Difference between revisions of "Immobilization of salts"

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<bibimport />
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Author: [[user:Hschwarz|Hans-Jürgen Schwarz]]<br>
 
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English Translation by [[user:SLeithaeuser|Sandra Leithäuser]]<br>
Author: [[user:Hschwarz|Hans-Jürgen Schwarz]]
 
 
<br>
 
<br>
back to [[Salt Conversion]]
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back to [[Salt conversion]]
 
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{{UnderConstruction}}
 
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== Abstract ==
 
  
==Bariummethode==
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==Barium method==
  
Die Bariummethode beruht darauf, dass  bei Vorhandensein leicht löslicher Sulfatsalze, das Sulfat mit einer leicht löslichen Bariumverbindung als Bariumsulfat gefällt wird und es damit als Schadsalz aus dem System genommen wird.
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The so-called "barium" method is based on the fact that when a soluble barium compound is added to a solution containing soluble sulfate salts, the highly insoluble barium sulfate will precipitate out and be 'immobilized' given its extremely low solubility. However, other soluble salts may remain from the counter ions of the original and barium compound added. These, however, may be less damaging.
  
=== Gipsumwandlung  ===
 
  
Die Gipsumwandlung<ref>http://www.fead-gmbh.de/Naturstein%20Gips.html, gesehen 17.1.2011</ref>, die sich insbesonder auf das Entfernen von Gipsausblühungen und Gipskrusten bezieht, wird seit vielen Jahres eingesetzt <bib id="Hammer:1996" /> und hat sich in geeigneten Fällen als Methode bewährt <bib id="Pursche:2001" /> .
+
=== Gypsum conversion  ===
  
Die Gipsumwandlung<ref> http://www.baufachinformation.de/denkmalpflege.jsp?md=1988017124771, gesehen 17.1.2011</ref> erfolgt in fünf Schritten <bib id="Matteini:1991" />:  
+
The above approach is used for the conversion of gypsum <ref>http://www.fead-gmbh.de/Naturstein%20Gips.html, gesehen 17.1.2011</ref>, in particular for gypsum efflorescence and crusts, into barium sulfate. It has been in use for several years <bib id="Hammer:1996" /> and has proven to be effective when used appropriately.
 +
The gypsum conversion <ref> http://www.baufachinformation.de/denkmalpflege.jsp?md=1988017124771, gesehen 17.1.2011</ref> is best carried out in five steps <bib id="Matteini:1991" />:
  
'''1. Lösen des Gips'''  
+
'''1. Dissolution of gypsum'''  
  
 
CaSO<sub><font size="1">4</font></sub>•2H<sub><font size="1">2</font></sub>O + (NH<sub><font size="1">4</font></sub>)<sub><font size="1">2</font></sub>CO<sub><font size="1">3</font></sub> → (NH<sub><font size="1">4</font></sub>)<sub><font size="1">2</font></sub>SO<sub><font size="1">4</font> </sub>+ CaCO<sub><font size="1">3</font></sub> + 2H<sub><font size="1">2</font></sub>O  
 
CaSO<sub><font size="1">4</font></sub>•2H<sub><font size="1">2</font></sub>O + (NH<sub><font size="1">4</font></sub>)<sub><font size="1">2</font></sub>CO<sub><font size="1">3</font></sub> → (NH<sub><font size="1">4</font></sub>)<sub><font size="1">2</font></sub>SO<sub><font size="1">4</font> </sub>+ CaCO<sub><font size="1">3</font></sub> + 2H<sub><font size="1">2</font></sub>O  
  
