Electrostatic Separation Method Research Articles

Gravity and electrostatic separation of unburned coal from a selected fly ash

Unburned coal grains make it difficult to use fly ash economically, which causes energy losses in the fuel. The article presents the possibilities of separating unburned coal from selected fly ash. In order to assess the possibility of separation of unburned carbon, the analysis of grain density and ash composition was used. Unburned coal was separated by four methods – one wet gravity and three dry methods. It has been found that despite very fine ash grains, the quality and quantity of separation products are significantly dependent on the separation method used and the separated grains’ qualitative characteristics. The analysis of the coal grains under an electron microscope has revealed that they contain mineral inclusions. Their presence enables selective separation of carbon without first grinding the middling grains. The most advantageous results of the separation of unburned coal were obtained by the electrostatic separation method. Separated coal can be used in high-value carbon applications.

Microplastics in soil: Current status and evaluation of the greenness of various analytical methods of identification

• Terrestrial environments can be considered as potential sinks of Microplastics (MPs). • Both primary and secondary sources of MPs contribute to a significant amount of MPs in soil. • The greenness of analytical methods can be evaluated using AGREE software. • The electrostatic separation method of MPs can be considered as green quantification method. Microplastics (MPs) have received increasing attention because of their ubiquitous and persisting nature and high degree of resistance to degradation, and bioaccumulation. There has been growing evidence of their direct and indirect impacts on the ecosystem's health. Although the extensive research has been carried out to assess the impact of MPs on aquatic environment, terrestrial environment is a significant research hotspot that needs to be focused more as it is highly polluted by anthropic plastic usage. The overarching aim of this study was to assess the current research trends on MPs analysis and the evaluation of the greenness of existing quantification methods, particularly in soil samples. In the last three years the trend in the quantification of MPs in soil media is found to be exponential and few studies have reported significant concentration of MPs of about 85,000 particles per kg dry weight of soil samples, raising an alarm to the policy makers to implement stringent policies. It has been observed that the existing quantification methodologies are not following the sustainable principles of green analytical chemistry due to their low score obtained from AGREE method. In this context, the electrostatic method of separation of MPs can be considered green, while the magnetic and Olive oil-based separation methods are classified as worse based on the greenness parameter. This paper attempts to provide some new information on the implementation of sustainable methods of MP quantification.

Multi-stage Electrostatic Separation for Recovering of Aluminum from Fine Granules of Black Dross

Separation of aluminum from fine granules of black dross, which is a waste by-product in secondary aluminum production, was investigated. The separation was performed by a multi-stage electrostatic separation method. There are three stages to complete the separation, including preliminary separation, pulse charging enhancement and secondary concentration. Chemical and mineralogical compositions of collection products were analyzed and determined by X-ray diffraction (XRD) and X-ray Fluorescence (XRF). After multistage electrostatic separation, the Al2O3 content of the collection products increases from 50.74% to 69.77%. The mineralogical phase analysis indicates that the final recovery of metallic aluminum phase increases from 8% to 37%, and the aluminum oxide phase increases from 20% to 26%. The research results show the multi-stage electrostatic separation method is effective for recovering of aluminum from fine granules of black dross, and upgrades the black dross to a recoverable material.

Physicochemical characterization of a navy bean (Phaseolus vulgaris) protein fraction produced using a solvent-free method

A solvent-free electrostatic separation method was employed to separate navy bean flour (NBF) into protein-rich (PR) and starch-rich (SR) fractions. The physicochemical properties of NBF and separated fractions were compared to proteins (navy bean isolate (NBI) and 7S globulin) prepared using a wet process. Gel electrophoresis confirmed that the protein distribution in the isolated fractions was similar to that of NBF. The protein profile of NBI and 7S globulin was found to be devoid of certain proteins that were found in the NBF and PR fraction. Amino acid analysis revealed that the NBI and 7S globulin had a lower content of sulfur-containing amino acids compared to NBF and the electrostatically isolated fractions. CD and fluorescence spectroscopy confirmed that denaturation of the proteins during the acid precipitation is likely. This novel solvent-free electrostatic separation process preserves the native protein structure found in NBF and improves the recovery of some of the smaller MW proteins.

