JPH057703A - Solvent extraction method transferring only water phase - Google Patents

Abstract

PURPOSE:To provide a method for solvent extraction in macro concentration and an extraction operation method based on a metal exchange reaction. CONSTITUTION:In a solvent extraction method in which an objective metal is separated from among two or more kinds of metals contained in a water phase, an organic phase is not transferred but only a water phase is transferred. In this way, the objective metal concentration is increased. Moreover, multistage extraction vessels each of which comprises the organic phase added with an extractant and the water phase containing two or more kinds of metals are installed. The solvent extraction in each stage is conducted in the manner that the organic phase is not transferred but only the water phase is transferred from one stage to the next in sequence so that the objective metal can efficiently be separated from among coexistent metals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel extraction method used for solvent extraction and an extraction / separation operation method using the same.

[0002]

BACKGROUND OF THE INVENTION Conventionally, separation and recovery of metals by solvent extraction are represented by a mixer-settler, which is a method in which an organic phase added with an extractant and an aqueous phase added with a substance to be extracted are moved in countercurrent. Is common. When recovering a target metal from a solution having a small treatment amount, batch multistage extraction is considered to be an appropriate method.

By the way, it is generally known that separation of a target metal from a water phase in which two or more kinds of metals are mixed by solvent extraction is based on the following mechanism. The two types of metals added to the aqueous phase are indicated by A and B, the chemical species of the extractant are indicated by HG, and the extraction mechanism will be discussed below by taking the chelate extraction system as an example.
The extraction reaction between the extractant and metals A and B is

[0004]

## EQU1 ## A ²⁺ +2 [HG] o = [AG ₂ ] o + 2H ⁺

[0005]

[Expression 2] B ²⁺ +2 [HG] o = [BG ₂ ] o + 2H ⁺ Here, suffix "0" represents a chemical species of an organic phase, and no mark represents a chemical species of an aqueous phase. When the equilibrium constant K _ex associated with the extraction equilibrium and the partition ratio D between the organic phase and the aqueous phase are D,

[0006]

[Equation 3]

[0007]

[Equation 4] It is represented by. The separation coefficient S of the two types of added metals A and B is
Since it is defined by the ratio of the distribution ratio D of each metal,
And from the number 4,

[0008]

[Equation 5] S = D _A / D _B = K _{ex (A)} / K
_It is expressed as _{ex (B)} . Therefore, the separation coefficient S is, as shown in Equation 5,
It is represented by the ratio of the extraction equilibrium constants K _{ex (A )} and K _{ex (B)} (including the stability term of the complex _{) of} each metal A and B.

[0009]

However, this number 5
Can be applied when extracting with an organic phase containing an excess of an extractant with respect to a metal having a micro concentration, and when extracting a metal having a macro concentration on an industrial scale, the above formula 5 is used.
Is not applied. That is, in such a state, it is necessary to consider the metal exchange reaction between the metal ion in the organic phase and the metal complex extracted in the organic phase.

Therefore, in order to confirm this metal exchange, the inventor of the present invention used 0.5 mol and 0.2 mol of an organic extraction reagent N, N-bis (2-ethylhexyl) glycine (hereinafter abbreviated as "D2EHG"). Palladium in each phase 23.
85 g / l and 8.33 g / l of the extracted organic phase were added to 1 mol of hydrochloric acid of the same volume and platinum of 8.08 g / l.
The extraction operation was repeated by using an aqueous solution containing a. The number of operations and the amounts of palladium and platinum in the organic phase were measured, and the results are shown in FIG. From the results of FIG. 1, as the number of operations increases, palladium in the organic phase is back-extracted by platinum in the aqueous phase and moves to the aqueous phase, and platinum in the aqueous phase moves to the organic phase. Metal exchange confirmed To be done.

Here, two kinds of additive metal concentrations are [A] _in
, [B] _in , the concentration of the organic phase after extraction is [A
Assuming that G ₂ ] _O and [BG ₂ ] _O are the metal concentrations of the aqueous phase after extraction are [A] and [B], the relationship between the concentrations of the metal A in the organic phase and the aqueous phase is

[0012]

[Equation 6] [A] _in = [AG ₂ ] _O + [A] Since the addition metal concentration [A] _in and the metal concentration [AG ₂ ] _O extracted in the organic phase are From 3 and Equation 6, the following Equation 7 is obtained.

[0013]

[Equation 7] here,

[0014]

[Equation 8] And Similarly, with respect to the metal B, the following Expression 9 is given.

