Separation, Enrichment And Application Of Carbon From Waste Cathode Of Electrolytic Aluminu

In this paper,waste cathode carbon blocks from an electrolytic aluminium plant in Guizhou were used as raw materials.The physical composition,elemental composition,particle size and dissociation degree of the main minerals and the embedding characteristics of the main minerals of the waste cathodes were investigated by means of X-ray diffraction,BPMA,X-ray fluorescence spectroscopy and thermogravimetric tests.Based on the study of the mineral properties of the waste cathodes,ultrasonic washing and ultrasonic leaching were used to separate and enrich the carbon from the waste cathodes,and reasonable parameters for ultrasonic washing and ultrasonic leaching were optimised.（1）The main minerals in the waste cathodes are graphite,sodium fluoride,sodium cryolite,silicon carbide,etc.The main elements are carbon,fluorine,aluminium,sodium,iron,silicon and potassium,etc.The mineral embedding relationship in the used cathodes is complex and contains more fine particles,which are difficult to separate by physical methods.（2）The waste cathode was crushed and ground to-150 mesh,and most of the sodium fluoride was dissolved in water by three water washes at a liquid-to-solid ratio of 3.5:1,an ultrasonic power of 420 W and a water wash time of 50 s.The recovery rate of 0.84 g of sodium fluoride was 95.13%.The carbon content of the wasted cathode after water washing reached 79.68%.（3）The use of ultrasound-assisted leaching of the water-washed spent cathodes in acidic aluminium ion-containing solutions increased the leaching time,leaching temperature,leaching aluminium ion dosage,leaching hydrogen ion dosage,leaching ultrasonic power and leaching liquid-to-solid ratio within a certain range to improve the leaching rate of the electrolyte.The optimal parameters for the ultrasonic leaching of spent cathodes were determined by single-factor tests:leaching time of 20 min,leaching temperature of 70°C,leaching ultrasonic power of 360 W and liquid-solid ratio of 6:1(solution H⁺concentration 0.34 mol/L,Al³⁺concentration 0.27 mol/L),with an improved carbon purity of 89.23%.（4）A kinetic study of leaching revealed that the reaction rate of the leaching process was controlled by both interfacial chemistry and internal diffusion.The apparent activation energy was calculated from the Arrhenius equation to be 16.72k J/mol.（5）Molecular simulations of the adsorption of aluminium ions on cryolite show that there are two adsorption configurations of aluminium ions on the cryolite surface during the leaching process,and that there is an obvious electron transfer between aluminium ions and fluorine atoms during the adsorption process,and that the reaction path between aluminium ions and the cryolite surface is"reactant-transition state-product".The reaction path between the aluminium ions and the cryolite surface is"reactant-transition state-product".The graphite also adsorbs during the leaching process,which reduces the concentration of aluminium ions in the leaching solution and thus affects the leaching effect.（6）The optimum conditions for the preparation of silicon carbide from leached waste cathodes are:a temperature of 1550°C,a molar ratio of carbon to silicon of 3:1,a holding time of 3 h.