The Effect of Polymeric Flocculants on Settling and Filtration of Iron Ore Slimes

Abstract

During the wet processing of iron ores, a substantial amount of fine particles known as slimes are generated in downstream which need to be recovered effectively for their usage and beneficiation. Besides water from slime ponds overflow remains contaminated with very fine particles which are difficult to settle and cause environmental pollution when contaminated water is discharged to the downstream river. The settling behaviour in the slime pond gets affected in particular when ore contains hydrated oxides. The above problems necessiatate to study the settling and filtration behaviour of the slimes by means of effective flocculants. The flocculants namely, amylopectin-g-polyacrylamide (Ap-g-PAM), sodium alginate-g-polyacrylamide (SAG) were synthesized by graft copolymerization using redox initiated catalyst. The high molecular weight flocculants, namely, magnafloc (1011) superfloc (N 300) were used for comparative studies. The present paper reports the settling and filtration behaviour of iron ore slimes.

The experiments show that sedimentation rate increases with increasing flocculant dose upto a certain limiting value. The settling rate decreases with increasing the pulp density. The volume of filtrate increases with increasing flocculant dose. The filtration efficiency of synthesized polymer is comparable with the commercial one, i.e., magnafloc (1011) at natural pH.     

The Effect of Particle Sedimentation on Gravity Filtration

ABSTRACT

Simulation of cake formation of mono-sized and dual-sized particles under gravitational sedimentation and filtration is presented. The dynamic analysis proposed by Lu and Hwang in 1993 is applied to examine the local cake properties formed under a falling head by considering the hindered settling effect of particles in the slurry and the variation of the pressure drop across the filter septum. Results of this study show that, at a given position in a cake, the solid compressive pressure reaches a maximum value and then decreases for a gravity filtration due to the decrease in the driving head. A cake constructed with dual-sized particles has a more compact structure than does one with mono-sized particles, and larger particles will form looser packing than will smaller ones for mono-sized particles. A dual-dispersed suspension with a lower fraction of large particles will result in the lowest cake porosity and the highest specific filtration resistance of cake. Comparison of the porosity distribution in filter cake formed by means of gravity filtration and constant head filtration shows that the porosity near the filter septum of gravity filtration has a convex behavior while that of constant head filtration has a tendency toward concavity. This discrepancy is mainly due to the change in the driving head during the filtration process. Both theoretical and experimental results show that the uniformity of particle size distributions in the filter cake will be much better when the relative settling velocity between large and fine particles is reduced.     

ELECTROSTATIC BENEFICIATION OF EASTERN OIL SHALES

A dry electrostatic process for beneficiating Eastern oil shales was investigated. Scanning electron microscope analysis showed a need to grind the shale to an average particle size of less than 5 μm for nearly complete liberation of mineral inclusions from the organic matrix. The carbonaceous and noncarbonaceous components of shale were imparted positive and negative surface charges, respectively, with a copper tribocharger. Tests in a batch electrostatic separator showed kerogen enrichments from 12 percent in feed up to a value of 34 percent in the product stream. The efficacy of beneficiation was found to be strongly dependent on hydrodynamic conditions, such as particle velocity, particle concentration in the carrier gas, electric field strength, geometry of the separator, etc. Furthermore, the extent of separation was found to be limited by a strong cohesive force acting between the finely ground shale particles which results in the formation of agglomerates.     

Improvement of performance efficiency of a hydrocyclone with design modification by suppressing air core

Hydrocyclones have been used for beneficiation of coal and mineral in coal washeries and mineral process industries. To enhance the efficiency of hydrocyclone, it is very essential to quantify the presence or absence of air core within the hydrocyclone. In the present study, for the first time, a new hydrocyclone design has been conceptualized and tested for its efficiency in separation of particles based on gravity. Experimental investigations have been carried out using design of experiments and the results have been analyzed statistically. The results have shown that suppressing the air core improves the separation efficiency of the hydrocyclone. Efforts have been made to explain the concept through fundamentals of fluid flow in hydrocyclone. The air core has a significant effect on particle separation as the relative density of the particles approach to the fluid density. The results will be used in the development of a new design of dense medium hydrocyclone at industrial scale that will improve the separation efficiency of the hydrocyclones by separating the near gravity particles more efficiently.     

