Metallurgical apparatus – Having means for leaching and subsequently precipitating a...
Reexamination Certificate
2000-09-12
2003-09-02
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Having means for leaching and subsequently precipitating a...
C266S170000
Reexamination Certificate
active
06613271
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to apparatus and methods for recovering valuable metals. particularly gold using an in line leach reactor. In particular non-limiting aspects, the invention also provides apparatus for dewatering and leach reactors which may be suitable for carrying out the method the invention.
BACKGROUND OF THE INVENTION
Processes for the recovery of gold from gold bearing feeds have typically involved the use of a cyanidation step to convert the elemental gold into a soluble ionic form. The gold in solution can then be separated from the bulk mineral material which stays in solid form by a simple liquids/solids separation process (e.g. sedimentation or filtration).
The solution containing dissolved gold is then subjected to a gold recovery process such as the carbon-in-pulp process. In this process the gold in solution is adsorbed on an activated carbon substrate in the form of carbon granules and the gold is subsequently recovered.
While such processes have been successful in retrieving a significant proportion of the gold embedded in certain minerals, they suffer from significant disadvantages. For example, if the gold is present as nuggets or flakes larger than microscopic pieces, the cyanidation process, because of the relatively low concentration of the reagents used in the process, will generally not succeed in dissolving the larger pieces of gold. As a result. these larger pieces may be lost with the waste minerals discarded following the cyanidation process.
Furthermore, it is often the case that the minerals associated with gold deposits also include a proportion of native carbon. Unfortunately, this carbon is generally in a form which cannot be readily recovered or separated from the minerals. During the cyanidation process, the native carbon can adsorb a proportion of the gold during the leaching process. Depending upon the level of native carbon present in the mineral, the time taken for the leaching process and the concentration of the leaching reagents (i.e. sodium or potassium hydroxide and sodium or potassium cyanide) the amount of gold lost in this way can be quite significant.
Given the large volumes of mineral material which need to be treated using the cyanidation process, it is not practical to use high concentrations of reagents because of their cost, and also because of the environmental concerns associated with the use of large quantities of dangerous reagents. Thus, one is often faced with a situation where the relatively low concentrations of the reagents require high residence times for leaching. The longer the residence time the greater the proportion of gold which will be adsorbed by the native carbon. Thus the presence of native carbon in the minerals being leached means that a significant proportion, perhaps 25% or even 50% or higher of the gold which goes into solution as a result of the leaching reaction can be adsorbed by the carbon in the mineral and is ultimately lost when the leached mineral solids are discarded.
It is possible to ameliorate this problem to some extent by burning off the carbon in a roasting operation prior to leaching. However, it has been found that roasting, whilst it can drive off a significant proportion of the carbon in the mineral as carbon dioxide, is not totally effective in that a substantial quantity of the carbon can still survive the roasting process and remain in solid form intimately admixed or bound with the mineral. Thus, even after roasting, a significant proportion of the gold may be adsorbed by the remaining native carbon in the mineral during leaching. Furthermore, because the process of roasting is very energy intensive, the economics of the gold recovery process can be significantly worsened. This is particularly in light of the fact that gold deposits generally include only extremely small quantities of gold (of the order of grams per tonne) with the result that a huge amount of energy needs to be expended to roast tonnes of ore only to yield grams of gold.
Thus there is a need for a process and apparatus which avoids the need for a roasting step but which can yield high gold recovery rates not withstanding the fact that the minerals with which the gold is associated may include significant amounts of native carbon and/or pieces of gold of a size which are larger than a microscopic size i.e. large enough to be captured by a screen of 500 microns or even 1000 microns.
It is also desirable that the process and/or apparatus have a broad range of applications such as the recovery of gold from sulphide bearing minerals and concentrates or any other minerals which do not give high recoveries with normal gravity processes. It is even more desirable that the process and apparatus be adaptable to recover other valuable materials such as copper.
SUMMARY OF THE INVENTION
The invention provides, apparatus for the separation of a dense valuable material from a feed, including:
concentrator means for forming a concentrator containing the dense valuable material from the feed,
a leach reactor which includes a hollow member with inlet means and outlet means,
supply means for continuously supplying an aqueous leach reagent and the concentrate to the inlet means,
drive means for rotating the hollow member,
flow control means in the hollow member for controlling the rate of flow of the mixture of aqueous leach reagent and concentrate through the hollow member from the inlet means to the outlet means;
a solids/liquids separator for separating pregnant liquor from solids arranged to receive the mixture from the outlet means,
a recovery station for recovering dense valuable material from solution in the pregnant liquor to leave a spent leachate, and
recycle means for recycling the spent leachate to the leach reactor.
The term concentrator includes any form of apparatus for concentrating dense material in a feed or for separating dense material from a feed. Thus it includes conventional jigs or separators such as the “Harz Jig”, “Hancock Jig” or a separator of the type described and claimed in Australian Patent No. 684153 hereinafter referred to as the “In Line Pressure Jig”. It also includes banks of two or more concentrators joined in parallel or series.
An In Line Pressure Jig is a pressurised concentrator which uses an agitated bed to separate dense particulates from a slurry. The slurry flows across the top of the bed with dense particulates from the slurry passing through the bed to be collected in a hutch. The less dense tailings pass over the outer edge of the bed to be discharged via a tailings outlet.
The apparatus may be associated with a conventional gold recovery circuit such as a cyanidation circuit.
Suitably, the apparatus includes at least one concentrator which is an In Line Pressure Jig. The apparatus may include more than one concentrator. Where there is more than one concentrator the concentrators may be in series or in parallel. Most preferably they are in series.
In a preferred form of the invention the apparatus includes two In Line Pressure Jigs in series.
The or each concentrator may include an inlet, an overflow and an outlet. Thus the inlet may be arranged to receive incoming material containing the feed. The incoming material is most suitably mixed with water. The outlet may constitute an outlet for material which has been concentrated by the concentrator. The overflow may be arranged to allow material rejected by the concentrator to flow out of the concentrator.
Means for crushing a feed, such as a gold bearing feed, may be provided in association with the apparatus. The means for crushing may include a grinding mill.
Primary separator means may he associated with the apparatus. The primary separator means may be arranged to receive crushed feed from the means for crushing and to redirect it into a light fines stream, a heavy fines stream and a coarse material stream. Suitably the primary separator means is arranged to redirect the coarse material stream into the means for crushing.
The light fines stream may be directed to a gold removal circuit.
The heavy fine
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Kastler Scott
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