A method for preparing ferric chloride for precision etching

Abstract

The application belongs to the technical field of ferric chloride production, and particularly relates to a method for preparing ferric chloride for precision etching. The method for preparing ferric chloride for precision etching comprises the following steps: S1. etching waste liquid / ferriferrous chloride solution is heated to 60-90 DEG C, 1%-10% of reduced iron powder by weight of the solution is added, reaction is carried out until pH>3.0, pressure filtration is carried out, and the filtrate is impurity-removed ferrous water; S2. the impurity-removed ferrous water is pumped into a reaction kettle, heated, oxygen is introduced, the reaction pressure is positive pressure, reaction is carried out for 0.5-2h, pressure filtration is carried out, the filter residue is washed, and refined hydroxyl ferric oxide is obtained; S3. the refined hydroxyl ferric oxide is added with theoretical amount of 1.01-1.02 times of hydrochloric acid, heated to 60-80 DEG C, and kept until clear and transparent, and ferric chloride for precision etching is prepared, which is applied to precision etching and improves the qualified rate of products.

Description

Technical Field

[0001] This invention belongs to the field of ferric chloride production technology, specifically relating to a method for preparing ferric chloride for precision etching. Background Technology

[0002] Ferric chloride is a widely used metal etchant in the etching industry. Currently, most etching processes are automated and continuous. The etching solution is regenerated by stabilizing the addition of oxidant and hydrochloric acid, thus maintaining the ORP (Original Rate of Etching) within ±50mV. When the amount of dissolved metal reaches a certain value, causing a decrease in the etching rate, some etching solution is discharged and replenished with new etching solution to maintain the etching rate. Precision etching, on the other hand, stabilizes the ORP value of the etching solution within ±10mV and maintains a stable impurity content by fixing the addition flow rate of new etching solution and the discharge flow rate of waste solution. This achieves precise control of the etching rate and improves etching quality. If the ORP value of the new ferric chloride is unstable or the impurity content is high, it will affect the addition rate of new etching solution and oxidant, thereby affecting the etching rate and the stability of etching quality, and reducing the product yield.

[0003] The ORP of ferric chloride used in some etching processes continues to rise and cannot be stabilized within a certain range, making it difficult to control the ORP value of automated etching lines and failing to meet the requirements of ferric chloride for precision etching. Summary of the Invention

[0004] To address at least one deficiency in existing technologies, this invention aims to provide a method for preparing ferric chloride for precision etching. This method, through the combined effect of selecting appropriate operational steps and determining optimal conditions during preparation, results in ferric chloride with a stable redox potential (ORP) and high purity, suitable for application in the precision etching industry.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing ferric chloride for precision etching, comprising the following steps: S1. The etching waste liquid / ferrous chloride solution is heated to 60~90℃, and 1%~10% of the weight of reduced iron powder is added. The reaction is carried out until the pH>3.0, and then filtered under pressure. The filtrate is ferrous water after impurity removal. S2. The purified ferrous water is pumped into the reactor, heated, and oxygen is introduced to make the reaction pressure positive. The reaction is carried out for 0.5~2 hours, filtered, and the filter residue is washed to obtain purified ferric hydroxide. S3. Refined ferric hydroxide is added to 1.01~1.02 times the theoretical amount of hydrochloric acid, heated to 60~80℃, and allowed to dissolve and become clear to obtain ferric chloride for precision etching.

[0006] As one embodiment of the method for preparing ferric chloride for precision etching according to the present invention, in step S1, the copper content in the purified ferrous water is <200mg / L and the nitrate nitrogen content is <10mg / L.

[0007] In one embodiment of the method for preparing ferric chloride for precision etching according to the present invention, in step S2, the heating is to raise the temperature to 70~85°C.

[0008] In one embodiment of the method for preparing ferric chloride for precision etching according to the present invention, the reaction pressure in step S2 is 0.2~0.3 MPa.

