Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Utilizing fused bath
Reexamination Certificate
1999-10-28
2001-04-24
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Utilizing fused bath
C205S564000, C204S243100, C204S244000, C204S245000, C204S247100, C204S247200
Reexamination Certificate
active
06221232
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrolytic refining method for gallium and an apparatus for use in the method.
2. Description of the Related Art
Recently, the demand for metallic gallium is increasing because of its use as a raw material for GaAs, GaP, and the like, which are used as compound semiconductor devices and light emitting devices. Gallium is mainly produced as a by-product in a process for producing alumina or for smelting zinc, but, in addition thereto, scraps of semiconductor materials are also available as a raw gallium material.
As methods for refining gallium from such raw gallium materials (i.e., metallic gallium accompanied by impurities), usually well-known are the crystallization refining method, the lifting of single crystals, and the electrolytic refining method.
The crystallization refining method is a method for obtaining solid gallium, which comprises incorporating a seed crystal into the cooling medium during the solidification of the melted raw gallium material, thereby allowing the seed crystal to grow by the cooling effect exerted by the cooling medium and obtaining the refined solid gallium in the thus grown crystalline side. For instance, in Japanese Patent Laid-Open No. 50926/1990 is disclosed a crystallization refining method comprising performing the crystal growth above in multiple steps.
The method of lifting a single crystal is a refining method which comprises bringing the front end of a seed crystal in contact with a melted raw gallium material, and then slowly pulling up impurity-free single crystals having been grown from the seed crystal. For instance, Japanese Patent Laid-Open No. 243727/1990 teaches that the efficiency of refining is improved by forming an acidic solution layer on the surface of melted gallium.
The electrolytic refining method comprises performing electrolysis in an electrolytic solution using a raw gallium material as an anode. In this case, gallium and metals that are electrochemically more basic than gallium elute into the electrolytic solution, while metals that are electrochemically more precious than gallium electrolytically deposit on a cathode together with gallium. Thus, refined metallic gallium can be obtained on the cathode. For example, Japanese Patent Laid-Open No. 192877/1994 discloses a method comprising placing a melted raw gallium material on the bottom of an electrolytic cell and then performing electrolysis between the melted raw material used as an anode and a rod-like cathode. In this case, the metallic gallium deposited on the surface of the cathode drops down in the form of drops and is collected in a receptor provided on the lower side, while impurities such as indium, copper, and lead remain on the anode side.
In the crystallization refining method, the purity of gallium can not be increased unless otherwise repeating the operation. Moreover, because the process is complicated and the productivity is low, in many cases the application of this method is limited to the refinement in a high-purity region, i.e., the method is applied to the use of metallic gallium having a purity of 5N (99.999%) or higher as a raw material in order to obtain a product with a higher purity of 6N or 7N (99.9999% or 99.99999%) or even higher. That is, the method is not suitable for those having a purity of about 2N or 3N because the yield is too low. Also, concerning the method of lifting a single crystal, its application is limited to that in a high-purity region, and furthermore, it has a disadvantage that the facilities are expensive.
In contrast, the electrolytic refining method is simple as compared with the above-described two methods, does not substantially require manual operations and is inexpensive in terms of apparatus. Thus, this method is advantageous in that it is applicable as a low-purity refining method to be performed as a step until the high-purity refining method (i.e., as a pretreatment). However, the related art electrolytic refining method comprises concentrating indium, copper, lead, etc. in an anode and leaving them. Thus, if a predetermined or more amount of impurities are concentrated in the anode, the impurities are incorporated into an electrolytic solution, resulting in lowering the purity of gallium deposited on a cathode. Thus, in case where the purity of the refined gallium is regulated, the electrolysis life is automatically determined. Furthermore, the related art electrolytic refining method involves a problem that “gold ” contained in semiconductor scraps, etc. can not be removed therefrom.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to develop an electrolytic refining method for gallium capable of removing impurities such as gold, which have not been able to be removed in the related art methods, while increasing a degree of concentration of impurities in an anode and prolonging an electrolysis life, yet taking advantages of the related art electrolytic refining method for gallium, that is inexpensive, simple in process and substantially free of manual operation, and to refine gallium in a high yield.
The present inventors have found that in the electrolytic refining method by depositing high-purity refined metallic gallium on a cathode while using melted metallic gallium containing impurities as an anode, when a centrifugal force is applied to a melted raw gallium material, thereby rotating (rotating around a vertical shaft) it, a scum generated on the anode can be gathered in the center of rotation and that when the scum is discharged out of the system, the electrolysis life can be markedly prolonged as well as gold can be removed.
Specifically, the invention provides an electrolytic refining method for gallium by depositing refined gallium on a cathode in an electrolytic solution while using a melted metallic gallium containing impurities (which is referred herein as a “melted raw gallium material) as an anode, wherein a centrifugal force is applied the melted raw gallium material in the electrolytic solution, thereby rotating (rotating around a vertical shaft) it, and scums gathered in the central portion of thereto are discharged out from an electrolytic cell.
Furthermore, as an apparatus for advantageously conducting the method above, the invention provides an apparatus for use in electrolytic refining of gallium, which comprises an electrolytic cell into which is charged an electrolytic solution maintained at a temperature not lower than the melting point of gallium, the electrolytic cell comprising anodic chamber for containing a melted raw gallium material as an anode and a cathodic chamber for collecting refined gallium deposited in a cathode, and the anodic chamber and the cathodic chamber being partitioned from each other such that the electrolytic solution is communicated between the chambers, wherein the anodic chamber is constructed by a cylindrical vessel for containing the melted raw gallium material, a magnet rotator is provided at a lower side and outside of the cylindrical vessel, and a suction pipe is placed in a central portion inside of the cylindrical vessel, and if desired, the suction pipe is connected to an intermediate cell provided at the outside of the electrolytic cell, and a piping connecting from the intermediate cell to the electrolytic cell via a filter is provided.
Still further, the invention provides an electrolytic refining method for gallium in accordance with the method above, wherein the method further comprises circulating the electrolytic solution into an electrowinning cell provided at the outside of the electrolytic cell and performing an operation of depositing gallium in a cathode of the electrowinning cell, thereby maintaining the concentration of gallium in the electrolytic solution within a predetermined range during the electrolysis. Furthermore, as an apparatus for advantageously conducting the method above, there is provided an apparatus for electrolytic refining for gallium as above, wherein an auxiliary electrolytic cell (the electrowinning
Tayama Kenichi
Tayama Kishio
Yanata Nagayasu
Dowa Mining Co. Ltd.
McDermott & Will & Emery
Phasge Arun S,.
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