Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-09-03
2002-02-26
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S234000, C266S168000, C266S170000
Reexamination Certificate
active
06350354
ABSTRACT:
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
CROSS REFERENCE TO RELATED APPLICATIONS
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to a plant for use in recovering metal from metal ore using a hydrometallurgical process. More specifically, this plant is a modular solvent extraction plant for extracting a metal such as nickel, cobalt, uranium, or copper from its corresponding metal ore. Still further, this plant may include an organic scrub station, which can be used to remove contaminants or other metals from organic solutions used in extracting the metal.
Metal may be recovered from metal ore through pyrometallurgical or hydrometallurgical processes. Pyrometallurgical processes use smelting to separate desired metals from undesired components and are the way a large percentage of metals produced today are obtained. A typical pyrometallurgical plant includes crushing, grinding, flotation, concentrating, smelting, and refining equipment. One disadvantage with pyrometallurgical processes is that certain metal ores cannot be satisfactorily treated by smelting. Another disadvantage of pyrometallurgical processes is that they create sulfur dioxide emissions. Still another disadvantage of pyrometallurgical processes is that they are less economically efficient.
Hydrometallurgical processes involve extracting metals from ores by dissolving them in aqueous chemical solutions. These processes are often more cost effective than pyrometallurgical processes. However, only certain ores, such as chalcocite (Cu
2
S), are leachable and thus amenable to hydrometallurgical treatment. Still further, controlling the leaching operation in the hydrometallurgical process is difficult in regions that have heavy or continuous rainfall because of the resulting high silt levels in the leachate.
Currently, conventional hydrometallurgical plants include multiple sets of dynamic pumper-mixers and large settlers that primarily use gravity to separate components in the various stages of hydrometallurgy including extraction, scrubbing, and stripping. Dynamic pumper-mixers, which have dynamic agitators, combine mixing and pumping functions in one piece of equipment. Thus, when increased flow rates are required, the dynamic mixer's speed (rpm) must be increased. The shear imparted by a dynamic mixer/agitator increases with the angular velocity of the agitator, which in turns increases with the radius of the impeller blade and pumper shroud. When agitation speed is increased, the higher shear creates a wider distribution of particle sizes, including the generation of a fine entrainment.
Dynamic mixers and mixer boxes that are conventionally used in hydrometallurgical plants are typically sized so as to require at least about 2 minutes of mixing. Still further, conventional settlers used in hydrometallurgical plants require approximately 6 to 8 minutes for settling because they are normally large vats that work only by allowing gravity to separate an emulsion mixture into a lighter organic phase and a heavier aqueous phase.
One disadvantage with the dynamic pumper-mixers that are currently used in hydrometallurgical plants is that they provide poor process control. For example, they have poor entrainment control for both oil phase into aqueous and vice-versa. As a result, conventional plants have higher operating costs because entrained fluid must be replaced, and certain entrained contaminants require treatment steps, although these combined costs are generally less expensive than the operating costs of pyrometallurgical plants. A disadvantage of conventional settlers is that large and unstable gunk layers (an emulsion of solid particulates, organic, air and aqueous solutions) regularly build up in the settler due to the dynamic mixer action and air being entrained by the mixer. When operating it, oil/aqueous (O/A) ratios close to 1/1, the gunk layer is unstable, and phase inversions occur frequently which require extensive operator attention to remediate. Another disadvantage with conventional hydrometallurgical equipment is that it requires a large inventory of expensive organic solution to be used in the settler(s) to allow gravity separation to take place, and because entrained organic solvent is created by excess shear, it is lost back to the leach areas. Furthermore, such plants can often be inefficient in transferring metal to an organic solution. Still further, entrained aqueous contaminants require expensive bleed streams and special additives in conventional plants in order to maintain a high quality metal electrolyte solution for making metal cathodes in the electrowinning tankhouse. Lastly, ions of iron in the aqueous entrainment reduce electrolytic efficiency by wasting electrical energy on the Fe
+++
⇄Fe
++
reaction.
In addition to the inefficient equipment in use in conventional hydrometallurgical extraction plants, another problem with these plants is that they are fixed in one location. Therefore, it becomes necessary to pump leach solutions back and forth from remote locations as a mine site matures and expands. Still another problem with such conventional plants is that they are basically open systems, which allows air entrainment and air-borne dust into the system and allows air pollution from the evaporation of the organic. Indeed, environmental regulations are forcing the installation of covers over the entire apparatus. A further problem with conventional hydrometallurgical extraction plants is that they require large amounts of flat surface land area for construction in a location that is normally hilly or mountainous. Thus, large capital expenditures are required to build such mineral processing plants.
Another disadvantage with hydrometallurgical plants is that during the leaching step of a hydrometallurgical process, contaminants, such as iron, manganese, and chlorides, are often leached along with a desired metal by a raffinate and enter into the hydrometallurgical plant as part of the pregnant leach solution. These contaminants are then transferred to the metal electrolyte solution via either entrainment or by the chemical binding of the contaminants to the organic solution used in the extracting stage. When these contaminants are found in the metal electrolyte solution, which is to be sent to the electrowinning tankhouse, this contamination, especially iron contamination, has a serious impact on the electrical deposition current efficiency of the metal electrolyte solution. Also, manganese will attack the anodes and thereby reduce their usable life.
A conventional contaminant and/or secondary metal removal strategy includes construction of an organic scrub circuit, which includes a dynamic pumper mixer-settler. The wash or scrub solution is one that is lean in the contaminant or secondary metal. The dynamic pumper mixer-settler acts to flood the organic solution that includes contaminants with a scrub solution, can simply reduce the concentration of contaminants in the system by dilution, or can chemically remove contaminants by extraction into the aqueous phase. This organic wash circuit works by continuously bleeding out contaminants. In such a process, large volumes of bleed streams result as waste. Fresh make-up solution is then required to keep the recirculating stream whole. One disadvantage with such a method is that the removal of contaminants by this method is typically 40% to 50%. Still another disadvantage with a conventional organic wash circuit is that it is capital intensive in its initial construction. It is also expensive to operate because large volumes of bleed streams and fresh make-up streams are needed.
In order to overcome the deficiencies found with conventional hydrometallurgical extraction plants, a solvent extraction plant that has an optimized extraction efficiency and capacity, a method for making such a plant, and a process for using such a plant are needed. In addition, such a plant should be a closed system. Still further, such a plant should be modular
Cusack Roger
McLoughlin Kevin
Neuman Mark
Gorgos Kathryn
Koch-Glitsch, Inc.
Nicolas Wesley A.
Shook Hardy & Bacon LLP
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