Corona Electrostatic Separation Research Articles

New Approach Study on Dry Coal Cleaning System with Two-Stage Corona Electrostatic Processes for High-Sulfur Low-Grade Fine Coals

Corona electrostatic separation can remove inorganic materials from coal, reduce coal ash content and sulfur content and improve coal quality, reduce air pollution caused by smoke dust, SOX, and COX. The performance of corona electrostatic separation technology in cleaning a middle ash medium-ash, high-sulfur coal was experimentally investigated. The electrode voltage, drum rotational speed, and feeding speed were tested, whereas other parameters were maintained constant during the experiment. The results indicate that the performance of this technology in cleaning medium-ash, high-sulfur coal can be improved by optimizing the process parameters. The results demonstrate that corona electrostatic separation is effective for the beneficiation of this grade coal. In addition, the efficiency of coal cleaning is significantly improved by adding the second stage beneficiation to clean the middlings out from the first stage beneficiation. In this study, the first stage of beneficiation recovered 38.00% (by weight) of clean coal (ash content below 20%), and the second stage recovered 48.58% (by weight) of clean coal, improving the overall separation efficiency from 0.69 to 1.74. Furthermore, the sulfur content was reduced from 4.71% (raw coal) to 3.53% (clean coal). Our result show that corona electrostatic separation can effectively reject inorganic sulfur from raw coal, and the two-stage separate is also very helpful for coal purification.

Selection of process for aluminium separation from waste cables by TOPSIS and WASPAS methods

The separation process, particularly gravity and electrostatic separation, is very important in the recycling processing industry. Some characteristics of waste cable, as well as separation have a significant impact on the results and effects of aluminium recycling. At the same time, this process requires a significant amount of energy which significantly affects the overall recycling costs. This paper focuses on the recycling of waste aluminum cable by gravity and electrostatic separation. Experimental tests were performed on three different separators. Therefore, this paper presents the application of multiple criteria decision making (MCDM) methods, combining TOPSIS and AHP methods, as well as WASPAS and AHP methods, which should enable an efficient selection of the separation process. Also, the impact of the criteria weights to the ranking order of alternatives was performed in order to verify the obtained results. Results of all the studies presented in this paper show that a corona-electrostatic separation process is the most acceptable process for waste aluminium cable recycling.

Beneficiation of Talc-Magnesite Ore with Cu-Co Mineralization

Magnesite ore with a low chalcopyrite – cobaltite mineralization was subjected to a series of separations designed to evaluate thepossible concentration of the two accessory minerals. Although the Cu-Co grade in the ore (> 0.01% Co, > 0.1% Cu) is significantlylower than the typical economic grades, content of the main valuable mineral for which the ore is mined and processed incombination with a listing of cobalt as a critical raw material, coupled with their higher price might compensate for the additionalbeneficiation stages. The ore was first crushed and subsequently classified to -100 μm and +100 -400 μm size fractions. The finefraction was upgraded by froth flotation processing in laboratory froth flotation cell. The coarser fraction was processed in severalseparation stages including gravity separation on shaking table, magnetic separation and corona electrostatic separation. The sameprocedure was also repeated with a higher-grade sample as a verification of the procedures. Preliminary results suggest that theaccessory minerals can be separated from the talc-magnesite ore and individual mineral concentrates with about 19% Co and 28%Cu were prepared. However, further work must be done to achieve desirable recoveries for the processing to be economically viable.

Environment-friendly technology for recovering cathode materials from spent lithium iron phosphate batteries.

The consumption of lithium iron phosphate (LFP)-type lithium-ion batteries (LIBs) is rising sharply with the increasing use of electric vehicles (EVs) worldwide. Hence, a large number of retired LFP batteries from EVs are generated annually. A recovery technology for spent LFP batteries is urgently required. Compared with pyrometallurgical, hydrometallurgical and biometallurgical recycling technologies, physical separating technology has not yet formed a systematic theory and efficient sorting technology. Strengthening the research and development of physical separating technology is an important issue for the efficient use of retired LFP batteries. In this study, spent LFP batteries were discharged in 5 wt% sodium chloride solution for approximately three hours. A specially designed machine was developed to dismantle spent LFP batteries. Extending heat treatment time exerted minimal effect on quality loss. Within the temperature range of 240°C-300°C, temperature change during heat treatment slightly affected mass loss. The change in heat treatment temperature also had negligible effect on the shedding quality of LFP materials. The cathode material and the aluminium foil current collector accounted for a certain proportion in a sieve with a particle size of -1.25 + 0.40 mm. Corona electrostatic separation was performed to separate the metallic particles (with a size range of -1.5 + 0.2 mm) from the nonmetallic particles of crushed spent LFP batteries. No additional reagent was used in the process, and no toxic gases, hazardous solid waste or wastewater were produced. This study provides a complete material recovery process for spent LFP batteries.

