CA1176470A - Production of aluminium and uranium products - Google Patents
Production of aluminium and uranium productsInfo
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- CA1176470A CA1176470A CA000383338A CA383338A CA1176470A CA 1176470 A CA1176470 A CA 1176470A CA 000383338 A CA000383338 A CA 000383338A CA 383338 A CA383338 A CA 383338A CA 1176470 A CA1176470 A CA 1176470A
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- acid
- leach
- uranium
- stage
- aluminium
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Abstract
ABSTRACT
The invention concerns a process for recovering uranium and/or aluminium from a refractory silico-aluminous material. The silico-aluminous material is leached in one or more stages to give a pregnant solution which contains little or no acid that would inhibit the recovery of the uranium and/or aluminium from the leach solution. Generally the pH will be in the range of about 1,5 to 2 so that the maximum amount of free acid will be about 5 grams per liter.
The desired materials are recovered from the leach solution.
The invention concerns a process for recovering uranium and/or aluminium from a refractory silico-aluminous material. The silico-aluminous material is leached in one or more stages to give a pregnant solution which contains little or no acid that would inhibit the recovery of the uranium and/or aluminium from the leach solution. Generally the pH will be in the range of about 1,5 to 2 so that the maximum amount of free acid will be about 5 grams per liter.
The desired materials are recovered from the leach solution.
Description
THIS INVENTION relates to the production of aluminium and uranium products from silico-aluminous materials.
Uranium bearing silico-aluminous materials such as clay, shale and ash from the roasting of coal are refractory materials. They require severe treatment to extract the aluminium, uranium and any other valudble metals that may be present.
Procedures that have been proposed are to leach these materials with a high concentration of sulphuric, hydrochloric or nitric acid. However, to ensure maximum extraction of the metals, (i.e. about 90~)~ it has generally been found necessary for the acid concentration at the termination of the leach to be very high. This effect, using sulphuric acid as a leach reagent, is iLlus-trated in rrable I. I~ other words, the amount of acid added to the material has to be well in excess of that which will be consumed by the silico-aluminous material. The resultan-t highly acidified slurry also contains a high concen-tration of di.ssolved sal-ts and generally presents considerable crystallization difficulties, in separa-ting the leached solids from the liquid. In addition, after separation of the leached ~' '7 ti ~ t?~
solid, the leach liquor containing the soluble metal salts has such a high concentration of acid as to present technical difficulties and poor economics for the recovery of the valuable metals from this solution. This particularly applies to uraniferous silico-aluminous materials in which the amount of uranium in the leach solution is of such a low concentration that a solid or liquid ion exchange process is required to extract the uranium. If a high concentration of acid is present this will inhibit the extraction of uranium by the solid or liquid ion exchanger.
TABLE I
EFFECT OF ACID CONCENTRATION ON THE LEACHING ON
UR~L~IUM BEARING SILICO-AUMINOUS ORE AT 2:1 LIQUID/SOLID XATIO
-Metal Dissolved Initial ~I2SO4Terminal H2SO4 Concentration ConcentrationUranium Aluminium g~l g/l %
684 409,5 91,1 89,7 514 262,6 86,8 81,5 358 ~ 159,7 79,0 74,5 200 36,2 65,5 63,4 A further difficulty is that the concentrated acid leach will also extract undesirable metals, such as iron from the silico-aluminous material ancl which, if not removed from the leach liquor, will contaminate the aluminium salt recovered and subsequently the alumina that is obtained on calcining the aluminium salt. The high acidity and -the presence of any metal ~ sulphates in solution will also present difficulties for the removal of the metals.
The Applicants have now provided d process which reduces the problems of the pri.or art referred to above.
An aspect of the invention is as follows:
A process for recovering both uranium and aluminium from a refractory silico-aluminous material, which comprises the steps of (1) leaching the silico-aluminous material in a first leach stage with an acid comprising sulphuric acid at a temperature of 85 to 130C;
10 (2) ssparating the solid and liquid phases to give a pregnant-containing solution insufficient acid to inhibit the recovery of uranium and aluminium therefrom, : the amount of acid utilized for the leaching in the first step being so calculated as to give a pregnant solution which contains insufficient acid to inhibit the recovery of said metals;
(3) passing the residue from the first leach stage to a second leach stage, (4) introducing strong sulphuric acid at a pH of 1,~
to 2 into the second leach stage;
(5) carrying out leaching with the strong acid in the - second leach stage at a temperature of 10 to 30C
higher than the temperature in the first leach stage;
25 l6) washing the solid material from the second leach stage with water and separating the liquid and solid phases from the second leach stage to give a solid phase and an aqueous phase containing dilute sulphuric acid;
J~l ~.J~
-4a-(7~ recycling the liquid phase to the first leach stage to act as the acid for leaching in that stage;
(8) separating uranium from the pregnant solution from the first leach stage;
19) removing iron present from the barren effluent obtained following the removal of uranium; and (lO) thereafter separating aluminium from the substan-tially iron-free solution obtained after removal of the uranium.
The refractory silico-aluminous material may be obtained by roasting coal. The coal contains aluminium and uranium and can be roasted at a temperatuxe in the region of about 400-800C. If it is desired to extract carbonaceous liquid materials from the coal, lower temperatures in the range of about 400-550C can be used, whereas temperature in the range of about 500 800C can ~e used if the recovery of liquid carbonaceous material is not important.
The ash obtained can be subjected to a leach con-taining strong acid~ e.g. sulphuric, hydrochloric or the like acid, at elevated temperatures up to about l30C.
Conveniently, the temperatures used may be in the region of about 85-120C.
