JP2014009395A - Method for recovering rare earth - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and easily recover rare earths from a phosphoric acid plaster obtained as residue (waste) or the like after the recovery of phosphorous from phosphorous ore in the production of phosphoric acid.SOLUTION: In the method for recovering rare earths from a phosphoric acid plaster comprises: a leaching step of leaching rare earths from the phosphoric acid plaster into a leach liquor as a water solution including a chelate agent by a hydrothermal leaching method using the leachate to obtain a leach noble liquor including the rare earths; and a rare earth recovering step of separately recovering the rare earths from the leach noble liquor.

Description

  The present invention relates to a method for recovering rare earth from phosphogypsum.

  Rare earths are used in various electrical and electronic products, but because they depend on imports for the procurement of raw materials, technologies for recovering rare earths from waste and the like are being studied.

  On the other hand, in a wet phosphoric acid production process using phosphorus ore as a raw material, a large amount of phosphate gypsum is discharged as a by-product. It is known that the phosphate gypsum can be used as a rare earth-containing resource because the rare earth derived from the phosphate ore as a raw material is contained as a residue.

  In Non-Patent Document 1, an operation of leaching rare earth from phosphate gypsum using an aqueous solution of sulfuric acid, rare earth is adsorbed and eluted from the leachate with a cation exchange resin, and separated by precipitation by adding oxalate or the like to rare earth. Is disclosed.

However, in Non-Patent Document 1, a sulfuric acid aqueous solution is used as the leachate. For example, the pH of a 0.5 mol / dm ³ sulfuric acid aqueous solution is about 0.1. However, even if such equipment is prepared, there is a problem that deterioration due to use is quick. In practice, it is desired to perform leaching under mild conditions that do not require special equipment as much as possible. In addition, it was necessary to use a cation exchange resin to separate the rare earth and sulfuric acid.

Saki Fujimoto et al., “Recovery of rare earth in phosphogypsum using cation exchange resin”, Spring Conference Lecture, Japan Society of Resources and Materials, March 26, 2012, p. 399-400

  An object of this invention is to collect | recover rare earths efficiently and simply from the phosphate gypsum obtained as a residue (waste) etc. after the phosphorus collection | recovery from the phosphorus ore in the case of phosphoric acid manufacture.

The present invention is a method for recovering rare earth from phosphate gypsum,
A leaching step of obtaining a leachable noble liquid containing the rare earth by leaching rare earth into the leachate from the phosphate gypsum by a hydrothermal leaching method using a leachate that is an aqueous solution containing a chelating agent;
A rare earth recovery step of separating and recovering the rare earth from the leached noble liquid.

The pH of the leachate is preferably 3.0 to 7.0.
In the rare earth recovery step, it is preferable to separate and recover the precipitated rare earth by adding an acid that generates a rare earth and a sparingly soluble salt to the leachable noble solution.

The temperature of the leaching solution used in the leaching step is preferably 50 to 200 ° C.
Moreover, in the said leaching process, it is preferable that the quantity of the said phosphate gypsum with respect to the said leaching liquid is 5 to 25 weight%.

  It is preferable to include a chelating agent recovery step of separating and recovering the chelating agent from the leached noble liquid before the rare earth recovery step.

  According to the present invention, by using an aqueous solution of a chelating agent as a leachate, rare earth can be efficiently and simply recovered from phosphogypsum.

It is a flowchart for demonstrating an example of the collection | recovery method of this invention. It is a graph which shows the experimental result (leaching rate of a rare earth) of Example 1. It is a graph which shows the experimental result (REE leaching rate / Ca leaching rate) of Example 1. It is a graph which shows the leaching rate (the relationship between leaching temperature (pressure) and leaching rate) of rare earth in Examples 2-4. It is a graph which shows the experimental result (relationship of the leaching rate of a rare earth, and the leaching processing time) of Example 4. It is a flowchart for demonstrating the recycling rate of EDTA.

