Patent Description:
In the prior art, it is a common practice to apply plating, typically nickel electroplating to the surface of rare earth magnets, typically Nd-Fe-B permanent magnets, for the purpose of imparting corrosion resistance thereto. When the plating bath is used over a long term, rare earth metal ions are leached out of the rare earth magnets, i.e. the work being plated, and gradually accumulate in the plating bath, adversely affecting plating quality.

In particular, nickel electroplating baths are sensitive to impurities. Even traces of impurities, if introduced, can incur detrimental phenomena such as adhesion failure, covering power shortage, and hard brittle coatings. Impurities are composed of fine solids suspended in the plating bath or settled on the plating tank bottom and soluble impurities dissolved in the plating bath. Fine solid impurities may be removed by a physical removal method, typically filtration. Of the soluble impurities dissolved in the plating bath, some transition metals may be removed by effecting dummy electrolysis with a low current flow for allowing impurity metal ions to deposit on the cathode. Rare earth metal ions, however, are quite difficult to remove.

For removal of rare earth metal ions such as Nd and Dy in the nickel electroplating bath as impurities, <CIT> proposes a method involving adding a less than equivalent amount of an extractant to the nickel plating bath, mixing and agitating until the extractant is associated with rare earth metal ions to form an associated gel, separating and removing the associated gel from the plating bath, and recovering the plating bath for reuse.

This method, however, has many problems. If more than equivalent of the extractant is added, the extractant does not gel. Then separation is difficult. Complete removal of rare earth metal impurities such as Nd and Dy is impossible. This leads to expensive rare earth metals such as Nd and Dy being discarded, and the extractant is also discarded. There is left an industrial waste in gel form, acceptable to few waste disposal facilities and difficult to treat in an industrially acceptable manner. The operation of withdrawing the gel waste poses a burden to the worker.

<CIT> describes a liquid-liquid extraction method and apparatus useful in multistage separation for the production of rare earth elements. It describes a tank with opposed sidewalls, one with upper and lower inlets respectively for the aqueous and organic phases, and the other with upper and lower outlets respectively for the organic and aqueous phases. There may be a central upright partition, with flow clearances above and below.

<CIT> discloses an apparatus and a process for treating hydrocarbon oils and tars, wherein hydrocarbon oils or tars are intimately mixed with a liquid reagent by impacting two or more powerful streams of the oil or tar and introducing the reagent into one or more of the streams before or at the point of impact.

An object herein is to provide new and useful methods and apparatus for extracting and removing rare earth metal ion impurities from a plating solution without leaving an industrial waste, such that rare earth metal components such as Nd and Dy may be recycled. The method and apparatus are useful especially in a plating method, especially a nickel plating process, especially a method of plating rare earth magnets.

The invention provides apparatus for extracting and removing rare earth metal ions from a plating solution containing rare earth metal ions as impurities, a method for extracting and removing rare earth metal ions from a plating solution in the apparatus, and a plating method combined with the extracting/removing method and/or using the apparatus, as defined in the claims.

The method for extracting and removing rare earth metal ions from a plating solution according to the invention is a treatment method of dispersing atomized solutions without a need for an agitating machine. Specifically, the extraction tank is filled with the plating solution and the extracting solution of an extractant in a water-insoluble organic solvent. The extracting solution is atomized preferably through a spray or full-cone nozzle and injected in the tank at a lower position while the plating solution is atomized, preferably through a nozzle e.g. spray or full-cone nozzle, and injected in the tank at an upper position. The atomized extracting solution having a lower specific gravity moves upward whereas the atomized plating solution having a higher specific gravity moves downward. During upward and downward movements, the dispersed extracting and plating solutions are brought in mutual contact. Upon contact, extraction reaction takes place at the water/oil interface having an increased surface area by virtue of the atomization, leading to efficient metal extraction.

Since no mechanical agitation operation need be involved in the extraction reaction, a uniform water/oil mixed phase (i.e. emulsion phase) is not formed throughout the system, and phase separation is definite. This enables to increase the throughput and allows for efficient removal of rare earth metal ions such as Nd and Dy. Additionally, the extracted rare earth metals may be recycled by back-extraction via similar dropwise contact with an acid such as hydrochloric acid, preferably using a spray or full-cone nozzle.

We find that the use of the present method and apparatus enables a saving of industrial waste disposal expense and reuse of extractant and rare earth metals.

Comparison of the plating solutions before and after the extraction treatment indicates that it is possible for rare earth metal components to be completely (<NUM>%) extracted without affecting plating solution ingredients. The extractant can be repeatedly used via back-extraction without gelation and discard. The back-extraction enables expensive rare earth metals such as Nd and Dy to be recycled without a loss by discard. The operation of withdrawing a gelled metal-extractant compound is unnecessary. Since the plating solution after treatment can be substantially free of rare earth metal ions such as Nd and Dy (in a low concentration if any), it may be reused in plating of stable quality.