After the first leach, the solution may be filtered and the residue subjected to a second leach using concentrated acid. The second leach may be carried out in the sarne tempera-_5 ~ture range. ~t appear~ preferable for thR tem~erature of t~e second leach to ~e slightly higher than the temper~ure of the first leach, hy about 1~-30C. ThN,$! the fîrst ~each may, for example, be carried out at ahout qOC and the second leach a-t about 115C.
After the second leach stage, the li~uid and solid may be separated from each other. The solid res:Ldue may be ! passed to a ~aste dump. The separation conveniently is carried out in a piurality of settlers followed by filtration. The filter cake may be ~ashed wîth water and the water circulated back to the settlers. The solution from the settlers may be allo~ed to overflow and recycle back to the first stage leach.
By doing that, the acid which is recycled is ~eaker -than the concentrated acid which is submitted to the second stage leach.
This solution which is recycled contains the desired metals, namely aluminium and uranium, as well as very little or no free acid. The pH is in the range 1,5 to 2, preferably about 1,7.
The maximum amount of free acïd is about 5 grams per liter, more conveniently a~ou~ 2 grams per liter.
The pregnant solution from the first stage leach is thereafter submitted to recovery of the uranium, e.g. by means of ion exchange or other known process Eor obtaining ur~nium from a solution.
Conveniently, the solu-tion obtained after recoVery of uranium, can be submitted to an aluminium reco~ery step. IE
- the soluti:on conta:Lns lron, as is usually the case, it is necessary to remove the iron before recovering the aluminium.
7~
The iron will be in the ferrous state and can be removed by bacterial oxidation. A very convenient process is the commercially available process for oxidising the iron by passing it through a honeycomb-like structure containing tortuous passages submerged within sulphuric acid, the walls of the passages being coated with a bacterial oxidising agent, and the passages being wide enough to permit the ions of the solution to pass through.
The ferric sulphate obtained can be removed ~y conventional solid or liquid ion exchange procedures.
Thereafter, the aluminium can be recovered from the solution.
The invention is illustrated in non-limiting manner by reference to the accompanying drawings, in which Figure 1 is a flow sheet showing the overall process of the invention; and Figure 2 is a flow sheet showing, in greater detail, the part of the first flow sheet which is shown in broken lines.
.~
In these Figures, a silico-aluminous material 10 is passed to a first leach stage 12 where leaching takes place at about 90C with strong acid. The slurry was fil-tered at 14 and the filter cake :Eorming the first leach residue 16 was passed along line 18 to a second leach s-tage 20 where leaching with strong acid was carried out at about 115C. The slurry from the second leach stage was passed alony line 22 to a pa:ir of settlers 24, 26. The settled ma-terial passing along line 28 was filtered at 30 and washed with water through pipe 32.
The washed residue 34 was disposed of.
~'7~7~3 The filtrate from the filter 30 was passed back along line 36 to the second settler 26. The overflow from the second settler 26 was recirculated back to the first settler 24 along line 37. The overflow from the first settler 24 was recir-culated back to the first and second leaching stages alonglines 38, 40 and 42. Fresh concentrated acid is in-troduced into the second leach stage 20 along line 44.
The liquid phase from the first leach stage 12 is a pregnant solution which is passed along lines 48, 50 to a uranium recovery stage 52. The uranium is extracted by an ion exchanger to give a uranium concentrate in line 54.
The uranium barren effluent passes along line 56 -to an oxidation stage 58 where iron present is oxidised. The solution containing ferric iron passes along line 60 to an iron recovery stage 62. The iron solution 64 obtained is passed to an iron concentrate step 64.
The raffinate from the iron recovery s-tep 62 passes along line 66 to an aluminium recovery step 68 and crystalline aluminium salts are removed at 70. The waste solution from the aluminlum recovery stage 68 passes along line 72 to was-te.
Referring now in more deta:Ll to Figure 2, a compara-tively low acld flltrate ln line 36 ls obtalned after the second stage leach. A portion of t~lis flltrate is passed through lines 38 and 40 -to hot leach the first stage. This extracts a portion oE the metals present with the silico-aluminous material consuming most of the acid. At the same time, any potassium and ferric iron present will form potassium Jarosite which, as a resultant low acid slurry, passes along line 13 to the filter stage 14. It is easy to filter, and the filtrate or pregnant solution passing along line 48 with all the metals, has so little free acid that it is amenable to ion exchange processing.
In the second stage leach, strong acid along line 44, with some solution rom a previous second stage leach and passing along line 42, is then added to the partially leached first stage (unwashed) filter cake. The acid concentration is not so high as to dissolve the Jarosite present. This solubilises about 80 to 90~ of the metals present. The leached high acid slurry passing along line 22 is subjected to a liquid~solid separation procedure in the settlers 24 and 26. The solubility of the salts of the leached-out metals in the solution should not be exceeded. Thi~ is to prevent crystallization that would otherwise hinder subsequent processing. As the acid concentra-tion o the leach liquor in the second stage leach 20 is high, and will be highly corrosive, the liquid/solid separation conveniently is accomplished by a counter-current operation in which dilution of the acid is achieved by the filtrate and water wash of the following filtration step passing along lines 36 and 37. The water wash using water through pipe 32 also ensures maximum removal of entrained salts. The washed residue 34 is discarded.
!C
~ ~'7~ '7~
The filtrate and washings passing alone line 40 are used in the next first stage leach of fresh ore. The conditions conveniently are so arranged as to give a pregnant solution 46 that has an acidity of pH 1,7 or higher. The uranium in the pregnant solution is extracted using a solid or liquid ion exchanger to give a uranium concentrate passing along line 54.
The uranium barren effluent passing along line 56 will invariably contain iron in the ferrous state which, if not removed, contaminates the final aluminium product.