Performance of teetered bed separator for non-coal applications

In the present investigation, the effect of the most important process variables, which are teeter water velocity (TW) and pressure set point (SP), on the classification and beneficiation performance of a laboratory-scale teetered bed separator (TBS) was evaluated and discussed. Pure silica sand, magnetite concentrate and their artificial mixture were used to observe the effect of mineral density. Classification test results revealed that separation cut size linearly increases with increasing TW and SP. From the beneficiation studies and the size-by-size chemical analysis of artificial mixture, it can be concluded that significant removal of silica is possible by employing TBS.     

Collection of Airborne Microorganisms into Liquid by Bubbling through Porous Medium

A new method for the removal of airborne particles by air bubbling through fibrous filters immersed into a liquid has recently been developed (Agranovski et al. 1999) and shown to be very efficient for cleaning air environments with ultra-fine aerosol particles. The principal objective of the present study was to evaluate the new bubbling technique for the collection of airborne bacteria into a liquid for subsequent physical and microbiological analysis. It was found that the technique is capable of achieving a physical collection efficiency of 98.5% or higher for particles larger than 0.3 w m in aerodynamic diameter. The physical collection efficiency of the prototype bubbler remained at that high level for 8 h of continuous operation with negligible variation of the pressure drop across the device. Evaporation of the collection fluid did not exceed 20% during 8 h, and the reaerosolization effect on the physical collection efficiency of the bubbler prototype was <8%. The recovery rate of gram-negative Pseudomonas fluorescens bacteria collected for 20 min was shown to be as high as 74% - 10%. Its decrease with time was not statistically significant: the recovery rate reached 63% - 15% and 58% - 16% after 4 and 8 h of continuous operation, respectively. Thus the bubbling technique was demonstrated to be suitable for collecting viable airborne bacteria even if they are sensitive to the stress.     

新型溢流器高效回收钛白酸解尾渣中的钛

中国是世界上最大的硫酸法钛白生产国,目前已累计堆积超过千万吨副产品酸解尾渣。酸解尾渣中含有大量未反应的粒径大于25 μm的钛铁精矿,酸解尾渣堆积而不利用就造成了严重的环境污染和资源浪费。根据酸解尾渣颗粒沉降实验分析,发现酸解尾渣料浆具有良好的沉降和易分层特性。通过建立干扰沉降末速度计算式,得出酸解尾渣中颗粒切割粒度25 μm的沉降速度为0.60 mm·s^-1。基于流动、分选机理和沉降特性分析,设计了适用于酸解尾渣分离工艺的新型DTB（draft tube babbled）溢流分离器,并进行了结构参数优化,获得了溢流器最优结构参数和最佳分离效果。结果表明,外排溢流含有极少量大于25 μm的钛铁精矿颗粒,回收的钛品位达27%,回收率为73%。这些结果为大规模回收酸解尾渣中钛资源提供了基础数据。     

Comparative performance analysis of electrospun TiO2 embedded poly(vinylidene fluoride) nanocomposite membrane for supercapacitors

For an efficient energy storage system, effective material is to be used. In the present work, novel poly(vinylidene fluoride)/titanium oxide (PVdF/TiO₂) composite membranes were developed using electrospinning technique, as separator for supercapacitors. Different weight percentages of TiO₂ nanoparticle (0, 5, 10, 15, and 20 wt%) were mixed with 20 wt% of PVdF in a 50:50 wt% of tetrahydrofuran and dimethylacetamide solvent. Various physical and electrochemical properties including fiber diameter, thermal stability, crystallinity, porosity, and electrolytic uptake were studied to identify the best membrane with optimum TiO₂ wt% exhibiting superior characteristics. SEM and TGA studies revealed that the developed PVdF/TiO₂ composite membrane with 10 wt% showed improved properties with a lower average diameter of about 66 ± 8 nm, enhanced thermal stability up to 513.15°C and higher porosity of 89%, respectively compared to other membranes. The crystallinity, ionic conductivity, and specific capacitance of the nonwoven separator membranes were determined using X-ray diffraction technique, electrolytic uptake, and charge–discharge studies, respectively. The present study revealed that the addition of TiO₂ nanoparticles improved the physical and thermochemical properties of the separator membrane substantially and PVdF/TiO₂ composite membrane with 10 wt% displayed superior performance compared to other membranes.     

