Mineralogy and Geochemistry of Sub-Bituminous Coal and Its Combustion Products from Mpumalanga Province, South Africa

Abstract

Analytical Chemistry 48 in coal are emitted into flue gas, fly ash or bottom ash of combustion plants. In a flue gas stream, trace elements are fixed in ash particles and in by-products such as gypsum and sludge if wet flue gas desulphurization unit is equipped. Coal fly ash is a solid residue from the combustion processes of pulverised coal for the production of electrical power in power generating stations, especially when low-grade coal is burnt to generate electricity [7, 8, 9]. The coal burning power stations in the Mpumalanga Province, South Africa generates over 36.7 Mt of fly ash annually in which only 5 % is currently utilized, the rest being disposed of in the ash dams, landfills, or ponds [9, 10]. During combustion, mineral impurities in the coal, such as clay, feldspars, and quartz, are fused in suspension and float out of the combustion chamber with exhaust gases. As the fused material rises, it cools and solidifies into spherical glassy particles called fly ash [11]. The properties of the coal fly ash depend on the physical and chemical properties of the parent coal, coal particle size, the burning process and the type of ash collector. This article presents results obtained from mineralogical and chemical characterization of coal and its combustion products from a coal burning power station in the Mpumalanga Province, South Africa. The main objective of the study is to understand the role of combustion process, chemical interaction of fly ash with ingressed CO2 and percolating rain water on the mineralogy and chemical compositions of fly ash. 2. Methodology/research approach 2.1. XRF and LA-ICPMS analyses Pulverised coal samples and its combustion products were analysed for major element using Axios instrument (PANalytical) with a 2.4 kWatt Rh X-ray Tube. Further, the same set of samples were analysed for trace element using LA-ICPMS instrumental analysis. LA-ICP-MS is a powerful and sensitive analytical technique for multi-elemental analysis. The laser was used to vaporize the surface of the solid sample and it was the vapour, and any particles, which was then transported by the carrier gas flow to the ICP-MS. The detailed procedures for sample preparation for both analytical techniques are reported below. 2.1.1. Fusion bead method for Major element analysis  Weigh 1.0000 g ± 0.0009 g of milled sample  Place in oven at 110 ºC for 1 hour to determine H2O- Place in oven at 1000 ºC for 1 hour to determine LOI  Add 10.0000 g ± 0.0009 g Claisse flux and fuse in M4 Claisse fluxer for 23 minutes.  0.2 g of NaCO3 was added to the mix and the sample+flux+NaCO3 was pre-oxidized at 700 °C before fusion.  Flux type: Ultrapure Fused Anhydrous Li-Tetraborate-Li-Metaborate flux (66.67 % Li2B4O7 + 32.83 % LiBO2) and a releasing agent Li-Iodide (0.5 % LiI).

Gemological features of diaspore in sodra—Milas (mugla) region

“…V/(V+Ni) and Ni/Co diagrams of bauxite and diaspores were drawn to reveal oxic, semi-oxic, anoxic, and redox conditions in the study area (Supplementary Figure S14A). Ni/Co ratios of <5 in rocks reflect oxygenated conditions, >5 reflects suboxic and anoxide conditions (without oxygen) in the formation of clays in the basin, and V/(V+Ni) ratios (0.4-0.60) reflect dioxide conditions (Rimmer, 2004;Akinyemi et al, 2012). In light of these data, bauxite formations in the region are concentrated mainly in the semi-oxic region, and diaspores are concentrated in the anoxic region according to their V/(V+Ni) ratios.…”