65 u00b0 c a solution is obtained which may contain about 180 g fe l if material according to table 1 is leached by raising the temperature to 100 u00b0 c the solubility is lowered so that only about 120 g fe l remains in the solution whereby about 60 g fe l can be crystallized when sulfuric acid is added the solubility of iron sulfate lowers further and it has been shown that by adding for example 150 g h 2 so 4 l it is possible to precipitate 90 95 g fe l which means that by using this acid addition more sulfate can be removed from the process than has been added to it as sulfate 150 g h 2 so 4 corresponds to about 85 5 g fe it is evident that an equal amount of sulfate must be separated in the form of crystals as is added in acid form since otherwise the amount of solution in the process increases by this procedure it is thus possible to crystallize iron 100 g l which is very advantageous in terms of the technical implementation of the process such removal of iron is effected without evaporation a fact which is a great advantage since a considerable amount of energy is.