Hydroxyapatite nanoparticle-modified apple pomace as a biosorbent for copper and iron removal: Isotherm and kinetic analysis

Abstract

The present study investigates the potential application of activated biomass waste decorated with hydroxyapatite nano-particles (HANP), i.e., HANP@AP, for decontamination of Cu and Fe metals from aqueous medium. We presumed that Cu and Fe ions can be removed from water contaminated with these ions efficiently owing to the electrostatic interaction provided by phosphate (PO₄)^3- and (-OH) groups of HANP. Thus, the adsorption experiments have been designed to explore the potential of this HANP modified activated biomass waste. The influence of various factors like time (5-180 min), adsorbent dose (0.01-0.1 g), metal concentration (20-300 mg L^-1), and pH (2-8) on the adsorption process have also been investigated. The Langmuir adsorption isotherm is suited for the adsorption of both Cu and Fe showed that the maximum adsorption capacity of 76.3 mg g^-1 for copper and 166.6 mg g^-1 for iron when batch adsorption experiments are performed with initial metal ion concentration of 20-300 mg L^-1 at pH 5 over the period of 180 min for Cu and 5 min for Fe using 0.1 and 0.04 g of adsorbent, respectively. It is observed that the pH plays quite an important role for the adsorption of Cu on to the surface of HANP@AP whereas the adsorption of iron on its surface remains unaffected by pH variations. Further, to understand the mechanism for the adsorption of copper and iron the surface of HANP@AP, kinetic studies are done in the time range of 20-180 min. The kinetics study data revealed that the Cu and Fe adsorption on activated waste following pseudo-second kinetics. Further, a comparison study with the previously reported biomass based biosorbents is also done which showed the superiority of HANP@AP for the decontamination of these heavy metal ions.