Improving the recovery of copper from electric cable waste derived from automotive industry by corona-electrostatic separation

The aim of this work is to demonstrate the possibility of using electric field forces for the recovery of copper from a fine PVC/Cu granular mixture of low metal content (less than 15%), obtained as “PVC fraction” in the recycling process of electric cable waste from automotive industry, using vibrating table technology. Electrostatic separation of copper granules which are “impurities” in the PVC fraction, increased the overall recovery of copper close to 100%. Granular size classification proved to be a very useful operation in the electrostatic separation process of a particular mixture. The −0.63 mm size class contains the majority of the copper granules and the electrostatic separation allows the recovery of up to 95% copper contained in the granular waste, at purity higher than 99.8%. Copper represents less than 1% in the +0.63 mm size class and can also be recovered with high purity by improving the chopping technology of the cable waste, as well as the separation between the copper and the high conductivity rubber granules.

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.

Recovery of residual metals from fine nonmetallic fractions of waste printed circuit boards using a vibrated gas-solid fluidized bed

Abstract Nonmetallic fractions are essential byproducts of the physical-mechanical recycling process of waste printed circuit boards. Large amounts of metals remain in fine nonmetallic fractions because it is very hard for recycling metals from fine size fraction by traditional technologies. In this study, a vibrated gas-solid fluidized bed was utilized to recover residual metals from fine particles (−0.25 mm size) of nonmetallic fractions obtained from the corona electrostatic separation process. The basic mineralogical characteristics and properties of nonmetallic fractions with a size of −0.25 mm indicated that a considerable amount of clavate glass fibers existed in these nonmetallic fractions. The content of residual metals in the −0.25 mm nonmetallic fractions was up to 19.84 wt%. The major metallic elements found in the nonmetallic fractions were Fe, Cu, Pb, and Sn. The results indicated that removing glass fibers from nonmetallic fractions by triboelectric separation can strengthen the gravity-segregation process between heavy and light particles in fine nonmetallic fractions, resulting in improved metal recovery from 76.39% to 81.41%. Based on this research, an industrial flowsheet for the recovery of metals from fine WPCBs is proposed.

Application of Chloride Metallurgy and Corona Electrostatic Separation for Recycling Waste Multilayer Ceramic Capacitors

Electronic-waste recycling has become a global issue owing to its potential environmental pollution and rich metal resource. Waste multilayer ceramic capacitors (MLCCs), widely existing in discarded electronic devices, are rich in valuable metals such as silver (Ag) and palladium (Pd). However, how to effectively and in an environmentally friendly manner recycle waste MLCCs is seldom considered. This study developed an efficient and integrated process for recovering valuable materials from waste MLCCs by chloride metallurgy (CM) and corona electrostatic separation (CES). In CM, NH4Cl was used as the chlorinating agent. The results demonstrated that BaTiO3, Ag, and tin (Sn) can be chlorinated. The generated gas-phase SnCl4 was collected in the condensing zone. BaCl2 and AgCl were sequentially separated by leaching with water and sodium thiosulfate solution. The recovery efficiencies of Ag, Ba, and Sn could reach 99.21, 98.76, and 99.83%, respectively. The optimal CM parameters were considered to be 400 °C,...