The present invention is a method for recovering rare earth from phosphate gypsum,
(1) A leaching step of obtaining a leachable noble liquid containing rare earth by leaching rare earth into the leachate from a phosphate gypsum by a hydrothermal leaching method using a leachate that is an aqueous solution containing a chelating agent;
(2) a rare earth recovery step of separating and recovering the rare earth from the leachable noble liquid.

  In the present invention, “phosphate gypsum” is phosphate gypsum containing rare earth, and is, for example, phosphate gypsum discharged as a by-product in a wet phosphoric acid production process using phosphorus ore as a raw material.

  Rare earths (rare earth elements) are 17 elements from scandium (Sc: atomic number 21), yttrium (Y: atomic number 39), lanthanum (La: atomic number 57) to lutetium (Lu: atomic number 71). It is a group consisting of At the position of the periodic table, it is an element from the fourth period to the sixth period in the third group.

  Examples of the rare earth contained in the phosphate gypsum include Ce, Nd, La, Pr, Y, Pm, Eu, Dy, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It is done. The total amount of rare earth contained in the phosphate gypsum varies depending on the phosphate ore used as a raw material, but is, for example, about 3000 ppm.

(Leaching process)
The hydrothermal leaching method in the present invention is a method in which a pulverized product of phosphogypsum or the like is added to a leachate in a high temperature state, and rare earth is leached into the leachate.

  The chelating agent contained in the leachate used in hydrothermal leaching is not particularly limited as long as it is a chelating agent capable of leaching a rare earth. For example, ethylenediaminetetraacetic acid (hereinafter abbreviated as “EDTA”), N— (2-hydroxyethyl) ethylenediaminetriacetic acid (hereinafter abbreviated as “HEDTA”), diethylenetrinitrilopentaacetic acid (DTPA), triethylenetetranitrilohexaacetic acid (TTHA), ethylenediamino-N, N′-disuccinic acid ( EDDS), trans-1,2-cyclohexylene dinitrilotetraacetic acid (CyDTA), 2-hydroxytrimethylleninitrilotetraacetic acid (HTMDTA), DL-2,3-dihydroxytetramethylenedinitrilotetraacetic acid (o-EEDTA) , Ethylene bisoxyethylene nitrilotetraacetic acid (EGTA) Thio bis ethylene nitrilo tetraacetic acid (TEDTA) and the like. Among these, EDTA can be preferably used.

  The concentration of the chelating agent in the leachate is not particularly limited. For example, when EDTA is used as the chelating agent, it is preferably 0.01 to 0.6M.

  The pH of the leachate is preferably 3.0 to 7.0, more preferably 3.3 to 4.5. When the chelating agent is EDTA, if the initial pH of the leachate is 3.0 or less, EDTA may be precipitated during the leaching, and if the pH exceeds 7.0, the rare earth leaching rate decreases. In the present invention, by using an aqueous solution containing a chelating agent as a leachate, it is possible to leach rare earth from phosphate gypsum even at such a mild pH. Therefore, it is possible to recover rare earth by a simple method without requiring special acid-resistant equipment or the like in the leaching process.

  The temperature of the leachate used in the leaching step is not particularly limited, but is preferably 50 to 200 ° C, more preferably 90 to 150 ° C. When the temperature is lower than 50 ° C., it is considered that the rare earth recovery efficiency becomes too low. On the other hand, when it exceeds 200 degreeC, heating cost becomes high industrially and becomes inefficient in terms of energy. In particular, when the temperature is 90 to 150 ° C., rare earth can be efficiently leached into the leaching solution while suppressing leaching of Ca from phosphogypsum.

  The pressure condition in the leaching step is adjusted according to the temperature condition, and is preferably adjusted to a saturated vapor pressure at that temperature at 100 to 150 ° C. and to atmospheric pressure at 100 ° C. or less.

