An improved microwave assisted sequential extraction method followed by spectrometric analysis for metal distribution determination in South African coal samples

Abstract

Some metal pollutants are corrosive in nature, are associated with fouling and slagging challenges of the coal boilers, are highly volatile and might cause air pollution and are catalyst poisoners during Fischer–Tropsch catalytic reaction. Therefore, this work describes an improved microwave-assisted sequential extraction (MW-ASE) method followed by ICP-OES/MS analysis for metal distribution determination in South African coal samples. The multivariate optimum conditions for each sequential step were 0.1 g, 200 °C and 5 min for sample amount, microwave temperature and extraction time, respectively. Under the optimum conditions, Ga, Sr and Ba were the only metals that showed solubility towards water, therefore, these metals are classified as highly mobile and eco-toxic under wet environmental conditions. Additionally, all the investigated metals showed solubility towards acidic conditions (HCl and HNO3). These results suggest that, most metal ions are predominantly bonded to sulphate, sulphide, and carbonate coal minerals. Alternatively, Ce, Cr and Y showed total extraction recoveries of ≤ 90%, confirming their strong affinity towards quartz coal minerals. In overall, the proposed MW-ASE method reported short extraction time (0.34 h), environmentally friendly reagents (H2O and diluted H2O2) and rapid multivariate optimization with acceptable extraction efficiencies (79–98%) and reproducibility (RSD ≤ 5%).

Simultaneous Determination of REEs in Coal Samples Using the Combination of Microwave-Assisted Ashing and Ultrasound-Assisted Extraction Methods Followed by ICP-OES Analysis

“…Therefore, the low recoveries of REEs in SARM 20 might be due to the strong interaction between REEs and the minerals of the coal, since SARM 20 has 1:1 ration of carbon and mineral contents. These findings are also supported by previously published reports [10,37].…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…A method developed by Mketo et al , 85 described an improved microwave assisted sequential extraction method followed by ICP-OES/MS detection. The study aimed to develop a rapid and eco-friendly microwave-based sequential extraction procedure for heavy metal distribution determination and mobility in coal samples.…”