Method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid

Abstract

The invention discloses a method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid, and belongs to the technical field of waste acid treatment. The method comprises the following steps: S1, respectively putting a cathode and an anode at two ends of an electrolytic cell, putting a diaphragm to separate the cathode and the anode, filtering the iron-containing waste hydrochloric acid, removing suspended matters and solid residues, and introducing the iron-containing waste hydrochloric acid into the electrolytic cell; s2, measuring the content of iron element and the content of free acid in the iron-containing waste hydrochloric acid, and adding a neutralizing agent to neutralize redundant free acid; s3, applying voltage between the cathode and the anode according to the content of the iron element, performing electrolytic reaction to generate an oxidation intermediate, and oxidizing the iron element by using the oxidation intermediate to obtain a precipitate iron oxide and a calcium chloride solution; and S4, adding a proper amount of water into the reaction solution for dilution, filtering to obtain iron oxide, and concentrating the filtrate to obtain calcium chloride. According to the method, the oxidation intermediate generated by waste hydrochloric acid electrolysis is used as the oxidizing agent, the ferrous ions in the waste hydrochloric acid are selectively oxidized, other oxidizing agents do not need to be additionally added, new impurities cannot be generated in the oxidation process, the treatment time is short, the product is controllable, and remarkable economic benefits and social benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of waste acid treatment, and in particular to a method for electrochemically recovering iron-containing waste hydrochloric acid to prepare iron oxide and calcium chloride. Background Art

[0002] In the industrial production of steel, a large amount of hydrochloric acid is consumed for pickling before hot-dip galvanizing, electroplating, plastic spraying, electrophoresis and other surface treatments to remove rust on the surface. The generation of iron-containing waste hydrochloric acid is inevitable. For steel surface treatment companies, hundreds of tons of waste acid are discharged every day. The hydrochloric acid pickling wastewater generally consists of 1%~10% free acid content and 5%~30% ferrous chloride content, accompanied by some heavy metals and other impurities. If these acid waste liquids are discharged without treatment, it will not only pollute the environment, but also waste precious resources. Therefore, the preparation of industrial products with market value has long-term social significance.

[0003] Traditional methods for treating waste hydrochloric acid containing iron mainly include neutralization method, evaporation concentration method, etc. The neutralization method is to add alkaline substances (such as lime, sodium hydroxide, etc.) to react with the acidic substances in the waste acid to generate corresponding salts and water, thereby achieving the purpose of reducing the acidity of the waste acid. This method is simple to operate and easy to use. Although it has a small one-time investment, the operating cost is high. Its fatal disadvantage is that it produces a large amount of sludge and a large amount of wastewater. The COD and heavy metal values ​​of the wastewater are not easy to meet the national emission standards, resulting in secondary pollution, and the resource recovery rate is low. The evaporation concentration method is to evaporate the water in the waste acid by heating, thereby increasing the concentration of the waste acid, which is convenient for subsequent treatment and utilization. However, this method has high energy consumption, serious equipment corrosion, and poor treatment effect on waste acid containing more impurities.

[0004] In view of the shortcomings of traditional methods, some new iron-containing waste hydrochloric acid treatment technologies have emerged in recent years. The Chinese patent application with application number 201910645685.8 discloses a method for preparing ferric chloride products by two-stage oxidation of iron-containing waste hydrochloric acid. The method proposes to introduce compressed air or oxygen for catalytic oxidation for the first step of oxidation, and then use hydrogen peroxide or sodium chlorate for secondary oxidation. Although this method does not introduce new impurities, does not waste resources, and completely recycles waste, the oxidation speed is slow, the secondary oxidation takes 4 to 9 hours, and the oxidant cost is high, which is not conducive to large-scale waste acid recovery.

