Effects of pyrolysis temperature on nitrate-nitrogen (NO3--N) and bromate (BrO3-) adsorption onto date palm biochar.

Biochars (BCs) produced through biomass pyrolysis are highly efficient adsorbents for retaining dissolved cations in soil and water. However, their anionic sorption characteristics are unclear and depend on the feedstock used and the pyrolysis temperature. Herein, the adsorption of nitrate-nitrogen (NO3--N) and bromate (BrO3-) anions onto date palm biochar was evaluated by considering the pyrolysis temperature in relation with the initial concentrations, initial pH, and adsorbent dose. Biochars from date palm rachis were produced at 300 °C (BC300) and 700 °C (BC700). The latter exhibited the highest adsorption efficiency of NO3--N from aqueous solutions at an initial pH of 2, which was 25.8%-44.3% (at an adsorbent dose of 4 g L-1) and 47.0%-73.0% (at an adsorbent dose of 10 g L-1). In contrast, BC300 adsorbed BrO3- with an adsorption efficiency of 19.3%, 14.5%, 14.9%, and 13.6% at initial added concentrations of 5, 10, 15, and 20 μg L-1, respectively. However, BC700 showed zero adsorption for BrO3-. The results also showed that the non-linear models of Langmuir and/or Freundlich for NO3--N and BrO3- adsorption described the adsorption data better in most cases. It could be concluded that high pyrolysis temperature BC are suitable for adsorbing NO3--N, and low pyrolysis temperature BC may be used to adsorb BrO3-.