Dissolution rates of silicate minerals in water from a subcritical to a supercritical state: effect of solvent properties

Abstract

Hydrothermal reaction experiments of silicate minerals (actinolite, pyroxene, etc.) were carried out using flow-through reactors in the temperature range from 25 to 400°C at 23 MPa. The dissolution in water of a multi-oxide silicate mineral, for example actinolite or pyroxene may require the breaking of more than one type of metal-oxygen bond. Differences between the rates at which these bonds break are often sufficiently large for dissolution to be non-stoichiometric. Dissolution rates (of Si) for actinolite and pyroxene in water were found to increase with increasing T from 25 to 300°C, and then decrease with increasing T from 300 to 400°C. The maximum release rates of Si are reached at 300°C. The different metals in the minerals often have different release rates at a fixed temperature. At T \ 300°C the release rates of Na, Ca, Mg, Fe, and Al from minerals are usually higher than that of Si. In contrast, release rates of Si are higher than those of the others at T C 300°C. The hydrolysis of Si-O-Si bonds and metal ion-H ? exchange reactions at T \ 300°C are different from reactions at T C 300°C, at 23 MPa, because the solvent properties of water (decreasing density and dielectric constant in the region from sub-critical to supercritical state) affect reaction rates. log r (dissolution rates of Si) increases with 1/dielectric constant, as the temperature rises to close to 300°C (or up to 374°C) and at the critical pressure.

Green production of a novel sorbent from kaolin for capturing gaseous PbCl2 in a furnace

“…Under high pressures and high temperatures in aqueous solution, the solubility of silicon and aluminium such as hydrated silica Si(OH)4 and aluminium hydroxide Al(OH)3 were dramatically increased. Thus, the metakaolin was persistently solved to release silicate and aluminium which were dispersed in the water as precursors (Cassiers et al, 2002;Zhang et al, 2011). On the other hand, a part of solute agglomerated and precipitated into solid cores, so that sphere particulates in size of about 100 nm were seen in the SEM and TEM images.…”

“…Hydrothermal treatment is widely used for the synthesis of zeolite from aluminosilicate including kaolin, and the product generated can be altered by varying the operating parameters and additives used in the production (Krol et al, 2018;Wu et al, 2013). Pressurised hydrothermal treatment can generate different minerals and accelerate the synthesis process (Zhang et al, 2011;Hayashi et al, 2010), and has proved to create larger surface area silicates (Sun et al, 2008). However, only a two studies in the literature have reported modifying kaolin by hydrothermal methods and most focused on the dihydrogen during the hydrothermal treatment, but neither studied its aluminosilicate structure nor have been further used as a high temperature sorbent (Zemenová et al, 2014;Kloužková et al, 2013).…”

Semi‐Empirical Model for Limestone Dissolution in Adipic Acid for Wet Flue Gas Desulfurization

“…The values of the activation energy E a and K o are obtained from a linear relationship between -lnK r and 1/T. The activation energy for a product layer diffusion-controlled reaction is usually below 20 kJ mol -1 and for a chemically controlled reaction 40-80 kJ mol -1 [18,19]. Therefore, a precise evaluation of the activation energy is needed in order to determine the reaction mechanism.…”