Sequential Extraction and Spectrophotometric Estimation of Heavy Metals from Thermal Power Plant Generated Coal Fly Ash and its Admixtures

An attempt is made to study the extractability of heavy metals from fly ash generated from Thermal Power Plant which is used as an admixture with cement, brick manufacturing, land filling and in agriculture. From the utilization point of view, it was notable that the total heavy metal concentrations (Cu, Pb, Zn, Ni, Fe, and Mn) in fly ash from a coal-fired power plant were lower than those limit values. A six-stage sequential extraction procedure was used to evaluate the extractability of different elements in fly ash into the following fractions: (1) the water-soluble fraction, (2) the exchangeable fraction (1M MgCl₂ at pH 7), (3) Carbonate bound (1M Na-OAC at pH 5), (4) Fe- Mn bounded (0.04M NH₂OH, HCl in 25% acetic acid), (5) Organically bound (0.02 M nitric acid and 30% H₂O₂ at pH 2 and 90^oC, followed by 1.2 M ammonium acetate in 10% nitric acid) and (6) Residual metal ions (HNO₃ and HClO₄ acid digestion until dryness).