Effect of deacetylation on sorption of dyes and chromium on chitin

Abstract

Deacetylated chitins (10.7-67.2fl ) were prepared by alkaline hydrolysis to determine an optimal degree of deacetylation (DD) which can effectively remove four dyes and chromium ions from textile effluent. Sorption isotherms were carried by varying the treatment time, pH, and initial concentration of dyes or chromium ions. Experimental results were analyzed in three ways: (1) equilibrium sorption capacity and sorption rate constant, (2) Langmuir isotherms, and (3) separation factor. Results indicated that except for the chitin with a 67.2% DD, rate and capacity of the dye sorption on the chitin increased with the increase of the DD in chitin for each pH but decreased with the increase of pH for each deacetylated chitin. This was mainly due to the increase of-NH 3 + groups in chitin with a high DD and the low pH of the system. On the contrary, dye desorption from the deacetylated chitin was highly effective at 80°C and pH ≥ 10, which could facilitate the reduction of-NH 3 + ions and the increase of electrostatic repulsion. The number of chromium ions sorbed on the chitin also increased with the increase of the DD at a specific time. Therefore, by controlling the DD of the deacetylated chitin maximum efficiency can be achieved in the removal of dyes and metal ions from textile effluent.