Reaction system for producing high-purity solid ferric chloride

Abstract

A reaction system for producing high-purity solid ferric chloride comprises a crystallization reactor, a solid-liquid separator, a crystallization filter and a circulation reactor which are sequentially arranged, and is technically characterized in that a first feeding end of the crystallization reactor is communicated with a feeding pipe of waste acid liquid containing FeCl2, and a second feeding end of the crystallization reactor is communicated with a hydrogen chloride gas pipeline; a first discharge end at the top is communicated with a tail gas absorption pipeline, and a second discharge end at the top is communicated with a feed end of the solid-liquid separator; the solid-liquid separator is further provided with a first liquid outlet end and a second liquid outlet end which are used for being communicated with the acid liquid recycling pipeline and the first feeding end of the crystallization filter respectively. The method has the advantages of simple process, low preparation threshold, environmental protection and the like.

Description

Technical Field

[0001] The invention relates to a harmless recovery method of iron ions and chloride ions in waste acid liquid, in particular to a reaction system for producing high-purity solid ferric chloride. Background Art

[0002] Whether it is the pickling waste liquid discharged by the steel industry or the electroplating industry, it has the characteristics of high iron ion concentration, high acid concentration, high corrosiveness, and high environmental pollution. At present, it has been managed as hazardous waste by various countries. The United States has included it in the "Resource Conservation and Regeneration Act", and my country has also included it in the "National Hazardous Waste List". The main hazards caused by the illegal discharge of pickling waste liquid are: corrosion of sewer pipes and hydraulic structures such as reinforced concrete; causing crops to wither and affect the growth of aquatic crops; pickling waste liquid seeps into the soil, which will cause soil calcification over time, destroy the loose state of the soil layer, and thus affect the growth of crops; it can poison fish; drinking contaminated water by humans and animals can cause gastrointestinal inflammation or even burns; the pollution caused to water bodies, toxicity to organisms, and even the ultimate harm to human health are very huge. According to national environmental protection regulations, pickling waste liquid is not allowed to be discharged directly, but the output of such pickling waste liquid in my country is astonishing, and the phenomenon of illegal discharge has been repeatedly banned.

[0003] There are many methods for treating steel pickling waste liquid at home and abroad. It is necessary to select appropriate treatment technologies based on the specific characteristics of different pickling waste liquids and the conditions of the acid-related enterprises themselves. At present, the commonly used pickling waste liquid treatment technologies mainly include: neutralization precipitation method, direct roasting method, evaporation crystallization method, ion exchange resin method, membrane separation method, extraction method, chemical conversion method, etc. However, these treatment methods are targeted at the components in the pickling waste liquid, and are not convenient for large-scale application in the resource recovery and utilization of hydrochloric acid pickling waste liquid of steel products. Summary of the invention

[0004] The purpose of the present invention is to provide a reaction system for producing high-purity solid ferric chloride, which fundamentally solves the above problems and has the advantages of simple process, low preparation threshold, green and environmental protection, etc.

[0005] To achieve the above object, the present invention provides the following technical solution: The reaction system for producing high-purity solid ferric chloride comprises a crystallization reactor, a solid-liquid separator, a crystallization filter, and a circulation reactor which are arranged in sequence, and the technical key points are: The first feed end of the crystallization reactor is connected to the feed pipe of the waste acid solution containing FeCl2, the second feed end is connected to the hydrogen chloride gas pipeline, the first discharge end at the top is connected to the tail gas absorption pipeline, and the second discharge end at the top is connected to the feed end of the solid-liquid separator; The solid-liquid separator is also provided with a first liquid outlet and a second liquid outlet, which are respectively used to connect to the acid recovery pipeline and the first feed end of the crystallization filter; The crystallization filter is divided into a crystal zone and a liquid zone by a perforated plate, the crystal zone is connected to the second liquid outlet end of the solid-liquid separator through a first feed end, the liquid zone is connected to the chlorine pipeline through a second feed end provided with an air inlet grid, the discharge end of the liquid zone is connected to the first feed end of the ejector through a centrifugal pump, the second feed end of the ejector is connected to the chlorine pipeline, and the discharge end of the ejector is connected to the feed end at the top of the circulation reactor; The first discharge end at the top of the circulation reactor is connected to the tail gas absorption pipeline, the second discharge end at the bottom of the circulation reactor is connected to the third feed end of the ejector, and the third discharge end at the bottom of the circulation reactor is connected to the feed end of the solid-state machine.