  In the leaching step, the amount of the phosphogypsum with respect to the leaching solution is preferably 5 to 25% by weight, more preferably 10 to 25% by weight. This is because if it exceeds 25% by weight, the fluidity of the leachate tends to deteriorate and industrial processing tends to be difficult. On the other hand, if the amount is less than 5% by weight, the recovery efficiency per operation is deteriorated, resulting in inefficiency.

  The treatment time in the leaching step is preferably about 1 hour to 14 hours, more preferably about 1 hour to 6 hours, from the viewpoint of the recovery efficiency of the rare earth as the entire recovery operation.

In the present invention, as a method for dissolving a trace amount of rare earth existing in the phosphate gypsum into the liquid phase, a hydrothermal leaching method using a dilute chelating agent solution is adopted, whereby the main component (CaSO ₄ : about 75% by weight) is suppressed (Ca dissolution rate is, for example, 10% by weight or less), and rare earth can be efficiently dissolved in the liquid phase (rare earth dissolution rate is, for example, 55 to 70). weight%).

(Chelating agent recovery process)
The recovery method of the present invention preferably includes a chelating agent recovery step of separating and recovering the chelating agent from the leached noble liquid before the rare earth recovery step. Thereby, the recovered chelating agent can be reused in the next leaching step.

  Also, in the state where the rare earth is complexed with the chelating agent in the leachable noble solution, it is difficult to separate the rare earth in the rare earth collecting step, but by separating the rare earth and the chelating agent, the next rare earth collecting step The rare earth is precipitated by the addition of an acid that forms a rarely soluble salt with the rare earth, and the rare earth can be easily recovered. Examples of acids that generate rare earth and sparingly soluble salts include oxalic acid and carbonic acid.

  As a specific method of the chelating agent recovery step, for example, there is a method in which an acid is added to the leaching precious liquid obtained in the leaching step so that the pH of the leaching precious liquid is 2.3 or less. Examples of the acid include hydrochloric acid, nitric acid, hydrobromic acid and the like which do not produce a rare earth and hardly soluble salt. The pH of the leachable noble solution in this step is more preferably 1.4 to 2.1.

  By this operation, the rare earth is separated from the chelating agent, and the chelating agent can be precipitated while being dissolved in the leachable noble solution. In addition to the chelating agent bonded to the rare earth, excess chelating agent is also recovered. For example, EDTA salt (EDTA combined with rare earth) and excess EDTA2Na can be precipitated and recovered as EDTA.

(Rare earth recovery process)
The recovery of the rare earth is preferably performed by a method of separating and recovering the precipitated rare earth by adding an acid to the leachable noble solution. At this time, the acid added to the leaching noble solution is not particularly limited as long as it can precipitate the rare earth as a salt, but is preferably a weak acid. Examples of the weak acid include oxalic acid and carbonic acid.

  There is no need for pH adjustment in the rare earth recovery step. The pH of the leachable noble solution after the recovery of the rare earth is 1.3 to 2.0 when, for example, EDTA is used as the chelating agent and the rare earth is separated and recovered as the oxalate.

  The temperature of the leaching noble liquid after adding the acid is not particularly limited, and is appropriately set within a temperature range in which the leaching noble liquid can exist as an aqueous solution.

  As a specific method for separating and recovering the precipitated rare earth, for example, a filtering method can be mentioned. The rare earth crude product obtained by such a method can be purified by various known purification methods.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

(Measurement of chemical composition in phosphogypsum)
Table 1 shows the chemical composition in the phosphogypsum used in the following Examples in advance.

Example 1
In this example, only the leaching process in the recovery method of the present invention was performed, and the recovery efficiency of rare earths according to the type of leaching solution was compared.

  An aqueous solution of EDTA2Na or HEDTA, which is a chelating agent, was used as a leaching solution, and hydrothermal leaching of rare earth from phosphogypsum was performed to obtain a leachable noble solution containing rare earth. For comparison, hydrothermal leaching was similarly performed using an aqueous solution of sodium citrate as the leaching solution.

