JP5988018B2 - Metal recovery method in cement manufacturing process - Google Patents

Description

  The present invention relates to a metal recovery method in a cement manufacturing process.

  In cement production facilities, chlorine is a problem as a cause of blockage of the preheater. For this reason, a chlorine bypass system for extracting chlorine by extracting a part of combustion gas from the kiln exhaust gas passage from the kiln bottom of the cement kiln to the bottom cyclone is used. In this chlorine bypass system, when the extracted combustion gas is cooled, chlorides such as potassium and sodium and solids (chlorine bypass dust) mainly containing cement raw materials are recovered.

In recent years, various wastes have been used as cement raw materials or fuels, but since the waste contains a large amount of salt, the amount of chlorine bypass dust generated increases as the amount of use increases. doing.
Chlorine bypass dust can be reused as a cement raw material by removing chlorine by washing with water. However, the chlorine bypass dust contains metals and inorganic elements having a boiling point relatively close to that of chlorine compounds such as potassium chloride. When water is washed, chlorine is eluted and selenium is also eluted. Since the selenium effluent reference value is as strict as 0.1 mg / L, effluent treatment is required.

Conventionally, selenium-containing wastewater generated by water washing of chlorine bypass dust removes selenium by agglomeration precipitation using a flocculant. However, a large amount of agglomeration agent is required and the cost is increased. There was also a problem that sludge was generated.
For this reason, after adding water to chlorine bypass dust to make a slurry, it is separated into a primary cake and a primary filtrate containing selenium, and a pH adjuster and a ferrous compound are added to the primary filtrate containing selenium. Is added to reduce the selenium concentration, and then separated into a secondary cake and a secondary filtrate containing selenium, and the secondary filtrate containing selenium is passed through an electrodialyzer to remove concentrated salt water and selenium. A treatment method (Patent Document 1) that separates into salt water and circulates the demineralized water containing the selenium as a part of the water added to the dust collected has been studied.

  On the other hand, selenium is a kind of rare metal and is used in a wide range of applications as a semiconductor manufacturing material, a colorant raw material, and the like. In recent years, its demand has increased and its resource value has increased.

JP 2004-330148 A

  Accordingly, an object of the present invention is to provide a method for efficiently recovering a metal such as selenium from chlorine bypass dust generated in a cement manufacturing process.

  As a result of various studies in view of such circumstances, the present inventors have efficiently cleaned metals such as selenium by washing chlorine bypass dust with an aqueous solution of a specific elution aid and treating it with microorganisms and / or enzymes. The present invention was completed by finding that it can be recovered.

That is, the present invention relates to chlorine bypass dust generated in the cement manufacturing process, alkali metal and alkaline earth metal hydroxides, alkali metal and alkaline earth metal oxoacid salts, organic acids and organic acid salts, water-soluble Provided is a method for recovering metal from chlorine bypass dust, comprising an elution step of eluting the metal by washing with an aqueous solution of at least one elution aid selected from the group consisting of carbonate and strong acid It is.
However, one, two or more other arbitrary preparation steps may be included before, after, or between these steps. Examples of the preparation process include, but are not limited to, filtration, dilution, pH adjustment, salt concentration adjustment process, and the like.

  ADVANTAGE OF THE INVENTION According to this invention, metals, such as selenium, can be efficiently collect | recovered from chlorine bypass dust in a cement manufacturing process. Of the recovered metals, in particular, selenium can be reused as a resource for a wide range of applications as a semiconductor manufacturing material, a colorant raw material, and the like. In addition, since selenium in the eluate is recovered, the selenium concentration can be made lower than the drainage standard.

The elution aid used in the present invention is selected from alkali metal and alkaline earth metal hydroxides, alkali metal and alkaline earth metal oxoacid salts, organic acids and organic acid salts, water-soluble carbonates and strong acids. It is.
Examples of the alkali metal and alkaline earth metal hydroxides include sodium hydroxide, potassium hydroxide, calcium hydroxide and the like, and sodium hydroxide is particularly preferable.
Examples of oxo acid salts of alkali metals and alkaline earth metals include phosphates and borates, such as disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, dihydrogen phosphate. Examples thereof include potassium, and dipotassium hydrogen phosphate and potassium dihydrogen phosphate are particularly preferable.
Examples of the organic acid and organic acid salt include hydroxy acids such as citric acid, lactic acid, malic acid, and tartaric acid, acetic acid, propionic acid, and alkali metal salts thereof such as sodium and potassium. Is preferred.
Examples of the water-soluble carbonate include sodium carbonate and potassium carbonate, and sodium carbonate is particularly preferable.
Examples of the strong acid include sulfuric acid, nitric acid, hydrochloric acid and the like, and sulfuric acid is particularly preferable.
These dissolution aids are used as an aqueous solution, and the concentration thereof is preferably 0.1 to 3M, particularly 0.5 to 2M.
Moreover, what was prepared as a buffer solution can also be used suitably for an elution adjuvant.

In the present invention, chlorine bypass dust generated in the cement manufacturing process is washed with the aqueous solution of the dissolution aid as described above.
The aqueous solution used for washing is preferably 1 to 50 times by mass, particularly 2 to 20 times by mass, with respect to the mass of the chlorine bypass dust, because the metal can be efficiently eluted.

