Disparate activation routes of developing adsorbents from waste biomass: A comparative studies

Abstract

Abstract This work investigated the convenience of thermally prepared adsorbent over chemically modified absorbent made from Carica papaya tree for chromium eradication from tannery wastewater. Chemically modified Carica papaya tree adsorbents were developed employing zinc chloride (ZnCl2), potassium hydroxide (KOH), and nitric acid (HNO3) individually followed by calcination at 600°C where, thermally modified adsorbents was prepared by direct calcination at 600°C for 3 h. The potentiality of differently prepared adsorbents was evaluated by considering their efficacy in removing chromium from wastewater as well as the process simplicity. The chromium removal efficiencies obtained for ZnCl2, KOH, HNO3 modified and thermally modified Carica papaya tree adsorbents were 71.33%, 73.58%, 76.25%, and 99.89%, respectively. The chromium adsorption on different Carica papaya tree adsorbents was assessed by Fourier Transform Infrared (FT-IR) spectroscopy and Energy-dispersive X-ray spectrometry (EDX) analysis. The optimum condition for the maximum adsorbent’s efficacy was determined by conducting the batch experiments with varying the adsorbent doses, stirring time and settling time. Results revealed the maximum chromium removal efficiency of thermally modified Carica papaya tree adsorbent was 99.88% at 0.25 g/25 mL of adsorbent dose for a 20 min stirring time. Analysis from Freundlich and Temkin isotherm revealed the adsorption reaction as an endothermic chemisorption reaction with strong interaction between the adsorbent and chromium ion. In terms of kinetics, the Pseudo 2nd order equation had the best fitting with the experimental data considering the regression coefficient value (R2 = 0.9997). Thermally modified adsorbent from agricultural waste such as Carica papaya tree can be in use to reduce pollution load from tannery wastewater.