Study On The Preparation Of Electroltic Aluminium Carbon Anode With Anthracite

Carbon anode is the key to electrolytic aluminium production. Petroleum coke and coal pitch are still the principal raw materials of carbon anode though there is a quite great progress in the production technology, ratio of constituents and other aspects. In order to release the situation that increasingly scarcity petroleum resources and utilize anthracite resources more efficiently of China, a new electrolytic aluminium carbon anode was adopted to replace petroleum coke carbon anode.In this paper, low ash content anthracite was taken as the investigated subject, thermolysis process of anthracite and petroleum coke were investigated at the same time. The effect of calcined and acid-base deliming to the structure and ash constituent of anthracite was analysised. Particle properties difference between calcined anthracite and calcined petroleum coke were studied in the same time. The results show that thermolysis process of petroleum coke acted in a width temperature range form 200℃to 850℃, and the structure reconstructe at 1050℃, thermolysis process of anthracite mainly concentrated in a narrow temperature range form 550℃to 900℃and electrolytic calcine would made anthracite more graphitization and the structure transformed more compacted at the meantime, diffraction angle of (002) crystal plane form 25.83o inceased to 25.89o. The ash content of calcined anthracite descended form 2.0% to 0.58% after deliming treatment and acid-base deliming has some decomposition effect to the structure of anthracite, stack thickness form 10.78782nm reduced to 8.95094nm and the number of carboncycle in microcrystallite carbon form 153 reduced to 123.All impurity elements content of deliminged calcined anthracite are in the range of requirements, assembly average of some elements for example Ni and V that have catalysis effect are far below the standard of petroleum coke. Besides this, sulfur content of calcined anthracite is only 0.1% while the value is 1.22% in calcined petroleum coke. Calcined anthracite has better abradability and lower resillent-elasticity recovery coefficient than petroleum coke, withal particle crushing strength coefficient exceeded the value of petroleum coke 10~30%. The best size fraction batch formula that determined by orthogonal test was listed as follows: 4~2mm:20%, 2~1mm:15%, 1~0.075mm:20%, -0.075mm:45%.Effect of calcined anthracite content, coal pitch content and roasting technology to carbon anode properties were researched in carbon anode preparation process. The results show that ash content is 0.95%, volume density(1.452g/cm3) and porosity(22.77%) match well, compression strength(37.59MPa) and electrical resistivity(54.72μ?·m) are all in range of the first class standard of carbon anode of China when carbon anode including calcined anthracite content and coal pitch content is 40% and 18% respectively. Heating-up speed has a relative great effect to the structure of carbon anode and obscure to the properties. Electron transition occupated principal position and the carbon anode shown negative temperature coefficient of resistance when the temperature raised from room-temperature to 950℃. The relationship of electrical resistivity with temperature changed could been described as follows:ρt =ρ20 +α(t ? 20). Temperature coefficient of resistance is -0.00932 when carbon anode was made by total petroleum coke, and the value is -0.01750 when carbon anode had 40% calcined anthracite content.CO2 reactivity of petroleum coke and calcined anthracite carbon anode at temperature 970℃were investigated in this paper, the effect of additives to CO2 reactivity at temperature 970℃were explored at the same time. The results show that oxidization degree and slough degree of calcined anthracite carbon anode is 17.61% and 4.42% respectively, 1.29% and 0.13% lower than petroleum coke carbon anode sample in the same condition. Aluminium serial additives could obviously reduced oxidization degree, slough degree and total consumption speed. In all additives, 0.8% Al powder content could decreased oxidization degree and slough degree both to minimum value, 32.8% and 70% lower than no Al powder addition respectively ,and total consumtion speed has the mininum value 39.28 mg·cm-2·h-1. The additive CaF2 would increased oxidization degree more than 3% compared with no additive carbon anode, slough degree would increased four times and total consumtion speed would raised to more than two times. The catalysis effect of NaF additive is more markedly than the others. When the content of NaF is reach to 1.6%, oxidization degree would arrived to 29.76%, slough degree would increased to 33.85% and total consumtion speed would raised to three times compared with no additive carbon anode.Oxidation mechanics of calcined anthracite carbon anode and petroleum coke carbon anode were both analysed,and it draw a conclusion that adding calcined anthracite into carbon anode could impeded air oxidate burning at 600℃temperature and CO2 reactivity at temperature 970℃improvement must consider form two aspects: microstructure of carbon anode improved and depress reactivity of coal pitch coke.