CA2014001A1 - Method for re-using waste sulphuric acid - Google Patents
Method for re-using waste sulphuric acidInfo
- Publication number
- CA2014001A1 CA2014001A1 CA 2014001 CA2014001A CA2014001A1 CA 2014001 A1 CA2014001 A1 CA 2014001A1 CA 2014001 CA2014001 CA 2014001 CA 2014001 A CA2014001 A CA 2014001A CA 2014001 A1 CA2014001 A1 CA 2014001A1
- Authority
- CA
- Canada
- Prior art keywords
- sulphuric acid
- metal salts
- concentration
- suspension
- weight
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B34/00—Obtaining refractory metals
- C22B34/10—Obtaining titanium, zirconium or hafnium
- C22B34/12—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08
- C22B34/1236—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 obtaining titanium or titanium compounds from ores or scrap by wet processes, e.g. by leaching
- C22B34/124—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 obtaining titanium or titanium compounds from ores or scrap by wet processes, e.g. by leaching using acidic solutions or liquors
- C22B34/125—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 obtaining titanium or titanium compounds from ores or scrap by wet processes, e.g. by leaching using acidic solutions or liquors containing a sulfur ion as active agent
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/90—Separation; Purification
- C01B17/901—Recovery from spent acids containing metallic ions, e.g. hydrolysis acids, pickling acids
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
- Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
Abstract
Abstract The approximately 23% waste sulphuric acid resulting from the digestion of raw titanium material is concentrated (CS) to approximately 70% by weight and completely, or at least for the most part, roasted (R) with the precipitated metal salts. whereas the metal oxides (MeO) resulting from the roasting are conveyed to a waste dump, the sulphur oxide gases which are produced are converted, with the addition of water, to highly concentrated, e.g. 98%, sulphuric acid (HCS), which is returned to the raw titanium material digestion process. As the proportion of recycled metal compounds is greatly reduced during recirculation, a titanium dioxide pigment of a better quality can be produced with little expenditure in terms of equipment and energy.
Description
0 0 ~
Mcthod for re-u~in~ waste sulphuric acid The invention relates to a method for re-using the low-concentration waste sulphuric acid resulting from the production of titanium dioxide according to the sulphate method, in which the resulting waste sulphuric acid is concentrated from an initial concentration of 20 - 24% by weight to 65 - 82~ by weight, preferably to - 75% by weight, some of the dissolved metal saltes are precipitated and form a suspension with the concentrated sulphuric acid, and highly concentrated sulph~ric acid is returned to the raw titanium material digestion process.
A method of this kind i~ known from the DE-A-2 729 755, for example.
The production of titanium dioxide entails the compelling problem of disposiny of the waste products, in particular the resulting low-concentration sulphuric ~40~
acid and the metal salts which it contains. The only solution which is feasible on a long-term basis lies in re-using the waste sulphuric acid, the so-called weak acid, for the digestion of raw titanium materials.
However as sulphuric acid o~ a higher concentration is required for this, i.e. a concentration of between approximately 85 and 92~ by weight, accorcling to the starting material, the weak sulphuric acid has to be brought to a higher concentration. Yet, for reasons relating to practicalities and energy, it is advisable and usual only to concentrate the sulphuric acid to a final concentration of approximately 65 to 82% by weight, if possible of only 65 to 75~ by weight, and to mix the concentrated sulphuric acid with sulphuric acid of a very high concentration of at least 95% by weight, so as to obtain the concentration required for starting the raw titanium material digestion reaction.
The removal of the metal salts contained in the waste sulphuric acid, in particular heavy metal sulphates, presents a further problem. In fact most of the metal salts are precipitated and form a suspension when the weak sulphuric acid is concentrated. The majority of the precipitated metal salts can be separated and removed by filtering the concentrated acid, so that, apart from metal salts which are still dissolved, the concentrated sulphuric acid only contains traces of precipitated metal salts.