[0015]

[Equation 9] here,

[0016]

[Equation 10] And

When the extractant is present in a large excess, both metals A and B are extracted. Then, if the stability of the extracted complex of metal A is greater than that of metal B, the transmetallation reaction is

[0018]

[BG ₂ ] ₀ + [A] = [AG ₂ ] ₀
+ [B], and the exchange constant K is

[0019]

[Equation 12] It is represented by. In this way, the exchange constant K becomes equal to the separation constant S.

From the above, the metal concentration in the organic phase [M] _O
Is

[0021]

[M] _O = [AG ₂ ] ₀ + [BG ₂ ] _{0 Since} the target concentration of the metal A [AG ₂ ] ₀ is increased,

[0022]

[Equation 14] By substituting the above equations 7, 9, and 12 into the equation (14), the following equation (15) is derived.

[0023]

[Equation 15] Here, α = [B] _in / [A] _in .

That is, as is clear from the equation (15), the smaller α is, that is, the higher the addition concentration [A] _in of metal A in the mixed addition aqueous solution of metal A and metal B is, and the larger the exchange constant k is. , The concentration of metal A in the organic phase [AG ₂ ] ₀ becomes high. That is, it is considered that in order to efficiently separate the target metal A, the addition concentration [A] _in of the target metal A and the exchange constant K, that is, the separation coefficient S are affected.

The above formula 15 can be considered as a general formula which can be similarly applied to not only the chelate type but also a solvation type and an ion pair type extraction system. From the above,
The inventor has found that the additive metal concentration [A]
_{Since in} is the sum of the metal concentration [AG ₂ ] ₀ of the organic phase and the metal concentration [A] of the aqueous phase, the state in which the amount of free extractant is small (increasing the metal concentration [AG ₂ ] ₀ of the organic phase) Even if it is not possible), by focusing on the extraction and separation of the target metal A by the metal exchange reaction by increasing the metal concentration [A] of the aqueous phase, by allowing only the aqueous phase without moving the organic phase , The principle of solvent extraction method at macro concentration was found. In addition, the present invention also provides a novel operation method capable of predominantly recovering the target metal from the mixed aqueous solution by arranging the extraction tanks in multiple stages and performing the operation.

The object of the present application is to disclose a solvent extraction method and an extraction / separation operation method using the same, which are based on the above principle.

[0027]

In order to achieve the above object, the following method is adopted. That is, in the method of separating the target metal from the plurality of metals contained in the aqueous phase by solvent extraction, by moving only the aqueous phase without moving the organic phase, the target added metal concentration is increased. .

Further, an extraction tank comprising an organic phase to which an extractant is added and an aqueous phase to which a plurality of metals are added is arranged in multiple stages, and the water is kept without moving the organic phase for each extraction in each stage. If only the phase is sequentially moved to the next stage for solvent extraction, the target metal can be efficiently separated from the coexisting metal.

[0029]

Example 1 Next, in order to demonstrate the effect of the solvent extraction method according to the present invention, it was applied to a separation operation of a platinum / palladium mixed solution. This will be described below. An aqueous solution prepared by dissolving platinum and palladium in hydrochloric acid is used as an aqueous phase, and 0.5M
D2EHG (N, N-bis (2-ethylhexyl) glycine) of 1. was diluted with toluene and used as the organic phase.
The hydrochloric acid concentration of the aqueous phase is 1 molar (1M) in terms of extraction efficiency.
Hydrochloric acid is used.

The arrangement of the extraction tanks for recovering the target metal platinum is, as shown in FIG. 2, five extraction tanks 1 are arranged in a circle, and the NO.1 extraction tank contains hydrochloric acid containing platinum and palladium. The solution was injected and the extraction was repeated. The organic phase is not moved for each extraction, but only the aqueous solution of the aqueous phase is moved to the NO.2 extraction tank. When the extraction is repeated a certain number of times, the extractability decreases as the concentration of free extractant in the organic phase decreases. The metal ions remaining in the aqueous phase are extracted in the next extraction tank.

When the palladium is slightly left in the water tank of the NO.5 extraction tank by repeating the extraction as described above, the injection of NO.1 into the extraction tank is stopped and the extraction tank of NO.2 is moved to the extraction tank. Switch injection of mixed aqueous solution. The organic phase of the extraction tank NO.1 was back-extracted with a mixed aqueous solution of dilute hydrochloric acid and dilute perchloric acid, the organic phase was washed with water, and then arranged so as to receive the aqueous phase flowing out of the extraction tank of NO.5. It was

FIG. 3 shows the relationship between the concentration ratio of platinum and palladium extracted in the organic phase and the number of extraction stages when the mixing ratio of platinum and palladium is different in the above-mentioned embodiment. In addition, the composition and platinum ratio of the mixed solution of platinum and palladium used for extraction, and the ratio of platinum in the organic phase of the first extraction phase after five-stage extraction [Pt / (Pt + P
d)]% is shown in Table 1.

