Red dye 40 removal by fixed-bed columns packed with alginate-chitosan sulfate hydrogels

Modified Chitosan was used for the removal of red dye 40 from aqueous solutions at a pH of 5.0. The adsorption was carried out making use of fixed-bed columns packed with beads of Alginate-Chitosan Sulfate (Alg-ChS) hydrogels. Two columns with heights of 13 and 33 cm, and two feed rates (20 and 40 mL/h) were used. The pH of the dye solutions at the exit of the columns was much higher than that at the entrance which can be explained by protons transfer from the aqueous solution to the amino and hydroxyl groups of the Alg-ChS and to the carboxilate groups of the alginate. The increase in pH was favorable for the removal of the dye. The breakthrough time and the amount of dye removed decreased when the flow rate was increased. A greater dye removal was achieved when the higher column was used. After the breakthrough time, the columns continued to remove appreciable amounts of dye and even after 50 hours of operation, column saturation was not obtained.

Keywords: chitosan sulfate, alginate, fixed-bed column, pH increase, Red Dye 40.