Method and apparatus for mining of ocean floors

Suboceanic particulate solids containing useful metal values are recovered from ocean floors by extending a recovery tube from above an ocean surface to the ocean floor and confining a column of sea water therein, injecting a pressurized gas into the base of said tube, while separately contemporaneously injecting thereat an aqueous solution of at least one water-soluble, high molecular weight suspension enhancing polymer, whereby forming a diluted dispersion of particulate ocean floor solids and propelling same to the ocean surface, and there recovering said particulate solids from the dilute dispersion.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention relates to the mining of undersea formations, and, 
more especially, to the recovery of oceanic solids containing metal values 
from deep submarine deposits, e.g., ocean floors. 
2. Description of the Prior Art: 
Metal bearing deposits present on the surface of certain ground regions, or 
strata, covered by seawaters and the oceans constitute potentially 
enormous sources of metallurgical values. These are in widely differing 
forms, varying from muds rich in metals to polymetallic nodules and 
metal-containing chimneys. The abundance of valuable metals in these 
deposits has heightened interest in the industrial exploitation or mining 
recovery thereof. However, their recovery presents certain obvious 
economic and technical problems, as such values are located at ocean 
depths of up to 6,000 meters. Moreover, the dimensions of these solid 
particulates vary from a few millimeters to tens of centimeters. This, 
together with their weight, directly affects the efficiency of any 
recovery/collection thereof. 
It has already been considered, on an experimental scale, to apply the 
airlift pumping method for the mining of suboceanic deposits/formations 
(J. P. Jacquemin, J. F. Lapray, R. Porte, "IInd International Colloquium 
on the Exploitation of the Oceans", Bordeaux, Oct. 1-4, 1974). 
According to this technique, air is injected into the lower region of a 
tube partially submerged in a body of water. The gas lightens the column 
of water confined in the tube and raises its level. Beginning with a 
certain stream of air, the two-phase mixture escapes at the upper end of 
the tube, thereby generating or establishing a pumping effect. However, 
the raising of heavy or large particles, such as boulders, is very 
difficult at great depths in view of the low suspension capacity of a 
two-phase air/water mixture. 
SUMMARY OF THE INVENTION 
Accordingly, a major object of the present invention is the provision of an 
improved process for the recovery of deep suboceanic mineral values which 
conspicuously avoids those disadvantages and drawbacks to date 
characterizing the state of this art. 
Briefly, the present invention features the recovery of solid metal values 
from deep submarine formations by the injection of a gas into the lower 
end of a column of sea water confined in a tube submerged in the ocean and 
causing the establishment and entrainment of a dispersion of particulate 
solids in the water. Consistent therewith, an aqueous solution containing 
at least one suspension enhancing additive selected from among the high 
molecular weight, water soluble polymers, is injected and diluted in the 
dispersion at the base of the column, the dispersed mixture is forced 
toward the surface by the pressure of the gas, and the solids are then 
separated therefrom.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
More particularly according to the present invention, exemplary of high 
molecular weight, water soluble polymers having a good suspending power, 
and suitable for the production of the aqueous solution, are fermented 
polysaccharides, natural gums, acrylic polymers such as polyacrylamides 
and polymethacrylamides, cellulose derivatives such as 
hydroxyethylcellulose and carboxymethylcellulose, and the various mixtures 
thereof. 
Among such polymers, preferred are the polysaccharides of microbial origin, 
which are products of the fermentation of a carbohydrate under the action 
of microorganisms, for example bacteria belonging to the genus 
Xanthomonas, the genus Arthrobacter, the genus Azotobacter, the genus 
Agrobacterium, the genus Erwinia, the genus Alcaligenes, and fungi 
belonging to the genus Sclerotium. Xanthan gum is most particularly 
preferred in view of its excellent stability in sea water, its good 
suspension capability and its lack of toxicity relative to underwater 
flora and fauna. 
An aqueous solution is advantageously used which contains xanthan gum and 
at least one other water soluble polymer desirably synergistic therewith 
as regards the ability for suspending solid particles. As specific 
examples, mixtures of xanthan gum and of the galactomannans, such as guar 
gum, carob gum, cassia gum, tara gum and the like, are particularly 
representative. 
