WO2009102115A1

WO2009102115A1 - Method for recovering molybdenum from molybdenum etching solution

Info

Publication number: WO2009102115A1
Application number: PCT/KR2008/007786
Authority: WO
Inventors: Jong-Jin Pak; Jin-Goo Kang; Min-Ho Park; Yong-Seok Kim
Original assignee: Iucf-Hyu (Industry-University Cooperation Foundation Hanyang University)
Priority date: 2008-02-13
Filing date: 2008-12-30
Publication date: 2009-08-20
Also published as: KR100940116B1; KR20090087615A

Abstract

There is provided a method for recovering molybdenum from a molybdenum etching solution, in particular for recovering and reclaiming a molybdenum containing product from a molybdenum etching solution, which is to be used as ferro-molybdenum materials, by a simple method without undergoing complicated pretreatment at high temperature. The method for recovering molybdenum comprises: preparing a molybdenum etching solution in which molybdenum is dissolved in hydrogen peroxide aqueous solution; adding CaO to the molybdenum etching solution while stirring the molybdenum etching solution; and recovering precipitate formed by the addition of CaO with stopping the addition of CaO when the pH value of the molybdenum etching solution reaches in the range of 5 to 10 by the addition of CaO.

Description

[DESCRIPTION] [Invention Title]

METHOD FOR RECOVERING MOLYBDENUM FROM MOLYBDENUM ETCHING SOLUTION [Technical Field]

The present invention relates to a method for recovering molybdenum from a molybdenum etching solution, in particular for recovering and reclaiming a molybdenum containing product from a molybdenum etching solution, which is to be used as molybdenum materials, by a simple method without undergoing complicated pretreatment at high temperature.

[Background Art]

Molybdenum (Mo) is an element that functions to improve the corrosion resistance and the strength of steel products. Therefore, Mo is added as an alloying element to various grades of steel products. However, Mo is a very expensive element among those elements added to steels, and the addition of a large amount of Mo may cause an increase in steel production cost.

Therefore, there have been various attempts to find a molybdenum source that is as cheap as possible.

Apart from these attempts, when a Mo-containing waste acids produced from a process of etching molybdenum metals with acids is neutralized with sodium hydroxide and discharged into waste water system, the loss of Mo in this manner is economically significant, and the discharge of heavy metals like Mo into the nation's rivers is undesirable from the environmental view. Therefore, the recovery of Mo from such waste acids has been found very important, not only from the viewpoint of conserving and reusing resources but also from the viewpoint of preventing environmental pollution.

Accordingly, there have been many attempts to recover Mo-containing compounds in the form of precipitate from Mo-containing waste acids, which can be used to manufacture the ferro-molybdenum alloys used in the steelmaking processes.

Among them, the invention disclosed in Korean Registered Patent No. 10-0510213 is related to the recovery of molybdenum from the epoxidation catalyst, comprising: acidifying a water-soluble stream separated from a reaction catalyst, separating CO₂ from the acidified stream, adding a calcium

(Ca) compound at least at a ratio of 1:1 in molar basis to react with Mo at a high temperature of 80^°C or above, and separating the generated solid CaMoO₄ precipitate.

The invention is related to the recovery of CaMoO₄ precipitate from an epoxidation catalyst. Here, CaMoO₄ is recovered by separating a water-soluble stream from the epoxidation catalyst, acidifying the separated water-soluble stream and adjusting the quantitative ratio of Ca to Mo at a high temperature of 80^°C or above. In this case, in order to control the quantitative ratio of Ca to Mo in the solution, the initial concentration of Mo in the solution should be determined in advance, or always be maintained to a constant level. This would cause the recovery process very complicated and lead to an increase in the cost of manufacturing facilities and processes.

Another method to recover Mo is disclosed in US Patent No. 5,585,077. US Patent No. 5,585,077 discloses a process comprising: collecting aqueous stream containing molybdenum (Mo) and sodium (Na) values from epoxidation catalyst values, previously adjusting the pH value of the collected aqueous stream with sodium hydroxide, and adding a calcium (Ca) compound so that Ca can react with Mo at the ratio of 1:1 at a high temperature of 80^°C or above, thereby recovering solid CaMoO₄ formed in the solution.

However, the prior art described in the US Patent No. 5,585,077 undergoes complicated pretreatment processes of adjusting the pH value of the etching solution and controlling a quantitative ratio of Ca to Mg at high temperature, etc.

