KR20210078990A - Method for pretreatment of titanium scraps by using ultrasonic cleaning in alkaline solution with low concentration and high temperature drying - Google Patents

Abstract

The present invention relates to a titanium scrap pretreatment method by ultrasonic immersion cleaning and high temperature drying in a low-concentration alkali solution, and more specifically, comprising steps of: (S1) immersing a titanium scrap in an aqueous solution containing sodium pyrophosphate (Na4P2O7, TSPP), and washing the titanium scrap by applying ultrasonic waves to the aqueous solution; and (S2) drying the washed titanium scrap at a temperature of 100 to 400°C.

Description

Method for pretreatment of titanium scrap by ultrasonic immersion cleaning and high temperature drying in low-concentration alkaline solution

The present invention relates to a titanium scrap pretreatment method by ultrasonic immersion cleaning and high-temperature drying in a low-concentration alkali solution, and more particularly, it is eco-friendly by excluding the use of acids or organic solvents, and is economical by using a relatively low-concentration alkali solution. It relates to a pre-treatment method of titanium scrap that can wash titanium scrap by the method and can greatly reduce carbon, oxygen and nitrogen contents through a high-temperature drying step.

In general, domestic titanium metal is entirely dependent on imports except for some recycling of scrap, which can be seen because there is essentially no industrial base for manufacturing sponge titanium from titanium ore.

On the other hand, advanced countries such as the United States and Japan, where a large amount of titanium scrap is generated, have small and large specialized titanium pretreatment companies and manufacture titanium ingots by remelting titanium scrap. However, in the domestic titanium scrap market, the demand/supply of exporting at low prices and importing at high prices is unstable, and the industrial base for recycling technology for titanium scrap is weak.

In the future, demand for general industrial and consumer products as well as aircraft market will continue to grow and global demand will continue to exceed production. However, the titanium recycling market is relatively weak.

Due to such a request, a request for recycling of titanium has been raised in recent years, and a technique for refining and recycling metal scrap or sponge is in the spotlight.

However, conventionally, due to the high melting point and high chemical activity of titanium, high technology and a lot of energy are consumed in the smelting-refining-melting process. There was a problem being

In addition, in the case of high-quality titanium scrap, it is possible to produce ingots through remelting, but titanium scrap with a high content of impurities (oxygen, nitrogen, carbon, etc.) mainly generated during processing of plate and wire rods does not have a separate refining process. It is difficult to obtain high-purity titanium.

On the other hand, in order to remove impurities from titanium scrap having many impurities, conventionally, it was washed using an acid such as nitric acid, hydrochloric acid, or hydrofluoric acid, or was washed using an organic solvent such as alcohol and acetone. There are problems in the environment and safety due to the use of solvents.

In addition, even when washing using an alkali solution, there is an inefficient problem in that a high-concentration alkali solution must be used because the cutting oil attached to the titanium scrap is dissolved and removed.

Accordingly, it is an object of the present invention to provide an eco-friendly pretreatment method of titanium scrap by excluding the use of acids and organic solvents during the pretreatment process for recycling of titanium scrap.

Another object of the present invention is to provide a method for pretreatment of titanium scrap that is cost-effective by using a relatively low-concentration alkali solution and can greatly reduce carbon, oxygen and nitrogen contents through a high-temperature drying step after washing.

The pretreatment method of titanium scrap according to an aspect of the present invention includes (S1) _{immersing the titanium scrap in an aqueous solution containing sodium pyrophosphate (Na 4} P ₂ O ₇ , TSPP), and then applying ultrasonic waves to the aqueous solution to apply ultrasonic waves to the titanium scrap. washing; and (S2) drying the washed titanium scrap at a temperature of 100 to 400 °C.

In this case, in the step (S1), the frequency of the ultrasonic wave may be 25 to 40 kHz.

And, the step (S1) may be made through a stirring device.

In addition, in step (S1), the pH of the aqueous solution may be 9.5 to 10.5.

And, in the step (S1), the concentration of the sodium salt in the aqueous solution may be 10 to 20 g / L.

Meanwhile, the step (S2) may be performed at the temperature for 30 to 90 minutes.

According to the pretreatment method of titanium scrap according to an embodiment of the present invention, it is possible to wash the titanium scrap in an eco-friendly way by excluding the use of an acid or an organic solvent, and when the pretreatment is performed in this way, the impurity content of the titanium scrap is greatly reduced do.

In addition, by increasing cleaning efficiency through ultrasonic cleaning, it is economical to use an alkaline solution with a lower concentration compared to the conventional alkaline solution concentration, and it is possible to shorten the process time through a high-temperature drying step after cleaning, and to reduce impurities such as carbon, oxygen and nitrogen. The content can be greatly reduced.

The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the detailed description of the present invention to be described later, so the present invention is described in such drawings should not be construed as being limited only to
1 is a photograph showing a titanium scrap.
2 is a view schematically showing a contact angle and a roll-up mechanism of impurities attached to titanium scrap.
3 is a graph showing the impurity content in the titanium scrap according to the drying temperature.

