A method for regenerating titanium metal pickling waste liquid

Abstract

The present invention belongs to the technical field of titanium metal processing waste acid treatment, and specifically relates to a method for regenerating titanium metal pickling waste liquid. The regeneration method comprises the following steps: adding a fluorosilicic acid solution to the titanium metal pickling waste liquid and mixing uniformly, then adding a potassium salt solution, stirring the reaction at room temperature, and centrifuging or filtering after the reaction is complete to separate the solid portion as a potassium fluorotitanate / potassium fluorosilicate complex; and the liquid portion as a regenerated titanium metal pickling liquid. The method of the present invention can significantly improve the titanium ion recovery rate without destroying the pickling liquid components. The titanium metal pickling waste liquid can be regenerated and reused, and has the advantages of good treatment effect and simple treatment process.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium metal processing waste acid treatment, and particularly relates to a method for regenerating titanium metal pickling waste liquid. Background Art

[0002] Titanium is a common metal in industries such as industry and aviation. Its high strength and excellent corrosion resistance make it a widely used, high-quality material. However, after heat treatment, titanium often forms a titanium oxide layer on its surface, which not only affects its appearance but also adversely affects subsequent processing and its surface adhesion to other coatings. Therefore, treatment of this layer is essential. Pickling is a common method for removing this titanium oxide layer, typically using a mixed acid solution of HF and HNO3. However, during the pickling process, titanium ions continuously dissolve into the titanium pickling solution. After a certain amount of use, the titanium ion accumulation in the titanium pickling solution increases its viscosity, impairing its ability to corrode and remove the titanium oxide layer. When the titanium ion concentration in the solution reaches 50 g / L, the pickling solution's ability to remove the titanium oxide layer on the titanium metal surface decreases sharply, degrading the surface quality of the titanium metal and causing the solution to reach its solubility limit and become scrapped. Spent pickling solution contains large amounts of acid and titanium ions. How to effectively utilize the active ingredients in it so that it is beneficial to environmental protection and the effective utilization of waste liquid has become an important issue that needs to be solved.

[0003] The main method for treating waste pickling liquid at present is resin bed adsorption. The anion resin bed absorbs fluoride ions (F - ) and nitrate ions (NO3 - ), as the use time increases, the cationic groups on the resin are gradually occupied by anions, resulting in a decrease in the exchange capacity of the resin. At this time, it is necessary to restore its activity through a regeneration process. The regeneration process usually uses sodium hydroxide solution to - and NO3 - The ions are replaced and the anion exchange capacity of the resin is restored. When the regeneration liquid (such as sodium hydroxide) is injected into the resin bed, these adsorbed anions react with OH - The ions are exchanged and released, then react with sulfuric acid to produce hydrofluoric acid (HF) and nitric acid (HNO3), which are then recycled. However, the solution that passes through the resin bed only removes anions, leaving most of the Ti ions unrecoverable. This portion of the solution is typically collected and processed by a waste liquid treatment company, which is costly and untimely.

[0004] There are reports on separating and recovering Ti ions in the form of potassium fluorotitanate precipitate by adding potassium salts. For example, CN104745822 A uses the ability of potassium ions to combine with fluorotitanate ions in the solution to generate potassium fluorotitanate, which is then filtered after refrigeration at 0°C to obtain potassium fluorotitanate. However, the removal rate of titanium ions precipitated with potassium fluorotitanate alone can only reach about 90%, and it needs to be treated at a low temperature of 0°C, which consumes a lot of energy and has a complicated treatment process. CN 102786081 A discloses the reaction of fluorotitanic acid in titanium alloy chemical milling waste liquid with potassium ions to generate potassium fluorotitanate, and the addition of anhydrous ethanol to accelerate the precipitation of potassium fluorotitanate. However, the addition of anhydrous ethanol will destroy the components of the pickling solution, resulting in the inability to regenerate the milling waste liquid for titanium alloy chemical milling treatment.

[0005] Therefore, providing a treatment method that can significantly improve the titanium ion removal rate under normal temperature conditions and enable the pickling waste liquid to be regenerated and used has good industrial application prospects. Summary of the Invention

[0006] In view of the shortcomings and deficiencies of the above prior art, the object of the present invention is to provide a method for regenerating titanium metal pickling waste liquid.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for regenerating titanium metal pickling waste liquid comprises the following steps:

[0009] Add the fluorosilicic acid solution to the titanium metal pickling waste liquid and mix evenly, then add the potassium salt solution, stir and react at room temperature, and after the reaction is completed, centrifuge or filter to separate. The solid part is the potassium fluorotitanate / potassium fluorosilicate complex; the liquid part is the regenerated titanium metal pickling liquid.

[0010] Preferably, the hydrosilicic acid solution is a hydrosilicic acid aqueous solution with a mass concentration of 25% to 40%.

[0011] Preferably, the titanium metal pickling waste liquid is a hydrofluoric acid-nitric acid type titanium metal pickling waste liquid with a titanium ion concentration of 30 to 50 g / L.

[0012] Preferably, the potassium salt solution is a saturated aqueous solution of potassium fluoride or potassium nitrate.

