The
solid–liquid equilibria data of the aqueous SrCl2–NH4Cl–MgCl2–H2O quaternary system at T = 298 K were measured.
Results show that there are three three-salt cosaturation invariant
points and five crystallization regions corresponding to one single
salt ammonium chloride (NH4Cl), three hydrate salts bischofite
(MgCl2·6H2O), strontium chloride hexahydrate
(SrCl2·6H2O), strontium chloride dihydrate
(SrCl2·2H2O), one double-salt ammonium
carnallite (NH4Cl·MgCl2·6H2O), and seven univariant curves in the phase diagram. The sizes of
the crystalline regions of the salts are in the order of NH4Cl > SrCl2·6H2O > NH4Cl·MgCl2·6H2O > SrCl2·2H2O > MgCl2·6H2O.
The solubilities of system
SrCl2–NH4Cl–MgCl2–H2O at 298 K were calculated based on the Pitzer ion interaction
model and its extended Harvie–Weare model. It can be seen from
the comparison of experimental and calculation diagrams that the predictive
solubilities agree well with the experimental values.
The equilibrium data on the aqueous quaternary system NH 4 Cl−CaCl 2 −AlCl 3 −H 2 O at 298.15 K were investigated by using the isothermal dissolution method, and the corresponding diagrams were constructed. There are three fields of crystalline in the phase diagram, which correspond to three single salts, aluminum chloride hexahydrate (AlCl 3 •6H 2 O), ammonium chloride (NH 4 Cl), and calcium chloride hexahydrate (CaCl 2 •6H 2 O). The main crystallization field is salt NH 4 Cl. The water content reaches the minimum value at the quaternary invariant point F, while the refractive index goes to the maximum value at point F. The equilibrium thermodynamics data of the calculation of the aqueous quaternary system NH 4 Cl− CaCl 2 −AlCl 3 −H 2 O at 298.15 K were done by using the Pitzer and extended Pitzer−Harvie−Weare thermodynamic model. It can be seen that the calculation values agree well with the experimental data.
The phase equilibria of the quaternary systems NH 4 Cl−SrCl 2 −AlCl 3 −H 2 O and NH 4 Cl−MgCl 2 −AlCl 3 −H 2 O at 298.2 K were investigated by using the isothermal dissolution method. The solubility, density, and refractive index of the systems were measured experimentally, and the related phase diagrams, density/refractive index versus composition diagrams, are plotted. There is one quaternary invariant point and three crystallization regions corresponding to single salts NH 4 Cl, AlCl 3 •6H 2 O, and SrCl 2 •6H 2 O in the phase diagram of the system NH 4 Cl−SrCl 2 −AlCl 3 −H 2 O at 298.2 K, which belongs to a simple system. In addition to the single salts NH 4 Cl, AlCl 3 •6H 2 O, and MgCl 2 •6H 2 O, the double salt NH 4 Cl•MgCl 2 •6H 2 O is formed in the quaternary system NH 4 Cl−MgCl 2 −AlCl 3 −H 2 O at 298.2 K, which indicates that the addition of magnesium makes the interaction relationship between Al 3+ , NH 4+ , and Mg 2+ more complex and increases the difficulty of separation of magnesium. The crystallization region of NH 4 Cl is the largest in both the systems, which indicates that NH 4 Cl is much easier to separate than the other salts from the two systems.
The East Asian monsoon system is an important part of global atmospheric circulation; however, records of the East Asian monsoon from different regions exhibit different evolutionary rhythms. Here, we show a high-resolution record of grain size and pollen data from a lacustrine sediment core of Dajiuhu Lake in Shennongjia, Hubei Province, China, in order to reconstruct the paleovegetation and paleoeclimate evolution of the Dajiuhu Basin since the late Middle Pleistocene (~237.9 ka to the present). The results show that grain size and pollen record of the core DJH-2 are consistent with the δ18O record of stalagmites from Sanbao Cave in the same area, which is closely related to the changes of insolation at the precessional (~20-kyr) scale in the Northern Hemisphere. This is different from the records of the Asian summer monsoon recorded in the Loess Plateau of North China, which exhibited dominant 100-kyr change cyclicities. We suggest that the difference between paleoclimatic records from North and South China is closely related to the east–west-oriented mountain ranges of the Qinling Mountains in central China that blocked weakened East Asia summer monsoons across the mountains during glacial periods.
Solid–liquid phase equilibria of quaternary system
NH4
+, Mg2+, Ca2+//Cl––H2O are investigated at T = 298.2
and 323.2 K and p = 94.77 kPa by the isothermal dissolution
equilibrium method, and the corresponding stable phase diagram, density
vs composition, and water content diagram are plotted at 298.2 and
323.2 K. Results show that when the temperature is 298.2 K, there
are three quaternary invariant points and five crystallization fields
corresponding to two double salts (2MgCl2·CaCl2·12H2O, NH4Cl·MgCl2·6H2O), two hydrate salts (MgCl2·6H2O, CaCl2·6H2O), and one single
salt (NH4Cl) in the phase diagram. When the temperature
is 323.2 K, the phase diagram structure of the system and the crystalline
form of the salt have changed, and there are four quaternary invariant
points and six crystallization regions including the four crystallization
forms existing at 298.2 K. The salt change is mainly reflected when
CaCl2·6H2O is dehydrated into CaCl2·2H2O at 323.2 K and a new double salt (2NH4Cl·CaCl2·3H2O) is formed at
323.2 K. The composition of double salt 2NH4Cl·CaCl2·3H2O is determined by chemical analysis and
thermogravimetric analysis.
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