Analysis of coal ash samples from thermal power plants of India for their gallium content using NAA and EDXRF techniques.

Coal fly ash (CFA) is an important secondary source for the recovery of gallium (Ga) which has a high potential for its wide applications in many strategic fields such as cellular communications and direct broadcast satellite. Various coal fly and bottom ash samples obtained from thermal power plants located in different parts of India were investigated for their gallium content using NAA and EDXRF techniques. The concentration of gallium in NIST SRM 1633b CFA is not available in NIST certificate and hence was established using k based IM-NAA method along with the other certified elements like As, Ce, Co, Eu, Fe, K etc. In addition, the gallium concentration in the NIST SRM was also obtained by relative NAA using GaO as a standard towards the validation of IM-NAA. Using the NIST SRM, the gallium content in the ash samples of Bituminous coal collected from South Central and Eastern India was found to be from 17.2 to 47.9 mg/kg whereas the same was 6.3-33.3 mg/kg for the ash samples of Lignite coal collected from the South-Central India and Western India. The gallium concentrations obtained by NAA in coal ash samples were compared with another non-destructive assay technique, i.e. EDXRF and the results are found to be in good agreement. These samples were proved to be a potential secondary source of gallium, available in India.