Poisoning Behavior And Mechanism Of Cobalt To ?-hydroxime Extractant

Hydroxime extractant is one of the chelating extractant commonly used in copper,nickel and cobalt hydrometallurgy.However,in the extraction practice,it is found that cobalt will poison to hydroxime extractant,which seriously restricts the application and development of cobalt extraction metallurgy.In this paper,Mextral 84H(hydroxyl ketone oxime)and Mextral 860H(hydroxyl aldoxime),which are typical P-hydroxime extractants,were used to study the extraction of cobalt in ?-hydroxyl oxime system and the toxic behavior and mechanism of cobalt to ?-hydroxyoximes,providing a theoretical basis for solving the toxic problem of cobalt to ?-hydroxime extractant.Firstly,the effects of concentration of extractant,temperature and equilibrium pH on the extraction efficiency of Co2+extracted by ?-hydroxime were studied,and the optimum process parameters for cobalt extraction with P-hydroxime extraction agent were determined as follows:equilibrium pH 7.0,extraction agent concentration 0.1 mol/L,extraction temperature 40?,O/A=1:1.The molecular formula of cobalt and ?-hydroxime was CoL2·pH2O by slope method.In addition,through the extraction of thermodynamics calculation,the extraction reaction's ?H was greater than zero,indicating that the extraction process was endothermic reaction,and the temperature increase was beneficial to the extraction reaction.Secondly,the effects of the cobalt loading time of organic phase,the concentration of extractant,the concentration of Co2+ in the original solution,the oxidation temperature and other factors on the toxicity were investigated.It was found that the longer the oxidation reaction time of the supported organic phase and the higher the oxidation reaction temperature,the lower the reverse extraction rate of cobalt,that is,the more serious the toxicity of cobalt to ?-hydroxime extractant.On this basis,the effects of Cu2+?Mn2+?Fe2+ions on the poison were investigated.The results showed that Cu2+ had little effect on the poisoning.However,in the presence of Mn2+ or Fe2+ ions in the system,the poisoning rate of Co2+to P-hydroxime extraction agent decreased,and Mn2+ and Fe2+ could affect the poisoning of Co2+ to ?-hydroxime extraction agent to a certain extent.Finally,spectral analysis and quantum chemical calculation were used to study the extraction mechanism of cobalt in ?-hydroxime system and its poisoning to extractant.According to UV-Vis absorption spectroscopy and infrared spectroscopy,N atom of the oxime group and O atom of the phenolic hydroxyl group in the hydroxime extraction agent participated in the coordination,and water molecules were also involved in the coordination.So the structure of the extracted complex was hexagonal regular octahedral structure,and formula of extracted complex was CoL2·2H2O.In addition,the geometrical structures of Co2+and extractants Mextral 84H or Mextral 860H were optimized at the B3LYP/6-311+G(d,p)density functional level,and the molecular frontier orbitals of the extracted compounds were analyzed.It was found that the extracted complex formed by cobalt and ?-hydroxime extractant was easy to be excited due to its low HOMO-LUMO energy level,which made oxygen easily react with it,resulting in the formation of extremely stable extracted complex,thus leading to the poison.