23 
sulfates is necessary before conversion to metallic form. The remain- 
ing manganese sulfates can then be processed further to yield ferro- 
manganese. 
The entire process is rather involved and exacting, but its overall 
complexity may be no greater than other methods. Companies that 
have sulfur dioxide to dispose of (as from copper smelters) may find 
this method attractive. 
Among the disadvantages are that the sulfate system is difficult to 
operate as a closed cycle and it is reported that 45 percent of the sulfur 
used is not recovered.1® This may present a pollution problem. How- 
ever, disposal of the unrecovered sulfate ion may be easier than sulfur 
dioxide if the latter were a disposal problem initially as in the case of 
smelter gas. 
AMMONIACAL LEACHING 
A third process, whereby only the associated metals of nickel, copper, 
cobalt, and molybdenum are recovered from the nodules, involves the 
use of ammoniacal solutions (ammonia plus an ammonium salt such 
as a carbonate, chloride, or sulfate). In order to dissolve the metals 
using ammoniacal solutions, the oxides must first be reduced (Fig. 12). 
This is accomplished by roasting with a gaseous reducing agent such 
as carbon monoxide or hydrogen. Elevated temperatures and pressures 
are used to improve the metal recovery from the reduction and leach- 
ing operation. This process is reported to recover 85 percent or better 
of the copper, nickel, cobalt, and molybdenum leaving the manganese 
and iron essentially intact.?® 
nodle? Fig. 12 Ammonia leach process 
F : 
©) ne Reduction 
came : ny . 
‘ Leaching and washing 
I 
Drying =a 
Fuel t 
OS 
| 
Wash solution 
Air 
Copper recovery KI QA Stripping 
Air 
See: | ky (7 stages) 
electrowinning 
Steam 
LG f Tailings 
lS = disposal 
electrowinning > Nickel > 
Ammonia NH3 makeup 
Cobalt recovery 
Source: Sisselman, R. op. cit., p. 84. Copyright 1975, Engineering and Mining Journal, 
1221 Avenue of ‘the Americas, New York, N.Y. 10020 
Nickel recovery 
38 Brooks, P. T. and D. A. Martin, Processing manganiferous sea nodules. U.S. Bureau of 
Mines, Report of Investigations 7473, 1971. 
19 Cardwell, op. cit., p. 41. 
