Tea waste based natural adsorbent for toxic pollutant removal from waste samples

Alkali treated tea waste (ATTW) was investigated as a novel alternative cost-effective natural adsorbent to decontaminate the pollutant of chromium (Cr(VI)) in the polluted water with the variation of equilibration time, solution pH, initial Cr(VI) concentration, adsorbent dosage, and temperature with a view to ensuring a safe disposal as well as sustainable management of the discarded bulk quantities of industrial tea leaves wastes. The adsorbent characteristic was confirmed the significant amount of Cr(VI) accumulation onto ATTW surfaces. The adsorption processes were satisfactorily described by pseudo-first order (PFO), pseudo-second order (PSO) and intra-particles diffusion models (IDM) where the PSO model evidently shows a better fitting with the regression coefficient (R2 = 0.994). Exploration of Langmuir, Freundlich, Flory-Huggins, and Temkin isotherm models were also investigated and the best fitting was observed for the Langmuir model as it was produced the highest regression coefficient value (R2 = 0.993). The maximum adsorption ability of ATTW according to the Langmuir model was found to be 158.73 mg/g. These results demonstrate that Cr(VI) adsorption was a complex process involving a physicochemical spontaneous monolayer and multiple rate-limiting states, which was predominantly chemical or chemisorption due to ion-exchange or electrostatic attraction/surface complexation formation, film diffusion and intra-particle diffusion. Furthermore, the substrates exhibited an excellent regeneration capacity upon using 0.10 M HNO3 as eluent and ATTW was reused several cycles without influencing the adsorption performance. The results of this study thus concludes that ATTW could be a promising environmentally friendly and cheap bio-adsorbent for Cr(VI) remediation with profound implications in water and wastewater treatment for a large-scale environmental pollutant clean-up laden with toxic Cr(VI) ions.