Roasted copper ore containing cus04 is to be extracted in a counter-current stage extractor using pure water each hour, 100 tons of roasted copper ore, which contains 90 wt.% inert solids, 8 wt% cuso4 and 2 wt% of water is to be treated. the strong solution produced is to consist of 20 wt% cuso4. the recovery of cuso4 from the ore is 95 %. after each stage, 1 ton of inert solids retain 0.25 ton of water (just water) in addition to the copper sulfate dissolved in water. equilibrium is attained in each stage.