JPS62292748A - Recovering apparatus for edta from solution thereof - Google Patents

Abstract

PURPOSE:To continuously, efficiently and stably obtain EDTA crystals having a large crystal grain diameter and crystal shape close to sphere, by providing a sensor for an interface of suspended crystals in the upper part of a crystallization tank and connectedly driving the detector with a crystal taking out valve at the bottom of the tank. CONSTITUTION:Free acid (H4Y) of ethylenediaminetetraacetic acid (EDTA) as a seed crystal is filled in a crystallization tank 2 and an EDTA solution 1 and a circulating solution 10 at <=3pH are fed from the bottom into the tank 2. The crystals 3 are fluidized in upward streams to grow the grain diameter and the interface of suspended crystals slowly rising with the growth is detected with a sensor 12 provided in the upper part of the crystallization tank 2. When the interface is raised to a given position, a taking out valve 14 for the grown crystals is connectedly operated to take out and recover H4Y crystals having >=1.1mm average grain diameter. An ultrasonic sensor, photosensor, etc., preferably >=370nm light wavelength, etc., is used as the sensor for the interface.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention The present invention relates to a chemical plating waste liquid, etc., which is comprised of a classified layer type crystallizer in which the stock solution and the circulating liquid are introduced from the bottom of the crystallization tank. , E which is a valuable product from a solution containing ethylenediaminetetraacetic acid
The present invention relates to a device for recovering DTA.

Traditionally, to recover EDTA from an EDTA solution, H2
pH was adjusted using SO4 and Na4Y.

Na,, HY, Na2HZ Y or NaH:lY
The sodium salt of EDTA, present as an insoluble H4
After crystallizing as Y, solid-liquid separation was performed and collected.

The crystallization method at that time is to attach a stirrer to the crystallization tank and use ED
It consists of precipitating H4Y by lowering p)I to pH 1 to 2, where the H4Y concentration is minimum, while stirring and mixing the TA solution and the added H2S Oa.

However, in such conventional methods, the precipitated crystal grain size is small at 0.05 to 0.21, and the crystal shape is dendrite, making it difficult to perform solid-liquid separation in the subsequent stage, and the precipitation tank As the size of crystals increases, expensive acid-resistant high-speed centrifuges must be used to prevent crystal leakage and improve the cleaning effect during the cleaning and dehydration processes necessary to reuse crystals. I had to.

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

However, even if such a classified bed type crystallizer is used, as the crystals in the crystallization layer grow, the interface at the top of the fluidized bed rises, resulting in the formation of fine crystals. It becomes easy to be carried over into the circulating fluid, and when this is accumulated in the circulating fluid, the rate of generation of fine crystals becomes even faster, and the grain size does not grow sufficiently.

In addition, the amount of grown crystals to be extracted is normally controlled by extracting the amount of grown crystals from the bottom of the crystallization tank that corresponds to the amount of inflow of stock solution, but with this method, the balance between the input and output amounts of EDTA is Since it is impossible to precisely control
The interface at the top of the crystallization tank varied widely (carryover into the circulating fluid was likely to occur).Furthermore, the particle size of the extracted crystals varied widely, and the crystals adhered to each other. Aggregated crystals, which are difficult to wash and dehydrate, tend to form.

Therefore, the present invention eliminates the drawbacks of the prior art, stably, continuously and efficiently converts Ha Y from an EDTA solution using a classified layer crystallizer, and produces crystals with larger crystal grain size and crystal shape. By crystallizing with high purity as a nearly spherical shape and automatically controlling the extraction of the growing crystals, the equipment for the subsequent solid-liquid separation, washing, and dehydration processes can be simplified, and H and Y crystals can be obtained with a high recovery rate. The object of the present invention is to provide an EDTA recovery device that can be economically recovered.

The present invention solves the above problems by providing a detector for the interface of floating crystals at the top of the crystallization tank and interlocking this with a crystal extraction valve at the bottom of the tank. This is what I did.

That is, in the present invention, a crystallization tank is filled with crystals of H4Y, which is a free acid of EDTA, as a seed crystal, and the EDTA solution and pH
In this device, H4Y crystals that have grown to a predetermined particle size are extracted from the bottom and collected by flowing a circulating liquid of 3 or less from the bottom and fluidizing the crystals with an upward flow. The present invention relates to an apparatus for recovering EDTA from an EDTA solution, characterized in that a detector for detecting the interface of floating fine crystals is installed, and a growing crystal extractor is installed at the bottom of a crystallization tank in conjunction with the detector.

The interface of fine crystals floating above the crystallization layer is clear enough to be visible, and gradually rises as the crystals within the crystallization layer grow, so in the present invention, it is possible to determine the presence or absence of fine crystals. A detector detects when the interface has risen to a predetermined position, and a motor-operated valve at the bottom extracts a certain amount of the growing crystal, lowering the crystal interface to a predetermined position.

In order to increase the crystal grain size of H4Y, it is necessary to suppress the generation of excess nuclei as much as possible. Therefore, in the present invention, the generation of supersaturation is suppressed at the bottom of the crystallization tank where the seed crystals are fluidized.
The stock solution and circulating fluid were mixed at an arbitrary ratio.

