Thermal separation of arsenic and antimony oxides
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I.
INTRODUCTION
THE problem
of separating arsenic from antimony oxides arises as one of the purification steps in the production of commercial-grade antimony oxide (82 pet) component of the solid solution, it was considered to have an activity coefficient of 1 and the activity coefficient of As203 was varied. The same volume of nitrogen as used for the pure solid case was used for the calculations. The results, presented in Table V, demonstrate that the formation of a solid solution greatly restricts the removal of arsenic from antimony trioxide; the only solid phases produced with an arsenic content below 0.5 wt pet As were at 535 ~ and 587 ~ for an activity coefficient of AszO3 of 10. The METALLURGICAL AND MATERIALS TRANSACTIONS B
Table III.
Gibbs Free Energies of Formation of Oxides in the As-Sb-O System I7'9! AG~ =
a + bT + cT 2 + d/T
+ e T ln
T
Species
a
b
(J moI) c
d
e
Sb203 (s)
-723,257 -719,448 -452,025 -668,379 -644,770 -674,030 -1,231,186 -1,266,139 -1,240,772 -1,242,426 -1,251,321 -1,254,586 -1,261,870 -1,266,746
481.43 482.06 167.48 491.44 636.27 433.25 1192.9 811.87 1088.3 1092.7 992.12 1000.7 900.28 913.15
0 0 0 0 0.0749 0 0.1499 0 0.1239 0.1239 0.0749 0.0749 0.0375 0.0375
0 0 0 0 100,004 0 199,765 0 149,974 149,974 99,983 99,983 49,991 49,991
-29.422 -30.395 2.3274 -32.178 -68.408 -30.396 -136.82 -60.793 -117.46 -117.81 -98.096 -98.804 -78.734 -79.798
Sb204(s) As203 (s) As203 (1) Sb203(1) As406(g) Sb406(g) AszSbO6 (g) AszSb206 (g) AsSb306 (g)
Table IV. Results of Gibbs Free Energy Minimization Calculations for Selective Volatilization in the As-Sb-O System at 1 Arm with Inert Gas, Assuming Pure Solid Phases (Initial Amounts 40.9 moi N2, 75.3 tool Sb203, and 24.7 moi As203)
Temperature Range (K) 298 to 879 879 to 929 298 to 1173 298 to 551 551 to 730 929to1425 >298 >298 730 to 850 880to920 730 to 850 880to920 730 to 850 880 to 920
Table VI. Results of Gibbs Free Energy Minimization Calculations for Selective Volatilization in the As-Sb-O System at 1 Atm to Produce Sb203 Containing Less than 0.5 pct As in Solid Solution (Initial Amounts: 75.3 mol Sb203 and 24.7 tool As203)
Temperature (~
Solid composition
Pct As in Vapor
Pct Sb in Vapor
Temperature (~
N2 (mol)
Pct Sb in Vapor
379 425 479 535 587
100 pct SbzO 100 pct Sb203 100 pct Sb203 100 pct Sb203 100 pct Sb203
100 100 100 100 100
1.0 1.8 3.2 5.7 9.6
379 425 479 535 587
75,000 22,090 6,520 2.220 940
7.52 10.2 14.5 20.9 29.6
volatilization of arsenic trioxide from the solid solution was limited by the volume of nitrogen. The results of calculations performed to find the volume of nitrogen that is required to remove arsenic from the solid phase to below commercial-grade requirements for the case of an ideal solution are summarized in Table VI. The table shows that at low temperatures, a large volume of nitrogen is needed to achieve the separation, and that at higher temperatures, the removal of arsenic to the required level would be accompanied by a large loss of antimony trioxide to the vapor.
Because antimony
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