[0009] In this invention, reduced iron powder is added to the etching waste liquid / ferrous chloride solution to remove copper ions and nitrate nitrogen. No catalyst is added during oxygen oxidation to avoid introducing substances that cause ORP instability. No acid is added during oxidation to prevent Fe from being affected. 3+ Ferric hydroxide, hydrolyzed into a solid state, is then filtered and washed to separate the ferrous hydroxide from ferrous chloride and impurity ions, yielding high-purity ferric hydroxide. This high-purity ferric chloride is then dissolved in hydrochloric acid. The specific reaction equations are as follows: Cu 2+ + Fe = Cu + Fe 2+ NO3 - + 10H + + 4Fe = NH4 + + 3H₂O + 4Fe 2+ 12FeCl2 + 3O2 + 2H2O = 4FeOOH↓ + 8FeCl3 FeOOH + 3HCl = FeCl3 + 2H2O In step S1 of the preparation method of this invention, impurities such as copper, nitrate nitrogen, nickel, and chromium in iron-containing waste acid or ferrous chloride solution are replaced by adding reduced iron powder. When the reaction reaches pH > 3, copper ions and nitrate nitrogen in the ferrous chloride solution can be reduced to undetectable levels. Easily hydrolyzed metals such as chromium and tin are also hydrolyzed into solids and separated from the ferrous chloride solution. The ORP of the obtained ferric chloride is stable only when copper ions and nitrate nitrogen are not introduced into the ferrous chloride solution and during the oxidation process. Increasing the temperature and the amount of iron powder are beneficial to the reaction. When the amount of iron powder added is < 1% or the temperature is below 60°C, the reaction time is long and the removal efficiency of copper and nitrate nitrogen is poor. When the amount of iron powder added is > 10% or the temperature is above 90°C, the reaction is too fast, which easily forms ferric hydroxide precipitate, resulting in more solids and increasing the difficulty of pressure filtration separation.

[0010] In step S2, since the efficiency of oxygen oxidation without a catalyst is initially fast and then slows down, Fe...2+ When the concentration is less than 1%, the subsequent oxidation efficiency is low, making it difficult to oxidize ferrous iron to the acceptable level. Therefore, oxygen oxidation is performed directly without adding hydrochloric acid. In the absence of acid, ferrous chloride is oxidized to produce solid ferric hydroxide and liquid ferric chloride, with the remainder being Fe. 2+ It exists in liquid ferric chloride, and after solid-liquid separation, Fe is removed by washing. 2+ The etching waste liquid contains a large amount of impurities such as Na, Ca, Mg, and Mn, which are washed into the wash water during the washing process. 2+ <0.8% is sufficient to neutralize the Fe in ferric hydroxide. 2+ If the requirements are met, ferric hydroxide with no ferrous chloride and low impurity content can be obtained. The Fe in ferric hydroxide... 3+ =33%~45%, Fe 2+ <0.4%, with individual impurities <5ppm, indicating very high purity.

[0011] In step S2 of the preparation method of this invention, controlling the reaction pressure within the range of 0.2~0.3 MPa can increase the solubility of oxygen in the liquid phase and the mass transfer driving force, thereby facilitating the reaction between oxygen and Fe. 2+ Sufficient contact significantly accelerates the oxidation reaction rate, shortens the reaction time, and improves production efficiency. Simultaneously, within this pressure range, oxygen can be more fully absorbed and utilized, reducing the emission of unreacted oxygen in the exhaust gas, thereby lowering oxygen consumption and waste gas treatment load. Moderate pressure helps maintain the gas-liquid balance of the solution system, preventing localized overheating or violent agitation caused by excessive pressure, which could lead to Fe... 2+ or Fe 3+ The hydrolysis side reaction is controlled to ensure that the content of impurities such as ferric oxide or ferric hydroxide in the generated ferric chloride is kept at a low level. When the reaction pressure is below 0.2 MPa, the oxidation rate decreases significantly, oxygen solubility is insufficient, mass transfer is limited, and Fe... 2+ Oxidized to Fe 3+ The reaction time is significantly prolonged, production efficiency is reduced, oxygen utilization is low, a large amount of oxygen escapes from the system, resulting in raw material waste, increasing the difficulty of tail gas recovery or treatment, and incomplete oxidation is prone to occur, leading to the loss of some Fe. 2+ Residual ferrous chloride content in the product exceeds the standard, affecting the quality indicators of ferric chloride products. When the reaction pressure exceeds 0.3 MPa, the risk of side reactions easily increases. Under high pressure conditions, excessively high oxygen solubility may cause local peroxidation or violent exothermic reactions, promoting Fe... 3+ The ferric hydroxide colloid generated by hydrolysis is difficult to wash away with water to remove impurities, resulting in a decrease in product purity. At the same time, it increases equipment investment and maintenance costs, as well as safety risks. Oxygen comes into contact with organic matter or reducing substances in the solution under high pressure, which increases the potential risk of exothermic oxidative runaway and places higher demands on operational safety.

