Toda United Indusrial (Zhejiang) Co., Ltd.

The textile effluents composition is complex since it contains diverse dyes and other products such as dispersants, acids, alkalis, salts and some heavy metals. In general the effluent is highly colored, with a high biological (BOD) and chemistry demands of oxygen (COD).

Oxides and metal hydroxides have also been used as adsorbents in the textile industry. The adsorption of cationic and anionic dyes on hydrated zirconium oxide or iron oxide has been reported. These materials are common as adsorbents by their limited solubility and their amphoteric properties. However, sometimes these oxides present low surface area and this aspect is a problem to resolve.

In a previous work we have investigated the efficiency of three iron oxide (goethite, Co-goethite and magnetite) to remove synthetic dyes (Alizarin, Eriochrome Blue Black R and Fluorescein) from aqueous solutions as a function of initial dye concentration and the contact time on adsorption process. The objective of this work is to compare the results the adsorption of two iron oxide with those using a biopolymer (chitosan). These dyes were chosen because of their structures, which are commonly present in dyes of the textile industry. Thermodynamics and kinetics data were analyzed and discussed with the goal of a further understanding of the dyes adsorption process.

Methods: Kinetic experiments

Iron oxide

A known quantity of adsorbent was contacted with 100 mL of the dye solution with predetermined initial dye concentration of 25 mg/L, in a thermostatic shaker bath at room temperature for a given recorder time. The initial pH of the solutions was adjusted to 7.10 ± 0.1 by the addition of either diluted solutions of sodium hydroxide or hydrochloric acid. The concentration of adsorbent was 1 g/L for goethite and 2 g/L for magnetite considering that the BET surface area of magnetite was lower than the BET surface area of goethite. After a specified stirring time period, the reaction mixture was vacuum filtered.

The adsorbed amounts at different contact times were expressed as mmol of dye/g of adsorbent. They were determined by the difference between initial and final concentration measured spectrophotometrically with a Cecil UV-VIS Spectrophotometer.

Chitosan

The interaction between chitosan and Alizarin, Eriochrome Blue Black R and Fluorescein at room temperature and pH 7.10 ± 0.1 was studied. The dye concentration used for Alizarin was between 50 and 300 mg/L, for Eriochrome Blue Black R between 2.5 and 125 mg/L, and for Fluorescein between 2.5 and 125 mg/L. All the solutions used were prepared in double distilled water. The relation between adsorbent/adsorbate was 0.1 g of chitosan/L of dye solution.

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