Difference between revisions of "Immobilization of salts"

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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.
+
The barium method bases on the theory, that in the presence of readily soluble sulfate salts, the sulfate precipitates with a readily soluble barium compound to become barium sulfate, and hereby removes the damaging salt from the system.
  
=== 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" /> .
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=== 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 conversion of gypsum <ref>http://www.fead-gmbh.de/Naturstein%20Gips.html, gesehen 17.1.2011</ref>, which particularily refers to the removal of gypsum efflorescence and gypsum crusts has been in use for several years <bib id="Hammer:1996" /> and has proven to be effective, when used in appropriate cases.
 +
Gypsum conversion <ref> http://www.baufachinformation.de/denkmalpflege.jsp?md=1988017124771, gesehen 17.1.2011</ref> is 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).  
+
In the first step the application of an ammonium carbonate poultice  leads to the conversion of gypsum into soluble ammonium sulfate. It migrates to one part into the poultice and to another part it stays in the the surface layer and eventually migrates into lower layers. If calcite forms under the surface of the plaster, it achieves a positive, consolidating effect; if it forms on the surface, it has to be removed dilligently. Excess ammonium carbonate decomposes to become ammonia, carbon dioxide and water. (Ammonium carbonate alters proteinaceous coatings).
  
'''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.  
+
The insoluble ammonium sulfate of the first reaction becomes the insoluble barium sulfate.
  
'''3. Erste festigende Reaktion'''  
+
 
 +
'''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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Excess barium hydroxide with ambient carbon dioxide converts to 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.  
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A heterogeneous reaction converts the outer regions of the calcite corns into calcium hydroxide gel.
 +
 
  
 
'''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.)  
+
A consolidating effect is achieved due to carbonation. (The reactions 4 and 5 have not yet been investigated well enough and need better understanding.)
  
Die Methode sollte dann nicht eingesetzt werden, wenn ''Nitrate'' in hoher Konzentration vorkommen, wenn ein ''organisches Bindemittel ''vorliegt und wenn eine ''Klebewirkung'' verlangt wird.  
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The method should not be used when ''nitrate'' is present in high concentration, when ''organic binders'' are present and when an ''adhesive effect'' is required.
  
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.
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Nitrates cause the formation of barium nitrate, which is slightly soluble and leads to visible crystallization on the surface. The organic binders in tempera or oil paintings do not tolerate the high alkalinity of barium hydroxide and lead to hydrolysis or saponification. '''Matteini''' <bib id="Matteini:1991" /> is of the opinion, that in old paintings, these organic binders have largely transformed to become inorganic compounds (like calcium oxalate) and the above reactions will not necessarily take place, the use of this method can therefore be justified.
  
=== [[Magnesiumsulfatumwandlung]]===
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=== [[Magnesium sulfate conversion]]===
  
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"/>.
+
Magnesium sulfate, like gypsum, can also be converted into the slightly soluble barium sulfate and ideally become magnesium carbonate,  rendering harmless the damaging salt<bib id="Friese.etal:1999"/>.
  
  
== Behandlung mit Bleihexafluorosilikat==
 
  
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.
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== Treatment with lead hexafluorosilicate ==
  
Bleihexafluoroisilikat reagiert mit Sulfat und Chloridverbindungen in komplexer Reaktion unter Bildung verschiedener Produkte, die nahezu alle schwer- oder unlöslich sind.  
+
A chemical salt conversion using lead hexafluorosilicate was sometimes recommended for the treatment with hydrophobic restoration plasters/mortars (link), because the restoration mortars are not hydrophobic, when they are freshly applied. Salts can therefore easily migrate into the pore structure of the plaster. To reduce the risk of a rapid salinization of the restoration mortar, the pretreatment of the substrate with a "salt treatment agent" is recommended. The different manufacturers suggest a variety of combinations. The most important ones are produced on the basis of lead hexafluorosilicate. Barium containing agents are also on offer. 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. 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 impregnating agents, that have a hydrophobic and a compacting effect on the capillaries.  Once the agents are activated and capillary compacting and hydrophobizing takes place, a reduction of salt migration to the surface is effected. Potential problems when applying the plaster are to be considered. As active ingredients sodium silicate compounds and potassium methyl siliconate/ fluate, i.e. salts of  hexafluorosilicic acid are usually present.  
  