Removal of iron can be best achieved with it in the ferric state. Oxidation of the ferrous ion conveniently is achieved in the oxidation stage 58 by a non-polluting chemical reagent, eg hydrogen peroxide. The solution passing along line 60 is conveniently treated with a solid or liquid ion exchanger to remove the iron. With a sulphuric acid leach and a low acid effluent in line 56, a bacterial oxida-tion of the ferrous iron can be carried out as given by the inexpensive BACFOX process (S.A. Patent No. 76/6191). The raffinate in , b line 66 is evaporated to crystallise out the aluminium sulphate in stage 68, and calcined to alumina.
~: .
The invention is illustrated by reference to the ~ollowlng non-limiting Examples. In Example 1, a two-stage sulphuric acid weak/strong acid leach is effected over 15 leach tests with recycle of s-trong acid liquor from the second stage leach to -the next flrst stage leach. The ash used as starting ma-terial was derived rom a coal roasted at abol1t 700C under oxidising conditions. Sulphuric acid is used as the leach _ ~L~'7~
reagent for this Example. In this Example, only filtration i5 used for -the second stage liquid/solid sep~ration and not a decant-filtration.
1500 grams of ash were divided into 12 equal portions of 125 grams each. To commence the test, 270 ml of 147 g/1 sulphuric acid (to simulate a solution from a previous leach) were used to leach the ~irst 125 grams sample of ash at 90C for 6 hours.
The slurry was filtered and the uranium-aluminous bearing filtrate (now pregnant solution) which contains very little or no frae acid, was sent for recovery of uranium and removal of iron. (Details are given in Example 4).
The partially leached unwashed wet filter cake was repulped with 100 ml water to which 79,7 grams of concentrated acid were added to bring the acid concentration for the second stage equivalent to 586 ~ of H2SO4/litre. The slurry was heated to 115C for 6 hours, with s-tirring. Water was added to the leached slurry. This diluted the liquid phase to prevent crystallization of aluminium sulphate. The slurry was fil-tered at a temperature a few degrees above ambient temperatures.
The cake was given a displacement water wash to remove entrained salts. Thi,'~ fil-trate and washings were split into two portions. A portion was used to leach the next 125 grams sample, and the other portion, plus concentratecl H2SO4, to repulp it aEter the first stage leach. (This was efEected in place of the 100 ml of water used in -the first cycle).
This cycle was repeated until all the 12 samples had been leached. Metal dissolution results in the 12 leaches are given in Table II. From this leach only two products are produced, namely a leached solid and the pregnan-t solution containing the metals.
OF ASH
125 gram of ash taken f~r each test containing 1,3 kg U308/ton, 17,4~ Al, 3,0 Fe.
Sec~nd Stage Leach_ First Stage Leach Filtrate + Metals Dissolved Test Initial Pregnant Initial Wash No. H~S04 g/4 H2S04 g/~ H2S04 gf~ H2S04 g/~ U Al Fe 1 147 Nil 586 126 89,3 81,9 88,1 15 2 126 " 591 115 8?,4 79,9 84,8 3 115 " 589 118 87,4 74,9 67,5 4 118 " 601 112 83,6 76,2 79,9 112 " 657 156 89,3 80,6 79,7 6 156 " 836 98 88,7 79,9 78,3 20 7 98 .Nil 534 96 85,5 72,5 76,4 8 96 " 551 109 87,4 76,4 68,3 9 109 2,2 571 122 88,7 77,6 67,2 122 8,6 588 132 88,1 75,7 53,9 11 132 4,8 557 125 88,1 76,2 72,9 2512 125 1,0 534 114 88,1 76,0 44,2 ~ean121,3 1,4 599,8118,6 87,6 77,3 71,8 Table III below shows that the water wash given to the filter cake reduced the dissolved loss oE uranium (the mos-t valuable metal) -to a neylible amount. This clid not unduly dilu-te the metal concentrations as is shown by the preynant solution _ analysis.
4'7~
TABLE III DISSOLVED LOSS AND CON OENTRATIO~ OF METALS
IN _THE PREGN~NT SOLUTION
Dissolved Loss Pregnant Solution Analysis - 1st Filtrate Test No. ~ U U ~/~ Al g/~ FeII g/~ ~eIII g/~ H250 _ 51 1,9 0~395 11,2 1,5 0,1 Nil
Uranium bearing silico-aluminous materials such as clay, shale and ash from the roasting of coal are refractory materials. They require severe treatment to extract the aluminium, uranium and any other valudble metals that may be present.
Procedures that have been proposed are to leach these materials with a high concentration of sulphuric, hydrochloric or nitric acid. However, to ensure maximum extraction of the metals, (i.e. about 90~)~ it has generally been found necessary for the acid concentration at the termination of the leach to be very high. This effect, using sulphuric acid as a leach reagent, is iLlus-trated in rrable I. I~ other words, the amount of acid added to the material has to be well in excess of that which will be consumed by the silico-aluminous material. The resultan-t highly acidified slurry also contains a high concen-tration of di.ssolved sal-ts and generally presents considerable crystallization difficulties, in separa-ting the leached solids from the liquid. In addition, after separation of the leached ~' '7 ti ~ t?~
solid, the leach liquor containing the soluble metal salts has such a high concentration of acid as to present technical difficulties and poor economics for the recovery of the valuable metals from this solution. This particularly applies to uraniferous silico-aluminous materials in which the amount of uranium in the leach solution is of such a low concentration that a solid or liquid ion exchange process is required to extract the uranium. If a high concentration of acid is present this will inhibit the extraction of uranium by the solid or liquid ion exchanger.
