Effect of poultice composition on multi-ion transport in fired-clay bricks during electrokinetic desalination

Abstract

The crystallization of water-soluble salts in the pores of a material severely affects the building structures and is a serious threat to the historical buildings of cultural importance. Electrokinetics (EK) has been investigated as a promising method for salt removal from fired-clay brick using low DC electric potential applications. This research work is focused on the desalination of fired-clay brick specimens intentionally contaminated with salt mixture (NaCl, Na₂SO₄, and NaNO₃). In order to hinder the pH ingress in the brick and to enhance the removal efficiency, the kaolin clay poultice mixed with buffering agents was applied across the specimens, i.e., CaCO₃ at the anode and CH₃COOH at the cathode side. The effect of poultice composition on the removal of Na⁺, Clˉ, ${\mathrm{SO}}_4^{2-}$ and ${\mathrm{NO}}_3^{-}$ ions was investigated by performing EK experiments for 24 h by employing kaolin clay with and without containing buffering agents. However, the effect of treatment time (i.e., 24, 36, and 48 h) on the removal of NaCl from brick samples was examined using clay poultice enriched with buffers. The results demonstrated that the clay poultice with buffering agents effectively suppressed the pH changes and enhanced the desalination efficiency in the salt mixture (66 % for Na⁺, 80 % for Clˉ, 79 % for ${\mathrm{SO}}_4^{2-}$, and 72 % for ${\mathrm{NO}}_3^{-}$ over 24 h) and NaCl case (93 % for Na⁺, 95 % for Clˉ over 72 h). Moreover, the EK treatment time is a critical parameter, with maximum removal rate occurring within the first 24 h, indicating that extending the treatment time beyond this duration is less efficient.