Preparation method of electrode material for electrically-controlled bromine extraction of sea brine

Abstract

The invention belongs to the technical field of electrochemical separation, and discloses a preparation method of an electrode material for electrically controlling bromine extraction from sea brine. The method comprises the following steps: synthesizing SrBiO2Br nanosheets through a hydrothermal reaction, dispersing the SrBiO2Br nanosheets in a polar solvent, adding a pyrrole monomer, and carrying out in-situ chemical oxidation polymerization by using bromine water under an ice bath condition to prepare a SrBiO2Br coated PPy electrode material with a uniform PPy coating layer; and then, mixing the electrode material with conductive carbon black and a binder, coating the mixture on a conductive substrate, and drying to obtain the composite electrode. The composite electrode has high bromine ion adsorption capacity, high selectivity, excellent cycle stability and reusability, is used for electrically-controlled bromine extraction from sea brine, and is mild in preparation process and free of secondary pollution.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion separation and recovery, specifically to the technical field of electrochemical separation, and particularly relates to a method for preparing an electrode material for electrically controlled bromine extraction from sea brine. Background Art

[0002] Bromine, a key chemical raw material, is widely used in industries such as pharmaceuticals, pesticides, and rubber. Most of it exists in the form of bromide ions in liquid mineral resources such as seawater and brine. Currently, commonly used bromine extraction methods, such as air extraction, steam distillation, resin adsorption, and membrane separation, suffer from high energy consumption, poor selectivity, and secondary pollution. Electronically controlled ion exchange (ESIX) technology utilizes electrochemical methods to achieve targeted adsorption and release of target ions, offering advantages such as high selectivity and environmental friendliness.

[0003] In recent years, studies on the construction of composite membrane electrodes based on BiOBr and conductive polymers (such as polypyrrole, PPy) have shown that the use of layered structure and imprinting effect can significantly improve the material's Br - The adsorption rate and capacity of BiOBr composite electrodes are good. However, traditional BiOBr composite electrodes have problems such as insufficient conductivity and poor cycle stability. For example, Chinese patent CN117845270A discloses a BiOBr / PPy-Br composite membrane electrode for electro-controlled bromine extraction from concentrated seawater and its preparation method. The patent uses a hydrothermal method to prepare BiOBr nanosheets, and performs an intercalation reaction under the action of formamide. The pyrrole monomer is intercalated and polymerized by an in-situ chemical oxidation method to form an imprinted Br - While this method improves the poor conductivity and low stability of traditional inorganic electroactive materials to some extent, it still has the following shortcomings: First, the low conductivity of BiOBr itself limits the overall electrochemical performance of the composite membrane; second, while achieving high adsorption capacity, the in situ intercalation reaction often significantly reduces the adsorption rate; and third, the composite membrane suffers from dissolution during repeated cycles, resulting in insufficient long-term stability.

[0004] Therefore, it is necessary to develop an electrode material and a composite electrode thereof so that it has Br - It has high adsorption capacity and excellent conductivity, bromide ion adsorption rate and cycle stability. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention provides a method for preparing an electrode material for electrically controlled bromine extraction from sea brine. BiOBr is modified with Sr and the in-situ chemical oxidation process is optimized to prepare an electrode material. The electrode material is used to prepare a composite electrode with high bromide ion adsorption capacity, high selectivity and excellent cycle stability, which is used for electrically controlled bromine extraction from sea brine. The preparation process is mild and has no secondary pollution.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A first aspect of the present invention provides a method for preparing an electrode material for electrically controlled bromine extraction from sea brine, comprising the following steps:

[0008] (1) Hydrothermal synthesis of SrBiO2Br nanosheets:

[0009] Bi(NO3)3·5H2O and bromine salt in equal molar ratios were dissolved in ultrapure water, and the pH was adjusted to 5.5-6.5 after ultrasonic stirring to obtain a mixed solution. The mixed solution was placed in a polytetrafluoroethylene-lined stainless steel autoclave, and the temperature was increased to 155-165°C at a heating rate of 3-6°C / min and kept constant for 20-28 hours. The dried product was filtered, washed, and dried to obtain a dry product. The dried product and SrCO3 in a molar ratio of 1:1 were fully mixed and calcined at 650-750°C to obtain SrBiO2Br nanosheets.

