Effects of anthracite calcination and formulation variables on properties of bench scale aluminum smelting cell cathodes
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undertaken: a) to establish quantitatively the effect of higher anthracite calcination temperature on cathode swelling and electrical resistivity, since e l e c trically calcined anthracite, which has been subjected t o a higher a v e r a g e temperature than anthracite calcined in a gas-fired rotary kiln, is becoming a more favored cathode aggregate material; b) to determine effects of anthracite variables on cathodes fabricated u s i n g higher anthracite calcination temperatures than in the previous work; and c) t o study formulation variables. EXPERIMENTAL Anthracites used in this work were selected from those described previously2 and measured g r e e n p r o p e r t i e s are repeated in Table I. All the tests, except the one for conchoidal fracture, were conducted according to standard analytical methods. The test for conchoidal fracture is believed t o give a rough indication of anthracite lithotype concentrations (highly conchoidal particles indicate a high vitrain content, highly nonconchoidal particles indicate high fusain and durain contents). In addition, s e v e r a l commercial electrically calcined anthracite samples were tested. G r e e n anthracites were calcined first under a nitrogen atmosphere at an upheat rate of 25°C/h to 1135°C and held at that temperature for 10 h. These anthracites then were inductively heated t o higher temperat u r e s under a nitrogen purge using the apparatus shown schematically in Fig. 1. Upheat rate v a r i e d from about 20°C/min initially to about 5°C/min near the final temperature and the c h a r g e was held at the final temperature for 1 h. In some cases, anthracites were crushed f i r s t to give the approximate particle size distribution to be used in an experimental cathode so that a single calcination run could be used for each 2-kg m i x e r load. When it b e c a m e c l e a r that such precrushing did not result in a product comparable to that produced when calcining l a r g e r particles (see below), s e v e r a l loads of pea (-21 mm +14 mm diam) or buckwheat (-14 mm + 7 mm diam) size particles of an anthracite were calVOLUME 8B, DECEMBER 1977-591
Table I. Green Anthracite Properties Arbitrary Anthracite Designation A B C D E F G H I J K L
Ash,Wt Pet
Iron, Wt Pct
7.6 7.8 8.6 9.5 9.7 9.9 10.2 10.5 10.7 11.2 11.7 11.8
0.22 0.25 0.42 0.39 0.29 0.56 0.30 0.29 0.58 0.56 0.39 0.30
Sulfur, Wt Pet 0.68 0.49 0.47 0.60 0.86 0.67 0.69 0.84 0.75 0.73 0.77 0.69
Silicon,Wt Pct
Volatile Matter, Wt Pct
1.8 1.9 1.9 2.1 2.7 2.4 2.3 2.6 2.7 2.4 2.3 2.7
5.6 3.6 3.5 4.0 4.5 4.6 4.5 4.5 4.5 4.5 4.7 4.4
TUNGSTEN-S% RHENIUM VS. TUNGSTEN-76% RHENIUM THERMOCOUPLE IN ALUMINA SHEATH (REPLACED BY SIGHT PORT FOR OPTICAL PYROMETER FOR TEMPERATURES ABOVE ISSO~C)
Fixed Carbon, Wt Pct
Conchoidal Fracture, Wt Pct
86.1 88.1 87.4 85.9 84.9 84.8 84.6 84.2 84.0 83.6 82.8 83.1
51 78 58 64 68 80 82 69 74 85 82 71
Table II. Sizings Used in Cathode Fabrication
Anthracite Wt Pct Tyler Mesh Fractions +3/8 -3/8+4 -4+8 -8+14 -14+28 -28+48 - 4 8 + 100 - 100+200 -200
Fig.
1--Apparatu
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