Salt conversion

<bibimport /> Author: Hans-Jürgen Schwarz

back to Measures

Abstract

By transforming damaging salts in insoluble or poorly soluble compounds they can no longer take part in damaging processes. Secondly the chemical converion can be used to make insoluble salts more soluble in order to remove them more easily out of the system.

Removal of salts by salt conversion

Various methods for removing soluble salts and salt crusts are common. Often acids such as hydrochloric acid or acetic acid were used to remove calcium carbonate crusts which afterwards favor in many cases further damage processes.[Hammer:1996]Title: Salze und Salzbehandlung in der Konservierung von Wandmalerei und Architekturoberfläche.
Author: Hammer, Ivo
Hexafluorosilicic acid was also often used. The forentine method [Matteini:1991]Title: In Review: An Assessmant of Florentine Methods of Wall Painting Conservation Based on the Use of Mineral Treatments
Author: Matteini, Mauro
of "gipsum transformation" also includes the dissolution of the gypsum crust with ammonium carbonate. Ion exchangers are also used for many years to remove crusts.[Pursche:2001]Title: Konservierung von Wandmalerei, Reaktive Behandlungsmethoden zur Bestandserhaltung

Immobilization of salts

Immobilization is the conversion of readily soluble salts into sparingly soluble or insoluble, and thus relatively harmless compounds. This sounds simple and obvious but in practice, however, has a number of problems. First, in the masonry you will find not only a defined salt, such as Calcium nitrate or magnesium sulfate, but a more or less complex mixture which may be partly crystalline, partly present as a salt solution. Looking to the usual anions and katoions it should be noted that nitrate compounds can not be converted into insoluble salts, as there are no slighly soluble or insolible nitrate compounds. This leaves us with the possibilities for chlorides, sulfates and some limited options for carbonates.

While today in most cases barium solutions are used, formerly lead hexafluorosilicate was often used.

Literature

[Filter missing]