Method for preparing ferric salt water purifying agent by utilizing iron-containing waste acid
By using a continuous flow reaction process and oxygen oxidation to prepare iron salt water purification agents, the safety risks and product quality issues of the catalytic oxidation process of iron-containing waste acid have been resolved, achieving efficient and safe production of iron salt water purification agents and reducing the cost of exhaust gas treatment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-10
AI Technical Summary
Existing catalytic oxidation processes for iron-containing waste acid have high safety risks, low product quality, and require the use of nitrogen-containing catalysts, resulting in high tail gas treatment costs and increased process complexity.
A continuous flow reaction process is used, with oxygen as the oxidant, to control the mass fraction of hydrogen ions in the iron salt raw material, the conveying flow rate, and the reaction pressure within a specific range, in order to prepare iron salt water purification agent and avoid the use of catalysts.
The Fe3+ ion content of the iron salt water purifier has been increased while the content of free acid and insoluble matter has been reduced, thereby improving safety and reducing exhaust gas treatment costs. The product quality meets industrial requirements.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of iron-containing waste acid utilization technology, and more specifically, relates to a method for preparing iron salt water purification agent using iron-containing waste acid. Background Technology
[0002] Industries such as iron and steel metallurgy, metal product processing, titanium dioxide production, and surface treatment generate large amounts of acidic wastewater during pickling and etching processes using hydrochloric acid or sulfuric acid. The main characteristic of this wastewater is the presence of high concentrations of ferrous ions (Fe2+). 2+ The wastewater containing iron and residual free acid is collectively referred to as iron-containing waste acid. This type of wastewater has a complex composition, potentially including suspended solids, grease, and trace amounts of other metal ions in addition to ferrous ions and free acid. Direct discharge will severely pollute the environment; simple neutralization treatment will waste the iron and acid resources and generate large amounts of difficult-to-dispose iron-containing sludge. Therefore, converting iron-containing waste acid into high-value-added products is an ideal way to achieve its resource recovery and harmless disposal.
[0003] The mainstream resource utilization method for iron-containing waste acid is to use oxidants to oxidize the ferrous ions to ferric ions, and then prepare iron-based water purification agents (such as ferric chloride, polyferric chloride, and polyferric sulfate). Typically, to ensure the Fe... 2+ To achieve complete oxidation, this process requires nitrogen-containing compounds (such as nitrites and nitrates) as catalysts for Fe. 2+ Catalytic oxidation is carried out to obtain iron salt products that can be used as water purification agents, such as polyferric chloride (polychlorinated chloride) with Chinese patent, a method for preparing polyferric chloride using waste acid and its application.
[0004] However, since nitrogen oxides (NO, NO2) are indispensable gaseous intermediates in the existing iron-containing waste acid catalytic oxidation process, they will continuously escape from the liquid phase during the reaction process, and eventually leave a large amount of tail gas containing nitrogen oxides that needs to be treated. This not only greatly increases the investment and operating costs of the tail gas treatment system (such as alkali consumption and energy consumption), but also generates nitrogen-containing waste liquid that needs further treatment, increasing the complexity of the entire process. On the other hand, the batch reaction system (such as reaction vessel, tank) used in the existing iron-containing waste acid catalytic oxidation process has significant defects: (1) High safety risk: In batch operation, a large amount of material is added at once or accumulated in a cycle. The reaction occurs in a closed space, which can easily lead to concentrated release of reaction heat, uncontrolled temperature and pressure, and the risk of explosion. (2) Limited product quality: The batch system has a weak buffering capacity for changes in feed. Impurities in the iron-containing waste acid (such as oil and suspended matter) are easy to accumulate in the vessel, which not only affects heat and mass transfer, but may also promote side reactions and affect the quality of the water purification agent product. Summary of the Invention
[0005] To address the issues of high safety risks, low product quality, and the need for nitrogen-containing catalysts in existing iron-containing waste acid oxidation processes, this invention provides a method for preparing iron salt water purification agents using iron-containing waste acid. This method employs a continuous reaction process instead of the traditional intermittent reaction, eliminates the need for catalysts, and yields iron salt water purification agents with high iron ion content, meeting the quality requirements for water purification agents used in industrial wastewater and sludge dewatering treatment.
