CN105784816A - Method for determining total iron concentration in Fe/Cr flow battery electrolyte - Google Patents
Method for determining total iron concentration in Fe/Cr flow battery electrolyte Download PDFInfo
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Abstract
The invention provides a method for determining total iron concentration in Fe/Cr flow battery electrolyte. Firstly, the influence of chromium ions on redox titration is eliminated through pretreatment, then all iron is converted into F2<2+>, titration is performed by using K2Cr2O7 standard solution, and determination of total concentration in electrolyte is completed according to a reaction quantitative relationship of Fe<2+> and K2Cr2O7 and blank experiment data; in addition, concentration of Fe<3+> can be further calculated according to the determined total iron concentration. The method avoids the influence of the chromium ions on iron concentration titration testing; colorful ions in solution are enabled not to influence the determination of Fe<3+> concentration, no special instrument is needed, and the obtained analysis result is accurate and reliable and can be used for evaluating the performance of Fe/Cr flow batteries.
Description
Technical field
The present invention relates to the detection method of a kind of total concentration of iron, particularly relate to the assay method of total concentration of iron in a kind of Fe/Cr fluid cell electrolyte.
Background technology
Electrochemistry flow battery (electrochemicalflowcell), referred to as flow battery, being generally also called redox flow batteries (flowredoxcell or redoxflowcell) is a kind of novel bulk electrochemical energy storage device.One as flow battery; Fe/Cr flow battery has the characteristic of following excellence: high efficiency, low cost, life-span length, fast response time, remarkable big electric current repid discharge ability, broad adaptive temperature scope, safety is good, non-pollutant discharge, design scale are changeable; can cushion, store the output of solar energy and wind energy; improve solar energy and the output stability of wind energy electric power, and application and electric energy peak clipping in the regenerative resource such as wind energy, solar energy, fill out the scale energy-storage systems such as paddy in illustrate very big advantage.
The both positive and negative polarity electrolyte of Fe/Cr flow battery is containing Fe3+/Fe2+、Cr3+/Cr2+The solution of hybrid ionic, it is not only conducting medium, realizes the electroactive material of energy storage especially, is Fe/Cr flow battery energy storage and the core of energy conversion.As conductive materials and electrolyte, in charge and discharge process, in its electrolyte, the concentration of the ion of different valence state directly affects the performance of this battery, so the iron concentration of different valence state is significant in Accurate Determining electrolyte.
According to the test in battery charge and discharge process, as long as measuring Fe3+/Fe2+Namely the concentration of ion is it can be inferred that the quality of this battery performance.Measure Fe3+The conventional method of concentration is spectrophotometer method, but, cannot accurately measure owing to electrolyte existing various interfering of ion color；Fe2+Concentration then can be measured accurately by potentiometric titrimeter-dichromate titration；If it follows that record the concentration of total ferrum in this electrolyte, then just can release Fe3+Concentration, thus determining whether the quality of battery performance.
In prior art, GB GB/T6730.65-2009, GB/T223.73-2008, GB6730.8-86 all achieve the mensuration of iron content, and principle is that the ferrum of different valence state in raw material is reduced into ferrous iron, then adopt potassium dichromate method to carry out redox titration；Wherein adopt the spectrophotometer method direct analysis Fe of routine3+Concentration, but, being as noted previously, as in this electrolyte interfering of various ion colors also cannot accurately measure.
Owing to, in Fe/Cr fluid cell electrolyte, there is also chromium ion, thus having had a strong impact on the redox titration that last employing potassium dichromate carries out；Further, the color of each ion existed in this electrolyte influences each other, and causes the Accurate Determining of total concentration of iron that prior art can not be adopted to complete in Fe/Cr fluid cell electrolyte；Therefore, in the practical application of Fe/Cr flow battery, it is necessary to a kind of effective detection method, for detecting the total concentration of iron in Fe/Cr fluid cell electrolyte exactly, and Fe is released further3+Concentration, thus finally judging the quality of battery performance.
Summary of the invention
In order to solve the above-mentioned technical problem existed in prior art, inventor intends the impact getting rid of chromium ion existing in Fe/Cr fluid cell electrolyte with assorted ion pair detection, it is intended to realizes the mensuration of total concentration of iron, and completes Fe3+The indirect determination of concentration.
