Thermally activated adsorbent over chemically modified Carica papaya tree adsorbents for removal of chromium from tannery wastewater

This work investigated on the adsorption efficacies of contrasting Carica papaya tree adsorbents in removing chromium from the tannery wastewater. The convenience of thermally activated adsorbent was evaluated over chemically modified adsorbents developed employing ZnCl2, KOH, and HNO3 individually followed by calcination (600 °C) for 3 h. Chromium removal efficiencies obtained for ZnCl2, KOH, and HNO3 modified and thermally modified Carica papaya tree adsorbents were 71.33 %, 73.58 %, 76.25 %, and 99.89 %, respectively. Chromium adsorption on different Carica papaya tree adsorbents was assessed by FTIR, EDX, TEM, and BET surface area analysis. The maximum chromium removal efficiency of thermally modified adsorbent was 99.88 % at 0.25-g/25 mL of adsorbent dose for a 20 min stirring time. Both the Pseudo-second-order equation and Freundlich isotherm showed the best fitting with determination coefficients R2 = 0.9997 and R2 = 0.9999, respectively. Freundlich isotherm and Pseudo-second-order kinetic revealed the adsorption reaction as a chemisorption reaction with stronger interaction between adsorbent and chromium. [Display omitted] •Disparate activation routes of developing adsorbents from Carica papaya tree•Thermally activated adsorbent showed maximal Cr adsorption of 99.88 %.•Freundlich isotherm revealed adsorption reaction chemisorption•Pseudo-second-order kinetic showed the best fitting of Cr adsorption.