U.S. patent application number 10/404194 was filed with the patent office on 2003-11-27 for process for the utilization of vanadium in chromium ore as ammonium metavanadate.
This patent application is currently assigned to Bayer Aktiengesellschaft. Invention is credited to Batz, Michael, Block, Hans-Dieter, Weber, Rainer.
Application Number | 20030219367 10/404194 |
Document ID | / |
Family ID | 7714382 |
Filed Date | 2003-11-27 |
United States Patent
Application |
20030219367 |
Kind Code |
A1 |
Weber, Rainer ; et
al. |
November 27, 2003 |
Process for the utilization of vanadium in chromium ore as ammonium
metavanadate
Abstract
A process for recovering the vanadium present in the chromium
ore chromite. as ammonium metavanadate, as a by-product of the
fusion of the chromium ore with alkali and its work-up to produce
sodium chromate solution and sodium dichromate.
Inventors: |
Weber, Rainer; (Odenthal,
DE) ; Block, Hans-Dieter; (Leverkusen, DE) ;
Batz, Michael; (Leichlingen, DE) |
Correspondence
Address: |
WILLIAM GERSTENZANG
NORRIS, MCLAUGHLIN & MARCUS, P.A.
220 EAST 42ND STREET, 30TH FLOOR
NEW YORK
NY
10017
US
|
Assignee: |
Bayer Aktiengesellschaft
Leverkusen
DE
|
Family ID: |
7714382 |
Appl. No.: |
10/404194 |
Filed: |
April 1, 2003 |
Current U.S.
Class: |
423/67 |
Current CPC
Class: |
C01G 31/00 20130101;
C22B 34/32 20130101; C22B 34/22 20130101; Y02P 10/20 20151101; Y02P
10/234 20151101; C22B 3/44 20130101 |
Class at
Publication: |
423/67 |
International
Class: |
C22B 034/22 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2002 |
DE |
10217207.2 |
Claims
We claim:
1. Process for recovering the vanadium present in the chromium ore
chromite, as ammonium metavanadate (NH.sub.4).sub.4V.sub.4O.sub.12,
as a by-product from the vanadium-containing chromate solution
produced in the process of preparing sodium chromate and sodium
dichromate from said ore, which comprises 1. precipitating calcium
vanadate from the sodium chromate solution by adding calcium oxide,
calcium hydroxide, calcium dichromate or calcium chromate at a pH
of 12-13, said pH being established by addition of sodium hydroxide
to the sodium chromate solution, 2. separating the calcium vanadate
precipitate from the solution to form a low-vanadium content sodium
chromate solution, 3. treating the calcium vanadate precipitate
with 1.5 to 10-fold quantity of water, based on the dry weight of
the precipitate, and (a) at least quantity of sodium carbonate
which is stoichiometrically equivalent to the calcium content of
the precipitate or an excess of sodium carbonate and quantity of
carbon dioxide or sodium bicarbonate sufficient to establish a pH
of 8.5-12.3, or (b) with a molar quantity of sodium bicarbonate
which is at least 1.0 times the molar quantity of calcium in the
precipitate, stoichiometry based on the CO.sub.2 content, or an up
to 3-fold molar excess of sodium bicarbonate, or (c) with carbon
dioxide in an at least stoichiometric quantity based on the calcium
content and sodium hydroxide in a quantity sufficient to establish
a pH of at least 8, to form a calcium carbonate precipitate, 4.
separating the calcium carbonate precipitate from the solution, 5.
adding ammonium salts selected from the group consisting of
ammonium carbonate, ammonium hydrogen carbonate, ammonium
carbamate, ammonium hydrogen carbonate-ammonium carbamate double
salt, ammonium chromate (ammonium monochromate), ammonium
dichromate, ammonium polychromate, mixed sodium-ammonium salts of
the foregoing, and associated polyvalent anions as pure substances
or mixtures among one another or as aqueous solutions of the
above-mentioned substances, and adding ammonia in an amount
sufficient to establish a pH of from 7.5 to 11, to the solution
remaining after separation of the calcium carbonate in step 4, with
the molar amount of ammonium salt added being from 2.5 to 20 times
the molar amount of vanadium, and maintaining the resulting mixture
at from 0.degree. C. to 50.degree. C. for at least one hour, to
form a sparingly soluble ammonium metavanadate
(NH.sub.4).sub.4V.sub.4O.sub.12/(NH.sub.4VO.sub.3) in the solution,
6. separating the precipitated ammonium metavanadate
(NH.sub.4).sub.4V.sub.4O.sub.12/(NH.sub.4VO.sub.3) from the
solution, 7. alkalizing the remaining solution to a pH of at least
10.5, heating the solution to the boiling point while maintaining a
pH of 10.5 or above to liberate such ammonia or ammonium compounds
as are present and continuing until all the ammonia and ammonium
compounds liberated have been driven off, and recovering the
solution which has been freed of ammonium ions and ammonia and
recycling it to the sodium chromate production process.
