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Electrochemical desalination of historic Portuguese tiles-Removal of chlorides, nitrates and sulfates
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Advisor(s)
Abstract(s)
Soluble salts cause severe decay of historic Portuguese tiles. Treatment options for removal of the salts
to stop the decay are few. The present paper deals with development of a method for electrochemical
desalination, where an electric DC field is applied to the tiles. Laboratory experiments were conducted
with single 18th century tiles from Palácio Centeno, Lisbon, Portugal. Large parts of the glaze and parts
of the biscuit were lost from salt decay. The major aim of the investigation was to see if the method
could offer sufficient salt removal in the biscuit and in the interface between biscuit and glaze, where salt
crystals were clearly identified by SEM-EDX before desalination. The concentrations of chloride and especially nitrate were very high in the tiles (around 280 mmol Cl−/kg and 450 mmol NO3
−/kg respectively).
Both anions were successfully removed to below 6 mmol/kg during the electrochemical treatment. The
removal rate was similar for the two anions so the chloride concentration reached the lowest concentration level first. At this point the electric resistance increased, but the removal of nitrate continued
unaffected till similar low concentration. The sulfate concentration was initially very low, but nevertheless, sulfate removal started at the point where chloride and nitrate concentrations were very low in
the tiles. Investigating the interface between biscuit and glaze after the treatment showed no signs of
crystallized salts, so also in this important point, the desalination was successful. Based on the obtained
results an important step is taken towards development of an electrochemical technique for desalination
of tile panels.
Description
Keywords
Azulejos Tiles Electrokinetic Desalination Nitrates Chlorides Salt decay
Citation
Publisher
Elsevier