Low-Concentration Phosphate Removal Using Microwave-Assisted Granular Activated Carbon Modified by Magnesium

Objectives : In this study, we propose a new method for preparing magnesium-modified granular activated carbon (Mg-GAC) using microwave irradiation. The objective is to identify the optimal factors for efficiently removing low-concentration phosphate using the Mg-GAC.Methods : We impregnated Mg on activated carbon and modified Mg-GAC using microwave irradiation. Experiments were conducted with modification parameters such as impregnation time (1-12 hours), impregnation solution concentration (0.5-3 M), and microwave irradiation time (0-20 minutes). Factors affecting phosphate removal were set as pH (2-10) and reaction time (0-240 minutes), and were applied to kinetic models and isothermal adsorption models.Results and Discussion : After modification, particle distribution on the adsorbent's surface and 40-time increase in percent composition of Mg showed that Mg effectively coated to the GAC surface. At initial concentration of 2 mg P/L, the optimal modification conditions were 1-M Mg impregnation solution concentration, 2-hr impregnation time, and 10-min microwave irradiation time. The optimal experimental conditions for low phosphate removal efficiency were pH 4 and 180-min adsorption time. The difference of maximum removal efficiency between Mg-GAC (91.9%) and GAC (63.6%) was 28.3%. Mg-GAC is suitable for both Langmuir and Freundlich isotherm models, and the reaction kinetics followed a pseudo-second-order model. The microwave irradiation time for Mg-GAC preparation was 10 min, and the energy consumption was 0.55 kWh/g, which showed that microwave irradiation is one of promising methods for modification of GAC by metal.Conclusion : The Mg-GAC modified by magnesium and microwave irradiation enhanced removal efficiency for low-concentration phosphate compared with GAC.