[0006] Another object of the present invention is to provide a method for preparing high-purity solid ferric chloride using the above reaction system, the technical main points of which are as follows: Step S1, under stirring conditions of 30r~50r / min, the supernatant of the waste acid solution with a FeCl2 content of ≥15wt% after complete precipitation is introduced into the crystallization reactor through the first feed end thereof; Step S2, introducing hydrogen chloride gas into the crystallization reactor through the second feed end thereof, and reacting the mixture for more than 50 minutes under the conditions of 20-25° C. and a pressure of 0.1-0.12 MPa; Step S3, when the hydrogen chloride in the crystallization reactor is ≥20wt% and crystals are precipitated, the reaction is considered as the end point, the solid-liquid mixture in the crystallization reactor is passed into a solid-liquid separator through the discharge end at the bottom thereof, and FeCl2·4H2O is separated for standby use; Step S4, placing the separated FeCl2·4H2O crystals on the perforated plate of the crystallization filter, and introducing chlorine gas of more than 99 wt% through the air inlet grid of the liquid zone, so that the FeCl2·4H2O in the crystal zone is liquefied and then enters the liquid zone; Step S5, passing the liquefied FeCl2·4H2O into the first feed end of the ejector (0.10-0.12 MPa, 0.5 m 3 / min), 99wt% or more chlorine gas (0.10-0.12MPa) is continuously introduced into the second feed end or air inlet of the ejector, and the discharge end of the ejector passes the partially reacted FeCl2 mixture into the liquid level below the circulating reactor through the feed end of the circulating reactor, and the reaction is circulated at 70℃-90℃ until FeCl2<0.1wt% is the reaction end point; Step S6, naturally cooling to 40°C, sending the liquid from the reaction container to a solid state machine through a pipeline to be converted into particles with a diameter of 5-10 mm, thereby obtaining solid FeCl3·6H2O.

[0007] Beneficial effects of the present invention: In terms of the overall technical solution, the present invention replaces the evaporation concentration of the existing crystallization process of waste hydrochloric acid solution for steel washing with a hydrogen chloride method, so that the iron ions in the waste acid solution of a certain concentration are precipitated as high-purity ferrous chloride crystals, and then the ferrous chloride is fully reacted with chlorine oxidation in a chlorine atmosphere to generate ferric chloride.

[0008] In summary, the present invention does not require heating and concentration processes, saves time and effort, has high safety, does not require waste disposal, and meets environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0010] The specific contents of the present invention are described in detail below through specific embodiments.

[0011] The following combination Figure 1 The specific content of the present invention is described in detail through specific embodiments. The preparation method of high-purity solid ferric chloride mainly undergoes the following reactions.

[0012] FeCl2·4H2O + HCl↑ (excess HCl gas) → FeCl2·4H2O (crystal precipitation) Formula (1) 2FeCl2+ Cl2 (excess gas) → 2 FeCl3 Formula (2) FeCl3+ 6H2O + Cl - (Excess Cl2 gas) → FeCl3·6H2O (crystal precipitation) Formula (3) Example 1

