Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group vb metal
Reexamination Certificate
1994-07-14
2001-10-23
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group vb metal
C423S150100, C423S155000
Reexamination Certificate
active
06306356
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the hydrometallurgical art, and is more particularly concerned with a novel method of separating vanadium values from natural bitumen ash in high yields and substantially free from nickel and magnesium values in the ash.
BACKGROUND OF THE INVENTION
As has been long known, vanadium-containing fuel oil ashes can be treated with mineral acid to dissolve the vanadium. Recovery is improved by adding a reducing agent to the leach solution prior to filtering to remove the ash residue from the acidic leach liquor. But this procedure is useful to advantage only if the vanadium recovery need not be so high that other metal values in the ash such as nickel and magnesium interfere with vanadium separation, making more complex and expensive vanadium separation steps necessary.
Another procedure for recovering vanadium from such ash containing 10 to 80% carbon involves selectively dissolving the vanadium in a caustic soda solution. An oxidizing agent is used in sufficient quantities to oxidize the vanadium as reduced vanadium is difficult to dissolve under alkaline conditions. The nickel and magnesium are left behind in the ash residue as vanadium is removed from the solution by solvent extraction, ion exchange or precipitation. But when the ash is that of natural bitumen and contains 10% or more of magnesium as the sulfate, for example, reagent consumption must be high in order to obtain soluble vanadium recoveries as high as 80-90%. Additionally, leaching at high base concentration is required for efficient reaction rate and further significantly increases the cost of the alkali leach process.
SUMMARY OF THE INVENTION
In accordance with this invention, based upon our discovery and novel concepts set out below, it is possible to recover vanadium in very high yields from natural bitumen ash in condition of purity amenable to furnacing or conventional vanadium recovery. Moreover, nickel and magnesium values can also be recovered in high yields and virtually free from vanadium and each other. Further, these new results can be obtained economically and without complex processing or high capital cost.
We have found that natural bitumen ash can be treated in such manner that essentially all its vanadium values are readily separated and removed from the nickel and magnesium values by dissolving them in water and then precipitating the vanadium as polyvanadate and filtering to separate the resulting solid and liquid phases.
This invention is also based upon our concept of slurrying the ash with water and establishing and maintaining the slurry pH below about 6.5 preferably about 2-3. At that stage, we oxidize the vanadium to pentavalant state preparatory to or coincident with heating the slurry to convert the vanadium to polyvanadate.
Filter cake consisting mainly of polyvanadate and containing virtually none of the nickel or magnesium content of the original ash, and the filtrate containing virtually none of the vanadium of the original ash, are further treated to produce the vanadium alloy or other vanadium product on the one hand, and to separate the nickel or magnesium values from each other and recover them in the form desired on the other hand.
In the broadest terms, the method of this invention comprises the steps of mixing natural bitumen ash with water to produce a slurry of 1-40% solids content, maintaining a 1-6.5 pH, agitating the slurry at 20-100° C. and precipitating the vanadium as polyvandate, and separating the solid phase from the liquid phase.
More specifically the new method of this invention embodying this discovery and these new concepts comprises the steps of adjusting the pH of the slurry to below about 6.5 then oxidizing the vanadium values to the pentavalent state, heating the acidified slurry and thereby precipitating the pentavalent vanadium values as polyvanadate and finally removing the solid phase containing substantially all of the vanadium values from the liquid phase containing substantially all the nickel and magnesium values of the ash.
DETAILED DESCRIPTION OF THE INVENTION
In the presently preferred practice of this invention natural bitumen ash is used as a source of recoverable vanadium values. This ash is produced from the burning of an emulsified bitumen marketed under the registered trade name Orimulsion. Orimulsion is produced in the Orinoco Belt in Venezuela by Petroleos de Venezuela S.A. and is offered world wide as a replacement for fuel oil and coal in electric power generating plants. It is produced by emulsifying the bitumen with water using a surfactant. A magnesium salt is also added to the emulsion which thus contains approximately 30% water.
In contrast to ashes resulting from burning fuel oils and coal, Orimulsion ash normally contains 1% of carbon or less and never more than 5% of carbon at most. Fuel oil ashes run 10 to 80% carbon and ashes from flexicoker units and ashes from burning petroleum cokes, while containing some of the same metals as Orimulsion ash, typically contain 75-80% carbon. Orimulsion ash is unique in that it contains 95% or more of the compounds of vanadium, nickel and magnesium. Most of these metal values are as metal sulfates and the ash is also unique in that it is up to 75% or more soluble in water. Fuel oil, petroleum coal and flexicoker ashes are typically insoluble or only slightly soluble (less than 5%) in water.
Depending upon how bitumen emulsion of the Orimulsion type is burned, the proportion of trivalent, tetravalent or pentavalent vanadium in the ash will vary according to the amount of oxygen available in the combustion atmosphere. Most of such ashes contain from 20 to 50% of vanadium in reduced form that is either trivalent or tetravalent state.
The orimulsion-type ash is first mixed with water to form a slurry of from 1 to 40% of slurry weight being the weight of the original ash added. A 20% solids slurry is preferred (i.e. the weight of the original ash is 20% of the total weight of the water and ash). Enough of an inorganic acid, preferably sulfuric acid, is added to the slurry to bring the pH below 6.5, preferably in the range of 2.0 to 3.0. In the usual case the ash will be acidic to the extent that no acid addition is required. If magnesium oxide or other alkali has been added to the ash, as previously mentioned, an acid addition may be necessary to bring the pH to the desired level.
An oxidizing agent is then added to the slurry, preferably in the form of sodium chlorate but suitably hydrogen peroxide, ozone, air, chlorine, potassium chlorate or sodium hypochlorite. In some instances, however, the vanadium is almost completely oxidized in the original ash and no oxidizing agent addition is required.
The slurry is agitated from 1-24 hours at 20-100° C. while the vanadium precipitates as oxidized polyvanadate, precipitating more rapidly at the upper end of the temperature range. A temperature of 80-85° C. is consequently preferred and under these circumstances 94-99+ % of vanadium precipitates, and also typically 95-99%+ of the nickel and magnesium contained in the ash is retained in solution in the leach liquor.
A novel feature of the process just described which distinguishes it from the typical acid leach is that vanadium is deliberately rendered insoluble.
When the precipitation is complete, the slurry is filtered and washed and solid filter cake contains precipitated vanadium as concentrated vanadium solid (typically 28-34% V). This product may be economically treated for vanadium recovery. The filtrate can be treated by conventional practice to separate the nickel values from the magnesium values, 95-100% of the nickel and magnesium present in the original ash being contained in the filtrate. The separation of nickel from magnesium for metals recovery can thus be done without interference from high levels of vanadium. For purposes of recovering the nickel, the ion exchange procedure commonly used in the prior art is suitable and the magnesium may be then recovered by precipitating the carbonate or hydroxide. The filter cake is
Rigsby Ledell
Woolery Michael R.
Bos Steven
Crutcher William C.
U.S. Vanadium Corporation
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