Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2001-07-05
2002-08-13
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C075S743000, C252S088100, C423SDIG001
Reexamination Certificate
active
06432166
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for the control of dust during mining operations.
BACKGROUND OF THE INVENTION
In the mining and processing of ores, ore handling points such as milling, crushing, stockpiling, dump pockets and conveyor belt transfer points give rise to significant airborne dust pollution problems. This is a particular problem with ores such as copper ores since many copper mines are located in arid regions of the world. There are increasing pressures to control dust for environmental reasons as well as for protecting the health of mine workers. Conventional mine dust suppression methods typically comprise spraying a solution of a dust suppressant composition onto surfaces that normally generate dust such as haul roads, etc. These compositions and methods are, however, often not satisfactory for use on ore at transfer points where the ore is dumped from one conveyor belt onto another or dumped from a conveyor belt onto a heap, since such dust suppressant compositions can interfere with further processing of the ore such as leaching and solvent extraction steps. This is a particular problem where bacteria are involved in heap leaching the ore. Dust control agents based on formulations containing conventional surfactants such as nonylphenol ethoxylates, alkylbenzene sulfonates, alcohol ethoxylates, etc., are toxic to these bacteria or are toxic to the bacteria when the quantities of the dust control agents are not closely monitored and controlled.
There is a strong need for dust control agents that can be freely used on ores during crushing, milling, conveying and stockpiling, i.e. dust control agents that do not interfere with the further processing of the ores, including the bioleaching of sulfide ores.
SUMMARY OF THE INVENTION
It has now been discovered that aqueous dust suppressing compositions (dust control agents) containing certain alkyl polyglucosides which exhibit fast wetting times and weak emulsifying properties result in minimal interference with the phase separation step of the solvent extraction process for the recovery of heavy metals from their ores such as the recovery of copper from copper ore using heap, dump, or vat leaching in combination with solvent extraction and electrowinning, and in addition exhibit very low toxicity to the bacteria responsible for leaching copper and other metals from sulfide ores. Hence, the aqueous dust suppressing compositions of the invention can be applied directly to ore crushing, milling and transport, especially on conveyor belts, preferably at conveyor belt transfer points, as highly effective dust control agents.
The alkyl polyglucosides used in the aqueous compositions of the invention have alkyl groups that contain an average of from 8 to 12 carbon atoms and a degree of polymerization of from 1.4 to 1.6. Such alkyl polyglucosides rapidly wet the solid material such as the ore and dust, etc., onto which they are applied, retard the rate of water evaporation from the applied solids, exhibit acceptable foaming levels and are environmentally acceptable in that they are readily biodegradable and exhibit low toxicity and favorable aquatic and eco-toxicity. The present invention accordingly relates to a process for suppressing dust on conveyor belts or at conveyor belt transfer points which comprises contacting the conveyor belt contents with a dust suppressing effective amount of an aqueous solution of an alkyl polyglucoside or alkyl polyglucoside mixture of the formula I
R
1
O(Z)
a
I
wherein R
1
is a monovalent alkyl radical having on average from 8 to 12 carbon atoms; Z is a glucose residue; a is a number having a value from 1.4 to 1.6.
The above alkyl polyglucosides and mixtures thereof also provide rapid phase disengagement, clean interface after phase separation, rapid kinetics of metal extraction, good selectivity for metals such as copper over iron extraction, low tendency for foaming, and low viscosity for ease of handling.
DETAILED DESCRIPTION OF THE INVENTION
Other than in the operating examples, or where other indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”.
While the present methods and compositions can be used with metal ores including metal sulfide ores other than copper ores, the following description will be directed to copper ores for which the invention will most likely have the greatest applicability.
Prior methods and compositions for dust suppression, as discussed above, are not all satisfactory for use in open pit copper oxide ore mining operations using solvent extraction for metal recovery because many of those surfactants used in the spray solutions interfere with the phase separation step. More specifically, in open pit copper mining operations wherein the ore is referred to as oxide ore, the copper is recovered from the ore by leaching with aqueous acid. The leaching is accomplished by trickling aqueous acid, such as dilute sulfuric acid, over and through pieces of ore having a relatively large surface area. The leach solution dissolves salts of copper and other metals as it trickles through the ore, to provide an aqueous solution of the mixture of metal values. The aqueous solution is mixed in tanks with an extraction reagent which is dissolved in an organic solvent, e.g., a hydrocarbon fraction. This is commonly referred to as the organic phase. The reagent includes an extractant chemical which selectively forms metal-extractant complex with the copper ions in preference to ions of other metals. The step of forming the complex is called the extraction or loading stage of the solvent extraction process. The organic phase is transferred to a large settling tank, where the organic solvent, now containing the copper-extractant complex in solution, is separated from the depleted aqueous solution (aqueous phase). This part of the process is called phase separation. Usually, the process of extraction is repeated through two or more mixer/settler stages, in order to more completely extract the desired metal. The process is described in detail in U.S. Pat. No. 4,582,689, the entire contents of which are incorporated herein by reference.
If the ore that is used is coated with conventional surfactants used for dust control and these surfactants enter the leach solution during the leaching step, phase separation does not occur cleanly when the leach solution is mixed with the organic phase during the solvent extraction process. That is, the surfactant acts as an emulsifier, causing the organic and aqueous phases to become suspended in each other thereby retarding the rate of phase separation and increasing entrainment values, thus adding cost to the entire process.
The compositions of the present invention cause minimal interference with the phase separation step, and this is true for sulfide ores as well as for oxidic ores and ores of other chemical composition.
With specific reference to copper sulfide ores and other metal sulfide ores, the sulfide ores are typically bioleached with iron and sulfur oxidizing bacteria, such as
Thiobacillus ferrooxidans, Leptospirillum ferrooxidans, Thiobacillus thiooxidans,
Sulfobacillus species (which naturally develop within bioheaps when the temperature rises above 40° C.), and other microorganisms such as the extremely thermophilic Archaea microorganisms that include Sulfolobus, Acidianus, and Metallosphaera species. In general, some or all of these bacteria are endemic in the ore. In the bioleaching step, iron oxidizing bacteria oxidize ferrous iron to ferric iron which in turn oxidizes the sulfide ion to sulfur, resulting in liberation of the copper from the insoluble sulfide. It has now been discovered that the application of effective quantities of the aqueous dust suppressing compositions of the invention to the sulfide ores during crushing, milling or conveying, preferably at conveyor belt transfer points, does not result in toxic effects on the bacteria during the bioleaching step. In addition, cl
Fisher G. Timothy
Olafson Stephen M.
Virnig Michael J.
Andrews Melvyn
Cognis Corporation
Drach John E.
Millson, Jr. Henry E.
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