Mg/Al-layered double hydroxide modified biochar for simultaneous removal phosphate and nitrate from aqueous solution

To enhance the removal of phosphate and nitrate nutrients in wastewater with hard biochar, a two-step wet impregnation method was used to prepare a series of modified almond shell biochar (ASB) having different atomic ratios (x) of Mg/Al hydroxides (ASB-x). Several techniques (XRD, SEM/EDS, FTIR and N2 adsorption/desorption) were used to characterize the structure and adsorption behavior of the adsorbents. The results showed that both Mg/Al hydroxides were successfully introduced onto the surface of ASB in the form of the low crystallinity Mg/Al-layered double hydroxide structure. Optimum adsorption rates for phosphate (47.5%) and nitrate (27.7%) were attained when x was equal to three (ASB-3). The specific surface area (4.51 m2 g−1) and total pore volume (0.023 cm 3 g−1) of ASB-3 were greater than those of ASB (2.18 m2 g−1, 0.012 cm 3 g−1). Adsorption kinetics and isotherm studies also showed that ASB-3 had an improved rate of adsorption, affinity and capacity for phosphate and nitrate. ASB-3 may provide a potential alternative to carbon-based adsorbents for the removal of phosphates and nitrates from aqueous solutions.