[0006] Another object of the present invention is to provide an iron salt water purification agent.
[0007] The above-mentioned objective of this invention is achieved through the following technical solution: A method for preparing iron salt water purification agent using iron-containing waste acid includes the following steps: Iron-containing waste acid and added acid solution are mixed to obtain iron salt raw material; then the iron salt raw material is reacted with oxygen in a continuous flow to obtain iron salt water purification agent; The mass fraction of hydrogen ions in the iron salt raw material, calculated as hydrogen chloride, is 4.8–8.5%. In the continuous flow reaction, the conveying velocity of the iron salt raw material is 500-2000 kg / h, and the ratio of the conveying velocity of the iron salt raw material to the conveying velocity of oxygen is 1000:(10-20). The continuous flow reaction is carried out at a temperature of 100-165°C and a pressure of 1.25-2 MPa.
[0008] It should be noted that: Compared to batch reaction processes, continuous flow reaction processes are characterized by higher safety.
[0009] The inventors of this invention discovered through research that, using continuous flow reaction technology without the use of a catalyst, and by coordinating four aspects—using oxygen as an oxidant, controlling the hydrogen ion mass fraction in the iron salt raw material within a specific range, controlling the conveying flow rate of the iron salt raw material within a specific range, and controlling the pressure of the continuous flow reaction within a specific range—the iron salt water purifier can be produced with high Fe content. 3+ It has a high ion content, and low free acid content and low insoluble matter content.
[0010] Furthermore, since the method of the present invention does not require the use of a catalyst, the cost of exhaust gas treatment caused by a catalyst can be reduced.
[0011] Preferably, before mixing, the process further includes a step of pretreating the iron-containing waste acid to remove insoluble impurities.
[0012] More preferably, the pretreatment method is filtration; specifically, one of plate and frame filter press, quartz sand filtration, and microfiltration can be used, or multiple methods can be used in combination.
[0013] More preferably, the TOC content of the pretreated iron-containing waste acid is ≤300 ml / L.
[0014] Preferably, the acidity of the added acid solution is 32-36%.
[0015] Preferably, the added acid solution is at least one of hydrochloric acid and sulfuric acid.
[0016] Preferably, the continuous flow reaction is carried out in a continuous flow reactor; the continuous flow reactor is one of a tubular reactor, a disc reactor, or a microchannel reactor.
[0017] More preferably, the tubular reactor has a pipe length of 1-3m and an inner diameter of 10-200mm.
[0018] Preferably, the material of the continuous flow reactor is at least one of silicon carbide, carbon fiber reinforced graphite, and aluminosilicate glass.
[0019] This invention also protects an iron salt water purifier, prepared by the above-described method.
[0020] Preferably, the iron salt water purifier is a ferric chloride water purifier, a ferric sulfate water purifier, or a polyferric sulfate water purifier.
[0021] Compared with the prior art, the beneficial effects of the present invention are: This invention, through the combined use of four aspects—using oxygen as an oxidant, controlling the mass fraction of hydrogen ions in the iron salt raw material within a specific range, controlling the conveying flow rate of the iron salt raw material within a specific range, and controlling the pressure of the continuous flow reaction within a specific range—obtains an iron salt water purification agent with Fe content... 3+ With high ion content, low free acid content, and low insoluble matter content, the method of this invention has the characteristics of higher safety. Furthermore, since the method of this invention does not require the use of a catalyst, it can reduce the cost of tail gas treatment associated with catalysts. Simultaneously, the resulting iron salt water purification agent can be used for industrial wastewater and sludge dewatering treatment without further processing (e.g., concentration), and can also meet sales standards after further processing (e.g., adding ferric chloride or polyferric sulfate to achieve the corresponding concentration requirements). Detailed Implementation
[0022] The present invention will be further described below with reference to the specification and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.
