Lanthanum carbonate grafted ZSM-5 for superior phosphate uptake: Investigation of the growth and adsorption mechanism

High-efficiency phosphate removal from wastewater is crucial for protecting environmental stability. In this work, a lanthanum carbonate grafted ZSM-5 adsorbent (LC-ZSM-5) was prepared and optimized by a BoxBehnken design. The higher temperature, molar ratio of urea to lanthanum and initial lanthanum concentration are beneficial for LC-ZSM-5 synthesis, and the adsorption capacity of LC-ZSM-5 under optimistic conditions was 91.2 mg-PO43-/g. The growth mechanism indicates that the LC particles grow larger with synthesis time and finally agglomerate, and 12 h is the best synthesis time. The thermodynamic results show that phosphate adsorption over LC-ZSM-5 is a spontaneously exothermic and combined physicochemical adsorption process. Kinetic studies suggest that higher temperatures help increase the phosphate adsorption rate, and chemical adsorption plays an important role during adsorption with an activation energy Ea of 42.7 kJ/mol. The adsorption mechanism of the phosphate uptake process includes electrostatic attraction and ligand exchange, through which LC is changed to lanthanum phosphate (LP) during adsorption. Finally, the regeneration study revealed that LC-ZSM-5 still exhibited a high adsorption capacity after 5 cycles, showing its satisfactory regeneration ability and potential industrial application.