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Crystal growth kinetics of iron fluoride trihydrate
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.ORCID iD: 0000-0002-3239-5188
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
2006 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 296, no 2, 213-220 p.Article in journal (Refereed) Published
Abstract [en]

Crystal growth of beta-FeF3 • 3H(2)O has been investigated in mixtures of 3 mol kg(-1) hydrofluoric acid and 3 mol kg(-1) nitric acid at 30, 40 and 50 degrees C. Seeded isothermal desupersaturation experiments have been performed in the range: 1.3 < S < 3.6. Solution samples were analysed for total iron concentration with inductively coupled plasma atomic emission spectroscopy. The true supersaturation driving force was estimated by a proper speciation using the software SSPEC using appropriate stability constants. Growth rate parameters of the BCF surface diffusion growth rate equation and the empirical power-law equation have been estimated by fitting the supersaturation balance equation using a nonlinear optimization procedure. The results show that the growth rate is surface integration controlled. The growth rate at a supersaturation ratio of 2 was found to be 3.5 x 10(-12) m s(-1) at 30 degrees C, 7.4 x 10(-12) m s(-1) at 40 degrees C and 16 x 10(-12) m s(-1) at 50 degrees C. The activation energy of the rate constant of crystal growth was found to be 61 kJ mol(-1). .

Place, publisher, year, edition, pages
Royal Inst Technol, Dept Chem Engn & Technol, KTH, S-10044 Stockholm, Sweden., 2006. Vol. 296, no 2, 213-220 p.
Keyword [en]
growth from solutions, acids, inorganic compounds, WATER EXCHANGE, BETA-FEF3.3H2O, DISSOLUTION, FEF3.3H2O, MOSSBAUER, IRON(III), MIXTURES
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-14094DOI: 10.1016/j.jcrysgro.2006.08.035ISI: 000242325300014Scopus ID: 2-s2.0-33750515216OAI: oai:DiVA.org:kth-14094DiVA: diva2:329672
Note
QC 20100713Available from: 2010-07-13 Created: 2010-07-13 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Crystallization of Metal Fluoride Hydrates from Mixed Acid Solutions
Open this publication in new window or tab >>Crystallization of Metal Fluoride Hydrates from Mixed Acid Solutions
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work crystal growth and nucleation of b-FeF3×3H2O and crystallization of chromium (III), iron (III) and nickel (II) fluoride hydrates from mixed acid (1-3 mol/kg HNO3 and 1-6 mol/kg free HF) have been investigated.

The solubility of b-FeF3×3H2O has been determined in solutions of different hydrofluoric acid (1-7mol/ kg) and nitric acid (0-7mol/ kg) concentrations at 30, 40 and 50°C. The total iron concentration at equilibrium ranges from about 1 to 35 g/kg solution. In the range of investigated conditions the solubility in terms of total iron content increases with increasing temperature and decreases with increasing concentration of hydrofluoric acid and nitric acid. The results are analysed by examining the chemical speciation in the solutions.

The crystal growth kinetics of b-FeF3×3H2O crystals have been studied by performing seeded isothermal desupersaturation experiments in solutions of 1.5-3.0 mol/ kg nitric acid and 1.4- 5.6 mol/ kg free hydrofluoric acid at 30, 40 and 50°C. The results show that the crystal growth is surface integration controlled. When the driving force is based on a proper speciation no clear correlation of the growth rate with hydrofluoric acid or nitric acid concentration is found. The rate is about the same in industrial pickle liquor as in pure acid solutions. The growth rate at a supersaturation ratio (c(FeF3)free/cs(FeF3)free) of 2 was found to be 5.2×10-12m/s at 30°C, 7.9×10-12m/s at 40°C and 20×10-12m/s at 50°C. Thus, the crystal growth rate at 50°C is about four times higher than at 30°C. The temperature dependence of the rate constant corresponds to an activation energy of 55kJ/ mol.

Crystallization from solutions supersaturated with both Cr(III) and Fe(III) has been investigated and it has been observed that Fe(III) and Cr(III) crystallizes in the form of Cr(Fe)F3×3H2O which is isostructural with CrF3×3H2O. Iron(III) and nickel(II) crystallizes into an unidentified fluoride hydrate crystal.

The crystal growth rate of CrF3×3H2O at 50°C is about the same as the growth rate of b-FeF3×3H2O crystals.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. xii, 65 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:27
Keyword
crystallization, crystal growth, b-FeF3.3H2O, iron fluoride trihydrate, CrF3.3H2O, pickling, pickle bath, hydrofluoric acid, nitric acid, stainless steel
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-10619 (URN)978-91-7415-348-4 (ISBN)
Public defence
2009-06-12, D2, Lindstedtsvägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100713Available from: 2009-06-04 Created: 2009-06-04 Last updated: 2011-02-15Bibliographically approved
2. Crystallization of iron fluoride trihydrate from mixed acid solutions
Open this publication in new window or tab >>Crystallization of iron fluoride trihydrate from mixed acid solutions
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2005. x, 51 p.
Series
Trita-KET, ISSN 1104-3466 ; 216
Keyword
Physical chemistry, Fysikalisk kemi
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-347 (URN)91-7178-079-3 (ISBN)
Presentation
2005-06-02, K2, Teknikringen 28, Stockholm, 10:00
Supervisors
Note
QC 20110114Available from: 2005-08-01 Created: 2005-08-01 Last updated: 2011-01-14Bibliographically approved

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