1 A soluble solid in an ore must be leached with water in a continuous counter current extraction cascade. 100 kg of the ore containing 8% solute, 12% moisture and 80% inert material must be treated per an hour. The final extract solution must contain 18% solute and must be free from solid material. 95% of the solute in the ore must be extracted. The underflow is constant throughout containing 1.7 kg water/ kg inert material. Determine the number of equilibrium washing stages required. 2 Halibut oil is extracted from granulated halibut livers in a countercurrent multi-batch arrangement using ether as the solvent. The solids charge contains 0.35 kg oil/kg of exhausted livers and it is desired to obtain a 90 per cent oil recovery. How many theoretical stages are required if 50 kg of ether are used/100 kg of untreated solids. The entrainment data are: 0 0.1 0.2 0.3 0.4 0.5 0.6 0.67 Concentration of overflow (kg oil/kg solution) Entrainment (kg solution/kg extracted livers) 0.28 0.34 0.40 0.47 0.55 0.66 0.80 0.96