JP6607561B2 - Method for removing molybdenum from wastewater - Google Patents

Description

  The present invention relates to a method for removing molybdenum in molybdenum-containing wastewater.

  Molybdenum is a metal that is widely used in the manufacturing field of alloys, catalysts, electronic materials, filaments, and the like, and waste liquids and waste water generated in these factories contain molybdenum compounds. Molybdenum is of concern for ecological toxicity, and was added to the items requiring monitoring in the water quality and environmental standards revised in March 1993. Therefore, a method to reduce the concentration of molybdenum in treated wastewater as much as possible. Establishment of is desired.

For the treatment of most heavy metals, a coagulating sedimentation method is used in which an alkaline agent such as caustic soda or slaked lime is added to waste water to produce a water-insoluble hydroxide and remove the precipitate.
However, since molybdenum exists as an anion of oxyacid in water, a hydroxide is not generated, and a general coagulation precipitation method cannot be applied.

As a method for removing such molybdenum from molybdenum-containing wastewater, for example, the following proposal has been made.
In Patent Document 1, ferric ions are added to molybdenum-containing wastewater, and then ferric hydroxide is generated with an acid or alkali agent at a pH of 4 to 8, and the generated suspended solids are separated into solid and liquid. In addition, a method for treating molybdenum-containing wastewater is disclosed in which molybdenum is removed by returning a part of the obtained sludge to a reaction tank and circulating the sludge. However, according to the embodiment, the molybdenum concentration of the wastewater is as low as 20 mg / L, and in order to sufficiently reduce the molybdenum concentration in the treated water, a part of the concentrated sludge is returned to the reaction tank. It is necessary to repeat this operation several times, which requires a long processing operation.
In Patent Document 2, an inorganic flocculant such as polyaluminum chloride, ferric chloride, and aluminum sulfate is added to wastewater containing an antimony compound and / or a molybdenum compound, and the pH of the wastewater is made neutral or alkaline. An antimony compound and / or a molybdenum compound in water is adsorbed in a state where flocs are generated. Thereafter, by contacting with zeolite, the antimony compound not adsorbed on the floc in water and / or the molybdenum compound and these compounds adsorbed on the floc are both adsorbed on the zeolite and separated and removed from the wastewater. Is disclosed. However, the molybdenum concentration of the wastewater is as low as 10 ppm, and the removal rate of molybdenum in the wastewater after treatment is 75.3% at the maximum value, which is not high.
Patent Document 3 contains molybdenum oxygenate ions that fill the column with an iron oxide-based adsorbent obtained by firing ferric hydroxide powder at 300 to 700 ° C., and pass wastewater therethrough. A method for treating wastewater is disclosed. However, the wastewater to be treated is a strongly acidic molybdenum-containing wastewater having a pH of 2 or less, and the molybdenum content is a wastewater having a low concentration of 10 mg / L.
Patent Document 4 describes a method for treating boron-containing wastewater by precipitating and separating under basic conditions in the presence of a polyvalent anionic substance and rare earth element ions. However, there is no disclosure regarding molybdenum.

JP 2000-117265 A JP 11-347568 A JP 2010-29760 A JP 2004-963 A

  The present invention has been made in view of the above, and there is provided a method for removing molybdenum in wastewater that can greatly reduce the molybdenum concentration by a single treatment even in wastewater containing high concentration of molybdenum. The purpose is to provide. Another object of the present invention is to provide a treatment method for reducing as much as possible the amount of sludge that becomes industrial waste in factory wastewater by the removal method.

As a result of intensive studies, the present inventors added a water-soluble iron salt and a rare earth element to the molybdenum-containing wastewater, and solid-liquid separated the generated suspended solids, so that the molybdenum in the molybdenum-containing wastewater is efficiently removed. It was found that it can be removed. In particular, it has been found that by adjusting the pH of the wastewater to 3.0 to 6.0, the molybdenum removal efficiency in the wastewater is remarkably increased.
In addition, after the production of suspended solids by adding a water-soluble iron salt such as ferric chloride and a rare earth element-containing solution, a cationic polymer flocculant is added to flock the suspended solids to form a solid liquid. It has been found that separation is facilitated efficiently.

