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Reagents for Water Treatment
Published in Willy J. Masschelein, Unit Processes in Drinking Water Treatment, 2020
Water of lime or lime-water is a solution containing dissolved and ionized calcium hydroxide. A saturated solution (25 °C) has a pH of about 12.4. The slaking process is less good with cold slaking water. Heating the process water to 25 to 40°C is recommended to improve the result. A vapor vent system must be mounted at the top of the slaking vessel.
Differentiation between Iron-II-Sulphate (Copperas) Staining and Natural Ochre Pigmented Lime Finishes on Lime Plaster
Published in International Journal of Architectural Heritage, 2022
Gesa Schwantes, Alison Trachet
The staining of the plaster surface observed for copperas finishes is a clear optical difference easily visible in cross sections. The copperas finishes with the best applicability (Mixes 1, 5, 9 and 11) show a horizon of yellowish stained lime plaster. However, no staining occurred in Mixtures 2, 6, 10 and 12, which were more produced with lime wash and were more viscous formulations. For mixtures with lime water, the calcium hydroxide solution is at its saturated limit, and at most only 0.17 g of calcium hydroxide will dissolve into 100 mL of water (approximately 0.0023 moles). Approximately 0.195 moles of iron sulphate are available to react; if all the dissolved calcium hydroxide reacts with dissolved iron sulphate, there remains 0.193 unreacted moles of iron sulphate. The iron and sulphate ions are then free to move into the lime plaster matrix, assuming sufficient porosity. The ionic radius of the Fe2+ in water is 0.072 nm, while the ionic radius of the sulphate ion is 0.242 nm (Marcus 1988). Due to its smaller size, the iron ion will likely penetrate into the lime plaster layer and react with hydroxyl ions and dissolved oxygen to form the golden stained region. The sulphate ion is much larger and may have travel migrating into the plaster matrix. Lime wash mixtures will produce more reactants at the surface, using up additional iron ions, and the higher viscosity prohibits easy penetration into the matrix. Thus, there is no staining observed in these mixtures.
Preliminary Investigations of Compatible Nanolime Treatments on Indiana Limestone and Weathered Marble Stone
Published in International Journal of Architectural Heritage, 2022
J. Otero, A. E. Charola, V. Starinieri
Restoring the mechanical properties of weathered historic structures is the aim for using consolidating products. One of the most important points is that the used consolidant must meet the “compatibility with the original substrate” condition, as stated by the 1972 Italian Carta delRestauro (1972) and considered as one of the three conservation principles by Brandi (1977). In the last four decades, most of the consolidating products used for restoration treatments are silica-based precursors (e.g. TEOS or MTMOS) (Wheeler 2008). These products were originally developed for the consolidation of sandstone, and then extended to other types of stone thanks to their ease of application, good penetration capability, immediate strength enhancement and effectiveness for silica-based substrates (Wheeler 2005). However, in the case of calcareous substrates, these consolidants present low physical and mechanical compatibility with the treated material, which in many cases cause cracks and significant damage in the long term (Ferreira-Pinto and Delgado-Rodrigues 2008; Wheeler 2008, 2005). For this reason, lime-based consolidants such as lime-water were traditionally preferred due to their higher compatibility with the matrix and durability (Baglioni et al. 2014; Brajer and Kalsbeek 1999). The consolidation effect of lime-water (aqueous suspension of lime particles) occurs by the carbonation reaction of lime particles (portlandite (Ca(OH)2)) when exposed to atmospheric CO2 and H2O, producing new CaCO3, which is obviously totally compatible with the matrix of calcareous materials. Thus, this method presents a high compatibility with the substrate, as “adds more of its natural cementing materials to the substrate”. However, this lime-water consolidation technique presents some important limitations such as a reduced impregnation depth (few millimetres), a very slow carbonation process, a low amount of lime particles applied in each application and the limited access of lime particles to the pores with small diameters; which in many cases leads to unsatisfactory treatments (Price, Ross, and White 1988).