Abstract
The amine-rich surfaces of pyrolyzed human solid waste (py-HSW) can be "primed" or "regenerated" with carbon dioxide (CO(2)) to enhance their adsorption of ammonia (NH(3)) for use as a soil amendment. To better understand the mechanism by which CO(2) exposure facilitates NH(3) adsorption to py-HSW, we artificially enriched a model sorbent, pyrolyzed, oxidized wood (py-ox wood) with amine functional groups through exposure to NH(3). We then exposed these N-enriched materials to CO(2) and then resorbed NH(3). The high heat of CO(2) adsorption (Q (st)) on py-HSW, 49 kJ mol(-1), at low surface coverage, 0.4 mmol CO(2) g(-1), showed that the naturally occurring N compounds in py-HSW have a high affinity for CO(2). The Q (st) of CO(2) on py-ox wood also increased after exposure to NH(3), reaching 50 kJ mol(-1) at 0.7 mmol CO(2) g(-1), demonstrating that the incorporation of N-rich functional groups by NH(3) adsorption is favorable for CO(2) uptake. Adsorption kinetics of py-ox wood revealed continued, albeit diminishing NH(3) uptake after each CO(2) treatment, averaging 5.9 mmol NH(3) g(-1) for the first NH(3) exposure event and 3.5 and 2.9 mmol NH(3) g(-1) for the second and third; the electrophilic character of CO(2) serves as a Lewis acid, enhancing surface affinity for NH(3) uptake. Furthermore, penetration of (15)NH(3) and (13)CO(2) measured by NanoSIMS reached over 7 μm deep into both materials, explaining the large NH(3) capture. We expected similar NH(3) uptake in py-HSW sorbed with CO(2) and py-ox wood because both materials, py-HSW and py-ox wood sorbed with NH(3), had similar N contents and similarly high CO(2) uptake. Yet NH(3) sorption in py-HSW was unexpectedly low, apparently from potassium (K) bicarbonate precipitation, reducing interactions between NH(3) and sorbed CO(2); 2-fold greater surface K in py-HSW was detected after exposure to CO(2) and NH(3) than before gas exposure. We show that amine-rich pyrolyzed waste materials have high CO(2) affinity, which facilitates NH(3) uptake. However, high ash contents as found in py-HSW hinder this mechanism.