(2) Copper and ferrous sulfate solids are recovered from wastewater, and the added metal reacts with copper sulfate without generating new impurities, so the extra metal X to be added is iron, and the extra iron can be removed by dilute sulfuric acid, so Y is sulfuric acid. The solutions obtained in the first step and the second step both contain ferrous sulfate, which can save the cost when mixing, so: iron, H2SO4, saves the cost.