TABLE I
EFFECT OF ACID CONCENTRATION ON THE LEACHING ON
UR~L~IUM BEARING SILICO-AUMINOUS ORE AT 2:1 LIQUID/SOLID XATIO
-Metal Dissolved Initial ~I2SO4Terminal H2SO4 Concentration ConcentrationUranium Aluminium g~l g/l %
684 409,5 91,1 89,7 514 262,6 86,8 81,5 358 ~ 159,7 79,0 74,5 200 36,2 65,5 63,4 A further difficulty is that the concentrated acid leach will also extract undesirable metals, such as iron from the silico-aluminous material ancl which, if not removed from the leach liquor, will contaminate the aluminium salt recovered and subsequently the alumina that is obtained on calcining the aluminium salt. The high acidity and -the presence of any metal ~ sulphates in solution will also present difficulties for the removal of the metals.
The Applicants have now provided d process which reduces the problems of the pri.or art referred to above.
An aspect of the invention is as follows:
A process for recovering both uranium and aluminium from a refractory silico-aluminous material, which comprises the steps of (1) leaching the silico-aluminous material in a first leach stage with an acid comprising sulphuric acid at a temperature of 85 to 130C;
10 (2) ssparating the solid and liquid phases to give a pregnant-containing solution insufficient acid to inhibit the recovery of uranium and aluminium therefrom, : the amount of acid utilized for the leaching in the first step being so calculated as to give a pregnant solution which contains insufficient acid to inhibit the recovery of said metals;
(3) passing the residue from the first leach stage to a second leach stage, (4) introducing strong sulphuric acid at a pH of 1,~
to 2 into the second leach stage;
(5) carrying out leaching with the strong acid in the - second leach stage at a temperature of 10 to 30C
higher than the temperature in the first leach stage;
25 l6) washing the solid material from the second leach stage with water and separating the liquid and solid phases from the second leach stage to give a solid phase and an aqueous phase containing dilute sulphuric acid;
J~l ~.J~
-4a-(7~ recycling the liquid phase to the first leach stage to act as the acid for leaching in that stage;
(8) separating uranium from the pregnant solution from the first leach stage;
19) removing iron present from the barren effluent obtained following the removal of uranium; and (lO) thereafter separating aluminium from the substan-tially iron-free solution obtained after removal of the uranium.
The refractory silico-aluminous material may be obtained by roasting coal. The coal contains aluminium and uranium and can be roasted at a temperatuxe in the region of about 400-800C. If it is desired to extract carbonaceous liquid materials from the coal, lower temperatures in the range of about 400-550C can be used, whereas temperature in the range of about 500 800C can ~e used if the recovery of liquid carbonaceous material is not important.
The ash obtained can be subjected to a leach con-taining strong acid~ e.g. sulphuric, hydrochloric or the like acid, at elevated temperatures up to about l30C.
Conveniently, the temperatures used may be in the region of about 85-120C.
After the first leach, the solution may be filtered and the residue subjected to a second leach using concentrated acid. The second leach may be carried out in the sarne tempera-_5 ~ture range. ~t appear~ preferable for thR tem~erature of t~e second leach to ~e slightly higher than the temper~ure of the first leach, hy about 1~-30C. ThN,$! the fîrst ~each may, for example, be carried out at ahout qOC and the second leach a-t about 115C.
After the second leach stage, the li~uid and solid may be separated from each other. The solid res:Ldue may be ! passed to a ~aste dump. The separation conveniently is carried out in a piurality of settlers followed by filtration. The filter cake may be ~ashed wîth water and the water circulated back to the settlers. The solution from the settlers may be allo~ed to overflow and recycle back to the first stage leach.
By doing that, the acid which is recycled is ~eaker -than the concentrated acid which is submitted to the second stage leach.
This solution which is recycled contains the desired metals, namely aluminium and uranium, as well as very little or no free acid. The pH is in the range 1,5 to 2, preferably about 1,7.
The maximum amount of free acïd is about 5 grams per liter, more conveniently a~ou~ 2 grams per liter.
The pregnant solution from the first stage leach is thereafter submitted to recovery of the uranium, e.g. by means of ion exchange or other known process Eor obtaining ur~nium from a solution.
Conveniently, the solu-tion obtained after recoVery of uranium, can be submitted to an aluminium reco~ery step. IE
- the soluti:on conta:Lns lron, as is usually the case, it is necessary to remove the iron before recovering the aluminium.
7~
The iron will be in the ferrous state and can be removed by bacterial oxidation. A very convenient process is the commercially available process for oxidising the iron by passing it through a honeycomb-like structure containing tortuous passages submerged within sulphuric acid, the walls of the passages being coated with a bacterial oxidising agent, and the passages being wide enough to permit the ions of the solution to pass through.
The ferric sulphate obtained can be removed ~y conventional solid or liquid ion exchange procedures.
Thereafter, the aluminium can be recovered from the solution.
The invention is illustrated in non-limiting manner by reference to the accompanying drawings, in which Figure 1 is a flow sheet showing the overall process of the invention; and Figure 2 is a flow sheet showing, in greater detail, the part of the first flow sheet which is shown in broken lines.
.~
In these Figures, a silico-aluminous material 10 is passed to a first leach stage 12 where leaching takes place at about 90C with strong acid. The slurry was fil-tered at 14 and the filter cake :Eorming the first leach residue 16 was passed along line 18 to a second leach s-tage 20 where leaching with strong acid was carried out at about 115C. The slurry from the second leach stage was passed alony line 22 to a pa:ir of settlers 24, 26. The settled ma-terial passing along line 28 was filtered at 30 and washed with water through pipe 32.
The washed residue 34 was disposed of.
~'7~7~3 The filtrate from the filter 30 was passed back along line 36 to the second settler 26. The overflow from the second settler 26 was recirculated back to the first settler 24 along line 37. The overflow from the first settler 24 was recir-culated back to the first and second leaching stages alonglines 38, 40 and 42. Fresh concentrated acid is in-troduced into the second leach stage 20 along line 44.