[Disclosure] [Technical Problem]

The present invention has been made to solve the foregoing problems with the prior art, and therefore an aspect of the present invention is to provide a novel method capable of readily recovering a molybdenum (Mo) compound from a Mo etching solution at room temperature without undergoing complicated pretreatment processes.

[Technical Solution]

In order to achieve the object as above mentioned, the present invention provides a method recovering Mo from a Mo etching solution. The method comprises: preparing a molybdenum etching solution in which molybdenum is dissolved in hydrogen peroxide aqueous solution; adding quicklime (CaO) to the molybdenum etching solution while stirring the molybdenum etching solution; and recovering precipitate formed by the addition of CaO with stopping the addition of CaO when the pH value of the molybdenum etching solution reaches in the range of 5 to 10 by the addition of CaO.

In this method, the pH value of the molybdenum etching solution is preferably in the range of 6.5 to 8.5 at the point of stopping the addition of CaO.

The recovered molybdenum precipitate may have a particle size range of 10 to 100 //m(micrometer).

[Advantageous Effects]

As described above, the method according to one exemplary embodiment of the present invention may be useful to readily recover molybdenum from the molybdenum etching solution without undergoing complicated processes of heating or adjusting the pH value of the etching solution, or determining the initial concentration of Mo prior to calcium compound additions. In the present invention, regardless of the initial Mo concentration in the Mo etching solution, the pH value of the solution can be controlled by simply adding CaO at room temperature, and the CaMoθ₄ precipitates can be recovered at an appropriate pH value in the range above mentioned.

[Description of Drawings]

FIG. 1 is a flow chart illustrating a procedure of recovering molybdenum according to one exemplary embodiment of the present invention.

FIG. 2 is a graph illustrating the change in the pH value of a Mo etching solution with CaO additions.

FIG. 3 is a graph illustrating the change in the content of Mo according to the pH change of the Mo etching solution.

FIG. 4 is a photograph of the Mo precipitates recovered in Example 1.

FIG. 5 shows the XRD analysis result of the Mo precipitates shown in FIG. 4.

FIG. 6 is a graph illustrating the change in the pH value of a Mo etching solution with CaO additions after adjusting the pH by the addition of NaOH as described in Comparative example 1.

[Best Mode]

Hereinafter, the exemplary embodiments of the present invention are described in more detail.

The present inventors have made many ardent attempts to solve the above problems regarding the present invention, and found that CaMoθ₄ could be readily recovered from a Mo containing waste acid solution obtained by etching molybdenum with a hydrogen peroxide aqueous solution by adding CaO into the solution at room temperature. Therefore, the present invention was completed on the basis of the above facts.

A solution (hereinafter, referred to as a 'molybdenum etching solution') obtained by etching molybdenum with hydrogen peroxide aqueous solution refers to a solution formed in dissolving a molybdenum wire used as a core wire of tungsten filament, or washing a molybdenum metal layer adhered to the inside of a molybdenum sputtering apparatus, but the present invention is not particularly limited thereto. Here, Mo is generally dissolved in an etching solution in the range of 1 to 8 % by weight, and the balance is comprised of hydrogen peroxide aqueous solution and other impurities, and the pH value of the etching solution is generally 1.5 or less depending on the dilution ratio of water.

There is no particular pretreatment or pH adjustment of the molybdenum etching solution. In accordance with the present invention, when CaO was added to the molybdenum etching solution, the pH value of the molybdenum etching solution increased, and Mo ions can be precipitated in the form of CaMoO₄. From these results, the present inventors have made attempts to recover molybdenum as CaMoO₄ only by the addition of CaO to the molybdenum etching solution without undergoing any complicated procedures.

FIG. 1 shows a method for recovering molybdenum according to one exemplary embodiment of the present invention. As shown in FIG. 1, first of all, a molybdenum etching solution is prepared. Then, the addition of CaO to the molybdenum etching solution is performed. A molybdenum compound can be formed by the addition of CaO without any other particular pH adjustment.

It is preferable to stir the molybdenum etching solution with the addition of CaO to increase the Mo recovery rate and improve the efficiency of the CaO. The stirring may be performed according to conventional stirring methods, and the temperature of the Mo etching solution may be maintained at room temperature without heating procedure. The stirring as above mentioned was carried out to dissolve CaO rapidly. Therefore, the addition of CaO and the stirring of the Mo etching solution may be performed at a similar time point, and it is not necessary to declare their preferable orders. That is, it should be considered that adding CaO to the Mo etching solution while stirring, stirring the Mo etching solution to which CaO is added, or performing the addition of CaO and the stirring of the Mo etching solution at the same time has the same meaning as the step of "adding CaO to the molybdenum etching solution while stirring the molybdenum etching solution", as defined in the claims of the present invention.

