Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group vib metal
Reexamination Certificate
2001-05-09
2004-05-04
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group vib metal
C423S056000
Reexamination Certificate
active
06730279
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the process of producing ammonium dimolybdate for conversion to pure molybdenum oxide or other pure chemicals from molybdenite concentrates and more particularly to a process of producing chemical grade ammonium dimolybdate for conversion to chemical grade molybdenum oxide through a process that includes the pressure oxidation of low-grade molybdenite concentrates.
BACKGROUND OF THE INVENTION
Extraction of molybdenum from molybdenite-containing materials by an aqueous process has been the subject of study for over 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.
2
Sada, Koji, “Extraction of molybdenum,” Japanese patent 15.207('62), assigned to Awamura Mining Co., Ltd.
In another process disclosure
3
, alkali hydroxide and alternatively ammonium hydroxide was added continuously to the aqueous solution to neutralize the acid as it formed and maintain the pH at 7-12. Other authors
4
postulated 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.
3
Hallada, Calvin J., et al., “Conversion of molybdenum disulfide to molybdenum oxide,” German patent 2,045,308 (1971).
4
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.
Early applications of molybdenum solvent extraction utilized tertiary amine to extract the molybdenum solubilized by sodium hydroxide leaching of roasted molybdenite calcines. Secondary amines and quaternary ammonium compounds extract anionic molybdenum using a similar chemistry. Amines also were used for extraction of molybdenum from molybdenite roaster scrubber solutions.
Molybdenum is an impurity in many uranium ores. When uranium ores are acid leached, some molybdenum reports to the acid leach solution. The tertiary amines readily available during the 1950′s and early 1960′s tended to have an amine-molybdenum complex with poor solubility in aliphatic diluents (kerosene).
Several Russian researchers worked with acid leaching of oxide ores. In many cases the acidity was sufficient for most of the molybdenum to be in a cationic form. Therefore, the cation exchanger (di, 2, ethylhexyl phosphoric acid (DEHPA)) received much study regarding the recovery of molybdenum from complex acid solutions. Karpacheva et al.
5
determined that in acid solutions the molybdenum was not present as the simple molybdenyl cation but, the molybdenum was present as polymeric cations. The co-extraction of iron is a major problem when using DEHPA. The authors noted that in a nitric acid system, the acid concentration needs to equal or exceed 3 molar to prevent significant iron extraction. Other authors
6
reported on the
5
Karpacheva, S. M. et al., “Extraction of molybdenum and iron (III) by di-2-ethylhexyl hydrogen phosphate,” Russian Journal of Inorganic Chemistry, V 12, 7, p 1014-1016 (1967).
6
Chiola, Vincent, “Separation of molybdenum values from tungsten values by solvent extraction,” U.S. Pat. No. 3,607,008 (1971). benefit of modifiers in reducing the iron coextraction, e.g. tributyl phosphate, dibutyl butyl phosphonate.
Palant et al.
7
made a detailed study of the extraction of molybdenum by DEHPA. The solutions studies were prepared by dissolving MoO
3
in sulfuric acid, hydrochloric acid, or nitric acid solutions.
7
Palant, A. A. et al., “Extraction of molybdenum (VI) with bis(2-ethylhexyl) hydrogen phosphate from an acidic medium,” Inst. Metall. im. Baikova, Moscow, USSR, Report deposited (1979) pp. 1-19.
Amine exchange has also received much study during the past 40 to 50 years. The difficulties presented by the poor solubility of the amine-molybdenum complex were addressed by using aromatic diluents. Macinnis et al.
8
used tri-n-capryl amine (ALAMINE 336) with the aromatic diluent #28
9
. The authors discuss amine extraction of a complex sulfate-bearing anion. At pH values of 3 and higher, they determined that the ion exchange type mechanism shown in Equation I below predominates.
2MoS
2
+6H
2
O+9O
2
→2H
2
MoO
4
↓4H
2
SO
4
(I)
At pH values below 3, they postulate that the following occurs along with Equation I.
n(R
3
NH.HSO
4
)+(Mo
x
O
y
H
z
)
n
.(SO
4
)
m
→(R
3
NH)
n
.(Mo
x
O
y
H
z
)
n
.(HSO4)
n
.(SO
4
)
m
(II)
8
MacInnis, M. B., Kim, T. K., and Laferty, J. M., “The use of solvent extraction for the production and recovery of high-purity ammonium paramolybdate from normal alkali molybdate solution,” First Intl Conf on Chemistry and Uses for Molybdenum, p. 56-58 (1973).
9
Aromatic diluent #28 is a solvent from 1960 available from Missouri Solvents & Chemicals. The solvent had a boiling range of 165 to 193° C., a flash point of 122° F., a Kauri butanol value of 73, and was 74% aromatics.
Equation II infers that (Mo
x
O
y
H
z
)
n
.(SO
4
)
m
is not ionized and MacInnis postulates some cation transfer. This postulation is based on the fact that
35
S tagged sulfur was found to transfer both from the organic to the aqueous phase and from the aqueous to the organic phase.
Litz found in 1970, that tris, tridecyl amine could be used successfully for molybdenum solvent extraction with an aliphatic diluent. There still was potential for formation of insoluble molybdenum-amine complexes, but the molybdenum-tris tridecyl amine complex's solubility in the diluent was much higher than with other tertiary amines. Tris tridecyl amine in an aliphatic diluent was used in a number of pilot circuits for molybdenum solvent extraction from roaster scrubber solutions and to recover byproduct from uranium leach solutions, but it may never have been used in a commercial circuit.
The transfer of sulfate from strongly acid solutions is a problem with using amines. Also, the amines are relatively nonselective and will transfer silicon, phosphorus, and arsenic probably as heteropoly compounds.
The coextraction of silicon and subsequent solids precipitation during stripping has been a major problem during other studies. The silicon problem was addressed by filtration of the first stripping stage mixture prior to advancing to the settler. Sulfate transfer was high because the solvent could not be fully loaded with molybdenum, i.e., to avoid diluent-insoluble molybdenum-amine complexes, the sulfate transfer was large.
Efficient recovery of chemical-grade ammonium dimolybdate (ADM) requires high purity feed solutions containing 200 to 230 g Mo per liter. Impurities in the solution must be removed to avoid inclusion in the ADM. Impurities, that form hydroxides or sulfides, can be removed by additions or pH-control. Other impurities will build up and unless the mother liquor is bled from the crystallization will report to the ADM.
Typical molybdenum solvent extraction systems acidulate the feed solution, if necessary, prior to contact with the extractant in the mixer. Generally this means that the extractant is converted to the bisulfate form by acid in the feed solu
Balliett Robert W.
Kummer Wolfgang
Litz John E.
McHugh Lawrence F.
Nauta Harry H. K.
Akoril Godfried R.
Eyl Diderico van
H. C. Starck Inc.
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