Investigations on various characteristics of novel cyclone separator with helical square fins

ABSTRACT

Cyclone separators are very energy intensive devices primarily used in power and process industries to separate the particles from hot gases. Hence in the present study, the barrel wall of the cyclone separator was modified by fixing the helical square fins of sizes 5, 7.5, and 10 mm, with 30 and 50 mm pitch variations to improve its separation efficiency. Hence in the present study, various fluid dynamic characteristics which affect the separation efficiency such as axial and tangential velocities, axial pressure drops were investigated. Computational results were validated using the published experimental data for the non-finned cyclone separator and further CFD simulations were performed for novel finned cyclone separators. It was observed that for the particles’ sizes below 3 µm, finned cyclone separator with fin size 10 mm and pitch 50 mm was giving separation efficiency more than other 5 finned cyclone separators. Also 5 to 10% improvement in the separation efficiency was observed over the separation efficiency of the non-finned cyclone separator. Since main function of separating the particles from gas was unaffected rather it was improved using finned cyclone separator(s) which is important in a view of reducing serious fine particulate matter (PM2.5) emissions causing serious health issues.     

Separation of a Two-Component Particulate Material Mixture by a Vibro-Impacting Separator

Abstract

The vibro-impacting separator, the so-called Paddy table, is widely used for the separation of the components of binary mixtures of particulate materials. This paper presents an improved mathematical model of vibro-impacting separation and experimental results aimed at the further investigation of vibro-impacting motion, the adequacy of the model, and the improvement of the efficiency of vibro-impacting separation, with special attention to friction between the particles and the operational element of the separator. It is concluded that friction decreases the instability of the periodic symmetric motion of the particles and that the model adequately represents the physical system in the range of the operational variables tested. Also, it is found that the formulas obtained are suitable for design purposes and that friction decreases the separation efficiency. In conclusion, we believe that vibro-impacting separation is a promising candidate for many fields of industry.     

Geology and mineralogy of the Berezovo crystalline magnesites

Conclusions An analysis of the chemical and mineral compositions and of the physical and structural properties of raw and fired crystalline Berezovo magnesites resulted in the identification of four varieties. The normal and partly deformed varieties can be used for the production of refractories without beneficiation but the dolomitized, dolomitic, and some of the deformed magnesites must first be concentrated.Translated from Ogneupory, No. 6, pp. 18–22, June, 1977.     

FLUID1ZED BED SPRAY GRANULATION AND FILM COATING A NEW METHOD FOR THE INVESTIGATION OF THE COATING PROCESS ON A SINGLE SPHERE

ABSTRACT

The coating and granulation of solid particles in a fluidized bed is a process which converts pumpable and atomizable liquids (solutions, slurries, melts) into granular solids in one step through drying. Although this process has been applied in industry for several years, there is still a lack of understanding the physical fundamentals and the mechanisms by which spherical granules are formed. Hence a new method was developed which allows the direct observation of the subsequent particle-forming mechanisms such as droplet deposition, spreading, wetting and drying. The authors will present a laboratory scale apparatus in which a single freely suspended particle can be coated under well defined and constant coating and drying conditions. With this device, particle-growth-rate and the development of particle morphology were measured and investigated under various experimental conditions.     

Real-time measurement of nano-agglomerate and aggregate mass and surface area concentrations with a prototype instrument

Abstract

A prototype instrument was developed to measure geometric surface area (GSA) concentrations and mass or volume concentrations for agglomerated or aggregated particles at a time resolution of 1?s. It couples a diffusion charger with two sets of electrostatic precipitators and electrometers to monitor two current signals synchronously. In this way, we refined the measurements with a weighted-sum method. Initially, we tested the ability to distinguish different particle morphologies. Subsequently, theoretical volume and GSA measurements of single agglomerates and aggregates were performed to calibrate the instrumental sensitivity for particle sizes. Experimental results with polydisperse silver particles indicated that a diffusion charger coupled with a differential mobility analyzer and a condensation particle counter could identify particle shapes having different fractal dimensions. Above all, the instrument could be used to measure GSA, volume, or mass concentrations of both agglomerates and aggregates in real time. A favorable comparison with results obtained with a scanning mobility particle sizer suggested great potential for commercial applications.