First, a first aspect of the present invention, provide the assay method of total concentration of iron in a kind of Fe/Cr fluid cell electrolyte, the general thought of the method for must carry out pre-treatment before carrying out total determining iron concentration to this electrolyte to be measured, then complete to measure by titrimetry, specifically comprise the following steps:
(1) pipette electrolyte to be measured to volumetric flask, and press extension rate dilute with water, constant volume, mix homogeneously；
(2) from by after step (1) process, the electrolyte of gained pipettes V0ML, to conical flask, adds some beades, and adds perchloric acid；Heating the mixed solution in this conical flask, solution to be mixed stopping is cooled to room temperature, adds concentrated nitric acid dilute, then heated and boiled after smoldering, to dissolve the salt that the ion in electrolyte is formed with the perchloric acid of addition, concentrated nitric acid；
(3) to by the mixed liquor of gained after step (2) process adding a part of strong aqua ammonia until having ferrum to precipitate and occurring, add the strong aqua ammonia that another part is excessive again, then heated and boiled, stand, filtered while hot, then conical flask and filter paper are cleaned with the weak ammonia of heat, until when last chromium ion is kept completely separate, washing liquid is colourless；
(4) the ferrum precipitation filtering gained by step (3) is put back in former conical flask with this filter paper in the lump, it is subsequently adding nitric acid and perchloric acid, heating gained mixed liquor is until stopping smoldering, concentrated hydrochloric acid is added after being cooled to room temperature, then dilute, heated and boiled so that iron salt fully dissolves；The stannous chloride aqueous solution adding preformulation while hot presents light yellow to this mixed liquor, it is subsequently cooled to room temperature, drip some sodium tungstate aqueous solutions again, and drip the titanous chloride. hydrochloric acid solution of preformulation until this mixed liquor becomes blue, then potassium dichromate weak solution it is slowly added dropwise until the sudden change of this mixed liquor is to colourless, add sulfur-phosphorus nitration mixture and the diphenylamine sulfonic acid sodium salt as indicator, and use concentration known C immediately1The K of mol/L2Cr2O7Standard solution carries out titration, and it is titration end-point that color is sported hepatic that time by green；
(5) carry out some groups of parallel tests according to above-mentioned steps (1)-(4), read the K that each group of parallel test each consumes2Cr2O7The volume of standard solution, and calculate the K of consumption2Cr2O7The bulk averaged value V of standard solution1mL；
(6) carry out blank experiment with reference to above-mentioned steps (1)-(5), wherein, add sulfur-phosphorus nitration mixture and as the diphenylamine sulfonic acid sodium salt of indicator before, in blank solution, first add l ferrous ammonium sulfate solution, use K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution2mL；Take same blank solution again and be added thereto to the l ferrous ammonium sulfate solution that equivalent is identical, again using K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution3ML, calculating blank experiment bulking value is V23=V2-V3；
(7) calculating total concentration of iron is C2Mol/L=C1×(V1-V23)/V0× extension rate.
Preferably, in said determination method, the mass fraction of the perchloric acid described in step (2) is 70-72%, namely containing HClO470-72%.
Preferably, in said determination method, the persistent period being heated in step (3) boiling is 5～10min.
Preferably, in said determination method, filter paper described in step (3) is quantitative filter paper at a slow speed.
Preferably, in said determination method, described in step (4), the mass fraction of nitric acid is 65-68%, namely containing HNO365-68%；The mass fraction of described perchloric acid is 70-72%, namely containing HClO470-72%；The concentration of described sodium tungstate aqueous solution is 250g/L, and in described titanous chloride. hydrochloric acid solution, the mass fraction of titanous chloride. is 15-20%, namely containing TiCl315-20%.
