Optimization of salting-out crystallization for an efficient in situ separation of synthetic anthraquinone- and azo-type reactive dyes

A solute can be deposited from solution by the addition of another soluble substance which effectively reduces the solubility of original solute. The process is referred to as ‘salting-out’ and it is one of the proper methods for effective separation of synthetic reactive dyes in industry. To develop an efficient salting-out process for recovering representative anthraquinone- and azo-type reactive dyes, Reactive Blue 49 and Reactive Black 8 in high yields, various factors such as the kind and amount of inorganic salts, concentration of dye solution, operating temperature, stirring speed, complete time of crystallization were investigated. Reactive Blue 49 could be recovered from 15 wt% of dye solution in approximately 70% yield under the optimized conditions (15 wt% of NaCl, 25 °C, 100 rpm, 12 h) and Reactive Black 8 was obtained from 20 wt% of dye solution in over 90% yield by using 10 wt% of NH4Cl at room temperature and 100 rpm within 1 h.