However the filter cake, which preferably consists of metal sulphates and adhering sulphuric acid, is processed further in a roasting plant, with the 2 ~
resulting sulphur oxide gases being used to produce very highly concentrated sulphuric acid, which is returned to the raw titanium material digestion process.
.he known method entails the disadvantrage that the metal salts remaining in the concentrated sulphuric acid have a negative effect on the quality of the titanium dioxide which is produced, in particular the chromium or vanadium salts which, due to their colouring action, have a particularly powerful effect on the pigment quality. Although an improvement could be achieved by further concentration of the sulphuric acid in a high concentration plant, in which more metal salts would be precipitated, this requires expensive and energy-intensive auxiliary equipment.
The object of the present invention is to eliminate the above-mentioned disadvantages of the prior art and provide a method for re-using the waste sulphuric acid resulting from the production of titanium dioxide according to a simple concept which does not require any expensive auxiliary components, in which the sulphuric acid does not need to be concentrated to more than 65 - 75% by weight and in which the recycled acid nevertheless clearly contains few metallic impurities.
It should also be possible to use the method for different starting products, in particular titanium slag and ilmenite, as the raw material for the production of titanium dioxide.
2 ~
According to the invention, none, or at most only a por-tion of the concentrated sulphuric acid which has been obtained from the waste sulphuric acid is directly returned to the di-gestion process after separating the precipitated metal salts, while the remainder of the suspension is roasted, without the metal salts being separated, and possibly also the metal salts which have been separated from the recycled portion of the concen-trated sulphuric acid, the sulphur oxides resulting from the roasting are converted to highly concentrated sulphuric acid, and that this highly concentrated sulphuric acid is returned to the digestion process.
Thus, the invention provides a method for re-using a low concentration waste sulphuric acid resulting from a digestion pro-cess of a raw titanium material in the production of titanium dioxide according to a sulphate method, the said low-concentration waste sulphuric acid having a sulphuric acid concentration of 20 to 24% by weight and containing metal salts dissolved therein, which method comprises:
[A] concentrating the low-concentration waste sulphuric acid to a sulphuric acid concentration of 65 to 82% by weight and at the same time causing a precipitation of a part of the dis-solved metal salts, thereby forming a suspension;
[B] roasting the entire or a portion of the suspension without separating the precipitated metal salts, thereby producing sulfur oxide and roasted metal salts;
2 ~
- 4a - 22511-151 [C] mixing the thus-produced sulfur oxide with water, thereby producing highly concentrated sulphuric acid;
[D] returning the thus-produced highly concentrated sulphuric acid to the digestion process of a raw titanium material; and [E] where only a portion of the suspension is roasted in step [B], (i) separating the precipitated metal salts from the remainder of the suspension, to produce separated metal salts and a concentrated sulphuric acid having a concentration of about 65 to 82% by weight and substantially free of precipitated metal salts, and (ii) returning the said concentrated sulphuric acid to the digestion process.
In a preferred embodiment, the proportion of concentra-ted sulphuric acid which is directly returned to the digestion process may even be zero, i.e. all of the concentrated suspension is conveyed to the roasting plant. The method thus becomes parti-cularly simple, as no filtration system is required for the sus-pension.
Even if some of the concentrated sulphuric acid, advantageously at most 25~, although usually less, i9 directly returned to the digestion process (namely, at least 75% of the suspension is roasted), the amount of metal salts contained in the concentrated acid is reduced to a fraction of the impurities in known methods, which means that the pigment quality is distinctly 2 ~
- 4b - 22511-151 improved.
The accompanying figures are diagrams showing the circulation of the sulphuric acid in methods according to the invention with different starting materials and 2 ~
different proportions of recycled concentrated sulphuric acid. In the figures:
Fig. 1 is a circulation diagram using QIT slag and with the entire suspension being transferred for roasting, Fig. 2 is a circulation diagram for QIT slag with direct recycling of approximately one fifth of the concentrated sulphuric acid, and Fig. 3 is a circulation diagram using an ilmenite mixture as the raw material.
