Evaluation of some optimum moisture and binder conditions for coal fines briquetting

Coal mining is a thriving industry and 53% of the coal mined in South Africa is used for electricity generation. Mechanization has made coal mining more efficient, but fines generation has subsequently increased. Up to 6% of the run of mine material can report to the -200 μm fraction. Common problems associated with fines handling include dust formation, storage problems, and high moisture levels. A method to turn this material into a saleable product instead of stockpiling it can add value to a company. Briquetting is a pressure agglomeration method where loose material is compacted into a dense mass (FEECO International, 2014). The briquettes must be able to withstand rigorous handling and transport operations without disintegrating. This study aims to investigate the optimum binder and moisture conditions required to produce a mechanically strong briquette using two different binders – a PVA powder (binder A) and a starch powder (binder B). It was found that for binder A the optimum moisture level was 12% to 14%. At this moisture level the greatest compression strength gains were observed, and low amounts of fines produced in impact and abrasion tests. The minimum amount of binder added while still obtaining a strong briquette was 0.5% binder A. For binder B the optimum moisture level was also 12% and the minimum amount of Binder B to be added was found to be 1%. Briquettes that were dried outside reached their peak strength after about four days, whereas the briquettes that dried inside took about 20 days to reach their strength plateau. Hardly any degradation took place on the surface of the binder A film after exposure of 300 hours of artificial weathering. Thermogravimetric analysis confirmed that neither binder A nor binder B will add to the ash content of the coal fines, as both binders totally decompose above 530°C. Binder B yielded stronger briquettes after 15 days and also generated less fines. It is therefore superior to binder A and would be recommended for further use.Paper written on final year project work carried out in partial fulfilment of B.Eng degree in Coal Beneficiationhttp://www.saimm.co.za/journal-papersam201

Positron emission particle tracking inside a laboratory batch jig

Owing to decreasing high-grade ore reserves, there is a need for better understanding of the jigging process to improve the recovery efficiency of finer, lower grade material. The use of positron emission particle tracking (PEPT) was examined as a technique to study the motion of iron ore particles inside a laboratory batch jig. PEPT is a non-invasive method that can provide three-dimensional kinetic data on a particle in laboratory-scale processing units and has been successfully used to study mills, hydrocyclones, and flotation. Experiments were conducted to determine whether PEPT would be a viable technique to study iron ore jigging and what valuable information could be obtained. The results indicated that detailed information on the stratification rate of a particle could be obtained, with adequate resolution to track the particle’s movement through an individual jig pulse.This paper was first presented at the, Physical Beneficiation 2013 Conference, 19–21 November 2013, Misty Hills Country Hotel and Conference Centre Cradle of Humankind, Muldersdrift.http://www.saimm.co.za/am201

Determination of the coefficients of restitution, static and rolling friction of Eskom-grade coal for discrete element modelling

The aim of the project was to experimentally determine the coefficient of restitution, and static and rolling friction of Eskomgrade coal for discrete element modelling (DEM). These parameters will be used in further DEM studies to simulate the flow and behaviour of coal during conveyance. For the simulation to yield realistic results, the parameters for the different coal shapes identified in the samples were determined. DEM uses spherical particles, and it was found that the difference between the DEM default parameters and those measured is significantly different, by as much as 97%, which illustrates the importance of experimentally determining these parameters. The spherical particles in DEM can be used to construct the various coal shapes identified, and the parameters measured can be used to simulate realistic results. The conveyance system can then be optimized accordingly.The author would like to thank Anglo American Thermal Coal’s Navigation coal processing plant and Exxaro’s Inyanda coal mine for providing the coal samples, the University of Pretoria for all the support, and Dr Naudé for her supervisionhttp://www.saimm.co.za/am2014ai201

