JPS63297348A - Recovery apparatus for edta - Google Patents

Abstract

PURPOSE:To provide an apparatus for the continuous recovery of ethylenediaminetetraacetic acid (EDTA) as high-purity crystal in high efficiency, by filling free acid of EDTA in a crystallization tank as seed crystal and forming a specific discharging port at the outer circumference of a stock liquid nozzle attached to the bottom of the crystallization tank. CONSTITUTION:Free acid (H4Y) of EDTA is filled in a crystallization tank 5 as a seed crystal. An EDTA-containing liquid and a circulation liquid having a pH of <=3 are introduced into the tank from its bottom and the crystal is fluidized by ascending flow of the liquids to effect the growth of H4Y crystal 6 to a prescribed particle diameter. The grown crystal 6 is extracted from the tank bottom provided with one or more discharging ports 4 of the circulation liquid (circulation liquid nozzle) around the outer circumference of a stock liquid nozzle 2 attached to the bottom of the crystallization tank. An ascending flow of the circulation liquid is formed parallel to the direction of the stock liquid flowing out through the stock liquid nozzle and the direction of crystal flow. The local increase in the supersaturation at the bottom of the crystallization tank and the turbulence of the flow of supersaturated solution are prevented and the amount of residual nuclei can be decreased by the use of the present EDTA-recovery apparatus. The EDTA-recovery apparatus improves the efficiency of the following washing and dehydration processes and simplifies the operation of the processes.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an apparatus for recovering EDTA, which is a valuable substance, from a solution containing EDTA, such as chemical plating waste liquid, and particularly relates to an apparatus for recovering EDTA, which is a valuable substance, from a solution containing EDTA, such as a chemical plating waste liquid. This invention relates to a classified layer type crystallizer in which a stock solution and a circulating liquid are introduced from the bottom of a crystallization tank.

(Prior art) Conventionally, in order to recover EDTA from an EDTA-containing liquid, H
! Adjust the pH using S O,a and
The sodium salt of EDTA, present as Y-NaiHY, NagHzY or NaH3Y, is insoluble H4Y.
After crystallization, solid-liquid separation was performed and collected. The crystallization method at this time is to use a stirrer attached to the crystallization tank.
It is configured to precipitate H4Y by adding pn to pH 1 to 2, where the HAY concentration is minimum, while stirring and mixing the EDTA stock solution and the added H, SO, and so on.

(Problems to be Solved by the Invention) However, in such a conventional method, the precipitated crystal grain size is as small as 0.05 to 0.2 am, and the crystal shape is dendritic, so that the subsequent solidification is difficult. Liquid separation becomes difficult and settling tanks become larger. In order to prevent crystal leakage and improve the cleaning effect during the cleaning and dehydration steps required to reuse crystals, expensive acid-resistant high-speed Centrifuges, etc. had to be used.

It is also known that crystal grain size can be increased and crystal shape improved by using a classified layer type crystallizer in which the stock solution and circulating liquid are introduced from the bottom of a crystallization tank filled with EDTA seed crystals. There is.

However, methods such as installing two stock solution nozzles and circulating fluid nozzles side by side at the bottom of the crystallization tank, or methods in which the stock solution and circulating fluid are mixed in advance to create a supersaturated state and then introduced into the tank bottom do not allow local Excess nuclei are often generated due to an increase in supersaturation degree and turbulence in the flow of supersaturated solution. in this way,
Conventional method: In a crystallization tank, many fine crystals are generated at the bottom of the tank where the stock solution and circulating liquid mix and form an upward flow.As these crystals accumulate in the circulating liquid, the rate of generation of fine crystals slows down. This accelerates the rate of growth, making it difficult to grow the grain size.

In addition, due to the problem of scaling on the tip of each nozzle or the wall of the tank, it was often necessary to interrupt continuous operation to remove the scale, making it difficult to maintain good operating performance.

Therefore, the present invention solves the drawbacks of the prior art, and in a classified layer crystallizer, H4Y can be stably, continuously and efficiently produced from an EDTA-containing liquid into crystals with larger particle size and near spherical shape. It can be crystallized with high purity as a H
The object of the present invention is to provide an EDTA recovery device that can economically recover 4Y crystals.

(Means and effects for solving the problem) The present invention allows a part of the processing solution (Va reflux solution) and the stock solution to flow in from the bottom of the crystallization tank to form an upward flow to form HdY seed crystals. The above-mentioned problem is solved by allowing the circulating liquid to flow in parallel to the flow direction of the raw solution and the crystals so as to surround the outer periphery of the raw solution flow flowing out from the raw solution nozzle during fluidization.

That is, in the present invention, a crystallization tank is filled with EDTA free acid (HdY) as a seed crystal, an EDTA-containing stock solution and a circulating liquid with a pH of 3 or less are introduced from the bottom, and the crystals are fluidized by an upward flow. An EDTA apparatus for extracting and recovering H4Y crystals grown to a predetermined particle size from the bottom, characterized in that one or more circulating liquid discharge ports are provided around the outer periphery of a stock solution nozzle at the bottom of a crystallization tank. Relating to a recovery device.

According to the present invention, by providing one or more circulating liquid discharge ports around the outer periphery of the concentrate nozzle, the flow direction of the concentrate flow flowing out from the concentrate nozzle and the flow direction of the crystals are parallel to the flow direction of the circulating liquid flow. A countercurrent is formed. This prevents a local increase in the degree of supersaturation at the bottom of the crystallization tank and turbulence of the supersaturated solution flow, thereby reducing the generation of excess nuclei.

