JP2010284570A - Method of treating antimony-containing water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antimony removing method capable of simply and economically treating antimony-containing water using a small amount of a chemical agent while reducing the production amount of sludge in highly treating the antimony-containing water, wherein antimony is contained in water to be treated at a concentration of 2 mg/L or above, to reduce the concentration of antimony to 0.2-0.01 mg/L. <P>SOLUTION: This method of treating the antimony-containing water includes a first process for adding a ferric salt and an alkali agent to water to be treated containing antimony to precipitate and separate antimony to obtain antimony-containing water with a concentration of 2 mg/L or below and a second process for succeedingly adding a rare-earth element salt solution based on cerium and the alkali agent to the separated solution in the first process to separate the residual antimony as a hardly soluble precipitate to reduce the concentration of antimony in the separated solution to 0.2-0.01 mg/L. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a treatment method for separating and removing antimony from wastewater discharged from industries using antimony or antimony and its compounds, or from antimony-containing water eluted from soil or groundwater. It is.

Antimony (In general, antimony in wastewater coexists with colloidal antimony compounds and dissolved oxyantimony ions, but in this specification we shall refer to both antimony contained in water, and the weight of antimony. Is expressed as antimony concentration) and is a highly toxic substance and has not yet been designated as a wastewater control substance by the Ministry of the Environment. There is a move to review (Ministry of the Environment press release on February 26, 2004). For the removal of antimony from antimony-containing water, a coagulation-precipitation method (for example, Patent Documents 1 and 2) in which an iron compound is added as a coagulant is generally known. A large amount of sludge is generated as a result. In addition, trivalent antimony has a lower removal rate than pentavalent antimony, and therefore requires an oxidation treatment in advance. Furthermore, there are problems such as being effective for inorganic antimony but decreasing for organic antimony.

In order to solve these problems, a method in which the pH is adjusted to 5 or higher after adding a titanium salt (Patent Document 3), a metal element compound selected from lanthanum, cerium, zirconium, etc. is added. A coagulation-precipitation method (Patent Document 4) that performs a sum treatment has been proposed. Since these methods have a large amount of adsorption to dissolved oxyantimony ions compared to the above method using an iron compound, a low concentration treatment is possible with a small amount of use. For example, the antimony concentration is about 2 mg / liter or more. In the case of the treatment with high concentration of water, the unit cost of these flocculants is expensive, so that the treatment cost becomes excessive. In addition, a method of adsorbing oxyantimony ions with a zeolite adsorbent (Patent Document 5), an anion exchangeable inorganic ion exchanger adsorbent (Patent Document 6), etc. has been proposed. Since the agent cannot be reused by a regeneration process, it must be treated as a waste, resulting in an excessive running cost.

JP 63-236592 A Japanese Patent Laid-Open No. 08-080490 JP-A-10-290986 Japanese Patent Laid-Open No. 11-010170 JP 2002-143846 A JP-A-11-216356

In view of the above problems, the object of the present invention is to remove high-concentration antimony-containing water having an antimony concentration of 2 mg / L or more in water to be treated to a concentration of 0.2 to 0.01 mg / L or less. It is an object of the present invention to provide a method for removing antimony that can be easily and economically processed with less sludge generation.

As a result of examining the processing efficiency of the coagulation precipitation method using ferric salt to solve the above-mentioned problems, the present inventors have a relatively high removal efficiency up to about 2 mg / L of antimony. It is necessary to add a large amount of flocculant to process to a high concentration, and it dissolves in the hydroxide formed by adding rare earth salt mainly composed of cerium and alkali agent to low concentration antimony-containing water. It was found that when antimony was coprecipitated as a hardly soluble precipitate, antimony could be removed almost completely with the use of a small amount of rare earth salt, and the present invention was achieved by combining both.