The invention is directed to a method for extracting and removing rare earth metal ions from a plating solution containing rare earth metal ions as impurities. Although the plating solution to be treated is not particularly limited, it is commonly selected from plating solutions for imparting corrosion resistance to rare earth magnets, typically Nd-Fe-B permanent magnets, such as nickel, copper and chromium electroplating solutions. A nickel electroplating solution, such as Watts nickel bath, is typical. The composition of the nickel plating bath is not particularly limited, while the bath may be either a dull, semi-bright, or bright plating bath.

The rare earth metal ions to be removed vary depending on the use e.g. on a particular rare earth magnet to be plated, and include Pr, Nd, Tb, Dy and the like in the case of Nd-Fe-B permanent magnets.

In the case of a nickel plating solution, for example, detrimental phenomena such as covering power shortage, adhesion failure, blister and peeling may occur if noticeable amounts of rare earth metal ions accumulate. It is then recommended to carry out the rare earth extraction/removal method of the invention whenever the total concentration of rare earth metal ions in the nickel plating solution reaches <NUM> ppm or higher, especially <NUM>,<NUM> ppm or higher. It is, of course, acceptable to carry out the inventive method before the concentration reaches the indicated level.

The extraction/removal method of the invention is a method for extracting and removing rare earth metal ions from a plating solution in an extraction tank using an extracting solution. The extraction tank includes a lower zone filled with the plating solution and an upper zone filled with the extracting solution. The plating solution is of course aqueous and contains rare earth metal ions as impurities.

The extracting solution contains an extractant dissolved in organic solvent that is water-insoluble and has a lower specific gravity than the plating solution so that the solutions form separate layers in the respective zones. In the method, the extracting solution is atomized, typically through an atomizing nozzle such as a spray nozzle, which may be a full-cone nozzle, into the plating solution in the tank lower zone, and the plating solution is atomized, typically through an atomizing nozzle such as a spray nozzle, which may be a full-cone nozzle, into the extracting solution in the tank upper zone. The double atomization and ensuing upward/downward flows bring the plating solution in contact with the extracting solution to extract rare earth metal ions from the plating solution into the extractant for removal.

As the extractant, any desired compound may be used herein as long as it does not extract or react with main metal ions such as nickel in the plating solution, but can extract rare earth metal ions. Suitable extractants are well known and include cation exchangers such as di-<NUM>-ethylhexylphosphoric acid, mono-<NUM>-ethylhexyl <NUM>-ethylhexylphosphonate (trade name PC-88A), and carboxylic acid extractants (e.g. trade name Versatic™ acid <NUM> or VA-<NUM>). The organic solvent in which the extractant is dissolved is not particularly limited as long as it is water insoluble and has a lower specific gravity (density) than water. Suitable solvents include kerosine, dodecane, toluene and hexane. The concentration of the extractant in the organic solvent is preferably <NUM> to <NUM> mol/l, more preferably <NUM> to <NUM> mol/l, though not limited thereto.

Referring to <FIG>, a reference apparatus (not part of the invention) is described in detail. The apparatus comprises an extraction tank <NUM> which includes a lower zone filled with a lower layer <NUM> of the plating solution and an upper zone filled with an upper layer <NUM> of the extracting solution having a lower specific gravity than the plating solution. A plating solution feed line <NUM> fitted at a distal end with a nozzle for atomizing liquid as droplets, preferably spray nozzle or full-cone nozzle, is extended into the tank <NUM> such that the nozzle at the distal end of the feed line may be positioned in the upper layer of extracting solution <NUM>. The plating solution containing rare earth metal ions is fed through the feed line <NUM> and atomized downward from the nozzle into the upper layer of extracting solution <NUM>. An extracting solution feed line <NUM> fitted at a distal end with a nozzle for atomizing liquid as droplets, preferably a spray nozzle or full-cone nozzle, is extended into the tank <NUM> such that the nozzle at the distal end of the feed line may be positioned in the lower layer of plating solution <NUM>. The extracting solution is fed through the feed line <NUM> and atomized upward from the nozzle into the lower layer of plating solution <NUM>. A mixing zone of the atomized plating solution and the atomized extracting solution is depicted at <NUM>.

With respect to the filling of the tank with the plating solution layer <NUM> and the extracting solution layer <NUM>, the tank <NUM> may be previously filled with predetermined volumes of the solutions prior to the start of atomization or spray injection of the solutions. Alternatively, the tank may be gradually filled with increasing volumes of the solutions by the atomization or spray injection of the solutions. In the case where the tank <NUM> is previously filled with the plating solution layer, that plating solution is preferably a plating solution from which rare earth metal ions have been extracted and removed.