[0023] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.
[0024] Example 1 This embodiment provides a method for preparing iron salt water purification agent using iron-containing waste acid, the steps of which are as follows: (1) The iron-containing waste acid 1 (iron-containing waste acid generated by pickling the surface of thin plate with hydrochloric acid) was subjected to plate and frame filter press, quartz sand filter and microfiltration in sequence to remove insoluble impurities and obtain pretreated iron-containing waste acid; in this embodiment, the TOC content of the pretreated iron-containing waste acid is 220 mg / L. (2) Add 30% hydrochloric acid to 1t of pretreated iron-containing waste acid. The amount of hydrochloric acid added is 116kg to obtain iron salt raw material. In this embodiment, the iron content (calculated as iron oxide) of the iron salt raw material is 10.75%, and the hydrogen ion content (calculated as hydrochloric acid) is 4.91%. (3) Under the conditions of 150℃ and 1.8MPa, iron salt raw material is transported at a flow rate of 1000kg / h and oxygen is transported at a flow rate of 10.75kg / h into the pipeline of the tubular reactor (the length of the pipeline is 2m and the inner diameter is 100mm). The effluent from the reactor is collected, which is the iron salt water purification agent product.
[0025] Example 2 This embodiment provides a method for preparing iron salt water purification agent using iron-containing waste acid, the steps of which are as follows: (1) The iron-containing waste acid 2 (iron-containing waste sulfuric acid generated by pickling steel pipes with sulfuric acid) is subjected to plate and frame filter press, quartz sand filter and microfiltration in sequence to remove insoluble impurities and obtain pretreated iron-containing waste acid; in this embodiment, the TOC content of the pretreated iron-containing waste acid is 180 mg / L. (2) Add 25% hydrochloric acid to 2t of pretreated iron-containing waste acid, with an addition amount of 25kg, to obtain iron salt raw material; in this embodiment, the iron content (calculated as iron oxide) of the iron salt raw material is 15.8%, and the hydrogen ion content (calculated as hydrochloric acid) is 7.22%; (3) Under the conditions of 165℃ and 2MPa, iron salt raw material is transported at a flow rate of 2000kg / h and oxygen at a flow rate of 31.6kg / h into the pipeline of the tubular reactor (the length of the pipeline is 2m and the inner diameter is 100mm). The effluent from the reactor is collected, which is the iron salt water purification agent product.
[0026] Example 3 This embodiment provides a method for preparing iron salt water purification agent using iron-containing waste acid, the steps of which are as follows: (1) The iron-containing waste acid 3 (iron-containing waste acid generated by using hydrochloric acid on iron tower parts) is subjected to plate and frame filter press, quartz sand filter and microfiltration in sequence to remove insoluble impurities and obtain pretreated iron-containing waste acid; in this embodiment, the TOC content of the pretreated iron-containing waste acid is 230mg / L. (2) Add 32% hydrochloric acid to 1t of pretreated iron-containing waste acid. The amount of hydrochloric acid added is 223kg to obtain iron salt raw material. In this embodiment, the iron content (calculated as iron oxide) of the iron salt raw material is 16.35% and the hydrogen ion content (calculated as hydrochloric acid) is 7.47%. (3) Under the conditions of 100℃ and 1.5MPa, iron salt raw material is transported at a flow rate of 900kg / h and oxygen at a flow rate of 14.715kg / h to the pipeline of the tubular reactor (the length of the pipeline is 2m and the inner diameter is 100mm). The effluent from the reactor is collected, which is the iron salt water purification agent product.