[0012] In one embodiment of the method for preparing ferric chloride for precision etching according to the present invention, in step S2, the reaction endpoint is the reaction reaching Fe. 2+ <1%.

[0013] In one embodiment of the method for preparing ferric chloride for precision etching according to the present invention, in step S2, the filter residue washing involves washing the filter residue until Fe in the wash water is removed. 2+ <0.4%.

[0014] In step S3, ferric hydroxide is readily soluble in hydrochloric acid. Adding a slight excess of hydrochloric acid maintains the HCl content in the ferric chloride solution below 0.5%. Increasing the temperature to improve the reaction rate, reaching 80°C, allows the solution to dissolve completely within 0.5 hours.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) Existing technology suggests that the change in ORP of ferric chloride is mainly due to Fe 3+ / Fe 2+ The cause is due to changes in concentration and temperature; it is also possible that the solution contains nitrate nitrogen or copper ions. Through mechanistic investigation and experimental verification, the inventors identified the root cause and subsequently improved the technical approach. They removed impurities such as nitrate nitrogen and copper ions from the ferrous chloride solution using iron powder, and produced ferric hydroxide by oxygen oxidation under sub-acid conditions without adding a catalyst. Free Fe was then removed by water washing. 2+ Impurities and hydroxyferric acid are dissolved to obtain ORP-stable, Fe 2+ Qualified ferric chloride with low impurity content.

[0016] (2) Using oxygen, which is the lowest cost and safest oxidant, results in low production costs, simple production equipment, and easy-to-achieve process conditions, making it suitable for large-scale production applications.

[0017] (3) No catalyst is introduced during oxidation, the stripping step is omitted in the process flow, and there is no problem with nitrogen oxide tail gas treatment.

[0018] (4) The obtained ferric chloride ORP is stable and has high purity, and can be applied to the precision etching industry.

[0019] (5) Do not use regulated strong oxidants such as chlorine, hydrogen peroxide, sodium chlorate, potassium permanganate, etc., as their use is restricted by factors such as the environmental impact assessment, qualifications, site, storage equipment, emergency equipment, and policies of the production enterprise, thus avoiding the safety hazards caused by the use of strong oxidants. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise specified, the experimental methods used in the examples and comparative examples are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0022] Example 1: A method for preparing ferric chloride for precision etching S1. 10 kg of iron-containing waste acid was heated to 60°C, 1000 g of reduced iron powder was added, and the reaction was carried out for 1 hour. The pH was 2.82. The mixture was then filtered under pressure, and the filtrate was ferrous water after impurities were removed. S2. The purified ferrous water is pumped into the reactor, heated to 70°C, and oxygen is introduced to make the reaction pressure 0.3 MPa. The reaction is carried out for 0.5 h, then filtered. The filter residue is washed with 2 kg of water in an online filter press to obtain 1.1 kg of purified ferric hydroxide. S3. Add 1.01 times the theoretical amount of hydrochloric acid to the refined ferric hydroxide, heat to 60°C, and react for 2 hours until the solution is clear, thus obtaining ferric chloride Al for precision etching.

[0023] Example 2: A method for preparing ferric chloride for precision etching S1. 10 kg of ferrous chloride solution was heated to 75°C, 100 g of reduced iron powder was added, the reaction was carried out for 0.5 h, pH=3.02, and the solution was filtered under pressure. The filtrate was ferrous water after impurity removal. S2. The purified ferrous water is pumped into the reactor, heated to 85°C, and oxygen is introduced to make the reaction pressure 0.2 MPa. The reaction is carried out for 1 hour, then filtered under pressure. The filter residue is washed with 1.5 kg of water in an online pressure filter to obtain 1.2 kg of purified ferric hydroxide. S3. Add 1.02 times the theoretical amount of hydrochloric acid to the refined ferric hydroxide, heat to 75°C, and dissolve until clear after 1 hour to obtain ferric chloride A2 for precision etching.

[0024] Example 3: A method for preparing ferric chloride for precision etching S1. 10kg of etching waste liquid is heated to 90℃, 600g of reduced iron powder is added, the reaction is carried out for 0.5h, pH=2.65, and then filtered under pressure. The filtrate is ferrous water after impurity removal. S2. The purified ferrous water is pumped into the reactor, heated to 100°C, and oxygen is introduced to make the reaction pressure 0.1 MPa. The reaction is carried out for 2 hours, then filtered under pressure. The filter residue is washed with 1.8 kg of water in an online pressure filter to obtain 1.1 kg of purified ferric hydroxide. S3. Add 1.01 times the theoretical amount of hydrochloric acid to the refined ferric hydroxide, heat to 80°C, and dissolve until clear after 0.5 h to obtain ferric chloride A3 for precision etching.