[0010] (2) Intercalation reaction of SrBiO2Br nanosheets:

[0011] The SrBiO2Br nanosheets obtained in step (1) are dispersed in a polar solvent and homogenized by ultrasonication to form a uniform SrBiO2Br dispersion. Pyrrole (Py) monomer is then added, and an oxidant is added dropwise. The reaction is stirred in an ice bath at 2 to 5°C for 10 to 14 hours. The pyrrole monomer is in situ polymerized on the surface of the SrBiO2Br nanosheet to form a PPy (polypyrrole) layer. At the same time, bromide ions enter the polymer as a dopant. The SrBiO2Br@PPy electrode material is obtained by filtration, washing, and vacuum drying.

[0012] Furthermore, the concentrations of Bi(NO3)3 and bromine salt in the mixed solution of step (1) are both 0.1-0.2 mol / L.

[0013] Furthermore, in step (2), the ratio of the mass of the SrBiO2Br nanosheets, the volume of the polar solvent, and the mass of the pyrrole monomer is 0.5-1 g: 40-60 ml: 0.1-0.2 g.

[0014] Furthermore, the bromide salt is KBr or NaBr, and the polar solvent is formamide or N-methylpyrrolidone.

[0015] Furthermore, in step (2), the ratio of the volume of the oxidant to the mass of the pyrrole monomer is 20-30 ml: 0.1-0.2 g, and the oxidant is a FeCl2 solution with a concentration of 0.3-0.5 mol / L.

[0016] Furthermore, in step (2), the power of ultrasound is 200-500W, and the time is 20-120 minutes.

[0017] Furthermore, the stirring rate in step (2) is 100 to 300 r / min.

[0018] Furthermore, the washing in step (2) uses ultrapure water or ethanol, and the ultrapure water washing is performed 5 to 8 times, and the ethanol washing is performed 5 to 8 times.

[0019] The second aspect of the present invention provides a SrBiO2Br@PPy electrode material for electrically controlled bromine extraction from sea brine, which is prepared by the above-mentioned preparation method and is composed of a composite of layered SrBiO2Br nanosheets and a uniform polypyrrole (PPy) conductive layer generated by in situ polymerization on their surface, and has a sheet-like or block-like stacked morphology.

[0020] The third aspect of the present invention provides a SrBiO2Br@PPy composite electrode prepared from the SrBiO2Br@PPy electrode material.

[0021] Furthermore, the preparation method of the SrBiO2Br@PPy composite electrode includes: mixing the SrBiO2Br@PPy electrode material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 8:1:1 to 4:1:1, adding N-methylpyrrolidone (NMP) to form a slurry, grinding and coating it on a conductive substrate, and then vacuum drying at 55 to 65°C for 20 to 30 hours to obtain a SrBiO2Br@PPy composite electrode.

[0022] Furthermore, the conductive substrate is one of stainless steel mesh, titanium mesh, graphite plate, and carbon plate.

[0023] The fourth aspect of the present invention provides a SrBiO2Br@PPy composite electrode at a concentration of 50 to 500 mg·g -1 The application of electric controlled bromine extraction from sea brine.

[0024] Furthermore, the SrBiO2Br@PPy composite electrode was used for electrically controlled bromine extraction, and Br - The reversible adsorption and release of the electrode has an adsorption capacity of 80 to 130 mg·g -1 range, and in Br - Separation factors of 9 to 15 and 7 to 10 can be achieved for the separation of Cl- and Mg-, respectively. After adsorption, the composite electrode can be regenerated in situ by applying a reverse potential. During repeated adsorption-release cycles, the electrode material dissolution rate is less than 5%, ensuring long-term stability and reusability.

[0025] Furthermore, in the preparation of the composite electrode, an appropriate amount of a second conductive polymer or an interfacial modifier may be selected to copolymerize or modify the PPy layer to further improve the conductivity and structural stability of the electrode.

[0026] Furthermore, the composite electrode can be applied to Br in sea brine under continuous industrial operation conditions. - It can achieve efficient electric-controlled extraction and can be mass-produced through modular electrode assemblies.