2. Process according to claim 1, wherein an excess of carbonate or
bicarbonate is present after step 4, and part of the carbonate or
bicarbonate excess is recovered as sodium bicarbonate after step 4
and before step 5 by passing carbon dioxide into the solution at a
pH of from about 7 to 9 under a carbon dioxide pressure of from 0.9
to 10 bar and cooling the solution to from about -10 to 20.degree.
C. and separating precipitated sodium bicarbonate from the
solution.
3. Process according to claim 1, comprising the further step of
drying the ammonium metavanadate produced in step 6.
4. Process according to claim 1, wherein the ammonia or ammonium
compounds liberated from the solution in step 7 is absorbed by a
sodium dichromate solution, a sodium polychromate solution, an
ammonium chromate solution, an ammonium polychromate solution, or a
chromic acid solution to form a solution which is enriched in
ammonium and chromate ions, and said solution which is enriched in
ammonium and chromate ions is used as an ammonium source for the
precipitation of the ammonium metavanadate in step 5.
5. Process according to claim 1, wherein said calcium vanadate
precipitate obtained in step 2 is washed with water or with water
which has been made alkaline by sodium hydroxide.
6. Process according to claim 1, wherein the treatment of calcium
vanadate precipitate with water in step 3 is washing said calcium
vanadate precipitate with from 2 to 4 times its amount of water,
based on the dry weight of the precipitate.
7. Process according to claim 1, wherein the treatment with carbon
dioxide in part (c) in step 3 is carried out at elevated
temperature in the treatment solution for a time of from about 0.1
to 5 hours.
8. Process according to claim 6, wherein the treatment with carbon
dioxide in part (c) in step 3 is carried out at elevated
temperature in the treatment solution for a time of from about 0.1
to 5 hours.
9. Process according to claim 1, wherein after the calcium
carbonate has been separated off in step 4, it is washed with water
to produce a wash water having a vanadium concentration of from 5
to 100 g of V/litre.
Description
[0001] The invention relates to a process in which the vanadium
present in the chromium ore chromite is recovered as ammonium
metavanadate during the course of the fusion of the chromium ore
with alkali and its work-up to produce sodium chromate solution and
the important chromium chemical sodium dichromate.
BACKGROUND OF THE INVENTION
[0002] All processes used for producing sodium dichromate
Na.sub.2Cr.sub.2O.sub.7-2H.sub.2O via sodium chromate solution
employ a procedure having the same principle:
[0003] Chromium spinel or chromite is mixed with residue sodium
carbonate and/or sodium hydroxide and iron oxide (recycled ore)
residue and heated at 1000-1100.degree. C. in the presence of
oxygen. The sodium chromate produced is leached from the resulting
reaction mixture by means of water at a controlled pH. During this
procedure, the vanadium present in the chromite also goes into
solution as sodium vanadate. Control of the pH is necessary to
suppress the dissolution of iron, aluminium, silicon and magnesium.
In general, addition of an acid, e.g. a dichromate solution, is
necessary to adjust the pH. After leaching with water is complete
the sodium chromate solution produced is converted into a sodium
dichromate solution by addition of sulphuric acid or preferably of
carbon dioxide under pressure. Solid sodium dichromate is recovered
from the solution by evaporation and crystallization. This process
is described in BUCHNER, SCHLIEBS, WINTER, BCHEL "Industrielle
Anorganische Chemie", Weinheim 1984, and in Ullmann's Encyclopedia
of Industrial Chemistry, Fifth ed., Vol A 7, Weinheim 1986, p.
67-97.
[0004] It has now been found that the vanadium content of the
sodium dichromate (about 0.2% of V.sub.2O.sub.5 in the
Na.sub.2Cr.sub.2O.sub.7.2- H.sub.2O) interferes in various
applications of the sodium dichromate and its downstream products,
so that purification of the sodium chromate fusion solution to
remove the vanadium before conversion into sodium dichromate is
desirable.
[0005] The removal of vanadium is preferably carried out by
addition of calcium oxide to the sodium chromate solution produced
by leaching and filtration to remove insoluble material. The
solution is in this way brought to a pH of 12-13 (EP-A-0 047 799,
EP 0 453 913 B1), resulting in precipitation of a filterable
calcium hydroxyvanadate Ca.sub.5(OH)(VO.sub.4).sub.3. The removal
of the calcium which has been introduced in excess is carried out
by subsequent precipitation of calcium carbonate from the sodium
chromate solution, as described in EP 0 453 913 B1.
[0006] A consequence of the precipitation of calcium
hydroxyvanadate from a solution having a high concentration of
chromate ions is the high contamination of the calcium
hydroxyvanadate by coprecipitated calcium chromate and sodium
chromate and by entrained calcium oxide. The V.sub.2O.sub.5 content
of the dried "calcium vanadate" precipitate is about 10-20% and is
thus significantly below the V.sub.2O.sub.5 content of pure calcium
hydroxyvanadate Ca.sub.5(VO.sub.4).sub.3OH of 48.7%, but also
significantly higher than the V.sub.2O.sub.5 content of naturally
occurring vanadium-containing ore of not more than 2.4% of
V.sub.2O.sub.5 (cf. Ullmann's Encyclopedia of Industrial Chemistry,
5.sup.th ed., Vol. A27, p. 370). The "calcium vanadate"
precipitate, having a V.sub.2O.sub.5 content of 10-20%, is thus an
attractive starting material for producing vanadium oxide, due to
its high vanadium content as well as its high reactivity which
results from its finely divided nature and low crystallinity. In
addition, the disposal of such a material as waste in a landfill is
not acceptable, because chromate and vanadate would be released to
the environment over time, and the material therefore would have to
be made inert by treatment with reducing agents such as
iron(II)sulphate or sulphur dioxide or the like before it could be
disposed of in a landfill.