Copyright © 2019 American Association for Aerosol Research     

Assessment and Mechanism Investigation of Selective Flocculation Process for Ultrafine Chromite Particle

During beneficiation of low-grade chromite ore, huge amounts of ultrafine tailings are generated and contain substantial metal values which need to be recovered. Selective flocculation technique is one of the processes for beneficiation of ultrafine particles. Here an attempt was made to establish selective flocculation process by using two types of synthetic mixtures. In addition to this, selective flocculation was also attempted on natural tailings. It was found that it is possible to enrich the chromite value using the selective flocculation process. The selectivity of the wheat starch to the chromite mineral was also investigated using image analysis, FTIR analysis, and zeta potential analysis.     

Impact of Particle Generation Method on the Apparent Hygroscopicity of Insoluble Mineral Particles

Calcite (CaCO ₃ ) mineral particles are commonly generated by atomization techniques to study their heterogeneous chemistry, hygroscopicity, and cloud nucleation properties. Here we investigate the significant artifact introduced in generating calcium mineral particles through the atomization of a saturated suspension of the powder in water, by measuring particle hygroscopicity via CCN activation curves. Particles produced from atomization displayed hygroscopicities as large as κ_app > 0.1, 100 times more hygroscopic than that obtained for dry-generated calcite, κ_app = 0.0011. The hygroscopicity of the wet-generated particles increased as a function of time the calcite powder spent in water, and with decreasing particle size. Wet-generated calcium oxalate was more hygroscopic through wet- (κ_app = 0.34) versus dry-generation (κ_app = 0.048). Atomized calcium sulfate particles, however, were only slightly more hygroscopic (κ_app = 0.0045) than those generated dry (κ_app = 0.0016). Single-particle analysis by ATOFMS and SEM/EDX, and bulk analysis of the calcite powders by ICP-MS and IC revealed no significant soluble contaminants. The atomized particles were likely composed of components that dissolved from the powder and then re-precipitated, and appeared to contain little of the original mineral powder. The increased hygroscopicity of atomized calcite may have been caused by aqueous carbonate chemistry producing Ca(OH) ₂ , Ca(HCO ₃ ) ₂ , and metastable hydrates with increased solubility. Surface water adsorption may have also played a role, in addition to uncharacterized soluble components produced by wet-generation, and the precipitation of amorphous phases including glassy states. This study suggests that using wet-generation methods to suspend mineral dust samples will not produce particles with the correct physicochemical properties in laboratory studies, a finding which has important implications for past and future laboratory studies focusing on understanding relationships between the hygroscopicity and chemistry of mineral dust particles.     

Numerical optimization and experimental investigation of the aerodynamic performance of a three-stage gas-solid separator

The present research investigates and optimizes the aerodynamic performance of a newly designed compact size three stage mobile gas-solid separator. This separator is designed to collect solid particles with different characteristics at a minimum pressure drop. The minimum particle diameter to be completely collected is 1 μm at solid loading 20 g/m³. The first stage of the separator is a settling chamber which is designed to collect coarse particles (particles down to particle diameter 100 μm). The second stage is a cyclone separator where medium to fine particles (particles down to particle diameter 15 μm) are to be collected. Particles escaping the cyclone separator are collected in the third stage which is a bag filter.A separator conceptual aerodynamic design is first performed to obtain overall separator dimensions. CFD simulation is used in order to optimize the separator aerodynamic performance and reduce the separator size. The separator is then constructed and experimentally investigated. Comparison between CFD results at design point and measured separator total pressure drop shows good agreement.     