A molybdenum compound, more particularly CaMoO₄ is precipitated from the molybdenum etching solution as the pH of the solution increases by the addition of CaO. According to the experimental results of present inventors, the pH value of the Mo etching solution increases continuously as the amount of CaO addition increases. This illustrates a peculiar point of the present invention in that the pH value of the Mo etching solution can be sufficiently increased by the CaO addition only, without heating the solution to a high temperature.

In this new method, there is no need to adjust the ratio of Ca to Mo as compared to the conventional methods. The CaO addition operation can be stopped to recover CaMoθ₄ precipitates when the pH value of the Mo etching solution reaches in the range of 5 to 10, preferably 6.5 to 8.5, by simply observing the change of the pH value of the Mo etching solution with CaO additions. That is, when the pH of the Mo etching solution reaches to a value near 5 by the addition of CaO, the Mo concentration in the solution decreases rapidly. A significant amount of molybdenum is removed from the Mo etching solution when the pH of the solution reaches in the range of 6 to 7. Nearly all of the molybdenum is removed from the solution when the pH value reaches to about 8.5.

Since the molybdenum in the solution is removed in the form of CaMoO₄ precipitates, the CaMoO₄ powder product can be recovered by filtering and drying the precipitates after the pH value become at a proper range described above. When the pH of the Mo etching solution is less than the above range, the precipitation of CaMoO₄ is not completed, and thus a large amount of Mo is remained in the solution. On the contrary, when the pH of the Mo etching solution exceeds the range, the excess amount of CaO is present in the precipitates which leads to decrease the Mo content in the final product.

Therefore, the method according to one exemplary embodiment of the present invention includes: preparing a molybdenum etching solution in which molybdenum is dissolved in hydrogen peroxide aqueous solution; adding CaO to the molybdenum etching solution; stirring the etching solution to which CaO is added; and recovering a molybdenum precipitate formed by the addition of CaO after the addition of CaO is stopped when the pH value of the molybdenum etching solution reaches in the range of 5 to 10 by the addition of CaO.

In this case, there are no special limitations on the shape and size of CaO as an additive to the Mo etching solution. CaO can be readily dissolved in the Mo etching solution regardless of its shape and size. The CaMoO₄ precipitates formed in the above pH range have the particle sizes in the range of 10 to lOOμm (mean particle size: ~30μm) with a relatively uniform size distribution.

[Mode for Invention]

Hereinafter, the exemplary embodiments of the present invention are described in more detail with reference to the accompanying drawings.

However, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the scope of the invention. EXAMPLES

Example 1

CaO additions were made to a molybdenum etching solution (i.e., a hydrogen peroxide aqueous solution) of 500CC containing 7.73 % of molybdenum by weight at room temperature and the solution was stirred without heating or cooling process. After each CaO addition, the pH value and Mo content in the solution were measured. The results are listed in Table 1. Also, the precipitates formed in the solution were filtrated and analyzed for Mo content. The results are also listed in Table 1.

Hereinafter, the expression "Mo recovery rate" refers to a ratio of Mo removed from the Mo etching solution by the formation of precipitates (products) as represented by the following Equation 1.

Equation 1

Mo recovery rate (%) = (initial [%Mo] Current [%Mo])/initial [%Mo] x 100

Here, the initial [%Mo] and current [%Mo] represent Mo contents in the etching solution.

[Table 1]

As shown in Table 1, the Mo content in the solution does not change significantly until the pH of the etching solution reaches 3.19. No precipitates were formed up to this point. It was observed that the precipitates started to form when the pH of the solution reaches above 4. At the pH values above 4.5, the Mo content in the solution decreased drastically, and 90% or more of molybdenum was removed in the form of precipitates at the pH value of 7.22. As the pH of the solution increased, the Mo content deceased further down until the pH value reaches 9.91. However, at this pH level, the Mo content in the precipitates was slightly lower compared to the precipitates formed at the pH values of 4.80 and 7.22.

Hereinafter, the recovery rate of molybdenum is described in more detail with reference to FIGS. 2 and 3.

