Phenomenological study of viscosity and density of alkali metal hydroxide solutions
Alkaline solutions are widely used in many industries. For dilute solutions, physicochemical properties, such as solubility of gases, hydration numbers and mobility of ions are well known. A relatively new trend is using concentrated alkaline solutions to obtain ferrates. In these processes, the solution concentration of more than 8 M is used. Studying the processes of transport of mat- ter and charge in concentrated alkaline solutions requires updat- ing the data on the hydration numbers and radii of ions, the effect of concentration, viscosity and nature of electrolytes on them.A method for determining the hydration numbers of alkali metal cations in hydroxide solutions, based on calculating the num- ber of water moles per mole of cations at concentrations close to the limit was proposed. In addition, the influence of ions, strengthening and breaking the solution structure on the density and viscosity of alkali metal solutions was examined. It was shown that primary hy- dration of ions has the predominant impact on the solution viscosity in dilute solutions, and secondary - in concentrated.It was found that a sharp increase in the solution viscosity with increasing concentration occurs with decreasing distance between ions up to 3,7 × 10-7 m.At high concentrations, the solution density is higher in hy- drated cations with smaller dimensions. High density of lithium hydroxide solutions in concentrations of from 2 to 4 M can be explained by the fact that the positively hydrated cation is em- bedded in the structure of water without a significant increase in its volume.