A second aspect of the present invention, it is provided that Fe in a kind of Fe/Cr fluid cell electrolyte3+The assay method of concentration, comprise the following steps:
(1) pipetting electrolyte to be measured, equivalent is divided into A part and B part；And moved in volumetric flask by electrolyte to be measured for A part, and press extension rate dilute with water, constant volume, mix homogeneously；
(2) from by after step (1) process, A part electrolyte of gained pipettes V0ML, to conical flask, adds some beades, and adds perchloric acid；Heating the mixed solution in this conical flask, solution to be mixed stopping is cooled to room temperature, adds concentrated nitric acid dilute, then heated and boiled after smoldering, to dissolve the salt that the ion in electrolyte is formed with the perchloric acid of addition, concentrated nitric acid；
(3) to by the mixed liquor of gained after step (2) process adding a part of strong aqua ammonia until having ferrum to precipitate and occurring, mend another part again and add excessive strong aqua ammonia, then heated and boiled, stand, filtered while hot, then conical flask and filter paper are cleaned with the weak ammonia of heat, until when last chromium ion is kept completely separate, washing liquid is colourless；
(4) the ferrum precipitation filtering gained by step (3) is put back in former conical flask with this filter paper in the lump, it is subsequently adding nitric acid and perchloric acid, heating gained mixed liquor is until stopping smoldering, concentrated hydrochloric acid is added after being cooled to room temperature, then dilute, heated and boiled so that iron salt fully dissolves；The stannous chloride aqueous solution adding preformulation while hot presents light yellow to this mixed liquor, it is subsequently cooled to room temperature, drip some sodium tungstate aqueous solutions again, and drip the titanous chloride. hydrochloric acid solution of preformulation until this mixed liquor becomes blue, then potassium dichromate weak solution it is slowly added dropwise until the sudden change of this mixed liquor is to colourless, add sulfur-phosphorus nitration mixture and the diphenylamine sulfonic acid sodium salt as indicator, and use concentration known C immediately1The K of mol/L2Cr2O7Standard solution carries out titration, and it is titration end-point that color is sported hepatic that time by green；
(5) carry out some groups of parallel tests according to above-mentioned steps (1)-(4), read the K that each group of parallel test each consumes2Cr2O7The volume of standard solution, and calculate the K of consumption2Cr2O7The bulk averaged value V of standard solution1mL；
(6) carry out blank experiment with reference to above-mentioned steps (1)-(5), wherein, add sulfur-phosphorus nitration mixture and as the diphenylamine sulfonic acid sodium salt of indicator before, in blank solution, first add l ferrous ammonium sulfate solution, use K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution2mL；Take same blank solution again and be added thereto to the l ferrous ammonium sulfate solution that equivalent is identical, again using K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution3ML, calculating blank experiment bulking value is V23=V2-V3；
(7) calculating total concentration of iron is C2Mol/L=C1×(V1-V23)/V0× extension rate；
(8) potentiometric titrimeter-dichromate titration is directly adopted to record Fe in B part electrolyte to be measured2+Concentration: C3mol/L；
(9) Fe is calculated3+Concentration: C4Mol/L=C2-C3。
In assay method provided by the present invention, first pass through pre-treatment and eliminate the chromium ion impact on redox titration, more all of ferrum is converted into Fe2+, utilize K2Cr2O7Standard solution carries out titration, according to Fe2+And K2Cr2O7Reaction quantitative relationship and blank experiment data, complete the mensuration of total concentration of iron in electrolyte.As can be seen here, compared to prior art, technical scheme provided by the present invention avoids the impact that in electrolyte, iron content titration is tested by chromium ion；The ion of shades of colour in solution is made to have no effect on Fe3+The mensuration of concentration, and instrument that need not be special, income analysis result is accurately and reliably, it is possible to for assessing the performance of Fe/Cr flow battery.
Detailed description of the invention
A first aspect of the present invention, provide the assay method of total concentration of iron in a kind of Fe/Cr fluid cell electrolyte, the general thought of the method, for this electrolyte to be measured must carry out pre-treatment before carrying out total determining iron concentration, then completes to measure by titrimetry, specifically comprises the following steps:
(1) pipette electrolyte to be measured to volumetric flask, and press extension rate dilute with water, constant volume, mix homogeneously；
(2) from by after step (1) process, the electrolyte of gained pipettes V0ML, to conical flask, adds some beades, and adds perchloric acid；Heating the mixed solution in this conical flask, solution to be mixed stopping is cooled to room temperature, adds concentrated nitric acid dilute, then heated and boiled after smoldering, to dissolve the salt that the ion in electrolyte is formed with the perchloric acid of addition, concentrated nitric acid；
