Lead(II) removal from aqueous solution using Citrus limettioides peel and its modified form: isotherms, kinetics and thermodynamic studies

Abstract

The Pb(II) adsorption capacity of carbon derived from Citrus limettioides peel (CLPC), which is a novel waste material, was evaluated regarding the contact time, pH and adsorbent dose during batch adsorption processes with raw C.limettioides peel (CLP). The optimal contact time for the adsorption of Pb(II) ions onto the peel and peel carbon was 3 h, and the optimal pH ranged from 4.0 to 5.0 for CLP and 4.0–6.0 for CLPC, respectively. The equilibrium data fit well with Langmuir isotherm, indicating that the Pb(II) ions formed a homogenous monolayer on the adsorbent surface. Maximum monolayer adsorption capacity of Pb(II) ions on peel (CLP) and peel carbon (CLPC) was found to be 125.00 and 166.67 mg g−1, respectively. The kinetic studies showed that the adsorption data followed a pseudo-second-order kinetic model. The surface morphology and functionality of the CLP and CLPC were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and FT-IR. Various thermodynamic parameters, including the standard Gibbs free energy (∆G°), standard enthalpy (∆H°) and standard entropy (∆S°), were evaluated. The CLP and CLPC were tested with Pb(II) plating wastewater through a batch mode process over five cycles; CLPC showed better results than CLP.