Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ib metal
Reexamination Certificate
1999-12-09
2001-05-29
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ib metal
C423S022000, C423S029000, C252S184000
Reexamination Certificate
active
06238632
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods and compositions for removing precious metals, such as gold, from activated carbon.
BACKGROUND OF THE INVENTION
As their common name implies, precious metals have great value. Precious metals have a large number of uses in a wide range of products. For example, gold is used in electronics as well as jewelry.
As a result of the substantial value of precious metals, they are widely sought after. Also, in processes involving precious metals, such as deposition on electronic structures, methods are employed to maximize their efficient use and reduce as much as possible the waste of precious metals. In view of the value of precious metals, materials and methods have been developed to be employed to optimize the removal of precious metals from precious metal-containing ore. Similarly, to help reduce waste, processes have also been developed to help ensure maximum removal of precious metals not utilized in any process.
In one example of a process for obtaining precious metals, activated carbon is utilized. For example, activated carbon may be utilized in extracting gold from gold-containing ore. Gold, which may be associated with one or more other materials, may be taken up by activated carbon. The gold must then be disassociated from the activated carbon.
SUMMARY OF THE INVENTION
To address the desire to increase precious metals in the context of a process that includes activated carbon for removing the precious metals, the present invention concerns a process for removing precious metals from activated carbon. According to the process, activated carbon containing precious metals is contacted with an aqueous solution of methyl ethyl ketoxime and sodium hydroxide.
According to one particular embodiment, the present invention provides a process for recovering gold. The process includes removing gold from gold-containing ore to a sodium cyanide solution. The gold and sodium cyanide solution is contacted with activated carbon. Then, the gold laden activated carbon is contacted with an aqueous solution of methyl ethyl ketoxime and sodium hydroxide.
The present invention also relates to a solution. The solution includes methyl ethyl ketoxime and sodium hydroxide.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.
DETAILED DESCRIPTION OF THE INVENTION
As stated above, activated carbon may be utilized in obtaining precious metals. As utilized herein, “obtaining” can include originally extracting precious metals from ore containing the precious metals, as well as recovering precious metals from processes involved in utilizing precious metals, such as electroplating. Activated carbon, which is derived from coconut shell, could be used in one portion of a process to obtain the precious metals from ore that includes the precious metals, for example. Extruded carbon could also be utilized in this process. Extruded carbon is activated carbon that has been gone through a molding process. The structure is substantially the same as the coconut shell fragments only pressed or man made. According to another example, activated carbon could be utilized to recover precious metals from a plating bath. Activated carbon may also have other uses for obtaining precious metals.
According to the particular process described above for extracting gold from gold-containing ore, pulverized ore is washed with a solution that includes sodium cyanide. Once in contact with the sodium cyanide, the gold will complex with the cyanide. While the sodium cyanide solution will help to extract gold from the raw ore, the gold must then be disassociate from the sodium cyanide.
To facilitate breakup of the gold and cyanide complex, the gold-cyanide complex may be contacted with activated carbon. The activated carbon acts as a sort of sponge, collecting the gold-cyanide complex, which is in solution. The activated carbon will continue to take up the gold-cyanide complex until a large portion or substantially all of the active sites on the activated carbon have been taken up, the gold “loading” of the activated carbon slows down. At this point, the gold needs to be separated from the activated carbon and cyanide.
To remove gold or other precious metals from activated carbon, the activated carbon with attached precious metals may be subjected to a hot caustic wash or strip at a temperature of about 200° F. to about 325° F. Sodium cyanide may be utilized in the wash. Typically, the caustic solution utilized includes about 1% to about 3% NaOH and has a pH of about 12.5. Such a wash is particularly useful when the precious metal is gold.
The wash removes the precious metal(s) from the activated carbon to the solution used in the wash. The precious metal laden solution may be referred to as “pregnant” solution. After removing the precious metal(s) from the activated carbon, the solution may be cooled below a flash point of the solution. The cooled solution may be passed through plating cells for removing the precious metal(s) from the solution through electroplating. Such cells are often referred to as “e-cells”.
According to a typical example of the above-described process, the activated carbon is processed in batches. Each batch involves the processing of about 8 to about 12 tons of precious metal laden, or loaded, activated carbon. In the case where the precious metal is gold, the activated carbon typically includes about 150 to about 350 ounces of gold per ton of activated carbon.
Prior to the hot wash or strip, the activated carbon may be subjected to a rinse process. The rinse process may be carried out with an acidic solution. Along these lines, the solution typically has a pH of about 4 to about 6 Typically, hydrochloric acid or nitric acid is utilized, although any suitable acid may be employed. The rinse may be employed to remove carbonates from the activated carbon. The rinse may also remove base metals.
In the event that a rinse, and particularly an acidic rinse, is utilized, the activated carbon may again be rinsed prior to precious metal removal. In the case of utilization of an acidic rinse, the additional rinse typically is carried out with fresh water. The fresh water may neutralize the acid that may have been previously used to rinse the activated carbon.
After any pre-rinses as described above, the activated carbon may be rinsed to separate the precious metal(s) from the activated carbon. According to typical examples, the rinse is carried out with a caustic solution. According to one example, a sodium hydroxide solution is utilized. Typically, such a solution includes about 1% to about 2% sodium hydroxide.
While the time that the precious metal removing rinse is carried out may vary, typically, the rinse takes place over a time period of about 8 hours to about 20 hours. In the rinse, temperature may affect the strip rate. Along these lines, higher temperatures typically increase strip rate. Another fresh water rinse may be carried out after the caustic rinse. The fresh water rinse may be carried out for about 20 minutes to about 30 minutes. The caustic and also the possible subsequent fresh water solution include the precious metal(s).
After removal of the precious metal(s), the activated carbon may be treated for reuse. According to one process, the activated carbon may be regenerated by heating. The heating may be carried out to any suitable temperature. For example, the activated carbon may be heated to a temperature of about 750° F. to about 1100° F. prior to being reused in
Ashland Inc.
Bos Steven
Connolly Bove Lodge & Hutz
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