[0027] Furthermore, the process parameters such as the hydrothermal reaction, in-situ chemical oxidation and coating drying can be optimized and adjusted according to the target bromine extraction efficiency and actual operating conditions to adapt to different concentrations of Br in seawater. - extraction requirements.

[0028] The advantages and beneficial effects of the present invention are:

[0029] (1) The present invention utilizes Sr modification to regulate the BiOBr interlayer structure, providing more active sites. The PPy layer is uniformly covered on the surface of the SrBiO2Br nanosheets in the form of in situ polymerization. Bromide ions enter the polymer and the interlayer as dopants, and the PPy layer is tightly bound to the SrBiO2Br layer. The prepared SrBiO2Br@PPy electrode material has excellent conductivity and electrochemical activity, and significantly improves the bromide ion adsorption rate.

[0030] (2) The SrBiO2Br@PPy composite electrode prepared by the present invention using SrBiO2Br@PPy electrode material has a high Br - Adsorption capacity (up to 80-130 mg g -1 ) and high selectivity, when used for electro-controlled bromine extraction from sea brine, the electrode still maintains low dissolution loss in multiple adsorption and desorption cycles, ensuring Br - It has high adsorption capacity and excellent conductivity and cycle stability, achieving the goal of Br - Highly efficient and selective extraction.

[0031] (3) The preparation process of the present invention is mild and simple, and no additional chemical reagents are added, resulting in no secondary pollution, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Characterization diagram of the morphology and elemental composition of the SrBiO2Br@PPy electrode material prepared in Example 1, where: (a) is a scanning electron microscope (SEM) photograph; (b) is the overall scanning result of the energy dispersive spectroscopy (EDS); (c) to (g) are surface distribution diagrams of C, N, Br, Sr, and Bi elements on the surface or cross-section of the material, respectively.

[0033] Figure 2The crystal structure and functional group characterization diagram of the SrBiO2Br@PPy electrode material prepared in Example 1, wherein: (a) is the X-ray diffraction (XRD) spectrum; (b) is the Fourier transform infrared spectroscopy (FTIR) spectrum.

[0034] Figure 3 The test results of the cycle stability and material dissolution of the SrBiO2Br@PPy composite electrode prepared in Example 2 during the electrochemical bromine extraction process are shown in the figure below. The left side shows the specific capacity (mAh·g) of the electrode as the number of cycles increases. -1 ) over time and the corresponding Coulombic efficiency (%) curve; on the right is the material dissolution rate test result diagram.

[0035] Figure 4 This is the adsorption of different bromine-chlorine ratios of the SrBiO2Br@PPy composite electrode prepared in Example 4. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0037] Example 1: Preparation of SrBiO2Br@PPy electrode material

[0038] A method for preparing a SrBiO2Br@PPy electrode material for electrically controlled bromine extraction from sea brine comprises the following steps:

[0039] (1) Synthesis of SrBiO2Br nanosheets:

[0040] 1.94 g Bi(NO3)3·5H2O and 0.476 g KBr were dissolved in 60 mL of ultrapure water. After ultrasonic stirring, the pH was adjusted to 6 with NaOH and HNO3 to obtain a mixed solution. The mixed solution was placed in a polytetrafluoroethylene-lined stainless steel autoclave, heated to 160°C at a heating rate of 5°C / min and kept at this temperature for 24 h. The mixture was filtered, washed with water and ethanol, and dried at 60°C to obtain a dry product. The dry product and SrCO3 at a molar ratio of 1:1 were fully mixed and calcined at 700°C to obtain SrBiO2Br nanosheets.

[0041] (2) Intercalation reaction of SrBiO2Br nanosheets:

[0042] 0.76 g of SrBiO2Br nanosheets obtained in step (1) were dispersed in 50 mL of water and ultrasonically stirred at a power of 400 W for 60 min to form a uniform SrBiO2Br dispersion. 0.17 g of pyrrole (Py) monomer was then added, and 25 mL of 0.4 mol / LFeCl2 solution was added dropwise. The mixture was stirred in an ice bath at 5°C for 10 to 14 h at a stirring rate of 200 r / min. The pyrrole monomer was in situ polymerized on the surface of the SrBiO2Br nanosheet to form a PPy (polypyrrole) layer. At the same time, bromide ions entered the polymer as a dopant. The mixture was filtered, washed with ultrapure water 5 times, and vacuum dried to obtain a SrBiO2Br@PPy electrode material.

