MALACHITE GREEN DYE REMOVAL USING PRETREATED RICE HUSK AS LOW COST ADSORBENT

Abstract

Dyes are usually soluble substances used to impart colour to textile fabrics, paper and leather, ceramic, plastic, cosmetics, food etc. and also they are used to prepare ink, paints and varnishes1. These compounds consist of chromophore and auxochrome groups attached to one or more benzene rings. Their characteristic colour is due to the chromophore group and dyeing affinities due to the auxochrome group. The chromophore groups may be azo, quinonoid, nitroso, nitro, carbonyl, vinyl, sulphonate and carboxyl group etc. General auxochrome groups include either electron donating groups such as amino, methyl amino, dimethyl amino, hydroxy, alkoxyl group etc., or electron accepting group such as nitro2,4. The dyes can be broadly classified into cationic dyes, anionic dyes and nonionic dyes. Cationic dyes are those, which dissociate in aqueous solution to give positively charged ions. All the basic dyes and some of the direct, azo and disperse dyes are cationic dyes. Anionic dyes are those, which dissociate in aqueous solution to give negatively charged ions. Some examples are the direct, acid and reactive dyes. Nonionic dyes are those, which do not ionize in aqueous solutions. All the disperse dyes are nonionic dyes.