[0027] Example 4 This embodiment provides a method for preparing iron salt water purification agent using iron-containing waste acid, the steps of which are as follows: (1) The iron-containing waste acid 4 (iron-containing waste acid generated by pickling the surface of thin plate with hydrochloric acid) was subjected to plate and frame filter press, quartz sand filter and microfiltration in sequence to remove insoluble impurities and obtain pretreated iron-containing waste acid; in this embodiment, the TOC content of the pretreated iron-containing waste acid was 260 mg / L. (2) Add 26% hydrochloric acid to 1t of pretreated iron-containing waste acid. The amount of hydrochloric acid added is 82kg to obtain iron salt raw material. In this embodiment, the iron content (calculated as iron oxide) of the iron salt raw material is 18.48%, and the hydrogen ion content (calculated as hydrochloric acid) is 8.44%. (3) Under the conditions of 100℃ and 1.8MPa, iron salt raw material is transported at a flow rate of 500kg / h and oxygen at a flow rate of 9.24kg / h to the tubular reactor (the length of the pipe is 2m and the inner diameter is 100mm). The effluent from the reactor is collected, which is the iron salt water purification agent product.
[0028] Example 5 This embodiment provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Embodiment 1 is that the reaction pressure in step (3) is 1.25 MPa.
[0029] Example 6 This embodiment provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Embodiment 1 is that the reaction pressure in step (3) is 2 MPa.
[0030] Example 7 This embodiment provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Embodiment 1 is that the conveying flow rate of iron salt raw material in step (3) is 500 kg / h.
[0031] Comparative Example 1 This comparative example provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Example 1 is that the amount of hydrochloric acid added in step (2) is 100 kg. In this comparative example, the iron content (calculated as iron oxide) of the iron salt raw material is 10.91%, and the hydrogen ion content (calculated as hydrochloric acid) is 4.55%.
[0032] Comparative Example 2 This comparative example provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Example 1 is that the amount of hydrochloric acid added in step (2) is 150 kg. In this comparative example, the iron content (calculated as iron oxide) of the iron salt raw material is 10.43%, and the hydrogen ion content (calculated as hydrochloric acid) is 5.65%.
[0033] Comparative Example 3 This comparative example provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Example 1 is that in step (3), the conveying flow rate of the iron salt raw material is 400 kg / h.
[0034] Comparative Example 4 This comparative example provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Example 1 is that in step (3), the conveying flow rate of the iron salt raw material is 2500 kg / h.
[0035] Comparative Example 5 This comparative example provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Example 1 is that the reaction pressure in step (3) is 2.2 MPa.
[0036] Comparative Example 6 This comparative example provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Example 1 is that the reaction pressure in step (3) is 1.0 MPa.
[0037] Comparative Example 7 This comparative example provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Example 1 is that the oxygen in step (3) is replaced with air at the same delivery flow rate.
[0038] Comparative Example 8 This comparative example provides a method for preparing iron salt water purification agent using iron-containing waste acid. The difference from Example 1 is that the reaction temperature in step (3) is 90°C.
[0039] Performance testing The iron salt water purification agents obtained in each embodiment and comparative example were subjected to Fe... 3+ The detection methods for ion content and free acid content are as follows: (1) Fe 3+Ion content (converted to iron oxide): Under acidic conditions, excess potassium iodide solution was added to the iron salt water purification agent sample, and then titrated with sodium thiosulfate standard solution using starch as an indicator to determine the Fe content. 3+ Ion content.
[0040] (2) Free acid content: Potassium fluoride reacts with iron ions to produce tripotassium hexafluoroferrate, which is titrated with sodium hydroxide standard titration solution using phenolphthalein as an indicator.
[0041] (3) Determination of insoluble content: After the sample is dissolved, it is filtered, washed and dried to constant weight, and the insoluble content is calculated.
[0042] Fe in the iron salt water purification agents of each embodiment and comparative example 3+ The results of the ion content and free acid content detection are shown in Table 1.
