Batch and continuous studies for adsorption of anionic dye onto waste tea residue: Kinetic, equilibrium, breakthrough and reusability studies

In the present article, adsorption of anionic dye (Acid Blue 25) using waste tea residue (WTR) was investigated in batch and continuous operation. Clear insight of functional groups, surface charge, morphology, composition, surface area and particle size of WTR was obtained by the characterization techniques of FTIR, zeta potential, SEM-EDX, BET, and DLS analysis. Influence of operating pH, adsorbent loading, influent concentration, contact duration of adsorption and temperature on dye remediation was investigated in batch studies. Evaluated kinetic data was in better agreement with pseudo 2nd order model whereas equilibrium data was in better agreement with Redlich Peterson model. Multiple steps were found to control the mechanism of the studied adsorption. Maximum dye uptake was obtained as 127.14 mg g−1 at optimized pH of 1, loading of 3.5 g L −1 and higher temperature as 318 K. Adsorption process was found to be spontaneous, physical and favored with the rise in temperature. Reusability of WTR in multiple cycles showed a slight drop in dye uptake from 27.95 ± 0.26 mg g−1 at 1st cycle to 26.24 ± 0.21 mg g−1 at 3rd cycle. Continuous studied were also conducted in packed column and influence of column operating parameters as packing height (3–6 cm), concentration (50–200 mg L−1) and the flow rate of influent (5–9 mL min−1) on the efficacy of dye remediation were investigated. Thomas model was reported to be in better agreement with the evaluated breakthrough data. Maximum uptake in continuous studies was reported as 50.82 mg g−1. The obtained results of batch and continuous studies depicted that WTR could be used effectively for remediation of targeted anionic dye from the aqueous phase.