Infiltration Of Salt Solutions Research Articles

Infiltration of salt solutions through illite particles: Effect of nanochannel size and cation type

Water infiltration through soil particles is of great importance in determining the availability of elements and soil texture. However, process of water infiltrate into the capillary nanochannels and influence of nanochannel size and cation type as well as the underlying mechanism are still lacking, especially at the molecular level. Here, molecular dynamics simulation was used to investigate the infiltration of NaCl and CaCl2 solutions through 1.5, 3, 5, and 10 nm illite channels. At the initial stage, obvious regression of the advanced frontier of salt solution was observed. Water molecules and cations easily accumulated at the entrance of nanochannels, which was clearer in small-sized nanochannels. The infiltration velocity increased with increasing nanochannel size, though time for water saturating the illite nanochannel showed an opposite trend. Both Na+ and Ca2+ exhibited obvious inner-sphere adsorption during the infiltration, but Ca2+ showed more outer-sphere adsorption compared to Na+. Diffusion coefficients of both water and cations were higher in the small- than large-sized nanochannel, which was related to the unsaturated condition, capillary force, and interplay between illite-water interaction and surface tension. By using MD method, this study is the first time, to our knowledge, to investigate the unsaturated capillary infiltration of water in clay soil nanochannels, which is hard to achieve using traditional experimental tools. Results showed that, besides the generally considered interaction between soil particles, cation-clay interactions coupled with nanochannel size were of great importance in affecting the unsaturated infiltration of water and cations. This study provides a new clue in understanding the availability of soil water and stability of soil aggregates.

Swelling deformation of compacted GMZ bentonite experiencing chemical cycles of sodium-calcium exchange and salinization-desalinization effect

In China, GMZ bentonite has been recognized as the first choice of buffer material while Beishan area in Gansu province has been considered as the potential disposal site for high-level radioactive waste (HLW) repository. As the groundwater at the repository field is rich in Na+ and Ca2+, the swelling properties of compacted GMZ bentonite will be affected by the chemistry of groundwater. In this work, the swelling deformation behaviors of compacted GMZ bentonite were tested at a vertical stress of 0.1MPa to assess the influence of cation exchange between Na+ and Ca2+, as well as the salinization-desalinization effect by cyclical infiltrations of distilled water and saline solutions. Results show that Na-bentonite is partly transformed into Ca-bentonite once NaCl solution is replaced with CaCl2 solution. Comparing to NaCl solution, the inhibiting effect of CaCl2 solution is weak, and thus the additional swelling is observed. Along with chemical cycles, the total strain of compacted GMZ bentonite gradually increases, while the chemical sensitivity of strain behavior reduces. This tendency is also detected for GMZ bentonite experiencing the desalinization path of distilled water prior to each infiltration of salt solution. Regarding the relative strain of GMZ bentonite, the difference in osmotic suction between distilled water and salt solution is more relevant than the sodium-calcium replacement.

Specific Water Regime in Technogenic Soils: Preferential Water Flow Formation

Technogenic soil (technozem) was created on the surface of the former sludge pond of the iron-ore quarry in the course of land rehabilitation. The upper chernozemic layer in the technozem was underlain by sandy or loamy layers. The soil land reclamation constructions were created 20 years ago: the chernozemic 60-cm layer with classical granular fine and medium-size aggregates (1-5mm) was sprinkled on the deep layer of sand. This construction was in agricultural use during the last 20 years. At present, the layers of prismatic coarse peds (>50mm) bounded by flat to rounded vertical faces and columnar, very thick, vertically oriented blocks (>100mm) have been formed at the depths 20-40 and 40-60cm. The water regime of these soils differed from that of the background automorphic natural soils and was characterized by periods of water stagnation at the boundary between the two layers. In the course of 20 years, this type of water regime resulted in the development of a columnar structure in the lower part of the chernozemic layer. The coatings on the ped faces in this part of the profile had an increased content of Fe and Ca ions. There was no differentiation of the carbon of organic substances and carbonates in the soil profile. Field studies of water flows in this soil based on starch label and laboratory experiments on infiltration of salt solutions though the soil columns with determination of breakthrough curves demonstrated the existence of preferential water flows in technozem. Rapid infiltration of water through preferential water paths in chernozemic layer after abundant rainfalls and during the snowmelt season leads to the development of perched water above the textural boundary. This preferential water and matter flows are generated along the faces of the peds and form the perched water layer on the sand. Such kind of water phenomenon with preferential flows and perched water table formation transforms the granular aggregates into columnar blocks by the temporary gleyzation process.

Structural status of technogenic soils and the development of preferential water flows

A technogenic soil (technozem) created on the surface of the former sludge pond of the Lebedinskii iron-ore quarry in the course of land rehabilitation was studied. The upper chernozemic fill in the technozem was underlain by the sandy or loamy layers. The water regime of this soil differed from the water regime of background automorphic natural soils and was characterized by a periodic stagnation of water at the boundary between the two layers. In 20 years, this type of the water regime resulted in the development of a columnar structure in the lower part of the chernozemic layer. The coatings on ped faces in this part of the profile had an increased content of Fe and Ca ions, and the soil texture became coarser under conditions of the alkaline medium. There was no differentiation of the carbon of organic substances and carbonates in the soil profile. Field studies of water flows in this soil with the use of starch label and laboratory experiments on infiltration of salt solutions through the soil columns with determination of ion concentrations in separate portions of the filtrate demonstrated the existence of preferential water flows in the technozem. Rapid infiltration of water through preferential water paths in the chernozemic layer after abundant rainfalls and during the snowmelt season leads to the development of perched water above the textural boundary. Temporary water stagnation in this zone ensures an increased water content in the intraped mass of columnar peds in the lower part of the chernozemic layer.

Doping of optical fiber preforms via porous silica layer infiltration with salt solutions

A process is described for reproducible deposition of porous layers uniform along the preform axis, and the effect of the nature of the solvent on the infiltration of salt solutions into the porous layer is analyzed in relation to the fabrication of fiber preforms with controlled doping level. Data are presented on the variation of the retention volume in the porous layer with sintering temperature.