Separation Of Chromium From Chromium Salt Cleaning Process And Preparation Of Sodium Dichromate

Chromium is an important resource in China,and its chromium salt products are widely used.The traditional production process of chromium salt has some problems,such as low utilization of resources and energy,large discharge of chromium slag and serious environmental pollution.The development of green and clean production process is the only way for sustainable development of the environment.The Process Engineering Research Institute of the Chinese Academy of Sciences has developed a clean production process of chromium salt by liquid-phase oxidation of chromium iron ore molten salt.The problem of environmental pollution of chromium slag has been solved from the source.On the basis of improving resource utilization,the reaction temperature and energy consumption have been greatly reduced,and the real green sustainable development has been realized.The cleaning process uses caustic alkali as reaction medium,and chromium salt after oxidation leaching can be separated by dilution and crystallization to prepare chromium salt products.In order to reduce the energy consumption and simplify the chromium-alkali separation process steps,the chromium salt in the high-concentration alkaline condition is used as the raw material,and the chromate in the liquid phase is transferred to the solid phase by introducing the separation medium and using the precipitation conversion method.The high-efficiency and low-cost separation of chromate and high-concentration hydroxide;the precipitation intermediate is converted to prepare chromium salt product,which is well connected with the above clean production process.This paper has made the following innovations:?1?It is determined that the process of separating chromium alkali by introducing barium hydroxide is an exothermic reaction.The standard Gibbs free energy decreases slowly with the increase of reaction temperature,and the equilibrium constant of reaction decreases with the increase of temperature.The system experiment was carried out on the mixed iron ore liquid phase leaching liquid mixture system.The process research showed that the reaction temperature was 60°C,70°C,alkali concentration 50%,60%?mass fraction?,reaction time 120 min,material ratio 1:1?chromium The molar ratio of sodium salt to barium hydroxide?,under the condition of undiluted,the conversion rate of sodium chromate reached 92%or more,and the separation effect was good.?2?The solid-liquid reaction ball milling strengthens the conversion of precipitation intermediate barium chromate to sodium dichromate by impacting and peeling the product particles on the surface of solid reactants.Through process optimization,when the conversion rate of strontium chromate is almost the same,the required reaction time is shortened from 400 min in the conventional mode to 120 min.The reaction of separating chrome from cerium hydroxide is a first-order reaction.The apparent activation energy of the reaction process is E_a=6.87kJ/mol.The kinetic equation of the reaction is-7)9)?1-?3?=6?,where k=A·e^-6870/RT,A=0.06min^-1.?3?The orthogonal experimental results show that the influence of reaction conditions on the conversion of strontium chromate is:time>reaction temperature>rotational speed.The solid-liquid heterogeneous reaction process for the preparation of sodium dichromate by hydrothermal conversion of strontium chromate was studied.The results show that the control step of the reaction is the diffusion of the product layer.The apparent activation energy of the reaction process is E_a=17.53kJ/mol.The kinetic equation of the reaction is 1-3?1-?2?3+2?1-?=6),where k=A·e^-17530/RT,A=0.29min^-1.?4?Under the optimal chromatographic separation process,the conversion rate of sodium chromate in the actual chromite liquid phase oxidation leaching solution reached89%,which was 3%difference with the simulation results,and the separation effect was good.Under the optimal conversion process of chromium,the conversion rate of strontium chromate reached 88%,which was 5%difference from the simulation results,and the conversion effect was good.?5?The research on the washing and detoxification process of barium sulfate showed that the washing temperature was 40°C,the liquid-solid ratio was 20:1?the solution volume and barium sulfate mass ratio,ml/g?,the washing time was 120 min,and the washing time was 3 times.The content of?VI?is reduced to 1 mg·kg^-1.