The numerical values given in the circulation diagrams denote the respective quantities of 100% sulphuric acid in the acid or suspension of the indicated sulphuric acid concentration in tonnes, related to one tonne of produced titanium dioxide.
Canadian QIT titanium slag from the Quebec Iron and Titanium Corp. with a TiO2 content of 78.5% is used in the diagrams reproduced in Figures 1 and 2, a considerable portion of the iron sulphate contained in the ore, in particular in the ilmenite, already haviny been separated, so that the titanium slag only comprises a small portion of iron, although greater proportions of other metals, for example aluminium and magnesium, and in particular undesirable proportions of chromium and vanadium.
2 ~
; - 6 -2.323 t of sulphuric acid, related to 100%, with a concentration greater than 90,5% by weight, e.g. 95% by weight, as well as steam are required for each tonne (t) of titanium dioxide which is produced in the example illustrated in Pigure l. In the titanium dioxide production process which follows the digestion of the raw material 1,3961 t of waste sulphuric acid, related to 100%, with a metal sulphate proportion corresponding to 0.5779 t of sulphuric acid is obtained as a weak acid DS, as well as 0.3490 t of 5% sulphuric acid as a weak filtrate DF. ~he latter has to be disposed of, as it would be highly uneconomical to reprocess it. ~he weak sulphuric acid is concentrated in a multistage evaporation plant C to a concentration of approximately 70% by weight, with the majority of the salts contained in the waste acid, in particular the metal sulphates, being precipitated and passing into suspension. Steam of the usual pressures and temperaturs, some of which results from the subsequent roasting, yet some of which may also be taken as waste heat 'rom the titanium dioxide production process, can be used for the concentration process. This also has a favourable effect on the energy costs, in addition to the advantages of the multistage system.
The suspension ~slurry) CS which i9 formed and which has a sulphuric aoid content in liquid form of 1.3961 t and in the form of metal sulphates of 0.5779 t is conveyed to a roasting plant R, where it is disintegrated. l.7766 t of highly concentrated sulphuric acid HCS i9 'ormed from the resulting gaseous sulphur oxides andthe addition of water.
.. . .
2~1 ~0~1 This highly concentrated sulphuric acid HCS, which is obtained from the roasting, is returned to the digestion process, the sulphuric acid loss resulting from the operation being compensated by the addition of 0.5464 t of fresh acid FS. The metal oxides ~leO
resulting from the oxidation, which are largely free of sulphuric acid, are removed and conveyed to a waste dump.
Figure 2 shows an embodiment in which QIT slag is also used as the raw material. However, in contrast to the example illustrated in the preceding figure, after being concentrated to 70% by weight, some of the suspension CS, with a 0.270 t proportion of sulphuric acid~ related to 100%, is separated off. This portion is conveyed to a filter press F, in which the precipitated salts ~IS are separated. ~he filtered concentrated sulphuric acid FCS is returned to the raw titanium material digestion process, while the filter salts ~IS are conveyed to the roasting plant R with the unfiltered portion of the suspension CS having a liquid sulphuric acid content of 1.1261 t and a sulphuric acid content in the form of sulphates of 0.5779 t. 1.5336 t of sulphuric acid HCS with a concentration of 98% by weight is obtained from the roasting gases and the addition of water and returned to the digestion process. In this case 0.5194 t of 98% fresh acid FS has to be added to compensate for` the losses.
. .
Figure 3 is a cicu~ation diagram in which a mixture of different ilmenites, i.e. a mixture-of ,50% Malaysian, 20% Thai and 30% Australian ilmenite, is used as the 2 ~
xaw material for digestion. 3.3782 t of sulphuric acid are required in the digestion process, and the waste acid amounts to 2.023 t, of which 0.5229 t is lost in suspension as 5% weak filtrate DF with 0.0757 t of metal sulphates, as well as 0.7249 t as adherent acid of the precipitated copperas. 1.5001 t of 23% weak sulphuric acid DS with 0.5546 t of acid in the sulphates are then still available for recirculation.
