**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*


#### *2.1.2. Pressed pellet method for Trace element analysis*

Weigh 8 g ± 0.05 g of milled powder

48 Analytical Chemistry

collector.

below.

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

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

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

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

 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

Li2B4O7 + 32.83 % LiBO2) and a releasing agent Li-Iodide (0.5 % LiI).

Flux type: Ultrapure Fused Anhydrous Li-Tetraborate-Li-Metaborate flux (66.67 %

sludge if wet flue gas desulphurization unit is equipped.

water on the mineralogy and chemical compositions of fly ash.

**2. Methodology/research approach** 

*2.1.1. Fusion bead method for Major element analysis* 

 Place in oven at 110 ºC for 1 hour to determine H2O- Place in oven at 1000 ºC for 1 hour to determine LOI

Weigh 1.0000 g ± 0.0009 g of milled sample

700 °C before fusion.

**2.1. XRF and LA-ICPMS analyses** 


#### **2.2. Loss on ignition determination**

Loss on Ignition (LOI) is a test used in XRF major element analysis which consists of strongly heating a sample of the material at a specified temperature, allowing volatile substances to escape or oxygen is added, until its mass ceases to change. The L.O.I. is made of contributions from the volatile compounds H2O+, OH- , CO2, F- , Cl- , S; in parts also K+ and Na+ (if heated for too long); or alternatively added compounds O2 (oxidation, e.g. FeO to Fe2O3), later CO2 (CaO to CaCO3). In pyro-processing and the mineral industries such as lime, calcined bauxite, refractories or cement manufacture, the loss on ignition of the raw material is roughly equivalent to the loss in mass that it will undergo in a kiln, furnace or smelter.

#### **2.3. XRD analysis**

Coal samples and its combustion products were analysed for mineralogical composition by X-ray diffraction (XRD). A Philips PANalytical instrument with a pw 3830 X-ray generator operated at 40 kV and 25 mA was used. The pulverised samples were ovendried at 100 °C for 12 h to remove the adsorbed water. The samples were pressed into rectangular aluminium sample holders using an alcohol wiped spatula and then clipped into the instrument sample holder. The samples were step-scanned from 5 to 85 degrees 2 theta scale at intervals of 0.02 and counted for 0.5 sec per step.
