METALLURGY

STIBNITE ORES are the most desirable due to high recoveries and lower costs of conversion. Oxide ores are least desirable due to poor recoveries and the high cost of conversion.

WHAT IS METALLURGY?

Metallurgy is the art and science of extracting metals from their ores and modifying the metals for use. Metallurgy customarily refers to commercial as opposed to laboratory methods.

LIQUATION:

Liquation is the melting of stibnite into “crudum” or “needle antimony”. It is carried out between 550 and 600 degrees C. If the temperature is lower, the recovery is poor. If the temperature is any higher, the stibnite volatilizes into oxide. This method is used to upgrade low-grade ores. The ore is placed on a grate, and the stibnite melts out of the ore and through the grate to collect in pans.

Sb2S3 melts at 550° C. (Pelabon); at 540° (Wagemann); at 546° (Borgstrom).

Sb2S3 volatilizes, in the absence of air, between 650° and 917° (S.A. Chakhov and I.I. Slobodskai).

VOLATILIZATION ROASTING:

Volatilization Roasting is the process of volatilizing the sulfur and forming antimony crude oxide (Sb2O3) Sb2S3 +9O→Sb2O3+3 SO2; begins at 290°, rapid at 520° and finishes at 560° (Saito); begins at 290°, if the size of the grain is 0·1 mm. in diameter, at 343° of 0·1 to 0·2 mm., and 430° if 0·2 mm. (Friedrich); commences at 190°, proceeds energetically at 340° and terminates at 445°
(S.A. Chakhov and I.I. Slobodskai).

DEAD ROASTING:

This is the process of de-sulfurizing sulfide ore where the oxide is not volatilized but remains as the tetraoxide or pentoxide. The Sb2O4 and Sb2O5 is then reduced to metal. Sb2O3 + Sb2O5 — Sb2O4

ENGLISH PRECIPITATION:

In this process, sulfur is removed from stibnite by using scrap iron in the fusion. This also requires soda ash to enhance slag removal Sb2S3+3 Fe→2Sb+3FeS

FUMING CRUDE OXIDE TO FINISHED OXIDE:

Sb2O3+O→Sb2O4 at above 445° (Chakhov and Slobodskai).

Sb2O4+O→Sb2O5; commences at 900° and finishes at 1030° (Chakhov and Slobodskai). Sb2O5→Sb2O4+O at between 750° and 800° (A. Simon and E. Thaler). Sb2O4→Sb2O3+O at 930° (A. Simon and E. Thaler).

REDUCTION OF CRUDE OXIDE TO METAL:

This is done using carbon and soda ash.

Sb2O3+3C→Sb2+3 CO at red heat. Sb2o4+4C→Sb2+4CO

LEACHING AND ELECTROWINNING OR OXIDATION:

Sb2S33 Na2S = 2 Na3SbS3 Leaching stibnite with sodium sulfide

2 Na3SbS3 + 6NaOH = 2 Sb + 6 Na2S + 3 H20 + 3/2 O2 Electrowinning

Na3SbS3 + 3 H = Sb + 3 NaSH Electrowinning

SULFIDE ORES:

The mineral dressing of sulfide ores is primarily accomplished by flotation although it can be accomplished by gravity and hand -sort methods. Recoveries of un-oxidized sulfides can be in the mid 90% range with concentrate grades of 60 to 68% for stibnite ores. The stibnite concentrates are then fumed to a crude oxide that is either fumed to a finished oxide or reduced to metal and then fumed to finished oxide. Tetrahedrite concentrates are usually leached in alkaline solutions that are electro-won to recover antimony metal or oxidized to sodium antimonite. Jamesonite concentrates are generally reduced to antimony-lead bullion (generally 50%-50%) that is selectively fumed to recover a crude oxide that is then reduced to metal and fumed to finished oxide.

OXIDE ORES: Oxide ores are upgraded by gravity methods including jigs, tables, and heavy media separators (HMS plants). The mineral dressing of oxide ores generally result in recoveries of less than 50% and concentrate grades in the 25 to 40% antimony range at best. These concentrates are typically reduced directly to metal or fumed to crude oxide that is then fumed to finished oxide. In either case, the cost of reduction or initial fuming requires massive amounts of fuel and results in very high costs.