24 
Kennecott has obtained a number of patents for ammoniacal leach- 
ing methods. This process is similar to one used to extract nickel from 
laterite ores and is believed to be the process favored by Kennecott for 
commercial use in nodule processing. 
SULFURIC ACID LEACHING 
Several investigators have tried leaching ferromanganese nodules in 
sulfuric acid under various conditions of time, temperature, and 
acidity (Fig. 13). The basis of this method is that individual metals 
exhibit differing degrees of solubility under varying conditions of 
acidity. The problems mainly involve a trade-off between the efficiency 
of extraction and the amount of unwanted material extracted or selec- 
tivity of extraction. In general, the method is not regarded as bein 
selective enough for commercial operations. Copper, nickel, and cobalt 
are readily dissolved, but appreciable amounts of manganese and iron 
along with several trace metals are also leached. This leads to problems 
in further separation. An additional disadvantage is the large amount 
of acid consumed, about ten times that equivalent to the dissolved 
metals. Presumably this is due to the large amount of basic material 
trapped within the nodules.*° Furthermore, if a closed loop system is 
devised, the concentration of trace metals will build up in the leach 
liquor making purification of the economic metals more difficult. 
Wet nodules Fig. 23 Sulphuric acid process 
Pressure leaching 
Srushing eal on 
Grinding i ' 
ste 
> 2804 -— (OS ofA] 
P. 
am 
H.P. steam A 
tPE : Wash 
Leaching H50 U) esning 
autoclaves Flash 
Steam 
Limestone 
: Tailings 
: disposal 
= Copper (6 stages) 
electrowinning 
Cobalt recovery 
Nickel recovery 
ag [t A : Cobalt 
electrowinning 
electrowinning 
Ammonium A alohate 
Steam sulphate plant mse 
‘ 
Source: Sisselman, R. op. cit., p. 85. Copyright 1975, Engineering and Mining Journal 
1221 Avenue of the Americas, New York, N.Y. 10020. z mn z i 
20 Toid. p. 41. 
