M. Le Roux

• Doctor of Engineering
• Professor (Associate) at North-West University

Coal resources, such as those from the South African Waterberg coal field and the Mozambique coalfields, often contain highly interlayered structures of coal macerals and mineral matter. The mineral matter, which is incombustible, reduces the coal’s calorific value and poses challenges during coal processing due to its adverse impact on plant yield...

Synopsis The results of coal sink and float tests are plotted as washability curves. Analysis of these curves indicates the most effective method by which the coal can be cleaned. Sink and float experiments are sampling-dependent, destructive, and use toxic chemicals. The present research introduces an alternative method based on a 3D imaging syste...

Density is one of the key factors of coal that provides useful information about its physical and chemical composition. Traditional coal washability analysis is determined by conducting float–sink test, which is time consuming, destructive, and uses environmentally hazardous chemicals. The motivation for this work is to develop a new technique as a...

Moisture is one of the most important indexes upon which a coal product is graded. The removal of moisture from coal is essential to minimize economic loss, handling, and transportation problems and to maximize the calorific value of coal. Apart from the process water carried over into the mine and mineral processing final product, extra water afte...

Excessive coal moisture leads to a lower heating value and power plant efficiency, and increased transportation costs. Therefore, coal stockpile management and moisture control are particularly important in regions with heavy precipitation. This paper and Part 2 address factors influencing moisture retention and migration in coal stockpiles. Part 1...

Additional moisture added in coal stockpiles due to rain and other climatic processes causes a significant problem worldwide, which leads to not only decrease in the heating value of the coal but also creates an extra efficiency penalty. Therefore, it is important to make some predictions for control of coal moisture within stockpiles after the rai...

The separation performance of solid phase bed material, at various particle size ranges, in an air dense medium fluidized bed (ADMFB), were evaluated during this study. The coal particles were separated into +0.5mm-1mm, +1mm-2mm, +2mm-2.8mm, +2.8mm-4mm, +4mm-4.75mm and +4.75mm-5.6mm particle size ranges and fed to the fluidized bed in these fractio...

Density is one of the key elements of coal and useful in providing information about their physical and chemical composition. Traditional coal washability analysis is determined by conducting sink-float test, which is destructive and uses environmentally hazardous chemicals. Information from float-sink technique is employed to specify the yield and...

The aim of this study was to determine the acid-generating potential of coal mine tailings located in the Middelburg area, South Africa, using conventional assessment techniques. Four coal-tailing samples were collected from different layers of a coal-tailing pile. The acid-base accounting (ABA), acid-buffering characteristic curve (ABCC), and net...

This paper investigates the air dense medium fluidized bed (ADMFB) as a suitable dry beneficiation technique to upgrade +5.6 mm-13.2 mm South African coal. The separation efficiency of the ADMFB was assessed by determining the effect, if any, of particle size range, medium to coal feed ratios, and the addition of vibration on the separation ability...

This paper introduces contact sorption with ceramic sorbents as a method to reduce the moisture content of coal fines produced by coal processing plants. The proposed method was tested on laboratory scale where ceramic spheres with diameters of 3 mm and 5 mm were combined with wet coal fines of size fractions between 0.25 mm and 2 mm. The coal had...

Spent coffee grounds were transformed into biochar using a hydrothermal method. Some of the biochar product was pre-treated through surfactant impregnation with sodium dodecyl sulphate (SDS) to enhance its adsorption capacity. The non-treated(NT) and pre-treated(PT) biochars were characterized using FTIR spectroscopy and SEM-EDS analyses, which rev...

Studies have shown that contact sorption drying is a feasible technique to dewater fine (+0.15mm–0.5mm) and ultra-fine (−0.15 mm) coal. The aim of this article is to further investigate the drying mechanism involved. It could be shown that moisture transfer occurred primarily in the liquid phase, requiring direct contact between the coal and sorben...

It is proposed to introduce contact sorption drying as a method to reduce the moisture content in coal fines. The aim of this study was to investigate the possibility of drying fine and ultra-fine coal using porous ceramic as the moisture sorbent. The main focus of this report is to define how the air temperature, particle size variations and mixin...

Imagine that a sample of coal could be crushed unlimited times to the same or different top size; a different washability would be obtained for each crushing experiment. Depending on the size and distribution of the raw coal components (say vitrinite, inertinite, and mudstone), better yields for a low ash product are obtained as a top size is appro...

Water scarcity is driving the development of dry coal beneficiation processes. A lot of research has gone into the development of dry dense medium fluidized bed technology (DMFB), especially in China. However, these processes focus mainly on +6 mm particles while little work has gone into the development of dry processes for -2 mm particles. This p...

