In a process for removing NO.sub.x and SO.sub.2 from a gas stream containing same by contacting said stream with a mixture of iron (II) chelate of an amino acid moiety having at least one--SH group, wherein said amino acid moiety is selected from amino acids, N-substituted amino acids, natural peptides or synthetic peptides, and an alkali wherein said alkali comprises a basic salt selected from the salts of sodium, potassium, lithium, calcium or magnesium, to form NO.sub.x and SO.sub.2 contaminated iron (II) amino acid chelate and alkali, the improvement consisting of:
- (1) recovering a mixture of solids of the NO.sub.x and SO.sub.2 contaminated mixture of said iron (II) amino acid chelate and alkali metal compound;
- (2) washing said solids with a relatively neutral aqueous solution and separating said solids from the aqueous liquid;
- (3) subjecting the solids from step (2) to at least two additional sequential treatments comprising washing with one of an acidic aqueous solution of a mineral acid or an alkaline aqueous solution followed by washing the separated solids with the other of said acid or alkaline aqueous solutions;
- and
- (4) adding said aqueous mixture to a gas stream for removal of NO.sub.x and SO.sub.2.