Leaf char: An alternative adsorbent for Cr(III)

The speciation of Chromium, a well-known human carcinogen, recently turns to be trivalent Cr(III) in waste waters from metal plating industries due to the progress in plating technology. Leaf char was prepared and testified to act as an alternative for Cr(III) adsorption in this study. Various factors were investigated and the optimums were found to be: dosage = 2.5 g L− 1, adsorption capacity at 69 mg g− 1, equilibration duration > 25 min and pH > 1.88–4.79. The adsorption is sensitive to and will be enhanced at higher temperature at initial Cr(III) concentrations less than 900 mg L− 1 while the opposite occurred at concentrations more than 900 mg L− 1. The changes of enthalpy and entropy during Cr(III) adsorption were predicted at 22.32 to −11.15 kJ mol− 1 and 168.25 to 12.18 J mol− 1 K− 1, respectively. The IR spectroscopy revealed the relationship between Cr(III) adsorption and the functional groups of carboxyl, amine and phosphate in the adsorbent while XRD indicated the effect of carbon black.