The Bayer process is used to recover aluminum oxide (alumina, Al2O3) from bauxite ore. The first step is to dissolve the alumina with NaOH to produce soluble NaA1O2. The residue (called red mud) is a mixture of insoluble impurity oxides and leach solution, and leaves the leaching step as a slurry. The liquid portion of the slurry contains valuable NaA1O2 as a solute, so it is important to separate the solution from the mud as effectively as possible before the mud is discarded. This is done by pumping the slurry to a washing tank and washing with water or a recycled solution (which may contain some suspended particulates and ions). The mud slurry is discarded after several washings and settlings. In one of those washing/settling steps, the red mud slurry enters at the rate of 1000 lb/h, with a solids mass fraction of 10 %. The red mud composition is undefined, and does not change throughout the process. The liquid part of the inlet slurry consists of water containing two soluble species: NaOH = 11 wt%, and NaA1O2 = 16 wt%. The wash water inlet stream contains NaOH = 2.0 wt%. The decanted solution exit stream (free of solid) contains 95 % H2O and the exit washed mud slurry contains 20 % solids. We want to calculate the recovery of NaA1O2 in the decanted exit stream.