Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group vib metal
Reexamination Certificate
2001-05-09
2004-11-16
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group vib metal
C423S027000, C423S150100
Reexamination Certificate
active
06818191
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the process chemistry during pressure oxidation of molybdenite concentrates and more particularly to a process for controlling and optimizing the process chemistry during the pressure oxidation of molybdenite concentrates.
BACKGROUND OF THE INVENTION
Extraction of molybdenum from molybdenite-containing materials by an aqueous process has been the subject of study for almost 50 years. In 1952, E. S. Usataya
1
reported on the oxidation of molybdenite in water solutions. He found that in neutral, acidic, or weakly alkaline solutions the decomposition products precipitate on the molybdenite surface and protect the molybdenite from further oxidation. He found that strong bases and strong oxidizing agents impede the formation of the protective layers. Increasing temperature accelerated the oxidation rate in alkaline solutions, but up to 60° C. had no effect in acidic solutions.
1
Usataya, E. S., “Oxidation of molybdenite in water solutions,” Zapiski Vsesoyuz Mineral Obshschestva, v 81, 298-303 (1952).
A Japanese patent
2
was issued for oxygen pressure oxidation (POX) of molybdenite in 1962. The example in this patent leached a 55.5% Mo, 36.4% S, and 4.4% Cu concentrate at 9% solids at 200° C. and 200 atmospheres oxygen. The molybdic acid precipitate that formed during leaching was dissolved using ammonia for recovery of an ammonium molybdate. The reaction formula was:
2 MoS
2
+6H
2
O+9O
2
→2H
2
MoO
4
↓+4H
2
SO
4
1)
2
Sada, Koji, “Extraction of molybdenum,” Japanese patent 15.207('62), assigned to Awamura Mining Co., Ltd.
In 1971, AMAX patented similar reactions
3
but chose a temperature greater than 80° C. and a pressure greater than 3.5 atmospheres. In a second AMAX patent
4
, alkali hydroxide or ammonium hydroxide was added continuously to neutralize the acid as it formed and maintain the pH at 7-12.
3
Barry, Henry F. et al, “Aqueous phase oxidation of molybdenum disulfide,” German patent 2,043,874 (1971).
4
Hallada, Callvin J., et al., “Conversion of molybdenum disulfide to molybdenum oxide,” German patent 2,045,308 (1971).
Mel'nikov
5
in 1970 and K. Ya. Shapiro et al.
6
in 1973 reported on pressure oxidation in the presence of sulfuric acid. Shapiro postulated the soluble molybdenum species as MoO
2
SO
4
. Mel'nikov used an oxidized concentrate containing 17% Mo and 15% Fe, at 16% solids and 100° C. Shapiro's conditions for a 47% Mo concentrate were 9% solids, 225° C., and less than 10 atmospheres oxygen pressure, for three hours.
5
Shapiro, K. Ya, et al., “Sulfuric acid processing of oxidized molybdenum raw materials,” Nauk. Tr. Vses. Nauch.-Issled. Proekt. Inst. Tugoplavkikh Metal. Tverd. Splavov, 1970.
6
Mel'nikov, B. S. et al., “Oxidative water-autoclave leaching of molybdenum concentrate,” Nauchn Tr., Vses. Nauchno-Issled. Proektn. Inst. (1973) 14, 251-157.
A 1970 paper by Irkov
7
reports the solubility of molybdic oxide in sulfuric acid solutions at 22, 50, 71, and 89° C. The paper shows molybdenum solubility decreasing with increasing temperature and the effect of acid concentrations above 20 percent.
7
Irkov, F. Ya, Palant, A. A., and Reznichenko, V. A., “Solubility of anhydrous molybdenum (VI) oxide in aqueous solutions of sulfuric acid,” Russian Journal of Inorganic Chemistry, v 15, 5, 695-697 (1970).
A 1975 paper by Shapiro and B. S. Mel'nikov
8
reports on POX decomposition studies of 1) pure molybdenite, 99.5% MoS
2
, 2) high grade concentrate, 47% Mo, and 3) a low grade industrial product containing 16% Mo and 15% Fe. The leaching conditions were 9% solids, less than 160 to 225° C., 5 to 20 atmospheres oxygen overpressure, and 15 to 195 minutes.