  The concentration of the leachant in each leachate was 0.1 M, and the initial pH of the leachate was 4.5. The initial pulp concentration (in the leaching step, the amount of phosphogypsum relative to the leaching solution) was 10% by weight, and the phosphogypsum was pulverized and charged into the leaching solution. The operation time of the leaching process was 1 hour, the temperature of the leaching solution was 120 ° C., and the pressure of the atmosphere was 2 atm.

  When each of the above three types of leaching agents was used, the concentration of each rare earth (Y, La, Ce, Pr, Nd) and Ca in the leaching noble solution after the leaching step was measured with an ICP emission spectrometer. FIG. 2 shows the results of calculating the leaching rate of each rare earth from phosphogypsum in each case based on the results. FIG. 3 shows the ratio of the leaching rate of each rare earth to the Ca leaching rate from phosphogypsum (phosphate ore waste) (REE leaching rate / Ca leaching rate).

  From the results shown in FIG. 2 and FIG. 3, it is possible to recover rare earth more efficiently when a chelating agent (EDTA2Na, HEDTA) is used as the leaching agent than when sodium citrate is used as the leaching agent. I understand. Of the chelating agents, EDTA2Na has a higher overall recovery efficiency of rare earth, and it is considered that the rare earth can be selectively hydrothermally leached by suppressing calcium leaching.

(Example 2)
In this example, the rare earth was recovered from the phosphate ore waste (phosphate gypsum) by carrying out each process as shown in the flow chart of FIG. Hereinafter, each step will be described.

(1) Leaching step This step was the same as in Example 1 using EDTA2Na as the chelating agent, but the dipping time was 6 hours. That is, a 0.1M-EDTA2Na aqueous solution (pH 4.5) was used as a leachate, and a pulverized phosphate gypsum (initial pulp concentration of 10% by weight) was immersed in the leachate at 120 ° C. for 6 hours. The atmosphere pressure in the leaching process was 2 atmospheres. Thereafter, the residue of phosphogypsum was recovered by filtration to obtain a leachable noble solution.

(2) Chelating Agent Recovery Step To 20 mL of the leaching noble liquid (initial pH 3.6) obtained by the leaching step, the pH is adjusted to 2.1 or less by adding a 2M-HCl aqueous solution, thereby removing the leaching noble liquid. The EDTA was precipitated and collected. That is, an aqueous HCl solution was added to reach a predetermined pH (0.5, 1.0, 1.4, 2.1), and then the leaching noble solution was allowed to stand for 30 minutes. The precipitate produced after standing was filtered and collected with a membrane filter (pore size 0.2 μm).

As a result of measuring the dry weight of the recovered material, the largest amount of 0.49 g of recovered material is obtained at pH 2.1, and assuming that all of the recovered material is H ₄ EDTA, the recovery rate is 85%. However, the amount of EDTA recovered decreased when the pH was 1.4 or lower.

  Further, the EDTA concentration and the rare earth (REE) concentration of the leachable noble liquid after the chelating agent recovery step under each pH condition were measured with an ICP analyzer. It was confirmed that the rare earth does not coprecipitate with the chelating agent under the condition of pH 0.5 to 2.1.

  As mentioned above, it is preferable to adjust the pH of the leachate in a chelating agent collection | recovery process to 0.5-2.1, and it is more preferable to adjust pH to 1.0-1.4. EDTA recovered as a precipitate can be recycled as a leaching agent.

(3) Rare earth recovery process 0.1M-oxalic acid aqueous solution was added to the leaching precious liquid (filtrate) after the chelating agent recovery process (only when the pH conditions were 2.1 and 1.4). When an aqueous oxalic acid solution was added, the solution became cloudy. After standing for 1 hour, the precipitate was filtered through a membrane filter (pore size 0.2 μm). Thereby, precipitation and collection | recovery of the rare earth as an oxalate were performed.