[0007] In the processing of this calcium vanadate precipitate, its
valuable constituents, namely vanadium as V in the oxidation state
+5 and chromium as Cr in the oxidation state +6, have to be
obtained as separate or easily separable species, the vanadium in
particular in a readily usable and commercial form and the chromium
in a utilizable form, e.g. one that is able to be reintroduced into
the chromate production process, i.e. recyclable, species or
solution. Readily soluble sodium compounds, which are undesirable
in the wastewater, are to be recovered as a utilizable, recyclable
species and the calcium as insoluble species which can be disposed
of in a landfill or as precursor of a reusable calcium oxide or
reusable calcium chromate or calcium dichromate.
[0008] Solutions containing sodium ions and chromium in the
oxidation state +6 to be reintroduced into the chromate production
process can be so utilized only if they do not contain appreciable
amounts (e.g. >0.1%) of interfering extraneous material.
However, any elements and oxidation states which are not already
present to an appreciable extent in the product stream into which
this solution is to be introduced will interfere. For this reason,
only water H.sub.2O, hydroxide OH- or hydroxonium H.sub.3O.sup.+
ions, carbonate, bicarbonate, carbon dioxide, chromate, dichromate,
polychromate, chromic acid, sodium and also calcium and vanadate in
very minor concentrations are acceptable as constituents of the
solutions which are to be reintroduced into the chromite production
process. Depending on the pH, these solutions can be introduced
into the acidification steps of the sodium chromate process (e.g.
after or during leaching of the furnace clinker) or the
alkalization steps (e.g. before or during vanadate
precipitation).
[0009] The digestion of the calcium vanadate precipitate by means
of sulphuric acid, separation of the precipitated calcium sulphate
from the solution in accordance with a treatment of insoluble
calcium salts which is frequently practiced in industry and
subsequent precipitation of the vanadium as V.sub.2O.sub.5 from the
filtrate by-means of sulphuric acid is prior art.
[0010] However, a consequence is that the chromium is obtained as a
polychromate or chromic acid solution having a high sulphate
content. As the many proposals for removing sulphate from sodium
chromate and dichromate demonstrate, the amounts of sulphate always
introduced as sulphuric acid in earlier processes for producing
sodium chromate and sodium dichromate are nowadays totally
undesirable for further processing of these products (EP 0 453 913
B1).
[0011] Another possible way of treating sparingly soluble salts is
digestion of the calcium vanadate precipitate by means of sodium
carbonate in aqueous solution and subsequent precipitation of the
vanadium as ammonium metavanadate (NH.sub.4).sub.4V.sub.4O.sub.12,
also referred to as NH.sub.4VO.sub.3 for short, by addition of an
excess of ammonium salts. Ammonium metavanadate is a versatile
intermediate, in particular in the route to the most important
vanadium chemical V.sub.2O.sub.5 (cf. Ullmann's Encyclopedia of
Industrial Chemistry, 5.sup.th edition, Vol. A27, Weinheim 1996).
However, in this case too, the resulting solution containing the
chromium as chromate is contaminated with the ions of the
precipitation reagent, i.e. with ammonium ions and the associated
anions, and can therefore not be reused or recycled without
problems. Furthermore, the proportion of the vanadium in the
calcium hydroxyvanadate which is dissolved by means of sodium
carbonate is less than 50% and therefore completely unsatisfactory
unless economically nonviable sodium carbonate excesses are
employed.
[0012] The routes known from the prior art are therefore not
suitable for dissolving vanadium from the calcium vanadate
precipitate obtained from the sodium chromate production process in
such a way that an introduced, readily utilizable and commercial
grade vanadium chemical can be obtained and the valuable chromium
present obtained as a usable or recyclable product which would meet
the above-described requirement.
[0013] The present invention now provides a route by means of which
the vanadium present in the leaching solution from the fusion of
chromium ore with alkali can be obtained as valuable ammonium
metavanadate (NH.sub.4).sub.4V.sub.4O.sub.12 and the valuable
constituents chromium in the oxidation state +6 and sodium ions are
made available as utilizable and recyclable chemicals.
