Abstract: The invention provides a method and a system for separating lignin from a lignin containing liquid medium, such as pulp mill black liquor, and treating the separated lignin. The method comprises at least the following steps: a) a precipitation stage (1), wherein a pH lowering agent (A) is added to the lignin containing slurry for precipitating lignin, b) followed by a first separation stage (2), wherein the precipitated lignin is separated as a lignin cake from the remaining liquid phase of the lignin containing slurry, c) a suspending stage (3), wherein the lignin cake is suspended for obtaining a lignin suspension, d) a hydrothermal carbonization stage (4), wherein the lignin suspension is treated for obtaining a slurry of carbon containing material, and e) a second separation stage (5), wherein the carbon containing material is separated from the slurry.

Abstract: The invention provides a method and a system for separating lignin from a lignin containing liquid medium, such as pulp mill black liquor, and treating the separated lignin. The method comprises at least the following steps: a) a precipitation stage (1), wherein a pH lowering agent (A) is added to the lignin containing slurry for precipitating lignin, b) followed by a first separation stage (2), wherein the precipitated lignin is separated as a lignin cake from the remaining liquid phase of the lignin containing slurry, c) a suspending stage (3), wherein the lignin cake is suspended for obtaining a lignin suspension, d) a hydrothermal carbonization stage (4), wherein the lignin suspension is treated for obtaining a slurry of carbon containing material, and e) a second separa-tion stage (5), wherein the carbon containing material is separated from the slurry.

Abstract: Please delete the Abstract as originally filed and substitute therefore the attached substitute Abstract which is submitted in both marked-up and clean copy versions.