[0025] Comparative Example 1 The ferric hydroxide obtained in step S2 was not washed with water to remove impurities, and the rest was the same as in Example 1, to obtain ferric chloride A4.

[0026] Comparative Example 2 In step S2, 2‰ sodium nitrite was added to the ferrous water for oxidation, and the rest was the same as in Example 1, to obtain ferric chloride A5.

[0027] Comparative Example 3 Ferric chloride is produced using a conventional oxygen oxidation process: 1.01 times the theoretical volume of hydrochloric acid is added to a ferrous chloride solution, followed by a 3‰ nitric acid solution. The mixture is heated to 85°C, and oxygen is introduced at 0.25 MPa. After reacting for 1 hour, Fe... 2+ =0.08%, ferric chloride was transferred to a stirred tank and air was introduced to remove nitrogen oxides for 1 hour to obtain ferric chloride A6.

[0028] Experimental Example 1: The Influence of Different Ferric Chloride Processes on Etching Rate and Product Yield Ferric chloride obtained in Examples 1-3 and Comparative Examples 1-3 was used to prepare precision etched products. The preparation method was a conventional technical operation in the field. Data such as the fluctuation range of the corresponding etching rate and the pass rate of the precision etched products were tested.

[0029] The test results are shown in Table 1.

[0030] Table 1. Experimental data of the experimental cases and comparative examples.

[0031] Analyzing the data from ferric chloride A1, A2, and A3, in step S1, copper ions and nitro nitrogen were reduced to undetectable levels by the reduced iron powder; in step S2, after washing, the ferrous content and impurities in ferric hydroxide were very low; the resulting ferric chloride had a stable ORP, and when applied to precision etching, the etch rate fluctuation range was reduced from ±0.2 μm / min to within ±0.05 μm / min, and the product yield was significantly increased from 55% to approximately 80%.

[0032] Analysis of data from Comparative Examples 1-3: Comparative Example 1 did not wash the ferric hydroxide, and the resulting product contained Fe. 2+The product failed to meet the requirements. Although the ORP of the product was stable, the high Na and Mn content increased the solution viscosity, affecting the flow and ion diffusion of the solution during the etching process. When applied to precision etching, the product's pass rate did not improve significantly due to the low etching rate. In Comparative Example 2, a catalyst was added during oxidation, but the nitrate nitrogen in the solid ferric hydroxide could not be completely removed by washing. The ORP of ferric chloride was unstable, and the product's pass rate was only 57% when applied to precision etching due to the unstable etching rate. In Comparative Example 3, no impurities were removed from the raw materials, and copper ions were present in the solution. A catalyst was added during oxidation, but the remaining nitrate nitrogen in the ferric chloride could not be completely removed by the stripping process. The ferric chloride product contained copper ions and nitrate nitrogen, and the ORP was unstable. The product's pass rate was only 49% when applied to precision etching.

[0033] Therefore, the copper and nitro nitrogen content in ferric chloride should be controlled to stabilize the ORP, while the impurity content of ferric chloride should also be controlled to avoid high solution viscosity which would affect the ion diffusion rate, so as to maintain a high and stable etching rate and improve the yield of precision etched products.

[0034] Experimental Example 2: Study on Factors Affecting the Stability of Ferric Chloride ORP The ORP of some ferric chloride products continues to increase, and the reasons need to be investigated. The following discusses the factors affecting the stability of ferric chloride ORP: (1) Effect of temperature According to existing technology, "Study on the Corrosion Behavior of Metals in Oxidizing Metal Salt Solutions," the higher the solution temperature, the higher the ORP value. A correction equation was fitted to the relationship between temperature and ORP value, which is ORP. 25 =0.78(25-T)+ORP T In the formula, ORP 25 This is the theoretical value of ORP at 25℃. T This represents the imaginary value of ORP at the experimental temperature. According to this formula, the change in ORP of the sample at room temperature (20-23℃) should be less than 3mV with temperature. However, the actual change over 20 days was approximately 86mV. Therefore, it can be ruled out that the change in ORP was caused by temperature variation.