SUMMARY OF THE INVENTION
[0014] The present invention relates to a process for recovering
the vanadium present in the chromium ore chromite as ammonium
metavanadate (NH.sub.4).sub.4V.sub.4O.sub.12 in the course of the
preparation of sodium chromate and sodium dichromate, characterized
by
[0015] 1. precipitation of a calcium vanadate precipitate from the
sodium chromate solution (after pH-controlled removal of the
residue from the chromium ore) by addition of calcium oxide,
calcium hydroxide, calcium dichromate or calcium chromate at pH
12-13 set by addition of sodium hydroxide to the sodium chromate
solution,
[0016] 2. separation of the calcium vanadate precipitate from the
solution by customary solid/liquid separation operations, e.g. by
filtration or centrifugation, and, if appropriate, washing of the
precipitate with water or with water which has been made alkaline
by means of dilute sodium hydroxide solution,
[0017] 3. treatment of the calcium vanadate precipitate with 1.5 to
10-fold quantity of water (ratio based on the dry weight of the
residue), preferably from 2 to 4-fold quantity of water, and (a) at
least that quantity of sodium carbonate which is stoichiometrically
equivalent to the calcium content of the precipitate or an excess
of sodium carbonate and the quantity of carbon dioxide or sodium
bicarbonate necessary to set the pH to 8.5-12.3, preferably 9-11,
or (b) with a molar quantity of sodium bicarbonate which is at
least 1.0 times the molar quantity of calcium in the precipitate
(stoichiometry based on the CO.sub.2 content) or an up to 3-fold
molar excess of sodium bicarbonate, preferably from 1.3- to 2-fold
amount of sodium hydrogen carbonate, or (c) with carbon dioxide in
an at least stoichiometric amount based on the calcium content and
sodium hydroxide in the amount necessary to set a pH of at least 8,
with this treatment preferably being carried out at an elevated
temperature in the treatment solution, e.g. from 50 to 110.degree.
C., for a time of from about 0.1 to 5 hours, preferably from 0.5 to
1.5 hours,
[0018] 4. separation of the calcium carbonate formed from the
solution by means of customary solid/liquid separation operations
and washing of the calcium carbonate with water in such a way that
the vanadium concentration in the aqueous filtrate is from 5 to 100
g of V/litre, preferably 20-50 g of V/litre, particularly
preferably 35-45 g of V/litre, and, if desired, further washing of
the calcium carbonate,
[0019] 5. addition of ammonium salts selected from the group
consisting of ammonium carbonate, ammonium hydrogen carbonate,
ammonium carbamate, ammonium hydrogen carbonate-ammonium carbamate
double salt, ammonium chromate (ammonium monochromate), ammonium
dichromate, ammonium polychromate or mixed sodium-ammonium salts of
the above-mentioned, associated polyvalent anions as pure
substances or mixtures among one another or as aqueous solutions of
the above-mentioned substances, and of ammonia, in such a way that
a pH of from 7.5 to 11, preferably from 9.5 to 10.3, is
established, to the aqueous phase obtained after step 4, with the
molar amount of ammonium salt added being selected so that it is
from 2.5 to 20 times, preferably from 3 to 6 times, the molar
amount of vanadium, and maintenance of the resulting mixture at
from 0.degree. C. to 50.degree. C., preferably from 15 to
40.degree. C., for at least one hour, preferably for from 3 to 5
hours,
[0020] 6. separation of the precipitated ammonium metavanadate
(NH.sub.4).sub.4V.sub.4O.sub.12/(NH.sub.4VO.sub.3) formed from the
solution by means of customary solid/liquid separation operations
and, if desired, washing with water or aqueous solutions,
[0021] 7. alkalization of the remaining aqueous phase to a pH of at
least 10.5, heating of the solution to the boiling point while
maintaining a pH of 10.5 or above until all the ammonium liberated
has been driven off, if desired absorption of this ammonia in water
or aqueous solutions and recovery of the solution which has been
freed of ammonium ions and ammonia for the sodium chromate
production process and recirculation and
[0022] 8. if desired, drying of the ammonium metavanadate produced
in step 6.
[0023] If desired, part of the carbonate or bicarbonate which has
been used in excess is recovered as sodium bicarbonate after step 4
and before step 5 by passing carbon dioxide into the solution at a
pH of from about 7 to 9 under a carbon dioxide pressure of from 0.9
to 10 bar and cooling the solution to from about -10 to 20.degree.
C., preferably from 0 to 5.degree. C., and separation of the
precipitated sodium bicarbonate from the solution.
DETAILED DESCRIPTION
[0024] In the case of the ammonium salts to be added in step 5, it
is of no consequence whether they are added as such, in solution or
in undissolved form, or as their precursors which immediately form
the desired ammonium salts in the reaction solution. Thus, instead
of adding ammonium carbonate or bicarbonate or carbamate, it is
possible to introduce a corresponding amount of carbon dioxide
which reacts immediately with the ammonia introduced to form
ammonium carbonate and/or bicarbonate. Similarly, the ammonium
chromates indicated above can be produced by addition of chromic
acid, sodium polychromate or sodium dichromate to the reaction
solution, without introducing fresh impurities.