That is, the present invention relates to the following (1) to (8).
(1) It was generated by adding a water-soluble iron salt and a rare earth element to the molybdenum-containing wastewater, or by adding a pH regulator as necessary, so that the pH of the wastewater was 3.0 to 6.0. A method for removing molybdenum from wastewater by solid-liquid separation of suspended substances.
(2) The water-soluble iron salt is any one or more selected from the group consisting of ferric chloride, ferric nitrate, ferrous sulfate and polyferric sulfate. Molybdenum removal method.
(3) The rare earth element is used as a rare earth element oxide, hydroxide, carbonate, phosphate, acetate or halide aqueous solution, hydrochloric acid solution or sulfuric acid solution (1) or (2) ) Molybdenum removal method in waste water.
(4) The method for removing molybdenum from wastewater according to any one of (1) to (3), wherein the rare earth element is lanthanum or a mixture of lanthanum and another rare earth.
(5) The pH of the wastewater is adjusted to 3.5 to 5.5 by adding a water-soluble iron salt and a rare earth element, or further adding a pH adjuster as necessary, (1) to (4 ) The method for removing molybdenum from wastewater according to any one of the above.
(6) The method for removing molybdenum from wastewater according to any one of (1) to (5), wherein a water-soluble iron salt is added to the molybdenum-containing wastewater, and then a rare earth element is added.
(7) The method for removing molybdenum from wastewater according to any one of (1) to (6), wherein a cationic polymer flocculant is further added after the addition of the water-soluble iron salt and the rare earth element.
(8) The method for removing molybdenum from wastewater according to any one of (1) to (7), wherein a water-soluble iron salt is added to the wastewater at a rate of 0.005 to 1.0 w / v%.

According to the present invention, a water-soluble iron salt and a rare earth element are added to a molybdenum-containing wastewater, and the pH of the wastewater is adjusted with a pH adjuster to be 3.0 to 6.0 as necessary. By solid-liquid separation of suspended substances, even waste water containing high-concentration molybdenum can be removed to a low concentration by a single treatment.
In addition, after the suspension material is generated, a cationic polymer flocculant is added to make the suspension material flocculated, so that solid-liquid separation is efficiently facilitated and the amount of sludge that becomes industrial waste is minimized. A processing method can be provided.

The present invention is described in detail below.
Molybdenum-containing wastewater to which the method of the present invention can be applied may be wastewater of any origin in various mining industries, and is usually suitably applicable to wastewater containing about 50 to 3,000 mg / L of molybdenum in the wastewater.

As the water-soluble iron salt used in the present invention, one or more water-soluble iron salts such as ferric chloride, ferric nitrate, ferrous sulfate and polyferric sulfate are preferably used. Among these, ferric chloride is preferable because even if it is used alone, a high molybdenum removal rate is achieved by adding a rare earth element-containing solution.
In the present invention, in addition to the water-soluble iron salt, a water-soluble aluminum salt such as aluminum sulfate or polyaluminum chloride may be added.
In addition, you may use a water-soluble iron salt as 20-60 mass% (especially 30-50 mass%) aqueous solution.
In the present invention, the amount of water-soluble iron salt added depends on the molybdenum concentration of the wastewater to be treated, but is usually about 0.005 to 1.0 w / v%, preferably 0.01 to 0.00% with respect to the wastewater. It is about 7 w / v%, More preferably, it is about 0.02-0.3 w / v%. If the addition of water-soluble iron salt is less than 0.005 w / v%, molybdenum removal efficiency may not be achieved, and if it exceeds 1.0 w / v%, the amount of sludge increases, which is preferable for industrial waste treatment. There is no.

In the present invention, rare earth elements are present in the water to be treated.
This rare earth element serves as a molybdenum remover. The rare earth element to be added to the molybdenum-containing wastewater may be in any state as long as the object of the present invention can be achieved. However, it is preferably added as a rare earth element-containing solution, rare earth element oxide, hydroxide, carbonate It is preferable to add them as an aqueous solution of phosphate or halide, hydrochloric acid solution or sulfuric acid solution. The concentration thereof is not particularly limited, but in consideration of operability, for example, in the case of a hydrochloric acid solution of a rare earth element oxide, the rare earth element in the hydrochloric acid solution is preferably 10 to 40% by mass, more preferably It is 20-35 mass%.

