Reexamining ultrafiltration and solute transport in groundwater

Abstract

Geologic ultrafiltration-slowing of solutes with respect to flowing groundwater-poses a conundrum: it is consistently observed experimentally in clay-rich lithologies, but has been difficult to identify in subsurface data. Resolving this could be important for clarifying clay and shale transport properties at large scales as well as interpreting solute and isotope patterns for applications ranging from nuclear waste repository siting to understanding fluid transport in tectonically active environments. Simulations of one-dimensional NaCl transport across ultrafiltering clay membrane strata constrained by emerging data on geologic membrane properties showed different ultrafiltration effects than have often been envisioned. In relatively high-permeability advection-dominated regimes, salinity increases occurred mostly within membrane units while their effluent salinity initially fell and then rose to match solute delivery. In relatively low-permeability diffusion-dominated regimes, salinity peaked at the membrane upstream boundary and effluent salinity remained low. In both scenarios, however, only modest salinity changes (up to $3 g L 21) occurred because of self-limiting tendencies; membrane efficiency declines as salinity rises, and although sediment compaction increases efficiency, it is also decreases permeability and allows diffusive transport to dominate. It appears difficult for ultrafiltration to generate brines as speculated, but widespread and less extreme ultrafiltration effects in the subsurface could be unrecognized. Conditions needed for ultrafiltration are present in settings that include topographically-driven flow systems, confined aquifer systems subjected to injection or withdrawal, compacting basins, and accretionary complexes. By the early 20th century, it had been found that clay aggregates exhibit semipermeability [e.g., Lynde, 1912] and at least as early as 1933 it was suggested that clay-rich formations might behave as ultrafilters on a grand scale [Russell, 1933]. The idea resurfaced in succeeding years [e.g., Mackay, 1946; De Sitter, 1947; Berry, 1959], and for about two decades starting in the 1960s there was substantial interest in the notion of clay-rich formations as geologic membranes. Numerous experiments using refined, reconstituted, and occasional undisturbed clay materials demonstrated ultrafiltration [

Reactive Transport Modeling of Coupled Processes in Nanoporous Media

“…The low permeability of nanoporous media limits mass transport by advection, with the result that hydrodynamic dispersion is dominated in this case by molecular diffusion (Patriarche et al 2004a,b;Mazurek et al 2011). Consequently, the contribution of mechanical dispersion to the total flux is usually neglected for the modeling of nanoporous media (Gonçalvès et al 2015;Neuzil and Person 2017).…”

“…Because of their large specific surface area, most of the fluid volume in nanoporous media is influenced by the close proximity of mineral 1 surfaces, which explains the very low transmissivity of these materials. As a consequence, the experimental characterization of their permeability requires special techniques (Neuzil and Person 2017). Also, the large specific surface area of nanoporous material provides them with very high adsorption capacity.…”

“…These properties arise from the interactions of charged mineral surfaces with water and solutes present in the nanopores, which leads to coupling between flux terms. These couplings manifest themselves in macroscopic observations that have intrigued geologists for more than one century, such as geologic ultrafiltration, i.e., the accumulation of solutes on the inflow side of clay-rich lithologies (Lynde 1912;Neuzil and Person 2017).…”

Gravity‐Induced Bubble Ripening in Porous Media and Its Impact on Capillary Trapping Stability

“…This violates assumptions (5) and (7) listed in section S3. Classical single-phase Fickian diffusion may be more appropriate for describing CO 2 migration within cap rocks, although the exact physics are debated (Neuzil, 2013;Neuzil & Person, 2017). A detailed study is deferred to the future.…”

Research the Effect of the Filtration Coefficient's Deposit of Thin Clayinclusion From the Concentration of Chemical Substances on Value of Jump Pressures

“…Тобто, є актуальною задача дослідження взаємопов'язаних консолідаційних процесів та поширення забруднюючих речовин при наявності тонких включень. В роботі [1] досліджено явище ультрафільтрації (зворотного осмосу) в природних пористих середовищах, яке пов'язане з напівпроникними властивостями глин. Як відмічають автори, хоча вказане явище для глин було встановлене ще на початку 20-го століття, воно залишається до кінця не вивченим.…”