The cleaning method is not particularly limited, and for example, chlorine bypass dust may be added to the aqueous solution, and it may be allowed to stand or stir at 4 to 60 ° C. for about 1 to 24 hours.
By washing in this way, the metal in the chlorine bypass dust can be efficiently eluted into the aqueous solution.
Here, the metal is mainly contained in chlorine bypass dust, and includes rare metals such as selenium; heavy metals such as lead and cadmium; light metals such as aluminum.

The eluate containing the metal obtained in the elution step can be further recovered by subjecting it to biological treatment and / or chemical treatment.
Metals obtained by biological treatment using microorganisms, enzymes, proteins, cells, cell tissues, etc., in particular microorganism treatment steps for treatment by contacting with microorganisms and / or enzyme treatment steps for treatment by contacting with enzymes. Is preferably recovered. Selenate-reducing bacteria, particularly aerobic selenate-reducing bacteria are preferably used in the microbial treatment step, and extracted from selenate-reducing bacteria, particularly aerobic selenate-reducing bacteria, in the enzyme treatment step. Selenate reductase is preferably used.
As an aspect of the treatment step, not only an aspect in which microorganisms, enzymes, proteins, cells, cell tissues, etc. are dispersed in the eluate, but also an aspect in which it is supported on a carrier, an aspect in which granules are formed, etc. can be applied. It is not limited to these.
Metals can be recovered even by chemical treatment such as coagulation and precipitation, but biological treatment is superior in that it is excellent in the selectivity of the target metal or can obtain a high concentration of recovered metal. . In addition, by combining chemical treatment and biological treatment, more efficient treatment may be possible.

In the obtained eluate, selenium exists as water-soluble selenic acid (SeO ₄ ²⁻ ) or selenious acid (SeO ₃ ²⁻ ). By treating this eluate with selenate-reducing bacteria, selenate in the eluate can be reduced to a solid elemental state and recovered as a solid. It is also possible to recover selenic acid by reducing it to gaseous methylated selenium.
As the selenate-reducing bacteria, known ones can be used, and examples thereof include Pseudomonas stutzeri NT-I strain (NITE P-685), Enterobacter cloacae SLD1a-1, Bacillus selenatarsenatis SF-1. Among these, the Pseudomonas stutzeri NT-I strain (NITE P-685) is particularly preferable because selenium can be recovered under aerobic conditions.

In order to treat the eluate with selenate-reducing bacteria, a known method may be used. For example, when Pseudomonas stutzeri NT-I strain (NITE P-685), which is an aerobic selenate-reducing bacterium, is used, it can be performed according to the method described in JP 2010-142166 A. More specifically, the NT-I strain may be cultured in an eluate containing selenic acid under aerobic conditions at 28 to 38 ° C. for about 8 hours to 20 days. Is reduced to solid elemental selenium and further to gaseous methylated selenium via selenious acid (water-soluble) and can be recovered as a solid or gas.
The microorganism used for the microorganism treatment may be a genetically modified microorganism having at least one foreign gene encoding an enzyme having a selenate reducing function. Furthermore, for example, even in a biological treatment using selenate reductase possessed by the NT-I strain, selenate in the eluate can be reduced and selenium can be recovered as a solid elemental body or a gaseous selenium compound. .

  EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not restrict | limited to these at all.

Example 1
As elution aids, four types of (1) sodium hydroxide, (2) sodium carbonate, (3) dipotassium hydrogen phosphate, and (4) trisodium citrate dihydrate were used, each with a final concentration of 0. An aqueous solution was prepared to 75M. In addition, the example using only water, without using an elution adjuvant was also performed as a comparison.
100 mL of each aqueous solution was fractionated into a 300 mL Erlenmeyer flask, and 10 g of chlorine bypass dust (salt content 20.6%, selenium content 368 mg / L) was added to each. This was sealed with a butyl rubber stopper and rotated and shaken (120 rpm, 28 ° C.) for about 24 hours. In the example using only water, the treatment was performed at 60 ° C.
Thereafter, the aqueous solution was filtered using a glass filter (GF / B, Whatman) having a pore size of 1.0 μm to obtain each eluate. Table 1 shows the final pH of the eluate, the salt concentration and the selenium concentration of the obtained eluate.
The final pH is measured before filtration using a pH meter F-52 (HORIBA), and the salt concentration of the eluate is appropriately diluted after filtration using a salt concentration meter SK-5S (Sato meter). It was measured. In addition, each eluate obtained was filtered through a microfilter with a pore size of 0.22 μm to remove suspended substances, and then subjected to an ICP emission spectrometer (SPS7800, SII Nano Technology) to determine the total water-soluble selenium concentration. It was measured.

