Adsorption Characteristics of Phosphate Ions by Pristine, CaCl₂ and FeCl₃-Activated Biochars Originated from Tangerine Peels

• Main Authors: Changgil Son, Wonyeol An, Geonhee Lee, Inho Jeong, Yong-Gu Lee, Kangmin Chon
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Separations
• Subjects: adsorption; biochar; chemical activation; phosphate ions; tangerine peel
• Online Access: https://www.mdpi.com/2297-8739/8/3/32

This study has evaluated the removal efficiencies of phosphate ions (PO₄³⁻) using pristine (TB) and chemical-activated tangerine peel biochars. The adsorption kinetics and isotherm presented that the enhanced physicochemical properties of TB surface through the chemical activation with CaCl₂ (CTB) and FeCl₃ (FTB) were helpful in the adsorption capacities of PO₄³⁻ (equilibrium adsorption capacity: FTB (1.655 mg g⁻¹) > CTB (0.354 mg g⁻¹) > TB (0.104 mg g⁻¹)). The adsorption kinetics results revealed that PO₄³⁻ removal by TB, CTB, and FTB was well fitted with the pseudo-second-order model (R² = 0.999) than the pseudo-first-order model (R² ≥ 0.929). The adsorption isotherm models showed that the Freundlich equation was suitable for PO₄³⁻ removal by TB (R² = 0.975) and CTB (R² = 0.955). In contrast, the Langmuir equation was proper for PO₄³⁻ removal by FTB (R² = 0.987). The PO₄³⁻ removal efficiency of CTB and FTB decreased with the ionic strength increased due to the compression of the electrical double layer on the CTB and FTB surfaces. Besides, the PO₄³⁻ adsorptions by TB, CTB, and FTB were spontaneous endothermic reactions. These findings demonstrated FTB was the most promising method for removing PO₄³⁻ in waters.