8
Mel'nikov, B. S. and Shapiro, K. A., “Water-autoclave decomposition of molybdenite raw material,” Protsessy Poluch. Rafinirovaniya Tugoplavkikh Met. (1975) 113-120, 253-260.
The paper shows the effect of temperature on the oxidation rate with 15 atmospheres oxygen overpressure. The oxidation rate was rapid above 190° C. The paper also shows the effect of oxygen overpressure on the oxidation rate at 225° C. The oxidation rate was directly proportional to the oxygen overpressure. The authors postulate that the oxidation rate as affected by temperature and oxygen overpressure controls the amount of soluble molybdenum.
The paper also includes the effect of adding iron to the high grade molybdenite. The addition of iron greatly accelerates the oxidation of the molybdenite. The temperature effect on the rate is less with the added iron. With iron present, the molybdenum in solution reaches a peak near the 60% molybdenite oxidation point and then decreases to a level about twice that with no iron added. The authors postulate the formation of a molybdenum-iron heteropoly complex that decomposes as the acid concentration increases. It also may be a ferrous complex that decomposes as the soluble iron is oxidized to ferric.
Oxidation of the low-grade industrial-grade concentrate was also studied and the effect of temperature (150-225° C.) on the rate of oxidation, the solubility of molybdenum, the iron and sulfuric acid concentrations at less than 15 atmospheres oxygen overpressure is shown. The data clearly illustrate an incubation period while sufficient pyrite/chalcopyrite is oxidized to generate sufficient sulfuric acid to begin the molybdenite oxidation. Rapid oxidation of the molybdenite did not occur until the soluble iron was about 8 g/l and the sulfuric acid concentration was about 40 g/l. The data indicate that batch testing using water as the lixiviant would not produce data that could be translated to a continuous reactor.
Rothmann
9
in 1980 and Bauer
10
in 1984 patented an oxygen pressure leaching processes in which molybdenite was added to a reacted mixture containing up to 100 g/l sulfuric acid. The leaching was done at 250 to 300° C. and 10 to 20 atmospheres-oxygen overpressure.
9
Rothmann, Hans W. and Bauer, Guenter, “Method for recovering molybdenum oxide,” German patent DE 2,830,394 (1980).
10
Bauer, Guenter and Eckert, Joachim, “Recovery of molybdenum oxide,” German patent DE 3,128,921 (1983).
In 1986, Gock
11
patented the oxidation of molybdenite (97.5%) while not completely oxidizing the contained flotation reagents. This would keep the molybdenum as soluble, reduced-valence species, not hexavalent species that would precipitate. The conditions (acid lixiviant of 0.2 to 0.6 pH, 160-220° C., and oxygen overpressure) do not indicate how the reaction control can prevent complete oxidation of the flotation reagents.
11
Gock, Eberhard, “Pure molybdenum trioxide produced by way of extraction of molybdenum from sulfate solutions,” German patent DE 84 3,443,806 (1986).
In 1998, Cyprus Amax
12
patented a process in which molybdenite is added to the filtrate from a prior reaction and allowed to react to 70 to 95% oxidation. Unreacted molybdenite is recovered from the solids by froth flotation. The unreacted molybdenite and some residual liquid are recycled to the leaching reactor. Oxidation conditions are 175-225° C. and 50 to 300 psig oxygen overpressure. The flotation tails, molybdic oxide and/or molybdic acid also contain a small amount of molybdenite and must be calcined prior to sale as molybdic oxide. The balance of the residual liquid from the autoclave is treated for recovery of rhenium and copper.
12
W. H. Sweetser and L. N. Hill, “Process for autoclaving molybdenum sulfide,” U.S. Pat. No. 5,804,151 (1998).
A Canadian patent by Brassier and Pascal
13
followed the formation of heteropoly compounds when leaching crude calcium molybdate precipitates with sulfuric acid. The data in this patent indicated significant formation of heteropoly phosphates and silicates when leaching was done at less than 0.5 molar sulfuric acid (49 g/l). When leaching was done at 1 molar sulfuric acid, the quantities of heteropolys were reduced by more than one order of magnitude. The inference from these data is that the initial leach feed must contain sufficient free acid to avoid the lo
Litz John E.
Queneau Paul B.
Wu Rong-Chien
Bos Steven
Franks James R.
Gil Joseph C.
H. C. Starck Inc.
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