Estudo da remediação de alterabilidades nos principais quartzitos ornamentais do Ceará

Abstract

The growing demand for natural materials with high strength and distinctive aesthetics has driven the use of Brazilian ornamental quartzites in the construction industry. However, the performance of these materials when exposed to everyday chemical agents, particularly in domestic environments, still requires detailed investigation. In this context, the present research aimed to investigate the physicochemical alterability of three commercial varieties of quartzite from Ceará — Perla Santana, Cristallo Pink, and Taj Mahal — focusing on aesthetic degradation processes and the effectiveness of remediation methods. The methodology adopted was multidisciplinary, involving standardized tests (gloss, porosity, density, and absorption), physico-structural analyses (PUNDIT and SEM/EDS), and application/removal tests with chemical agents (KOH, HCl, NaCl, sodium hypochlorite, paints, among others). Samples were initially polished in a standardized manner and subsequently subjected to the controlled action of reagents over varying periods, simulating different scenarios of use and exposure. In gloss measurements, performed with a 60° glossmeter, KOH caused the greatest losses, exceeding 16% in some samples, particularly in Cristallo Pink. Sodium hypochlorite produced an almost negligible visual impact, indicating a distinct surface behavior. Colorimetric analyses in the CIELAB scale revealed significant variations in the L, a, and b* parameters, with ΔE values exceeding 3, a threshold perceptible to the human eye. Structural analysis by PUNDIT testing demonstrated a correlation between wave propagation velocity and microstructural integrity. Compact and minimally altered zones exhibited velocities above 4000 m/s, whereas values below 2500 m/s indicated microcracks and internal heterogeneity. SEM analyses revealed scaly structures, oriented laminae, and fracture filling by secondary minerals such as kaolinite and micas, while EDS confirmed high aluminum and potassium contents consistent with muscovite and altered feldspars. In the remediation stage, scouring powder, citric acid, sodium bicarbonate, vinegar, and lemon juice were tested. Organic stains responded more effectively to organic acids, and scouring powder proved effective in removing paints. Stain depth and exposure time to aggressive reagents were decisive factors in cleaning efficiency. The results indicate a strong relationship between porosity, microcracking, and susceptibility to aesthetic alteration. Rocks with higher porosity exhibited greater gloss losses and colorimetric changes, suggesting that pore connectivity facilitates the penetration of aggressive agents. Thus, the chemical resistance of quartzites depends not only on mineralogical composition but also on physical integrity, grain size distribution, foliation orientation, and degree of compaction. It is concluded that the integrated approach adopted provides a robust technical assessment of the aesthetic durability of quartzites from Ceará in domestic applications, offering valuable insights for the ornamental stone sector. For future perspectives, the application of XRD, X-ray tomography, and accelerated aging tests is recommended to deepen the understanding of the evolution of these rocks under different usage conditions.