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，用于农业土壤改良、碳封存和水处理技术。 虽然生物炭在其物理和化学性质方面得到了很好的研究，但其中相当一部分是由纳米颗粒热解碳（NPC）组成的。 很少有研究调查NPC的性质，其中只有少数研究了解NPC对水和土壤中发现的金属和营养物质的表面化学和反应性。 为了解决这一差距，该研究计划提出从多种类型的生物质（包括木材，草，污水污泥和城市垃圾）产生的生物炭中提取NPC，并彻底表征其组成，表面化学和对水性物种的反应性。 使用湿化学和光谱方法，将开发表面络合模型，以预测金属和营养物质结合到NPC在广泛的环境条件。 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。 使用与上述相同的一组生物炭，将对散装生物炭进行干湿加速老化，以模拟长达100年的老化，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物结合的变化以及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（高达32%）最终被运往海洋，其中大部分通过河流和溪流。 出于这个原因，我们还将进行光氧化实验，以模拟阳光对NPC功能性和反应性增加的影响。 通过将这些调查与全球热解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过去的地质中。 森林火灾出现在泥盆纪，在白垩纪和早二叠世至中二叠世达到顶峰，当时大气中的氧气含量可能高达35%。 在这些条件下，NPC可能有相当大的作用-即使相比粘土和浮游微生物-在运输的水性物种的河口。 如果NPC是营养物质和生物必需金属的源或汇，则它可能通过限制或促进微生物的生长而对河口的初级生产力产生直接而深刻的影响。 反过来，这将直接影响细胞与其他颗粒物质（如粘土、铁氢氧化物和黑碳）的絮凝程度，沉积物的形成，以及最终影响我们今天观察到的海洋岩石记录的地球化学。

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.