Im ersten Schritte führt die Anwendung von Ammoniumcarbonat in einer Kompresse zu einer Umwandlung des Gipses in lösliches Ammoniumsulfat. Dieses wandert z. T in die Kompresse, z. T verbleibt sie in der Oberflächenschicht und wandert eventuell in tiefer gelegen Schichten. Falls der Calcit in der Putzschicht entsteht, zeigt er eine positive, festigende Wirkung, bildet er sich an der Oberfläche, so muss er sorgfältig entfernt werden. Überschüssiges Ammoniumcarbonat zersetzt sich zu Ammoniak und Kohlendioxid und Wasser. (Ammoniumcarbonat verändert darüber hinaus proteinhaltige Überzüge).  
+
The first step is the application of an ammonium carbonate containing poultice to the surface to be treated. This leads to the conversion of the relatively insoluble gypsum into soluble ammonium sulfate that partly migrates into the poultice. The remaining ammonium sulfate will eventually migrate and distribute itself in the material. The reaction will also form calcium carbonate (calcite) and this will have a consolidating effect. However, any calcite forming on the surface has to be removed diligently to avoid its whitening effect. Any excess ammonium carbonate decomposes into gaseous ammonia, carbon dioxide and water. It is to be taken into account that ammonium carbonate may alter decorative mural paintings that contain proteinaceous additives.
 +
 
  
'''2. Ausfällen als unlösliches Sulfat.'''  
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'''2. Precipitation of the insoluble salts'''  
  
 
(NH<sub><font size="1">4</font></sub>)<sub><font size="1">2</font></sub>SO<sub><font size="1">4</font></sub> + Ba(OH)<sub><font size="1">2</font></sub> → BaSO<sub><font size="1">4</font></sub>↓ + 2NH<sub><font size="1">3</font></sub><font size="1"></font>+ 2H<sub><font size="1">2</font></sub>O  
 
(NH<sub><font size="1">4</font></sub>)<sub><font size="1">2</font></sub>SO<sub><font size="1">4</font></sub> + Ba(OH)<sub><font size="1">2</font></sub> → BaSO<sub><font size="1">4</font></sub>↓ + 2NH<sub><font size="1">3</font></sub><font size="1"></font>+ 2H<sub><font size="1">2</font></sub>O  
  
Das Ammoniumsulfat der ersten Reaktion wird in unlösliches Bariumsulfat überführt.  
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The second step is the application of a barium hydroxide containing poultice. The soluble ammonium sulfate in the substrate will react to form the highly insoluble barium sulfate. The counter ions, hydroxyl and ammonium will evaporate as ammonia and water.
 +
 
  
'''3. Erste festigende Reaktion'''  
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'''3. First consolidating reaction'''  
  
 
Ba(OH)<sub><font size="1">2</font></sub> + CO<sub><font size="1">2</font></sub><font size="1"></font>→ BaCO<sub><font size="1">3</font></sub>↓ + H<font size="1">2</font>O  
 
Ba(OH)<sub><font size="1">2</font></sub> + CO<sub><font size="1">2</font></sub><font size="1"></font>→ BaCO<sub><font size="1">3</font></sub>↓ + H<font size="1">2</font>O  
  
Überschüssiges Bariumhydroxid wandelt sich mit dem Kohlendioxid der Luft in Bariumcarbonat um. Dies zeigt eine festigende Wirkung
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Any excess barium hydroxide will react with ambient carbon dioxide to form barium carbonate. This has a consolidating effect.
 +
 
  
'''4. Zweite festigende Reaktion'''  
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'''4. The second consolidating reaction'''  
  
 
Ba(OH)<sub><font size="1">2</font></sub> + CaCO<sub><font size="1">3</font> </sub>→ BaCO<sub><font size="1">3</font></sub>↓+ Ca(OH)<sub><font size="1">2</font></sub>  
 
Ba(OH)<sub><font size="1">2</font></sub> + CaCO<sub><font size="1">3</font> </sub>→ BaCO<sub><font size="1">3</font></sub>↓+ Ca(OH)<sub><font size="1">2</font></sub>  
  
Eine heterogene Reaktion wandelt die äußeren Bereiche der Calcitkörner in Caliumhydroxidgel um.  
+
There may be an exchange reaction between any existing calcite in the substrate and the barium hydroxide where the outer surface of the calcite grains turn into calcium hydroxide gel while barium carbonate may also accrue on other crystals.
 +
 
  
 
'''5.''' Ca(OH)<sub><font size="1">2</font></sub> + CO<sub><font size="1">2</font></sub> → CaCO<sub><font size="1">3</font></sub>↓+ H<sub><font size="1">2</font></sub>O  
 
'''5.''' Ca(OH)<sub><font size="1">2</font></sub> + CO<sub><font size="1">2</font></sub> → CaCO<sub><font size="1">3</font></sub>↓+ H<sub><font size="1">2</font></sub>O  
  
Durch die Karbonatisierung wird eine festigende Wirkung erreicht. (Die Reaktionen 4 und 5 sind noch wenig untersucht und müssen noch besser verstanden werden.)
+
Any calcium hydroxide formed will re-carbonate increasing the consolidating effect. The reactions 4 and 5 have not as yet been thoroughly investigated and require further studies.  
 