That is, the present invention includes the following (1) to (4).
(1) A first step in which ferric salt and an alkaline agent are added to water to be treated containing antimony to precipitate and separate insoluble antimony particles and dissolved antimony, followed by cerium as a main component in this separated liquid A method for treating antimony-containing water comprising a second step of adding a rare earth salt solution and an alkali agent to separate the remaining dissolved antimony as a difficult-to-be-precipitated precipitate.
(2) In the above (1), the water to be treated having an antimony concentration of antimony-containing water having an antimony concentration of 2 mg / liter or more is treated to 2 mg / liter or less in the first step and subsequently treated to 0.2 mg / liter or less in the second step. The method for treating antimony-containing water as described.
(3) The aggregation precipitation in the first step is performed at pH 6-11, and then, as the second step, slaked lime is added to the rare earth salt solution mainly composed of cerium to adjust the pH to 9-12 (1) ) Or the method for treating antimony-containing water according to (2).
(4) The method for treating antimony-containing water according to any one of (1) to (3), wherein the precipitate generated in the second step is returned to the first step and the first step is performed.

According to the method of the present invention, a first step using a ferric salt as a flocculant in antimony-containing water having a high concentration of 2 mg / L or more, followed by a second step using a rare earth salt mainly composed of cerium. The antimony concentration can be reduced to 0.2 to 0.01 mg / L or less by performing the two-stage coagulation sedimentation treatment consisting of Cost can be reduced. Moreover, processing efficiency can be further improved by returning the deposit of a 2nd process to a 1st process, and performing a 1st process.

Hereinafter, the present invention will be described in detail.
Antimony-containing water to be treated in the present invention includes metal antimony production, compound semiconductors such as InSb and AlSb, electronic parts such as varistors, wastewater discharged from the production of plating, flame retardants, catalysts, etc., and naturally derived And groundwater from which antimony is eluted from the soil of the factory. In addition to soluble trivalent and pentavalent oxyantimony ions, insoluble antimony compounds such as metals, oxides (trivalent and pentavalent), and fluorides are colloidally dispersed in water. It can also be applied when The antimony-containing water can also be applied when ions of heavy metals such as fluorine, arsenic, boron, selenium, phosphorus, iron, chromium, lead, and molybdenum coexist. In particular, the method of the present invention is suitable for treating antimony-containing water having a high concentration of antimony concentration of 2 mg / L or more, more preferably about 1000 to 5 mg / L.

The first step in the treatment of the antimony-containing water of the present invention is to adjust the pH to 4 to 11, and preferably to pH 6 to 11, by adding a ferric salt and an alkaline agent to the water to be treated, and the resulting precipitate is subjected to solid-liquid separation. To do. As a ferric salt used for this invention, arbitrary things, such as ferric sulfate, ferric chloride, poly ferric sulfate, can be used, These can be used individually or in combination. Alternatively, the ferric salt may be formed by blowing air into the reaction vessel to which the ferrous salt has been added or by adding an oxidizing agent such as sodium hypochlorite or hydrogen peroxide. When ferrous salt is used, if the dissolved antimony is trivalent, the antimony is oxidized at the same time as the oxidation of iron ions, so that the antimony removal efficiency may be improved.

The amount of ferric salt added varies depending on the antimony concentration of the water to be treated and the target treatment concentration, but in the present invention, the antimony concentration of the water to be treated is 2 mg / L or more, and the treatment liquid is 2 to 2. Treating to about 1 mg / L is the most efficient method of using ferric salt, and 0.5 to 3 as a weight ratio is a standard with respect to the antimony concentration 1 of the water to be treated. Incidentally, when processing the processing liquid to 1 mg / L or less, about 10 to 100 is required as Fe, and in this case, the amount of sludge generated becomes very large and the running cost becomes high.

As the alkaline agent used in the first step of the present invention, any of caustic soda, caustic potash, slaked lime, magnesium hydroxide and the like can be used, and these can be used alone or in combination. In particular, the use of slaked lime is preferable because the floc produced has good cohesiveness and is economically advantageous. The amount used is the amount necessary to adjust the pH of the reaction vessel to 6-11. Specifically, the amount of chemistry required to produce a ferric hydroxide precipitate from the ferric salt to be added. This is the sum of the equivalent amount and the amount necessary for pH adjustment during the reaction.

Since the reaction in the first step occurs immediately after adding the ferric salt and the alkali agent to the treated water, it is not necessary to consider time restrictions in particular. However, when reacted for 5 to 30 minutes, antimony is insoluble with iron hydroxide. Since it becomes a precipitate and solidifies, the solid content is removed by solid-liquid separation. As a method of solid-liquid separation, a known method such as precipitation extraction, filtration, centrifugation, membrane filtration, or the like may be used. In addition, a polymer flocculant or an inorganic floc growth agent can be used to improve the sedimentation property of the flocs before solid-liquid separation.