[0043] The morphology and elemental composition of the SrBiO2Br@PPy electrode material prepared in Example 1 were characterized. Figure 1 As shown, (a) is a scanning electron microscope (SEM) photo, showing that the material has a flake or block stacking morphology; (b) is the overall scanning result of the energy dispersive spectrum (EDS), showing the characteristic peaks of the main elements Bi, Br, Sr, C, N, etc.; (c) to (g) are the surface distribution diagrams of C, N, Br, Sr, and Bi elements on the surface or cross-section of the material, respectively, indicating that each element is evenly dispersed in the electrode material, verifying the close combination of PPy and SrBiO2Br and the presence of bromine in the material.

[0044] The crystal structure and functional groups of SrBiO2Br@PPy electrode materials were characterized, such as Figure 2 As shown, (a) is an X-ray diffraction (XRD) pattern, showing the comparison of diffraction peaks of BiOBr, SrCO3, SrBiO2Br and SrBiO2Br@PPy electrode materials. It can be seen that after the introduction of Sr element and composite PPy, the main diffraction characteristic peaks of SrBiO2Br are still retained, and at the same time, moderate peak broadening or intensity changes occur, indicating the effective combination of PPy and the inorganic phase; (b) is a Fourier transform infrared spectrum (FTIR) spectrum, which compares the absorption peak changes of SrBiO2Br, PPy and SrBiO2Br@PPy, verifying the simultaneous existence of PPy characteristic functional groups (N–H, C=C, C–N, etc.) and SrBiO2Br related vibration peaks, indicating that the electrode material structure of the present invention has been successfully formed.

[0045] Example 2

[0046] A method for preparing a SrBiO2Br@PPy electrode material for electrically controlled bromine extraction from sea brine comprises the following steps:

[0047] (1) Synthesis of SrBiO2Br nanosheets:

[0048] 0.97 g Bi(NO3)3·5H2O and 0.238 g KBr were dissolved in 30 mL of ultrapure water. After ultrasonic stirring, the pH was adjusted to 6 with NaOH and HNO3 to obtain a mixed solution. The mixed solution was placed in a polytetrafluoroethylene-lined stainless steel autoclave, heated to 160°C at a heating rate of 5°C / min and kept at this temperature for 24 h. The mixture was filtered, washed with water and ethanol, and dried at 60°C to obtain a dry product. The dry product and SrCO3 at a molar ratio of 1:1 were fully mixed and calcined at 720°C to obtain SrBiO2Br nanosheets.

[0049] (2) Intercalation reaction of SrBiO2Br nanosheets:

[0050] 0.76 g of SrBiO2Br nanosheets obtained in step (1) were dispersed in 50 mL of water and ultrasonically stirred at a power of 400 W for 60 min to form a uniform SrBiO2Br dispersion. 0.17 g of pyrrole (Py) monomer was then added, and 25 mL of 0.4 mol / LFeCl2 solution was added dropwise. The mixture was stirred in an ice bath at 5°C for 10 h at a stirring rate of 200 r / min. The pyrrole monomer was in situ polymerized on the surface of the SrBiO2Br nanosheet to form a PPy (polypyrrole) layer. At the same time, bromide ions entered the polymer as a dopant. The mixture was filtered, washed with ultrapure water 8 times, and vacuum dried to obtain a SrBiO2Br@PPy electrode material.

[0051] Example 3

[0052] A method for preparing a SrBiO2Br@PPy electrode material for electrically controlled bromine extraction from sea brine comprises the following steps:

[0053] (1) Synthesis of SrBiO2Br nanosheets:

[0054] 1.46 g Bi(NO3)3·5H2O and 0.357 g KBr were dissolved in 40 mL of ultrapure water. After ultrasonic stirring, the pH was adjusted to 6 with NaOH and HNO3 to obtain a mixed solution. The mixed solution was placed in a polytetrafluoroethylene-lined stainless steel autoclave, heated to 160°C at a heating rate of 6°C / min and kept at this temperature for 24 h. The mixture was filtered, washed with water and ethanol, and dried at 60°C to obtain a dry product. The dry product and SrCO3 at a molar ratio of 1:1 were fully mixed and calcined at 700°C to obtain SrBiO2Br nanosheets.

