Synthesis of hydroxyapatite from avocado fruit peel and its application for hexavalent chromium removal from aqueous solutions - adsorption isotherms and kinetics study

Abstract

The potential of hydroxyapatite particles prepared from avocado peel (APH) for the removal of Cr (VI) ions from aqueous solutions was studied. The APH was characterized using x-ray diffraction; Fourier transforms infrared spectroscopy, and scanning electron microscopy. The adsorption of Cr (VI) ions from aqueous solutions onto APH was studied. The batch adsorption experiments were performed in 250-cm3 Erlenmeyer flasks containing 100 cm3 solution of Cr (VI) of known concentration with a known mass of adsorbent (APH) added to the solution. The flasks were agitated at 120 rpm on a rotary shaker incubator for a known time at 30°C. The impact of different parameters such as initial Cr (VI) concentration, adsorbent dosage, contact time, and pH of the solution was studied. The hexavalent chromium removal efficiency (91.27%) increased with increase in initial Cr (VI) ions concentration (50 to 200 mg/L), and adsorbent dosage (0.1 to 0.5 g/100 mL). The adsorption isotherms and kinetics of the process were also studied. The Freundlich adsorption isotherm well explained Cr (VI) adsorption onto APH. Cr (VI) adsorption onto APH very well agreed with the pseudo-second-order kinetic model as indicated by the R2 value (0.99). APH is an eco-friendly and low-cost adsorbent. APH is very effective for the removal of hexavalent chromium from aqueous solutions.