[0013] The preparation method of high-purity solid ferric chloride comprises the following steps: Step S1, under the stirring condition of 50r / min, 2m 3 The supernatant of the spent acid solution with a FeCl2 content of ≥20 wt% after complete precipitation for 10 h is introduced into the crystallization reactor through the first feed end thereof; Step S2, introducing hydrogen chloride gas into the crystallization reactor through the second feed end thereof, and fully reacting for more than 70 minutes under the conditions of 20-25° C. and 0.1-0.12 MPa; Step S3, when the hydrogen chloride in the crystallization reactor is ≥30wt% and no more crystals are precipitated, the reaction is considered as the end point, the solid-liquid mixture in the crystallization reactor is passed through the discharge end at the bottom thereof into a solid-liquid separator (e.g., a centrifuge), and FeCl2·4H2O is separated for later use; Step S4, placing the separated FeCl2·4H2O crystals on the perforated plate of the crystallization filter, and introducing chlorine gas of more than 99 wt% through the air inlet grid of the liquid zone, so that the FeCl2·4H2O in the crystal zone is liquefied and then enters the liquid zone; Step S5, the liquefied FeCl2·4H2O is introduced into the first feed end of the ejector (0.10 MPa, 0.5 m 3 / min), 99wt% or more chlorine gas (0.08~0.1MPa) is continuously introduced into the second feed end or air inlet of the ejector, and the discharge end of the ejector passes the partially reacted FeCl2 mixture into the liquid level below the circulation reactor through the feed end of the circulation reactor, and the reaction is circulated at 70℃~80℃ until FeCl2<0.1wt% is the reaction end point; Step S6, naturally cool to 40°C, take out the liquid from the reaction vessel, and send it to a solidification machine to obtain 1440 kg of solid FeCl3·6H2O (content Fe 3+ mass fraction ≥ 20%). Example 2

[0014] The preparation method of high-purity solid ferric chloride comprises the following steps: Step S1, under the stirring condition of 40r / min, 2m 3 The supernatant of the spent acid solution with a FeCl2 content of ≥18 wt% after complete precipitation for 10 h is introduced into the crystallization reactor through the first feed end thereof; Step S2, introducing hydrogen chloride gas into the crystallization reactor through the second feed end thereof, and fully reacting for more than 60 minutes under the conditions of 20-25° C. and 0.1-0.11 MPa; Step S3, when the hydrogen chloride in the crystallization reactor is ≥25wt% and no more crystals are precipitated, the reaction is considered as the end point, the solid-liquid mixture in the crystallization reactor is passed through the discharge end at the bottom thereof into a solid-liquid separator (e.g., a centrifuge), and FeCl2·4H2O is separated for later use; Step S4, placing the separated FeCl2·4H2O crystals on the perforated plate of the crystallization filter, and introducing chlorine gas of more than 99 wt% through the air inlet grid of the liquid zone, so that the FeCl2·4H2O in the crystal zone is liquefied and then enters the liquid zone; Step S5, the liquefied FeCl2·4H2O is introduced into the first feed end of the ejector (0.10 MPa, 0.5 m 3 / min), 99wt% or more chlorine gas (0.08~0.1MPa) is continuously introduced into the second feed end or air inlet of the ejector, and the discharge end of the ejector passes the partially reacted FeCl2 mixture into the liquid level below the circulation reactor through the feed end of the circulation reactor, and the reaction is circulated at 70℃~80℃ until FeCl2<0.1wt% is the reaction end point; Step S6, naturally cool to 40°C, take out the liquid from the reaction vessel, and send it to a solid state machine to obtain 1390 kg of solid FeCl3·6H2O (content Fe 3+ mass fraction ≥ 20%). Example 3

