The adsorption of
hexavalent chromium (Cr(VI)) onto calcined bauxite modified with ferrous iron
and ferric iron was investigated. Parameter optimization was conducted for both
the adsorbents and a comparative analysis of their efficiency was performed under
the same conditions. The optimum operating conditions for ferrous modified
calcined bauxite (FEMCB) was found to be 3 g/L adsorbent dose and 60 minutes
equilibrium time. pH and temperature had no significant impact on the removal
efficiency. At optimum conditions, a removal efficiency of >99% was
obtained. Ferric modified calcined bauxite (FRMCB) performed best (>99%) at
4 g/L adsorbent dose with an equilibrium time of 90 minutes. The optimum pH and
temperature were observed as 5±0.2 and 30 OC. Freundlich isotherm
fitted well for the adsorption of Cr(VI) using ferrous modified calcined
bauxite while for adsorption with ferric modified calcined bauxite, better fit
was obtained for Langmuir isotherm. FEMCB followed pseudo-second order kinetic
model and pseudo-first order kinetic model fitted well for FRMCB. Iron leaching
was observed in the effluent after adsorption with FEMCB.
The
application of FRMCB as an adsorbent for Cr(VI) from real mine drainage was
investigated and it showed good removal upto 98%. Optimized
operational conditions were 2 g/L adsorbent dose for 120 minutes at pH 4 and 30
OC. The reaction fitted well to Langmuir isotherm and first order
reversible kinetic model. The effluent was free from iron leaching.
Fixed bed
column study was performed using FRMCB for treating synthetic Cr(VI) wastewater
with varying bed depths, flow rates and initial concentrations. The column
study was carried out for real wastewater treatment also and a reduction in
column efficiency was observed may be due to the interference of other ions and
high pH. The column data was
fitted to Bohart-Adams model and resulting parameters were calculated.
Krishnadas P.
Assistant Engineer
LSGD Section
Kalliassery/Narath GP
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