In the present invention, lanthanum ions and cerium ions are preferred among the rare earth element ions, and lanthanum is more preferred.
In addition, the rare earth element-containing solution used as the molybdenum removing agent in the present invention can be used in the form of a rare earth element mixture solution, or a rare earth element alone or a mixed solution. The use of a solution of lanthanum and cerium and ytterbium is preferred, and a solution of lanthanum and cerium is more preferred. As a preferable specific example, a hydrochloric acid solution of lanthanum, cerium, and ytterbium (concentration is 32.5% by mass as an oxide, and the composition thereof is 95% by mass of lanthanum, 4.9% by mass of cerium, and 0.1% by mass of ytterbium. ). In addition, the solution of the said composition is marketed as Geranic R (registered trademark; wastewater treatment agent; environmental management organization limited company).

The solution containing rare earth elements used in the present invention can be prepared by removing impurities from ores containing rare earth elements and then dissolving them in hydrochloric acid. The hydrochloric acid concentration at this time is preferably about 0.1 to 12 N, more preferably about 5 to 12 N, and still more preferably about 8 to 12 N. The concentration of rare earth element ions is not particularly limited, but considering operability, the oxide is preferably 10 to 40% by mass, more preferably 20 to 40% by mass, and still more preferably 20 to 35% by mass. It is. The dissolution time may be completely dissolved, and is not particularly limited, but about 0.5 to 2 hours is sufficient.
In the present invention, the amount of rare earth element added depends on the concentration of molybdenum in the wastewater to be treated, but it is about 0.05 to 50 moles, preferably 0,1 to 30 moles as rare earth elements per mole of molybdenum in the wastewater. About mol, more preferably about 0.5 to 20 mol is used. It should be noted that it may be increased or decreased as appropriate.

In the present invention, after adding the water-soluble iron salt solution and the rare earth element-containing solution to the waste water, a pH adjuster is further added as necessary to adjust the pH to 3.0 to 6 in order to generate molybdenum precipitates. 0.0, preferably the pH is adjusted to 3.5 to 5.5. Molybdenum reacts and precipitates well in the weakly acidic region, but re-elutes in the neutral or alkaline region, and good removal cannot be expected.
As a pH regulator for adjusting the pH of such treated wastewater, alkaline substances such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, calcium hydroxide, or acidic substances such as hydrochloric acid, sulfuric acid, nitric acid are used. It is done.
In the present invention, when adding a water-soluble iron salt and a rare earth element-containing solution to a molybdenum-containing wastewater, a water-soluble iron salt is added and then a rare earth element is added, or a rare earth element is added and then water-soluble Any order of addition, in which an iron salt is added or a water-soluble iron salt and a rare earth element are added simultaneously, is possible. Preferably, the order in which ferric chloride is added first and then the removing agent A is added is preferable because the molybdenum removal rate is somewhat superior.

Furthermore, in the present invention, it is preferable to use a polymer flocculant in combination in order to flock the suspended substance by a coagulation sedimentation method and facilitate solid-liquid separation.
As the polymer flocculant, it is used for floc aggregation, polyacrylic acid ester, polydicyanamide, polyamidine, polydiallylamine, polyamine, polymethacrylic acid dimethylaminoethyl ester, polyethyleneimine, chitosan Cationic polymer flocculants such as
In addition, nonionic organic flocculants such as polyacrylamide, anionic organic flocculants such as polyacrylic acid, copolymers of acrylamide and acrylic acid, and salts thereof can also be used. However, since the reaction pH of molybdenum in the present invention is weakly acidic, nonionic and anionic polymer flocculants may not be used because they exhibit no agglutination reaction due to pH.
The addition amount of the polymer flocculant is usually about 0.5 to 10 mg / L, preferably about 1 to 7 mg / L in the treated wastewater.