However, in order to further increase the crystal grain size, it is necessary to suppress the carryover of fine crystals into the circulating fluid as much as possible, and to suppress the generation of excess nuclei. Furthermore, in order to prevent the generation of agglomerated crystals and to stably obtain coarse and uniform crystals, it is important to control the timing of extraction. However, the commonly used method of determining when to extract growing crystals based on the amount of input and output of EDTA cannot automatically measure the EDTA concentration of the stock solution, circulating fluid, and processing solution online, and is therefore sensitive to fluctuations in the concentration of the stock solution. It was difficult to maintain good operating conditions.

Therefore, in the present invention, a detector for floating crystals is provided at the top of the crystallization tank, and by detecting the rise of the interface, the timing of extraction is determined, and the electric valve at the bottom is operated, thereby causing the EDTA This makes it possible to perform stable continuous operation with well-balanced input and output amounts, and further increases the crystal grain size.

The amount of extracted growing crystals may be controlled by opening an electric valve for a certain period of time, or by detecting the lower limit of the interface that is lowered by extraction using another detector.

In the present invention, as a detector for floating crystals, an optical sensor such as a turbidity meter, an MLSS meter, a beam sensor, etc., or an ultrasonic sensor, such as an ultrasonic MLSS meter, etc. can be used. In the case of an optical sensor, the wavelength of light is preferably 370 nm or more.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

FIG. 1 is a flow sheet showing an embodiment of the recovery device of the present invention.

As shown in FIG. 1, in the recovery apparatus of the present invention, a crystallization tank 2 to which a stock solution supply pipe 1 and a circulating fluid supply pipe 10 are attached is filled with H,Y crystals 3. The pH of the liquid at the top of the crystallization tank is measured by pH meter 7, and the pH is 0.
．． Acid is added from the pipe 5 by opening and closing the valve 4 so that the concentration is 5 to 2.5. The overflow from the crystallization tank 2 is passed through the pH adjustment tank 6 to the flow meter 9 by the circulation pump 8, and the flow rate is adjusted to be circulated to the bottom of the crystallization tank 2 as a circulating liquid.

A floating crystal detector 12 is installed at the top of the crystallization tank 2 in order to detect the rise of the upper crystal interface that occurs as the crystals in the crystallization tank 2 grow. The detection result by the detector 12 is sent to the growing crystal extraction pipe 15 by the amplifier 13.
The crystals are transmitted to the valve 14 provided in the valve 14, which is opened and closed, and coarse crystals are extracted from the valve 14 in accordance with the rise of the interface.

Note that the detector 12 may be installed outside the crystallization tank 2 or may be configured to detect at any position within the tank using an optical fiber or the like.

The processing liquid flows out from the pipe 11.

Example 1 In the apparatus shown in FIG. 1, EDTA concentration (H4Y) = 26000 mg/I was placed in the conical crystallization tank 2 with a height of 3 m.
! The stock solution was introduced from the stock solution supply pipe 1 and was continuously treated for a long period of time. Over time, the average particle size of the H4Y crystals, the presence or absence of agglomerated crystals, and stability were evaluated.

For comparison, the same evaluation as above was performed by using a device without the detector 12 and implementing a conventional technique in which growing crystals are extracted in accordance with the amount of inflow of the stock solution.

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

(The following is a margin) Table 1 From the above experimental results, according to the present invention, H, Y crystals with an average grain size of 1.1** or more can be stably obtained for a long time, and the crystals at this time can be stably obtained. The shape was close to spherical, it was easy to wash and dehydrate, and the purity was high, making it sufficiently recyclable.

Although a conical crystallization tank was used in the examples, good results can also be obtained using a cylindrical or multistage cylindrical crystallization tank.

The present invention focuses on the fact that the interface of fine crystals floating in the upper part of the crystallization tank is clear enough to be visible, and that the rise of this interface correlates with the degree of growth of the crystals in the lower part of the crystallization tank. Since the structure is configured to detect the interface and extract the coarse crystals at the bottom, fine crystals are not carried over into the circulating fluid, crystal refinement does not occur, and coarse H and Y crystals can be efficiently extracted. Therefore, the recovery efficiency of EDTA is improved.

By using the apparatus of the present invention, the Ha Y crystal grain size can be coarsened stably, continuously and efficiently for a long time, and the crystal shape is close to spherical and has high purity, so it can be used in the subsequent washing and dehydration steps. It becomes possible to convert devices into cylinder elements.

Furthermore, when the apparatus of the present invention is used, the generation of micronuclei is small, so the leakage of crystals is also extremely small, and the recovery rate can be improved, so that not only the equipment cost but also the recovery cost can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing one embodiment of an EDTA recovery device according to the present invention.

Claims (3)

[Claims] (1) Fill a crystallization tank with free acid (H_4Y) of ethylenediaminetetraacetic acid (hereinafter referred to as EDTA) as a seed crystal,
In a device that flows an EDTA solution and a circulating liquid with a pH of 3 or less from the bottom and fluidizes the crystals with an upward flow, the H_4Y crystals that have grown to a predetermined particle size are extracted from the bottom and collected. An apparatus for recovering EDTA from an EDTA solution, characterized in that a detector for detecting the interface of fine crystals floating in a liquid is installed, and a growing crystal extraction device that works in conjunction with the detector is installed at the bottom of a crystallization tank. . (2) The EDTA recovery device according to claim 1, wherein the detector for detecting the interface of the microcrystals is an optical sensor. (3) The EDTA recovery device according to claim 1, wherein the detector for detecting the interface of the microcrystals is an ultrasonic sensor.