The atomization or spray injection of the plating and extracting solutions ensures efficient contact of the plating solution with the extractant whereby rare earth metal ions are extracted and removed from the plating solution.

According to the present process, water-and-oil is atomized or emulsified by means of an atomizing nozzle, preferably spray nozzle or full-cone nozzle, without using an agitating machine, whereby extraction reaction is carried out. Mixing and phase separation can be simultaneously accomplished within a common tank, ensuring definite phase separation.

When a spray nozzle is used as the atomizing nozzle, the flow rate of plating solution injected through the spray nozzle is preferably <NUM> to <NUM>/min, more preferably <NUM> to <NUM>/min. The flow rate of extracting solution injected through the spray nozzle is preferably <NUM> to <NUM>/min, more preferably <NUM> to <NUM>/min. The amount in equivalents of the extractant used is preferably at least <NUM> times the total amount in equivalents of rare earth metal ions in the plating solution. When the plating or extracting solution is atomized through the spray nozzle, the droplets preferably have a diameter of <NUM> to <NUM>,<NUM>, more preferably <NUM> to <NUM>,<NUM>.

A full-cone nozzle may be used instead of a spray nozzle. When a full-cone nozzle is used as the atomizing nozzle, the flow rate of plating solution injected through the full-cone nozzle is preferably <NUM> to <NUM>/min, more preferably <NUM> to <NUM>/min, and the flow rate of extracting solution injected through the full-cone nozzle is preferably <NUM> to <NUM>/min, more preferably <NUM> to <NUM>/min. The amount in equivalents of the extractant used is preferably at least <NUM> times the total amount in equivalents of rare earth metal ions in the plating solution. When the plating or extracting solution is atomized through the full-cone nozzle, the droplets preferably have a diameter of <NUM> to <NUM>,<NUM>, more preferably <NUM> to <NUM>,<NUM>. The above-disclosed flow rates and droplet sizes may apply also for other kinds of atomizing. Since each dispersed solution should separate and return to the main layer of that solution in a reasonable time, the droplets should not be too small; the skilled person can adjust taking into account the specific materials.

<FIG> illustrates extraction apparatus in an embodiment of the invention. A vertical partition <NUM> is disposed in the extraction tank <NUM> to divide the tank into two compartments, an extraction compartment <NUM> and a stationary compartment <NUM>. In the extraction compartment <NUM>, the plating solution feed line <NUM> and the extracting solution feed line <NUM> are extended as in the previous embodiment and extraction treatment is similarly carried out. A passage <NUM> is provided in a lower portion of the partition <NUM> for communication of the plating solution between the compartments <NUM> and <NUM>. In <FIG>, the lower end of the partition <NUM> is spaced apart from the bottom of the tank <NUM> to define the passage <NUM>. Accordingly, the plating solution which is treated in the extraction compartment <NUM> (i.e. from which rare earth metal ions have been extracted and removed) passes through the passage <NUM> into the stationary compartment <NUM> so that the compartment <NUM> is filled with the plating solution. Another passage <NUM> is provided in an upper portion of the partition <NUM> for communication of the extracting solution between the compartments <NUM> and <NUM>. The other passage <NUM> is typically formed as one or more ports extending throughout the partition <NUM>. The extracting solution passes from the extraction compartment <NUM> into the stationary compartment <NUM> through the other passage <NUM>. Then the stationary compartment <NUM> is also filled with the lower layer of plating solution <NUM> and the upper layer of extracting solution <NUM> in a separated manner. In the stationary compartment <NUM>, however, no mixing zone is formed at the interface between the plating solution layer <NUM> and the extracting solution layer <NUM>.

Further, as shown in <FIG>, another vertical partition <NUM> is disposed in the stationary compartment <NUM> near one side wall of the tank <NUM>. The lower end of the other partition <NUM> is spaced apart from the bottom of the tank <NUM> to define a gap <NUM> for communication of the treated plating solution. The other (outlet) partition <NUM> is spaced apart from the side wall of the tank <NUM> to define a channel <NUM> for the treated plating solution. The side wall of the tank <NUM> is provided with an outlet <NUM> for the treated plating solution. The treated plating solution in the stationary compartment <NUM> passes through the gap <NUM> into the channel <NUM> and flows upward in the outlet channel <NUM>, whereupon it is discharged through the outlet <NUM> for recovery. Another side wall of the tank <NUM> defining the stationary compartment <NUM> is provided with another outlet (not shown) for the extracting solution. The extracting solution having rare earth metal ions extracted and retained therein in the stationary compartment <NUM> is discharged through the other outlet for recovery.