[0033]

[Table 1] As is clear from Table 1 above, the ratio of the platinum concentration in the extracted organic phase is higher than the concentration ratio of platinum and palladium in the added aqueous solution, and the higher the platinum concentration in the added aqueous solution, the higher the platinum concentration in the organic phase. Is shown.

From the results of the above-mentioned implementation, the above-mentioned mathematical formula 15 is verified. Further, using NO. B in Table 1 as a representative example, the amounts of platinum and palladium extracted in the organic phase of each stage and the concentration of the free extractant were calculated and shown in Table 2 below.

[0035]

[Table 2] From Table 2 above, it is confirmed that the amount of platinum in the organic phase decreases as the number of stages increases, and conversely, the amount of palladium in the organic phase increases. The free extractant concentration at each stage is 0.00 to 0.
At about 02M, the extractant is effectively used for extracting metals.

Thus, even if the platinum concentration relative to palladium is low, by performing such an extraction operation method,
Platinum is preferentially concentrated over palladium, and recovery with enhanced selectivity can be performed. The metal with high stability is preferentially extracted, and the metal with low stability is back-extracted by the metal exchange reaction.

[0037]

Example 2 The solvent extraction method of the present invention which accelerates and utilizes the above-mentioned metal exchange reaction can utilize not only the above-mentioned mixed aqueous solution of platinum and palladium but also the metal exchange reaction based on the difference in stability with the extractant. The solvent extraction method according to the present invention can be widely applied to the solvent extraction of other mixed metal aqueous solutions.

For example, a metal exchange reaction is also observed in a mixed solution of samarium and praseodymium. samarium
An aqueous solution containing 0.05 M and 0.25 M hydrochloric acid was back-extracted with an organic phase containing 0.1 M praseodymium, and the number of operations and changes in the concentrations of praseodymium and samarium in the organic phase are shown in FIG. The results of back extraction with only 0.25 M hydrochloric acid are also shown. As a result, the result that the back-extracting effect was higher with the hydrochloric acid solution containing samarium at the same concentration was obtained as compared with the case of back-extracting with only hydrochloric acid. This is due to the metal exchange reaction
This is because samarium was extracted to reduce the concentration of free extractant in the organic phase. Therefore, the effectiveness of the operating method of the present invention was verified.

[0039]

[Effect] As described above, the solvent extraction method of the present invention allows extraction from a diluted aqueous solution by moving only the aqueous phase without moving the organic phase, and the hydrogen ion concentration that affects the extraction, By suppressing factors such as chloride ion concentration that promote complex formation in the aqueous phase to a low level, the extraction efficiency and the extractant in the organic phase are effectively used.

At the same time, metal is quantitatively extracted in a high extractant concentration range, the metal exchange reaction is promoted as the extract concentration decreases, and the metal having a higher stability with the extractant is predominantly extracted. It is possible to perform separation and recovery with high selectivity.

[Brief description of drawings]

FIG. 1 is a diagram showing the number of washings with a platinum aqueous solution and the amount of palladium exchanged in an organic phase.

FIG. 2 is a conceptual diagram of an extraction tank arrangement.

FIG. 3 shows the relationship between the concentration ratio of platinum and palladium extracted in the organic phase and the number of plates.

FIG. 4 is a diagram showing the relationship between the number of operations with samarium and hydrochloric acid aqueous solution and the praseodymium concentration in the organic phase.

[Explanation of reference numerals in the drawings] 1 Extraction tank

Claims (2)

[Claims] 1. A method of solvent extraction, wherein a target metal is separated from a plurality of metals contained in an aqueous phase by solvent extraction, and only an aqueous phase is moved without moving an organic phase. 2. A plurality of extraction tanks each comprising an organic phase to which an extractant is added and an aqueous phase to which a plurality of metals have been added are arranged in multiple stages, and the aqueous phase is injected from the first-stage extraction tank to each stage. An extraction and separation operation method characterized in that each time extraction is carried out, the organic phase is not moved and only the aqueous phase is sequentially moved to the next stage for solvent extraction.