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 N-2 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 m(2) g(-1)) and total pore volume (0.023 cm(3) g(-1)) of ASB-3 were greater than those of ASB (2.18 m(2) 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. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

In this study, modified almond shell biochar (ASB) with different Mg/Al ratios was prepared using a two-step wet impregnation method, with ASB-3 showing the highest adsorption rates for phosphate and nitrate. ASB-3 exhibited larger specific surface area and total pore volume, as well as improved adsorption kinetics, affinity, and capacity for phosphate and nitrate.