Investigation of physicochemical properties and leaching behavior of coal fly ash and bottom ash by using XRF and AAS: Multivariate analysis

Abstract

Fly ash and bottom ash samples, three each, were collected from different industries of Punjab and analyzed to determine the physical attributes and heavy metals contents along with sodium, potassium, calcium, aluminum, magnesium, sulfur and chloride. Using multiple reagents, the AAS results indicate that Zn (22.597–385.0 ppm) is the most abundant element in both fly ash and bottom ash samples, followed by Cr (0.5–100.8 ppm), Ni (1.1–87.3 ppm), and Cu (2.0–23.5 ppm) while Cd and Pb are present in trace amounts, with Cd (0.6–1.2 ppm) and Pb (2.3–4.2 ppm) detected in any of the samples. Both Na and K are present in very low amounts i.e. <2 ppm except in one sample of fly ash the concentration of Na reaches 2.25 ppm. Moisture content in all the samples is considerably high exceeding 34 %. Silica and alumina are found in significant amounts. XRF analysis confirmed permissible range of CaO, MgO, Fe₂O₃, SO₃, and chloride. However, sample F had the greatest quantities of SiO₂, Fe₂O₃, MgO, and Al₂O₃. The impact of the leaching agent on the quantity of metal that leaches was also examined, and the findings indicate that there is no specific pattern to leaching, most metals leach in acidic rather than basic media. To explain data fluctuation throughout the heavy metal testing procedure, statistical techniques such PCA, probability plots, heatmap and cluster correlation using Wards method were also used. To mitigate potential health hazards, heavy metals should be leached off with aqua-regia before land filling, disposal, or future use.