Hereinafter, the present invention will be described in more detail.

The pretreatment method of titanium scrap according to an aspect of the present invention includes (S1) _{immersing the titanium scrap in an aqueous solution containing sodium pyrophosphate (Na 4} P ₂ O ₇ , TSPP), and then applying ultrasonic waves to the aqueous solution to apply ultrasonic waves to the titanium scrap. washing; and (S2) drying the washed titanium scrap at a temperature of 100 to 400 °C.

1 is a photograph showing a titanium scrap. Since titanium metal is an expensive metal, titanium scrap generated during processing of titanium metal, or more precisely, titanium turning scrap, must be recycled. At this time, titanium scrap is widely used as a raw material for alloy ingots.

In titanium, turning scrap is generated through machining such as milling. At this time, the content of impurities such as oxygen and nitrogen in the scrap increases due to deterioration, and the content of carbon impurities increases rapidly due to contamination by cutting oil and oils. do. When an alloy ingot is manufactured using such scrap, the content of impurities such as oxygen, nitrogen and carbon also increases in the ingot, which adversely affects the physical properties of the final product.

Conventionally, washing was performed using an acid such as nitric acid, hydrochloric acid, or hydrofluoric acid, or washing using an organic solvent such as alcohol and acetone, but there was a problem in environment and safety due to the use of an acid or an organic solvent. However, in the present invention, _{by using an aqueous solution containing sodium pyrophosphate (Na 4} P ₂ O ₇ , TSPP), it is possible to secure safety and environmentally friendly washing.

Furthermore, in the present invention, by applying ultrasonic waves to the aqueous solution, the washing efficiency is increased, so that it is possible to use an alkali solution with a low concentration compared to the conventional alkali solution concentration, which is economical, and it is possible to shorten the process time through a high temperature drying step after washing, carbon, The content of impurities such as oxygen and nitrogen can be greatly reduced.

In this case, the washing in step (S1) may be performed at room temperature of about 20° C. for about 10 minutes.

Here, in the step (S1), the frequency of the ultrasonic wave may be 25 to 40 kHz. When the frequency of ultrasound is 25 kHz, the size of cavitation (microcavity) generated by ultrasound is about 3.5 μm, and in the case of 40 kHz, the size of cavitation is about 2.8 μm, which is a suitable size for cleaning. However, when the frequency of the ultrasonic wave is less than the numerical range, the size of cavitation increases, and on the contrary, when it exceeds the numerical range, the size of the cavitation becomes small and the efficiency in removing oil is lowered.

And, as the washing method of the step (S1), after simply immersing the titanium scrap in the aqueous solution, ultrasonic wave may be applied to washing, and after immersing the titanium scrap in the aqueous solution, stirring through a stirring device and ultrasonic wave at the same time may be added and washed. At this time, when a stirring device such as a drum washing machine is used to stir, a strong stirring force is applied, so even if the concentration of a substance contained in the aqueous solution is lowered, the effect of reducing impurities may be equal or superior.

And, in the step (S1), the pH of the aqueous solution may be 9.5 to 10.5. When the pH of the aqueous solution satisfies the numerical range, the contact angle formed by the attachment of impurities such as oil to the surface of the titanium scrap increases. As the force required to lift the impurities is reduced, the roll-up mechanism tends to occur.

Figure 2 schematically shows the contact angle and roll-up mechanism of impurities attached to the titanium scrap.

And, in the step (S1), the concentration of the sodium salt in the aqueous solution may be 10 to 20 g / L. The concentration of the sodium salt represents a lower concentration compared to the concentration of an alkali solution that has been used in the prior art, and even when a solution of such a low concentration is used by ultrasonic cleaning, the impurity removal performance is equal or superior.

On the other hand, when the aqueous solution does not contain sodium hydroxide and contains only sodium salts such as TSPP, washing tends to be better. This is considered to be the result of maintaining a relatively constant pH (pH 9.5 to 10.5) without significantly changing the pH of the aqueous solution before and after washing, even though sodium salt such as TSPP acts as a buffer in the solution and undergoes a washing process.

The step (S2) may be performed at the temperature for 30 to 90 minutes.

More specifically, by controlling the temperature increase rate of the dryer to about 10 ° C./min, the holding time may be dried for about 30 to 90 minutes from when the desired temperature among the temperatures of 100 to 400 ° C is reached.