[0043] Table 1. Test results of iron salt water purification agents in each embodiment and comparative example.
[0044] As can be seen from Table 1, Fe in each embodiment 3+ The ion content is not less than 10wt%, the free acid content is ≤0.24%, and the insoluble matter content is ≤0.02%, indicating that the iron salt water purification agent prepared by the method of the present invention is of good quality.
[0045] In Comparative Example 1, the amount of hydrochloric acid added to the iron-containing waste acid was too small, resulting in a low acidity of the system. This led to a high degree of hydrolysis of the iron salt, producing a large amount of insoluble matter, and the insoluble matter content of the iron salt water purification agent was too high.
[0046] In Comparative Example 2, the amount of hydrochloric acid added to the iron-containing waste acid was too high, resulting in excessively high acidity in the reaction system and thus excessively high free acid content in the prepared iron salt water purification agent.
[0047] The excessively low flow rate of the iron salt raw material in Comparative Example 3 led to an imbalance in the gas-liquid distribution of the reaction system, resulting in Fe... 3+ Low ion content.
[0048] The excessively high conveying velocity of the iron salt raw material in Comparative Example 4 resulted in incomplete reaction of the material in a flowing state, leading to an imbalance in the Fe content of the iron salt water purifier. 3+ Low ion content and excessively high free acid content.
[0049] In Comparative Examples 5 and 6, the reaction pressure was too high or too low, the gas-liquid distribution of the reaction system was unbalanced, or the reaction was incomplete, affecting the Fe content of the iron salt water purification agent. 3+ Low ion content and excessively high free acid content.
[0050] Comparative Example 7 uses air instead of oxygen as the oxidant, and the Fe in the iron salt water purification agent... 3+Low ion content and excessively high free acid content.
[0051] The reaction temperature in Comparative Example 8 was too low, resulting in incomplete reaction of the materials and the Fe content of the iron salt water purifier. 3+ Low ion content and excessively high free acid content.
[0052] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.
Claims
1. A method for preparing iron salt water purification agent using iron-containing waste acid, characterized in that, Includes the following steps: Iron-containing waste acid and added acid solution are mixed to obtain iron salt raw material; then the iron salt raw material is reacted with oxygen in a continuous flow to obtain iron salt water purification agent; The mass fraction of hydrogen ions in the iron salt raw material, calculated as hydrogen chloride, is 4.8–8.5%. In the continuous flow reaction, the conveying velocity of the iron salt raw material is 500-2000 kg / h, and the ratio of the conveying velocity of the iron salt raw material to the conveying velocity of oxygen is 1000:(10-20). The continuous flow reaction is carried out at a temperature of 100-165°C and a pressure of 1.25-2 MPa.
2. The method according to claim 1, characterized in that, Before mixing, the process also includes a step of pretreating the iron-containing waste acid to remove insoluble impurities.
3. The method according to claim 1, characterized in that, The iron salt raw material contains 10-19% iron by mass, calculated as iron oxide.
4. The method according to claim 1, characterized in that, The added acid solution is at least one of hydrochloric acid and sulfuric acid.
5. The method according to claim 1, characterized in that, The continuous flow reaction is carried out in a continuous flow reactor; the continuous flow reactor is one of a tubular reactor, a disc reactor, or a microchannel reactor.
6. The method according to claim 5, characterized in that, The tubular reactor has a pipe length of 1-3m and an inner diameter of 10-200mm.
7. The method according to claim 1, characterized in that, The temperature of the continuous flow reaction is 150~165℃, and the pressure is 1.8~2MPa.
8. The method according to claim 1, characterized in that, The iron salt raw material is transported at a flow rate of 1500–2000 kg / h.
9. A type of iron salt water purification agent, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.
10. The iron salt water purifier according to claim 9, characterized in that, The iron salt water purification agent is ferric chloride water purification agent, ferric sulfate water purification agent, or polyferric sulfate water purification agent.