Determination method of trivalent chromium in iron chromium flow electrolytes
The determination of trivalent chromium content was based on the titration method of"HG/T 4311-2012 Indus-trial Chromium Chloride".By using a multi-step oxidation method,Cr3+ in the iron chromium mixture was completely oxi-dized to Cr6+,achieving accurate and stable testing of Cr3+ content within a large concentration range,and solving the inter-ference of iron ions.At the same time,the main conditions that affected the accuracy of the measurement results,including the amount of distilled water,the amount of sodium hydroxide solution and the amount of hydrochloric acid,were experimen-tally verified and compared,and the experimental conditions were optimized.The main measurement steps of this method were as follows:firstly,in an acidic environment,Fe2+ was oxidized to Fe3+ with an excess sodium chlorate solution,then a so-dium hydroxide solution was added,and in alkaline environment,Cr3+ was preliminarily oxidized to Cr6+ with hydrogen perox-ide.At this point,as some of the Cr3+ encapsulated by the iron complex was not oxidized,a hydrochloric acid solution was added to adjust to the appropriate pH value to completely release the Cr3+ encapsulated by the complex.Then,hydrogen perox-ide was used to completely oxidize it to Cr6+.Then,sulfuric acid solution and phosphoric acid were added to mask the iron ions,and titrated with ammonium ferrous sulfate standard solution.The results showed that the relative standard deviation of Cr3+ determined by this method was 0.12%～0.51%,and the recovery rate of the added standard was 95.0%～99.2%.The de-termination results were basically consistent with those determined by spectrophotometry,meeting the requirements for the determination of trivalent chromium content in the electrolyte of iron chromium flow batteries.
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