In this case it is advantageous, after concentrating the weak acid to approximatelxy 70% by weight, to separate off this proportion and free it from the precipitated metal salts ~IS by filtration, so that 1,24 t of 70% sulphuric acid FCS can be returned to the digestion process. ~he remainder of the suspension CS
with 0.2601 t of sulphuric acid and 0.5546 t in the form of sulphates is roasted and processed to form 0.7332 t of 98% sulphuric acid, which is returned to the digestion process. A further 1.4050 t of highly concentrated fresh acid FS has to be added to the digestion process to compensate for the losses.
When compared with the example to be found in the DE-A-2 729 755, the content of metallic impurities in the reprocessed and recycled sulphuric acid is substantially reduced, i.e. to at most 20~ of the comparative example, althougll usually quite a lot less, as in the method according to the invention the concentrated suspension is completely, or at least for the most part, conveyed to the roasting plant, in wich a substantially greater portion of the impurities is separated than in a conventional filtration system. ~he quality of the titanium dioxide pigment which is 2 ~ 0 ~
produced is therefore clearly improved and its impurity content considerably reduced, without having to bring the waste sulphuric acid to higher concentrations by means of expensive equipment and an increased use of energy.
The individual numerical values must of course differ somewhat according to the origin of the raw materials.
When using South African, Canadian, ~orwegian or Australian titanium slag, or ilmenites of a different origin, the required quantities have to be adapted to the respective raw material composition, taking account of the teaching of the invention.
Mcthod for re-u~in~ waste sulphuric acid The invention relates to a method for re-using the low-concentration waste sulphuric acid resulting from the production of titanium dioxide according to the sulphate method, in which the resulting waste sulphuric acid is concentrated from an initial concentration of 20 - 24% by weight to 65 - 82~ by weight, preferably to - 75% by weight, some of the dissolved metal saltes are precipitated and form a suspension with the concentrated sulphuric acid, and highly concentrated sulph~ric acid is returned to the raw titanium material digestion process.
A method of this kind i~ known from the DE-A-2 729 755, for example.
The production of titanium dioxide entails the compelling problem of disposiny of the waste products, in particular the resulting low-concentration sulphuric ~40~
acid and the metal salts which it contains. The only solution which is feasible on a long-term basis lies in re-using the waste sulphuric acid, the so-called weak acid, for the digestion of raw titanium materials.
However as sulphuric acid o~ a higher concentration is required for this, i.e. a concentration of between approximately 85 and 92~ by weight, accorcling to the starting material, the weak sulphuric acid has to be brought to a higher concentration. Yet, for reasons relating to practicalities and energy, it is advisable and usual only to concentrate the sulphuric acid to a final concentration of approximately 65 to 82% by weight, if possible of only 65 to 75~ by weight, and to mix the concentrated sulphuric acid with sulphuric acid of a very high concentration of at least 95% by weight, so as to obtain the concentration required for starting the raw titanium material digestion reaction.
The removal of the metal salts contained in the waste sulphuric acid, in particular heavy metal sulphates, presents a further problem. In fact most of the metal salts are precipitated and form a suspension when the weak sulphuric acid is concentrated. The majority of the precipitated metal salts can be separated and removed by filtering the concentrated acid, so that, apart from metal salts which are still dissolved, the concentrated sulphuric acid only contains traces of precipitated metal salts.
However the filter cake, which preferably consists of metal sulphates and adhering sulphuric acid, is processed further in a roasting plant, with the 2 ~
resulting sulphur oxide gases being used to produce very highly concentrated sulphuric acid, which is returned to the raw titanium material digestion process.
.he known method entails the disadvantrage that the metal salts remaining in the concentrated sulphuric acid have a negative effect on the quality of the titanium dioxide which is produced, in particular the chromium or vanadium salts which, due to their colouring action, have a particularly powerful effect on the pigment quality. Although an improvement could be achieved by further concentration of the sulphuric acid in a high concentration plant, in which more metal salts would be precipitated, this requires expensive and energy-intensive auxiliary equipment.
