Dissolution behavior of Jordanian clay-rich materials in alkaline solutions for alkali activation purpose. Part I

Abstract In the framework of the search for non-traditional cements the dissolution behavior of three Jordanian clay-rich raw materials in alkaline solutions was investigated in different concentrations (2, 5 and 10 M) using (NaOH and KOH) at 25 °C. Different analytical techniques were used to characterize the raw materials mineralogically, chemically, thermally and structurally. The concentration of Si and Al was monitored using Atomic Absorption Spectroscopy (AAS) during dissolution. The solid residue was characterized using X-ray Diffraction (XRD), microscopic study, Scanning Electron Microscopy (SEM), Nuclear Magnetic Resonance Spectroscopy (NMR) and Thermo Gravimetric Analysis (TGA). The results indicate that the used materials, kaolinite, smectite-rich clay, and diatomaceous clay are to some degree soluble in concentrated alkaline solutions. The raw materials have a higher extent of dissolution with increasing concentration, time and temperature of dissolution. The extent of dissolution is somewhat higher in NaOH than in KOH solution. Si and Al dissolve congruently in the case of kaolinite. For the smectite rich clay Al dissolves faster while for diatomaceous rich clay Si dissolves faster. Characterization of solid residues of aluminosilicate materials revealed the formation of new phases of sodium aluminum silicate hydrate (SAS) and sodium aluminum carbonate silicate (SACS). This means that the conditions chosen do not purely evaluate the dissolution but that competition with precipitation needs to be taken into account. The studied Jordanian raw materials have a good potential to be used for alkali activation.