Studies on an economically viable remediation of chromium rich waters and wastewaters by PTPS fly ash

Application of fly ash, a waste material of thermal power plants for the removal of chromium from aqueous solutions and wastewaters has been investigated. The adsorption follows a first order rate kinetics and the value of Kad, rate constant for removal was found to be 3.0 × 10−2 s−1 at 298 K, 100 rpm, 2.5 pH and at other optimum conditions. Intraparticle diffusion was found to control the removal of Cr(VI) and the value of coefficient of intraparticle diffusion was found to be 2.25 × 10−11 cm2 s−1 at 298 K. The value of the coefficient of mass transfer, βl, 2.15 × 10−2 cm s−1 at 298 K, suggested the transfer of Cr(VI) onto the adsorbent surface to be rapid enough. The process of removal is highly dependent on pH of the solutions with maximum removal (89.12%) at pH 2.5. Values of Langmuir's constants were also calculated. Various thermodynamic parameters namely free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were calculated and found to be −0.68, 5.26 and 1.77 K cal mol−1at 298 K. Comparison of the adsorbent used with other non-conventional adsorbents shows that fly ash is a good adsorbent and can be recommended for treatment of metal rich wastewater in general and that of Cr(VI) in particular.