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

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 (R-2 = 0.999) than the pseudo-first-order model (R-2 >= 0.929). The adsorption isotherm models showed that the Freundlich equation was suitable for PO43- removal by TB (R-2 = 0.975) and CTB (R-2 = 0.955). In contrast, the Langmuir equation was proper for PO43- removal by FTB (R-2 = 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.

Automated summary

Chemically-activated tangerine peel biochars showed enhanced efficiency in removing phosphate ions, with the adsorption process following pseudo-second-order kinetics or Langmuir model. However, the removal efficiency decreased with increasing ionic strength.