 
Die Methode sollte dann nicht eingesetzt werden, wenn ''Nitrate'' in hoher Konzentration vorkommen, wenn ein ''organisches Bindemittel ''vorliegt und wenn eine ''Klebewirkung'' verlangt wird.
 
 
 
Nitrate führen zur Bildung von Bariumnitrat, das mäßig löslich ist und zur sichtbarer Kristallisation an der Oberfläche führt. Die organischen Bindemittel von Malereien in Tempera oder Öl vertragen die hohe Alkalinität von Bariumhydroxid nicht und es kann zur Hydrolyse und Verseifung kommen. '''Matteini''' <bib id="Matteini:1991" /> ist jedoch der Meinung, dass der größte Teil dieser organischen Bindemittel bei alten Malereien meist heute in anorganischen Verbindungen wie Calciumoxalat vorliegen, und obige Reaktionen kaum eintreten werden, so dass der Einsatz der Methode verantwortet werden kann.
 
  
=== [[Magnesiumsulfatumwandlung]]===
+
IMPORTANT NOTE:
 +
The method should not be used in the presence of a high concentration of ''nitrates'' or ''organic binders''.
 +
This approach does not provide an ''adhesive effect''.
  
Auch Magnesiumsulfat lässt sich ähnlich dem Gips in schwer lösliches Bariumsulfat und idealerweise Magnesiumcarbonat umwandeln und damit als Schadsalz unschädlich machen <bib id="Friese.etal:1999"/>.
+
Nitrates will result in the formation of barium nitrate, which is slightly soluble leading to its visible crystallization on the surface. The organic binders in tempera or oil paintings do not tolerate the high alkalinity of barium hydroxide resulting in their hydrolysis or saponification. '''Matteini''' <bib id="Matteini:1991" /> is of the opinion, that in old paintings, these organic binders have largely transformed into inorganic compounds such as calcium oxalate and the above reactions will not necessarily take place, the use of this method can therefore be justified.
  
 +
=== [[Magnesium sulfate conversion]]===
  
== Behandlung mit Bleihexafluorosilikat==
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Similarly, magnesium sulfate can also be converted into the highly insoluble barium sulfate and ideally turn into the relative insoluble magnesium carbonate, rendering harmless the damaging salt <bib id="Friese.etal:1999"/>.
  
Eine chemischen Salzumwandlung mit Bleihexafluorosilikat wurde z.T bei der Anwendung porenhydrophober Sanierputze empfohlen (link), da in frisch aufgebrachten Zustand die Sanierputze noch nicht hydrophob sind. Salze können also relativ leicht dann in das Porengefüge des Putzes einwandern. Um diese Gefahr einer schnellen Versalzung der Sanierputze zu verringern, wird häufig eine Putzgrundvorbehandlung mit einem "Salzbehandlungsmittel" angeraten. Dabei werden von den verschiedenen Herstellern verschieden Präparate bzw. Kombinationen empfohlen. Die wichtigsten sind dabei auf der Basis von Bleihexafluorosilikat aufgebaut. Daneben werden auch Barium-haltige Präparate angeboten. Obwohl eine gewisse Wirksamkeit dieser Behandlung erwiesen ist, ist zu betonen, dass lösliche Bleisalze nicht ungefährlich sind und so ein Problem für das Arbeitspersonal wie auch für den Umweltschutz darstellen. Aus diesem Grund sollte versucht werden, die gleiche Wirkung, d.h. die Vermeidung einer schnellen Salzeinwanderung, eher durch Imprägnierungen zu erreichen, die eine kapillar verdichtende und eine hydrophobierende Wirkung besitzen. Entwickeln sie ihre Wirksamkeit in Bezug auf Kapillarverdichtung und Hydrophobierung, kann eine Reduktion der Salzwanderung zur Oberfläche eintreten. Mögliche Probleme bei Aufbringen des nachfolgenden Putzes sind zu beachten. Als Wirkstoffe werden hier in der Regel Kaliwasserglasverbindungen und Kaliummethylsilikonat bzw. auch Fluate, also Salze der Hexafluorokieselsäure, eingesetzt.
+
== Treatment with lead hexafluorosilicate ==
  