The object of the present invention is to eliminate the above-mentioned disadvantages of the prior art and provide a method for re-using the waste sulphuric acid resulting from the production of titanium dioxide according to a simple concept which does not require any expensive auxiliary components, in which the sulphuric acid does not need to be concentrated to more than 65 - 75% by weight and in which the recycled acid nevertheless clearly contains few metallic impurities.
It should also be possible to use the method for different starting products, in particular titanium slag and ilmenite, as the raw material for the production of titanium dioxide.
2 ~
According to the invention, none, or at most only a por-tion of the concentrated sulphuric acid which has been obtained from the waste sulphuric acid is directly returned to the di-gestion process after separating the precipitated metal salts, while the remainder of the suspension is roasted, without the metal salts being separated, and possibly also the metal salts which have been separated from the recycled portion of the concen-trated sulphuric acid, the sulphur oxides resulting from the roasting are converted to highly concentrated sulphuric acid, and that this highly concentrated sulphuric acid is returned to the digestion process.
Thus, the invention provides a method for re-using a low concentration waste sulphuric acid resulting from a digestion pro-cess of a raw titanium material in the production of titanium dioxide according to a sulphate method, the said low-concentration waste sulphuric acid having a sulphuric acid concentration of 20 to 24% by weight and containing metal salts dissolved therein, which method comprises:
[A] concentrating the low-concentration waste sulphuric acid to a sulphuric acid concentration of 65 to 82% by weight and at the same time causing a precipitation of a part of the dis-solved metal salts, thereby forming a suspension;
[B] roasting the entire or a portion of the suspension without separating the precipitated metal salts, thereby producing sulfur oxide and roasted metal salts;
2 ~
- 4a - 22511-151 [C] mixing the thus-produced sulfur oxide with water, thereby producing highly concentrated sulphuric acid;
[D] returning the thus-produced highly concentrated sulphuric acid to the digestion process of a raw titanium material; and [E] where only a portion of the suspension is roasted in step [B], (i) separating the precipitated metal salts from the remainder of the suspension, to produce separated metal salts and a concentrated sulphuric acid having a concentration of about 65 to 82% by weight and substantially free of precipitated metal salts, and (ii) returning the said concentrated sulphuric acid to the digestion process.
In a preferred embodiment, the proportion of concentra-ted sulphuric acid which is directly returned to the digestion process may even be zero, i.e. all of the concentrated suspension is conveyed to the roasting plant. The method thus becomes parti-cularly simple, as no filtration system is required for the sus-pension.
Even if some of the concentrated sulphuric acid, advantageously at most 25~, although usually less, i9 directly returned to the digestion process (namely, at least 75% of the suspension is roasted), the amount of metal salts contained in the concentrated acid is reduced to a fraction of the impurities in known methods, which means that the pigment quality is distinctly 2 ~
- 4b - 22511-151 improved.
The accompanying figures are diagrams showing the circulation of the sulphuric acid in methods according to the invention with different starting materials and 2 ~
different proportions of recycled concentrated sulphuric acid. In the figures:
Fig. 1 is a circulation diagram using QIT slag and with the entire suspension being transferred for roasting, Fig. 2 is a circulation diagram for QIT slag with direct recycling of approximately one fifth of the concentrated sulphuric acid, and Fig. 3 is a circulation diagram using an ilmenite mixture as the raw material.
The numerical values given in the circulation diagrams denote the respective quantities of 100% sulphuric acid in the acid or suspension of the indicated sulphuric acid concentration in tonnes, related to one tonne of produced titanium dioxide.
Canadian QIT titanium slag from the Quebec Iron and Titanium Corp. with a TiO2 content of 78.5% is used in the diagrams reproduced in Figures 1 and 2, a considerable portion of the iron sulphate contained in the ore, in particular in the ilmenite, already haviny been separated, so that the titanium slag only comprises a small portion of iron, although greater proportions of other metals, for example aluminium and magnesium, and in particular undesirable proportions of chromium and vanadium.
