Steel mill wastes are treated to recover the iron values thereof by a two stage agglomeration process wherein relatively small size first agglomerates are formed by agglomeration of steel mill wastes from an aqueous suspension thereof and then relatively large size second agglomerates are formed by agglomeration of said first agglomerates from a suspension thereof in a hydrophobic organic liquid and simultaneously a reactant chemical reacts with the agglomerates to provide a solid binder material formed in situ during the second agglomeration procedure.