Study On The Technology Of Extracting Selenium And Arsenic From Smelting Smelting

Ni-Mo ores is a special multi-metal grandidierite in China and both pyrometallurgical and hydrometallurgical methods were used for treating Ni-Mo ores. Through roasting process in pyrometallurgical method, a lot of smelting dust was created and influenced the environment seriously after accumulated for years. After systematical researching the phases of selenium, arsenic and sulfur which existed in the dust, a specific technological process in this paper was proposed as follows: Ni-Mo ores smelted dust- desulfurization pretreatment-alkaline leaching- reducing and extracting selenium from the leaching solution- isolating and producing arsenic products from residual solution.1) The elemental sulfur can be effectively removed from dust through desulfurization pretreatment and the desulfurization ratio can be reached at 92.74%. The optimal parameters were as follows: the quality of 50 gram dust which particle size were all less than 0.1 mm, added into 250 ml kerosene which has already preheated to 130℃, stirred 30 minutes under the stirring ratio of 400 r/min, then immediate filtration.2) Selenium and arsenic can be leached effectively by sodium hydroxide solution under the optimal conditions, the leaching ratio of selenium and arsenic can be reached 98.54% and 99.02%, respectively. The optimal parameters were as follows: Mixed 10 gram pretreated dust with 50 ml sodium hydroxide solution which alkalinity was 4 mol/L, stirred 40 minutes at room temperature under the stirring ratio of 300 r/min. The relationship between leaching ratio of selenium and arsenic and time was investigated at different temperature, then obtained the leaching kinetic equation of selenium and arsenic were 1-2/3R-（1-R）2/3=118.60e-2.10207/RT?t and 1-2/3R-（1-R）2/3=769.38e-2.73924/RT?t; respectively. Calculated apparent activation energy of leaching reaction was 17.477 kJ/mol and 22.774 kJ/mol, respectively. This proved that the process of leaching selenium and arsenic were controlled by internal diffusion.3) Selenium can be reduced and extracted from the leaching solution by added the reducing agent Na2SO3, the average reducing ratio reached 99.01%. Optimal parameters: pre-adjusted the solution pH = 10.75, then heated to 95℃ by water bath, added a certain amount of reducing agent Na2SO3 into solution, stirred 180 minutes under the stirring ratio of 300 r/min, after reaction, filtered and dried, then obtained the selenium.4) Arsenic sulfide can be extract from residual solution after extracted selenium, the specific technological process was that took 50 ml arsenic-rich solution, under stirred ratio of 300 r/min, then added concentrated H2SO4 during stirring, until the pH reached between 3 and 4, then stopped adding concentrated H2SO4 and keeping stirred for another 5 minutes. After filtering and drying, relatively pure arsenic sulfide can be obtained. Arsenic sulfide can be effectively oxidized and desulfurized under the optimum conditions and oxidative desulfurization ratio can reached 94.08%. Optimal parameters: Mixed 5 gram arsenic sulfide powder with 100 ml distilled water, under the stirring ratio of 400 r/min and heated by water bath at 75℃, adjusted pH to 8.5 by adding NaOH powder. Then added 30% of H₂O2 at a speed of 0.5 rpm, after added H₂O2, kept running 30 minutes, filtered and obtained arsenic-rich solution. Acid precipitated: Concentrated arsenic-rich solution and increased concentration of arsenic to more than 60 g/L, added 10 gram Na2SO3 to concentrated solution, adjusted pH = 0, stationary for 24 hours, then obtained pure As₂O₃ powder after filtered and dried.