The moisture content of product coal is a major factor influencing the efficiency of downstream coal utilization processes. Product stockpiles are often used as a control measure to regulate the moisture content of the coal by gravity drainage and evaporation. An understanding of the mechanisms of water migration and retention in coal stockpiles ar...

Excessive amounts of moisture in product coal can influence the efficiency of downstream utilization processes due to a decreased calorific value and handling problems. Stockpiles can be used to decrease the moisture content of coal by means of gravity drainage and evaporation. This paper is focused on the evaporation of moisture from a coal stockp...

A tomographic study of coal microstructure (coal bedding planes, pre-existing cracks, microlithotype boundaries and mineral boundaries) was undertaken to explain its influence on coal degradation due to impact. A number of samples were cut from a large block of Waterberg run-of-mine coal. It was characterised using micro-focus X-ray computed tomogr...

Due to health and environmental factors involved with standard float-sink analytical methods, a water-only fractionation procedure was investigated. A laboratory scale 105 × 105 mm reflux classifier was built and used to fractionate fine coal into a number of density classes. The procedure was tested against standard float and sink methods. The ref...

A good correlation exists between the amount of moisture adsorbed and the oxygen content of medium-rank B vitrinite-rich and medium-rank C inertinite-rich bituminous coal. Total mass moisture adsorbed per gram of coal determined from the modified BET model provides a better approximation than the BET model. The relationship between the modified BET...

The production of unwanted coal fines during the handling and utilisation of coal is a serious problem in processes that rely on large or closely sized particles. Coal degradation occurs at many different steps within the beneficiation or utilisation processes and through many different mechanisms, none of which are understood thoroughly. In an eff...

Coal ore isn't a uniform material. In order to optimize the coal liberation process it is necessary to classify a coal ore sample into its constituent components as quickly and cheaply possible. This paper investigates whether it is feasible to employ image and pattern recognition to segment a photographic image of coal ore into its various mineral...

The demand for energy has continued to rise worldwide in line with population growth. The majority of South Africa's electricity is supplied by coal-fired power stations. The amount of fine coal (-2 mm) generated at coal processing plants has increased, due mainly to mechanized mining methods. Fine coal retains more water, which lowers its heating...

The degradation of coal and the production of coal fines during handling and transport is a serious problem in processes that depend on closely sized large particles. To minimize the production of fines, a fundamental understanding of coal breakage is required, so, to clarify the complex nature of coal breakage, a series of experiments was conducte...

Fluidized bed drying is currently receiving much attention as a dewatering option after the beneficiation of fine coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lowe...

Fluidised bed drying is currently receiving much attention as a dewatering option during the beneficiation of fine (defined here as between 1 mm and 2 mm particles) coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the remova...

Most coal supply contracts include strict limitations on the moisture content of the products. This limitation exists because of calorific, transport cost, and handling reasons. Managing the retention time on product stockpiles to facilitate drainage commonly controls the moisture content in coarser coal products. A large-scale pilot rig has been c...

Fine coal (-500 μm) is notoriously difficult to dewater. It is not uncommon for a dewatered product to have a moisture content as high as 30 per cent after vacuum filtration. This poses several handling and financial problems to such an extent that a lot of fine coal is discarded onto slurry waste ponds. A novel way of dewatering fine coal was deve...

The dewatering of coal, and particularly fine coal continues to challenge coal prepatration engineers to find a cost-effective solution. With known world oil reserves being depleted daily, it is envisaged that the future price of coal may justify the use of thermal drying to achieve lower coal product moisture levels. The effect of exposure of the...

An improved method of dewatering fine coal (−500 μm) by vacuum filtration was developed and optimized. Tests on a bench scale vacuum filter showed that when a filter cake was deliberately damaged, causing the airflow through the cake to increase and the applied vacuum to decrease, a lower final moisture content could be achieved as well as a higher...

An improved method of dewatering fine coal (−500 μm) by vacuum filtration was developed. Tests on a bench scale vacuum filter showed that when the applied vacuum was interrupted during the dewatering cycle, a lower final moisture content could be achieved. There was also an increase in the dewatering rate, as well as a lower breakthrough pressure....

Dewatering coal, and especially fine coal (-600μm), is a significant problem in the preparation of coal. The final moisture level of fine coal can be anything up to 30% by weight, depending on the type of dewatering equipment used. Moisture in coal can cause many problems, for example by increasing the transportation costs, as well as decreasing th...