[0055] (2) Intercalation reaction of SrBiO2Br nanosheets:

[0056] 0.76 g of SrBiO2Br nanosheets obtained in step (1) was dispersed in 50 mL of water and ultrasonically stirred at a power of 400 W for 60 min to form a uniform SrBiO2Br dispersion. Then, 0.17 g of pyrrole (Py) monomer was added, and 25 mL of 0.4 mol / LFeCl2 solution was added dropwise. The mixture was stirred in an ice bath at 3°C ​​for 14 h at a stirring rate of 300 r / min. The pyrrole monomer was in situ polymerized on the surface of the SrBiO2Br nanosheet to form a PPy (polypyrrole) layer. At the same time, bromide ions entered the polymer as a dopant. The mixture was filtered, washed with ultrapure water 5 times, and vacuum dried to obtain a SrBiO2Br@PPy electrode material.

[0057] Examples 4-6: Preparation of SrBiO2Br@PPy composite electrodes

[0058] A method for preparing a SrBiO2Br@PPy composite electrode comprises: mixing the SrBiO2Br@PPy electrode materials prepared in Examples 1 to 3 with conductive carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1, adding 0.975 mL of N-methylpyrrolidone (NMP) to form a slurry, grinding the mixture, coating the slurry on a graphite plate by a direct coating method, and then vacuum drying the mixture at 60°C for 24 hours to obtain a SrBiO2Br@PPy composite electrode.

[0059] Adsorption performance test

[0060] The SrBiO2Br@PPy composite electrodes prepared in Examples 4 to 6 were used to prepare the electrodes with an initial bromide ion concentration of 100 mg·g -1 The adsorption performance of the brine was tested using a 0.9 V adsorption voltage and a 300 min adsorption time. The bromide ion concentration in the sample was measured and the adsorption capacity was calculated. The results are shown in Table 1.

[0061] Table 1 Adsorption performance test of SrBiO2Br@PPy composite electrodes prepared in Examples 4 to 6

[0062]

[0063] According to the data in Table 1, it can be seen that under the synthesis conditions of small doses and different raw material configuration ratios, Example 4 has better results, which proves that the raw materials have a higher reaction degree under this ratio condition.

[0064] The SrBiO2Br@PPy composite electrode prepared in Example 4 was used for electrically controlled bromine extraction, and Br - The reversible adsorption and release of the electrode has an adsorption capacity of 80 to 130 mg·g -1 range, and in Br -Separation factors of 9 to 15 and 7 to 10 can be achieved in the separation of / Cl-, respectively. Figure 4 shown.

[0065] The cycle stability and material dissolution loss of the SrBiO2Br@PPy composite electrode prepared in Example 3 were tested during the electrochemical bromine extraction process. Figure 3 As shown in the figure below, the specific capacity of the electrode changes with time as the number of cycles increases, and the corresponding Coulomb efficiency curve. It can be seen that the specific capacity of the electrode remains at the original level after 10 cycles, and the specific capacity of the electrode remains at 90 mAh g after 30 cycles. -1 This indicates that the SrBiO2Br@PPy composite electrode prepared in this invention has good cycling stability and maintains excellent Coulombic efficiency after multiple charge and discharge cycles. This is because the introduction of doped metal Sr improves the overall conductivity of the material and optimizes its electrochemical activity.