[0025] The washing in step 6 of the ammonium metavanadate produced
in step 5 can be carried out using either water or aqueous
solutions having a pH of 7.5-11, preferably 9.5-10.3, when the pH
adjustment is carried out by means of ammonia or sodium hydroxide
and only the salts which are also suitable for step 5 are
introduced. The alkalization in step 7 can be carried out using
sodium hydroxide or sodium carbonate.
[0026] The ammonia which has been liberated and driven off in step
7 can be absorbed in water or in aqueous solutions containing the
anions to be used in step 5 as acid component if internal reuse in
the ammonium metavanadate process is sought.
[0027] The calcium carbonate obtained in step 4 can be passed to
calcium oxide production for use in step 1, or can be converted
into calcium chromate or calcium dichromate or calcium polychromate
by reaction with sodium dichromate or sodium dichromate/sodium
polychromate solution or sodium polychromate/chromic acid solution.
However, it can also, if desired, be deposited in a landfill as a
nonhazardous, insoluble waste material or be used as an auxiliary
in steel production. All other streams obtained can be fed back
into the sodium chromate production process directly and without
further treatment. The washing water which may be obtained in step
2 together with the filtrate generated previously forms the sodium
chromate stream for further conversion into sodium dichromate. The
sodium bicarbonate produced in the step which may optionally be
inserted between steps 4 and 5 is added to the sodium bicarbonate
which is formed in large quantities in the acidification step in
which sodium chromate is converted into sodium dichromate by means
of carbon dioxide under pressure and the combined sodium
bicarbonate is passed to sodium carbonate production for the
chromite fusion. The solution obtained in step 7 which is free of
ammonium ions and ammonia contains only chromate and carbonate and
hydroxide anions and residual vanadate ions and sodium cations in
appreciable amounts. It is added to the sodium chromate solution
obtained by leaching of the furnace clinker in the sodium chromate
production process as alkalizing agent prior to the calcium
vanadate precipitation with complete recovery of the chromium and
sodium present.
[0028] Likewise, the alkaline washing water obtained in step 4,
which contains sodium chromate and sodium vanadate and
sodium(hydrogen)carbonat- e, is added to the sodium chromate
solution prior to the calcium vanadate precipitation.
[0029] The entire process and also the individual steps can be
carried out either batchwise or continuously.
[0030] The invention is illustrated by the following examples:
EXAMPLE 1
Preparation of Calcium Vanadate
[0031] About 50 kg of the calcium vanadate precipitate (more
accurately: calcium hydroxy-vanadate) precipitated from sodium
chromate solution at pH 12.5 (setting of pH by means of sodium
hydroxide, addition of Ca as CaO) are dried at 110.degree. C. for 5
hours and is then found to have the following analytical
composition:
1 10.2% V = 18.2% V.sub.2O.sub.5 7.3% Cr = 14.0% CrO.sub.3 29.1% Ca
= 40.7% CaO 5.2% Na = 7.0% Na.sub.2O 1.3% CO.sub.3.sup.2-
[0032] Main constituents are therefore about 38% of calcium
vanadate Ca.sub.5(VO.sub.4).sub.3OH, about 10% of calcium chromate
CaCrO.sub.4, about 18% of CaO and about 13% of sodium chromate
Na.sub.2CrO.sub.4.
EXAMPLE 2
Digestion of Calcium Vanadate
[0033] 200 g of the dry calcium vanadate precipitate prepared in
Example 1 is in each case mixed with 400 g of water and 155 g of
sodium carbonate. The mixture was heated to 60.degree. C. while
stirring. To establish the desired pH values, carbon dioxide from a
pressure bottle was introduced. The reaction mixture was stirred at
60.degree. C. for 2 hours while continuing to monitor and adjust
the pH. The mixture was then filtered and the filtrate was analyzed
for chromium(VI) and vanadium(V). The filter residue was stirred
twice in succession with 250 ml in each case of water at 60.degree.
C. for 10 minutes and then filtered off again. The washing water
obtained as filtrate was likewise analyzed for chromium(VI) and
vanadium(V). The filter residue which remained was dried at
110.degree. C.
[0034] The results of the experiments carried out at pH 9, pH 10
and pH 111 are shown in the following table.
EXAMPLES 2a, 2b, 2c
[0035]
2 V yield [%] Cr yield [%] Example pH Filtrate Washing water Total
Filtrate Washing water Total Amount of residue [g] 2 a 9 45.2 44.7
89.9 49.2 41.6 90.8 237 2 b 10 46.0 42 88.0 52.4 43.0 95.4 223 2 c
11 60.0 32.3 92.3 65.4 27.0 92.4 193 % figures represent the
theoretical amount of V or Cr in the initial amount (100 g) of dry
calcium vanadate
[0036] In a comparative experiment (Example 2 d) without
introduction of carbon dioxide and thus without control of the pH,
a vanadium(V) yield of less than 50% was obtained.
EXAMPLE 3
Digestion of Calcium Vanadate
[0037] The procedure described in Example 2 was repeated, except
that 90.degree. C. instead of 60.degree. C. was selected as
temperature for the digestion mixture (reaction mixture) and for
the washing water.
[0038] The results with respect to the chromium(V) and vanadium(V)
recovery in the experiments at pH 9, pH 10 and pH 11 are shown in
the following table.
