Catalytic activation of peroxymonosulphate with manganese and cobalt coated micro sand particles for the treatment of Floor-wash containing Reactive Black 5 (RB5) dye

Abstract

Reactive Black 5 (RB5) is an azo dye widely used in various industries. This work is focused on treating Floor wash wastewater, which is one of the most voluminous and coloured streams emerging from RB5 manufacturing units. It is possible to reuse this water if it is efficiently decolorized. Water containing RB5 dye is hard to treat using conventional treatments due to its high stability and solubility. In this work, decolorization of simulated Floor-wash was investigated using peroxymonosulphate (PMS) and heterogeneous catalyst. The simulated floor-wash containing 100 mg/L of RB5 was prepared using tap water. The synthesis of manganese and cobalt-coated micro sand (MnCoMS) particles was done to efficiently activate peroxymonosulphate (PMS). The operational parameters such as catalyst dosage, PMS concentration, initial pH, reaction time, and reusability of MnCoMS were investigated. Under optimum conditions: 200 mg/L PMS, 10 g/L MnCoMS, and initial pH 9.5, 97.8 % of initial 100 mg/L RB5 was decolorized at the end of 60 min reaction time. RB5 decolorization was slightly slower at initial pH near neutral (7–7.8) as compared to that at acidic (4.5) or alkaline (9.5) pH values. The rate and extent of RB5 decolorization increased with an increase in PMS concentration from 50 mg/L to 200 mg/L. Similarly, the increase in MnCoMS concentration from 5 to 25 g/L increased the rate of RB5 decolorization. However the %RB5 decolorization at the end of 60 min was almost constant for MnCoMS concentration of 10 g/L and above. Experiments conducted in the presence of scavengers revealed that sulphate and hydroxyl radicals played important role in RB5 decolorization. The MnCoMS catalyst demonstrated excellent reusability with > 80 % RB5 decolorization achieved till the sixth use. Overall, PMS activation by heterogeneous catalyst MnCoMS is an efficient method for rapid decolorization of floor-wash containing RB5 dye.