The liquid phase from the first leach stage 12 is a pregnant solution which is passed along lines 48, 50 to a uranium recovery stage 52. The uranium is extracted by an ion exchanger to give a uranium concentrate in line 54.
The uranium barren effluent passes along line 56 -to an oxidation stage 58 where iron present is oxidised. The solution containing ferric iron passes along line 60 to an iron recovery stage 62. The iron solution 64 obtained is passed to an iron concentrate step 64.
The raffinate from the iron recovery s-tep 62 passes along line 66 to an aluminium recovery step 68 and crystalline aluminium salts are removed at 70. The waste solution from the aluminlum recovery stage 68 passes along line 72 to was-te.
Referring now in more deta:Ll to Figure 2, a compara-tively low acld flltrate ln line 36 ls obtalned after the second stage leach. A portion of t~lis flltrate is passed through lines 38 and 40 -to hot leach the first stage. This extracts a portion oE the metals present with the silico-aluminous material consuming most of the acid. At the same time, any potassium and ferric iron present will form potassium Jarosite which, as a resultant low acid slurry, passes along line 13 to the filter stage 14. It is easy to filter, and the filtrate or pregnant solution passing along line 48 with all the metals, has so little free acid that it is amenable to ion exchange processing.
In the second stage leach, strong acid along line 44, with some solution rom a previous second stage leach and passing along line 42, is then added to the partially leached first stage (unwashed) filter cake. The acid concentration is not so high as to dissolve the Jarosite present. This solubilises about 80 to 90~ of the metals present. The leached high acid slurry passing along line 22 is subjected to a liquid~solid separation procedure in the settlers 24 and 26. The solubility of the salts of the leached-out metals in the solution should not be exceeded. Thi~ is to prevent crystallization that would otherwise hinder subsequent processing. As the acid concentra-tion o the leach liquor in the second stage leach 20 is high, and will be highly corrosive, the liquid/solid separation conveniently is accomplished by a counter-current operation in which dilution of the acid is achieved by the filtrate and water wash of the following filtration step passing along lines 36 and 37. The water wash using water through pipe 32 also ensures maximum removal of entrained salts. The washed residue 34 is discarded.
!C
~ ~'7~ '7~
The filtrate and washings passing alone line 40 are used in the next first stage leach of fresh ore. The conditions conveniently are so arranged as to give a pregnant solution 46 that has an acidity of pH 1,7 or higher. The uranium in the pregnant solution is extracted using a solid or liquid ion exchanger to give a uranium concentrate passing along line 54.
The uranium barren effluent passing along line 56 will invariably contain iron in the ferrous state which, if not removed, contaminates the final aluminium product.
Removal of iron can be best achieved with it in the ferric state. Oxidation of the ferrous ion conveniently is achieved in the oxidation stage 58 by a non-polluting chemical reagent, eg hydrogen peroxide. The solution passing along line 60 is conveniently treated with a solid or liquid ion exchanger to remove the iron. With a sulphuric acid leach and a low acid effluent in line 56, a bacterial oxida-tion of the ferrous iron can be carried out as given by the inexpensive BACFOX process (S.A. Patent No. 76/6191). The raffinate in , b line 66 is evaporated to crystallise out the aluminium sulphate in stage 68, and calcined to alumina.
~: .
The invention is illustrated by reference to the ~ollowlng non-limiting Examples. In Example 1, a two-stage sulphuric acid weak/strong acid leach is effected over 15 leach tests with recycle of s-trong acid liquor from the second stage leach to -the next flrst stage leach. The ash used as starting ma-terial was derived rom a coal roasted at abol1t 700C under oxidising conditions. Sulphuric acid is used as the leach _ ~L~'7~
reagent for this Example. In this Example, only filtration i5 used for -the second stage liquid/solid sep~ration and not a decant-filtration.
1500 grams of ash were divided into 12 equal portions of 125 grams each. To commence the test, 270 ml of 147 g/1 sulphuric acid (to simulate a solution from a previous leach) were used to leach the ~irst 125 grams sample of ash at 90C for 6 hours.
The slurry was filtered and the uranium-aluminous bearing filtrate (now pregnant solution) which contains very little or no frae acid, was sent for recovery of uranium and removal of iron. (Details are given in Example 4).
The partially leached unwashed wet filter cake was repulped with 100 ml water to which 79,7 grams of concentrated acid were added to bring the acid concentration for the second stage equivalent to 586 ~ of H2SO4/litre. The slurry was heated to 115C for 6 hours, with s-tirring. Water was added to the leached slurry. This diluted the liquid phase to prevent crystallization of aluminium sulphate. The slurry was fil-tered at a temperature a few degrees above ambient temperatures.
The cake was given a displacement water wash to remove entrained salts. Thi,'~ fil-trate and washings were split into two portions. A portion was used to leach the next 125 grams sample, and the other portion, plus concentratecl H2SO4, to repulp it aEter the first stage leach. (This was efEected in place of the 100 ml of water used in -the first cycle).
This cycle was repeated until all the 12 samples had been leached. Metal dissolution results in the 12 leaches are given in Table II. From this leach only two products are produced, namely a leached solid and the pregnan-t solution containing the metals.
OF ASH
125 gram of ash taken f~r each test containing 1,3 kg U308/ton, 17,4~ Al, 3,0 Fe.
