Preparation and application of MgO-loaded tobermorite to simultaneously remove nitrogen and phosphorus from wastewater

In this work, three types of nanosized magnesium oxide (MgO) modified tobermorite (TOB) were synthesized through a gelation-calcination method. The prepared adsorbents were applied to simultaneously remove N and P from the simulated and actual wastewater through struvite method. Characterizations of the adsorbents including XRD, XPS, FTIR, SEM-EDS, TEM, BET and sedimentation experiment were conducted and proved that MgO was successfully loaded on TOB. The influences of contact time, adsorbent dosage, initial solution pH and temperature on N and P removal were explored. The modified TOB exhibited excellent removal performance in a wide range of pH due to the ability to regulate pH spontaneously, and this ability was under better control after carbon template was introduced. With suitable adsorbent dosage, both TOB@MgO2 and TOB@MgO3 could remove over 80 % of N and nearly 100 % of P in 15 min and 4 h respectively. Additionally, the removal efficiency was slightly affected by temperature. The process of N and P removal could be better described by the pseudosecond-order kinetic model, indicating it was mainly controlled by surface chemical reactions. TOB was not only used as the carrier for MgO loading but also could collaborate with MgO to remove N and P, especially for P removal. Besides the diversified chemisorption, physisorption also played a nonnegligible role in the removal. Finally, the pot experiment confirmed the feasibility of directly using the modified TOB after adsorption as a slow-release fertilizer.