[0005] A Chinese patent with application number 202111339620.4 discloses a method for preparing ferric phosphate using iron-containing waste hydrochloric acid. The patent proposes nitric acid as a catalyst to catalyze oxygen oxidation, followed by vacuum distillation to separate dilute hydrochloric acid and ferric phosphate solution. However, during the oxidation process, as the temperature changes, nitric acid may decompose into toxic gas nitrogen dioxide, and vacuum distillation requires a vacuum system, which has high requirements for containers and high energy consumption.

[0006] In addition, common methods include evaporation concentration method such as Chinese patent application No. 201510260004.8, solvent extraction method such as Chinese patent application No. 85108552 and Chinese patent No. 201610018595.2, etc. During the roasting process, the salt concentrate and iron oxide are easy to cause blockage and scarring in the equipment; the evaporation concentration method is only suitable for treating high-concentration waste hydrochloric acid solution, and the equipment investment is large; efficient extractants are generally toxic organic solvents, and the treatment process requires the use of a large amount of extractants, which is costly. Therefore, developing an efficient, environmentally friendly and economical method for treating iron-containing waste hydrochloric acid is of great significance for promoting the resource utilization of industrial waste acid and environmental protection. Summary of the invention

[0007] In view of the problems of large equipment investment, complex process flow, long reaction time and low purity of recovered products in the current recycling of iron-containing waste hydrochloric acid, the present invention provides a method for electrochemically recycling iron-containing waste hydrochloric acid to prepare iron oxides and calcium chloride. The present invention uses the oxidation intermediates produced by the electrolysis of waste hydrochloric acid as an oxidant to selectively oxidize the ferrous ions in the waste hydrochloric acid, does not require the addition of other oxidants, and does not generate new impurities during the oxidation process. The processing time is short, the product is controllable, and has significant economic and social benefits.

[0008] The method for electrochemically recovering iron-containing waste hydrochloric acid to prepare iron oxide and calcium chloride comprises the following steps: S1. Place a cathode and an anode at both ends of the electrolytic cell, respectively, place a diaphragm to separate the positive and negative electrodes, filter the iron-containing waste hydrochloric acid, remove suspended matter and solid residues, and then pass it into the electrolytic cell; S2, determining the ferrous ion content and free acid content in the iron-containing waste hydrochloric acid, and adding a neutralizing agent to neutralize the excess free acid according to the free acid content; S3, applying a voltage between the cathode and the anode according to the ferrous ion content, performing an electrolytic reaction to produce an oxidized intermediate, and utilizing the oxidized intermediate to oxidize the ferrous ions to obtain a precipitate of iron oxide and a calcium chloride solution; S4. Add an appropriate amount of water to the reaction solution to dilute it, filter to obtain iron oxide, and concentrate the filtrate to obtain calcium chloride.

[0009] Preferably, the material of the cathode described in step S1 includes one or more of the elements Pt, Ti, Ru, Ir, Sn, Pb, C, B, Ni, Mn, and Co.

[0010] Preferably, the material of the anode in step S1 includes Pt, Ti, graphite, Pd, Au, B, C 3 N 4 One or more of the .

[0011] Preferably, the iron-containing waste hydrochloric acid solution in step S1 has a free acid content of 1wt% to 20wt%, and a ferrous ion content of 5wt% to 30wt%.

[0012] Preferably, the amount of the iron-containing waste hydrochloric acid solution added in step S1 is 10% to 80% of the volume of the electrolytic cell.

[0013] Preferably, the neutralizing agent described in step S2 includes one or more of calcium hydroxide, calcium oxide, calcium bicarbonate, calcium dihydrogen carbonate, calcium carbonate, calcium sulfate, and calcium bisulfate.

[0014] Preferably, in step S3, the pH value of the solution in the electrolytic cell is controlled to be 8 to 13. Controlling the pH value of the solution in the electrolytic cell to be 8 to 13 is conducive to the formation of the required iron oxides. If the pH value exceeds this range, the formation speed slows down and the size of the obtained iron oxides is uneven.

