Natural Chitin Containing Materials for Colour Removal from Textile Wastewaters

Abstract

The main objective of this work was to study the ability of some low-cost materials containing chitin namely, Squid (Loligo vulgaris) and Sepia (Sepia officinalis) pens, and Anodonta shells (Anodonta cygnea), for colour removal by adsorption from textile wastewaters. A reactive and a direct green dyestuff, the Cibacron green T3G-E (CI reactive green 12) and the Solophenyl green BLE 155% (CI direct green 26) from CIBA, respectively, were selected for this study. The physical and chemical properties of the adsorbents were briefly characterised. Isotherms at 20 °C were determined for all systems using two different grain sizes. The experimental results were well fitted by both Langmuir and Freundlich models. Isotherms using pure chitin and activated carbon in the same conditions were also determined. Continuous adsorption experiments were performed in a packed column at 20 °C for the six pairs adsorbent / dyestuff and compared with experiments using chitin and activated carbon. These results and the mathematical simulation of the column runs with the studied adsorbents led to the conclusion that a very large internal resistance is present. In order to allow a more efficient use of the larger diameter particles in packed columns (decreasing their internal resistance), the adsorbents were submitted to various chemical treatments, namely, a demineralisation, followed by a deproteinisation step, or only one of these steps. The results show that, for the natural adsorbents, the Squid pen has the largest adsorption capacity; this is probably due to its larger specific surface area (8.8 m²/g as compared with the Anodonta shell with 1.4 nrVg) with more meso and micropores. The tests also show that the effective adsorption capacities of these materials decrease when increasing particle diameter.