Sec~nd Stage Leach_ First Stage Leach Filtrate + Metals Dissolved Test Initial Pregnant Initial Wash No. H~S04 g/4 H2S04 g/~ H2S04 gf~ H2S04 g/~ U Al Fe 1 147 Nil 586 126 89,3 81,9 88,1 15 2 126 " 591 115 8?,4 79,9 84,8 3 115 " 589 118 87,4 74,9 67,5 4 118 " 601 112 83,6 76,2 79,9 112 " 657 156 89,3 80,6 79,7 6 156 " 836 98 88,7 79,9 78,3 20 7 98 .Nil 534 96 85,5 72,5 76,4 8 96 " 551 109 87,4 76,4 68,3 9 109 2,2 571 122 88,7 77,6 67,2 122 8,6 588 132 88,1 75,7 53,9 11 132 4,8 557 125 88,1 76,2 72,9 2512 125 1,0 534 114 88,1 76,0 44,2 ~ean121,3 1,4 599,8118,6 87,6 77,3 71,8 Table III below shows that the water wash given to the filter cake reduced the dissolved loss oE uranium (the mos-t valuable metal) -to a neylible amount. This clid not unduly dilu-te the metal concentrations as is shown by the preynant solution _ analysis.
4'7~
TABLE III DISSOLVED LOSS AND CON OENTRATIO~ OF METALS
IN _THE PREGN~NT SOLUTION
Dissolved Loss Pregnant Solution Analysis - 1st Filtrate Test No. ~ U U ~/~ Al g/~ FeII g/~ ~eIII g/~ H250 _ 51 1,9 0~395 11,2 1,5 0,1 Nil
2 2~5 0~626 13~0 3~1 0~1
3 3,1 . 0,591 12,0 . 3,9 0,1 "
4 7,5 0,707 27,2 4,4 0,3
5 7,5 0~638 26,7 5,0 Nil "
10 6 6~9 0,716 16,7 4,9 0~3 7 1,9 0,603 22,2 4,9 0,1 "
8 2,5 0,618 21,8 4,8 0,4 9 S,0 0~615 25,6 4,6 0,5 2,2 10 7,5 0,631 21~7 4,9 0,6 8,6 15 11 6~9 0,569 22,3 4,5 0,6 4,8 12 11,9 0,632 22,4 4,9 0,2 1,0 Mean 5,4 0,612 20,2 4,3 0,3 . 1,4 . .
In this Example, another silico-aluminous ash which had been roasted at 670C, and which had lower acid-consuming properties, was used.
The procedure was similar to Example 1 except that a larger amount of sample was taken for each leach and -tha-t a counter-curren-t/filtration procedure was used Eor the l:Lquid/solid separation of the second stage leached sl.urry (ie as illustrated in Figure 2).
222,6 kilograms of ash were divided into 21 e~ual portions of 10,6 kilograms each. To commence the -test, 23 litres :~ ~'7~ 7~
of 138 g/l sulphuric acid were used to leach the first 10,6 kilogram of sample at 90C for 6 hours. The slurry was filtered and the uranium-aluminium bearing pregnant solution, which contained little or no free acid, was sent for uranium recovery and removal of iron. The partially leached unwashed wet filter cake was repulped with 8,5 litres of water to which were added 6,0 kilograms of concentrated sulphuric acid to bring the acid concentration to 419 gram/l. The slurry was heated to 115C for 6 hours. The filtrate washings were added to the leached slurry to prevent crystallization of the aluminium sùlphate. The solids were allowed to settle and the solution decanted off. This was repeated once more and then the settled solids were filtered and given a water wash. The filtrate plus washings were then used for a two-stage, counter-current wash and leach of the following 10,6 kilogram sample (in accGrdance with Figure 2)..
The cycle was repeated until all 21 samples had been leached.
Mean metal dissolutions ln the 21 cycles are given in Table IV.
Table V gives the mean dissolved loss and pregnant solution metal concentrations for the 21 leaches.
TA~LE IV EAN RESULTS OF 21 CONSECUTIVE LEACHES
OF SILICO-ALUMINOUS MATERIAL
2nd Stage Leach _ t Staqe Leach_ Filtrate ~ ~etal 3iSSolved No. o~ Initial Pregnant Initial Wash --Leaches ~I?S04 g/e ~I~SO4 g/~ SO4 g/~ ~2~ cJ/æ U Al Fe 21 96,2 4,2 362,~ 93,7 86,7 81,3 86,9 7~
TABLE V ME~N URANIUM DISSOLV~D LOSS AND
,_ _ PREGNANT SOLUTION METAL CON OE NTRRTIONS
, Pregnant Solution Analysis (1s~ F'iltrate) No. of Dlssolved Loss Leaches U % U g/4 Al g/4 FeII g/~ FeIII ~/~ H~SO4 g~
521 0,5 0,448 24,8 4,6 0,4 0,4 The extraction of ~ranium from a pregnant acidic iron salt solution by a solid or liquid ion-exchange is well known and practised world-wide. With th~e present invention, a dilute uranium solution containing a high concentra-tion of aluminium sulphate is provided. This solution is amena~le to treatment with a solid or liquid ion exchanger to recover the uranium.
Example 3 helow demons~rates that uranium can be extracted from such a solution.
A solution containing 0,464 g/l U3o8 and 162 g/l al2SO4 at a pH of 2,0 was passed through a series of four laboratory mixer-settlers at a flow rate o~f 240 ml/min. in counter-current to a flow of 110 ml/minute of 5~ ALAMINE 336 (an anion exchanger) in kerosene. The mixer settler area was 0,0067 m2.
The loaded organic kerosene solution was in turn passed through a further four mixer se-ttlers at a rate of 110 ml/minute in counter-current to 55 ml:minute of 15~ ammonia sulpha-te, maintained a-t pH 4,5 with ammonia, -to strip -the solvent off the loaded uranium. Results are given in Table VI.
.
'7~7~
TABLE VI EXT~CTION OF URANIUM FRO~ AI,UMINIUM
SULPHATE SOLUTION
Fe~d SOlution g/~ Raffinat~ g/~ ~NH4)S04 StriP I~iqUr 1~38 A12~0~ U30~ A1~03 U30~ g/4 0,464 162,0 0,003 16~,0 2,3~
Removal of iron from the raffinate solution was accomplished hy first oxidising the ferrous iron with a Thiobacillus ferro-oxidans bateria culture to the ferric state and then extracting the ferric ion with a suitable solvent.
