Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ib metal
Utility Patent
1997-09-24
2001-01-02
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ib metal
C423S038000, C423S041000
Utility Patent
active
06168766
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for leaching copper from copper sulfide using bacteria. More particularly, this invention relates to a process for promoting the velocity and rate of leaching of copper by keeping a redox potential of a leaching solution containing bacteria in a specific range.
2. Description of the Related Art
It is typical from an economical point of view to employ a process of extracting a target ore using lixiviate such as an acid and, thereby recovering precious metals from low grade ores. Leaching methods include an in-site leaching method, a heap leaching method, a vat leaching method, an agitation leaching method or the like. Among these methods, those considered to be suitable for treating the target ore, as well as the most economical, are employed. The in-site leaching method is characterized by a leaching solution directly disseminated into gob or ore deposit. In a dump leaching method or heap leaching method, dug ores are leached by scattering lixiviate solution on the ores. In the agitation leaching method, dug ores are mixed and agitated for extraction after milling.
The dump, or heap leaching method, is generally used in a leaching process for low grade ores. The rate of leaching of copper is 90% when copper oxide ores are treated with sulfuric acid for 1-2 months. However, when leaching treatment of copper sulfide ore is performed for one year, the rate of leaching of copper is 30% or less for primary copper sulfide (charcopyrite and the like), and 40% or less for secondary copper sulfide (chalcocite and covelline). These methods are uneconomical because of the low leaching rate.
As for leaching from copper sulfide, therefore, processes using bacteria are employed.
Thiobacillus ferrooxidans
(iron oxidizing bacteria),
Thioabacillus thiooxidan
(sulfur oxidizing bacteria) and the like are known bacteria species suitable for bacteria leaching. The various bacteria exhibit different characteristics depending on the district of origin. There are often cases where only bacteria sampled in a specific place arc effective depending on the sort of ores.
Bacteria leaching of copper sulfide includes two mechanisms, direct leaching and indirect leaching. In direct leaching, bacteria directly contribute to the oxidation of copper sulfide (see formula (1)). In indirect leaching, bacteria oxidize an iron source, such as pyrites and the like in ores, to produce trivalent iron ions that contribute to copper leaching. The trivalent iron ions are reduced to bivalent iron ions. The bivalent iron ions are oxidized to trivalent iron ions, and the leaching cycle is repeated (see formulae (2) and (3)). It is difficult to separate these reaction processes, and it is thought that these reaction processes proceed simultaneously.
Specifically, the direct leaching process (in the case of chalcocite) is represented by the following reaction formula:
Cu
2
S
+
2
1
2
O
2
+
H
2
SO
4
→
2
CuSO
4
+
H
2
O
(
1
)
The indirect leaching process (in the case of chalcocite) is represented by the following reaction formula:
4
FeSO
4
+
O
2
+
2
H
2
SO
4
→
2
Fe
2
(
SO
4
)
3
+
2
H
2
O
(
2
)
Cu
2
S
+
2
Fe
2
(
SO
4
)
3
+
1
1
2
O
2
+
H
2
O
→
2
CuSO
4
+
4
FeSO
4
+
H
2
SO
4
(
3
)
However, there is the problem that the rate of leaching of primary copper ores is not greatly improved over the conventional processes by using bacteria. Also, there is the problem that the optimum leaching conditions are different depending on the ores, shape of ores, storing condition of ores, properties of a mother rock, natural environment and the like. Besides the above conditions, essential factors relating to the process for leaching from copper ores include the number of bacteria, leaching temperature, leaching pH, amount of leaching solution, and amount of oxygen supplied.
SUMMARY OF THE INVENTION
This invention provides solutions to the problems described above. An object thereof is to provide improvements in the rate of leaching of copper in the bacteria leaching process with copper sulfide, as employed at present. Also, the present invention provides a process that promotes the overall velocity and rate of leaching.
The present inventors have studied the use of ores containing chalcocite to achieve the above object and, have developed the following processes of the present invention:
The invention is directed to a process for leaching copper by a bacteria leaching process using ores containing copper sulfide, wherein copper is leached with an acid leaching solution having a redox potential of from 550 to 750 mV, based on a silver/silver chloride electrode as a standard.
The invention is directed to a process for leaching copper, wherein the concentration of iron in the acid leaching solution is 5 g/IL or more, and the ratio of trivalent iron ions to bivalent iron ions (referred to as “Fe
3+
/Fe
2+
ratio,” hereinafter) is 50 or more. The invention is directed to a process for leaching copper, wherein iron is added to the acid leaching solution.
The invention is directed to a process for leaching copper, wherein a barren solution produced by recovering copper from the leached pregnant solution is repeatedly used as the acid leaching solution, and iron powder or a solution containing iron ions or iron powder is added to the acid leaching solution.
The invention is directed to a process for leaching copper, wherein the acid leaching solution contains one or both of an iron oxidizing bacteria and a sulfur oxidizing bacteria at a concentration of 10
6
microbes/mL.
The invention is directed to a process for leaching copper, wherein the acid leaching solution utilizes one or both of an iron oxidizing bacteria and a sulfur oxidizing bacteria and wherein the bacteria are contained in ores.
The object of the present invention is to provide a process that enables the leaching time period to be shortened by positively controlling the bacteria concentration and the redox potential that is determined by the iron ions utilized for copper leaching.
Illustrating the actions of the processes having the above figures, the iron oxidizing bacteria oxidize Fe
2+
to Fe
3+
, whereas the sulfur oxidizing bacteria oxidize S and H
2
S and also oxidize Fe
2+
to Fe
3+
at the same time. Both bacteria acquire energy for maintaining life by these oxidation processes. Utilization of Fe
3+
in the acid leaching solution promotes the ionization of copper. Also, a high redox potential is required so that copper elutes into the solution. The redox potential is the driving force for the elution. The relation between the Fe
3+
/Fe
2+
ratio and redox potential of the acid leaching solution is defined by the following formula (4):
E=0.77+0.0591og (aFe
3+
/aFe
2+
) (4)
wherein “E” represents a redox potential and “a” represents an ion concentration.
Besides the influences of other ions that are impurities, the redox potential is determined by the Fe
3+
/Fe
2+
ratio and it is necessary to increase this ratio. The amount of Fe
3+
in the acid leaching solution is increased and a high Fe
3+
/Fe
2+
ratio is maintained to promote the extraction of copper. Specifically, the oxidation by bacteria is promoted and oxidizing agents are added so that it is possible to keep a constant Fe
3+
/Fe
2+
ratio by controlling the amount of Fe
3+
and the redox potential.
Sulfuric acid, nitric acid, hydrochloric acid are given as the acid leaching solution used in the present invention. Of these, leaching using sulfuric acid is preferable since sulfur is contained in copper sulfide. Iron oxidizing bacteria, sulfur oxidizing bacteria and the like are used. These bacteria are generally bacteria growing under
Imai Tetsuo
Saitoh Atsushi
Bos Steven
Nippon Mining & Metals Co., Ltd.
Stockton LLP Kilpatrick
LandOfFree
Process for leaching copper from copper sulfide using bacteria does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for leaching copper from copper sulfide using bacteria, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for leaching copper from copper sulfide using bacteria will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2541997