[0015] Preferably, the voltage of the electrolysis reaction in step S3 is 1-200 V and the duration is 0.5-5 h.

[0016] Fe in solution 2+ Completely into ferric oxide and ferric oxide, an oxidant is needed to oxidize the ferrous ions, so the Fe 2+ As the content increases, more oxidizing substances are needed. Step S3 is to prepare the oxidizing substances, so more voltage and time are required.

[0017] Preferably, in step S3, the amount of electrons generated during the electrolysis process is 1.5 to 5 times the amount of iron ions.

[0018] Fe in waste hydrochloric acid 2+ The content is calculated according to formula (I): Formula (I) in, represents the amount of iron ions in the solution, in mol; V represents the volume of the solution, in L; The mass concentration of iron ions in the solution, in g / L; is the relative molecular mass of iron ion, which is 55.85 g / mol.

[0019] The relationship between the amount of electrons in the electrolysis process and the voltage and time is shown in formula (II): Formula (II) in, It represents the amount of electron substance, with the unit of mol; I represents the current corresponding to the electrolysis voltage, with the unit of A; t represents the electrolysis time, with the unit of s; 96500 is the Faraday constant, which represents the charge of 1 mol of electrons, with the unit of C / mol.

[0020] The Fe in the waste hydrochloric acid is electrolyzed 2+ Oxidation from +2 to +3, theoretically the amount of electrons is equal to Fe 2+ However, in the actual electrolysis process, there is a problem of conversion efficiency. Therefore, in order to ensure Fe 2+ To be fully recycled, the amount of electronic material should be 1.5 to 5 times in excess.

[0021] Preferably, in step S3, the temperature of the electrolysis reaction is 20-90°C.

[0022] The voltage, temperature, time and pH of the electrolysis reaction in step S3 directly affect the amount of the oxidation intermediates. The smaller the amount of electrolysis, the slower the reaction rate and the lower the purity of the product.

[0023] Preferably, the oxidation intermediate comprises hypochlorite, persulfate and / or hydrogen peroxide.

[0024] Preferably, the amount of water added in step S4 is 0.5 to 100 times the volume of the reactants.

[0025] Preferably, the iron oxide described in step S4 is one or both of ferroferric oxide and ferrous oxide.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. The ferrous ions are indirectly oxidized by electrolyzing the oxidized intermediates at the anode using an electrochemical method, without the need to add additional oxidants, thus reducing production costs.

[0027] 2. The electrolysis reaction is rapid, shortening the production cycle from the original 4-9 hours to 1 hour, significantly shortening the production cycle, saving energy consumption, and further reducing production costs.

[0028] 3. Compared with the above patents, the process is simple and easy to operate, and the recycling of iron-containing waste acid can be completed in only four steps, and the requirements for the recycling device are not high.

[0029] 4. Product diversity: the generated products can be controlled by adjusting the pH value, temperature, and the amount of iron in different valence states in the waste acid. DETAILED DESCRIPTION

[0030] The technical scheme of the present invention is further described below by way of examples. The raw materials used in the examples can be purchased from the market or prepared by conventional methods.

[0031] Example 1 A method for electrochemically recovering iron-containing waste hydrochloric acid to prepare iron oxide and calcium chloride comprises the following steps: S1. Place a cathode and an anode at both ends of the electrolytic cell, respectively, and place a diaphragm to separate the positive and negative electrodes. Filter the iron-containing waste hydrochloric acid solution, remove suspended matter and solid residue, and then place it in the electrolytic cell. The amount of iron-containing waste hydrochloric acid solution added is 10% of the volume of the electrolytic cell. Among them, the cathode is made of Pt sheet and the anode is made of graphite rod material; The free acid content in the iron-containing waste hydrochloric acid solution is 1wt%, and the ferrous ion content is 5wt%; S2, determining the ferrous ion content in the iron-containing waste hydrochloric acid solution to be 5wt% and the hydrochloric acid content to be 1wt%, slowly adding calcium hydroxide to neutralize the excess hydrochloric acid; S3, applying a voltage of 100 V between the cathode and the anode, and conducting an electrolytic reaction at a pH value of 8 and a temperature of 20 °C for 0.5 h to obtain a precipitate and a calcium chloride solution; S4. Take water in an amount 0.5 times the volume of the reactants and add it to the reaction solution to dilute it, filter to obtain iron oxide, and concentrate the filtrate to obtain calcium chloride.

