Use of kraft recovery cycle residues in mineralization of forest- Controlling leaching rates of easily/limited soluble species

Artikel i vetenskaplig tidskrift, 2005

We sought to find a method to recycle inorganic solid residuals from the kraft recovery cycle as vitalizing agents, especially in acidified forests. One such method is pelletization, followed by thermal treatment, which sinters the material into a more stable and dense matrix with a low dissolution rate due to the small available surface area. Predicting the leaching rate from pelletized residuals in natural environments requires an understanding of both the hydrodynamic mass transport properties of the acidic solution-pellet system and the heterogeneous reaction kinetics on the pellet surface. This study examines the leaching rates of limited soluble species, such as calcium, from single pellets of treated lime mud and green liquor dregs under well controlled laboratory leaching tests. Results indicate a significant effect of the physical structure of the pellets on leaching properties of calcium. We developed models that describe the leaching rates. We found that a combined mass transfer and surface reaction describes the leaching rate of limited soluble species at a pH level of 5.5. The mass transfer of hydrogen ions to the surface is determined as the rate-determining step at a pH level of 4.6. We concluded that by using a combination of well controlled experiments and mathematical modeling, it is possible to understand the different phenomena that control the leaching mechanism of limited soluble species.