2 ~
; - 6 -2.323 t of sulphuric acid, related to 100%, with a concentration greater than 90,5% by weight, e.g. 95% by weight, as well as steam are required for each tonne (t) of titanium dioxide which is produced in the example illustrated in Pigure l. In the titanium dioxide production process which follows the digestion of the raw material 1,3961 t of waste sulphuric acid, related to 100%, with a metal sulphate proportion corresponding to 0.5779 t of sulphuric acid is obtained as a weak acid DS, as well as 0.3490 t of 5% sulphuric acid as a weak filtrate DF. ~he latter has to be disposed of, as it would be highly uneconomical to reprocess it. ~he weak sulphuric acid is concentrated in a multistage evaporation plant C to a concentration of approximately 70% by weight, with the majority of the salts contained in the waste acid, in particular the metal sulphates, being precipitated and passing into suspension. Steam of the usual pressures and temperaturs, some of which results from the subsequent roasting, yet some of which may also be taken as waste heat 'rom the titanium dioxide production process, can be used for the concentration process. This also has a favourable effect on the energy costs, in addition to the advantages of the multistage system.
The suspension ~slurry) CS which i9 formed and which has a sulphuric aoid content in liquid form of 1.3961 t and in the form of metal sulphates of 0.5779 t is conveyed to a roasting plant R, where it is disintegrated. l.7766 t of highly concentrated sulphuric acid HCS i9 'ormed from the resulting gaseous sulphur oxides andthe addition of water.
.. . .
2~1 ~0~1 This highly concentrated sulphuric acid HCS, which is obtained from the roasting, is returned to the digestion process, the sulphuric acid loss resulting from the operation being compensated by the addition of 0.5464 t of fresh acid FS. The metal oxides ~leO
resulting from the oxidation, which are largely free of sulphuric acid, are removed and conveyed to a waste dump.
Figure 2 shows an embodiment in which QIT slag is also used as the raw material. However, in contrast to the example illustrated in the preceding figure, after being concentrated to 70% by weight, some of the suspension CS, with a 0.270 t proportion of sulphuric acid~ related to 100%, is separated off. This portion is conveyed to a filter press F, in which the precipitated salts ~IS are separated. ~he filtered concentrated sulphuric acid FCS is returned to the raw titanium material digestion process, while the filter salts ~IS are conveyed to the roasting plant R with the unfiltered portion of the suspension CS having a liquid sulphuric acid content of 1.1261 t and a sulphuric acid content in the form of sulphates of 0.5779 t. 1.5336 t of sulphuric acid HCS with a concentration of 98% by weight is obtained from the roasting gases and the addition of water and returned to the digestion process. In this case 0.5194 t of 98% fresh acid FS has to be added to compensate for` the losses.
. .
Figure 3 is a cicu~ation diagram in which a mixture of different ilmenites, i.e. a mixture-of ,50% Malaysian, 20% Thai and 30% Australian ilmenite, is used as the 2 ~
xaw material for digestion. 3.3782 t of sulphuric acid are required in the digestion process, and the waste acid amounts to 2.023 t, of which 0.5229 t is lost in suspension as 5% weak filtrate DF with 0.0757 t of metal sulphates, as well as 0.7249 t as adherent acid of the precipitated copperas. 1.5001 t of 23% weak sulphuric acid DS with 0.5546 t of acid in the sulphates are then still available for recirculation.
In this case it is advantageous, after concentrating the weak acid to approximatelxy 70% by weight, to separate off this proportion and free it from the precipitated metal salts ~IS by filtration, so that 1,24 t of 70% sulphuric acid FCS can be returned to the digestion process. ~he remainder of the suspension CS
with 0.2601 t of sulphuric acid and 0.5546 t in the form of sulphates is roasted and processed to form 0.7332 t of 98% sulphuric acid, which is returned to the digestion process. A further 1.4050 t of highly concentrated fresh acid FS has to be added to the digestion process to compensate for the losses.