In the second step of the present invention, after adding a rare earth salt solution containing cerium as a main component to the separation liquid in the first step, an alkaline agent is added to adjust the pH to 9 to 12, preferably 10 to 12. The produced precipitate is subjected to solid-liquid separation, and the antimony concentration of the treated water is treated to 0.2 to 0.01 mg / L or less.

The rare earth salt mainly composed of cerium to be used may be any salt selected from hydrochloride, sulfate and nitrate, and a salt of a rare earth element mixture containing cerium in an amount of 90% by weight or more, preferably 92% by weight or more. It is a solution. The concentration of the rare earth salt solution is not particularly limited, but is usually 40 to 20% by weight in terms of oxide (cerium oxide: CeO ₂ ). Cerium ions are adjusted to pH 8 to 12 with an alkali agent to efficiently combine with oxyantimony ions in the water to be treated to form precipitates. When a large amount of rare earth elements other than cerium is contained, there is a problem that the removal rate of antimony in the water to be treated decreases due to the solubility of the compound bonded to antimony. Materials other than cerium that may be mixed include scandium, yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium. , Lutetium, titanium, zirconium, compounds containing hafnium, and the like.

In the present invention, the addition amount of the rare earth salt solution depends on the antimony concentration in the separation liquid in the first step. For example, when processing 2 mg / L to a concentration of 0.2 to 0.01 mg / L or less, On the basis of cerium oxide (hereinafter referred to as a value obtained by converting a cerium salt into CeO ₂ ), a weight ratio of 0.01 to 0.1 is a standard for CeO ₂ with respect to an antimony concentration of 1. According to the experiments by the present inventors, the antimony equilibrium adsorption amount of the precipitate formed by adding the cerium salt and the alkali agent to the antimony-containing water is that the antimony equilibrium concentration in the aqueous layer is 0.1 mg / L. 100 mg-Sb / g-CeO ₂ , and 0.01 mg / L, which is very large (about 30 mg-Sb / g-CeO ₂ ) (see FIG. 1). Can remove antimony.

As the alkaline agent used in the second step of the present invention, any one such as caustic soda, caustic potash, slaked lime, magnesium hydroxide can be used, and these can be used alone or in combination. In particular, the use of slaked lime is preferable because the floc produced has good cohesiveness and is economically advantageous. The amount used is the amount necessary to adjust the pH of the reaction vessel to 9-12. Specifically, it is necessary to form a hydroxide precipitate from the rare earth salt mainly composed of cerium to be added. Is the sum of the chemical equivalent and the amount necessary for pH adjustment during the reaction. In the adjustment of the pH, a precipitate starts to be formed from about pH 8.5, but the antimony removal rate is improved by adjusting the pH within the range of 9 to 12, more preferably 10 to 12.

Further, if necessary, a floc growth agent can be used to enhance the sedimentation property of the generated precipitate. Specific examples include inorganic flocculants such as polyaluminum chloride and polyiron sulfate, cationized modified polyacrylamide, polydimethylaminoethyl ester of polyacrylic acid, dimethylaminoethyl ester of polymethacrylic acid, polyethyleneimine, chitosan, etc. Cationic organic flocculants, nonionic organic flocculants such as polyacrylamide, anionic organic flocculants such as polyacrylic acid, copolymers of acrylamide and acrylic acid, and salts thereof, and the like.

After completion of the series of second 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 a coagulation sedimentation treatment, a pressure flotation treatment, a filtration treatment, a centrifugal separation treatment, a filter filtration treatment, and a membrane separation treatment.

  When processing using a continuous reaction tank and a sedimentation tank, you may return the deposit of a 2nd process to the reaction tank of a 1st process. In this case, the amount of the alkaline agent used in the first step can be reduced by adding the precipitate in the second step to the first step in which the ferric salt is used as the flocculant. The amount of antimony adsorbed on the rare earth hydroxide can be increased by contacting the oxide precipitate with water containing high concentration of antimony, and the antimony removal rate in the first step can be improved. As a result, the amount of flocculant used is increased. Can be reduced. Furthermore, there is an advantage that two kinds of precipitates can be separated and recovered as one reduced sludge.