[0035] (2) Effect of residual oxidant The most common and economical method for preparing ferric chloride is by oxidizing ferrous chloride with oxygen. However, because the oxygen oxidation process occurs at a pressure of 0.1–0.3 MPa, residual oxygen, the oxidizing agent, may remain in the ferric chloride product, potentially allowing it to slowly oxidize any small amount of Fe in the ferric chloride. 2+This causes the ORP to rise slowly. It is common knowledge that the solubility of oxygen in solution decreases with increasing temperature. Therefore, ferric chloride was heated to boiling, stirred, subjected to negative pressure, and purged with inert gas for 30 minutes. After cooling the ferric chloride to room temperature and storing it for different periods of time, its ORP value continued to increase (see Table 2), which can eliminate the influence of residual oxidant oxygen.

[0036] Table 2. Changes in ORP after ferric chloride was removed from oxygen and left for different time periods.

[0037] Note: The temperature during testing is 20~24℃.

[0038] Besides oxygen oxidation, strong oxidizing agents such as chlorine and sodium chlorate are often used to oxidize ferrous chloride. As is common knowledge, when Fe is present in the solution... 2+ When exposed to (and / or acid), chlorine and sodium chlorate can instantly oxidize Fe. 2+ Fe 2+ It is impossible for ferric chloride to coexist with strong oxidants, and its application in etching will not cause a continuous increase in ORP.

[0039] (3) The effect of oxygen on ORP Since air contains a large amount of oxygen, an oxidizing agent, the effect of oxygen on the ORP of ferric chloride stored at room temperature was verified. Oxygen was bubbled into ferric chloride with stable ORP for 2 hours, and then allowed to stand for 0.5 hours. The ORP value was measured at different time points. The ORP value remained almost unchanged with prolonged storage time. This indicates that dissolved oxygen in the solution is insufficient to cause changes in ORP, thus eliminating the influence of dissolved oxygen in the solution.

[0040] Table 3. Changes in ORP after adding oxygen to ferric chloride and placing it for different times, resulting in ORP-stabilized ORP.

[0041] Note: The temperature during testing is 20~24℃.

[0042] (4) The effect of residual catalyst on ORP Oxygen oxidizes Fe 2+ In some cases, due to the slow oxidation rate, nitrate nitrogen is often added as a catalyst to increase the reaction rate, as in the example of "An Integrated Continuous Oxygen Oxidation Equipment and Method for Producing Ferric Chloride". Nitrogen is readily soluble in water, making it difficult to completely remove it after oxygen oxidation. Since a catalyst remains in ferric chloride, it can catalyze the oxidation of trace amounts of Fe by dissolved oxygen. 2+ The possible reaction equations in the solution are as follows: 3Fe 2+ + 4H + + NO3 -== 3Fe 3+ + 2H2O + NO↑ 2NO + O2 = 2NO2 NO2 + H2O = HNO3 + HNO2 3HNO2 = HNO3 + 2NO + H2O From the above reaction equations, it can be seen that NO3 is present in the solution. - and / or NO2 - At this time, it can catalyze the oxidation of Fe by oxygen. 2+ This causes the ORP to continue to rise until there is no Fe in the solution. 2+ Or without H + .

[0043] Different amounts of nitric acid solution were added to ORP-stable ferric chloride, and the solutions were left to stand for different periods of time, with ORP levels measured. The test results are shown in Table 4.

[0044] Table 4. Changes in ORP of ferric chloride with different nitrate nitrogen contents after different storage times.

[0045] Note: The temperature during testing was 20~24℃; the time unit was days; the ORP unit was mV; NO3 - (In N) The unit is mg / L.

[0046] The experimental data in Table 4 show that when ferric chloride contains 20 mg / L of nitro nitrogen in the preparation method of this invention, the ORP of the solution does not change significantly. However, when the nitro nitrogen content increases to 50 mg / L, it can cause a continuous increase in the ORP of the solution. The higher the nitro nitrogen content, the greater the increase in ORP.

[0047] (5) Effect of different copper ion contents on ORP The inventors, while studying the effect of impurities in ferric chloride on ORP, discovered that copper ions, as impurities, also cause changes in ORP. Different amounts of copper chloride solution were added to ORP-stable ferric chloride, and the solutions were left for different periods, with the ORP measured. The test results are shown in Table 5.

[0048] Table 5. Changes in ORP of ferric chloride with different copper contents after different storage times.

[0049] Note: The temperature during testing is 20~24℃; the time unit is days; the ORP unit is mV; the copper ion unit is mg / L.