(3) to by the mixed liquor of gained after step (2) process adding a part of strong aqua ammonia until having ferrum to precipitate and occurring, add the strong aqua ammonia that another part is excessive again, then heated and boiled, stand, filtered while hot, then conical flask and filter paper are cleaned with the weak ammonia of heat, until when last chromium ion is kept completely separate, washing liquid is colourless；
(4) the ferrum precipitation filtering gained by step (3) is put back in former conical flask with this filter paper in the lump, it is subsequently adding nitric acid and perchloric acid, heating gained mixed liquor is until stopping smoldering, concentrated hydrochloric acid is added after being cooled to room temperature, then dilute, heated and boiled so that iron salt fully dissolves；The stannous chloride aqueous solution adding preformulation while hot presents light yellow to this mixed liquor, it is subsequently cooled to room temperature, drip some sodium tungstate aqueous solutions again, and drip the titanous chloride. hydrochloric acid solution of preformulation until this mixed liquor becomes blue, then potassium dichromate weak solution it is slowly added dropwise until the sudden change of this mixed liquor is to colourless, add sulfur-phosphorus nitration mixture and the diphenylamine sulfonic acid sodium salt as indicator, and use concentration known C immediately1The K of mol/L2Cr2O7Standard solution carries out titration, and it is titration end-point that color is sported hepatic that time by green；
(5) carry out some groups of parallel tests according to above-mentioned steps (1)-(4), read the K that each group of parallel test each consumes2Cr2O7The volume of standard solution, and calculate the K of consumption2Cr2O7The bulk averaged value V of standard solution1mL；
(6) carry out blank experiment with reference to above-mentioned steps (1)-(5), wherein, add sulfur-phosphorus nitration mixture and as the diphenylamine sulfonic acid sodium salt of indicator before, in blank solution, first add l ferrous ammonium sulfate solution, use K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution2mL；Take same blank solution again and be added thereto to the l ferrous ammonium sulfate solution that equivalent is identical, again using K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution3ML, calculating blank experiment bulking value is V23=V2-V3；
(7) calculating total concentration of iron is C2Mol/L=C1×(V1-V23)/V0× extension rate.
In a preferred embodiment, the mass fraction of the perchloric acid described in step (2) is 70-72%, namely containing HClO470-72%.
In a preferred embodiment, the persistent period being heated boiling in step (3) is 5～10min.
In a preferred embodiment, filter paper described in step (3) is quantitative filter paper at a slow speed.
In a preferred embodiment, described in step (4), the mass fraction of nitric acid is 65-68%, namely containing HNO365-68%；The mass fraction of described perchloric acid is 70-72%, namely containing HClO470-72%；The concentration of described sodium tungstate aqueous solution is 250g/L, and in described titanous chloride. hydrochloric acid solution, the mass fraction of titanous chloride. is 15-20%, namely containing TiCl315-20%.
A second aspect of the present invention, it is provided that Fe in a kind of Fe/Cr fluid cell electrolyte3+The assay method of concentration, comprise the following steps:
(1) pipetting electrolyte to be measured, equivalent is divided into A part and B part；And moved in volumetric flask by electrolyte to be measured for A part, and press extension rate dilute with water, constant volume, mix homogeneously；
(2) from by after step (1) process, A part electrolyte of gained pipettes V0ML, to conical flask, adds some beades, and adds perchloric acid；Heating the mixed solution in this conical flask, solution to be mixed stopping is cooled to room temperature, adds concentrated nitric acid dilute, then heated and boiled after smoldering, to dissolve the salt that the ion in electrolyte is formed with the perchloric acid of addition, concentrated nitric acid；
(3) to by the mixed liquor of gained after step (2) process adding a part of strong aqua ammonia until having ferrum to precipitate and occurring, mend another part again and add excessive strong aqua ammonia, then heated and boiled, stand, filtered while hot, then conical flask and filter paper are cleaned with the weak ammonia of heat, until when last chromium ion is kept completely separate, washing liquid is colourless；
(4) the ferrum precipitation filtering gained by step (3) is put back in former conical flask with this filter paper in the lump, it is subsequently adding nitric acid and perchloric acid, heating gained mixed liquor is until stopping smoldering, concentrated hydrochloric acid is added after being cooled to room temperature, then dilute, heated and boiled so that iron salt fully dissolves；The stannous chloride aqueous solution adding preformulation while hot presents light yellow to this mixed liquor, it is subsequently cooled to room temperature, drip some sodium tungstate aqueous solutions again, and drip the titanous chloride. hydrochloric acid solution of preformulation until this mixed liquor becomes blue, then potassium dichromate weak solution it is slowly added dropwise until the sudden change of this mixed liquor is to colourless, add sulfur-phosphorus nitration mixture and the diphenylamine sulfonic acid sodium salt as indicator, and use concentration known C immediately1The K of mol/L2Cr2O7Standard solution carries out titration, and it is titration end-point that color is sported hepatic that time by green；