Electrostatic Separation of Peeling and Gluten from Finely Ground Wheat Grains

Sieving and air classification are not efficient enough for the extraction of the high-nutritional-value constituents of wheat. The aim of this article is to validate a simple electrostatic separation method of peeling and gluten, which are two such nutriments contained in finely ground wheat grains. The electrostatic separator is composed of metallic grounded belt conveyer and a rotating roll electrode connected to a high voltage supply. The electrostatic behavior of peeling and gluten powders was characterized using surface potential decay and direct charge measurements. These first set of experiments pointed out the conductive behavior of these powders: in contact with a grounded electrode, they lose their charge in less than 10 s. In a second set of experiments, mixtures of 50% peeling and 50% gluten powders were processed by electrostatic separation. Experimental design methodology was used to model the outcome of the separation process as function of two control variables: the high-voltage applied to the roll electrode and the speed of the belt conveyor electrode. In this way, it was possible to determine the optimal operational conditions for the recovery of high-purity peeling and gluten fractions.

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.

Electrostatics of spherical metallic particles in cylinder electrostatic separators/sizers

This paper presents a theoretical analysis of the dynamics of spherical metallic particles in electrostatic separators/sizers (ESSs). A computational algorithm is employed to depict the cylinder-type electrode arrangements applied in some electrostatic processes generating non-uniform electric fields. The ESS consists of a pair of conducting cylinders. The upper cylinder is energized by HVdc, while the lower one is grounded and mounted horizontally on a revolvable axis. The aim of this paper is to present a new electrode configuration and demonstrate the usefulness of numerical techniques for the evaluation of the particle's motion. A computer program was employed for analysing the behavior of spherical particles in a two-dimensional electrode arrangement that models the actual electric field configuration of cylinder-type electrostatic separators/sizers. The analysis is needed for the development of any new application of this cylinder-type electrode arrangement as an electrostatic separation method. The results reveal that the particle's motion depends on its radius and density and amplitude of the applied voltage. The actual granular mixtures with different specific mass and radius could be separated applying this cylinder-type electrostatic separation method; the lift voltage is an important parameter for separation. With a program for two-dimensional analysis of the electric field, the computational procedure presented in this paper could be employed for any particle shapes.

Modelling of conducting particle behaviour in plate-type electrostatic separators

The charging of conductive particles in contact with an electrode affected by a non-uniform electric field is a physical mechanism of paramount importance for various electrostatic technologies, including the separation of particulate mixtures. The aim of this paper is to model the behaviour of such charged particles in plate-type electrostatic separators. A computer program based on the boundary element method enabled the evaluation of the electric field strength at the surface of the plate electrode of these installations. The results of field computation were then employed for estimating the charge of perfectly-conducting spherical particles, as well as their position on the plate electrode, at the moment of detachment under the action of the electric force acting on them. The data reported in the paper point out the following factors which affect particle detachment and hence the efficiency of the electrostatic separation: the size and specific mass of the particles; the slope of the plate electrode; the dimensions and relative position of the high-voltage electrode; and the level of the high voltage applied to the electrode system. Experiments carried out with two kinds of particles (silver-plated polyamide spheres of radius 1.5 mm and mass 0.0192 g; and steel balls of radius 0.2-0.25 mm and average mass 0.000 45 g) confirmed the conclusions of numerical simulations. The modelling of particle behaviour in contact with plate electrodes facilitates the feasibility studies and can guide the experimental tests, which are needed for the development of any new application of the electrostatic separation method.

The application of an electrostatic method to the concentration of heavy minerals in some Polish sands

The electrostatic separation method was used in order to concentrate to the highest possible degree the heavy minerals occurring in some Polish sands. The processed raw materials and apparatus are briefly characterized and the results are discussed. It was concluded that valuable minerals of the tested heavy-mineral bearing sands may be highly concentrated by means of electrostatic separation and then utilized in various industries.