Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ib metal
Reexamination Certificate
1998-03-11
2001-02-06
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ib metal
C423S027000, C423S030000, C423S031000, C423S109000, C423S150100, C422S226000, C366S102000, C261S087000
Reexamination Certificate
active
06183706
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to autoclaves and specifically to autoclaves having high rates of oxygen transfer to metal-containing solutions.
BACKGROUND OF THE INVENTION
To oxidize sulfide sulfur and thereby permit solubilization of metals compounded with the sulfide sulfur, base metal ores and concentrates, and refractory gold ores and Concentrates are commonly treated by pressure oxidation. Pressure oxidation is typically performed by passing a feed slurry of a metal-containing material through a sealed autoclave (operating at superatmospheric pressure) having multiple compartments. To provide for oxidation of the sulfide sulfur in the slurry, oxygen is typically fed continuously to the autoclave by means of a sparge tube located below the impeller. Commonly a large portion of the oxygen reacts with the sulfide sulfur, but there is a smaller significant portion that is vented from the autoclave and may be considered not effectively utilized.
In designing an autoclave, there are a number of considerations. By way of example, the autoclave should permit reaction of as much of the oxygen as possible with sulfide sulfur. If the oxygen is inefficiently reacted with the sulfide sulfur, the autoclave can have higher oxygen plant capital and operating costs. The autoclave should provide as short a residence time as possible for a given volume of slurry while realizing a high rate of recovery for the metal. Finally, the autoclave should vent inert gases that build up in the autoclave above the slurry to prevent rupturing of the autoclave from high pressure gas. Some oxygen gas is inevitably vented along with these inert gases. Other processes, which rely on efficient and effective gas/liquid transfer of oxygen and which are commonly carried out in autoclaves, include catalytic chemistry reactions, such as the conversion of ferrous to ferric ions, reoxidation of NO by oxygen, and cuprous amine conversion to cupric amine.
SUMMARY OF THE INVENTION
These and other design objectives are satisfied by the autoclave of the present invention. The autoclave includes a vessel for containing a feed slurry material, such as a metal sulfide-containing slurry, or a liquid comprising dissolved chemical compounds and an impeller attached to a rotatable shaft for agitating the feed slurry material. The shaft has a passage for an oxygen-containing gas and an outlet in communication with the passage for dispersing the oxygen-containing gas in the slurry. In one configuration, the passage passes along the length of the rotatable shaft, and the outlet is located at or close to the tip of the impeller.
The autoclave can realize relatively high oxygen transfer rates to the feed slurry material relative to conventional autoclaves through better oxygen gas dispersion in the feed slurry material. Commonly, the autoclave can yield an oxygen transfer rate of at least about 2 kg moles oxygen/cubic meter of slurry/hour. At such high oxygen transfer rates, a high rate of metal recovery can be realized in a relatively short residence time, and therefore lower capital and operating costs for the autoclave equipment can be realized relative to conventional pressure oxidation processes.
The autoclave is able to accomplish such high oxygen transfer rates without the use of a sparge tube. The sparge tube has proven to be an ongoing source of maintenance problems in existing pressure oxidation processes.
To consume as much oxygen as possible, the rotatable shaft can have an inlet for the oxygen containing gas located at an upper end of the shaft that is above the slurry surface yet is contained within the vessel. The inlet will provide a suction, drawing the atmosphere in the autoclave into the passage. After passing through the passage, the gas is dispersed into the feed slurry material. In this manner, the oxygen is continuously recycled during pressure oxidation to provide a high rate of oxygen utilization. By efficiently reacting the oxygen, the autoclave can have lower oxygen plant capital and operating costs than conventional autoclaves.
New oxygen can be supplied to the autoclave either directly through the rotatable shaft or through a separate conduit such as one having an outlet in close proximity to the impeller shaft gas inlet or above the feed slurry material. In the latter case, the shaft must include the inlet at the upper end of the shaft to permit oxygen escaping from the agitated feed slurry material into the autoclave atmosphere and/or supplied to the atmosphere to be drawn into the shaft and thereby entrained in the agitated feed slurry material.
Autoclaves can include a discharge control means for controllably removing the gas atmosphere from the sealed autoclave to prevent rupture of the autoclave from high pressure gases. The system includes:
(a) analyzing means (e.g., a gas analyzer) for analyzing a selected component (e.g., carbon dioxide and/or molecular oxygen) in the gas atmosphere inside the autoclave;
(b) an outlet for removing gas in the gas atmosphere from the autoclave interior;
(c) a controller (e.g., a computer) for receiving a signal from the gas analyzer and generating a control signal in response thereto; and
(c) a control means (e.g., a valve) for controlling the amount of gas removed in response to the control signal received from the controller. The control means vents the gas atmosphere when the amount of the component exceeds or falls below a threshold amount. In this manner, the autoclave can vent oxygen gas and other gases that build up in the autoclave above the slurry while maintaining the oxygen gas in the autoclave as long as possible for consumption in the oxidation of sulfide sulfur.
In operation, pressure oxidation using the autoclave follows the following steps:
(a) agitating a feed slurry material in the autoclave using the impeller, and
(b) during the agitating step (a), passing an oxygen-containing gas through the rotatable shaft and dispersing the gas radially outward from the shaft into the feed slurry material. In one autoclave configuration, the gas is passed through a blade of the impeller outwardly into the slurry.
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EKATO Pamphlet; “Mixing Update for Gassing Applications: EKATO S Self-Aspirating Impeller System”; 2 pages, which is believed to have been published in 1997, no month.
Bos Steven
Placer Dome Inc.
Sheridan & Ross P.C.
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