The kinetics and thermodynamics of sorption of chromium(VI) onto the iron(III) complex of a carboxylated polyacrylamide-grafted sawdust

A novel, adsorbent was prepared and its adsorption properties for Cr(VI) were studied. The iron(III) complex of a carboxylated polyacrylamide-grafted sawdust has been found to be an effective adsorbent for the removal of Cr(VI) from aqueous systems. Experiments were carried out as a function of concentration of Cr(VI), agitation period, agitation speed, pH, ionic strength, and temperature. Maximum removal (> 99.0%) was observed at an initial concentration of 25.0 mg/L in the pH range 2.0-3.0. Coordination unsaturated sites for the iron(III) complex of polymer were considered to be the adsorption sites for Cr(VI) species, with the predominant species being HCrO4-. Rate constants as a function of concentration and temperature were evaluated with the help of a proposed second-order kinetic model. The percentage removal of Cr(VI) decreased with increasing ionic strength. The L-type adsorption isotherm obtained for the adsorbent indicated a favorable process. Adsorption isothermal data could be interpreted by the Langmuir and Freundlich equations. The uptake of Cr(VI) on adsorbent increased from 144.20 mg/g at 20 degreesC to 172.74 mg/g at 60 degreesC. Thermodynamic parameters such as DeltaG degrees, DeltaH degrees, and DeltaS degrees for the adsorption process were calculated. The isosteric heat of adsorption was also determined at various surface loadings of the adsorbent used. Simulated Cr(VI) electroplating wastewaters were also treated by the sorbent to demonstrate its efficiency in removing Cr(VI) from wastewater with other ions. Desorption studies showed that over 95.5% of Cr(VI) can be desorbed from the adsorbent using 0.1 M NaOH.