This paper introduces a novel additive for reducing the viscosity of black liquors with a high dry solids content that are produced in the kraft pulp industry. By controlling the viscosity of black liquors, their dry solids content can be increased into the range 70-85%. A number of positive impacts on the recovery process can then be achieved: easier operation, increased reduction efficiency, increased steam generation and power production, and decreased emission. The development of this new additive by the authors permits the reduction of the viscosity of black liquors without affecting either the process or the environment. (c) 2006 Elsevier B.V. All rights reserved.