Biosorption of Lead(II) from Aqueous Solution by Sodium Hydroxide Modified Auricularia auricular Spent Substrate: Isotherms, Kinetics, and Mechanisms

Abstract

In this study, Auricularia auricular spent substrate (AASS) was modified by sodium hydroxide and prepared as biosorbents to remove lead(II) from aqueous solution. The batch experiments showed that the biosorption capacity and biosorption percentage reached 36.35 mg g⁻¹ and 72.7% at initial concentration of 50 mg L⁻¹, pH 5, contact time of 200 min, and biosorbent dosage of 1 g L⁻¹. The biosorption of lead(II) onto modified AASS well fitted with the Langmuir isotherm model and the pseudo-second-order kinetic model with the maximum adsorption capacity(q _max) of 49.53 mg L⁻¹. The biosorption was an endothermic reaction and a spontaneous process based on positive value of ΔH ⁰ and negative value of ΔG ⁰. Fourier transform infrared (FTIR) analysis illuminated that amino and hydroxyl groups could bind lead(II) on biosorbent surface. Sodium hydroxide modification might enhance physical adsorption by enlarging surface area and pore volume as well as chemical adsorption by increasing ion exchange and forming crystalline species demonstrated by microscopy (SEM-EDX) and X-ray diffraction (XRD) analysis. After four regeneration cycles, the biosorption capacity of modified AASS still kept at 17.35 mg g⁻¹.

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