Behaviour of soft granules under compression: Effect of reactive and non-reactive nature of the binder on granule properties

Granulation is a process where primary powder particles are made to adhere to form multi-particle entities called granules and this is achieved by using a binder. The binders can be broadly classified into two categories viz. reactive (reacts with base powder) and non-reactive (does not react with the base powder). The effect of various parameters related to binder liquid (binder viscosity, addition rate, distribution over the bed etc.) on the mechanism of granulation and physical/mechanical properties of granules is well studied. However, comparison of physical and mechanical properties of granules made via reactive and non-reactive binder using the same base primary particles has not been reported. In this paper, granulation of sodium carbonate primary particles under reactive and non reactive conditions was studied. The mechanical properties of sodium carbonate granules were characterized using single granule compression measurements. The average single granule apparent strength of reactive granules was higher compared to non-reactive granules. It was observed that granules formed using non reactive binder were brittle and showed multiple breakages. However granules made using reactive binder showed single breakage followed by significant plastic flow. In addition, bulk granule compression measurements were also carried out. Known models of Heckel, Kawakita and Ludde, and Adams et al. (developed mainly for pharmaceutical and metal powders) were used to predict mechanical properties of soft detergent granules. The bulk granule compression measurements also showed that reactive granules have higher strength compared to non-reactive granules. However, the absolute values of granule strength obtained from the empirical models were lower than the granule strength obtained from single granule compression measurements.     

Multi-functional Al2O3-coated separators for high-performance lithium-ion batteries: Critical effects of particle shape

The technology of coating polyolefin-type separators with ceramics is gradually developing as an effective method to improve the safety of lithium-ion batteries (LIBs). However, the powder properties of ceramics can adversely affect the surface structure and ionic conductivity of separators; therefore, a new approach is required regarding the powder properties that affect the performance of the separator. Herein, the effect of the Al₂O₃ particle shape on the physical properties of Al₂O₃-coated separators and the performance of LIBs is investigated. In the separator coated with angular-shaped Al₂O₃ particles (Al₂O₃-A), the pores in the coating layer are uniformly distributed, improving physical properties such as porosity and wettability. The thermal shrinkage of separator is <10% when exposed to 150 °C for 1 h, considerably smaller than that of the commercial polyethylene separator (approximately 83%) under the same conditions. Moreover, the Al₂O₃-A-coated separator shows the highest ionic conductivity (0.531 mS cm⁻¹), and the LiNi_0.8Mn_0.1Co_0.1O₂/Al₂O₃-A-coated separator/Li battery displays improved stability than using the polyethylene separator under a current density of 5C. This proposes approach to improve the separator's performance through the shape control of ceramic particles paves the way for separators to contribute to the high-temperature safety and long cycle life of batteries.     

Aerosol-jet produced,magnetic carrageenan-gel particles: A new affinity chromatography matrix

A new method was developed to produce uniform spherical magnetic carrageenan-gel particles suitable for the affinity chromatography purification of large molecules. A sol-phase of k-carrageenan is pumped into an air jet to produce an aerosol of gel particles. The particle size can be varied by adjusting the air jet velocity. The gel particles are stable in 0-5 mol dm_?3 KCI to 190 psi. The gel particles were used to immobilize soy trypsin inhibitor for the affinity purification of trypsin. The affinity matrix was tested in a packed-bed separator, fluidized-bed separator and a magnetically-stabilized fluidized-bed separator with similar column capacity for each separator.     

Hydrophobic Flocculation Flotation for Beneficiating Fine Coal and Minerals

ABSTRACT

It is shown that hydrophobic flocculation flotation (HFF) is an effective process to treat finely ground ores and slimes so as to concentrate coal and mineral values at a fine size range. The process is based on first dispersing the fine particles suspension, followed by flocculation of fine mineral values or coal in the form of hydrophobic surfaces either induced by specifically adsorbed surfactants or from nature at the conditioning of the slurry with the shear field of sufficient magnitude. The flocculation is intensified by the addition of a small amount of nonpolar oil. Finely ground coals, ilmenite slimes, and gold finely disseminated in a slag have been treated by this process. Results are presented indicating that cleaned coal with low ash and sulfur remaining and high Btu recovery can be obtained, and the refractory ores of ilmenite slimes and fine gold-bearing slag can be reasonably concentrated, leading to better beneficiation results than other separation techniques. In addition, the main operating parameters affecting the HFF process are discussed.