  After the series of steps, the water to be treated is subjected to solid-liquid separation treatment. This solid-liquid separation can be performed by a conventional method, and examples thereof include filtration separation such as belt press and filter press, centrifugation, sedimentation separation, and the like.

Next, the present invention will be described in more detail with reference to examples.
The measuring instrument used for measuring molybdenum (hereinafter sometimes abbreviated as “Mo”) in the examples is a portable multi-item rapid water quality analyzer manufactured by HACH.

Reference example 1
A hydrochloric acid solution of a rare earth oxide (the concentration of the rare earth element is 32.5% by mass as an oxide, the composition is 95% by mass of lanthanum, 4.9% by mass of cerium, and 0.1% by mass of ytterbium) is used in the present invention. Remover A was designated.

Examples 1-1 to 1-5
In Examples 1-1 to 1-5, 100 mL of factory wastewater (molybdenum content 950 mg / L, initial pH 11.6) was added to the amount of ferric chloride (w / v%) described in Table 1 An iron 38% aqueous solution was used, a rare earth element-containing solution (removal agent A) (v / v%), 17% NaOH, and an anionic polymer flocculant. Table 1 shows the pH, molybdenum content, and molybdenum removal rate after addition of these components.
In Example 1-1, 0.13% ferric chloride and 0.1% removal agent A were added, and the Mo content was reduced to 20 mg / L.
In Examples 1-2 to 1-4, the removing agent A was added in increments of 0.05%. However, the Mo concentration decreased only by about 3 mg / L.
In Examples 1-3 to 1-4, it was judged that the addition of the rare earth element-containing solution (removal agent A) was sufficiently added, with no change at the Mo content of 14 mg / L.
In Example 1-5, when the pH was increased from 3.0 to 4.7 using sodium hydroxide solution, the Mo content decreased from 14 mg / L to 5 mg / L.
From these facts, it was found that the processing pH is about pH 3.0, and there is an appropriate pH for removing molybdenum. In addition, aggregation and precipitation with an anionic polymer flocculant did not occur at the pH in the acidic region in this test.

Ferric chloride: “Ferric chloride 38% aqueous solution Baume degree 40” manufactured by Lhasa Kogyo Co., Ltd. was used. However, the addition amount was calculated and described as ferric chloride. The same applies to the following embodiments.
Remover A: The rare earth element-containing solution shown in Reference Example 1 was used. For example, the addition of 0.1 mL to 100 mL of waste water is converted to 0.1 v / v%. The same applies to the following embodiments.
・ Himoloc A-210H; anionic polymer flocculant, sodium polyacrylate (Himo Corporation)

Examples 2-1 to 2-2
As Examples 2-1 to 2-2, 100 mL of factory wastewater (molybdenum content 935 mg / L, initial pH 11.4), ferric chloride (w / v%) in amounts shown in Table 2, and removal agent A (v / v%), 35% hydrochloric acid, 25% NaOH. Table 2 shows the pH, Mo content, and Mo removal rate after addition of these components.
In Examples 2-1 to 2-2, 0.15% ferric chloride and 0.1% removing agent A were added, and the pH was set to 4.2 to 4.5 with a pH adjuster. A good removal effect was obtained with a content of 2 to 3 mg / L (Mo removal rate 99.7 to 99.8%).

Examples 3-1 to 3-3, Reference Example 3-1.
As Examples 3-1 to 3-3 and Reference Example 3-1, 100 mL of factory wastewater (molybdenum content 930 mg / L, initial pH 11.2), ferric chloride (w / v%) in the amount shown in Table 3 Remover A (v / v%), 35% hydrochloric acid, 25% NaOH were added. Table 3 shows the pH, Mo content, and Mo removal rate after addition of these components.
In Reference Example 3-1, 0.15% ferric chloride and 0.1% removal agent A were added, the pH was 2.7, and the molybdenum content was only reduced to 64 mg / L (removal rate 93.1). %).
In Examples 3-1 to 3-2, when the pH was set to 3.8 to 4.0 with a pH regulator, the molybdenum content was about 2 mg / L, and a good removal effect was obtained (removal rate 99.8% ).
In Example 3-3, the molybdenum content was maintained at 4 mg / L even when the pH was raised to 4.5 (removal rate 99.6%).
These results show that when 0.15% ferric chloride and 0.1% removal agent A were added, the pH was 3.8 to 4.5 and the removal rate was maintained at 99 %% or more in the single digit range. Indicates.