Furthermore, in order to further reduce the generation of surplus nuclei, the flow rate of the circulating liquid should be 0.2 to 2
Preferably, it is 0.

(Example) Next, the present invention will be described in detail based on an example shown in the drawings, but the present invention is not limited thereto.

FIG. 1 is a system diagram showing one embodiment of the recovery device of the present invention, and FIG. 2 is an enlarged perspective view of the inflow portion of the stock solution and circulating fluid of the device of FIG. 1. In this device, when recovering EDTA from an EDTA-containing solution, the stock solution is supplied to the stock solution supply pipe 1.
The raw solution flows into the crystallization tank 5 through the nozzle 2. The circulating liquid is discharged from the circulating liquid supply pipe 3 to the crystallization tank 5 by a circulating liquid nozzle 4 attached so as to surround the outer periphery of the stock liquid nozzle 2. If the circulation nozzle 4 continuously surrounds the stock solution nozzle 2 as shown in FIG.
An upward flow is formed in which the circulating liquid stream surrounds the raw liquid stream flowing out from the undiluted liquid stream, and larger H4Y crystals than before are formed. The pH of the mixed solution at the top of the crystallization tank 5 is measured by the pH meter 7, and when pl+ rises, acid is supplied from the acid supply pipe 9, and the pH of the mixed solution is measured at pH 3 [measured by the pH meter 7 installed in the regulated tank 10]. When pl+ reaches 3 or less, preferably 1-2, valve 8 is closed. The circulating liquid whose pH has been adjusted in this way is supplied by the circulation pump 11 to the crystallization tank 5 from the i stock solution supply pipe 3 via the flow meter 12. At this time,
It is preferable to set the flow rate of the circulating liquid to 0.2 to 20 with respect to the flow rate of the stock solution when it is discharged from the nozzle.

The formed H4Y growth crystal is transferred to the growth crystal extraction pipe 1.
3 and the treated water flows out from the treated water pipe 14.

FIGS. 3 and 4 are perspective views showing the arrangement of stock solution nozzles and circulating fluid nozzles in another embodiment of the present invention. In FIGS. 3 and 4, the outer periphery of the stock solution nozzle 2 is surrounded by a plurality of circulating fluid nozzles 4. In FIG. In the case of the arrangement shown in FIG. 3 as well, an upward flow is formed in which the circulating liquid flow surrounds the concentrate flow flowing out from the concentrate nozzle 2.

In the arrangement shown in FIG. 4, two circulating liquid streams sandwiching the stock liquid stream form an upward flow in mutually parallel flow directions.

Example 1 An ED was applied to a conical classified layer type crystallization tank of the apparatus shown in FIG. 1, which had a stock solution nozzle and a circulating fluid nozzle as shown in FIG.
TA concentration (H4Y conversion) = 21000 mg/l stock solution was flowed in from the stock solution nozzle, and the circulating fluid was flowed in so that the flow rate ratio to the flow rate of the stock solution was 0.5 to 20. Over time, the average grain size of the H4Y crystals, the occurrence of fine crystals, and the occurrence of scale were evaluated.

For comparison, processing was carried out using a conventional type device in which two stock solution nozzles and two circulating fluid nozzles were installed side by side, and the same evaluation as above was performed.

The results of the evaluation are shown in Table 1 below.

(Margins below) Table 1 Note * = Scale generation on the stock solution nozzle ** = Scale generation on the tank wall From the above experimental results, according to the present invention, the average particle size is 1.1
H4Y crystals of dragon size or higher were stably obtained for a long time, and the shape of the crystals at this time was close to spherical, easy to wash and dehydrate, hard and pure, and of sufficient quality to be recyclable.

(Effect of the invention) By using the apparatus of the present invention, H4Y can be continuously and efficiently produced.
The particle size of the crystals can be increased, EDTA can be recovered as nearly spherical, highly pure crystals, and the subsequent washing and dehydration steps can be made more efficient and simpler. Furthermore, according to the apparatus of the present invention, the generation of surplus nuclei is extremely small, the recovery rate of EDTA can be improved, and troubles due to scaling can be prevented, so equipment costs and recovery costs can be significantly reduced, and maintenance costs can be reduced. can also be easily done.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an embodiment of the EDTA recovery device according to the present invention, Fig. 2 is an enlarged perspective view of the stock solution nozzle and circulating liquid nozzle in Fig. 1, and Figs. 3 and 4 are the present invention. FIG. 3 is an enlarged perspective view of a stock solution nozzle and a circulating fluid nozzle in another embodiment of an EDTA recovery device according to the present invention. Explanation of symbols

Claims (2)

[Claims] (1) The free acid (hereinafter referred to as H_4Y) of ethylenediaminetetraacetic acid (hereinafter referred to as EDTA) is filled into a crystallization tank as a seed crystal, and the EDTA-containing liquid and the circulating liquid with a pH of 3 or less are introduced from the bottom and the upper In a device that extracts and collects H_4Y crystals grown to a predetermined particle size by fluidizing the crystals in a countercurrent from the bottom, there is one or more circulating liquid discharges around the outer periphery of the stock solution nozzle at the bottom of the crystallization tank. An EDTA recovery device characterized by having an outlet. (2) A flow meter is attached to the circulating fluid supply piping, and the flow rate ratio of the circulating fluid to the flow rate of the stock solution discharged from the nozzle is 0.2 to
20. The collection device according to claim 1, which is set to 20.