Bleihexafluoroisilikat reagiert mit Sulfat und Chloridverbindungen in komplexer Reaktion unter Bildung verschiedener Produkte, die nahezu alle schwer- oder unlöslich sind.  
+
In the past, another conversion method based on the use of lead hexafluorosilicate was sometimes recommended when commercial restoration [[Renders/Mortars]], called Sanierputze in German, to prevent salts from migrating into the fresh render. The commercial restoration renders are formulated with a water repellent, mostly Na-oleate (that with the render turns into Ca-oleate) or Zn-stereate. Hydrophobicity of the render will prevent salts from penetrating it, and therefore, it will have a longer service-life. To be taken into account it that these commercial restoration renders were formulated mostly for old farm houses where walls tend to be saturated with salts. The render is applied to both sides so that salts are "trapped" within the wall which will remain moist due to salt hygrocopicity, but the renders will be dry because of their hydrophobicity. Different manufacturers suggest a variety of combinations. The most important ones are produced on the basis of lead hexafluorosilicate. Barium containing agents are also offered.  
  
Die Reaktionen können wie folgt aussehen: <br>
+
Even though a certain effectiveness of the treatment has been established, it must be stressed that soluble lead salts are a risk to the workforce and to the environment and should be avoided. For this reason, attempts should be made to achieve the same effect (the prevention of a rapid salt migration into the new plaster) through the use of additives to the render mix to reduce pore sizes and turn it hydrophobic. For this purpose sodium silicate compounds and potassium methyl siliconate/fluate, i.e., salts of hexafluorosilicic acid are usually used.
 +
This will reduce salt migration to the surface of the set render. However, there may be some problems when applying the render. As active ingredients
 +
Lead hexafluorosilicate reacts with sulfate and chloride compounds in complex reactions, forming a variety of products, which are nearly all hardly soluble or insoluble.
  
Na<sub>2</sub>SO<sub>4</sub> (ll) + PbSiF<sub>6</sub>(ll) → PbSO<sub>4</sub> (sl)+ Na<sub>2</sub>SiF<sub>6</sub> (sl) <br>  
+
The reaction may be as follows: <br>
 +
 +
Na<sub>2</sub>SO<sub>4</sub> (s) + PbSiF<sub>6</sub>(s) → PbSO<sub>4</sub> (sls)+ Na<sub>2</sub>SiF<sub>6</sub> (sls) <br>  
  
Na<sub>2</sub>CO<sub>3</sub> (ll) + PbSiF<sub>6</sub> (ll) → PbCO<sub>3</sub>(ul) + Na<sub>2</sub>SiF<sub>6</sub> (sl) <br>  
+
Na<sub>2</sub>CO<sub>3</sub> (s) + PbSiF<sub>6</sub> (s) → PbCO<sub>3</sub>(is) + Na<sub>2</sub>SiF<sub>6</sub> (sls) <br>  
  
MgSO<sub>4</sub> (ll) + PbSiF<sub>6 </sub>(ll) → PbSO<sub>4</sub> (sl) + MgSiF<sub>6</sub> (sl) <br>  
+
MgSO<sub>4</sub> (s) + PbSiF<sub>6 </sub>(s) → PbSO<sub>4</sub> (sls) + MgSiF<sub>6</sub> (sls) <br>  
  
