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Surface-charging and particles aggregation behavior of ascharite

Li Zhihang, Han Yuexin, Zuo Kesheng

Physicochemical Problems of Mineral Processing

2019

Vol. 55, iss. 4

991--1001

Surface charging and particles aggregation ascharite are investigated through Zeta potential measurement, XPS analysis, SEM analysis and dissolution experiments. The results show that more Mg2+ are removed from ascharite surface after dissolution, which confirms that incongruent dissolution of ions in the case of certain ionic substances like rmagnesium ions, hydroxyl groups and borate ions can lead to a net charge on surface. Isomorphous substitution of Fe3+ for Mg2+ is also regarded as one factor that causes surface charging behavior, which is in consistent with the experimental data. The dissolution process is analyzed to show more details about the dissolution reactions. The disparity in the bonding energy of B–O and Mg–OH surface groups and the difference in free energy of hydration of surface groups are considered to be the basic reason that lead to incongruent dissolution. Eventually, the effect of surface potential on particles aggregation is analyzed by DLVO theory, indicating that dissolution of ascharite has a detrimental effect on particles dispersion.

Weathering in a regolith on the Werenskioldbreen Glacier forefield (SW Spitsbergen). 2. Speciation of Fe, Mn, Pb, Cu and Zn in the chronosequence

Rzepa Grzegorz, Manecki Maciej, Jakubski Grzegorz, Kwaśniak-Kominek Monika, Czerny Jerzy, Górniak Dorota

Annales Societatis Geologorum Poloniae

2019

Vol. 89, No. 3

317--341

The evolution of chemical speciation of Fe, Mn, Pb, Cu, and Zn was investigated in the chronosequence of young sediments, exposed by a currently retreating Arctic glacier on Spitsbergen. Werenskioldbreen is a 27 km2 subpolar, land-terminated, polythermal glacier in recession, located near the SW coast of West Spitsbergen. Three samples of structureless till were collected at locations exposed for 5, 45 and 70 years. Four grain-size fractions were separated: > 63, 20–63, 2–20, and < 2 µm. Speciation of Fe, Mn, Pb, Cu, and Zn was determined using a 6-step sequential chemical extraction method: 1) 1 M sodium acetate, 2) 1 M hydroxylamine hydrochloride in acetic acid, 3) sodium dithionite in buffer, 4) acid ammonium oxalate, 5) boiling HCl, 6) residuum. The weathering in the proglacial area of the retreating glacier is very fast. The geochemical fates of the metals in question correlate with each other, reflecting a) the geochemical similarities between them, b) the similarities of their primary mineral sources, c) the significant role of incongruent dissolution. The weathering processes dominating the system are redox reactions and incongruent dissolution, followed by precipitation of secondary phases and partial sorption of aqueous species. As a result, the elements released from weathering minerals are only partially transported away from the system. The remaining part transforms by weathering from the coarse-grained fraction (dominated by fragments of primary minerals) into the fine-grained fraction (in the form of secondary, authigenic minerals or as species sorbed onto a mineral skeleton). This is very strongly pronounced within the chronosequence: the content of each of the metals studied correlates identically with the grain size, despite the differences in their chemical character and affinities. The microscope study presented herein indicates that the role of incongruent dissolution previously was underestimated. Also, the formation of coatings of secondary phases on primary mineral surfaces was observed. All these rapid weathering processes affect the mineral speciation of initial soils as well as the composition of mineral suspensions transported away by rivers to the nearby ocean.

Studium chemizmu działania szkła SiO2-PbO-K2O na cyrkonową (ZrSiO4) zaprawę ogniotrwałą, jako przypadku inkongruentnego rozpuszczania materiałów w stopie krzemianowym.

Stoch L., Wacławska I., Środa M., Ciecińska M., Trybalska B., Kuciński G.

Szkło i Ceramika

2003

R. 54, nr 1

10-16

Zbadano chemizm rozpuszczania cyrkonowej zaprawy ogniotrwałej w szkle, zawierającym SiO2, PbO i K2O jako składniki główne. Cyrkon (ZrSiO4) rozpuszcza się z równoczesną krystalizacją ZrO2 (baddeleyit). Występujący obok glinian CaAl2O4, zostaje zastąpiony przez Al2O3 (korund), który przechodzi następnie w leucyt (KAlSi2O6). Dla wyjaśnienia tych procesów porównano powinowactwa chemiczne tlenków w nich uczestniczących do SiO2 jako składnika więźbotwórczego szkła. Bardzo małe powinowactwo ZrO2 i Al2O3 do SiO2 w porównaniu z pozostałymi tlenkami pozwala aby krystalizowały w formie wolnych tlenków, mimo dużej koncentracji krzemionki w otoczeniu. Za miarę powinowactwa chemicznego przyjęto wartości entalpii swobodnej odpowiednich reakcji. Metoda ta może być zastosowana w badaniach każdego przypadku działania stopu krzemianowego na materiały.

Chemistry of dissolution of zircon (ZrSiO4) refractory mortar in the glass containing SiO2, PbO and K2O as main components has been studied. Zircon (ZrSiO4) dissolution is accompanied by the simultaneous crystallization of ZrO2 (baddeleyite). Similarly, aluminate (CaAl2O4) is replaced by Al2O3 (corundum). It transforms later in leucite (KAlSi2O6). To explain a reason of these phenomena, chemical affinity of oxides participating in the process to the SiO2 as glass network former has been compared. Very small affinity of ZrO2 and Al2O3 to SiO2 in comparison with oxides glass - modifiers, makes them possible to exist as free oxides, in spite of high content of SiO2 in the surrounding melt. Free enthalpy values of the proper reactions has been used as a measure of chemical affinity of oxides and SiO2. These procedure can be used in different materials and silicate melts interaction study.