The evaluation of sequentially extracted mercury fractions in Thar coal samples by using different extraction schemes

• To evaluate Hg fractions in coal of the Thar coalfield on the bases of different depths
• The fractionation study was carried out by different extraction schemes.
• Compare the BCR-SES with CSE and USE for the quantitative determination of Hg
• Statistical techniques used to elucidate the Hg fractions and other parameters in coal samples

In the present study, various sequential extraction methods were applied to assess the mercury (Hg) contents bounded with different chemical fractions of coal samples, collected from four different seams of the blocks III and V in Thar coalfield, Pakistan. The BCR sequential extraction (BCR-SE) method and two alternative modified schemes (conventional and ultrasonic assisted single step extractions) were designed and applied on the same operating conditions for each individual BCR fraction. Proximate and elemental analyses of coal samples were also performed to point out the physicochemical characteristics of the Thar coal samples. Validation of the desired methodologies was checked by the standard addition method to the real coal samples. The Hg concentration in extractable fractions was determined by cold vapor atomic absorption spectrometer (CV-AAS). The proposed conventional (CSE) and ultrasonic assisted single step (USE) extraction methods were non-tedious and time saving, as the extraction time was reduced from 51 h to 36 h and 2 h, respectively. The extraction efficiency of CSE and USE was comparable with those data obtained with the conventional BCR protocol. The relative mobility of Hg in coal samples obtained from different depths was found in the following increasing order: oxidizable fraction < reducible fraction < acid soluble fraction.