FIELD OF THE INVENTION
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The present invention relates to the recovery of AB5 alloy from spent nickel/metal hydride (NIMH) storage batteries and/or the electrode cells. More particularly, there is provided a process for the selective recovery of AB5 alloy from NIMH storage batteries without thermal melting or dissolving the AB5 alloy into solution.
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OF THE INVENTION
There are a number of processes described in the literature and patents for recycling NIMH batteries to recover the valuable nickel values contained in them as nickel metal grid, nickel plated foil, the nickel hydroxide in the cathode with some cobalt hydroxide and the nickel metal powder present in the anode as a nickel metal alloy with rare earth metals. Up to now the recovery processes have focused only on the nickel values which allowed for direct smelting of these batteries in furnaces as part of the feed for making high nickel alloys. The rare earth metals react under these conditions to form the rare earth oxides similar to how they are found in nature and end up in the molten oxide slag which is thrown away. More recently, processes have been described where these batteries are carefully melted and the slag volume and nature are controlled to end up with a richer rare earth slag more suitable for recovering the rare earths from the slag in the same way they are recovered by current production processes from rare ores. Another way that is being developed is the total solution of the isolated NIMH electrode materials to produce solutions of the nickel, cobalt and the rare-earth salt mixtures. These solutions are then processed by normal hydrometallurgical methods to separate the solution components into the nickel hydroxide (or carbonate), cobalt hydroxide (or carbonate) and the rare earth separated into a separate mixed rare earth component for processing on a standard rare earth oxide separation process line associated with rare earth ore processing. The reason for this change in the expansion of these recycle processes to recover the rare earth oxides is that the world supply of these oxides is 95% controlled by China and the use for rare earth compounds continues to expand. This has caused supply of rare earth to become tight and probably to remain so with the associated increase in the value of these materials.
The rare earths material are found in the NIMH battery in the unique hydrogen absorbing AB5 metal alloy anode (about 32% are earth metals primarily lanthanum-25%) powder which is the key anode material found in most NIMH batteries. There is a significant amount of energy and loss material in separating then converting a rare-earth ore to the purified rare earth compound mix (25% lanthanum). The correct rare earth oxide mix is converted to the highly reactive rare earth metal mixture (Misch metal) under vacuum and very high temperatures (>1400° C.) under vacuum. This Misch metal then must be mixed with the correct amount of nickel metal and re-melted in a vacuum induction furnace and then cooled rapidly and then ground to a −325 mesh powder under inert atmosphere due to its reactivity. The very hard alloy is difficult to grind. This is a very energy intensive and costly process.
The invention is more preferably used in a cell containing a negative electrode having hydrogen storage alloy materials of the so-called AB5-type, a common example of which is described in the basic formula MsNiAlxMn4Co3 and MsNi5(AlxMn4Co3)x wherein Ms represents a lanthanum-rich misch metal (REM), which includes various rare earth metals and wherein 2.5<r<5.0, 0<s<2.5, 0<t<0.5, and 0<u<0.5. Hydrogen absorbing alloys of this class (i.e., AB5) are disclosed, for instance, in U.S. Pat. No. 4,216,274 (Bruning et al) and U.S. Pat. No. 4,375,257 (Bruning, et al).
The typical AB2-type materials, as currently envisioned, are based on TiNi2 and typically have the basic atomic structure Ni—Ti—V—Cr—Zr—X—Y wherein X and Y can be other elements of various selection. The invention is more preferably used in a cell containing a negative electrode having hydrogen storage intermetallic alloy materials of the so-called AB5-type, a common example of which are described in the basic formula MmNirCosMntAlu, wherein Mm represents a lanthanum-rich misch metal, which includes various rare earth metals, and wherein 2.5<r<5.0, 0<s<2.5, 0<t<0.5, and 0<u<0.5 and MsNiAlxMn4Co3.
Negative electrode alloys used in NiMH batteries typically comprise La, Pr and Nd as rare earth elements and Zn, Mg and Ni. Cobalt, manganese and aluminum are common additives.
The components of the NIMH battery include nickel metal grid, Ni(OH)2, nickel coated iron, potassium hydroxide electrolyte, and most importantly a nickel metal alloy powder of up to 25-30% by weight. This alloy powder has been developed to absorb considerable hydrogen and is the source of the descriptor “nickel metal hydride” battery. Under charging conditions this nickel alloy absorbs significant amounts of hydrogen as the metal hydride is formed electrochemically. Under battery discharge conditions this absorbed hydrogen reacts electrochemically back to hydroxide and water providing the electrical current of the battery. The currently most well known nickel alloy used is termed ABS which is an alloy consisting of one part misch metal (mostly lanthanum or REM) to five parts nickel on a mole basis—theoretically 32.1% (REM) on a weight basis. Therefore the naturally occurring rare earth oxide mixture is used to form the misch metal which avoids the expense of separating the rare earth oxides into the individual elements before reducing them to the mixed metal and not to the pure metal such as pure lanthanum metal. This metal mixture is used which is called misch metal. Therefore the AB5 alloy is an alloy of a mixture of lanthanum group metals and nickel with some cobalt and other metals added in small amounts for optimized hydrogen formation and storage. This AB5 component is the most expensive raw material cost for this battery.