  The rare earth concentration and Ca concentration in this filtrate (leaching noble solution after the chelating agent recovery step) were measured by ICP emission analysis, and the recovery rates of rare earth and Ca were calculated based on these measured values. The recovery rate of rare earth was as high as 94%, and it was found that addition of oxalic acid is an effective method for separating and concentrating rare earths. It was also found that most of the calcium in the filtrate was dissolved and did not precipitate. Therefore, it has been clarified that the rare earth can be selectively recovered by adding oxalic acid in the rare earth recovery step.

  The solid recovered product (oxalate) was redissolved with 5M aqueous hydrochloric acid solution, and composition analysis was performed by ICP emission analysis. Table 2 shows the chemical composition and concentration ratio of this solid recovered product. In addition, in Table 2, the analysis result (similar to Table 1) of the chemical composition in the phosphogypsum before implementing a leaching process is also shown for the comparison.

  As shown in Table 2, the rare earth content in the solid recovered product is 31.3%. In the qualitative analysis, other rare earths (Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu) can also be confirmed, and the content of the whole rare earth is considered to be higher. On the other hand, the calcium content was as small as 3 ppm or less, and selective recovery of rare earth could be achieved.

  In summary, the rare earth (content 0.37%) in the phosphogypsum is concentrated as much as 83 times by applying the above method, and the rare earth content is recovered as a primary concentrate of about 30%. It became clear that we could do it.

  Therefore, according to the rare earth recovery method of the present invention, the rare earth in phosphogypsum can be concentrated and efficiently recovered. In the rare earth recovery step, it is considered that the recovery rate of the rare earth can be further improved by optimizing the addition amount of the acid such as oxalic acid and the treatment time. Moreover, although EDTA is an expensive chelating agent, it has been found that EDTA can be recovered from the leachable noble liquid at a high recovery rate.

(Example 3)
In this example, rare earth was recovered from phosphogypsum in the same manner as in Example 2 except that the temperature of the leachate was 150 ° C. and the pressure of the atmosphere in the leaching process was 4.7 atm. It was possible to separate and concentrate the rare earth in phosphate gypsum as oxalate (rare earth content: about 30%) with a high yield of 77% by weight.

Example 4
In this example, the temperature of the leaching solution is 90 ° C., the atmospheric pressure of the leaching step is atmospheric pressure, the treatment time is 24 hours, the cooling time after the leaching step is 1 hour, and 5 M hydrochloric acid is added to the leaching precious solution. Thus, the rare earth was recovered from the phosphogypsum in the same manner as in Example 2 except that the pH was adjusted to 1.5 and EDTA2Na was precipitated.

<Rare earth leaching rate>
In FIG. 4, the graph which put together the leaching rate of the rare earth in Examples 2-4 is shown. As shown in FIG. 4, the higher the temperature of the leaching solution, the higher the rare earth leaching rate, but the Ca leaching rate is less affected by the temperature of the leaching solution. In Example 4, the leaching rate of the total of four elements (La, Ce, Pr, Nd) (REE shown in FIG. 4) after the leaching operation for 24 hours was 55%.

  FIG. 5 shows the relationship between the leaching rate of each rare earth and the leaching processing time in Example 4. As shown in FIG. 5, at 90 ° C. and atmospheric pressure, it can be seen that the leaching reaction is almost completed in about 15 hours.

<Examination of EDTA recycling>
In this example, in the process of recovering EDTA from the leached noble liquid, the movement (mixing) of rare earth into the EDTA precipitate was 1% by weight or less. The recycling rate of EDTA was 92% by weight. Details of the recycling rate calculation will be described below.

Referring to FIG. 6, the factor determined by chelate titration of 0.1 M EDTA2Na aqueous solution was 0.88. Moreover, the factor of EDTA2Na in the leachable noble solution measured similarly was 0.76. As a result of weighing the EDTA starch, the EDTA recovery rate determined by regarding the starch as H ₄ EDTA was 96% (based on the weight of the starch).