(5) carry out some groups of parallel tests according to above-mentioned steps (1)-(4), read the K that each group of parallel test each consumes2Cr2O7The volume of standard solution, and calculate the K of consumption2Cr2O7The bulk averaged value V of standard solution1mL；
(6) carry out blank experiment with reference to above-mentioned steps (1)-(5), wherein, add sulfur-phosphorus nitration mixture and as the diphenylamine sulfonic acid sodium salt of indicator before, in blank solution, first add l ferrous ammonium sulfate solution, then use K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution2mL；Take same blank solution again and be added thereto to the l ferrous ammonium sulfate solution that equivalent is identical, again using K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution3ML, calculating blank experiment bulking value is V23=V2-V3；
(7) calculating total concentration of iron is C2Mol/L=C1×(V1-V23)/V0× extension rate；
(8) potentiometric titrimeter-dichromate titration is directly adopted to record Fe in B part electrolyte to be measured2+Concentration: C3mol/L；
(9) Fe is calculated3+Concentration: C4Mol/L=C2-C3。
Additionally, said method provided by the present invention has been carried out accuracy test by inventor:
Buy the l ferrous ammonium sulfate solution of known actual concentrations 0.1008mol/L, by calculating, pipette the l ferrous ammonium sulfate solution that concentration of iron total with in Fe/Cr fluid cell electrolyte is almost identical, adopt identical step and reagent in said determination method to carry out three groups of parallel tests, and read the K consumed2Cr2O7The average external volume V of standard solution4ML, calculates the total concentration of iron in l ferrous ammonium sulfate solution, and acquired results contrasts with concentration known when buying, thus judging the accuracy of the method for the invention acquired results.
Test result indicate that, total ferrum mean concentration C of the Ferrous ammonium sulfate that three groups of parallel tests are surveyed is (actual in Fe2+Concentration) for 0.1006mol/L, error amount RE=0.19%.
Below in conjunction with specific embodiment, technical scheme is further explained and illustrates.
Embodiment 1
To the total concentration of iron in Fe/Cr fluid cell electrolyte and Fe3+Concentration be measured:
(1) preparing electrolyte sample to be measured, equivalent is divided into A part and B part；And A part sample of 10～20mL is pipetted to 200mL volumetric flask (extension rate adopted is 10), dilute with water, constant volume, mix homogeneously is standby.
(2) from A part sample of gained after processing by step (1), pipette 5～15mL to conical flask, add several beades, and add 2～10mL perchloric acid (containing HClO470-72%), heat the mixed solution in this conical flask, after solution to be mixed stopping is smoldered, it is cooled to room temperature, adds 2～10mL concentrated nitric acid, be then diluted with water to 100mL, heated and boiled, to dissolve the salt that the ion in electrolyte is formed with the perchloric acid of addition, concentrated nitric acid；
(3) to by the mixed liquor of gained after step (2) process adding a part of strong aqua ammonia until having ferrum to precipitate and occurring, add the excessive strong aqua ammonia of 5～15mL again, heated and boiled 6min, stand, fume hood carries out filtered while hot with quantitative filter paper at a slow speed, then cleans conical flask and described quantitative filter paper at a slow speed with the weak ammonia of heat, until when last chromium ion is kept completely separate, namely, after cleaning up, washing liquid is colourless.
(4) the ferrum precipitation filtering gained by step (3) is put back in former conical flask with described quantitative filter paper at a slow speed in the lump, add 5～15mL nitric acid and 5～15mL perchloric acid, heating gained mixed liquor is until stopping smoldering, 5～15mL concentrated hydrochloric acid is added after being cooled to room temperature, then 150mL, heated and boiled it are diluted with water to；The stannous chloride aqueous solution adding preformulation concentration known while hot presents light yellow to this mixed liquor, it is subsequently cooled to room temperature, drip several 250g/L sodium tungstate solutions again, and drip the titanous chloride. hydrochloric acid solution of preformulation until this mixed liquor becomes blue, then potassium dichromate weak solution it is slowly added dropwise until the sudden change of this mixed liquor is to colourless, add sulfur-phosphorus nitration mixture and several diphenylamine sulfonic acid sodium salts, and use C immediately1(1/6K2Cr2O7) for the K of 0.0940mol/L2Cr2O7Standard solution carries out titration, and it is titration end-point that color is sported hepatic that time by green.