New technology for recovering residual metals from nonmetallic fractions of waste printed circuit boards

Recycling of waste printed circuit boards is important for environmental protection and sustainable resource utilization. Corona electrostatic separation has been widely used to recycle metals from waste printed circuit boards, but it has poor separation efficiency for finer sized fractions. In this study, a new process of vibrated gas-solid fluidized bed was used to recycle residual metals from nonmetallic fractions, which were treated using the corona electrostatic separation technology. The effects of three main parameters, i.e., vibration frequency, superficial air flow velocity, and fluidizing time on gravity segregation, were investigated using a vibrating gas-solid fluidized bed. Each size fraction had its own optimum parameters. Corresponding to their optimal segregation performance, the products from each experiment were analyzed using an X-ray fluorescence (XRF) and a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). From the results, it can be seen that the metal recoveries of −1+0.5mm, −0.5+0.25mm, and −0.25mm size fractions were 86.39%, 82.22% and 76.63%, respectively. After separation, each metal content in the −1+0.5 or −0.5+0.25mm size fraction reduced to 1% or less, while the Fe and Cu contents are up to 2.57% and 1.50%, respectively, in the −0.25mm size fraction. Images of the nonmetallic fractions with a size of −0.25mm indicated that a considerable amount of clavate glass fibers existed in these nonmetallic fractions, which may explain why fine particles had the poorest segregation performance.

Recovery of Valuable Materials from Waste Tantalum Capacitors by Vacuum Pyrolysis Combined with Mechanical–Physical Separation

Waste tantalum capacitors (WTCs), dismantled from waste printed circuit boards, are considered a high quality tantalum (Ta) resource. Ta is a rare and strategic material. Nearly half of the Ta consumption is used for manufacturing tantalum capacitors. Furthermore, large amounts of energy and chemicals are consumed during the Ta purification process. Therefore, recovering Ta from WTCs can sustainably utilize the Ta resource and reduce pollution. However, the recycling technology has been poorly developed. This study proposed vacuum pyrolysis (VP) and mechanical–physical separation (MPS) to recover Ta and other materials from WTCs. First, the WTCs were treated by VP to decompose the organics. The suitable VP parameters were considered as 400 °C, 50 Pa, and 60 min. Then, the residues were performed by MPS. Consequently, nickel–iron terminals were recovered by magnetic separation. Ta and silica were separated by corona electrostatic separation. The recovery rate and purity of Ta could reach 97.02 ± 0.85% and ...

Experimental study of a modified dual-type high-voltage electrode for electrostatic separation applications

Several electrode arrangements have been proposed to enhance the efficiency of insulating materials charging by corona discharge. Recent studies pointed out that the presence of metal strips in the proximity of a dual-type high voltage electrode increases the total current measured at the surface of the collecting electrode, decreases the corona onset voltage value and enlarges the reparation of current density as well. The aim of this paper is to evaluate the benefits of using such an electrode arrangement for corona charging of non-conductive particulate materials in belt-type corona-electrostatic separators. The experimental study was carried out with samples of Aluminum and Polystyrene particles in the size class 125–250 μm. The presence of grounded strips reduces the electric wind, which is associated to corona discharge but not tolerated in such processes that involve micronized materials. At the same time, it improves the corona charging conditions of non-conductive materials and as consequence the overall efficiency of the corona-electrostatic separation process. The use of the new electrode configuration is characterized by both high recovery rates and better purities of the separated products.

A Novel Designed Bioreactor for Recovering Precious Metals from Waste Printed Circuit Boards.

For recovering precious metals from waste printed circuit boards (PCBs), a novel hybrid technology including physical and biological methods was developed. It consisted of crushing, corona-electrostatic separation, and bioleaching. Bioleaching process is the focus of this paper. A novel bioreactor for bioleaching was designed. Bioleaching was carried out using Pseudomonas chlororaphis. Bioleaching experiments using mixed particles of Au and Cu were performed and leachate contained 0.006 mg/L, 2823 mg/L Au+ and Cu2+ respectively. It showed when Cu existed, the concentrations of Au were extremely small. This provided the feasibility to separate Cu from Au. The method of orthogonal experimental design was employed in the simulation bioleaching experiments. Experimental results showed the optimized parameters for separating Cu from Au particles were pH 7.0, temperature 22.5 °C, and rotation speed 80 r/min. Based on the optimized parameters obtained, the bioreactor was operated for recovering mixed Au and Cu particles. 88.1 wt.% of Cu and 76.6 wt.% of Au were recovered. The paper contributed important information to recover precious metals from waste PCBs.