Example 2
In Example 1, the eluate obtained with (3) dipotassium hydrogen phosphate and (4) trisodium citrate dihydrate was diluted 5-fold with pure water, and TSB medium components (Becton-Dickinson) Was added to adjust the pH to 8.0 using hydrochloric acid. These were filtered to remove the formed precipitate, and then 20 mL was dispensed into each 50 mL vial. To this, 1 mL of a culture solution of NT-I strain cultured in TSB medium was added, and the mixture was cultured under aerobic conditions by rotary shaking (120 rpm, 28 ° C.) for 120 hours. After centrifuging the solution, the supernatant was filtered, and the total water-soluble selenium concentration was measured in the same manner as in Example 1. Table 2 shows the results of the total water-soluble selenium concentration before and after the microorganism treatment process.
When the solution is centrifuged and the supernatant is filtered, solid selenium can be recovered. Furthermore, vaporizing selenium (dimethyl diselenide) can be recovered by continuing the culture.

Example 3
The same treatment as in Example 1 was carried out using 50 mL of 1.0 M K ₂ HPO ₄ -KH ₂ PO ₄ buffer solution (pH 6.8 to 7.0) and 20 g of chlorine bypass dust (selenium content 478 ppm) as elution aids. To obtain an eluate. The obtained eluate had a pH of 9.7 and a selenium concentration of 153 mg / L (elution rate 80%).

Example 4
(1) culture method;
To a 5 L jar fermenter (manufactured by Maruhishi Bioengineer, Bioneer-C500N type 5 L (S)), 90 g of TSB medium and 2600 mL of deionized water were added and autoclaved. 400 mL of the eluate obtained in Example 3 was added to the medium.
The culture solution obtained by pre-culturing the NT-I strain in TSB medium for 12 hours was collected by centrifugation, adjusted to OD660 = 1.0, inoculated with 30 mL (1%), and subjected to rotary shaking under aerobic conditions ( 250 rpm, 38 ° C.) and cultured for 120 hours.
Water soluble selenium concentration (selenium in liquid) remaining in the eluate after 120-hour culture, elemental selenium concentration reduced (insoluble) (solid selenium), and volatile methylated selenium concentration (gaseous selenium) were Was measured. The results are shown in Table 3.

(2) Sampling and measurement sample preparation;
The culture solution was collected from the jar fermenter and the microbial turbidity (OD600) was measured. 2 mL of the culture broth was collected and centrifuged at 15,000 rpm for 5 minutes. After centrifugation, a sample obtained by filtering the supernatant was used as a supernatant sample, and a pellet obtained by centrifugation was used as a precipitated sample.

(3) measurement of selenate and selenite concentrations;
100 μL of the supernatant sample was collected and diluted 1/10 times with 900 μL of ultrapure water. The diluted solution was subjected to ion chromatography (Dionex, ICS-1100; detector, CDM-3, DS6 conductivity cell; column, IonPac AS12A; guard column, AG12A; suppressor, ASRS300; eluent, 3.0 mM Na ₂ CO _3. The flow rate was 1.5 mL / min), and the concentrations of selenic acid and selenious acid (selenium in the liquid) were measured.

(4) Measurement of dissolved selenium concentration;
1000 μL of the supernatant sample was added to 8900 μL of ultrapure water to which 100 μL of concentrated nitric acid had been added, and diluted 1/10 times. Using this solution as a measurement sample, the total selenium concentration was measured by ICP-AES (Thermo Fisher iCAP6300 Duo senes).

(5) Measurement of elemental selenium concentration;
2 mL of ultrapure water was added to the precipitated sample, washed with vortex, and then collected by centrifugation. After repeated washing operations, 1500 μL of concentrated nitric acid and 50 μL of concentrated sulfuric acid were added to the precipitated sample, and the precipitate was dissolved by vortexing.
The lysate was centrifuged at 15,000 rpm for 5 minutes to separate the supernatant and the precipitate. The supernatant solution was dispensed into a 10 mL volumetric flask. The precipitate was dissolved again under the same conditions, the supernatant was collected, and fractionated into a volumetric flask from which the supernatant solution was collected. A 10 mL volumetric flask was added with ultrapure water up to the marked line, and a constant volume was used as a measurement sample. The measurement sample was selenium concentration (solid selenium) measured by ICP-AES.

(6) Gas recovery and analysis;
A fermented tube was connected to the exhaust port of the jar fermenter, and bubbling was performed to 150 mL of concentrated nitric acid added to a 250 mL reagent bottle. An air stone was connected to the contact surface with concentrated nitric acid. Concentrated nitric acid was sampled over time, and the selenium concentration (gas selenium) was measured by ICP-AES.

  From the results in Table 3, about 70% of the selenium in the eluate was recovered as gaseous selenium.

Claims (2)

Chlorine bypass dust generated in the cement manufacturing process is treated with alkali metal and alkaline earth metal hydroxides, alkali metal and alkaline earth metal phosphates and borates , organic acids and organic acid salts, and water-soluble carbonates. The selenium eluate obtained by washing with an aqueous solution of at least one elution aid selected from the group consisting of the following and eluting selenium is brought into contact with Pseudomonas stutzeri NT-I strain (NITE P-685). A method for recovering selenium from chlorine bypass dust, characterized in that it is treated . Elution aid, sodium hydroxide, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, selenium method of recovery from the chlorine bypass dust according to claim 1, wherein those selected from sodium citrate and sodium carbonate.