When compared with the example to be found in the DE-A-2 729 755, the content of metallic impurities in the reprocessed and recycled sulphuric acid is substantially reduced, i.e. to at most 20~ of the comparative example, althougll usually quite a lot less, as in the method according to the invention the concentrated suspension is completely, or at least for the most part, conveyed to the roasting plant, in wich a substantially greater portion of the impurities is separated than in a conventional filtration system. ~he quality of the titanium dioxide pigment which is 2 ~ 0 ~
produced is therefore clearly improved and its impurity content considerably reduced, without having to bring the waste sulphuric acid to higher concentrations by means of expensive equipment and an increased use of energy.
The individual numerical values must of course differ somewhat according to the origin of the raw materials.
When using South African, Canadian, ~orwegian or Australian titanium slag, or ilmenites of a different origin, the required quantities have to be adapted to the respective raw material composition, taking account of the teaching of the invention.
Claims (7)
1. A method for re-using a low concentration waste sulphuric acid resulting from a digestion process of a raw titanium material in the production of titanium dioxide according to a sulphate method, the said low-concentration waste sulphuric acid having a sulphuric acid concentration of 20 to 24% by weight and containing metal salts dissolved therein, which method comprises:
[A] concentrating the low-concentration waste sulphuric acid to a sulphuric acid concentration of 65 to 82% by weight and at the same time causing a precipitation of a part of the dis-solved metal salts, thereby forming a suspension;
[B] roasting the entire or a portion of the suspension without separating the precipitated metal salts, thereby producing sulfur oxide and roasted metal salts;
[C] mixing the thus-produced sulfur oxide with water, thereby producing highly concentrated sulphuric acid;
[D] returning the thus-produced highly concentrated sulphuric acid to the digestion process of a raw titanium material; and [E] where only a portion of the suspension is roasted in step [B], (i) separating the precipitated metal salts from the remainder of the suspension, to produce separated metal salts and a concentrated sulphuric acid having a concentration of about 65 to 82% by weight and substantially free of precipitated metal salts, and (ii) returning at most 25% of the said concentrated sulphuric acid to the digestion process.
[A] concentrating the low-concentration waste sulphuric acid to a sulphuric acid concentration of 65 to 82% by weight and at the same time causing a precipitation of a part of the dis-solved metal salts, thereby forming a suspension;
[B] roasting the entire or a portion of the suspension without separating the precipitated metal salts, thereby producing sulfur oxide and roasted metal salts;
[C] mixing the thus-produced sulfur oxide with water, thereby producing highly concentrated sulphuric acid;
[D] returning the thus-produced highly concentrated sulphuric acid to the digestion process of a raw titanium material; and [E] where only a portion of the suspension is roasted in step [B], (i) separating the precipitated metal salts from the remainder of the suspension, to produce separated metal salts and a concentrated sulphuric acid having a concentration of about 65 to 82% by weight and substantially free of precipitated metal salts, and (ii) returning at most 25% of the said concentrated sulphuric acid to the digestion process.
2. The method according to claim 1, wherein the highly concentrated sulphuric acid produced in step ID] has a concentration of at least 95% by weight.
3. The method according to claim 2 wherein at least 75% by weight of the suspension formed in step [A] is employed in the roasting step [B].
4. The method according to claim 3, wherein the entire of the suspension formed in step [A] is employed in the roasting step [B].
5. The method according to claim 3, wherein the separated metal salts produced in step [E] - (i) are returned to the roasting step [B].
6. The method according to any one of claims 1 to 5, wherein steam resulting from the roasting step [B] is used in the concentrating step [A].
7. The method according to any one of claims 1 to 5, wherein waste heat from the titanium dioxide production process is used in the concentration step [A].