The rate of oxidation of ferrous iron was at a reasonable fast rate for suitable application of the BACFOX process. To assess this, the oxidatlon rate was compared to a control using a solution that was known to be suitable for oxidation by a BACFOX uni-t. Details are given in Example 4.
_ 100 ml aluminium~ferrous iron solution containing 26 g/l Al and 5 g/l FeII at pH 1,8, were inoculated with 10 ml of a bacteria solution containing Th.ferro-oxidans and 5 gram/l ferric sulphate. A solution containing 4,9 g/l FeII and suitable nutrients but no aluminium was also inoculated with 10 ml of bacteria solut:ion as the control, Both solutions were aera-tad with a f:Lne stream of bubbles. Each day a small aliquot of each solu-tion was removed Eor ferrLc iron assay. The test was carried out at a temperature oE 3~QC. The rate of oxidation 25 of the ferrous iron to ferric in both solutions is given in Table VI.
~1~7~ '7~
T~BLE VI RATE OF OXIDATION OF FERROUS IRON BY
Tti.FERRO-OXIDANS
Al ~/~ FeII g/~ FeIII g/~ ~l25O4 g/~
Assay Aluminium Soln 27,0 4,00~2 0,3 Assay Control Nil 5,0 1,0 2,3 No. of Aluminium Solution Control Solution Days ~ FeII Oxidi_ed to FeIII S F~ ls~
O ' O O
1 7,0 0 2 24,7 1~8 3 44,0 7,1 4 Not done 8,9 92,0 48,2
10 6 6~9 0,716 16,7 4,9 0~3 7 1,9 0,603 22,2 4,9 0,1 "
8 2,5 0,618 21,8 4,8 0,4 9 S,0 0~615 25,6 4,6 0,5 2,2 10 7,5 0,631 21~7 4,9 0,6 8,6 15 11 6~9 0,569 22,3 4,5 0,6 4,8 12 11,9 0,632 22,4 4,9 0,2 1,0 Mean 5,4 0,612 20,2 4,3 0,3 . 1,4 . .
In this Example, another silico-aluminous ash which had been roasted at 670C, and which had lower acid-consuming properties, was used.
The procedure was similar to Example 1 except that a larger amount of sample was taken for each leach and -tha-t a counter-curren-t/filtration procedure was used Eor the l:Lquid/solid separation of the second stage leached sl.urry (ie as illustrated in Figure 2).
222,6 kilograms of ash were divided into 21 e~ual portions of 10,6 kilograms each. To commence the -test, 23 litres :~ ~'7~ 7~
of 138 g/l sulphuric acid were used to leach the first 10,6 kilogram of sample at 90C for 6 hours. The slurry was filtered and the uranium-aluminium bearing pregnant solution, which contained little or no free acid, was sent for uranium recovery and removal of iron. The partially leached unwashed wet filter cake was repulped with 8,5 litres of water to which were added 6,0 kilograms of concentrated sulphuric acid to bring the acid concentration to 419 gram/l. The slurry was heated to 115C for 6 hours. The filtrate washings were added to the leached slurry to prevent crystallization of the aluminium sùlphate. The solids were allowed to settle and the solution decanted off. This was repeated once more and then the settled solids were filtered and given a water wash. The filtrate plus washings were then used for a two-stage, counter-current wash and leach of the following 10,6 kilogram sample (in accGrdance with Figure 2)..
The cycle was repeated until all 21 samples had been leached.
Mean metal dissolutions ln the 21 cycles are given in Table IV.
Table V gives the mean dissolved loss and pregnant solution metal concentrations for the 21 leaches.
TA~LE IV EAN RESULTS OF 21 CONSECUTIVE LEACHES
OF SILICO-ALUMINOUS MATERIAL
2nd Stage Leach _ t Staqe Leach_ Filtrate ~ ~etal 3iSSolved No. o~ Initial Pregnant Initial Wash --Leaches ~I?S04 g/e ~I~SO4 g/~ SO4 g/~ ~2~ cJ/æ U Al Fe 21 96,2 4,2 362,~ 93,7 86,7 81,3 86,9 7~
TABLE V ME~N URANIUM DISSOLV~D LOSS AND
,_ _ PREGNANT SOLUTION METAL CON OE NTRRTIONS
, Pregnant Solution Analysis (1s~ F'iltrate) No. of Dlssolved Loss Leaches U % U g/4 Al g/4 FeII g/~ FeIII ~/~ H~SO4 g~
521 0,5 0,448 24,8 4,6 0,4 0,4 The extraction of ~ranium from a pregnant acidic iron salt solution by a solid or liquid ion-exchange is well known and practised world-wide. With th~e present invention, a dilute uranium solution containing a high concentra-tion of aluminium sulphate is provided. This solution is amena~le to treatment with a solid or liquid ion exchanger to recover the uranium.
Example 3 helow demons~rates that uranium can be extracted from such a solution.
A solution containing 0,464 g/l U3o8 and 162 g/l al2SO4 at a pH of 2,0 was passed through a series of four laboratory mixer-settlers at a flow rate o~f 240 ml/min. in counter-current to a flow of 110 ml/minute of 5~ ALAMINE 336 (an anion exchanger) in kerosene. The mixer settler area was 0,0067 m2.
The loaded organic kerosene solution was in turn passed through a further four mixer se-ttlers at a rate of 110 ml/minute in counter-current to 55 ml:minute of 15~ ammonia sulpha-te, maintained a-t pH 4,5 with ammonia, -to strip -the solvent off the loaded uranium. Results are given in Table VI.
.