  The EDTA starch was dissolved and diluted with 1M NaOH (so as to be 0.1M EDTA2Na) to obtain a recycle leachate. The factor determined by chelate titration of the obtained recycle leachate was 0.85, which was 96% of the factor of the EDTA2Na (reagent) aqueous solution. That is, since 96% of the chelating agent contained in the recycle leachate is effective, the EDTA recycling rate (EDTA recovery rate based on starch weight × effective rate) was 92%.

<Recover rare earth>
In this example, the rare earth was recovered from the phosphogypsum by changing the amount of oxalic acid added. The amount of oxalic acid added was 1.6 times, 2.0 times, and 3.0 times that of rare earth in weight ratio. In each case, the pH of the leaching noble solution after addition of oxalic acid was 1.46, 1.45, and 1.42.

The rare earth recovery rate was determined by the following equation.
Recovery rate = (REE amount in leachate-REE amount in residual liquid) / initial REE amount Here, the REE amount in leachate is the total value of Y, La, Ce, Pr, and Nd in leachate. The amount of REE in the residual liquid is the total value of the amounts of Y, La, Ce, Pr, and Nd in the residual liquid after the addition of oxalic acid, and the initial REE amount is the amount of Y in the ore before the leaching treatment, This is the total value of La, Ce, Pr, and Nd.

  Table 3 shows the chemical composition and concentration ratio of the solid recovered product when oxalic acid in an amount of 3 times by weight is added to the leached rare earth amount. In addition, in Table 3, the analysis result (similar to Table 1) of the chemical composition in the phosphogypsum before implementing a leaching process is also shown for the comparison.

  As shown in Table 3, the rare earth content in the solid recovery is 33.0%. In the qualitative analysis, other rare earths (Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu) can also be confirmed, and the content of the whole rare earth is considered to be higher. On the other hand, the calcium content was as small as 1.1 ppm, and the selective recovery of rare earth could be achieved.

  As a result, the recovery rate of the rare earth from the leachable noble solution correlates with the amount of oxalic acid added, but the correlation was particularly significant in La and Ce. When 3 times the amount of oxalic acid was added by weight to the amount of leached rare earth, the rare earth recovery rate was 53%, and the rare earth content in the recovered material (oxalate) was 33% (concentration). (Rate: 88 times).

  In summary, the rare earth (content 0.37%) in phosphogypsum is concentrated as much as 88 times by applying the above method, and can be recovered as a primary concentrate with a rare earth content of 33%. Became clear.

  Therefore, according to the rare earth recovery method of the present invention, the rare earth in phosphogypsum can be concentrated and efficiently recovered. In the rare earth recovery step, it is considered that the recovery rate of the rare earth can be further improved by optimizing the addition amount of the acid such as oxalic acid and the treatment time. Moreover, although EDTA is an expensive chelating agent, it has been found that EDTA can be recovered from the leachable noble liquid at a high recovery rate.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (6)

A method for recovering rare earth from phosphate gypsum,
A leaching step of obtaining a leachable noble liquid containing the rare earth by leaching rare earth into the leachate from the phosphate gypsum by a hydrothermal leaching method using a leachate that is an aqueous solution containing a chelating agent;
A rare earth recovery step of separating and recovering the rare earth from the leached noble liquid.   The method for recovering a rare earth according to claim 1, wherein the pH of the leachate is 3.0 to 7.0.   The method for recovering a rare earth according to claim 1 or 2, wherein, in the rare earth recovery step, the precipitated rare earth is separated and recovered by adding an acid to the leaching noble solution.   The method of recovering a rare earth according to any one of claims 1 to 3, wherein the temperature of the leachate used in the leaching step is 50 to 200 ° C.   The method for recovering a rare earth according to any one of claims 1 to 4, wherein in the leaching step, the amount of the phosphogypsum relative to the leachate is 5 to 25 wt%.   The method for recovering a rare earth according to any one of claims 1 to 5, further comprising a chelating agent recovery step of separating and recovering the chelating agent from the leachable noble solution before the rare earth recovery step.

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