Geochemical evolution of groundwater - the composition of groundwater changes along its flow path from fresh recharge water (CaHCO3 type) to different water types. How NaHCO3 type of water is formed? In some areas, the NaHCO3 type of water is found with high fluoride (F) and silica (SiO2) concentrations.
Check papers that cite Foster (1950, Geochimica et Cosmochimica Acta, v.1, p. 33-48). NaHCO3-type water forms when fresh groundwater invades an area that previously contained seawater or a sodium-rich brine derived from seawater. The Na in seawater takes up exchange sites in the sediments. When fresh groundwater invades, the Ca of standard Ca-HCO3-type groundwater exchanges with the Na. For silica, porewaters are often supersaturated with with SiO2 relative to quartz, e.g. Abercrombie et al. (1994, Geology v. 22, p. 539-542), so "high" silica is a relative term. High F sounds like a relatively local phenomenon, but you could start with Deng et al. (2011, Geochimica et Cosmochimica Acta 75:4476-4489).
Type of water - its formation & evolution with time & transport is governed by the principles of Chebotarev sequence as well as ion exchange mechanism between the fluid and its carrier medium. A bicarbonate type suggests young water. The Na may be either due to NaCl remnants or might be contributed by Sodic feldspars and feldspathoids in the country rock / sediment
The NaHCO3 type of groundwater is mainly derived from ion exchange process. The Na+-,adsorbed to the clay surfaces are successively being replaced by Ca2+-ions in order of increasing affinity for the clay or due to weathering of plagioclase feldspars in the groundwater .
Bicarbonate is mainly associated with precipitation and subsurface lithologic characters (particularly limestone aquifer) .
some places, mostly in coastal areas the NaHCO3 type indicate paleo marine depositional environment or passing through paleo marine channels
In my experience, either natural softening or the shale membrane effect may result in NaHCO3 waters, often with high fluoride and high pH. A couple of refs:
White 1965 Saline waters of sedimentary rocks, in AAPG symposium Fluids in Subsurface Environments, p 342-366.
van Everdingen 1968 Mobility of main ion species in reverse osmosis and the modification of subsurface brines, in Can J Earth Sciences vol 5, p 1253-1260.
When CO2 is dissolved in water, carbonic acid is formed and this is very much unstable. Soon it's formation carbonic acid changed to HCO3. Thus bicarbonate is formed. In water chemistry, ions are present in pair form ( anion and cation ). Bicarbonate has great affinity with Na and Ca ,and thus NaHCO3 and CaHCO3 are formed. However presence of F and SiO2 are depend upon natural ( mineral water interaction ) and anthropogenic sources along with dissociation and dissolution processes.in addition to this, various other factors are responsible.
It depends on the aquifer lithology from wich the water derived. Generally, the high SiO2 and F contents are always associated with water derived from Igneous (Granitic) aquifer. If the water passed through sedimentary sequence containing clay layers (before entring the Igneous aquifer), it may be subjected to cation exchange and acquire NaHCO3 type.
Я посмотрел все ответы. В них только часть процесса. Для того, чтобы получилась содовая вода необходимо убрать кальций и сульфаты. В этих водах кроме фтора есть сероводород, который появляется в результате деятельности специфических бактерий разлагающих сульфаты. А кальций обменивается на натрий в глинах. В результате вода частично деминерализуется.
Всего наилучшего!
dear Asit Kumar,
the paper in attached file is useful for you
best wishes
Thanks to Dr. Valeriy and Dr. Kamel for providing useful information.
I agree with the sincere views expressed by all others in this discussion.
Also, you may be aware of that "Groundwater with different flow paths may undergo different natures and extents of water-rock interaction. Na+, Ca2+, and HCO3 may be mainly derived from the weathering of plagioclase feldspar. The generally low HCO3 indicates low degrees of water-rock interactions in the form of weathering. Na+ and SiO2. The source of Na+ and SiO2 is likely to be the weathering of sodic feldspar. Plagioclase feldspar is usually the first primary mineral to be weathered significantly, followed by K-feldspar and biotite at a later stage, while quartz should be the most stable of all the minerals. Given the short residence time of shallow groundwater, K-feldspar and biotite may not be significantly weathered. High F and SiO2 presence may also depend on various dissociation and dissolution processes during rock-water interaction and contributions from anthropogenic sources.
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