EXAMPLES 3a, 3b, 3c
[0039]
3 V yield [%] Cr yield [%] Example pH Filtrate Washing water Total
Filtrate Washing water Total Amount of residue ([g] 3 a 9 63.8 27.9
91.7 65.7 27.8 93.5 196 3 b 10 79 16.8 95.8 74.0 18.1 92.4 169 3 c
11 77.9 19.3 97.2 77.4 18.5 95.9 164 % figures represent the
theoretical amount of V or Cr in the initial amount (100 g) of dry
calcium vanadate
[0040] Without introduction of carbon dioxide and thus without pH
control, vanadium(V) yields of less than 50% are obtained.
EXAMPLE 4
Digestion of Calcium Vanadate
[0041] The procedure described in Example 2 was repeated, except
that the reaction mixture was prepared from 200 g of dry calcium
vanadate precipitate, 800 g of water and 155 g of sodium carbonate.
The results at a reaction temperature and washing water temperature
of 60.degree. C. and at the pH values of 9, 10 and 11 are shown in
the table of Example 5.
EXAMPLE 5
Digestion of Calcium Vanadate
[0042] The procedure described in Example 4 was repeated, except
that the reaction temperature and the temperature of the washing
water was increased to 90.degree. C. The results are shown in the
following table.
4 V yield [%] Cr yield [%] Example Temperature [.degree. C.] pH
Filtrate Washing water Total Filtrate Washing water Total Amount of
residue [g] 4 a 60 9 75.2 21.2 96.8 73.7 20.3 94.0 171 4 b 60 10
84.7 11.4 96.1 85.0 12.1 97.1 165 4 c 60 11 84.7 12 96.7 83.9 12.0
96.9 164 5 a 90 9 74.9 21.0 95.9 70.3 22.6 92.9 170 5 b 90 10 80.6
11.9 92.5 85.6 13.2 98.8 166 5 c 90 11 83.0 12.7 95.7 84.8 13.2
97.0 166
EXAMPLE 6
[0043] The procedure described in Example 2 was repeated, except
that the reaction mixture was prepared from 200 g of dry calcium
vanadate precipitate, 1200 g of water and 155 g of sodium
carbonate. The results at a reaction temperature of 60.degree. C.
are shown in the table of Example 7.
EXAMPLE 7
[0044] The procedure described in Example 6 was repeated, except,
that the reaction temperature and the temperature of the washing
water was increased to 90.degree. C. The results are shown in the
following table.
5 V yield [%] Cr yield [%] Example Temperature [.degree. C] pH
Filtrate Washing water Total Filtrate Washing water Total Amount of
residue [g] 6 a 60 9 87.1 11.3 98.4 85.9 12.3 98.3 168 6 b 60 10
89.5 8.7 98.2 87.1 9.3 96.4 168 6 c 60 11 90.1 7.8 97.9 90.4 7.6 98
170 7 a 90 9 73.9 22.9 96.8 74.0 22.2 96.6 166 7 b 90 10 90.5 7.1
97.6 88.9 7.7 96.6 169 7 c 90 11 89.5 8.0 97.5 88.0 9.7 97.7
173
EXAMPLE 8
[0045] 500 g of the dry calcium vanadate precipitate prepared in
Example 1 is in each case mixed with 1100 ml of water and
increasing amounts of sodium bicarbonate and heated to 90.degree.
C. In the case of complete conversion of the bicarbonate into
carbonate ions by means of alkali, 305 g was the amount of sodium
bicarbonate stoichiometrically equivalent to the calcium content.
Over the course of one hour, the pH of the mixture rises as a
result of consumption of the bicarbonate (neutralization by bound
hydroxide or oxide, evolution of the carbon dioxide liberated).
After one hour at 90.degree. C., the mixture is filtered and the
filtrate is analyzed. The filter residue is stirred twice in
succession with 625 ml each time of water at 90.degree. C. for 10
minutes and then filtered off again. The chromium(VI) and
vanadium(V) contents determined in the washing water obtained in
this way were added to the values for the filtrates.
[0046] The results are recorded in the following table.
6 V yield [%] Cr yield [%] Amount of NaHCO.sub.3 Final in the in
the Example used [g] pH filtrate Total filtrate Total 8 a 610 9.2
78 98 77 94 8 b 375 12.1 77 98 75 95 8 c 300 12.5 58 74 66 86
EXAMPLE 9
[0047] 500 g of the dry calcium vanadate precipitate prepared in
Example 1 are mixed with 1100 ml of water and 400 g of sodium
bicarbonate and heated to 90.degree. C. while stirring vigorously.
Over the course of one hour at this temperature, the pH rises to
11.8.
[0048] After this time, the resulting calcium carbonate precipitate
is filtered off. The filtrate is isolated and treated with carbon
dioxide gas while cooling. The final temperature of 5.degree. C. in
the stirred mixture is maintained for 30 minutes. While continuing
the treatment with carbon dioxide gas, the sodium bicarbonate
precipitate formed is filtered off and subsequently converted into
sodium carbonate by drying at 110.degree. C. The final weight of
sodium carbonate is 100 g (corresponds to 177 g of dry sodium
carbonate), and the contents of vanadium(V) and of chromium(VI) are
3.0% of V and 2.5% of Cr.
