Role of colloidal biochar in metals sequestration and transport

生物炭是植物通过火自然热解的产物，也是多种生物质通过人为热解的产物，用于农业土壤修复、碳固存和水处理技术。虽然生物炭在物理和化学性质方面得到了很好的研究，但它的相当一部分是由纳米颗粒热原碳（NPC）组成的。很少有研究调查了NPC的性质，其中只有少数研究了解了NPC对水和土壤中金属和营养物质的表面化学和反应性。为了解决这一差距，该研究计划建议从多种生物质（包括木材、草、污水污泥和城市垃圾）产生的生物炭中提取npc，并彻底表征它们的组成、表面化学和对水性物质的反应性。使用湿化学和光谱方法，将开发表面络合模型来预测金属和营养物质在各种环境条件下与NPC的结合。了解生物炭的老化和npc在环境中的降解也是预测其表面反应性的关键考虑因素。使用上面讨论的同一组生物炭，干湿加速老化将应用于大量生物炭来模拟长达100年的老化，并且从这些老化生物炭的时间序列中提取的NPC用于限制NPC表面化学随时间的差异-这对于理解金属和营养结合的变化以及NPC通过含水层的运输至关重要。每年野火产生的生物炭中有相当一部分（多达32%）最终通过河流和溪流进入海洋。因此，我们还将进行光氧化实验来模拟阳光对NPC功能性和反应性增加的影响。通过将这些调查线与全球热原碳生产的现有限制相结合，我们的目标是限制NPC在水文集水区和全球海洋中的金属和营养物质运输中的作用，无论是在现在还是在地质过去。森林火灾出现在泥盆纪，在白垩纪和二叠纪早期到中期达到顶峰，当时大气中的氧气含量可能高达35%。在这些条件下，NPC可能在将含水物种运送到河口的过程中发挥了相当大的作用——甚至与粘土和浮游微生物相比也是如此。如果NPC是营养物质和生物必需金属的来源或汇，它可能通过限制或促进微生物的生长对河口的初级生产力产生直接而深远的影响。反过来，这将直接影响到细胞与其他颗粒物质（如粘土、氧化铁和黑碳）的絮凝程度，沉积物的形成，并最终影响到我们今天观察到的海洋岩石地球化学记录。

Biochar a product of the natural pyrolysis of plants by fire, and via anthropogenic pyrolysis of numerous types of biomass for use in agricultural soil amendment, carbon sequestration, and water treatment technologies. While biochar is well-studied in terms of its physical and chemical properties, a considerable fraction of it is comprised of nanoparticulate pyrogenic carbon (NPC). Few studies have investigated the nature of NPC, and of those, only a handful have developed an understanding of the surface chemistry and reactivity of NPC towards metals and nutrients found in water and soils. To address this gap, this research program proposes to extract NPCs from biochars produced from numerous types of biomass - including wood, grasses, sewage sludge, and municipal waste - and thoroughly characterize their composition, surface chemistry, and reactivity towards aqueous species. Using wet chemical and spectroscopic approaches, surface complexation models will be developed to predict metals and nutrients binding to NPC across a wide range of environmental conditions. Understanding the aging of biochar and degradation of NPCs in the environment is also a critical consideration in predicting their surface reactivity. Using the same set of biochars discussed above, wet-dry accelerated aging will be applied to the bulk biochars to simulate up to 100 years of aging, and NPCs extracted from a time series of these aged biochars used to constrain differences in NPC surface chemistry over time - critical to understanding changes in metals and nutrients binding, and NPC transport through aquifers. A considerable fraction (as much as 32%) of the annual wildfire-produced biochar is ultimately transported to the oceans, much of this via rivers and streams. For this reason, we will also conduct photooxidation experiments to simulate the effect of sunlight on increased functionality and reactivity of NPC. By combining these lines of inquiry with existing constraints on global pyrogenic carbon production, we aim to constrain the role of NPC in metals and nutrients transport in hydrologic catchments and to the global oceans, both in the present and in the geologic past. Forest fires emerged in the Devonian and peaked in the Cretaceous and early to middle Permian, when atmospheric oxygen levels may have reached as high as 35%. At these conditions, NPC may have had a considerable role - even as compared to clays and planktonic microorganisms - in the transport of aqueous species to estuaries. If NPC is a source or sink of nutrients and bioessential metals, it may have had a direct and profound impact on primary productivity in estuaries by limiting or promoting the growth of microorganisms. This, in turn, would have a direct effect on the degree of flocculation of cells with other particulate matter such as clays, iron oxyhydroxides, and black carbon, the formation of sediments, and ultimately the geochemistry of the marine rock record we observe today.