Adsorption of Inorganic Carbon on Volcanic Rock: Implications for Global CO2 Budgets and 14C-Dating of Groundwater (Pilot Study)

无机碳在矿物相上的吸附一直是许多不同研究领域的研究人员感兴趣的问题，但人们对形成岩石的矿物上的吸附在全球二氧化碳汇中可能起的作用知之甚少，也不知道它如何影响地下水中的14C定年。初步结果表明，CO2的吸附可能占陆地CO2汇的一小部分但很重要，并且水相和吸附相之间的交换可能影响地下水中的14C定年。初步数据来自对凝灰岩（长英质火山岩）的实验。岩心样品在钻探时从大气中分离出来，然后在真空下打开并加热，以从岩石孔隙中的水中提取无机溶解碳（DIC）。碳回收率超过可用DIC表明，在这些岩石中存在相当大的吸附碳储集层。提出了一项试点项目，研究在干燥、湿润和饱和条件下，代表长英质和基性矿物的5种火山岩材料对CO2的吸附和相关同位素分馏。样品在使用前将进行表面积、孔隙对称性和矿物学表征。对于干湿实验，破碎的岩石将在2000℃预热以产生吸附等温线，并在6000℃再次预热以确定可能存在的微量有机涂层的效果。吸附等温线将在干燥条件下和存在单层吸附水的情况下测量。同位素分馏将通过收集平衡后的顶空气体和测量初始和平衡CO2的碳碳含量来评估。同位素交换将通过重新引入具有独特d13 C特征的二氧化碳并在平衡后再次测量顶空气体来评估。通过将二氧化碳引入饱和泥浆的头部空间，并监测头部空间的二氧化碳浓度和pH值，以计算水相和吸附相的质量分配，可以测量饱和系统中的吸附作用。同位素分馏和交换的测量方法与干法和湿法实验相同。这项工作的结果将作为估计CO2作为大气CO2陆地汇的吸附量的第一步，以及吸附和交换可能改变地下水中14C活动的程度。这些结果也将用于制定更有针对性的吸附位点和机理的研究。该研究的教育影响包括研究生和本科生水平的学生培训。

Davidson-0210003Adsorption of inorganic carbon on mineral phases has been of interest to researchers in many different fields of study, but little is known about the role that adsorption on rock-forming minerals may play in global CO2 sink, or how it may affect 14C dating in groundwater. Preliminary results suggest that adsorption of CO2 could account for a small but significant percentage of the terrestrial CO2 sink, and exchange between the aqueous and adsorbed phase could influence 14C dating in groundwater. The preliminary data comes from experiments with tuff (felsic volcanic rock). Core samples were isolated from the atmosphere at the time of drilling, and were later opened and heated under vacuum to extract inorganic dissolved carbon (DIC) from water in the rock pores. Carbon recoveries in excess of available DIC suggest that a sizeable reservoir of adsorbed carbon exists in these rocks.A pilot project is proposed to investigate CO2 adsorption and associated isotopic fractionation on five volcanic rock materials representing suites of felsic and mafic minerals under dry, wetted, and saturated conditions. Samples will be characterized for surface area, porosymmetry and mineralogy before use. For dry and wetted experiments, crushed rock will be preheated at 2000C to generating adsorption isotherms, and again at 6000C in order to quatify the effect of trace organic coatings that may be present. Adsorption isotherms will be measured under drying conditions and in the presence of a mono-layer of adsorbed water. Isotopic fractionation will be evaluated by collecting head space gases after equilibration and measuring the d 13C of initial and equilibrated CO2. Isotopic exchange will be evaluated by reintroducing CO2 with a unique d13 C signature and measuring head space gases again after equilibration. Adsorption in saturated systems will be measured by introducing CO2 into the head space of a saturated slurry and monitoring the head space CO2 concentration and the pH to calculate the mass partitioned into the aqueous and adsorbed phases. Isotopic fractionation and exchange will be measured in the same fashion as for dry and wetted experiments.Results from this work will be used as a first step in estimating the magnitude of CO2 adsorption as a terrestrial sink of atmospheric CO2, and the extent to which adsoption and exchange may alter 14C activities in groundwater. The results will also be used to formulate a more targeted study of adsorption sites and mechanisms. Educational impacts of the study include student training at both the graduate and undergraduate level.