Carboxyl and hydroxyl groups enhance ammonium adsorption capacity of iron (III) chloride and hydrochloric acid modified biochars.

The effectiveness of the modification of wheat straw biochar using FeCl and HCl, alone or combined, on ammonium adsorption was evaluated using kinetic and isotherm models. The adsorption mechanisms were studied by comparative analysis of the surface properties of the biochars before and after ammonium adsorption. The results indicate that the modification methods enhanced the ammonium adsorption capacity by at least 14%, due to the increased OH and OCO functional groups and specific surface area, and increased Fe/Fe redox coupling serving as an electron shuttle. It can be concluded that chemical modification of wheat straw biochars using FeCl and HCl increased the effectiveness of biochars for the treatment of ammonium-contaminated wastewater.