Engineering MgFe-Layered Double Hydroxide/Biochar Composites from Date Palm Residues for Enhanced Removal of Nitrate, Ammonium, and Phosphate from Aqueous Solutions

Excessive N and P discharges into aquatic environments contribute to water pollution and eutrophication. Thus, there is an urgent need for low-cost and sustainable adsorbents for contaminant removal. In this study, biochar was prepared from date palm fronds, leaves, and pits through slow pyrolysis followed by MgFe-LDH modification at a Mg/Fe molar ratio of 3:1. The FTIR results demonstrate that the MgFe-LDH modification added more hydroxyl groups, interlayer carbonate species, and metal–oxygen bonds. The removal efficiency of the investigated nutrients increased considerably with increasing sorbent dosage, with MgFe-LDH modification being most effective. Generally, sorption followed typical hyperbolic adsorption patterns, approaching equilibrium after 120–180 min. Both Langmuir and Freundlich isotherms adequately described nutrient sorption on unmodified biochars, while the Freundlich model provided a better fit on MgFe-LDH. LDH/BC derived from pits exhibited excellent adsorption capacities, i.e., 105 mg/g for NO3-, 103 mg/g for NH4+, and 135 mg/g for PO43-. Pseudo-second-order kinetics best described NH4+ adsorption, while both pseudo-first-order and pseudo-second-order models were well fitted to NO3- and PO43- adsorption. Overall, MgFe-LDH modification offers a promising engineering strategy for converting date palm residues into multifunctional adsorbents and offers insight into the design of waste-derived materials for nutrient recovery and eutrophication control.