Direct numerical simulation of continuous lithium extraction from high Mg2+/Li+ ratio brines using microfluidic channels with ion concentration polarization

Abstract

A novel ion concentration polarization-based microfluidic device is proposed for continuous extraction of Li+ from high Mg2+/Li+ ratio brines. With simultaneous application of the cross-channel voltage that drives electroosmotic flow and the cross-membrane voltage that induces ion depletion, Li+ is concentrated much more than other cations in front of the membrane in the microchannel. The application of external pressure produces a fluid flow that drags a portion of Li+ (and Na+) to flow through the microchannel, while keeping most of Mg2+ (and K+) blocked, thus implementing continuous Li+ extraction. Two-dimensional numerical simulation using a microchannel of 120 µm length and 4 µm height and a model, highly concentrated brine, shows that the system may produce a continuous flow rate of 1.72 mm/s, extracting 25.6% of Li+, with a Li+/Mg2+ flux ratio of 2.81×103, at a pressure of 100 Pa and cross-membrane voltage of 100 times of thermal voltages (25.8 mV). Fundamental mechanisms of the system are elaborated and effects of the cross-membrane voltage and the external pressure are analyzed. These results and findings provide clear guidance for the understanding and designing of microfluidic devices not only for Li+ extraction, but also for other ionic or molecular separations.

A review: applications of ion transport in micro‐nanofluidic systems based on ion concentration polarization

“…Gong et al . proposed a novel microfluidic device based on the principle of ICP for the continuous extraction of Li + from high Mg 2+ :Li + ratio brine . They simultaneously applied a cross‐channel voltage that drives electro‐osmotic flow and a transmembrane voltage that causes ion depletion on the microfluidic device.…”

Continuous focusing, fractionation and extraction of anionic analytes in a microfluidic chip

“…For a more extensive theoretical description of ICPF the reader is referred to the recent report by Ouyang et al 11 In addition the feasibility of extraction of concentrated (cationic) analytes via ICPF was reported via numerical simulations of similar systems. 12,13 ICPF is based on differential ionic migration in an electric field gradient. The electrical field gradient is created by applying a steady potential difference over a microchannel which contains a region in the axial direction with a salt concentration gradient.…”

Ion concentration polarization and its application in molecular preconcentration in micro-nanofluidic systems

“…21世纪初以来, 微纳流控芯片技术的发展, 使得在 纳米尺度上精确控制离子和带电分子的输运成为可 能 [33~37] , 为离子选择性输运及ICP现象的研究提供了 新的手段, 也为开发其潜在应用提供了重要的技术基 础 [38~40] . 目前, 除前面提到的分子富集系统 [21~24] 外, 基 于 I C P 效 应 的 微 纳 流 控 技 术 还 在 分 子 或 离 子 分 离 [41,42] 、海水淡化 [43~46] 、能量收集 [47] 和生物传感 [48] 等领域得到了广泛的应用. [87,88] .…”