3687

Abstract

Pulp preconditioning using a stirred tank as a pretreatment process is vital to the flotation system, which can be used to improve the flotation efficiency of mineral particles. The kinetic energy that is dissipated in the stirred tank could strengthen the interaction process between mineral particles and flotation reagents to improve the flotation efficiency in the presence of the preconditioning. In this paper, the effect of the conditioning speed on the coal fly ash flotation was investigated using numerical simulations and conditioning-flotation tests. The large eddy simulation coupled with the Smagorinsky-Lilly subgrid model was employed to simulate the turbulence flow field in the stirred tank, which was equipped with a six blade Rushton turbine. The impeller rotation was modelled using the sliding mesh. The simulation results showed that the large eddy simulation (LES) well matched the previous experimental data. The turbulence characteristics, such as the mean velocity, turbulent kinetic energy, power consumption and instantaneous structures of trailing vortices were analysed in detail. The turbulent length scale (η) decreased as the rotation speed increased, and the minimum value of η was almost unchanged when the rotation speed was more than 1200 rpm. The conditioning-flotation tests of coal fly ash were conducted using different conditioning speeds. The results showed that the removal of unburned carbon was greatly improved due to the strengthened turbulence in the stirred tank, and the optimal results were obtained with an LOI of 3.32%, a yield of 78.69% and an RUC of 80.89% when the conditioning speed was 1200 rpm. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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15 pages, 4658 KiB

Open AccessCase Report

Heavy Mineral Sands in Brazil: Deposits, Characteristics, and Extraction Potential of Selected Areas

by Caroline C. Gonçalves and Paulo F. A. Braga

Minerals 2019, 9(3), 176; https://doi.org/10.3390/min9030176 - 13 Mar 2019

Cited by 19 | Viewed by 9066

Abstract

In Brazil, heavy mineral sand deposits are still barely exploited, despite some references to Brazilian reserves and ilmenite concentrate production. The goal of this project is to characterize and investigate the potential recovery of heavy minerals from selected Brazilian placer occurrences. Two areas of the coastal region were chosen, in Piaui state and in Bahia Provinces. In all samples, the heavy minerals of interest (ilmenite, monazite, rutile, and zircon) were identified by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques and also quantified by X-ray fluorescence spectrometry (XRF) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The total heavy minerals (THM) in the Piaui samples were 6.45% and 10.14% THM, while the figure for the Bahia sample was 3.4% THM. The recovery test of the Bahia sample, using only physical separation equipment such as a shaking table and magnetic separator, showed valuable metallurgical recoveries at around or greater than 70% for each stage, and the final concentrate of pure ilmenite was composed of up to 60.0% titanium dioxide after the differential magnetic separation. Another aim is to compile accessible information about Brazilian heavy mineral main deposits complemented with a short economic overview. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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12 pages, 5586 KiB

Open AccessTechnical Note

Separation of Monazite from Placer Deposit by Magnetic Separation

by Kwanho Kim and Soobok Jeong

Minerals 2019, 9(3), 149; https://doi.org/10.3390/min9030149 - 28 Feb 2019

Cited by 21 | Viewed by 6980

Abstract

In this study, mineralogical analysis and beneficiation experiments were conducted using a placer deposit of North Korea, on which limited information was available, to confirm the feasibility of development. Rare earth elements (REEs) have vital applications in modern technology and are growing in importance in the fourth industrial revolution. However, the price of REEs is unstable due to the imbalance between supply and demand, and tremendous efforts are being made to produce REEs sustainably. One of them is the evaluation of new rare earth mines and the verification of their feasibility. As a result of a mineralogical analysis, in this placer deposit, monazite and some amount of xenotime were the main REE-bearing minerals. Besides these minerals, ilmenite and zircon were the target minerals to be concentrated. Using a magnetic separation method at various magnetic intensities, paramagnetic minerals, ilmenite (0.8 T magnetic product), and monazite/xenotime (1.0–1.4 T magnetic product) were recovered selectively. Using a magnetic separation result, the beneficiation process was conducted with additional gravity separation for zircon to produce a valuable mineral concentrate. The process resulted in three kinds of mineral concentrates (ilmenite, REE-bearing mineral, and zircon). The content of ilmenite increased from 32.5% to 90.9%, and the total rare earth oxide (TREO) (%) of the REE-bearing mineral concentrates reached 45.0%. The zircon concentrate, a by-product of this process, had a Zr grade of 42.8%. Consequently, it was possible to produce concentrates by combining relatively simple separation processes compared to the conventional process for rare earth placer deposit and confirmed the possibility of mine development. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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