Die Reaktionen können wie folgt aussehen: <br>
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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>  
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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>
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(sls - slightly soluble; s - soluble; is - insoluble) <br>
  
 
==Weblinks ==
 
==Weblinks ==
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<bibprint/>
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[[category: Measures]][[category: Hschwarz]][[category: inProgress]]
 
[[category: Measures]][[category: Hschwarz]][[category: inProgress]]

Revision as of 14:54, 9 February 2012

<bibimport />

Author: Hans-Jürgen Schwarz
back to Salt conversion


Barium method

The barium method bases on the theory, that in the presence of readily soluble sulfate salts, the sulfate precipitates with a readily soluble barium compound to become barium sulfate, and hereby removes the damaging salt from the system.


Gypsum conversion

The conversion of gypsum [1], which particularily refers to the removal of gypsum efflorescence and gypsum crusts 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 in appropriate cases. Gypsum conversion [2] is 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

In the first step the application of an ammonium carbonate poultice leads to the conversion of gypsum into soluble ammonium sulfate. It migrates to one part into the poultice and to another part it stays in the the surface layer and eventually migrates into lower layers. If calcite forms under the surface of the plaster, it achieves a positive, consolidating effect; if it forms on the surface, it has to be removed dilligently. Excess ammonium carbonate decomposes to become ammonia, carbon dioxide and water. (Ammonium carbonate alters proteinaceous coatings).


2. Precipitation of the insoluble salts

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

The insoluble ammonium sulfate of the first reaction becomes the insoluble barium sulfate.


3. First consolidating reaction

Ba(OH)2 + CO2→ BaCO3↓ + H2O

Excess barium hydroxide with ambient carbon dioxide converts to barium carbonate. This has a consolidating effect.


4. The second consolidating reaction

Ba(OH)2 + CaCO3 → BaCO3↓+ Ca(OH)2

A heterogeneous reaction converts the outer regions of the calcite corns into calcium hydroxide gel.


5. Ca(OH)2 + CO2 → CaCO3↓+ H2O

A consolidating effect is achieved due to carbonation. (The reactions 4 and 5 have not yet been investigated well enough and need better understanding.)

The method should not be used when nitrate is present in high concentration, when organic binders are present and when an adhesive effect is required.

Nitrates cause the formation of barium nitrate, which is slightly soluble and leads to visible crystallization on the surface. The organic binders in tempera or oil paintings do not tolerate the high alkalinity of barium hydroxide and lead to 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 to become inorganic compounds (like calcium oxalate) and the above reactions will not necessarily take place, the use of this method can therefore be justified.

Magnesium sulfate conversion

Magnesium sulfate, like gypsum, can also be converted into the slightly soluble barium sulfate and ideally become 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

A chemical salt conversion using lead hexafluorosilicate was sometimes recommended for the treatment with hydrophobic restoration plasters/mortars (link), because the restoration mortars are not hydrophobic, when they are freshly applied. Salts can therefore easily migrate into the pore structure of the plaster. To reduce the risk of a rapid salinization of the restoration mortar, the pretreatment of the substrate with a "salt treatment agent" is recommended. The different manufacturers suggest a variety of combinations. The most important ones are produced on the basis of lead hexafluorosilicate. Barium containing agents are also on offer. 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. 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 impregnating agents, that have a hydrophobic and a compacting effect on the capillaries. Once the agents are activated and capillary compacting and hydrophobizing takes place, a reduction of salt migration to the surface is effected. Potential problems when applying the plaster are to be considered. As active ingredients sodium silicate compounds and potassium methyl siliconate/ fluate, i.e. salts of hexafluorosilicic acid are usually present.

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

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