Enhancing phosphate removal performance in water using La–Ca/Fe–LDH: La loading alleviates ineffective stacking of laminates and increases the number of active adsorption sites

Increasing the number of adsorption sites in layered bimetallic hydroxide (LDH), which is frequently used for phosphate removal in water, is a crucial step in enhancing phosphate adsorption. In this study, we investigate whether lanthanum (La) metal loading can improve the phosphate adsorption capacity of LDH. Based on Ca/Fe–LDH prepared through coprecipitation, a La–Ca/Fe–LDH composite is fabricated by La loading through impregnation. The adsorption capacity of La–Ca/Fe–LDH is 11.4% higher than that of Ca/Fe–LDH. The magnitude of adsorption and accelerated rate of adsorption of La–Ca/Fe–LDH satisfy the quasi-second-order kinetic and Langmuir isothermal equations. When comparing La–Ca/Fe–LDH to Ca/Fe–LDH, the adsorption capacity increased by 3.3%–328.39% in the pH range of 3–11; additionally, the resistance to pH influence and coexisting ion interference was considerably enhanced. However, under the coexistence of Cl−, NO3−, CO32−, SO42−, and F−, the adsorption capacity increased by 20.59%–27.6%. After three cycles of desorption, the phosphate removal abilit till increased by 11%, and the magnetic property was suitable for separation. The improvement of La–Ca/Fe–LDH adsorption capacity is attributed to the relief of ineffective stacking of LDH laminates and increased number of adsorption sites. The primary causes of adsorption are ion exchange, electrostatic attraction, and ligand exchange. In this study, a novel technique for enhancing LDH adsorption capability is proposed. This technique has numerous potential applications related to adsorbents in water treatment.