A computer‐aided methodology for the optimization of electrostatic separation processes in recycling

The rapid growth of technological products has led to an increasing volume of waste electrical and electronic equipments (WEEE), which could represent a valuable source of critical raw materials. However, current mechanical separation processes for recycling are typically poorly operated, making it impossible to modify the process parameters as a function of the materials under treatment, thus resulting in untapped separation potentials. Corona electrostatic separation (CES) is one of the most popular processes for separating fine metal and nonmetal particles derived from WEEE. In order to optimize the process operating conditions (i.e., variables) for a given multi‐material mixture under treatment, several technological and economical criteria should be jointly considered. This translates into a complex optimization problem that can be hardly solved by a purely experimental approach. As a result, practitioners tend to assign process parameters by few experiments based on a small material sample and to keep these parameters fixed during the process life‐cycle. The use of computer experiments for parameter optimization is a mostly unexplored area in this field. In this work, a computer‐aided approach is proposed to the problem of optimizing the operational parameters in CES processes. Three metamodels, developed starting from a multi‐body simulation model of the process physics, are presented and compared by means of a numerical and simulation study. Our approach proves to be an effective framework to optimize the CES process performance. Furthermore, by comparing the predicted response surfaces of the metamodels, additional insight into the process behavior over the operating region is obtained. Copyright © 2015 John Wiley & Sons, Ltd.

Real-time monitoring system for improving corona electrostatic separation in the process of recovering waste printed circuit boards.

Although corona electrostatic separation is successfully used in recycling waste printed circuit boards in industrial applications, there are problems that cannot be resolved completely, such as nonmetal particle aggregation and spark discharge. Both of these problems damage the process of separation and are not easy to identify during the process of separation in industrial applications. This paper provides a systematic study on a real-time monitoring system. Weight monitoring systems were established to continuously monitor the separation process. A Virtual Instrumentation program written by LabVIEW was utilized to sample and analyse the mass increment of the middling product. It includes four modules: historical data storage, steady-state analysis, data computing and alarm. Three kinds of operating conditions were used to verify the applicability of the monitoring system. It was found that the system achieved the goal of monitoring during the separation process and realized the function of real-time analysis of the received data. The system also gave comprehensible feedback on the accidents of material blockages in the feed inlet and high-voltage spark discharge. With the warning function of the alarm system, the whole monitoring system could save the human cost and help the new technology to be more easily applied in industry.

Effect of spark discharges on the trajectories of insulating particles in roll-type corona-electrostatic separators. Experimental and numerical study

Corona-electrostatic separation is a multi-variable process that has been thoroughly studied in connection with its various applications in the recycling industry. The aim of the present paper is to point out one parasitic phenomenon that adversely affects the efficiency of the separation: the sparks generated at the passage of conductive particles through the electric field zone. The experiments were carried out on a laboratory roll-type corona electrostatic separators, and the sparks were generated by introducing 16 calibrated copper pins in 40-g samples of granular insulating material (PVC; typical granule size: 1.5 mm) that were fed at a constant rate onto the surface of the grounded rotating roll electrode. The distribution of the PVC granules in the 14 boxes of the collector was altered by the occurrence of the spark discharges, as they were accompanied by the annealing of the electric field between the electrodes. The numerical simulation of insulating granules charging and movement under the action of the electric field enabled a better understanding of the interactions between the spark discharges and the other factors that influence their trajectories and affect the efficiency of the separation: roll-speed, particle size and ambient humidity. The particle dynamics equations were solved using an iterative scheme by using the electric field calculated in any point with the commercial software TRICOMP. The good agreement between the predictions made by these simulations and the experimental findings confirms the ability of the mathematical model to reflect the complexity of the physical phenomena. ► Sparks occur between the electrodes at the passage of conductive particles. ► Sparks aneal the electric field and limit the maxim charge of insulating particles. ► Sparks have a stronger effect on the trajectories of coarse particles. ► Purity of the separated products is poorer in the presence of sparks. ► Numerical modeling can provide an accurate description of the phenomenon.

