Efficient chromium(VI) adsorption by Cassia marginata seed gum functionalized with poly(methylmethacrylate) using microwave irradiation

Increasing cost of the chemicals and production of toxic sludge in the Cr(VI) treatment methods have attracted attention toward the use of biosorbents for Cr(VI) removal. The present study evaluates a novel biosorbent derived from Cassia marginata seed gum in the removal of Cr(VI) from the aqueous solution and wastewater. The adsorbent was synthesized using microwave irradiation in the absence of any radical initiator or catalyst in good yield. Adsorbents of different performances could be obtained by varying the amount of the methylmethacrylate, microwave power, and exposure time. A representative sample of microwave synthesized adsorbent was characterized using FTIR, XRD, TGA, and SEM analysis. Cr(VI) sorption was optimized using the copolymer sample of highest grafting ratio and efficiency (270% G and 59.65% E) where the removal was found to be pH and concentration dependent, pH 1.0 being the optimum value at which from 20 mL of 100 ppm Cr(VI) solution, 16.94 mg/g Cr(VI), could be removed using 5 g/L adsorbent dose at 30 degrees C. The adsorption data followed both Langmuir (R-2 = 0. 9703) and Freundlich isotherms (R-2 = 0.8957) probably due to the real heterogeneous nature of the surface sites involved in the metal uptake, and overall sorption of Cr(VI) on the biosorbent is complex and involves more than one mechanisms. The adsorption followed second order kinetics, the rate constant being 0.10 x 10(-5) g/(mg min) at 100 mg/L Cr(VI) concentration. The adsorbent was also found efficient in Cr(VI) removal from real industrial wastewater. Used copolymer was recycled after stripping off the adsorbed chromium with 2 M NaOH where after each cycle a successive decrease in the binding capacity was observed. To understand the advantage of using microwaves in the adsorbent synthesis, the copolymer synthesized using a K2S2O8/ascorbic acid redox pair at identical monomer concentrations (220% G and 48.6% E) was also evaluated as Cr(VI) sorbent, and the results obtained were compared with that of microwave synthesized copolymer.