Response surface methodology mediated process optimization of hexavalent chromium removal from water using spent tea leaves treated with ascorbic acid

Spent tea leaves were functionalized with ascorbic acid to obtain treated tea waste (t-TW) for adsorption of hexavalent chromium (Cr(VI)) from water. The adsorption removal of Cr(VI) was systematically investigated as a function of four experimental factors i.e. pH (2–12), initial Cr(VI) concentration (1- 100 mg.L − 1 ), t-TW dosage (0–4 g.L − 1 ), and temperature (10–50°C) by following statistical experimental design. Response surface methodology (RSM) based central composite rotatable experimental design was opted to establish an empirical model which assessed individual and combined effects of factors on the response; adsorption removal of Cr(VI). The model was experimentally verified and statistically validated by analysis of variance (ANOVA) before using to predict optimal adsorption removal of Cr(VI) from water. It was observed that, at optimized conditions, ≥ 99% of 1 mg.L − 1 Cr(VI) can be removed by 4 g.L − 1 t-TW at pH = 9. The adsorption mechanism was assessed by performing kinetics and equilibrium studies. The adsorption of Cr(VI) on t-TW followed pseudo-second-order kinetics model and could be described by Langmuir and Temkin isotherms; indicating monolayer adsorption and predominant adsorbate-adsorbent interaction. These results encourage the utilization of tea-waste for hazardous metal contaminant removal from aqueous systems.