A system configuration for treating antimony-containing water of the present invention is shown in FIG. 2 as a reference example. The treated water 1 is supplied to the first reaction tank A, the ferric salt and the alkali agent 2, and the returned second-step precipitation slurry 7 are mixed to precipitate ferric hydroxide at a predetermined pH. Thereafter, the polymer flocculant 3 is injected and separated into the sediment 6 and the supernatant liquid in the high-speed sedimentation layer B (first step). The supernatant liquid is then sent to the second reaction vessel C, where the rare earth salt solution and the alkali agent 4 are mixed to precipitate the rare earth hydroxide at a predetermined pH, and then the polymer flocculant 3 is injected and added. Along with the high-pressure water pressurized in the pressure tank C, it is sent to the pressurized levitation basin D and separated into the agglomerated slurry 7 and the clean treated water 5 (second step). The second-step sedimentation slurry 7 from the pressurized floating leash D is collected in the circulating sludge pit E and returned to the first reaction leash A. Further, the first-step sedimentation slurry 6 from the high-speed sedimentation basin B is sent to the waste sludge pit F, and subsequently recovered and discarded as dewatered sludge by a filter.

The present invention will be described in detail below, but the examples are for facilitating the understanding of the present invention and are not intended to limit the present invention. In the examples, “%” means “% by weight”.

Example 1
Antimony waste water containing colloidal particles discharged from an actual electronic component factory (pH 7.1, antimony concentration 32 mg / L, of which soluble antimony 4.4 mg / L) was used as water to be treated. As a first step, 100 mg / L of ferric chloride is added to this antimony wastewater, followed by adding slaked lime 80 mg / L and stirring for 5 minutes, and then adding 1 mg / L of anionic polymer flocculant, After leaving it to stand for 15 minutes, the supernatant was filtered through paper No. Filtered with 5A. The filtrate had a pH of 6.3 and an antimony concentration of 1.6 mg / L. Subsequently, as a second step, the filtrate cerium chloride solution (specific gravity 1.59, CeO ₂ concentration in terms of 29%) was 0.03 mL (CeO ₂ in terms 0.014 g) / L added, followed by addition of slaked lime After adjusting the pH to 11.0 and stirring for 10 minutes, 1 mg / L of an anionic polymer flocculant was added and allowed to stand for 15 minutes, and the precipitate was filtered. The antimony concentration of the filtrate was 0.13 mg / L. Moreover, as a result of measuring the weight of the filtrate obtained in each step, the amount of cake per 1 L of water to be treated was 450 mg from the first step and 94 mg from the second step, and the total amount was 544 mg.

Example 2, Comparative 1
Antimony concentration 1.6 mg / L filtrate obtained in the first step of Example 1, as a second step, cerium chloride solution (specific gravity 1.59, CeO ₂ concentration in terms of 29%) and 0.01 mL (CeO ₂ 0.005 g) / L (comparative-1), 0.06 mL (0.028 g in terms of CeO ₂ ) / L (Example 2-1), 0.1 mL (0.05 g in terms of CeO ₂ ) / L (implementation) After each of Examples 2-2) was added, the pH was adjusted to 11 by the addition of slaked lime. Subsequently, 1 mg / L of an anionic polymer flocculant was added and allowed to stand, and then the precipitate was filtered. Table 2 shows the antimony concentration calculated from the antimony concentration of each filtrate, the amount of antimony removed, and the amount of cerium chloride added (converted to the amount of CeO ₂ ). Further, from this result, an antimony adsorption isotherm of cerium (CeO 2 equivalent) is shown in FIG.

Example 3, Comparative 2
In the second step of Example 1, 0.04 mL (0.018 g in terms of CeO ₂ ) / L of cerium chloride solution was added, and the pH at the time of precipitation was changed by changing the amount of slaked lime used for neutralization. Table 2 shows the results of tests conducted in the same manner as in Example 1. From this result, it can be seen that when the precipitation pH is 10.5 (Example 3-1) or higher, treated water having a low antimony concentration can be obtained.

