35% Solids 17% NaOH H₂O F5 = 1.5F¹ Solids 4% NaOH 6% H₂O Б NaOH 2% H₂O 8 Mix 2 Solids 1/2% 3 NaOH H₂O 三 6 10 Solids 32.5% NaOH 2.5% H₂O Solids 1/2% NaOH H₂O Solids 0.4% NaOH H₂O As shown in this flow diagram a countercurrent thickener consisting of three stages is used in a Kraft paper mill to wash a "white mud" consisting of 35% solids (CaCO3) and 17% NaOH in water. Two wash streams are used, the first (stream 5) contains 4% suspended solids, 6% NaOH, and the rest H2O; the second (stream 8) contains no solids, 2% NaOH, and the rest H₂O. The clear liquids from stage I and stage II contain 0.5% suspended solids; the clear liquid from stage III contains 0.4% solids. The flow of wash liquid to stage II (stream 5) is 1.5 times the flow of the feed sludge (stream 1), and the washed sludge from stage II contains one third solids. The washed sludge from the third stage (stream 9) contains 32.5% solids and 2.5% NaOH, and the flow rates of streams 7 and 9 are equal. All compositions are given on a mass basis. Assume that in each stage the clear solution and the solution contained in the washed sludge have the same concentration. (a) Construct a degree-of-freedom table and determine whether the problem is correctly specified. F7F9 9 (b) Calculate the concentration og NaOH in stream 4​