2NaCl (ll) + PbSiF<sub>6</sub> (ll) → PbCl<sub>2</sub> (sl) + Na<sub>2</sub>SiF<sub>6</sub> (sl) <br>  
+
2NaCl (s) + PbSiF<sub>6</sub> (s) → PbCl<sub>2</sub> (sls) + Na<sub>2</sub>SiF<sub>6</sub> (sls) <br>  
  
(sl - schwer löslich; ll - leicht löslich; ul - unlöslich) <br>
+
(sls - slightly soluble; s - soluble; is - insoluble) <br>
  
 
==Weblinks ==
 
==Weblinks ==
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== Literatur ==
 
== Literatur ==
  
<bibprint/>
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<biblist/>
-->
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[[category: Measures]][[category: Hschwarz]][[category: inProgress]]
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[[category: Measures]][[category: Schwarz,Hans-Jürgen]][[category: approved]]

Latest revision as of 20:42, 11 November 2017

Author: Hans-Jürgen Schwarz
English Translation by Sandra Leithäuser

back to Salt conversion


Barium method

The so-called "barium" method is based on the fact that when a soluble barium compound is added to a solution containing soluble sulfate salts, the highly insoluble barium sulfate will precipitate out and be 'immobilized' given its extremely low solubility. However, other soluble salts may remain from the counter ions of the original and barium compound added. These, however, may be less damaging.


Gypsum conversion

The above approach is used for the conversion of gypsum [1], in particular for gypsum efflorescence and crusts, into barium sulfate. It has been in use for several years [Hammer:1996]Title: Salze und Salzbehandlung in der Konservierung von Wandmalerei und Architekturoberfläche.
Author: Hammer, Ivo
Link to Google Scholar
and has proven to be effective when used appropriately. The gypsum conversion [2] is best carried out in five steps [Matteini:1991]Title: In Review: An Assessmant of Florentine Methods of Wall Painting Conservation Based on the Use of Mineral Treatments
Author: Matteini, Mauro
Link to Google Scholar
:

1. Dissolution of gypsum

CaSO4•2H2O + (NH4)2CO3 → (NH4)2SO4 + CaCO3 + 2H2O

The first step is the application of an ammonium carbonate containing poultice to the surface to be treated. This leads to the conversion of the relatively insoluble gypsum into soluble ammonium sulfate that partly migrates into the poultice. The remaining ammonium sulfate will eventually migrate and distribute itself in the material. The reaction will also form calcium carbonate (calcite) and this will have a consolidating effect. However, any calcite forming on the surface has to be removed diligently to avoid its whitening effect. Any excess ammonium carbonate decomposes into gaseous ammonia, carbon dioxide and water. It is to be taken into account that ammonium carbonate may alter decorative mural paintings that contain proteinaceous additives.


2. Precipitation of the insoluble salts

(NH4)2SO4 + Ba(OH)2 → BaSO4↓ + 2NH3+ 2H2O

The second step is the application of a barium hydroxide containing poultice. The soluble ammonium sulfate in the substrate will react to form the highly insoluble barium sulfate. The counter ions, hydroxyl and ammonium will evaporate as ammonia and water.


3. First consolidating reaction

Ba(OH)2 + CO2→ BaCO3↓ + H2O

Any excess barium hydroxide will react with ambient carbon dioxide to form barium carbonate. This has a consolidating effect.


4. The second consolidating reaction

Ba(OH)2 + CaCO3 → BaCO3↓+ Ca(OH)2

There may be an exchange reaction between any existing calcite in the substrate and the barium hydroxide where the outer surface of the calcite grains turn into calcium hydroxide gel while barium carbonate may also accrue on other crystals.


5. Ca(OH)2 + CO2 → CaCO3↓+ H2O

Any calcium hydroxide formed will re-carbonate increasing the consolidating effect. The reactions 4 and 5 have not as yet been thoroughly investigated and require further studies.

IMPORTANT NOTE: The method should not be used in the presence of a high concentration of nitrates or organic binders. This approach does not provide an adhesive effect.

