World demand for manganese depends directly on the needs of the steel
industry. There are numerous grades of steel and each requires a different
amount of manganese. Unit consumption is determined by calculating the average
requirement of manganese per ton of steel. Some manganese which is to be
converted into steel is present in the iron (hot metal) coming either from the
iron ore charge or from the addition of manganese ore to the blast furnace.
This manganese is only a small part of the total requirement and it is partly
oxidized during the different processes that convert the hot metal into steel.
Hence most of the manganese addition is made in the steel melting shop. The
majority of it is in the form of manganese ferro-alloys, but there are some
cases when it can be added in the form of ore.
Part of the manganese is lost in the steelmaking process through
oxidation. In the 1960's and 70's, when the oxygen-blown process progressively
replaced the open hearth, Bessemer and Thomas processes, the subsequent
improved manganese yield caused a decline in unit consumption. In the 1980's
further improvements in steelmaking (brought about by the development of
combined blowing processes) meant even better manganese yields. Today, the
average unit consumption for industrialized countries is a little over 5.5 kg
of manganese per ton of steel, compared to some 6.5 kg in 1980 and over 7 kg in
the 1960's. Changes in steel grade chemistry have had an effect on manganese
requirements. For a constant unit consumption, manganese demand follows the
growth in steel production. Manganese requirements for other metallurgical
applications or for non-metallurgical uses do not represent a quantity large
enough to significantly affect the evolution of the overall manganese demand as
a direct function of steel production growth.