[0032] After X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) tests, the obtained iron oxide is ferric oxide.

[0033] Example 2 A method for electrochemically recovering iron-containing waste hydrochloric acid to prepare iron oxide and calcium chloride comprises the following steps: S1. Place a cathode and an anode at both ends of the electrolytic cell, respectively, and place a diaphragm to separate the positive and negative electrodes. Filter the iron-containing waste hydrochloric acid solution, remove suspended matter and solid residue, and then place it in the electrolytic cell. The amount of iron-containing waste hydrochloric acid solution added is 30% of the volume of the electrolytic cell. Among them, Ti rod is used as cathode and Pt rod is used as anode; The free acid content in the iron-containing waste hydrochloric acid solution is 10wt%, and the ferrous ion content is 15wt%; S2, determining the ferrous ion content in the iron-containing waste hydrochloric acid solution to be 15wt% and the hydrochloric acid content to be 10wt%, slowly adding calcium oxide to neutralize the excess hydrochloric acid; S3, applying a voltage of 130 V between the cathode and the anode, and conducting an electrolytic reaction at a pH value of 10 and a temperature of 40 °C for 1 h to obtain a precipitate and a calcium chloride solution; S4. Take water in an amount 10 times the volume of the reactants and add it to the reaction solution to dilute it, filter to obtain iron oxide, and concentrate the filtrate to obtain calcium chloride.

[0034] After X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) tests, the contents of ferric oxide and ferrosinone in the prepared iron oxide were 81wt% and 19wt%, respectively.

[0035] Example 3 A method for electrochemically recovering iron-containing waste hydrochloric acid to prepare iron oxide and calcium chloride comprises the following steps: S1. Place a cathode and an anode at both ends of the electrolytic cell, respectively, and place a diaphragm to separate the positive and negative electrodes. Filter the iron-containing waste hydrochloric acid solution, remove suspended matter and solid residue, and then place it in the electrolytic cell. The amount of iron-containing waste hydrochloric acid solution added is 50% of the volume of the electrolytic cell. Among them, Ni rod is used as cathode and B rod is used as anode; The free acid content in the iron-containing waste hydrochloric acid solution is 15wt%, and the ferrous ion content is 25wt%; S2, determining the ferrous ion content in the iron-containing waste hydrochloric acid solution to be 25wt% and the hydrochloric acid content to be 15wt%, and slowly adding sodium oxide to neutralize the excess hydrochloric acid; S3, applying a voltage of 170 V between the cathode and the anode, and conducting an electrolytic reaction at a pH value of 11.5 and a temperature of 70 °C for 5 h to obtain a precipitate and a calcium chloride solution; S4. Take water in an amount 50 times the volume of the reactants and add it to the reaction solution to dilute it, filter to obtain iron oxide, and concentrate the filtrate to obtain calcium chloride.

[0036] After X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) tests, the contents of ferric oxide and ferrosinone in the prepared iron oxide were 68wt% and 32wt%, respectively.

