1 Parallel and Sequential Extraction for Evaluating Leaching Behaviour of Different Elements Present in Pond Ash Prasenjit Ghosh and Sudha Goel Civil Engineering Department, IIT Kharagpur, Kharagpur 721302, India ami.prasenjit@gmail.com , sudhagoel@civil.iitkgp.ernet.in ABSTRACT Coal Combustion Residues (CCRs) form one of the largest fractions of solid wastes generated throughout the world. Its generation is estimated to be 25% of the total solid waste generation in India. Thermal Power Plants (TPPs) which generate more than 60% of the electricity in India are responsible for generation of huge quantity of CCRs. TPPs use pulverised coal as the fuel and dispose the CCRs generated mostly by wet sluicing process in ash ponds. Fly ash and bottom ash are mixed along with water and the resulting slurry is carried to ash ponds through drains. This slurry contains trace metals like As, Cr, Zn, Cd which are toxic in nature and sometimes radioactive elements like U, Th etc. which has high potential of getting leached into surrounding soil and groundwater. So, wet disposal of CCRs has serious environmental concerns. Three pond ash samples were collected from three different ash ponds situated around Kolaghat Thermal Plant in West Bengal, India. The leaching potentials of different elements present in the three pond ash samples were assessed by Parallel and Sequential Extraction procedures. The extracted solutions were filtered, acidified and analysed by ICP-MS and AAS to measure concentrations of different elements leached. Na, Al, Ti, Cr, V, Zn, Ni, Mo, Ag, Ba and Pb exhibited remarkable mobility in contact with the leaching solutions. Toxic elements like As, Cr, Zn, Pb, Cd and Cu also showed potential of getting leached varying from moderate to high ranges of concentrations. Radioactive elements like U and Th could also be detected. Results indicate high possibility of contamination of the surrounding soil and groundwater around the ash ponds. 1. INTRODUCTION The amount of CCR (coal combustion residue) released by factories and Thermal Power Plants (TPPs) has been increasing throughout the world. CCR characteristics depend on coal type, coal particle fineness, % of ash in coal, combustion technique applied, air/fuel ratio, number of burners used and type of burner. Its generation is estimated to be 25% of the total solid waste generation in India (Pappu et al., 2007). TPPs which generate more than 60% of the electricity in India are responsible for generation of huge quantity of CCRs. During the year 2010-2012, about 408 MT/year of coal was used and more than 130 MT/year of fly ash was generated by 88 TPPs all over India (http://flyash2012.moissionenergy.org/intro.html). CCRs include fly ash, bottom ash, pond ash and mound ash. Fly ash and bottom ash are mixed along with water in the TPPs and the resulting slurry is carried to ash ponds through drains (Shivpuri et al., 2011). This slurry contains trace metals like As, Cr, Zn, Cd which are toxic in nature and sometimes radioactive elements like U, Th etc., (leached from the ashes) which has high potential of getting leached into surrounding soil and groundwater (Mandal A. and Sengupta D, 2005). So, wet disposal of CCRs has serious environmental concerns. Due to presence of toxic elements, it is important to determine their leaching potential in various environmental conditions. Extraction methods are generally applied for that purpose. Various extraction procedures are followed under different controlled conditions (Quan S. X., Bin C., 1993; Chang et al., 2009). Sequential Extraction procedures have been recently