Optimizing the Extraction of Soluble Salts from Porous Materials by Poultices

Abstract

Poultices are often used to extract salts from salt-deteriorated objects, but the results achieved can be highly variable. Currently, poulticing materials and methodologies are selected empirically, but many variables affect the treatment outcome, so achieving the 'best fit' between available materials, application methods and substrate characteristics is somewhat arbitrary. This research, undertaken during the EC Desalination project (FP6 022714), investigated whether the extraction efficiency of drying poultices can be optimized by adjusting the poultice pore-size distribution to suit that of the substrate. Different substrate/poultice combinations of varying pore-size distributions (determined by nuclear magnetic resonance and mercury intrusion porosimetry) were selected for extraction efficiency tests. The results demonstrated that a prerequisite for efficient salt extraction by a drying poultice is that it has smaller pores than the substrate. However, the residual salt distribution after treatment was independent of the experimental factors tested. Thus, while manipulation of the poultice pore-size distribution can enhance salt extraction, this does not govern the location of residual salts. This study demonstrates that poultices should be adapted to suit the characteristics of the object undergoing treatment. However, the uncontrolled residual salt distribution and potential re-emergence of salt problems mean that the effectiveness of poulticing treatments requires long-term assessment.