Preferably, it may be dried with a holding time of about 30 minutes at a temperature of about 300 ° C., and up to 300 ° C. at a temperature increase rate of 10 ° C./min. Considering the temperature increase time, in the dryer for a total of about 1 hour. It may be drying.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

1. Carbon content of titanium scrap according to washing solution concentration and washing conditions

simple stirring Reduction rate (%) Stirring + Ultrasonic Treatment Reduction rate (%) scrap raw material 6,820 ppm NaOH 1M 1,001 ppm 85.32 1,132 ppm 83.40 ppm NaOH 1MTSPP 10g/L 686 ppm 89.94 773 ppm 88.67 ppm NaOH 1MTSPP 20g/L 693 ppm 89.84 435 ppm 93.62 ppm NaOH 0.5M 1,170 ppm 82.84 942 ppm 86.19 ppm NaOH 0.5MTSPP 10g/L 881 ppm 87.08 523 ppm 92.33 ppm NaOH 0.5MTSPP 20g/L 553 ppm 91.89 478 ppm 92.99 ppm

The carbon impurity content in Table 1 was measured by the method according to ASTM E1019-11. Referring to Table 1, the carbon content in the titanium scrap raw material was analyzed to be 6,820 ppm, and referring to the results of washing each titanium scrap according to the composition of the washing solution and the washing conditions, the method of ultrasonic treatment rather than washing by simple stirring In general, it can be confirmed that the carbon content is further reduced.

2. Carbon content according to aqueous solution conditions during ultrasonic cleaning within the pH range of 9.5 to 10.5

Carbon content in ultrasonic cleaning (ppm) Reduction rate (%) NaOH 3.2×10 ^-5 M (pH 9.50) 670 90.18 TSPP 10 g/L (pH 9.66) 166 97.57 TSPP 20 g/L (pH 10.00) 225 96.70

Referring to Table 2, it can be seen that the carbon reduction rate is significantly high in the aqueous solution containing only TSPP without sodium hydroxide. This appears to be the result of TSPP dissociating in solution to maintain a relatively constant pH concentration.

Furthermore, when the concentration of TSPP is 10 g/L, it seems to be a significant result in that the carbon reduction rate is larger than that of 20 g/L.

Table 3 below shows the pH before and after washing of the washing aqueous solution, and it can be seen that the aqueous solution containing only TSPP without NaOH has little change in pH before and after washing.

Before washing (pH) Before washing (pH) NaOH 1M 14 14 NaOH 3.2×10 ^-5 M 9.50 7.80 TSPP 10g/L 9.66 9.64 TSPP 20g/L 10.00 9.96

3. Measurement of impurity content in titanium scrap by high temperature drying

holding temperature carbon (C) Reduction rate (%) Oxygen (O) Nitrogen (N) scrap raw material 4,500 ppm - 70 ℃ (vacuum drying, 2 hours) 430 ppm 90.44 2,122 ppm 90 ppm 100 ℃ 613 ppm 86.38 2018 ppm 54 ppm 200 ℃ 145 ppm 96.78 1,970 ppm 60 ppm 300 ℃ 116 ppm 97.42 1,815 ppm 46 ppm 400 ℃ 91 ppm 97.98 2,310 ppm 69 ppm

With respect to the impurity content of Table 4, oxygen and nitrogen were measured by the method according to ASTM E1409-13, and carbon was measured by the method according to ASTM E1019-11.

3 is a graph showing the impurity content in the titanium scrap according to the drying temperature. Referring to FIGS. 3 and 4, the temperature increase rate of the dryer was adjusted to 10° C./min, and the holding time was set to 30 minutes. When the drying temperature was set to 200 °C, the carbon content was sharply decreased compared to the case of 100 °C. Until the drying temperature was 300 °C, the content of impurities also showed a tendency to steadily decrease as the drying temperature increased.

However, it can be inferred that the titanium scrap was oxidized at about 400 °C, as the oxygen content rapidly increased from the drying temperature exceeding 400 °C. And, although there was no significant change in nitrogen content, it showed a slight increase from about 400 °C.

As a result of this experiment, the optimum conditions for high-temperature drying were about 300 °C, and considering the temperature increase time and the holding time, the drying time was about 1 hour in total.

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

Claims (6)

(S1) immersing the titanium scrap in an aqueous solution containing sodium pyrophosphate (Na ₄ P ₂ O ₇ , TSPP), washing the titanium scrap by applying ultrasonic waves to the aqueous solution; and
(S2) A pretreatment method of titanium scrap comprising the step of drying the washed titanium scrap at a temperature of 100 to 400 ℃. According to claim 1,
In the step (S1), the frequency of the ultrasonic wave is a pretreatment method of titanium scrap, characterized in that 25 to 40 kHz. According to claim 1,
The (S1) step is a pretreatment method of titanium scrap, characterized in that made through a stirring device. According to claim 1,
In the step (S1), the pH of the aqueous solution is a pretreatment method of titanium scrap, characterized in that 9.5 to 10.5. According to claim 1,
In the step (S1), the concentration of the sodium salt in the aqueous solution is a pretreatment method of titanium scrap, characterized in that 10 to 20 g / L. According to claim 1,
The step (S2) is a pretreatment method of titanium scrap, characterized in that performed at the temperature for 30 to 90 minutes.

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