(5) two groups of parallel laboratory tests, its K each consumed are carried out by above-mentioned steps2Cr2O7The meansigma methods V of the volume of standard solution1For 9.67mL.
(6) carry out blank experiment with reference to above-mentioned steps (1)-(5), adopt same steps and use the reagent of equivalent to be operated.Wherein, add sulfur-phosphorus nitration mixture and as the diphenylamine sulfonic acid sodium salt of indicator before, first adding 20mL concentration in blank solution is the l ferrous ammonium sulfate solution of 0.1008mol/L, uses K2Cr2O7Standard solution titration, the K of consumption2Cr2O7The volume V of standard solution2For 8.06mL, then take same blank solution and be added thereto to the l ferrous ammonium sulfate solution that equivalent is identical, again using K2Cr2O7Standard solution titration, the K of consumption2Cr2O7The volume V of standard solution3For 8.065mL, then blank experiment bulking value is V23=V2-V3=0.005mL.
(7) according to Fe2+And K2Cr2O7Reaction quantitative relationship and blank experiment as a result, it is possible to calculate the Fe obtained through step (6)2+Concentration, i.e. total concentration of iron C2Mol/L=C1(1/6K2Cr2O7)×(V1-V23)/V0× 10=1.2117mol/L, error amount RE=1.0%.
(8) potentiometric titrimeter-dichromate titration is directly adopted to record Fe in B part sample2+Concentration: C3=1.1827mol/L.
(9) Fe in this Fe/Cr fluid cell electrolyte is calculated3+Concentration: C4=C2-C3=0.029mol/L.
Above-described embodiment is it is shown that total concentration of iron of obtaining of assay method provided by the present invention and Fe3+The data of concentration are accurately and reliably, it is not necessary to specific apparatus, it is possible to for assessing the performance of Fe/Cr flow battery.
Above specific embodiments of the invention being described in detail, but it is intended only as example, the present invention is not restricted to particular embodiments described above.To those skilled in the art, any equivalent modifications that the present invention is carried out and replacement are also all among scope of the invention.Therefore, the equalization made without departing from the spirit and scope of the invention converts and amendment, all should contain within the scope of the invention.
Claims (6)
1. the assay method of the total concentration of iron in a Fe/Cr fluid cell electrolyte, it is characterised in that comprise the following steps:
(1) pipette electrolyte to be measured to volumetric flask, and press extension rate dilute with water, constant volume, mix homogeneously；
(2) from by after step (1) process, the electrolyte of gained pipettes V0ML, to conical flask, adds some beades, and adds perchloric acid；Heating the mixed solution in this conical flask, solution to be mixed heating is cooled to room temperature, adds concentrated nitric acid dilute, then heated and boiled after smoldering to stopping, to dissolve the salt that the ion in electrolyte is formed with the perchloric acid of addition, concentrated nitric acid；
(3) to by the mixed liquor of gained after step (2) process adding a part of strong aqua ammonia until having ferrum to precipitate and occurring, add the strong aqua ammonia that another part is excessive again, then heated and boiled, stand, filtered while hot, then conical flask and filter paper are cleaned with the weak ammonia of heat, until when last chromium ion is kept completely separate, washing liquid is colourless；
(4) the ferrum precipitation filtering gained by step (3) is put back in former conical flask with this filter paper in the lump, being subsequently adding nitric acid and perchloric acid, heating gained mixed liquor, until stopping smoldering, adds concentrated hydrochloric acid after being cooled to room temperature, then dilute, heated and boiled；The stannous chloride aqueous solution adding preformulation while hot presents light yellow to this mixed liquor, it is subsequently cooled to room temperature, drip some sodium tungstate aqueous solutions again, and drip the titanous chloride. hydrochloric acid solution of preformulation until this mixed liquor becomes blue, then potassium dichromate weak solution it is slowly added dropwise until the sudden change of this mixed liquor is to colourless, add sulfur-phosphorus nitration mixture and the diphenylamine sulfonic acid sodium salt as indicator, and use concentration known C immediately1The K of mol/L2Cr2O7Standard solution carries out titration, and it is titration end-point that color is sported hepatic that time by green；
(5) carry out some groups of parallel tests according to above-mentioned steps (1)-(4), read the K that each group of parallel test each consumes2Cr2O7The volume of standard solution, and calculate the K of consumption2Cr2O7The bulk averaged value V of standard solution1mL；
(6) carry out blank experiment with reference to above-mentioned steps (1)-(5), wherein, add sulfur-phosphorus nitration mixture and as the diphenylamine sulfonic acid sodium salt of indicator before, in blank solution, first add l ferrous ammonium sulfate solution, use K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution2ML, then take same blank solution and be added thereto to the l ferrous ammonium sulfate solution that equivalent is identical, again use K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution3ML, calculating blank experiment bulking value is V23=V2-V3；(7) calculating total concentration of iron is C2Mol/L=C1×(V1-V23)/V0× extension rate.