Robust corona-electrostatic separation method for solid waste recycling

The objective was to reduce variation in the outcome of a corona-electrostatic separation process for solid waste recycling by finding operating conditions (high-voltage level, roll speed, splitter position) under which uncontrollable variation in 'noise factors' (ambient humidity, metal content in the feed) has minimal impact on the quantity and the quality of the recovered products. The samples of processed material were prepared from mm-size chopped electric wire wastes. The design and noise factors were first analysed using the classical Taguchi's approach, then combined into one single experimental design, so that a regression model of the process will be fitted.

Critical rotational speed model of the rotating roll electrode in corona electrostatic separation for recycling waste printed circuit boards

Waste printed circuit board (PCB) is increasing worldwide. The corona electrostatic separation (CES) was an effective and environmental protection way to recycle resource from waste PCBs. The aim of this paper is to analyze the main factor (rotational speed) that affects the efficiency of CES from the point of view of electrostatics and mechanics. A quantitative method for analyzing the affection of rotational speed was studied and the model for separating flat nonmetal particles in waste PCBs was established. The conception of “charging critical rotational speed” and “detaching critical rotational speed” were presented. Experiments with the waste PCBs verified the theoretical model, and the experimental results were in good agreement with the theoretical model. The results indicated that the purity and recycle percentage of materials got a good level when the rotational speed was about 70 rpm and the critical rotational speed of small particles was higher than big particles. The model can guide the definition of operator parameter and the design of CES, which are needed for the development of any new application of the electrostatic separation method.

Optimizing the operating parameters of corona electrostatic separation for recycling waste scraped printed circuit boards by computer simulation of electric field

The printed circuit board (PCB) has a metal content of nearly 28% metal, including an abundance of nonferrous metals such as copper, lead, and tin. The purity of precious metals in PCBs is more than 10 times that of rich-content minerals. Therefore, the recycling of PCBs is an important subject, not only from the viewpoint of waste treatment, but also with respect to the recovery of valuable materials. Compared with traditional process the corona electrostatic separation (CES) had no waste water or gas during the process and it had high productivity with a low-energy cost. In this paper, the roll-type corona electrostatic separator was used to separate metals and nonmetals from scraped waste PCBs. The software MATLAB was used to simulate the distribution of electric field in separating space. It was found that, the variations of parameters of electrodes and applied voltages directly influenced the distribution of electric field. Through the correlation of simulated and experimental results, the good separation results were got under the optimized operating parameter: U = 20–30 kV, L = L 1 = L 2 = 0.21 m, R 1 = 0.114, R 2 = 0.019 m, θ 1 = 20° and θ 2 = 60°.

Application of corona discharge and electrostatic force to separate metals and nonmetals from crushed particles of waste printed circuit boards

Printed circuit board (PCB) scrap has a metal content of nearly 28%, including an abundance of nonferrous metals such as copper, lead, and tin. The purity of precious metals in PCBs is more than 10 times that of content-rich minerals. Therefore, the recycling of PCBs is an important subject, not only from the viewpoint of waste treatment, but also with respect to the recovery of valuable materials. A new process was investigated which involved mechanical crushing, screening, drying and electrostatic separation via corona discharge. The results show that (1) a two-step crushing process could completely strip metals from base plates; (2) the effect of aggregation opposed the production on fine powders; (3) particle sizes between 0.6 and 1.2 mm are most feasible for separation in industrial application; (4) Corona electrostatic separation is an efficient and environmental means for recovering metals from PCBs.

Influence of high-voltage polarity on insulation-metal electroseparation

A comparative study of the physical phenomena involved in corona-electrostatic separation of insulation-metal granular materials at different polarities has been initiated. The experiments were carried out with a reversible, non-filtered, d. c. high-voltage supply (single-phase step-up transformer / full-bridge rectifier), which energized either a laboratory electroseparator, or a test-cell specially-arranged for the study of corona effects. The electroseparation tests, performed on a sample containing 50% polyvinyl chloride and 50% stranded copper, have demonstrated that both polarities can be employed to ensure a good insulation-metal electroseparation. Subtle differences between corona discharges at positive and negative polarities, in the presence of the materials to be separated, were made evident by several laboratory experiments. Positive corona ensures a wider range of operating voltages, and is more uniform. Negative corona provides greater current at the same voltage levels, and produces a less-intense electric noise. Intense back-corona is generated by the tips of the stranded copper particles.