Dye removal using waste beads: Efficient utilization of surface-modified chitosan beads generated after lead adsorption process

Abstract

In our earlier reported work we studied the removal of Pb2+ from aqueous media using surfactant-modified chitosan (SMCS) beads. There it was shown that,SMCS beads could be used as an efficient adsorbent (maximum adsorption capacity of 100.0 mg/g) for Pb2+ removal. However, after the removal of lead, the waste sludge (Pb-loaded SMCS beads) disposal becomes a real challenge. To face this problem, we have taken up the strategy to explore the possibility of further utilizing the waste beads for dye removal. Thus waste can serve as a resource. In industrial ecology this is recognized as ‘a closed-loop system’. Although this is an extended part of our previously published earlier work [3], but seems to be a very fruitful utilization of waste sludge. In the present paper we studied the removal of two model dyes e.g. crystal violet (CV) and tartrazine (TZ) using the waste SMCS beads generated after Pb2+ adsorption. These waste beads are designated as lead-loaded surfactant-modified chitosan (PbL-SMCS) beads. It was interesting to note that, even after adsorption of Pb2+, the SMCS beads were able to remove the dyes effectively. The kinetic studies showed rapid sorption dynamics following pseudo-second order kinetic model. Equilibrium time obtained was 2 h for both the dyes which led to remove 90% of the dyes. Studies on the effect of dose revealed that, 0.9 g/L dose was the optimum to obtain ∼99% removal of CV and TZ at a concentration of 20 mg/L under the optimum pH conditions of 6.0 and 3.0, respectively. Isotherm data were fitted well to the Langmuir and Freundlich isotherm for CV and TZ, respectively. Langmuir adsorption capacity obtained for CV and TZ removal was 97.09 and 30.03 mg/g, respectively. These approaches are important in today’s scenario to help in reducing the waste, and recycling and reusing the adsorbent.