Adsorptive Removal of Nitrate and Phosphate Using MCM-48, SBA-15, Chitosan, and Volcanic Pumice

The nitrate and phosphate adsorption capacities of laboratory made and naturally available adsorbents were studied in this study. Two mesoporous silica materials, Mobil composition of matter no. 48 (MCM-48) and Santa Barbara Amorphous-15 (SBA-15), were hydrothermally synthesized, and chitosan was made by reacting crab shells with sodium hydroxide. Pumice powder was prepared by grinding volcanic rocks. All adsorbent powders were characterized by nitrogen adsorption/desorption, X-ray diffraction, Fourier transform infrared (FT-IR), scanning electron microscope (SEM), and high-resolution transmission electron microscopy (TEM) to check their physical properties and surface morphology as adsorbent materials. The adsorption isotherm data of nitrate and phosphate were described by both Langmuir and Freundlich isotherm models. In general, phosphate adsorption isotherms seem to be favorable while some of nitrate adsorption isotherms are slightly unfavorable and linear. Furthermore, the pseudo-second kinetic model is good in describing the batch adsorption rates. Among four adsorbent materials, MCM-48 shows the highest adsorption capacity for both nutrients while the adsorption capacity of SBA-15 is much lower than expected. It should be noted that pumice has considerably high adsorption ability for phosphate and chitosan has good capacity for nitrate even if they have much lower Brunauer, Emmett, and Teller (BET) surface area than mesoporous silica materials.