Mathematical modeling of the effects of aerobic and anaerobic chelate211 bioegradation on actinide speciation

摘要

Biodegradation of natural and anthropogenic chelating agents directly and211u001eindirectly affects the speciation, and, hence, the mobility of actinides in 211u001esubsurface environments. We combined mathematical modeling with laboratory 211u001eexperimentation to investigate the effects of aerobic and anaerobic chelate 211u001ebiodegradation on actinide (Np(IV/V), Pu(IV)) speciation. Under aerobic 211u001econditions, nitrilotriacetic acid (NTA) biodegradation rates were strongly 211u001einfluenced by the actinide concentration. Actinide-chelate complexation reduced 211u001ethe relative abundance of available growth substrate in solution and actinide 211u001especies present or released during chelate degradation were toxic to the 211u001eorganisms. Aerobic bio-utilization of the chelates as electron-donor substrates 211u001edirectly affected actinide speciation by releasing the radionuclides from 211u001ecomplexed form into solution, where their fate was controlled by inorganic 211u001eligands in the system. Actinide speciation was also indirectly affected by pH 211u001echanges caused by organic biodegradation. The two concurrent processes of organic 211u001ebiodegradation and actinide aqueous chemistry were accurately linked and 211u001edescribed using CCBATCH, a computer model developed at Northwestern University to 211u001einvestigate the dynamics of coupled biological and chemical reactions in mixed 211u001ewaste subsurface environments. CCBATCH was then used to simulate the fate of Np 211u001eduring anaerobic citrate biodegradation. The modeling studies suggested that, 211u001eunder some conditions, chelate degradation can increase Np(IV) solubility due to 211u001ecarbonate complexation in closed aqueous systems.