Chemistry: molecular biology and microbiology – Carrier-bound or immobilized enzyme or microbial cell;...
Reexamination Certificate
1997-10-03
2001-09-25
Ware, Deborah K. (Department: 1651)
Chemistry: molecular biology and microbiology
Carrier-bound or immobilized enzyme or microbial cell;...
C435S168000, C435S170000, C435S176000, C435S180000, C435S283100, C435S289100, C435S822000
Reexamination Certificate
active
06294362
ABSTRACT:
BACKGROUND OF THE INVENTION
Microorganisms play an important role in the mining industry where they are now used in the bioleaching recovery of copper, uranium, and gold (see Rawlings, D. E., S. Silver [1995] “Mining With Microbes,”
Biotechnology
13(August):773-778). Until now, microorganisms have not been used in conjunction with commercial chemical leach processes.
Copper sulfide (Cu
2
S) is an acid soluble metal sulfide that is a component in the mineral known as chalcocite. Currently in the mining industry, a solution of ferric sulfate (Fe
2
(SO
4
)
3
) is used to solubilize the copper from chalcocite by producing soluble copper sulfate (CuSO
4
), along with insoluble elemental sulfur (S) and soluble ferrous sulfate (FeSO
4
). The reactions involved, in summary form, are:
Cu
2
S+Fe
2
(SO
4
)
3
→CuS+CuSO
4
+2FeSO
4
CuS+Fe
2
(SO
4
)
3
→CuSO
4
+S+2FeSO
4
The stripped leach solution, or raffinate, from this process contains ferrous sulfate (FeSO
4
). Ferrous sulfate is a product having little value or utility and is often a waste product from the leaching process. A means to rapidly convert the ferrous sulfate waste back to ferric sulfate would enhance the efficiency of the chemical leaching process as well as providing an environmentally beneficial effect.
Johnson et al. ([1988]
Mining Engineering
December:1119-1122) describe a microbial process by which the conversion of ferrous sulfate to ferric sulfate can be accomplished. In the biological process, ferrous sulfate (FeSO
4
) is acidified with sulfuric acid (H
2
SO
4
). Then, in the presence of oxygen (O
2
) and carbon dioxide (CO
2
), iron-oxidizing bacteria restore the iron sulfate to its oxidized ferric sulfate form. The reactions, in summary form, are:
4
FeSO
4
+
2
H
2
SO
4
+
&AutoLeftMatch;
O
2
⟶
iron
-
oxidizingbacteria
CO
2
2
Fe
2
(
SO
4
)
3
+
2
H
2
O
2
S
+
3
O
2
⟶
2
H
2
SO
4
BRIEF SUMMARY OF THE INVENTION
The subject invention concerns a unique system, including equipment and an improved process, for using bacteria to oxidize a metal cation. In a preferred embodiment, the system of the subject invention is used to reactivate raffinate to a high ferric sulfate solution in chemical leach operations. In this embodiment, the system of the subject invention is termed a “biological raffinate converter,” BRC. The structure and operation of the BRC, which comprises a passive bioreactor trickle filter, which does not require any moving parts or gas injection systems, are disclosed below.
The BRC of the subject invention is a distinct improvement over the Johnson et al., supra, process in that the invention process provides enhanced efficiency and commercial utility.
In a particular embodiment, the system of the subject invention utilizes a trickle bed reactor for the conversion of ferrous ions to ferric ions. This reactor can utilize oxidizing bacteria that reside in the reactor bed and are attached to a packing medium within the trickle bed. In a preferred embodiment, the packing medium is a high surface area material. This medium can be, for example, ring and pin configuration polyethylene balls. In a specific embodiment, the packing medium is coated with a substrate to which bacteria can attach and propagate. Advantageously, this substrate can provide an energy source for the attached bacteria. Substrates which can be used according to the subject invention include graphite and sulfide concentrates, such as pyrite. The substrate may be attached to the packing material by an appropriate bonding agent such as polyethylmethacrylate or paraffin. In one embodiment, the substrate can support the growth of fungi. In this embodiment, inoculation of the packing medium with acidophilic fungi advantageously provides carbon dioxide as a carbon source for oxidizing bacteria.
The system of the subject invention may consist of a single reaction chamber or cell, or it may consist of multiple cells connected in series. When multiple cells are utilized, venting may be provided between the cells.
The components of a preferred embodiment of the BRC of the subject invention comprise (1) a column through which raffinate is passed by gravity flow, (2) a high surface area substrate, e.g, one-inch to one and a half-inch “BIOBALLS,” coated with a bio-catalyst, which are loaded into the column. “BIOBALLS” are preferably polypropylene, but can be other appropriate polymeric material. The bio-catalyst can be coated onto the surface of the “BIOBALLS” by use of an adhesive medium, e.g., paraffin. The bio-catalyst-coated “BIOBALLS” can serve as a substrate for the growth of fungi and iron-oxidizing bacteria which synergistically provide the oxidizing environment for oxidizing (converting) ferrous ion content to a higher percentage ferric ion content in the raffinate. The synergistic relationship of the fungi and the iron-oxidizing bacteria involves the production by the fungi of carbon dioxide, a carbon source for the bacteria which oxidize the ferrous ion.
The application flow rate of the raffinate through the trickle filter of the subject invention can be, for example, about 60 liters/hour, with the conversion being 3.0 grams per liter per hour. See FIGS.
2
and
3
.
REFERENCES:
patent: 5246486 (1993-09-01), Brierley et al.
patent: 5766930 (1998-06-01), Kohr
patent: 5914441 (1999-06-01), Hunter et al.
Johnson, A.M., D.H. Carlson, S.T. Bagley, D.L. Johnson (1988) “Investigations related to in situ bioleaching of Michigan chalcocite ores” Mining Engineering, Dec., pp. 1119-1122.
Rawlings, Douglas E., Simon Silver (1995) “Mining with Microbes” Biotechnology 13:773-778.
Sharp James E.
Stuffle Kevin
MBX Systems, Inc.
Saliwanchik Lloyd & Saliwanchik
Ware Deborah K.
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