'7~7~
TABLE VI EXT~CTION OF URANIUM FRO~ AI,UMINIUM
SULPHATE SOLUTION
Fe~d SOlution g/~ Raffinat~ g/~ ~NH4)S04 StriP I~iqUr 1~38 A12~0~ U30~ A1~03 U30~ g/4 0,464 162,0 0,003 16~,0 2,3~
Removal of iron from the raffinate solution was accomplished hy first oxidising the ferrous iron with a Thiobacillus ferro-oxidans bateria culture to the ferric state and then extracting the ferric ion with a suitable solvent.
The rate of oxidation of ferrous iron was at a reasonable fast rate for suitable application of the BACFOX process. To assess this, the oxidatlon rate was compared to a control using a solution that was known to be suitable for oxidation by a BACFOX uni-t. Details are given in Example 4.
_ 100 ml aluminium~ferrous iron solution containing 26 g/l Al and 5 g/l FeII at pH 1,8, were inoculated with 10 ml of a bacteria solution containing Th.ferro-oxidans and 5 gram/l ferric sulphate. A solution containing 4,9 g/l FeII and suitable nutrients but no aluminium was also inoculated with 10 ml of bacteria solut:ion as the control, Both solutions were aera-tad with a f:Lne stream of bubbles. Each day a small aliquot of each solu-tion was removed Eor ferrLc iron assay. The test was carried out at a temperature oE 3~QC. The rate of oxidation 25 of the ferrous iron to ferric in both solutions is given in Table VI.
~1~7~ '7~
T~BLE VI RATE OF OXIDATION OF FERROUS IRON BY
Tti.FERRO-OXIDANS
Al ~/~ FeII g/~ FeIII g/~ ~l25O4 g/~
Assay Aluminium Soln 27,0 4,00~2 0,3 Assay Control Nil 5,0 1,0 2,3 No. of Aluminium Solution Control Solution Days ~ FeII Oxidi_ed to FeIII S F~ ls~
O ' O O
1 7,0 0 2 24,7 1~8 3 44,0 7,1 4 Not done 8,9 92,0 48,2
6 98,2 The results given in Table VI show that the rate of oxidation of the ferrous iron in the aluminium sulphate solution is faster than that of the control. This indicates that the same size commercial process can be used for the BACFOX unit that now oxidises the ferrous iron in a solution similar to the control.
Extraction of ferric iron from the aluminium solution was accomplished by solvent extraction using procedures well publici~ed in literature and technical magazines. As can be seen, the aluminium can be recovered as an aluminiutn salt.
Extraction of ferric iron from the aluminium solution was accomplished by solvent extraction using procedures well publici~ed in literature and technical magazines. As can be seen, the aluminium can be recovered as an aluminiutn salt.
Claims
1. A process for recovering both uranium and aluminium from a refractory silico-aluminous material, which comprises the steps of (1) leaching the silico-aluminous material in a first leach stage with an acid comprising sulphuric acid at a temperature of 85 to 130°C;
(2) separating the solid and liquid phases to give a pregnant-containing solution insufficient acid to inhibit the recovery of uranium and aluminium therefrom, the amount of acid utilized for the leaching in the first step being so calculated as to give a pregnant solution which contains insufficient acid to inhibit the recovery of said metals;
(3) passing the residue from the first leach stage to a second leach stage;
(4) introducing strong sulphuric acid at a pH of 1.5 to 2 into the second leach stage;
(5) carrying out leaching with the strong acid in the second leach stage at a temperature of 10 to 30°C
higher than the temperature in the first leach stage;
(6) washing the solid material from the second leach stage with water and separating the liquid and solid phases from the second leach stage to give a solid phase and an aqueous phase containing dilute sulphuric acid;
(7) recycling the liquid phase to the first leach stage to act as the acid for leaching in that stage;
(8) separating uranium from the pregnant solution from the first leach stage;
(9) removing iron present from the barren effluent obtained following the removal of uranium; and (10) thereafter separating aluminium from the substan-tially iron-free solution obtained after removal of the uranium.
(2) separating the solid and liquid phases to give a pregnant-containing solution insufficient acid to inhibit the recovery of uranium and aluminium therefrom, the amount of acid utilized for the leaching in the first step being so calculated as to give a pregnant solution which contains insufficient acid to inhibit the recovery of said metals;
(3) passing the residue from the first leach stage to a second leach stage;
(4) introducing strong sulphuric acid at a pH of 1.5 to 2 into the second leach stage;
(5) carrying out leaching with the strong acid in the second leach stage at a temperature of 10 to 30°C
higher than the temperature in the first leach stage;
(6) washing the solid material from the second leach stage with water and separating the liquid and solid phases from the second leach stage to give a solid phase and an aqueous phase containing dilute sulphuric acid;
(7) recycling the liquid phase to the first leach stage to act as the acid for leaching in that stage;
(8) separating uranium from the pregnant solution from the first leach stage;
(9) removing iron present from the barren effluent obtained following the removal of uranium; and (10) thereafter separating aluminium from the substan-tially iron-free solution obtained after removal of the uranium.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000383338A CA1176470A (en) | 1981-08-06 | 1981-08-06 | Production of aluminium and uranium products |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000383338A CA1176470A (en) | 1981-08-06 | 1981-08-06 | Production of aluminium and uranium products |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1176470A true CA1176470A (en) | 1984-10-23 |
Family
ID=4120623
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000383338A Expired CA1176470A (en) | 1981-08-06 | 1981-08-06 | Production of aluminium and uranium products |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1176470A (en) |
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| US7837961B2 (en) | 2007-05-21 | 2010-11-23 | Exploration Orbite Vspa Inc. | Processes for extracting aluminum and iron from aluminous ores |
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| US10174402B2 (en) | 2011-09-16 | 2019-01-08 | Orbite Technologies Inc. | Processes for preparing alumina and various other products |
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