Preparation Of Chromium Trichloride By Electrochemical Method

Chromium trichloride is an important inorganic salt product,usually in the form of hexahydrate,widely used in electroplating,catalysis,tanning,textile,metallurgy and other traditional fields.In addition,chromium trichloride,as the main active substance of iron chromium flow battery electrolyte,has been widely applied in the field of large-scale energy storage.At present,the production methods of chromium trichloride have some problems,such as long process,low utilization rate of chromium and large carbon dioxide emission.The development of short process,green and high efficiency chromium trichloride preparation technology is the internal demand of the development of chromium salt industry.In this paper,the possibility of preparation of trivalent chromium compounds by electrochemical oxidation of ferrochrome in different electrolytic liquid systems and the oxidation mechanism of carbon ferrochrome are systematically studied.By designing the experimental process,optimizing the experimental parameters and speculating the reaction mechanism,the following three research results are obtained.（1）The electrooxidation process of carbon ferric chromium was studied by using hydrochloric acid,sulfuric acid,nitric acid and phosphoric acid as electrolyte.The results showed that different kinds of acids could directly obtain trivalent chromium salt solutions.The process of direct electrosynthesis of chromium trichloride from hydrochloric acid electrolytic liquid was studied.The experimental parameters were optimized:hydrochloric acid concentration 3 mol·L^-1,current intensity 2 A,circulating flow rate 190 ml·min^-1,electrolytic temperature 65℃.Under the optimized experimental parameters,the current efficiency of chromium in carbon ferrochrome is 33.2%,the conversion rate of chromium is 98.34%,and the unit power consumption of chromium trichloride is 3827 k Wh/t.（2）In hydrochloric acid electrolytic liquid system,Cr and Fe in carbon ferrochrome are oxidized into the electrolyte.According to the composition characteristics of the electrolyte,the experimental scheme of iron ion separation by oxalic acid precipitation was designed.The results showed that under the conditions of 120%oxalic acid addition,solution p H 3.0,reaction temperature 25℃and stirring rate 150 r·min^-1,the iron removal rate was 97.90%and chromium loss rate was 3.24%,and the iron removal effect was good.The purified electrolyte can be applied to iron-chromium flow battery,and the by-product ferrous oxalate can be used as positive electrode material of lithium battery.（3）Cyclic voltammetry（CV）,linear sweep voltammetry（LSV）,electrochemical impedance spectroscopy（EIS）and scanning electron microscopy（SEM）,X-ray energy dispersive spectroscopy（EDS）were used to study the oxidation behavior of carbon ferrochrome in hydrochloric acid.Research results,chromium element Cr（0）,Cr（Ⅵ）,or Cr（0）-Cr₂O₃-Cr（Ⅵ）process into Cr（Ⅵ）,iron by Fe（0）and Fe（Ⅱ）process to generate Fe（Ⅱ）,Cr（Ⅵ）in the solution would Fe（Ⅱ）oxide generated Cr（Ⅲ）and FeⅢ).The results completely explain the phenomenon that the main product of electrolysis is Cr（Ⅵ）in the phosphoric acid system.Because the iron element in ferrochrome is oxidized to iron divalent,and forms ferrous phosphate precipitation with PO₄^3-in the solution,the REDOX reaction of Cr（Ⅵ）on ferrous iron is greatly reduced.In this paper,one step synthesis of chromium trichloride was achieved by electrochemical oxidation technology without the process of hexavalent chromium salt.The technology scheme of separating iron ions in the electrolyte by oxalic acid precipitation was designed,and the products of chromium trichloride and ferrous oxalate were obtained respectively,which provided a new idea for the development of short process and clean process of chromium trichloride.