Filtration by porous media: a microfluidics approach

<p>The transport of colloids in porous media is governed by deposition on solid surfaces and pore-scale flow variability. Classical approaches, like colloid filtration theory (CFT), do not capture behaviours observed experimentally, such as non-exponential steady state deposition profiles and heavy tailed BreakThrough Curves (BTC). In the framework of CFT, a key assumption is that the colloid attachment rate <span><span><span><span>𝑘</span></span></span></span> is constant and empirically estimated via a posteriori macroscopic data fitting. We design a novel experimental set-up based on time-lapse microscopy and continuous injection of fluorescent monodisperse colloids into a folded microfluidics device (1mt total length) designed with a controlled level of 2D spatial disorder. This set-up allows us to i) measure both BTC and deposition profile over several orders of magnitude and ii) to perform particle tracking and Lagrangian analysis of single colloid's trajectories. Based on this analysis, we propose a stochastic model that takes into account pore scale heterogeneities in terms of correlation length, velocity and attachment rate distribution, that captures the anomalous behaviour shown by the experimental data.</p>

Bentonite reactivity in alkaline solutions: interim results of the Cyprus Natural Analogue Project (CNAP)

Bentonite is one of the more safety-critical components of the engineered barrier system in the disposal concepts developed for many types of radioactive waste. It is used due to its favourable properties (including plasticity, swelling capacity, colloid filtration, low hydraulic conductivity, high retardation of key radionuclides) and its stability in relevant geological environments. However, bentonite is unstable under alkaline conditions and this has driven interest in low-alkali cements (leachate pH of 10–11). To build a robust safety case, it is important to have supporting natural analogue data to confirm understanding of the likely long-term performance of bentonite. In Cyprus, the presence of natural bentonite in close proximity to natural alkaline groundwaters permits the zones of potential bentonite/alkaline water reaction to be studied as an analogy of the potential reaction zones in the repository. Here, the results indicate minimal volumetric reaction of bentonite, with production of a palygorskite secondary phase.