Remedy for NaCl-induced sandstone weathering via crystallization inhibition by environmentally friendly iron tartrate

Salt weathering poses a major threat to porous sandstone in cultural heritage. Iron-tartrate complexes have been proposed to modify NaCl crystallization behavior and prevent clumping. However, their efficacy in stone conservation has remained unverified. This study presents the first systematic validation of iron-tartrate complexes as environmentally friendly inhibitors for the preservation of sandstone heritage. Through a multi-method experimental approach, potassium ferricyanide (FCN), ferrous meso-tartrate (Fe(II)-mTA), and ferric meso-tartrate (Fe(III)-mTA) are shown to markedly modify NaCl crystal habit, enhance material durability, and triple salt extraction efficiency, with negligible impact on pores below 10 µm. Molecular dynamics simulations further indicate that inhibitor adsorption energy on NaCl {100} and {111} crystal surfaces followed the order of FCN > Fe(III)-mTA > Fe(II)-mTA, which is consistent with the experimental findings. This work establishes iron-tartrate complexes as an effective and sustainable strategy for protecting sandstone heritage against salt damage, with the recognition that its performance is substrate-dependent and requires further long-term validation.