Identifying critical parameters in the settling of African kimberlites

Kimberlite is the host rock of diamonds and varies widely in geological and mineralogical features as well as color, processing capability, and dewatering characteristics. This study investigated the dewatering behavior of problematic Angolan kimberlites. The presence of clay minerals in kimberlite causes difficulties in dewatering due to high flocculant demand, poor supernatant clarity, and low settling rates. Identifying critical parameters governing the settling behavior will assist in managing the settling behavior of different kimberlite slurries. The influence of particle size, pH of the kimberlite slurry, cation exchange capacity, exchangeable sodium percentage, and smectite content of the kimberlite on the settling rate were investigated for 18 different African kimberlite samples. The settling rate and slurry bed compaction during natural settling were also measured for the kimberlite slurries. Seventeen different Angolan clay-rich kimberlites and one South African clay-rich kimberlite were tested, and, except for two kimberlites, colloidal stability was experienced during natural settling. The pH values of the kimberlite slurries ranged between 9 and 11, which is similar to the pH band where colloidal stability was found during earlier research. The results indicate that colloidal stable slurries were experienced with kimberlites that had exchangeable sodium percentages as low as 0.7%. The cation exchange capacity of the various kimberlites differentiated more distinctly between colloidal stability and instability. A new model is proposed whereby clay-rich kimberlites with a cation exchange capacity of more than 10cmol/kg will experience colloidal stability if the pH of the solvent solution is within the prescribed pH range of 9–11.http://www.tandfonline.com/loi/gmpr202018-11-02hj2018Materials Science and Metallurgical Engineerin

Kimberlite weathering : effects of organic reagents

Kimberlite material is one of the primary sources of diamonds. Accelerated weathering that leads to a physical breakdown of the material over a short period of time has possible benefits in diamond processing such as reduction in the energy consumption when used as a pre-comminution stage. This study investigated accelerated weathering by utilising organic reagents; acetic acid, ethanol, formamide, n-hexane, oxalic acid, and urea, in comparison to the use of Cu2+ solution that was previously shown to be very effective in weathering kimberlite. Oxalic acid was the organic agent that showed promising weathering capabilities. However, the use of organic solutions was not as efficient as with Cu2+ solutions. Results showed that 67% of the particles passed 12 mm screen size in Cu2+ weathering compared to 48% in oxalic acid. It was also found that time of exposure had a small effect on weathering. Increasing the organic chemical concentration twofold, from 0.025 M to 0.5 M, improved weathering by 20% points. Different weathering mechanisms were observed at different solution concentration between oxalic acid (1st to 2nd order) and Cu2+ (2nd to 3rd order).De Beers Grouphttp://www.elsevier.com/locate/minenghb201

Comparison of conventional crushing and high-voltage pulsed power technology as techniques for disaggregating different types of spent magnesia-carbon refractory bricks during recycling

Three different types of spent magnesia-carbon (MgO–C) bricks were chosen to evaluate the liberation of magnesia particles through high-voltage pulsed power technology (HVPPT) and conventional comminution (jaw and cone crushing). The primary objective was to determine how the different types of MgO–C bricks comminute and whether magnesia particles could be restored to their original raw material particle size distribution (PSD). Analytical results revealed that the bricks contained varying amounts of graphite and resin binder, indicating differences in their compositions and therefore comminution properties. The HVPP technique demonstrated its ability to liberate magnesia particles within the +1700 μm fraction, whereas conventional crushing predominantly formed composite particles (containing MgO and carbon) within this size range, with over 63% particles falling in this category. This finding suggests that MgO particles were not adequately liberated during the conventional crushing process, indicating the need for an additional comminution step to achieve the desired liberation.https://www.sciencedirect.com/journal/open-ceramicshj2024Materials Science and Metallurgical EngineeringSDG-12:Responsible consumption and productio

Enhanced Holland-Batt spline for describing spiral concentrator performance

The Holland-Batt spline is well known when it comes to plotting spiral separation performance. The spline, which consists of a linear curve and power curve, has been successfully used to fit test work data that is presented as cumulative recovery of a valuable mineral versus the cumulative mass yield to valuable mineral concentrate. The benefit of this curve fitting process is that it produces a mathematical expression that is essential for simple mass flow modelling calculations. Although the mathematics is simple, the fitting process can be quite cumbersome. This work enhances the Holland-Batt spline with a few adjustments to improve the fit accuracy and ease the fitting process through (1) smoothing the transition zone between the linear and power law curves, (2) applying the principles to both low and high density particles, (3) use Visual Basic user-defined functions to simplify test work sheets in Excel and (4) use Excel Solver to automate the curve fitting process. These steps are applied to an example test work data set to clearly demonstrate the approach. The enhanced method is easy and simple to apply to spiral concentrator mass flow modelling.http://www.elsevier.com/locate/mineng2017-06-30hb2017Mathematics and Applied Mathematic

