title: Adsorption and desorption of ammonium by maple wood biochar as a function of oxidation and pH.
abstract: The objective of this work was to investigate the retention mechanisms of ammonium in aqueous solution by using progressively oxidized maple wood biochar at different pH values. Hydrogen peroxide was used to oxidize the biochar to pH values ranging from 8.1 to 3.7, with one set being adjusted to a pH of 7 afterwards. Oxidizing the biochars at their lowered pH did not increase their ability to adsorb ammonium. However, neutralizing the oxygen-containing surface functional groups on oxidized biochar to pH 7 increased ammonia adsorption two to three-fold for biochars originally at pH 3.7-6, but did not change adsorption of biochars oxidized to pH 7 and above. The adsorption characteristics of ammonium are well described by the Freundlich equation. Adsorption was not fully reversible in water, and less than 27% ammonium was desorbed in water in two consecutive steps than previously adsorbed, for biochars with a pH below 7, irrespective of oxidation. Recovery using an extraction with 2M KCl increased from 34% to 99% of ammonium undesorbed by both preceding water extractions with increasing oxidation, largely irrespective of pH adjustment. Unrecovered ammonium in all extractions and residual biochar was negligible at high oxidation, but increased to 39% of initially adsorbed amounts at high pH, likely due to low amounts adsorbed and possible ammonia volatilization losses.
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China; Department of Crop and Soil Sciences, Cornell University, 909 Bradfield Hall, Ithaca, NY 14853, USA. Electronic address: wangbing@vip.gyig.ac.cn.
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, 909 Bradfield Hall, Ithaca, NY 14853, USA; Atkinson Center for a Sustainable Future, Cornell University, Ithaca, NY, USA.
authors.forename: Johannes
authors.initials: J
authors.lastname: Lehmann
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, 909 Bradfield Hall, Ithaca, NY 14853, USA.
authors.forename: Kelly
authors.initials: K
authors.lastname: Hanley
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, 909 Bradfield Hall, Ithaca, NY 14853, USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Hestrin
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, 909 Bradfield Hall, Ithaca, NY 14853, USA.
authors.forename: Akio
authors.initials: A
authors.lastname: Enders
mesh_terms: D031002:Acer; D000327:Adsorption; D064751:Ammonium Compounds / Q000032:analysis*; D002606:Charcoal / Q000737:chemistry*; D004787:Environmental Pollution / Q000517:prevention & control; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D010084:Oxidation-Reduction; D014934:Wood / Q000737:chemistry*
chemical_list: D064751:Ammonium Compounds; C540010:biochar; D002606:Charcoal
keywords: Adsorption; Ammonium; Biochar; Black carbon; Oxidation