2. assay method according to claim 1, it is characterised in that the mass fraction of the perchloric acid described in step (2) is 70-72%.
3. assay method according to claim 1, it is characterised in that the persistent period being heated in step (3) boiling is 5～10min.
4. assay method according to claim 1, it is characterised in that filter paper described in step (3) is quantitative filter paper at a slow speed.
5. assay method according to claim 1, it is characterized in that, described in step (4), the mass fraction of nitric acid is 65-68%, the mass fraction of described perchloric acid is 70-72%, the concentration of described sodium tungstate aqueous solution is 250g/L, and in described titanous chloride. hydrochloric acid solution, the mass fraction of titanous chloride. is 15-20%.
6. Fe in a Fe/Cr fluid cell electrolyte3+The assay method of concentration, it is characterised in that comprise the following steps:
(1) pipetting electrolyte to be measured, equivalent is divided into A part and B part；And moved in volumetric flask by electrolyte to be measured for A part, and press extension rate dilute with water, constant volume, mix homogeneously；
(2) from by after step (1) process, A part electrolyte of gained pipettes V0ML, to conical flask, adds some beades, and adds perchloric acid；Heating the mixed solution in this conical flask, solution to be mixed stopping is cooled to room temperature, adds concentrated nitric acid dilute, then heated and boiled after smoldering, to dissolve the salt that the ion in electrolyte is formed with the perchloric acid of addition, concentrated nitric acid；
(3) to by the mixed liquor of gained after step (2) process adding a part of strong aqua ammonia until having ferrum to precipitate and occurring, mend another part again and add excessive strong aqua ammonia, then heated and boiled, stand, filtered while hot, then conical flask and filter paper are cleaned with the weak ammonia of heat, until when last chromium ion is kept completely separate, washing liquid is colourless；
(4) the ferrum precipitation filtering gained by step (3) is put back in former conical flask with this filter paper in the lump, being subsequently adding nitric acid and perchloric acid, heating gained mixed liquor, until stopping smoldering, adds concentrated hydrochloric acid after being cooled to room temperature, then dilute, heated and boiled；The stannous chloride aqueous solution adding preformulation while hot presents light yellow to this mixed liquor, it is subsequently cooled to room temperature, drip some sodium tungstate aqueous solutions again, and drip the titanous chloride. hydrochloric acid solution of preformulation until this mixed liquor becomes blue, then potassium dichromate weak solution it is slowly added dropwise until the sudden change of this mixed liquor is to colourless, add sulfur-phosphorus nitration mixture and the diphenylamine sulfonic acid sodium salt as indicator, and use concentration known C immediately1The K of mol/L2Cr2O7Standard solution carries out titration, and it is titration end-point that color is sported hepatic that time by green；
(5) carry out some groups of parallel tests according to above-mentioned steps (1)-(4), read the K that each group of parallel test each consumes2Cr2O7The volume of standard solution, and calculate the K of consumption2Cr2O7The bulk averaged value V of standard solution1mL；
(6) carry out blank experiment with reference to above-mentioned steps (1)-(5), wherein, add sulfur-phosphorus nitration mixture and as the diphenylamine sulfonic acid sodium salt of indicator before, in blank solution, first add l ferrous ammonium sulfate solution, use K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution2mL；Take same blank solution again and be added thereto to the l ferrous ammonium sulfate solution that equivalent is identical, again using K2Cr2O7Standard solution titration, reads the K consumed2Cr2O7The volume V of standard solution3ML, calculating blank experiment bulking value is V23=V2-V3；
(7) calculating total concentration of iron is C2Mol/L=C1×(V1-V23)/V0× extension rate；
(8) potentiometric titrimeter-dichromate titration is directly adopted to record Fe in B part electrolyte to be measured2+Concentration: C3mol/L；
(9) Fe is calculated3+Concentration: C4Mol/L=C2-C3。
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