The effect of chitin preparation with HCl (chitin A) and with HCl and KOH (chitin B) and pH on the adsorption of reactive dyes (helactine, polactine and remazol) on chitin was investigated. The double Lang- muir equation was appropriate to analyze the dependence between amount of the adsorbed dye on chitin (Q) and its equilibrium concentration (C). It indicated the presence of two types of active sites which differed in both the maximum adsorption capacity (b) and adsorption affinity (K). Based on the dimensionless separation factor R it was found that the dye adsorption mechanism in type I sites was an ion exchange, whereas in the case of type II sites it was a physical adsorption. The adsorption capacity of the chitin A (deacetylation degree of 3%) for samples without pH adjustment ranged from 29 (Red D-8B) to 67 mg/g dry weight of chitin (Gelb GR). At pH 3.0 the adsorption capacity was higher from 1.9 to 2.3-fold. The most favourable effect of pH change was found for helactine dyes. The adsorption capacity of the chitin B (deacetylation degree of 5%) was from 66 (Brillantorange 3R) to 101 mg/g dry weight of chitin (Gelb GR). After pH adjustment to pH 3.0 the adsorption capacity ranged from 160 (Ruby F-2B) to 294 mg/g dry weight of chitin (Blau 3R). The most favourable effect of deacety- lation degree increase was found in the case of helactine dyes in the samples without pH adjustment, and polactine and remazol dyes at pH 3.0.
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