Nitrates will result in the formation of barium nitrate, which is slightly soluble leading to its visible crystallization on the surface. The organic binders in tempera or oil paintings do not tolerate the high alkalinity of barium hydroxide resulting in their hydrolysis or saponification. Matteini [Matteini:1991]Title: In Review: An Assessmant of Florentine Methods of Wall Painting Conservation Based on the Use of Mineral Treatments
Author: Matteini, Mauro
Link to Google Scholar
is of the opinion, that in old paintings, these organic binders have largely transformed into inorganic compounds such as calcium oxalate and the above reactions will not necessarily take place, the use of this method can therefore be justified.

Magnesium sulfate conversion

Similarly, magnesium sulfate can also be converted into the highly insoluble barium sulfate and ideally turn into the relative insoluble magnesium carbonate, rendering harmless the damaging salt [Friese.etal:1999]Title: Salze im Mauerwerk - Möglichkeiten zur Entsalzung und zur Salzumwandlung
Author: Friese, Peter; Protz, A.
Link to Google Scholar
.

Treatment with lead hexafluorosilicate

In the past, another conversion method based on the use of lead hexafluorosilicate was sometimes recommended when commercial restoration Renders/Mortars, called Sanierputze in German, to prevent salts from migrating into the fresh render. The commercial restoration renders are formulated with a water repellent, mostly Na-oleate (that with the render turns into Ca-oleate) or Zn-stereate. Hydrophobicity of the render will prevent salts from penetrating it, and therefore, it will have a longer service-life. To be taken into account it that these commercial restoration renders were formulated mostly for old farm houses where walls tend to be saturated with salts. The render is applied to both sides so that salts are "trapped" within the wall which will remain moist due to salt hygrocopicity, but the renders will be dry because of their hydrophobicity. Different manufacturers suggest a variety of combinations. The most important ones are produced on the basis of lead hexafluorosilicate. Barium containing agents are also offered.

Even though a certain effectiveness of the treatment has been established, it must be stressed that soluble lead salts are a risk to the workforce and to the environment and should be avoided. For this reason, attempts should be made to achieve the same effect (the prevention of a rapid salt migration into the new plaster) through the use of additives to the render mix to reduce pore sizes and turn it hydrophobic. For this purpose sodium silicate compounds and potassium methyl siliconate/fluate, i.e., salts of hexafluorosilicic acid are usually used. This will reduce salt migration to the surface of the set render. However, there may be some problems when applying the render. As active ingredients Lead hexafluorosilicate reacts with sulfate and chloride compounds in complex reactions, forming a variety of products, which are nearly all hardly soluble or insoluble.

The reaction may be as follows:

Na2SO4 (s) + PbSiF6(s) → PbSO4 (sls)+ Na2SiF6 (sls)

Na2CO3 (s) + PbSiF6 (s) → PbCO3(is) + Na2SiF6 (sls)

MgSO4 (s) + PbSiF6 (s) → PbSO4 (sls) + MgSiF6 (sls)

2NaCl (s) + PbSiF6 (s) → PbCl2 (sls) + Na2SiF6 (sls)

(sls - slightly soluble; s - soluble; is - insoluble)

Weblinks

Literatur

[Friese.etal:1999]Friese, Peter; Protz, A. (1999): Salze im Mauerwerk - Möglichkeiten zur Entsalzung und zur Salzumwandlung. In: Venzmer, H. (eds.): Entfeuchtung/Entsalzung 10. Hanseatische Sanierungstage FAS - Schriftenreihe Heft 10, 211-230Link to Google Scholar
[Hammer:1996]Hammer, Ivo (1996): Salze und Salzbehandlung in der Konservierung von Wandmalerei und Architekturoberfläche.. In: Pursche, Jürgen (eds.): Salzschäden an Wandmalereien, Bayerisches Landesamt für Denkmalpflege, 81-106Link to Google Scholar
[Matteini:1991]Matteini, Mauro (1991): In Review: An Assessmant of Florentine Methods of Wall Painting Conservation Based on the Use of Mineral Treatments. In: Cather, Sharon (eds.): The Conservation of Wall Paintings: Proceedings of a symposium organized by the Coutrauld Institut of Art and the Getty Conservation Institute, London, July 13-16, 1987, The Getty Conservation Institute, 137-148Link to Google Scholar