[0050] The experimental data in Table 5 show that the presence of 2000 mg / L of copper ions in ferric chloride in the preparation method of this invention can cause a significant and continuous increase in ORP in the solution. The higher the copper ion content, the greater the increase in ORP.

[0051] (6) Analyze and summarize the factors affecting the stability of ORP in ferric chloride. ORP increases with increasing temperature, but remains unchanged when the temperature is constant; residual dissolved oxygen in the solution has no effect on ORP; the presence of a certain amount of nitro nitrogen or copper ions in ferric chloride can cause an increase in the ORP of ferric chloride, therefore it is necessary to control the nitro nitrogen and copper ions in the solution.

[0052] Experimental Example 3: Effect of Catalyst on the Rate of Oxygen Oxidation of Ferrous Chloride When ferrous chloride is oxidized by oxygen, nitrate nitrogen is often added as a catalyst, which can reduce Fe to Fe within 1 hour. 2+ Oxidation to <0.17% meets the requirements of GB / T 1621-2023 "Industrial Ferric Chloride". However, without a catalyst, it takes 10 hours to oxidize ferrous chloride to the acceptable level, indicating extremely low oxidation efficiency. The catalyst has a significant impact on the rate of oxygen oxidation of ferrous chloride solution. How to efficiently prepare ORP-stable, Fe... 2+ The availability of qualified ferric chloride for precision etching with low impurity content is a technical problem that those skilled in the art hope to solve.

[0053] Table 6. Fe at different times during the oxygen oxidation of ferrous chloride reaction. 2+ content

[0054] Note: Fe 2+ The unit is %; the time unit is h.

[0055] Experiment 4: Removal of Copper and Nitro Nitrogen from Etching Waste Liquid The etching waste liquid was supplemented with a small amount of hydrochloric acid, heated, and reduced iron powder was added. When the reaction reached different pH values, samples were taken to detect ORP, temperature, nitrate nitrogen, and copper. The experimental data are recorded in Table 7.

[0056] Table 7 Experimental data on removal of nitrate nitrogen and copper from etching waste liquid

[0057] The experimental data in the table above show that: ① When the reaction temperature is low, the efficiency of iron powder in removing copper and nitrate nitrogen is low. The higher the reaction temperature and the more iron powder is added, the better the effect of removing copper and nitrate nitrogen. ② Iron powder can easily reduce nitrate nitrogen in etching waste liquid. When the pH of the solution is greater than 1.5, the nitrate nitrogen in the solution has been completely reduced. ③ Copper ions in the etching waste liquid are also more easily reduced by iron powder. When the reaction temperature is greater than 60℃ and pH is greater than 2.5, the remaining copper in the solution is less than 150ppm, which can be removed by subsequent water washing.

[0058] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing ferric chloride for precision etching, characterized in that, Includes the following steps: S1. The etching waste liquid / ferrous chloride solution is heated to 60~90℃, and 1%~10% of the weight of reduced iron powder is added. The reaction is carried out until the pH>3.0, and then filtered under pressure. The filtrate is ferrous water after impurity removal. S2. The purified ferrous water is pumped into the reactor, heated, and oxygen is introduced to make the reaction pressure positive. The reaction is carried out for 0.5~2 hours, filtered, and the filter residue is washed to obtain purified ferric hydroxide. S3. Add 1.01 to 1.02 times the theoretical amount of hydrochloric acid to the refined ferric hydroxide, heat to 60 to 80°C, and wait until it dissolves and becomes clear to obtain ferric chloride for precision etching.

2. The method for preparing ferric chloride for precision etching according to claim 1, characterized in that, In step S1, the copper content in the purified ferrous molten metal is <200 mg / L and the nitrate nitrogen content is <10 mg / L.

3. The method for preparing ferric chloride for precision etching according to claim 1, characterized in that, In step S2, the heating is to raise the temperature to 70~85℃.

4. The method for preparing ferric chloride for precision etching according to claim 1, characterized in that, In step S2, the reaction pressure is 0.2~0.3 MPa.

5. The method for preparing ferric chloride for precision etching according to claim 1, characterized in that, In step S2, the reaction endpoint is the reaction to Fe 2+ <1%.

6. The method for preparing ferric chloride for precision etching according to claim 1, characterized in that, In step S2, the filter residue washing involves washing the filter residue until Fe in the wash water is removed. 2+ <0.4%.

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