Investigation of the recycling of inorganic salts contained in the exhausted bath of cotton dyeing using reactive dyes

Abstract

The discharge of inorganic salts contained in the effluent of the dyeing of cotton using reactive dyes to the public environment has been under scrutiny. In the present investigation the flocculant polydimethyldiallyl ammonium chloride and an anion resin coded by D301 were employed for the purification of the exhausted bath discharged from the dyeing of cotton knitted fabrics using reactive dyes. Through the purification presented the exhausted bath is transferred to the concentrated inorganic salt solution and then reused in the next batch of dyeing. The process consists of the exhausted bath collection, precipitation formation by means of the flocculation and resin adsorption. The results indicated that the concentrated inorganic salt solution is suitable for all the reactive dyes employed in the dyeing of cotton. The K/S values, color evenness and color fastness properties of the dyed fabrics using the inorganic salt solution are basically the same as those using distilled water. The results also indicate that 72.0% of water and 71.1% of inorganic salt used for the dyeing can be saved when the inorganic solution is recycled four times, which means that the amount of the inorganic salt discharge to the environment can be reduced by 71.1%.