Die optimisering van vermalings-tegnieke vir ilmeniet erts

Thesis (M.Ing.) -- University of Stellenbosch, 1999.ENGLISH SUMMARY: The aim of this study was to minimise the production of the -38 μm fraction during the milling process of ilmenite ore from the Rooiwater Complex and to increase the grade of the iron oxide-rich concentrate during the magnetic separation process. An intensive investigation was done on different milling equipment and methods to minimise or prevent the fine fraction from forming. Conventional ball and rod milling methods with different size distribution of the mi11ing media (homogeneous and heterogeneous) were used in the investigation. From the results obtained, it was clear that it is impossible to prevent fines from being produced but it can be minimised to a certain extent. It was concluded that a new approach in the concentration of the ilmenite ore is needed. This approach can be by screening the fines before the· different magnetic separation processes, investigate new high intensity magnetic separators or design a whole new extraction route for the ilmenite ore.AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die produksie van die -38 μm fraksie tydens die vermaling van die ertse van die Rooiwater Kompleks te minimaliseer en om die graad van die ysteroksied ryke konsentraat gedurende die magnetiese skeidingsproses te verhoog. 'n Intensiewe ondersoek was gedoen op verskillende vermalings toerusting en metodes om die fyn fraksie te minimaliseer. Konvensionele bal- en staafvermalingsmetodes met verskillende grootteverspreidings van die vermalingsmedia (homogeen en heterogeen) was gebruik in die ondersoek. Vanuit die resultate verkry was dit duidelik dat dit onmoontlik is om die fyn fraksie te voorkom maar dit kan tot 'n mate geminimaliseer word. Daar is tot die slotsom gekom dat 'n nuwe benadering nodig is om die ilmeniet erts te konsentreer. Hierdie benadering kan wees deur die fyn fraksie uit te sif voor die verskillende magnetiese prosesse, ondersoek die nuwe hoe intensiteit magnetiese skeiers of om 'n nuwe ekstraksie roete vir ilmeniet te ontwerp.Maste

Investigating the effect on power draw and grinding performance when adding a shell liner to a vertical fluidised stirred media mill

A comparative testwork programme was conducted using a laboratory scale vertical fluidised stirred media mill. The mill was operated with and without the presence of a disc liner on the shell. Results showed that when the mill was operating with pin and disc type stirrers, the addition of a stationary liner to the mill shell significantly increased the mill power draw. In grinding experiments conducted with silica, it was found that the production rate was enhanced as a result of the higher power draw. No detrimental effect on the grinding energy efficiency was observed. It was postulated that the addition of the disc liner increased the stress intensity of the milling operation. The results of this study show that the addition of stationary internal disc liners have a potential to increase the production capacity of fluidised stirred media mills. Further work is recommended to confirm that these observations are valid at a larger scale and in continuous milling configuration.Mintek, South Africahttp://www.elsevier.com/locate/mineng2022-01-01hj2021Materials Science and Metallurgical Engineerin

Improved ultrafine coal dewatering using different layering configurations and particle size combinations

Coal fines produced during processing are difficult to dewater and result in a lower quality product and consequent lower value. A South African coal mine experiences severe difficulties with belt filter dewatering operations due to the presence of fines reporting from the thickener underflows. Plant 2 currently handles super-fine particles of size −34 μm and has low belt filter efficiency: excessive moisture retention lowers the product quality and strains downstream processing. It was necessary to determine an alternative method for dewatering these fines. Blending of fine material with coarser material was proposed as a solution. The effect of coal particle size and layering during ultrafines belt filter dewatering was evaluated using various blends of the fine Plant 2 material with coarser Plant 1 material. The best layering arrangement of the two materials and its optimum blend required to achieve reduced filter cake moisture content was determined in practise using a vacuum filter to simulate belt filtration. A blend of the two materials gave improved dewatering efficiency for the belt filters compared with that of the Plant 2 material alone. The best layering configuration was with Plant 2 material at the bottom and Plant 1 material on top. The optimum blend for industrial applications comprised 48% fines from Plant 2.EXXAROhttp://www.saimm.co.za/journal-papersam2021Materials Science and Metallurgical Engineerin