Examples 4-1 to 4-4, Reference examples 4-1 to 4-3
As Examples 4-1 to 4-4 and Reference Examples 4-1 to 4-3, the success or failure of various coagulating agents was confirmed. That is, using a solution obtained by adding 0.15% ferric chloride and 0.1% removing agent A to 100 mL of factory wastewater (molybdenum content 930 mg / L, pH 11.2), 25% NaOH was added to confirm the success or failure of the aggregation and precipitation ability. Table 4 shows the pH, Mo content, and Mo removal rate after addition of these components.
In order to perform solid-liquid separation (coagulation precipitation), coagulation precipitation must be completed. In Reference Examples 4-1 to 4-3, filter paper filtration can be performed using anionic polymer, but coagulation precipitation occurs. There wasn't.
In Examples 4-1 to 4-4, aggregation precipitation succeeded in an acidic region of pH 4.0 to 4.3 in all using cationic polymers having different molecular weights.

・ Himoloc A210H; anionic polymer flocculant, sodium polyacrylate (Himo Corporation)
・ Himoloc MS-882; Cationic (amphoteric) polymer flocculant, polyacrylate ester (Himo Corporation)
・ Himolock MP-184; Cationic polymer flocculant, polyacrylate ester (Himo Corporation)
・ Himolock MP-584; low molecular weight cationic polymer flocculant, polyacrylate ester (Himo Corporation)
・ Himoloc MP-384; medium molecular weight cationic polymer flocculant, polyacrylate ester (Himo Corporation)

Examples 5-1 to 5-6, Reference Example 5-1
As Examples 5-1 to 5-6 and Reference Example 5-1, 0.15% ferric chloride in the amount shown in Table 5 and removal agent in 100 mL of factory wastewater (molybdenum content 930 mg / L, pH 11.2) 0.1% of A and a pH adjuster were added. Table 5 shows the pH, Mo content, and Mo removal rate after addition of these components.
In Reference Example 5-1, it decreased only to 75 mg / L at pH 2.7 (removal rate 91.9%).
In Examples 5-1 to 5-5, the Mo content of about 10 mg / L was maintained in the pH range of 3.8 to 5.5 (removal rate 98.9 to 99.5%).
In Example 5-6, the Mo content was 20 mg / L at pH 5.9, and this pH value was judged to be the upper limit. It was determined that a pH of about 5.5 or less was preferable.
From this test, Mo content was 930 mg / L and high concentration of Mo removal, but 0.15% ferric chloride and 0.1% removal agent A were added, and 10 mg / L at pH 3.8-5.5. In particular, it was 5 mg / L at a pH of 5 and a single digit.

Example 6
As Example 6, waste water (molybdenum content 250 mg / L, pH 12.2) 100 mL, 0.06% ferric chloride solution in the amount shown in Table 6, 0.025% removal agent A, and pH regulator Was added. Table 6 shows the pH, Mo content, and Mo removal rate after addition of these components.
In Example 6, when the pH was adjusted to pH 4.8, the Mo content was in the single digit range of 3 mg / L. (Removal rate 98.8%)

Example 7
As Example 7, to 100 mL of waste water (molybdenum content 695 mg / L, pH 7.8), 0.10% of ferric chloride in the amount shown in Table 7, 0.05% of removal agent A, and pH regulator were added. did. Table 7 shows the pH, Mo content, and Mo removal rate after addition of these components.
In Example 7, when the pH was adjusted to 25 with 25% sodium hydroxide and the pH was raised to 4.5, the Mo content was 3 mg / L. Even in the case of wastewater with a high concentration of 695 mg / L of molybdenum, 0.10% of ferric chloride and 0.05% of the removal agent A were added at a low concentration of 3% / L, which was in the single digit range (removal rate 99.95%). 6%).

