Evaluation of Avocado Pear Seed Coat for Removal of Nickel and Chromium Ions from Aqueous Solution

Abstract

This research investigates the use of avocado (Persea americana) seed coat as a potential adsorptive material for removal of Ni(II) and Cr(VI) from aqueous solutions using a batch experimental technique of adsorption. Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive x-ray spectroscopy techniques were used to characterize the biosorbent. Biosorbent dose, pH, contact time, and concentrations of metal ions were varied to probe the adsorption efficiency of the avocado seed coat biosorbent. The effects of competing ions on the biosorption of nickel and chromium from aqueous solutions were also explored. Adsorption characteristics were well explained by the Elovich and Langmuir models with maximum monolayer coverages of 10.38 mg · g–1 (Ni2+) and 12.25 mg · g–1 (Cr6+). Removal of the metal ions was slightly inhibited by the presence of interference ions. The biosorption process was nonspontaneous and exothermic. Recovery of Ni(II) was more promising using ethylenediaminetetraacetic and hydrochloric acid than was the recovery of Cr(VI). Overall, avocado pear seed-coat powder is a good adsorbing material for removal of Ni(II) and Cr(VI) from water.