[0015] The preparation method of high-purity solid ferric chloride comprises the following steps: Step S1: 2 m 3 The supernatant of the spent acid solution with a FeCl2 content of ≥15 wt% after complete precipitation for 10 hours is introduced into the crystallization reactor through the first feed end thereof; Step S2, introducing hydrogen chloride gas into the crystallization reactor through the second feed end thereof, and reacting the mixture under the conditions of 20-25° C. and 0.1-0.11 MPa for more than 50 minutes; Step S3, when the hydrogen chloride in the crystallization reactor is ≥20wt% and no more crystals are precipitated, the reaction is considered as the end point, the solid-liquid mixture in the crystallization reactor is passed through the discharge end at the bottom thereof into a solid-liquid separator (e.g., a centrifuge), and FeCl2·4H2O is separated for later use; Step S4, placing the separated FeCl2·4H2O crystals on the perforated plate of the crystallization filter, and introducing chlorine gas of more than 99 wt% through the air inlet grid of the liquid zone, so that the FeCl2·4H2O in the crystal zone is liquefied and then enters the liquid zone; Step S5, passing the liquefied FeCl2·4H2O into the first feed end of the ejector (0.12 MPa, 0.5 m 3 / min), 99wt% or more chlorine gas (0.08~0.1MPa) is continuously introduced into the second feed end or air inlet of the ejector, and the discharge end of the ejector passes the partially reacted FeCl2 mixture into the liquid level below the circulating reactor through the feed end of the circulating reactor, and the reaction is circulated at 80℃~85℃ until FeCl2<0.1wt% is the reaction end point; Step S6, naturally cool to 40°C, take out the liquid from the reaction vessel, and send it to a solidification machine to obtain 1340 kg of solid FeCl3·6H2O (content Fe 3+ mass fraction ≥ 20%).

[0016] Regarding the preparation of chlorine in the examples, a review of research on chlorine purification technology mentions the chlorine distillation purification process disclosed in domestic and foreign patents.

[0017] Regarding the industrial preparation method of high-purity hydrogen chloride in step S2 of the embodiment, reference may be made to the technical solution disclosed by Dou Minghong et al. in "Preparation of High-Purity Hydrogen Chloride Gas": hydrogen and chlorine enter the synthesis furnace according to a certain molecular ratio (slightly excessive hydrogen) after their respective treatment processes, wherein hydrogen enters the burner at the bottom of the synthesis furnace through a flame arrester, and chlorine enters the inner tube of the synthesis furnace lamp holder, and is evenly mixed with the hydrogen in the outer sleeve from bottom to top through the inclined holes on the lamp holder to burn, and the combustion flame temperature is as high as 2000 ° C (even as high as 2490 ° C). The synthesized hydrogen chloride gas is cooled by the cooling water of the synthesis furnace jacket, and the outlet temperature of the synthesis furnace is reduced to 400-600 ° C, and is naturally cooled to 100-150 ° C by an air cooler, and then cooled by a graphite cooler and a deep-cooled graphite cooler, and enters the acid mist separator to remove the acid mist.

[0018] Reference may also be made to the technical solution disclosed by Yang Xiaobo et al. in "A Review of Preparation Methods of High-Purity Hydrogen Chloride Gas": the Mannheim method of reacting concentrated sulfuric acid with an alkali metal or an alkaline earth metal.

[0019] Taking NaCl as an example, the process goes through two stages: NaCl+H2SO4→NaHSO4+HCl (1), NaCl+NaHSO4→Na2SO4+HCl (2).

[0020] The reaction takes place in the Mannheim furnace, reaction (1) takes place at about 150°C, and reaction (2) takes place at about 550-660°C. Replacing the raw material with KCl is the Mannheim process of potassium sulfate co-production of hydrogen chloride. Specifically, 98% concentrated sulfuric acid and potassium chloride are added to the Mannheim furnace at a reaction molar ratio of 2:1, and the temperature in the furnace reaches 500-600°C through indirect heating with dry gas. At this temperature, continuous stirring is performed to make the mixture evenly mixed and fully reacted.

