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Recycling of waste pickle acid by precipitation of metal fluoride hydrates
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.
2007 (English)In: Minerals Engineering, ISSN 0892-6875, Vol. 20, no 9, 950-955 p.Article in journal (Refereed) Published
Abstract [en]

Stainless steel is pickled in mixed acid solutions (1-3 M HNO3 and 0.5-4 M HF). The spent solution is usually neutralized with lime, and in Sweden about 18,000 tons/yr of metal hydroxide sludge is disposed as landfill waste. We are developing a cost-saving and environmentally friendly process, involving crystallization of beta-FeF3 . 3H(2)O, where the metal content is recovered and the acid is recycled. Iron has been successfully separated from spent pickle bath solutions by precipitation of beta-FeF3 . 3H(2)O in a continuous crystallizer (10 L scale) where the solution is concentrated by nanofiltration. The crystal growth rate of beta-FeF3 . 3H(2)O has been determined in industrial pickle bath solutions at 50 degrees C and the results have been compared to previous measurements in pure HF/HNO3 solutions prepared in the laboratory. The growth rate of beta-beta eF(3) . 3H(2)O crystals at 50 degrees C is in the order of 10(-11) m/s in both industrial and pure acid mixtures.

Place, publisher, year, edition, pages
2007. Vol. 20, no 9, 950-955 p.
Keyword [en]
hydrometallurgy, waste processing, recycling, CRYSTAL-STRUCTURE, TRIHYDRATE, MIXTURES, BETA-FEF3.3H2O, MOSSBAUER, GROWTH
National Category
Chemical Engineering
URN: urn:nbn:se:kth:diva-14095DOI: 10.1016/j.mineng.2007.03.011ISI: 000249051000015ScopusID: 2-s2.0-34447256127OAI: diva2:329673
Conference: International Symposium on Material, Minerals and Metal Ecology (MMM 06). Cape Town, SOUTH AFRICA. NOV 14-15, 2006 Available from: 2010-07-13 Created: 2010-07-13 Last updated: 2011-09-13Bibliographically 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.
Trita-CHE-Report, ISSN 1654-1081 ; 2009:27
crystallization, crystal growth, b-FeF3.3H2O, iron fluoride trihydrate, CrF3.3H2O, pickling, pickle bath, hydrofluoric acid, nitric acid, stainless steel
National Category
Chemical Engineering
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)
QC 20100713Available from: 2009-06-04 Created: 2009-06-04 Last updated: 2011-02-15Bibliographically approved

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