FIG. 2 is a graph illustrating the change in the pH of the molybdenum etching solution by CaO additions with stirring in the above exemplary embodiments in the present invention. As seen from FIG. 2, the pH value of the Mo etching solution increased continuously as the amount of CaO addition increased. This illustrates that the pH value of the Mo etching solution can be sufficiently increased by the CaO addition only, without heating the solution to a high temperature.

FIG. 3 is a graph illustrating the change in the ratios of the Mo content ([%Mo]) to the initial Mo content ([%Mo]₀) in a molybdenum etching solution with the pH change by the additions of CaO. As seen from FIG. 3, the Mo content in the solution started to decrease drastically at the pH value of 5, significant amount of Mo was removed from the solution at the pH value of 6-7 and nearly all of the molybdenum was removed from the solution when the pH value reaches to about 8.5.

The shape of the precipitates and the result of XRD (X-ray diffraction) analysis on the precipitates recovered in this exemplary embodiment are shown in FIGS. 4 and 5, respectively. As seen in the photograph of FIG. 4, the precipitates were fine powder with a particle size range of 10 to 100 μm. As seen from the XRD analysis result in FIG. 5, it was also confirmed that peaks except for the CaMoU4 peak are scarcely observed.

Therefore, the molybdenum was present in the precipitates in the form of CaModi compound.

Therefore, it was revealed that it was effective to control the pH of the Mo etching solution in the range of 5 to 10, and more preferably in the range of 6.5 to 8.5 for a high Mo recovery rate, as defined in the present invent ion.

Example 2

In order to determine the optimum pH range to ensure both high Mo recovery rate from the Mo etching solution and high Mo content in the precipitates, pH of the molybdenum etching solution was adjusted within a more specific pH range. CaO was added to a molybdenum etching solution (i.e., a hydrogen peroxide solution) of 1000 cc containing 7.59 % of molybdenum by weight at room temperature without heating or cooling process. After each CaO addition, the pH value and Mo content in the solution were measured. The results are listed in Table 2. Also, the precipitates formed in the solution were filtrated and analyzed for Mo content. The results are also listed in Table 2.

[Table 2]

Similar to the results observed in Example 1, the Mo content in the solution decreased drastically at the pH values above 4.5, and 80% or more of molybdenum was removed in the form of CaMoθ4 precipitates at the pH range of 6 to 7. Nearly all of molybdenum was removed from the neutralized etching solution at a pH value of 8.37 (around 8.5). Therefore, it was revealed that it was effective to control the pH of the Mo etching solution in the range of 5 to 10, and more preferably in the range of 6.5 to 8.5 for a high Mo recovery rate, as defined in the present invention.

Comparative example 1

In order to check the effect of the pH adjustment prior to the addition of CaO to the Mo etching solution, a NaOH solution was added to a 500 cc molybdenum etching solution (initial pH: 1.11) containing 7.76 % of molybdenum by weight so that the pH of the solution was adjusted to 6.09. Then, CaO additions were made to the solution in order to observe the Mo recovery behavior. The experimental results are listed in Table 3 and shown in FIG. 6.

[Tab Ie 3]

As shown in FIG. 6, the pH of the Mo etching solution increased initially to 6.09 by the addition of NaOH, and it increased up to 12 with the similar amount of CaO addition made in Example 1. However, as shown in Table 3, the Mo content in the etching solution decreased only to nearly a half of the initial Mo content (initially 7.76 % to finally 3.34 % by weight) even at a high pH value of 12. As a result, the Mo recovery rate was determined as merely 57%. This result illustrates that the pH adjustment by the addition of NaOH is not effective for a high Mo recovery rate and the addition of CaO only to the Mo etching solution can recover molybdenum in the form of a compound with a high Mo recovery rate.

Therefore, it was confirmed that the method according to the exemplary embodiment of the present invention has useful effects.

Claims

[CLAIMS] [Claim 1]

A method for recovering molybdenum from a molybdenum etching solution, compri sing: preparing a molybdenum etching solution in which molybdenum is dissolved in hydrogen peroxide aqueous solution! adding CaO to the molybdenum etching solution while stirring the molybdenum etching solution! and recovering a molybdenum precipitate formed by the addition of CaO when the pH value of the solution reaches in the range of 5 to 10 with stopping the addition of CaO.

[Claim 2]

The method of claim 1, wherein the pH of the molybdenum etching solution is in a range of 6.5 to 8.5 at the point of time when the addition of CaO is stopped.

[Claim 3]

The method of claim 1 or 2, wherein the recovered molybdenum precipitate has a particle size in the range of 10 to 100 μm(micrometer).