Examples 8-1 to 8-2
As Examples 8-1 to 8-2, a comparative test was performed by changing the addition order of the water-soluble iron salt and the rare earth element added to the molybdenum-containing wastewater.
In Example 8-1, 0.02% of the removal agent A described in Table 8-1 was added to 100 mL of waste water (molybdenum content 116 mg / L, pH 12.2), and then ferric chloride was added 0.04%. % Was added to adjust the pH to 5.2, and a cationic polymer flocculant (Himoloc MP-584) was added. Table 8-1 shows the results of pH, Mo content, and Mo removal rate after the addition. The Mo content of the filtrate obtained by filtering the coagulation sedimentation paper was 6 mg / L (removal rate 94.8%).

In Example 8-2, using the same waste water as in Example 8-1, the ferric chloride solution was added first, and then the remover A was added.
That is, 0.04% of ferric chloride in the amount shown in Table 8-2 was added, then 0.02% of remover A was added, and the pH was adjusted to 4.0. MP-584) was added. Table 8-2 shows the results of pH, Mo content, and Mo removal rate after the addition. As a result of measuring the Mo content of the filtrate obtained by filtering the coagulation sedimentation back paper, the Mo content was 2.5 mg / L (removal rate 97.8%).
From the above results, there is no significant difference in the order of addition of the ferric chloride solution and the rare earth element-containing solution (removing agent A), but the order of adding the removing agent A first is followed by ferric chloride. It can be said that it was somewhat superior. Moreover, in order to acquire the effect of this invention, it does not interfere at all to administer both simultaneously.

・ Himolock MP-584; low molecular weight cationic polymer flocculant, polyacrylate ester (Himo Corporation)

Examples 9-1 to 9-3, Reference examples 9-1 to 9-2
As Examples 9-1 to 9-3 and Reference Examples 9-1 to 9-2, 0.04% of ferric chloride in an amount shown in Table 9 was added to 100 mL of waste water (molybdenum content 114 mg / L pH 12.1). The removal agent A was added to 0.02%, and the pH adjusting agent was added. Table 9 shows the pH, Mo content, and Mo removal rate after addition of these.
In Examples 9-1 to 9-3, in the range of pH 3.6 to 5.4, the Mo content was as good as 4.5 to 6 mg / L in single digits, and the fluctuation was slight.
In Reference Examples 9-1 to 9-2, the Mo content was changed from 24 mg / L to 43 mg / L as pH was increased from 6.8 to 8.1, and re-elution was confirmed. It was observed that Mo re-elution progressed with increasing pH.
Therefore, in this test, it was suggested that the pH range of 3.6 to 5.4 is an appropriate pH that keeps Mo in the floc.

Claims (6)

By adding a water-soluble iron salt to the molybdenum-containing wastewater, and then adding a rare earth element, and further adding a pH adjuster, the pH of the wastewater is set to 4.0 to 4.3 , and the cationic polymer flocculant is further added. A method for removing molybdenum from wastewater by solid-liquid separation of the suspended solids produced by the addition of. The method for removing molybdenum from wastewater according to claim 1, wherein the water-soluble iron salt is at least one selected from the group consisting of ferric chloride, ferric nitrate, ferrous sulfate and polyferric sulfate. . The wastewater according to claim 1 or 2, wherein the rare earth element is used as an aqueous solution, hydrochloric acid solution or sulfuric acid solution of an oxide, hydroxide, carbonate, phosphate, acetate or halide of a rare earth element. Method for removing molybdenum in it. The method for removing molybdenum from wastewater according to any one of claims 1 to 3, wherein the rare earth element is lanthanum or a mixture of lanthanum and another rare earth. The wastewater according to any one of claims 1 to 4, wherein the pH of the wastewater is 3.5 to 5.5 by adding a water-soluble iron salt and a rare earth element, and further adding a pH regulator. Of removing molybdenum. The method for removing molybdenum from wastewater according to any one of claims 1 to 5, wherein a water-soluble iron salt is added to the wastewater at a rate of 0.005 to 1.0 w / v%.