[0049] The calcium carbonate precipitate which has been filtered
off is stirred twice in succession with 625 ml in each case of
water at 90.degree. C. for 10 minutes and then filtered off again.
The washing water obtained in this way is collected separately and
stored.
EXAMPLE 10
[0050] The procedure of Example 9 is repeated, except that 600 g of
sodium bicarbonate are used in the digestion mixture.
[0051] After precipitation of calcium carbonate and filtration, the
filtrate is treated in the same way as in Example 9.
[0052] The sodium carbonate obtained by filtration and drying of
the precipitated sodium bicarbonate weighs 255 g.
EXAMPLE 11
[0053] 5 kg of the dry calcium vanadate precipitate prepared in
Example 1 is mixed with 11 l of water, 3700 g of sodium bicarbonate
and 1000 g of sodium carbonate and heated to 90.degree. C. while
stirring vigorously. After one hour at this temperature, the
calcium carbonate precipitate formed is filtered off and the
filtrate is isolated. The precipitate is stirred twice in
succession with 6.5 l each time of water at 90.degree. C. for
minutes and then filtered off again. The washing water obtained is
isolated.
[0054] The filtrate from the calcium carbonate precipitation is
transferred to a closable stainless steel vessel and in this vessel
is cooled and at the same time treated with carbon dioxide gas.
After displacement of the air by the carbon dioxide gas, the
stainless steel vessel is closed and further carbon dioxide gas is
introduced in the amount necessary to maintain a pressure of 3 bar.
After a temperature of -5.degree. C. has been reached, the mixture
is stirred for another 30 minutes, the stirrer is then turned off
and the contents of the stainless steel vessel are then pushed out
through a filter by means of the carbon dioxide atmosphere.
[0055] The sodium bicarbonate which has been filtered off is dried
at 110.degree. C. and then weighs 1990 g as sodium carbonate.
[0056] The filtrate from the sodium bicarbonate precipitation is
combined with the washing water from the calcium carbonate
precipitation, and the liquid mixture obtained serves as starting
material in some subsequent experiments. The vanadium(V) content
was determined as 19.3 g of V/litre, and the chromium(V) content
was determined as 13.3 g of Cr/litre.
EXAMPLE 12
[0057] The filtrate from experiment 8 a, containing 39 g of V and
28 g of Cr, is diluted with water to 6.5 l, resulting in a solution
containing 6.0 g of V/litre and 4.3 g of Cr/litre, and then mixed
with 690 g of ammonium carbonate.
[0058] The pH of 9 is set by addition of small amounts of sodium
hydroxide. The reaction mixture is stirred at 35.degree. C. for 4
hours, then stirred further at 20.degree. C. for 4 hours and the
ammonium metavanadate precipitate formed is filtered off. The
precipitate is washed with 40 ml of water and dried. The vanadium
content of 44.0% and the ammonium content of 15.0% determined are
close to the theoretical values and indicate the purity of the
ammonium metavanadate produced. As impurities, only 0.23% of
chromium, 0.23% of sodium, 0.001% of calcium and 0.44% of carbonate
were found.
EXAMPLE 13
[0059] The filtrate (1219 g) from experiment 8b, containing 38.4 g
of V and 27.4 g of Cr, is mixed with 160 g of ammonium carbonate at
35.degree. C. The pH is set to 9 by addition of carbon dioxide.
After 1 hour at 35.degree. C., the mixture is stirred at 20.degree.
C. for 4 hours. The precipitate is filtered off, washed with 20 ml
of water at +1.degree. C. and then dried at 110.degree. C. The
contents of 18% of vanadium, 20% of sodium, 30% of carbonate and 4%
of chromium and only 3% of ammonium determined by analysis indicate
that predominantly sodium metavanadate and sodium bicarbonate are
precipitated under the condition of the high sodium content.
EXAMPLE 14
[0060] The filtrate from the sodium bicarbonate precipitation in
Example 9 is mixed at 35.degree. C. with an approximately
three-fold stoichiometric amount relative to the vanadium content
of ammonium ions in the form of ammonium dichromate in aqueous
solution, i.e. 285 g of (NH.sub.4).sub.2Cr.sub.2O.sub.7, brought to
a pH of 9.3 by means of ammonia gas and then stirred at
20-30.degree. C. for 4 hours.
[0061] The ammonium metavanadate which has been filtered off weighs
95 g after drying, the vanadium content is 35.8%, i.e. 34 g of
vanadium corresponding to 85% of the vanadium which was present,
the chromium content is 5.7% and the sodium content is 0.84%.