The aqueous solution of the polymer may be prepared from a powder or an 
aqueous concentrate. In one advantageous embodiment of the invention, the 
solution is prepared at the surface and injected into a flow of gas, with 
the polymer concentration ranging from 0.5 to 5% by weight as a function 
of the polymer or polymers, such as to provide, after dilution with the 
sea water contained in the column, a useful concentration preferably 
ranging from 0.005 to 0.5% by weight. 
Referring specifically to the accompanying FIG. 1, the apparatus according 
to the invention comprises a principal tube member 1 equipped at its upper 
end with outlet conduits 2 and 3 and at its base with a mixing chamber 4. 
The pipes or conduits 2 and 3 may be connected to any means (not shown) 
for liquid/solid separation. A pipe 5 is mounted in the center of the tube 
1 for the introduction of the aqueous polymer solution into the chamber 4. 
Two lateral conduits 6 and 7, connected with a source of distribution, 
enable the injection of a gas under pressure into the chamber 4. 
The assembly is immersed to a depth h, which in practice is the height 
between the bottom and the surface of the ocean. The pressure equilibrium 
equalizes the water level in the tube 1 at the surface level. The process 
of the invention features injecting a gas, for example air, through 
conduits 6 and 7 under a pressure P +.rho.gh, (wherein .rho. is the 
density of the water, and g is the gravity), which makes it possible to 
initiate the pumping action. Simultaneously, an aqueous solution of the 
polymer is injected via line 5, at a rate of q'=aq, wherein 9 is the rate 
of the rise of the liquid in the tube 1 and 2 ranges from 0 to 1, 
preferably from 0.01 to 0.5. 
The injected air rises in 1 while lightening the column of water and 
initiating a pumping effect. The polymer solution is suctioned with the 
water of the surrounding sea, while entraining the solids to be elevated, 
which are retained in suspension along their ascending path in the 
apparatus 1, to the outlet lines 2 and 3. The dispersion is then collected 
and the valuable solids are separated from the aqueous phase, which may be 
recycled at level 5. 
The use of the polymer has the particular advantage of enhancing the 
laminar nature of the ascending countercurrent flow, this "laminar" mode 
being favorable to the rise of the particles in suspension. 
In order to further illustrate the present invention and the advantages 
thereof, the following specific example is given, it being understood that 
same is intended only as illustrative and nowise limitative of the scope 
of the claims. 
EXAMPLE 
An experiment was simulated in the laboratory using the apparatus shown in 
FIG. 1. The tube 1 had a height of 200 cm and a capacity of 5 liters. The 
device was confined in a cylindrical envelope filled with sea water to the 
height of h=180 cm, and at the base of which gravel having a mean 
dimension of 5 mm and a density of 2.5 was introduced. Air was injected 
through lines 6 and 7 at a rate of 20 to 27.5 dm.sup.3 /min. An aqueous 
solution of 0.5% by weight of xanthan gum (RHODOPOL 23.RTM., was injected 
through line 5 into the sea water at a rate such that, after dilution with 
the sea water suctioned therein at level 4, the concentration of the 
polymer in the water contained in tube 1 Was 0.05%. The solids raised were 
separated from the dispersion collected at outlets 2 and 3 and the 
solution was continuously recycled at level 5. 
The efficiency of the process was determined by measuring the weight of the 
gravel recovered in g/min as a function of the flow rate of the air. The 
results are shown in FIG. 2, curve 2, compared to the same experiment 
carried out under the same conditions, but without using the xanthan gum 
(curve 1). With a flow of air of 27.5 dm.sup.3 /min, according to the 
invention 130 g of solids were collected per minute, instead of 28 g per 
minute in the absence of xanthan gum. This constitutes an increase in 
yield by a factor of 4.5. 
While the invention has been described in terms of various preferred 
embodiments, the skilled artisan will appreciate that various 
modifications, substitutions, omissions, and changes may be made without 
departing from the spirit thereof. Accordingly, it is intended that the 
scope of the present invention be limited solely by the scope of the 
following claims, including equivalents thereof.