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH1315/89A CH677933A5 (en) | 1989-04-07 | 1989-04-07 | |
| CH1315/89-0 | 1989-04-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2014001A1 true CA2014001A1 (en) | 1990-10-07 |
Family
ID=4207571
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2014001 Abandoned CA2014001A1 (en) | 1989-04-07 | 1990-04-06 | Method for re-using waste sulphuric acid |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0392211B1 (en) |
| JP (1) | JP2569197B2 (en) |
| CA (1) | CA2014001A1 (en) |
| CH (1) | CH677933A5 (en) |
| DE (2) | DE3918771A1 (en) |
| ES (1) | ES2048350T3 (en) |
| FI (1) | FI94745C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113443649A (en) * | 2021-07-13 | 2021-09-28 | 攀钢集团研究院有限公司 | Intermittent acidolysis method and device for titanium slag |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110040698B (en) * | 2019-05-17 | 2022-07-29 | 成都先进金属材料产业技术研究院股份有限公司 | Method for treating titanium dioxide waste acid by using magnesium sulfate |
| KR102057976B1 (en) * | 2019-06-11 | 2019-12-20 | 한국지질자원연구원 | Refining method for sulfuric acid sludge |
| CN114438335B (en) * | 2021-12-29 | 2024-02-09 | 绵阳师范学院 | Treatment method of titanium-containing blast furnace slag |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL134070C (en) * | 1966-03-28 | 1900-01-01 | ||
| DE2210637B2 (en) * | 1972-03-06 | 1975-12-04 | Davy Powergas Gmbh, 5000 Koeln | Process for the production of a gas containing sulfur dioxide from a dilute acid obtained during the production of titanium |
| DE2339859A1 (en) * | 1973-08-07 | 1975-02-27 | Metallgesellschaft Ag | PROCESS FOR PROCESSING WASTE Aqueous SULFUR ACID |
| DE2630196A1 (en) * | 1976-07-05 | 1978-01-19 | Bayer Ag | METHOD FOR PRODUCING SULFURIC ACID FROM WASTE ACID AND IRON SULFATE |
| DE2729755C2 (en) * | 1977-07-01 | 1983-12-22 | Kronos Titan-Gesellschaft Mbh, 5090 Leverkusen | Process for the production of titanium dioxide by the discontinuous digestion of ilmenite ores with sulfuric acid |
| DE3327769A1 (en) * | 1983-08-02 | 1985-02-14 | Bayer Ag, 5090 Leverkusen | METHOD FOR THE TREATMENT OF THICK ACID |
-
1989
- 1989-04-07 CH CH1315/89A patent/CH677933A5/de not_active IP Right Cessation
- 1989-06-08 DE DE19893918771 patent/DE3918771A1/en not_active Withdrawn
-
1990
- 1990-03-16 EP EP19900104994 patent/EP0392211B1/en not_active Expired - Lifetime
- 1990-03-16 DE DE90104994T patent/DE59003996D1/en not_active Expired - Fee Related
- 1990-03-16 ES ES90104994T patent/ES2048350T3/en not_active Expired - Lifetime
- 1990-04-04 FI FI901702A patent/FI94745C/en not_active IP Right Cessation
- 1990-04-06 CA CA 2014001 patent/CA2014001A1/en not_active Abandoned
- 1990-04-06 JP JP9050190A patent/JP2569197B2/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113443649A (en) * | 2021-07-13 | 2021-09-28 | 攀钢集团研究院有限公司 | Intermittent acidolysis method and device for titanium slag |
| CN113443649B (en) * | 2021-07-13 | 2022-11-29 | 攀钢集团研究院有限公司 | Intermittent acidolysis method of titanium slag |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2569197B2 (en) | 1997-01-08 |
| FI901702A0 (en) | 1990-04-04 |
| DE59003996D1 (en) | 1994-02-10 |
| CH677933A5 (en) | 1991-07-15 |
| JPH02289406A (en) | 1990-11-29 |
| EP0392211A1 (en) | 1990-10-17 |
| FI94745C (en) | 1995-10-25 |
| ES2048350T3 (en) | 1994-03-16 |
| FI94745B (en) | 1995-07-14 |
| EP0392211B1 (en) | 1993-12-29 |
| DE3918771A1 (en) | 1990-10-11 |
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