[0062] A mother liquor from a chromic acid crystallization is
diluted to approximately half its concentration. 1300 ml of this
solution then contain 247.5 g (0.837 mol of
Na.sub.2Cr.sub.2O.sub.7.2H.sub.2O) of sodium dichromate and 170.5 g
of chromic acid (1.705 mol of CrO.sub.3), which corresponds to an
acid removal of 50.5%. This cooled solution is employed for
collecting and binding the ammonia liberated from the filtrate from
the ammonium metavanadate precipitation. This liberation of ammonia
is brought about by adding 50% strength sodium hydroxide solution
to this filtrate until a pH of 13.5 has been reached and then
heating this mixture to boiling. After 8-10 ml of water have
distilled over with the ammonia, heating is stopped. Ammonia and
ammonium ions are no longer detectable in the heated mixture.
Aqueous concentrated ammonia solution is then added to the solution
which has taken up the ammonia driven off until a pH of 10 has been
reached. The solution contains ammonium chromate (2.54 mol) and
sodium chromate (0.84 mol) and excess ammonia to adjust the pH.
EXAMPLE 15
[0063] The filtrate from the sodium bicarbonate precipitation of a
repetition of Example 9 is mixed at 35.degree. C. with 140 g of
ammonium carbonate (NH.sub.4).sub.2CO.sub.3. A pH of 8 is
established. After 75 minutes, precipitation of ammonium
metavanadate commences. After stirring at 20.degree. C. for 4
hours, the mixture is filtered. The amount of filter residue after
drying is 40.3 g, and its vanadium content is 40.0%, i.e. 16.1 g of
V, corresponding to a vanadium yield of 40.3%. The chromium content
is 1.2% and the sodium content is 1.3%.
[0064] The filtrate from the ammonium metavanadate precipitation is
admixed with sodium hydroxide until the pH is 13.7 and is then
heated. The ammonia which is given off is introduced into 30 ml of
water in a glass flask provided with a pH electrode and a dropping
funnel containing 40% strength chromic acid solution. This chromic
acid is added dropwise at such a rate that a pH of 8.5 is
maintained in the ammonium chromate solution which forms. This
treatment is continued until the pH remains stable for 2 minutes
while water continues to be distilled over.
[0065] The alkaline sodium chromate solution remaining after
heating is free of ammonia and ammonium ions, and the residual
vanadium content is 19.1 g/l.
EXAMPLE 16
[0066] The filtrate from the sodium bicarbonate precipitation of a
repetition of Example 9 is admixed at 35.degree. C. with 140 g of
ammonium carbonate and the resulting solution is then brought to a
pH of 10 by addition of ammonia solution. The precipitation of the
ammonium metavanadate commences after 10 minutes. After stirring at
20.degree. for 4 hours, the mixture is filtered. After drying, 65 g
of solid residue containing 42.9% of vanadium, i.e. 27.9 g of V
corresponding to a yield of 69.7% of the vanadium which was
present, are obtained. The chromium content is 0.19% and the sodium
content is 0.13%.
EXAMPLE 17
[0067] The filtrate from the sodium bicarbonate precipitation of a
repetition of Example 9 is admixed at 38.degree. C. with 280 g of
ammonium carbonate and the resulting solution is brought to a pH of
10 by means of ammonia gas. The precipitation of the ammonium
metavanadate commences immediately. After stirring for 4 hours at
30.degree. C. at first and then at 20.degree. C., the precipitate
is filtered off. The solid weighs 83 g after drying, and its
vanadium content is 42.2%, i.e. 35.0 g of V corresponding to a
yield of 87.6% of the vanadium which was present. The chromium and
sodium contents are each 0.77%.
[0068] After alkalization of the filtrate from the ammonium
metavanadate precipitation and driving off of the ammonia in a
manner analogous to that described in Example 15, a sodium chromate
solution having a residual vanadium content of 3.5 g/litre
remains.
EXAMPLE 18
[0069] The filtrate from the sodium bicarbonate precipitation of a
repetition of Example 9 is admixed at 35.degree. C. with 140 g of
ammonium carbonate and the resulting solution is then brought to a
pH of 10 by means of ammonia solution. The ammonium metavanadate
precipitation commences after 15 minutes. While continually cooling
the solution to room temperature, it is stirred for a total of 1
hour, and the precipitate is then filtered off and dried. The
weight is 35.9 g and the vanadium content is 42.3%, i.e. 15.2 g of
V corresponding to 38% of the vanadium present. The chromium
content is 0.28% and the sodium content is 0.16%.
EXAMPLE 19
[0070] 650 ml of the solution obtained in Example 11 from the
filtrate from the sodium bicarbonate precipitation and washing
water from the calcium carbonate precipitation are diluted with
water to 1000 ml, so that the vanadium concentration is now 12.54
g/l (total of 0.246 mol of V). 1180 g of ammonium carbonate are
introduced and the solution is treated with ammonia gas at
33.degree. C. until a pH of 10 has been reached. The ammonium
metavanadate precipitation commences immediately during this
treatment. After stirring at 20.degree. C. for 4 hours, the mixture
is filtered and the filter residue is dried. It weighs 190 g, the
vanadium content is 43.5% and sodium and chromium are present in
amounts of less than 0.1%. The vanadium yield is therefore
65.9%.
* * * * *