Understanding the dissolution of a mineral material in formic acid
Advancing the chemical engineering fundamentals
Particulate Systems (T2-3P)
Keywords: Dissolution, Particle size, Surface area, Conductivity, Kinetic modelling
A new low cost inorganic binder system for large volume products like fibre insulation, building materials, etc. has been developed based on sol-gel technology. The precursor for the binder system is an amorphous mineral raw material containing silica as the major component. The sol was prepared by dissolving the amorphous mineral material in formic acid and the mineral was dissolved in a few hours depending on the molarity and temperature of the formic acid. The derived binder shows good wetting properties to mineral fiber surfaces and a good strength of paper-binder composites [J.Puputti et al. 2005].
The experiments with dispersed particles were performed in an isothermal glass reactor at temperatures 288-313 K. Formic acid solutions between 0.6 and 3.75 M were used as the solvent. The conductivity and temperature were measured online. SEM-EDX and microscopic images were used to analyse the material before and after the reaction. Particle size distribution measurements were performed with laser diffraction. The change in the surface area of the particles during the reaction is investigated with nitrogen physisorption.
The dissolution rate increased with temperature as well as acid concentration. Elevating the agitation did not influence the reaction rate and thus it was concluded that the agitation was sufficient, in order to reach the kinetic regime. The conductivity was influenced by the concentration of the dissolved matter and formic acid as well as the temperature. A phenomenological correlation between conductivity and concentration was established. This correlation can be used as a robust tool in industrial on-line determination of the amount dissolved.
The SEM and microscopic images taken of the fresh particles showed that the surface was smooth prior to the reaction. The images taken of partly dissolved particles revealed that holes or “craters” were formed on the surface, while the overall shape was generally maintained. The laser diffraction measurements show that the particle size is maintained during the reaction while the amount of undissolved particles declined. This suggests that the silica skeleton of the mineral material maintains its radial dimensions fairly well during dissolution and that the particles become more porous, increasing their surface area, until they disintegrate, dissolving rapidly. Advanced modelling, including the morphology of the particles, was developed.
Presented Monday 17, 13:30 to 15:00, in session Particulate Systems (T2-3P).
