Research On The Process Of Recovering Selenium From Selenium-rich Acid Mu

The acid sludge produced by the smelter contains a large amount of valuable metals selenium and mercury,which will not only pollute the environment but also cause waste of valuable resources without reasonable recovery.At present,the selenium extraction methods mainly include two kinds of processes,namely,pyroprocess,which is highly efficient but with high energy consumption and environmental pollution,and is gradually replaced by wet process.And the current wet process suffers from low leaching rate,high experimental equipment requirements,serious corrosion and poor economic efficiency.Therefore,it is significant to explore a new recovery process that is efficient,environmentally friendly and economical.In this study,the wet leaching of selenium from the selenium-rich acid sludge of the smelter was analyzed using the hydrogen peroxide oxidation alkaline leaching experiment,and the optimal leaching process conditions were determined;the seleniummercury separation and recovery process from the leaching residue was studied using the sodium hypochlorite oxidation acid leaching experiment and the selective precipitation experiment of mercury,and the effects of hydrochloric acid concentration,sodium hypochlorite concentration,liquid-solid ratio,reaction time and reaction temperature on the leaching process were investigated;the Sodium sulfite reduction experiment was used to study the reduction recovery of selenium from the leaching enrichment solution.The specific studies were as follows:(1)Thermodynamic analysis showed that under alkaline conditions,when the solution p H was greater than 10.36,selenium could be oxidized to highly valent ionic compounds by using hydrogen peroxide as the oxidant and could exist stably in the solution.The effects of different hydrogen peroxide concentration,sodium hydroxide concentration,liquid-solid ratio,raw material particle size,reaction temperature and reaction time on the selenium leaching rate were investigated in the hydrogen peroxide oxidation alkaline leaching experiments,and the optimal process parameters were determined.Under these conditions,the leaching rate of selenium was 98.44% and the slag rate was 5.4%.Then the kinetic behavior of selenium leaching was described by the unreacted nucleodynamic model and the homogeneous reaction kinetic model,respectively.The results showed that the uniform reaction kinetic model was more suitable than the unreacted nucleodynamic model to describe the leaching of selenium from the acid sludge.The leaching kinetic equations were also solved.(2)The effects of different hydrochloric acid concentrations,sodium hypochlorite concentrations,liquid-to-solid ratio,reaction temperature and reaction time on the leaching rates of selenium and mercury were investigated in the sodium hypochlorite oxidation acid leaching experiment,and the optimal process parameters were determined.Under these conditions,the leaching rates of selenium and mercury were 92.1% and83.6%,respectively.The selective precipitation experiments of mercury showed that the maximum precipitation of mercury was 98.9% when the p H of the solution was 13.0.The red precipitation obtained at p H 13.0 was mercury oxide with 98.02%.(3)In the sodium sulfite reduction experiment,the effects of different sulfuric acid concentrations,sodium sulfite dosage,reaction temperature and reaction time on the selenium reduction rate were investigated,and the optimal reduction process parameters were determined.The reduction rate of selenium under these conditions was 98.2%.It was also observed during the experiment that red amorphous selenium appeared at a temperature of 60°C,which gradually changed to gray-black as the temperature increased,and by 80°C-90°C,the products were all gray-black hexagonal crystalline selenium.The reduction product was analyzed and determined to be crude selenium with a grade of 99.58%.