Use of Kraft Recovery Cycle Residues in Mineralization of Forest - Controlling Leaching Rates of Easily/Limited Soluble Species, 2004 International Chemical Recovery Conference

It is of interest to find a method for recycling inorganic solid residual from the kraft recovery cycle as vitalizing agents, especially for acidified forests. One such method is pelletization followed by thermal treatment, which sinters the material as well as transforms the components into minerals with low solubility. Prediction of the leaching rate from pelletized residues in natural environments requires understanding of both hydrodynamic mass transport properties of the pellet-acidic solution system and the kinetic of heterogeneous reaction on the pellet surface. This study examines the leaching rates of both easily and limited soluble species from single pellets of treated lime mud and green liquor sludge. Models that describe the leaching rates are developed. Results indicate the significant effect of the physical structure of pellets on leaching properties. It is also shown that mass transfer within and from the pellets is a rate-determining step as pertains to easily soluble species. A combined mass transfer and surface kinetic reaction describes the leaching rate of limited soluble species at a pH level of 5.5, while the mass transfer of hydrogen ions to the surface is determined as a rate-determining step for the leaching rate of limited soluble species at a pH level of 4.6.