SAWDUST: COST EFFECTIVE SCAVENGER FOR THE REMOVAL OF CHROMIUM(Ⅲ) IONS FROM AQUEOUS SOLUTIONS

摘要

Cr(Ⅲ) ions sorption onto sawdust of spruce (Picea smithiana) has been studied thoroughly using radiotracer technique. Maximum sorption (94%) of Cr(Ⅲ) ions (8.98 x 10~5 M) onto sorbent surface is achieved from deionized water in 20 min agitation time using 200 mg of sawdust. The sorption data followed the Freundlich, Dubinin-Radushkevich (D-R) and Langmuir isotherms. Fre-undlich constants l = 0.86 ± 0.07 and C_e = 85.0 ± 25.8 mmole g~(-1) have been estimated. Sorption capacity, X_m = 0.82 ? 0.3 mmole g~(-1), β = -0.00356 ± 0.00017 kJ~2 mole~(-2) and energy, E = 11.9 ± 0.3 kJ mole~(-1) have been evaluated using D-R isotherm. The Langmuir constants Q = 5.8 ± 0.2 μmole g~(-1) and b = (7.4 ± 0.5) x 10~4 dm~3 mole~(-1) have been calculated. The variation of sorption with temperature yields thermodynamic parameters ΔH = -11.6 ± 0.3 kJ mole~(-1), ΔS = -16.2 ± 0.9 J mole~(-1) K~(-1) and ΔG = -6.8 ± 0.3 kJ mole~(-1) at 298 K. The negative value of enthalpy and free energy reflect the exothermic and spontaneous nature of sorption respectively. Among the anions studied oxalate, citrate, carbonate and borate have reduced the sorption. The cations Y(Ⅲ), Ce(Ⅱ) and Ca(Ⅱ) suppressed sorption. The sawdust column can be used to separate Cr(Ⅲ) ion from Cs(Ⅰ), I(Ⅰ),Tc (Ⅶ) and Se (Ⅳ).