Ash Removal And Re-use Of Used Cathode In Aluminum Electrolytic Cells

The electrolytic aluminum scrap cathode carbon block has a high degree of graphitization for a long period of time,and contains about 50%to 70%of graphite.It has been explored to purify the graphite from the spent cathode carbon powder after flotation and then prepare the cathode carbon block through a forming process.A series of interlocking problems,such as the use of purified carbon powder to prepare cathode carbon blocks,will be eliminated for the recycling of spent cathode toners that have been phased out in the aluminum production process,reducing the use of land due to long-term disposal of waste cathodes,polluting the atmosphere,and damaging the groundwater quality,can properly reduce the production costs of enterprises,and fully realize the transformation of waste into treasure,regardless of economic development or ecological and environmental protection are of great significance.In this paper,high-ash carbon powder was obtained from the waste cathodes of an electrolytic aluminum enterprise after flotation.The high carbon content of the fixed carbon was determined to be 68.40%,the ash content was 27.30%,the volatile matter was 5.63%,and the SiO₂ in the carbon powder ash was determined.The content is37.90%,the content of Al₂O₃ is 30.40%,the content of CaO is 9.79%,the content of Fe₂O₃ is 4.90%,and the content of MgO is 2.30%.Alkaline acid method was used to purify the high ash carbon powder.The factors such as the amount of sodium hydroxide,baking temperature of sodium hydroxide,baking time of sodium hydroxide,acid leaching time of hydrochloric acid,acid leaching temperature,stirring speed of pickling,and concentration of hydrochloric acid were investigated.The effect of the fixed carbon content of the carbon powder after purification.Chemical analysis,X-ray diffraction,scanning electron microscopy and other analytical methods were used to analyze the relationship between the ash content and the purification process factors.The purified carbon powder was uniformly mixed with the mass ratio of carbon powder to asphalt of41:9,and the cathode carbon block forming experiment was carried out.During the graduated billet forming process,the pressure of the sample,the sample rate,the release rate,and the hold time were measured.The influence of other factors on bulk density.The effect of different cathode carbon block molding and roasting curves on the compressive strength of the cathode carbon block sample after calcination was discussed.Using the basic acid purification method and cathode carbon block forming experiment,the main conclusions are as follows:?1?The optimum process conditions for the purification by using the alkali acid method:the mass ratio of sodium hydroxide to high ash carbon powder is 0.4:1,the calcination temperature is 1000°C,the calcination time is 30 min,the hydrochloric acid concentration is 1 mol/L,and the acid leaching Temperature 70°C,acid leaching time120min,acid leaching stirring rate 400r/min,the fixed carbon content after purification from the original 68.80%to 94.52%,ash content from 27.30%to 4.02%.Since the carbon in the carbon powder exists mainly in the form of graphite,the micro-morphology characteristics of the graphite before and after purification are compared.It is concluded that the purification of the carbon powder by the alkaline acid method does not destroy the graphite crystal structure in the carbon powder.?2?Cathode carbon block forming experiment was conducted on the purified carbon powder to obtain the best molding conditions of the green body:pressure of 60kN,pressure rate of 20 mm/min,holding time of 240 s,and release rate of 10 mm/min.Through the analysis of the compressive strength of the cathode carbon block sample after roasting,it was determined that the baking temperature at the maximum temperature of 1200°C and the 27 hour calcination time was used to conduct the green forming experiment.The maximum compressive strength of the sample after the calcination curve was calcined 37.20 MPa,bulk density 1.426 g/cm³.