[0021] The potassium sulfate generated by the reaction enters the closed cooler through the discharge port, and is packaged as a finished product after lime neutralization and crushing. The hydrogen chloride generated by the reaction is introduced into the absorption process by a fan. After cooling and impurity removal, it is contacted with the dilute hydrochloric acid (21%) from the desorption process to be absorbed as concentrated hydrochloric acid (35%). Part of the concentrated hydrochloric acid is used for washing, and most of it is contacted with the 120°C hydrogen chloride vapor generated by the reboiler at the top of the desorption tower for heat and mass transfer, desorbing the hydrogen chloride in the concentrated hydrochloric acid until the bottom of the tower reaches a constant boiling composition. The desorbed hydrogen chloride is then subjected to processes such as water removal and acid mist removal to produce high-purity hydrogen chloride with a purity of more than 99%.

[0022] In addition, Li Xiuhua et al. also disclosed in "Discussion on Hydrogen Chloride Production Process" the concentrated sulfuric acid extraction distillation method, CaCl2 Aqueous solution extraction breaking azeotrope and pressure swing distillation breaking azeotrope.

Claims

1. A reaction system for producing high-purity solid ferric chloride, comprising a crystallization reactor, a solid-liquid separator, a crystallization filter, and a circulation reactor arranged in sequence, characterized in that: The first feed end of the crystallization reactor is connected to the feed pipe of the waste acid solution containing FeCl2, the second feed end is connected to the hydrogen chloride gas pipeline, the first discharge end at the top is connected to the tail gas absorption pipeline, and the second discharge end at the top is connected to the feed end of the solid-liquid separator; The solid-liquid separator is also provided with a first liquid outlet and a second liquid outlet, which are respectively used to connect to the acid recovery pipeline and the first feed end of the crystallization filter; The crystallization filter is divided into a crystal zone and a liquid zone by a perforated plate, the crystal zone is connected to the second liquid outlet end of the solid-liquid separator through a first feed end, the liquid zone is connected to the chlorine pipeline through a second feed end provided with an air inlet grid, the discharge end of the liquid zone is connected to the first feed end of the ejector through a centrifugal pump, the second feed end of the ejector is connected to the chlorine pipeline, and the discharge end of the ejector is connected to the feed end at the top of the circulation reactor; The first discharge end at the top of the circulation reactor is connected to the tail gas absorption pipeline, the second discharge end at the bottom of the circulation reactor is connected to the third feed end of the ejector, and the third discharge end at the bottom of the circulation reactor is connected to the feed end of the solid-state machine.

2. A method for preparing high-purity solid ferric chloride using the reaction system of claim 1, characterized in that: The following steps are involved: Step S1, under stirring conditions of 30r~50r / min, the supernatant of the waste acid solution with a FeCl2 content of ≥15wt% after complete precipitation is introduced into the crystallization reactor through the first feed end thereof; Step S2, introducing hydrogen chloride gas into the crystallization reactor through the second feed end thereof, and reacting the mixture under the conditions of 20-25° C. and 0.1-0.11 MPa for more than 50 minutes; Step S3, when the hydrogen chloride in the crystallization reactor is ≥30wt% and no more crystals are precipitated, the reaction is considered as the end point, the solid-liquid mixture in the crystallization reactor is passed into a solid-liquid separator through the discharge end at the bottom thereof, and FeCl2·4H2O is separated for standby use; Step S4, placing the separated FeCl2·4H2O crystals on the perforated plate of the crystallization filter, and introducing chlorine gas of more than 99 wt% through the air inlet grid of the liquid zone, so that the FeCl2·4H2O in the crystal zone is liquefied and then enters the liquid zone; Step S5, passing the liquefied FeCl2·4H2O into the first feed end of the ejector (0.10-0.12 MPa, 0.5 m 3 / min), 99wt% or more chlorine gas (0.08~0.1MPa) is continuously introduced into the second feed end or air inlet of the ejector, and the discharge end of the ejector passes the partially reacted FeCl2 mixture into the liquid level below the circulation reactor through the feed end of the circulation reactor, and the reaction is circulated at 70℃~80℃ until FeCl2<0.1wt% is the reaction end point; Step S6, naturally cooling to 40°C, taking out the liquid from the reaction container and sending it into a solid state machine to obtain solid FeCl3·6H2O.

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