After recovery, the treated plating solution is in reusable conditions and may be fed back to a plating tank (not shown). On the other hand, after recovery, the extracting solution having rare earth metal ions extracted and retained therein may be subjected to back extraction for recovering the rare earth metals. The back-extraction treatment may be carried out (e.g. in apparatus similar to <FIG> or <FIG>) by bringing the extracting solution in contact with a rare earth metal dissolving agent, e.g. hydrochloric acid, nitric acid or sulfuric acid for dissolving the rare earth metals in the dissolving agent, and separating the dissolving agent from the water-insoluble organic solvent containing the extractant.

Examples of the invention are given below by way of illustration.

From a nickel plating solution containing rare earth metal ions as impurities, rare earth metal ions were extracted and removed under the following conditions.

Table <NUM> shows the concentration of main ingredients in the plating solution before and after the extraction treatment, as measured by neutralization titration method.

As seen from Table <NUM>, the main ingredients in the plating solution were not affected by the extraction treatment.

Table <NUM> shows the concentration of rare earth elements in the plating solution before and after the extraction treatment, as measured by ICP emission spectrometry.

As seen from Table <NUM>, the rare earth metal components (Pr, Nd, Tb, Dy) in the plating solution were completely extracted.

Next, the extracting solution having the rare earth metals extracted therein was contacted with <NUM>. 5N hydrochloric acid for back-extraction.

Table <NUM> shows the concentration of rare earth elements in the extracting solution after the back-extraction with hydrochloric acid.

By the back-extraction via extractant/hydrochloric acid contact using spray nozzles, the rare earth elements once extracted in the extractant were completely back-extracted in hydrochloric acid so that the extractant might be recycled.

Table <NUM> shows the concentration of rare earth elements in the extracting solution after the back extraction with hydrochloric acid.

By the back-extraction via extractant/hydrochloric acid contact using full-cone nozzles, the rare earth elements once extracted in the extractant were completely back-extracted in hydrochloric acid so that the extractant might be recycled.

The plating solution and the extracting solution were mixed and agitated at <NUM> rpm for <NUM> hour.

As seen from Table <NUM>, the main ingredients in the plating solution were not affected.

As seen from Table <NUM>, of the rare earth metal components, <NUM> ppm of Pr, <NUM> ppm of Nd, and <NUM> ppm of Dy were not extracted and left in the plating solution. The extractant-rare earth metal compounds in gel form were discarded.

Under the conditions of this Reference Example the diameter of water/oil droplets was extremely fine. As a result, phase separation was unsatisfactory, that is, a large fraction of oil was introduced into the plating solution recovered. The test was interrupted.

Although some preferred embodiments have been described, many modifications and variations may be made thereto in the light of the above teachings. It is therefore to be understood that the invention may be practised otherwise than as specifically described as long as it is covered by the claims.

In respect of numerical ranges disclosed in the present description it will of course be understood that in the normal way the technical criterion for the upper limit is different from the technical criterion for the lower limit, i.e. the upper and lower limits are intrinsically distinct proposals.

Claim 1:
Apparatus suitable for extracting and removing rare earth metal ions from a plating solution containing rare earth metal ions as impurities, using an extracting solution of an extractant in a water-insoluble organic solvent having a lower specific gravity than water, said apparatus comprising
an extraction tank (<NUM>),
a plating solution feed line (<NUM>) fitted at a distal end with an atomizing nozzle to atomize the plating solution, and positioned in an upper zone of the extraction tank,
an extracting solution feed line (<NUM>) fitted at a distal end with an atomizing nozzle to atomize the extracting solution, and positioned in a lower zone of the extraction tank,
an outlet (<NUM>) from the extraction tank (<NUM>) for discharging plating solution from which rare earth metal ions have been extracted,
another outlet from the extraction tank for discharging extracting solution having extracted rare earth metal ions therein,
whereby in use the extracting solution is atomized from the nozzle at the distal end of the extracting solution feed line (<NUM>) into the tank lower zone so as to flow upward, and the plating solution is atomized from the nozzle at the distal end of the plating solution feed line (<NUM>) into the tank upper zone so as to flow downward, to bring the plating solution into contact with the extracting solution;
an outlet partition (<NUM>) defining a channel (<NUM>) leading to the plating solution outlet (<NUM>) from the lower zone, and separating the plating solution outlet from the upper zone,
characterized in that said apparatus further comprises:
a partition (<NUM>) disposed in the extraction tank to divide it into an extraction compartment (<NUM>) having said atomizing nozzles and a stationary compartment (<NUM>),
a lower passage (<NUM>) at a lower portion of the partition (<NUM>) for communication of the plating solution between said compartments (<NUM>,<NUM>), and
an upper passage (<NUM>) at an upper portion of the partition (<NUM>) for communication of the extracting solution between said compartments (<NUM>,<NUM>).