[0037] Example 4 A method for electrochemically recovering iron-containing waste hydrochloric acid to prepare iron oxide and calcium chloride comprises the following steps: S1. Place a cathode and an anode at both ends of the electrolytic cell, respectively, and place a diaphragm to separate the positive and negative electrodes. Filter the iron-containing waste hydrochloric acid solution, remove suspended matter and solid residue, and then place it in the electrolytic cell. The amount of iron-containing waste hydrochloric acid solution added is 80% of the volume of the electrolytic cell. Among them, the cathode is made of Pt rod, and the anode is made of Pt rod; The free acid content in the iron-containing waste hydrochloric acid solution is 20wt%, and the ferrous ion content is 30wt%; S2, determining the ferrous ion content in the iron-containing waste hydrochloric acid solution to be 30wt% and the hydrochloric acid content to be 20wt%, slowly adding sodium hydroxide to neutralize the excess hydrochloric acid; S3, applying a voltage of 200 V between the cathode and the anode, and conducting an electrolytic reaction at a pH value of 13 and a temperature of 90 °C for 4 h to obtain a precipitate and a calcium chloride solution; S4. Take water in an amount 100 times the volume of the reactants and add it to the reaction solution to dilute it, filter to obtain iron oxide, and concentrate the filtrate to obtain calcium chloride.

[0038] After X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) tests, the obtained iron oxide is ferroferric oxide.

[0039] It should be understood that the above embodiments are only used to illustrate the present invention and are not used to limit the scope of protection of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims

1. A method for electrochemically recovering iron-containing waste hydrochloric acid to prepare iron oxide and calcium chloride, characterized in that: The following steps are involved: S1. Place a cathode and an anode at both ends of the electrolytic cell, respectively, place a diaphragm to separate the positive and negative electrodes, filter the iron-containing waste hydrochloric acid, remove suspended matter and solid residues, and then pass it into the electrolytic cell; S2, determining the ferrous ion content and free acid content in the iron-containing waste hydrochloric acid, and adding a neutralizing agent to neutralize the excess free acid according to the free acid content; S3, applying a voltage between the cathode and the anode according to the ferrous ion content, performing an electrolytic reaction to produce an oxidized intermediate, and utilizing the oxidized intermediate to oxidize the ferrous ions to obtain a precipitate of iron oxide and a calcium chloride solution; S4. Add an appropriate amount of water to the reaction solution to dilute it, filter to obtain iron oxide, and concentrate the filtrate to obtain calcium chloride.

2. The method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid according to claim 1, characterized in that: The material of the cathode described in step S1 includes one or more of the elements Pt, Ti, Ru, Ir, Sn, Pb, C, B, Ni, Mn, and Co.

3. The method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid according to claim 1, characterized in that: The material of the anode described in step S1 includes one or more of Pt, Ti, graphite, Pd, Au, B, and C3N4.

4. The method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid according to claim 1, characterized in that: The free acid content in the iron-containing waste hydrochloric acid solution described in step S1 is 1wt%~20wt%, and the ferrous ion content is 5wt%~30wt%.

5. The method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid according to claim 1, characterized in that: The amount of the iron-containing waste hydrochloric acid solution added in step S1 is 10% to 80% of the volume of the electrolytic cell.

6. The method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid according to claim 1, characterized in that: The neutralizing agent described in step S2 includes one or more of calcium hydroxide, calcium oxide, calcium bicarbonate, calcium dihydrogen carbonate, calcium carbonate, calcium sulfate, and calcium bisulfate.

7. The method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid according to claim 1, characterized in that: The voltage of the electrolysis reaction described in step S3 is 1-200 V, the pH value is 8-13, the temperature is 20-90 ° C, and the duration is 0.5-5 h.

8. The method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid according to claim 1, characterized in that: The oxidative intermediates include hypochlorite, persulfate and / or hydrogen peroxide.

9. The method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid according to claim 1, characterized in that: In step S3, the amount of electrons generated during the electrolysis process is 1.5 to 5 times the amount of ferrous ions.

10. The method for preparing iron oxide and calcium chloride by electrochemically recovering iron-containing waste hydrochloric acid according to claim 1, characterized in that: The amount of water added in step S4 is 0.5 to 100 times the volume of the reactants; the iron oxide in step S4 is one or both of ferroferric oxide and ferrous oxide.