Sustainable remediation of nickel (II) in aqueous solutions using waste orange peel biomass as a bioadsorbent

A low-cost adsorbent for Ni(II) uptake was developed using orange peel waste after pretreatment with ethanol/water at 40 °C for 6 h. Various experimental factors such as pH, adsorbent dosage, and contact time were investigated, with optimal conditions determined to be pH 5, an orange peel dose of 2.5 g/L, and a contact time of 90 min. The characterization of the adsorbent was analyzed. The linear and nonlinear isotherm and kinetic models were investigated. The Langmuir model suggested chemisorption with a 19.42 mg/g capacity, following pseudo-second-order kinetics. The thermodynamic analysis revealed that the uptake was exothermic (ΔH° < 0), feasible, and spontaneous (ΔG° < 0). Regeneration studies (NaCl, NaOH, HCl, HNO), interference studies (Al, Cd, Ca, Na, mixed solution), and application studies with real water samples (wastewater, drainage water, tap water, bottled water) were also conducted. A possible uptake mechanism was suggested. Utilizing ethanol/water-pretreated orange peels (EOP) addresses organic biomass waste disposal and offers a cost-effective, readily available solution for heavy metal removal. Graphical Abstract: (Figure presented.)