Study On Thermodynamics And Technology Of Selenium Extraction From Copper Anode Slime By Sulphate Roasting-reduction

Selenium has broad application prospects in medical care,electronics industry,agriculture,glass industry,catalyst industry,etc.The main raw material of selenium recovery is copper anode slime,which is rich in gold,silver and other metals,and has a very high comprehensive recovery value.In the fire and wet methods for recovering selenium from copper anode slime,the sulphated roasting-reduction has the advantages of good separation effect of selenium and Te and high recovery rate,simple process,and suitable for various complex materials.Therefore,half of copper anode slime is recovered selenium through sulphated roasting-reduction.In this paper,the thermodynamics and process of sulfur roasting and reduction recovery of selenium in copper anode sludge with low arsenic,antimony,bismuth as raw material were studied,and the main conclusions were drawn as follows:Thermodynamic calculation of sulphate roasting-reduction process shows that there is selenium intermediate product when silver selenide and copper selenide react with sulfuric acid to form selenium dioxide at low temperature,but there is no intermediate product selenium at high temperature,and the selenium has a solid-liquid phase transition.The volatilization of copper,silver chloride and tellurium oxide is obvious when the temperature is above 700℃.The roasting temperature should be controlled at 350～650℃.At this time,selenide is transformed into selenium dioxide and enters the gas phase,while copper,silver and other metal compounds are transformed into sulfate and remain in the solid phase.The selenium and sulfur dioxide will form selenite sulfate into the solution,and the selenite sulfate decomposes to obtain elemental selenium in the strong acid solution.By calculating the reaction constant of selenium dioxide reduction,it can be known that all selenite acid can be reduced to elemental selenium in the strong acid solution of sodium sulfite and sulfur dioxide.The optimal conditions of sulfuric acid roasting and steaming selenium were as follows:roasting temperature is 500℃,holding time is 25 min,the amount of sulfuric acid is 1.0 times of the theoretical amount,solid-liquid ratio is 20:9,the steaming rate of selenium is 99.39%,and the residual rate of copper,lead,gold and silver is above 99.5%.The optimal conditions obtained by response surface optimization were as follows:roasting temperature is 522℃,roasting time is22.34 min,sulfuric acid dosage is 1.11 times,and evaporation selenium rate is 99.12%on average.The kinetic data of the sulphated roasting of low arsenic,antimony,bismuth copper anode mud fit the Avrami Erofeev equation well.The activation energy of the reaction is 28.118 k J/mol,and the reaction rate equation is k=3.607e^-3382/T,which is controlled by internal diffusion.The optimal conditions for the reduction of selenium dioxide by sodium sulfite were as follows:temperature is 55℃,reaction time is 20 min,sulfuric acid concentration is 2 mol/L,sodium sulfite dosage is 1.2 times of the theoretical amount,and the reduction rate of selenium is 99.66%.The optimal conditions for reducing selenium dioxide with sulfur dioxide are as follows:temperature is 40℃,reaction time is 30 min,sulfuric acid concentration is 1mol/L,sulfur dioxide entry rate is 55 m L/min,and the reduction rate of selenium is 99.56%.Compared with the two,the purity of selenium obtained by sulfur dioxide reduction is higher,and the product sulfuric acid can be recycled.When selenium dioxide is reduced by sulfur dioxide,the reduction reaction of selenium conforms to the first order reaction kinetics.The activation energy of the reaction is 6.80 k J/mol,and the kinetic equation-ln（1-x）=2.36(e^-817.9/T)t is controlled by internal diffusion.