Metal Interactions at the Biochar-Water Interface: Energetics and Structure-Sorption Relationships Elucidated by Flow Adsorption Microcalorimetry
Interest in biochars and their role in the biogeochemical cycling of metals have increased in recent years. However, a systematic understanding of the mechanisms involved in biochar-metal interactions and conditions under which a given mechanism is predominant is still needed. We used flow adsorption micro-calorimetry to study structure-sorption relationships between twelve plant-derived biochars and two metals of different ionization potential (Ip). Biochar structure influenced the amount of K+ (Ip = 419 kJ mol-1) or Cd(II) (Ip = 868 kJ mol-17 ) sorption but had no effect on the mechanism of sorption. Irrespective of the biochar, K+ sorption was exothermic, surface-controlled and occurred via an ion-exchange mechanism on negatively- charged sites with molar heats of adsorption (_Hads) of -4 kJ mol-1 on wood versus -8 kJ mol-1 on grass biochars. In contrast, Cd(II) sorption was endothermic and favored surface complexation on uncharged biochar surfaces with _Hads of around +17 kJ mol-1. Cadmium sorption transitioned from surface- to diffusion-controlled on biochars formed at ≥ 350 oC and _Hads for Cd(II) sorption was the same on grass and wood biochars. We concluded that, in general, metals with lower Ip favor electrostatic interactions with biochars, while metals of higher Ip favor more covalent-like interactions.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1023180
- Report Number(s):
- PNNL-SA-80244; ESTHAG; TRN: US201118%%483
- Journal Information:
- Environmental Science & Technology, 45(13):5550-5556, Vol. 45, Issue 13; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Sorption selectivity of birnessite particle edges: a d-PDF analysis of Cd(
The influence of temperature on the adsorption of cadmium(II) and cobalt(II) on kaolinite