[0013] Preferably, the molar ratio of fluorosilicic acid to potassium salt is 0.5 to 5:100.

[0014] Preferably, the molar ratio of the amount of potassium salt added to the titanium ions contained in the titanium metal pickling waste liquid is 2 to 2.1:1.

[0015] Preferably, the stirring reaction time is 1 to 5 minutes.

[0016] Preferably, the potassium fluorotitanate / potassium fluorosilicate complex is further purified by the method described in (a) or (b) below:

[0017] (a) washing and neutralizing a potassium fluorotitanate / potassium fluorosilicate complex with a solvent, adding the resulting solution to water, heating the solution to 50-100° C. to dissolve the potassium fluorotitanate, filtering the solution while hot to remove insoluble impurities, cooling the filtrate to below 10° C. to recrystallize the solution, and drying the solution to obtain purified potassium fluorotitanate;

[0018] (b) adding the potassium fluorotitanate / potassium fluorosilicate complex to a hydrochloric acid solution having a temperature of 0 to 20° C. and a concentration of 0.5 to 5 mol / L, stirring the solution to dissolve the potassium fluorosilicate, filtering the solid phase, washing, and drying the solid phase to obtain purified potassium fluorotitanate.

[0019] Preferably, the drying temperature in step (a) or (b) is 50-70°C.

[0020] Preferably, the solvent in step (a) is cold water, methanol, ethanol, acetone, etc.; and the neutralization refers to adjusting the pH to 4-6 using NaOH.

[0021] The purification method described in (a) above mainly utilizes the difference in solubility and stability between potassium fluorotitanate and potassium fluorosilicate in hot water, so that potassium fluorosilicate is removed in the form of an insoluble precipitate, thereby achieving the effect of purifying potassium fluorotitanate.

[0022] The purification method described in (b) above mainly utilizes the difference in properties that potassium fluorosilicate is soluble in cold hydrochloric acid while potassium fluorotitanate is slightly soluble, so that potassium fluorosilicate is removed in liquid phase to achieve the effect of purifying potassium fluorotitanate.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention adds potassium salt to the discarded pickling solution to precipitate titanium ions in the solution. The waste pickling solution is then reactivated and recycled. After the titanium oxide layer on the surface of the titanium metal is removed, the surface condition meets the performance requirements of subsequent processing. The precipitate is purified to form relatively pure K2TiF6 crystals, which can be used industrially to produce titanic acid and titanium metal. Both the filtrate and the filter residue can be well utilized, achieving the goal of recycling and green.

[0025] (2) The method of the present invention can further improve the recovery rate of titanium ions by pre-adding a small amount of fluorosilicic acid solution to the titanium metal pickling waste liquid through the co-precipitation reaction of potassium fluorotitanate and potassium fluorosilicate. The method does not destroy the components of the pickling liquid, and the titanium metal pickling waste liquid can be regenerated and reused. At the same time, the resulting composite precipitate can be purified by simple heating, filtration or pickling to obtain pure K2TiF6 crystals. It has the advantages of good treatment effect and simple treatment process. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0027] Example 1

[0028] (1) Add 900g of potassium fluoride to 1L of deionized water according to the ratio and stir thoroughly to form a saturated potassium fluoride solution for later use.

[0029] (2) 25 g of 30% fluorosilicic acid solution was added to 1 L of titanium metal pickling waste liquid (mixed acid pickling waste liquid of HF and HNO3 with a titanium ion mass concentration of 41.2 g / L) and mixed evenly, and then 216 g of the saturated potassium fluoride solution of step (1) was added and stirred at room temperature for 3 min to allow it to react fully.

[0030] (3) After the reaction, a precipitate appears in the solution. The above suspension is separated by centrifugation to obtain a precipitate and a supernatant. The precipitate is a potassium fluorotitanate / potassium fluorosilicate complex. The obtained supernatant can be reused as a titanium metal pickling solution.

[0031] (4) The titanium metal pickling waste liquid before and after treatment was tested by inductively coupled plasma technology (ICP), and the removal rate of titanium ions in the waste liquid was found to be 97.8%.

[0032] (5) The potassium fluorotitanate / potassium fluorosilicate complex was added to a 1 mol / L hydrochloric acid solution at 4°C and stirred for 15 minutes to dissolve the potassium fluorosilicate. The solid phase was filtered, washed, and dried at 60°C to obtain purified potassium fluorotitanate (K2TiF6). The purified K2TiF6 was tested to have a purity of 99.5% and a yield of 91%.

[0033] Example 2

[0034] (1) Add 400 g of potassium nitrate to 1 L of deionized water according to the ratio and stir thoroughly to form a saturated potassium nitrate solution for later use.

[0035] (2) 5 g of 30% fluorosilicic acid solution was added to 1 L of titanium metal pickling waste liquid (mixed acid pickling waste liquid of HF and HNO3 with a titanium ion mass concentration of 41.2 g / L) and mixed evenly, and then 623 g of the saturated potassium nitrate solution of step (1) was added and stirred at room temperature for 5 minutes to allow it to react fully.