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OF THE INVENTION
According to the present invention there is provided a method for the purification of a mixture of hydrogen storage intermetallic alloy AB5 obtained from the crushed nickel metal hydride batteries and the electrodes of spent nickel metal hydride batteries together with any lanthanum present and optionally, the separate recovery of Ni(OH)2 which is present. The process comprises the steps of (a) wet crushing nickel metal hydride batteries and cells, (b) screening the product of step (a) to recover metal particles and the resultant slurry, selectively dissolving Ni(OH)2 at a pH of about 2-5 without dissolving the ABS intermetallic alloy and lanthanum; (c) filtering the product of step (b) and washing the solids; and then (d) drying the solids under an inert atmosphere and recovering the ABS and lanthanum. Advantageously, the Ni(OH)2 is selectively dissolved by a non-oxidizing non-halogenated acid.
It is therefore a general object of the invention to purify a mixture containing hydrogen storage intermetallic AB5 which is obtained from the electrodes of spent nickel metal hydride batteries or the crushed batteries.
It is a further object of the invention to obtain AB5 and lanthanum from electrodes of spent nickel metal hydride batteries.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the invention there is provided a method for the purification and isolation of hydrogen storage intermetallic alloy AB5 and any lanthanum present from material obtained from spent nickel metal hydride batteries and cells which comprises the steps of:
A) wet crushing nickel metal hydride batteries and cells;
B) screening the product of step A) to recover the metal particles and the slurry formed,
C) selectively dissolving the nickel hydroxide in the slurry with a non-oxidizing non-halogenated acid without dissolving said intermetallic alloy AB5 and any lanthanum present; and then
D) recovering the solids.
Advantageously, the process is carried out under an inert atmosphere.
The non-oxidizing non-halogenated acid is preferably selected from the group consisting of acetic acid, glycolic acid, formic acid and sulfuric acid.
The product of Step B) can be screened through a 25 mesh screen and then through a −200 mesh screen.
Advantageously step C) is carried out at a pH of 2-4.
The present process consists of the crushing of the steel cased battery or cells in a water mist preferably in a hammer mill and under an inert atmosphere. The wet heavy separator mat which entangles much of the coarse grid collector metal on the top of a shaker table (+¼″) is screened off. This is sold for its coarse nickel metal content. It can also be pyrolyzed to remove the organic separator yielding all of the contained nickel metal powder and pieces free of organic material also for sale.
The rest of the water slurry after removing the +¼″ material is further screened to −200 mesh to yield a slurry containing 85% of the starting electrode material including the AB5 anode metal powder material and the nickel hydroxide cathode material with some binder. This −200 mesh slurry is neutralized to pH 5 with the non-oxidizing acid such as glycolic acid. At this point 70% glycolic acid (commercial grade) is preferably added to the aqueous slurry under an inert atmosphere in an estimated 50-95% of theory amount to dissolve the calculated molar mount of nickel hydroxide present (2 moles of glycolic acid per mole of nickel hydroxide). This addition is at room temperature with high shear stirring and cooling is maintained about 18-25° C. for four hours. The slurry is allowed to settle briefly to just allow the dense ABS to settle. The solution containing the dissolved nickel glycolate or other acid salt (with some cobalt glycolate) both from the cathode and a light brown haze from the liberated organic binder is decanted off and filtered. The nickel hydroxide is recovered from this solution by adding 50% sodium hydroxide to pH 10-11 and filtering the nickel hydroxide off and drying. The glycolic acid is recovered from this filtrate for recycling back to the process by acidifying this filtrate with sulfuric acid to pH 1-2 and distilling off the water and then the glycolic acid azeotrope.
The wash decantation of the AB5 metal powder may be needed several times to purge the residual binder from the AB5 powder. (This can also be accomplished in a continuous controlled cyclic wash with filtration of the circulating system). The cleaned AB5 is filtered and recovered under inert atmosphere. It is dried under vacuum at 100° C., cooled and screened through −325 mesh. The assay is 25% La and an oxygen content of <1.0%. The other rare earths including the cerium and yunum add up to about 6% with a few percent cobalt and aluminum. The nickel metal is the balance to about 65%. The overall recovery from the electrode is about 50-80% of the contained AB5 metal in the electrode mix.
The initial slurry after screening the metal particles may be treated with a magnet to remove any small casing particles.
This selective dissolution/purification procedure will work on any mixture of the nickel metal hydride and the Ni(OH)2 cathode material. It can be applied to those mixtures recovered from the processing and recycling of NIMH batteries. It can also be applied to electrode powders recovered from nickel/hydrogen batteries.
The following examples serve to explain the invention in more detail, where the examples are intended to facilitate understanding of the principle according to the invention and are not to be understood as meaning a limitation thereof.