Burned Clay Ceramics Used in Water Treatment ^†

This research is the result of a detailed study performed on construction bricks and traditional ceramics of fired clay involved in water treatments as the last stage of filtration after the active charcoal. Using the data obtained through the scanning electron microscope coupled with energy-dispersive X-ray analysis and pH analyses, on the basis of the atomic composition and free concentration of hydronium ions, the normal caustic (Si/Al) and summative [(Si+Ti+FeIII+Cl)/(Al+Ca+Mg+Na+K)] modules were assessed. These data were correlated with the free acidity and, respectively, the capacity of absorption and ionic exchange of the Fe³⁺ and Al³⁺ ions [1,2]. The base-acidic activity of these groups from the structure of the fired-clay ceramics is due to the Si:Al stoichiometric ratio (known in practice as the caustic module, which varies from 1:1 to 4:1), but also the position of the two coordination centers of the basic elementary cell [3,4]. The capacity for ionic exchange is attributed to the acidic structures Si(IV)–O^–H⁺, Ti(IV)–O^–H⁺, and Fe(III)–O^–H⁺. The ceramics with high concentrations of Al(III), Ca(II), and Mg(II) have a character that varies from amphoteric to weakly basic, while those with Si(IV), Ti(IV), and Fe(III) vary from amphoteric to acidic. As a conclusion, based on the caustic module of the ceramics with a high capacity for ionic exchange, the materials presented good performances, even though they have a low cost as waste materials or scraps from the technological flow of construction bricks/tiles or traditional ceramics.