A compound of formula wherein R is H; Ar is an aromatic group selected from phenyl; X is a phenyl group; R\u2032 is H or C1-C4 alkyl; each R1 is independently H or C1-C4 alkyl; and pharmaceutically acceptable salts thereof. A first leaching step wherein the furnace dust is leached at atmospheric pressure in a first leaching solution to produce a first leach liquor and a first leach residue, the first leaching solution consisting of an aqueous mineral acid solution. The filter also has an output port coupled to an output sum block that receives a signal from the first feed forward path. The spraying module has a spraying bar facing the front end of the road paver. Furthermore, a composite pigment obtained from the composite pigment original, a process for producing an ink composition using the composite pigment original, and an ink composition obtained by the production process are disclosed.