Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
Environ Sci Technol. 2010 Oct 15;44(20):7833-8. doi: 10.1021/es1019788.
A microfluidic pore structure etched into a silicon wafer was used as a two-dimensional model subsurface sedimentary system (i.e., micromodel) to study mineral precipitation and permeability reduction relevant to groundwater remediation and geological carbon sequestration. Solutions containing CaCl(2) and Na(2)CO(3) at four different saturation states (Ω = [Ca(2+)][CO(3)(2-)]/K(spCaCO(3))) were introduced through two separate inlets, and they mixed by diffusion transverse to the main flow direction along the center of the micromodel resulting in CaCO(3) precipitation. Precipitation rates increased and the total amount of precipitates decreased with increasing saturation state, and only vaterite and calcite crystals were formed (no aragonite). The relative amount of vaterite increased from 80% at the lowest saturation state (Ω(v) = 2.8 for vaterite) to 95% at the highest saturation state (Ω(v) = 4.5). Fluorescent tracer tests conducted before and after CaCO(3) precipitation indicate that pore spaces were occluded by CaCO(3) precipitates along the transverse mixing zone, thus substantially reducing porosity and permeability, and potentially limiting transformation from vaterite to the more stable calcite. The results suggest that mineral precipitation along plume margins can decrease both reactant mixing during groundwater remediation, and injection and storage efficiency during CO(2) sequestration.
采用硅片上蚀刻的微流控孔隙结构作为二维亚表面沉积系统（即微模型），研究与地下水修复和地质碳封存相关的矿物沉淀和渗透率降低。通过两个单独的入口引入含有 CaCl(2)和 Na(2)CO(3)的溶液，在四个不同的饱和度状态（Ω = [Ca(2+)][CO(3)(2-)]/K(spCaCO(3)))下，它们沿微模型的中心横向扩散混合，导致 CaCO(3)沉淀。随着饱和度状态的增加，沉淀速率增加，总沉淀物量减少，并且仅形成文石和方解石晶体（无霰石）。文石的相对量从最低饱和度状态（Ω(v) = 2.8 为文石）的 80%增加到最高饱和度状态（Ω(v) = 4.5）的 95%。沉淀 CaCO(3)前后进行的荧光示踪剂测试表明，CaCO(3)沉淀物沿横向混合区堵塞了孔隙空间，从而大大降低了孔隙度和渗透率，并可能限制了从文石向更稳定的方解石的转化。结果表明，羽流边缘的矿物沉淀可以降低地下水修复过程中的反应物混合程度，以及 CO(2)封存过程中的注入和存储效率。