Comparative Example 1
Using the water to be treated having an antimony concentration of 32 mg / L used in Example 1, using only ferric chloride as a flocculant in the water to be treated, the addition amount of ferric chloride and slaked lime was changed, and then an anionic polymer Table 2 shows the results of measuring the antimony concentration of the filtrate and the weight of the precipitate by adding 1 mg / L of the flocculant and performing the aggregation precipitation treatment. As a result, with only ferric chloride, the antimony concentration could not be reduced to 0.2 mg / L or less even with a large addition amount (Comparative Example 1-5).

Comparative Example 2
Using the water to be treated having an antimony concentration of 32 mg / L used in Example 1, ferric chloride and cerium chloride solution were simultaneously added to the water to be treated, followed by addition of a predetermined amount of slaked lime, and then anion. Table 4 shows the results of coagulation-precipitation treatment after addition of 1 mg / L of the system polymer flocculant and measuring the antimony concentration of the filtrate and the weight of the precipitate. As a result, it is clear that the antimony removal efficiency is lower in the coagulation precipitation separation using ferric chloride and cerium chloride in comparison with the method shown in Example 1.

Example 4
94 mg / L of the second step filtrate obtained in Example 1-treated water (water content 79%) was added to antimony wastewater (pH 7.1, antimony concentration 32 mg / L), and dispersed by stirring. As a step, 100 mg / L of ferric chloride was added, followed by addition of slaked lime 40 mg / L, and allowed to stand, followed by filtration. The filtrate had a pH of 7.2 and an antimony concentration of 1.2 mg / L. Subsequently, as the second step, 0.03 mL (0.014 g in terms of CeO ₂ ) / L of a cerium chloride solution (specific gravity 1.59, CeO ₂ equivalent concentration 29%) is added to this filtrate, and then slaked lime is added. The pH was adjusted to 11.0, 1 mg / L of an anionic polymer flocculant was added, and the precipitate was filtered. The antimony concentration of the filtrate was 0.06 mg / L. The first step filtrate obtained here had a water content of 72% and was 520 mg per liter of water to be treated. Moreover, since the filtrate obtained in the second step can be used for the treatment in the next first step, according to this method, the antimony concentration of the treated water is set to 0. 0 compared with the method of Example 1. The amount of sludge was reduced from 544 to 520 mg / L.

As a method for removing antimony from antimony-containing water, the two-step coagulation precipitation separation method of the present invention comprising a first step using a ferric salt as a flocculant and a second step using a cerium salt is a method of using a small amount of drug. Since antimony can be efficiently processed at a low concentration with a small amount of sludge generation, it is effective for the treatment of wastewater discharged from industries that use antimony and its compounds, and antimony-containing water eluted from soil and groundwater. .

The relationship between the antimony adsorption amount to the precipitated cerium hydroxide (CeO ₂ equivalent amount) and the antimony concentration in the liquid phase is shown using a cerium salt in the second step of the present invention.

A reference example of the antimony treatment system of the present invention is shown.

DESCRIPTION OF SYMBOLS 1 Water to be treated 2 Ferric salt and alkali agent 3 Polymer flocculant 4 Rare earth salt solution and alkali agent 5 Treated water 6 First step agglomerated slurry 7 Second step agglomerated slurry A First reaction tank B High-speed coagulation C Second reaction tank D Pressurized floating tank E Circulating sludge pit F Waste sludge pit G Pressure tank

Claims (4)

A first step in which ferric salt and an alkaline agent are added to water to be treated containing antimony to precipitate and separate insoluble antimony particles and dissolved antimony, followed by a rare earth mainly composed of cerium in the separated liquid A method for treating antimony-containing water, comprising a second step of adding a salt solution and an alkaline agent to separate the remaining dissolved antimony as a difficult-to-hold precipitate. The antimony according to claim 1, wherein the water to be treated having an antimony concentration of antimony-containing water of 2 mg / liter or more is treated in the first step to 2 mg / liter or less, and subsequently treated in the second step to 0.2 mg / liter or less. Treatment method of contained water. The flocculation and precipitation in the first step is performed at pH 6 to 11, and subsequently, as the second step, slaked lime is added to the rare earth salt solution mainly containing cerium to adjust the pH to 9 to 12. The method for treating antimony-containing water as described. The method for treating antimony-containing water according to any one of claims 1 to 3, wherein the precipitate produced in the second step is returned to the first step and the first step is performed.

Images