[0066] Figure 3 The middle right figure shows the electrode material dissolution rate test results, comparing the dissolution of key elements such as Bi and Sr in the electrode after cycling. The dissolution rate is low and the material retention rate is high. After adsorption, the composite electrode is regenerated in situ by applying a reverse potential. During repeated adsorption-release cycles, the electrode material dissolution rate is less than 5%, thereby ensuring long-term stability and reusability. It proves that the electrode of the present invention has good stability and reusability in multiple adsorption and desorption cycles. These characteristics are due to the fact that after Sr doping modification, the overall stability of the material is improved and the bond energy of each chemical bond in the crystal is increased. After Sr modification, elements such as Bi have a lower electrostatic potential, while the Br element also has a higher electrostatic potential. The two work together to make the bond more stable. The electrostatic potential of a single atom of SrBiO2Br is shown in Table 2, and the electrostatic potential of a single atom of BiOBr is shown in Table 3.

[0067] Table 2 Electrostatic potential of a single SrBiO2Br atom

[0068]

[0069] Table 3 Electrostatic potential of a single BiOBr atom

[0070]

[0071] In summary, the SrBiO2Br@PPy composite electrode prepared in this invention demonstrates its preparation method, material structure, and excellent performance in electrochemical bromine extraction applications. The electrode exhibits high adsorption capacity, good selectivity, and cyclic stability for bromide ions in high-salt solutions, providing a viable technical route for the efficient recovery of bromine from seawater or brine resources.

[0072] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an electrode material for electrically controlled bromine extraction from sea brine, characterized in that: The following steps are involved: (1) Synthesis of SrBiO2Br nanosheets by hydrothermal method: Bi(NO3)3·5H2O and bromine salt in equal molar ratios were dissolved in ultrapure water, and the pH was adjusted to 5.5-6.5 after ultrasonic stirring to obtain a mixed solution. The mixed solution was placed in a stainless steel autoclave, heated to 155-165°C, and reacted at this temperature for 20-28 hours. The dried product was filtered, washed, and dried to obtain a dry product. The dried product and SrCO3 in a molar ratio of 1:1 were fully mixed and calcined at 650-750°C to obtain SrBiO2Br nanosheets. (2) Intercalation reaction of SrBiO2Br nanosheets: The SrBiO2Br nanosheets obtained in step (1) are dispersed in a polar solvent by ultrasonication to form a uniform SrBiO2Br dispersion, and then pyrrole monomer is added, and then an oxidant is added dropwise. The reaction is stirred in an ice bath at 2-5°C for 10-14 hours, and the electrode material is filtered, washed and vacuum dried to obtain the electrode material.

2. The preparation method according to claim 1, characterized in that The concentrations of Bi(NO3)3 and bromine salt in the mixed solution of step (1) are both 0.1-0.2 mol / L.

3. The preparation method according to claim 1, characterized in that The ratio of the mass of the SrBiO2Br nanosheets, the volume of the polar solvent, and the mass of the pyrrole monomer in step (2) is 0.5-1 g: 40-60 ml: 0.1-0.2 g.

4. The preparation method according to claim 1, characterized in that The bromine salt is KBr or NaBr, and the polar solvent is formamide or N-methylpyrrolidone.

5. The preparation method according to claim 1, characterized in that The ratio of the volume of the oxidant to the mass of the pyrrole monomer in step (2) is 20-30 ml: 0.1-0.2 g, and the oxidant is a FeCl2 solution with a concentration of 0.3-0.5 mol / L.

6. An electrode material for electrically controlled bromine extraction from sea brine, characterized in that: The electrode material is prepared by the preparation method according to any one of claims 1 to 5, wherein the electrode material is composed of a composite of layered SrBiO2Br nanosheets and a uniform polypyrrole conductive layer generated by in-situ polymerization on its surface, and has a sheet-like or block-like stacking morphology.

7. A composite electrode prepared using the electrode material according to claim 6.

8. The composite electrode according to claim 7, characterized in that The preparation method is as follows: the electrode material, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1 to 4:1:1, and N-methylpyrrolidone is added to form a slurry, which is then coated on a conductive substrate after grinding, and then vacuum dried at 55 to 65°C for 20 to 30 hours to obtain a composite electrode.

9. The composite electrode according to claim 8, characterized in that The conductive substrate is one of stainless steel mesh, titanium mesh, graphite plate and carbon plate.

10. The composite electrode according to any one of claims 7 to 9 is used in sea brine with a bromine content of 50 to 500 mg·g -1 Electronically controlled bromine extraction.

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