[0036] (3) After the reaction, a precipitate appears in the solution. The above suspension is separated by centrifugation to obtain a precipitate and a supernatant. The precipitate is a potassium fluorotitanate / potassium fluorosilicate complex. The obtained supernatant can be reused as a titanium metal pickling solution.

[0037] (4) The titanium metal pickling waste liquid before and after treatment was tested by inductively coupled plasma technology (ICP), and the titanium ion removal rate in the waste liquid was found to be 95.1%.

[0038] (5) The potassium fluorotitanate / potassium fluorosilicate complex was washed with cold water, neutralized with a small amount of NaOH until the pH was adjusted to 4, washed with cold water several times, and then added to 60°C hot water to dissolve the potassium fluorotitanate. The insoluble impurities were removed by hot filtration, and the filtrate was cooled to 4°C for recrystallization and dried at 60°C to obtain purified potassium fluorotitanate (K2TiF6). The purity of the purified K2TiF6 was 99.3%, and the recrystallization yield was 87%.

[0039] Example 3

[0040] (1) Add 900g of potassium fluoride to 1L of deionized water according to the ratio and stir thoroughly to form a saturated potassium fluoride solution for later use.

[0041] (2) 40 g of 30% fluorosilicic acid solution was added to 1 L of titanium metal pickling waste liquid (mixed acid pickling waste liquid of HF and HNO3 with a titanium ion mass concentration of 41.2 g / L) and mixed evenly, and then 216 g of the saturated potassium fluoride solution of step (1) was added and stirred at room temperature for 1 min to allow it to react fully.

[0042] (3) After the reaction, a precipitate appears in the solution. The above suspension is separated by centrifugation to obtain a precipitate and a supernatant. The precipitate is a potassium fluorotitanate / potassium fluorosilicate complex. The obtained supernatant can be reused as a titanium metal pickling solution.

[0043] (4) The titanium metal pickling waste liquid before and after treatment was tested by inductively coupled plasma technology (ICP), and the removal rate of titanium ions in the waste liquid was found to be 98.9%.

[0044] (5) The potassium fluorotitanate / potassium fluorosilicate complex was added to a 2 mol / L hydrochloric acid solution at 10°C and stirred for 15 minutes to dissolve the potassium fluorosilicate. The solid phase was filtered, washed, and dried at 60°C to obtain purified potassium fluorotitanate. The purified K2TiF6 was tested to have a purity of 99.0% and a yield of 93%.

[0045] Comparative Example 1

[0046] The comparative example is a method for regenerating titanium metal pickling waste liquid. Compared with Example 1, the hydrofluorosilicic acid solution is not added in step (2), and the rest is the same.

[0047] The titanium ion removal rate in this comparative example was tested to be 84.9%.

[0048] It can be seen from the results of this comparative example and the examples that the present invention can significantly improve the removal rate of titanium ions in the waste liquid by pre-adding a small amount of fluorosilicic acid to the titanium metal pickling waste liquid.

[0049] The above embodiments are preferred implementations of the present invention, but the implementations of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for regenerating titanium metal pickling wastewater, characterized in that: The steps include: Adding fluorosilicic acid solution to titanium metal pickling waste liquid and mixing evenly, then adding potassium salt solution, stirring and reacting at room temperature, centrifuging or filtering after the reaction is completed, the solid part is potassium fluorotitanate / potassium fluorosilicate complex; the liquid part is regenerated titanium metal pickling liquid; The molar ratio of the fluorosilicic acid to the potassium salt is 0.5-5:100; the molar ratio of the added amount of the potassium salt to the titanium ions contained in the titanium metal pickling waste liquid is 2-2.1:

1.

2. The method for regenerating titanium metal pickling wastewater according to claim 1, characterized in that: The hydrosilicic acid solution is a hydrosilicic acid aqueous solution with a mass concentration of 25% to 40%.

3. The method for regenerating titanium metal pickling waste liquid according to claim 2, characterized in that: The titanium metal pickling waste liquid is a hydrofluoric acid-nitric acid type titanium metal pickling waste liquid with a titanium ion concentration of 30-50 g / L.

4. The method for regenerating titanium metal pickling waste liquid according to claim 3, characterized in that: The potassium salt solution is a saturated aqueous solution of potassium fluoride or potassium nitrate.

5. The method for regenerating titanium metal pickling waste liquid according to claim 1, characterized in that: The stirring reaction time is 1 to 5 minutes.

6. The method for regenerating titanium metal pickling wastewater according to claim 1, characterized in that: The potassium fluorotitanate / potassium fluorosilicate complex is further purified by the following method: The potassium fluorotitanate / potassium fluorosilicate complex is added to a hydrochloric acid solution with a temperature of 0-20°C and a concentration of 0.5-5 mol / L, and stirred to react to dissolve the potassium fluorosilicate. The solid phase is filtered, washed, and dried to obtain purified potassium fluorotitanate.

7. The method for regenerating titanium metal pickling wastewater according to claim 6, characterized in that: The drying temperature is 50-70°C.