Minerals Report - International Seabed Authority

The crushed and ground ore can be concentrated by preliminary
gravity concentration. Then differential froth flotation can separate the
different sulphides - pyrite, pyrrhotite, chalcopyrite, sphalerite, and galena –
from the gangue and between themselves. However, difficulties have been
encountered when processing finely crystallized material. To guaranty a good
differential recovery, grinding must break the different sulphides minerals
free of each other. If the crystals are too fine and too interwoven, grinding will
either not liberate each mineral species or produce a powder that is so fine
that flotation will be impossible. It is suspected that deep-sea sulphides might
fall in this category. For such complex ores, flotation may be unable to
separate the minerals completely: the copper concentrate can contain 10% of
lead and 8% of zinc, while for the same ore, the lead concentrate can retain
12% of zinc.
An alternative to flotation is bio-metallurgy where anaerobic bacteria –
possibly the same bacteria living in the hydrothermal environment - can be
used to destroy the sulphides and liberate sulphuric acid. The acid will leach
the metals, and the pregnant solution will be treated later by
hydrometallurgy. The major problem is the abundance of iron that must be
inhibited by controlling the redox, a delicate operation.
Concentrates obtained by ore processing are sent to metallurgic
treatment plants where two families metallurgical processes can be used to
obtain the metals of commercial interest:
- Hydrometallurgy after dissolution of the concentrates by an acid
reagent, then eventual separation by organic solvents and final
electro winning;
- Hydrometallurgy or smelting of the ore in a reduction furnace and
separation using the densities of the different metals and slag.
Direct leaching of the crude ore cannot be envisaged, because the
process will be time and space consuming, and the recovery very low, with
such a complex mineral assemblage.
Metals recoveries have not been established at the present time.
However, some highly speculative hypothesis can be made in comparison
INTERNATIONAL SEABED AUTHORITY 440