Process for treating a slurry of cellulosic material

A process for treating a slurry of cellulosic material which comprises:

• a. diluting the slurry to reduce its consistency to a flowable level;
• b. depositing the diluted slurry on a surface permeable to the liquid and solid phases thereof but which is substantially more permeable to the liquid phase;
• c. subjecting the deposited slurry to a pressure differential, whereby more of the liquid phase thereof than the solid phase passes through the permeable surface to increase the consistency of the slurry to a value between the consistency of the diluted slurry deposited on the surface and the consistency of the slurry prior to its dilution, thereby forming a mat of cellulosic material on said surface;
• d. recycling substantially all of the liquid and solids which pass through the surface for use as the slurry diluent in step (a);
• e. counter-currently applying a treating liquid in a plurality of treatment stages, including application of a fresh treating liquid in the last stage of said treatment stages, to the mat of cellulosic material, while the mat remains on the permeable surface and subject to the pressure differential, whereby the treating liquid displaces at least a portion of liquid present in the mat from the mat and through the permeable surface in each treatment stage;
• f. measuring the electrical conductivity of the liquid displaced from the mat in the last stage of said treatment stages and then
• g. adjusting the amount of fresh treating liquid applied in the last stage of said treatment stages in response to the deviation, from a predetermined norm, of the measured value of electrical conductivity of only the liquid displaced in the last stage of said treatment stages.