CA2030655A1 - Process for the recovery of sulfuric acid - Google Patents
Process for the recovery of sulfuric acidInfo
- Publication number
- CA2030655A1 CA2030655A1 CA002030655A CA2030655A CA2030655A1 CA 2030655 A1 CA2030655 A1 CA 2030655A1 CA 002030655 A CA002030655 A CA 002030655A CA 2030655 A CA2030655 A CA 2030655A CA 2030655 A1 CA2030655 A1 CA 2030655A1
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- Canada
- Prior art keywords
- evaporation
- stage
- sulfuric acid
- acid
- concentration
- 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.)
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Classifications
-
- 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
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
- Heat Treatment Of Water, Waste Water Or Sewage (AREA)
Abstract
A PROCESS FOR THE RECOVERY OF SULFURIC ACID
ABSTRACT OF THE DISCLOSURE
In the recovery of sulfuric acid from waste sulfuric acid containing metal sulfates by concentration through evaporation and removal of the solid metal sulfates, the improvement which comprises concentrating the waste sulfuric acid by evaporation to a concentration of 26 to 32% by weight H2SO4 in an evaporation stage 1 and concentrating the acid obtained by evaporation in a steam-heated evaporation stage 2 to such an extent that the water-soluble metal sulfates are partly suspended in solid form in the acid concentrated by evaporation, the vapors from evaporation stage 2 being used as heating medium in an evaporation stage 3 in which the suspension from evapora-tion stage 2 is concentrated by evaporation to a concentra-tion of 60 to 75% by weight H2SO4. As a result there is reduced consumption of steam and cooling water, reduced corrosion and shorter stoppages for cleaning.
Le A 27 318
ABSTRACT OF THE DISCLOSURE
In the recovery of sulfuric acid from waste sulfuric acid containing metal sulfates by concentration through evaporation and removal of the solid metal sulfates, the improvement which comprises concentrating the waste sulfuric acid by evaporation to a concentration of 26 to 32% by weight H2SO4 in an evaporation stage 1 and concentrating the acid obtained by evaporation in a steam-heated evaporation stage 2 to such an extent that the water-soluble metal sulfates are partly suspended in solid form in the acid concentrated by evaporation, the vapors from evaporation stage 2 being used as heating medium in an evaporation stage 3 in which the suspension from evapora-tion stage 2 is concentrated by evaporation to a concentra-tion of 60 to 75% by weight H2SO4. As a result there is reduced consumption of steam and cooling water, reduced corrosion and shorter stoppages for cleaning.
Le A 27 318
Description
203~
A PROCESS FOR THE RECOVERY OF SULFURIC ACID
This invention relates to a process for the recovery of sulfuric acid from wasteacids containing metal sulfates by concentration through evaporation and removal of the solid metal sulfates.
Sulfuric acid may be recovered from metal-sulfate-containing waste sulfuric acids, for example from spent pickling solutions or from thewasbe acid accumulating in the production of Tio2 by the sulfate method, by ~arious methods which can be attended by more or less serious tech-nical problems, according to the composition of the contam-inated waste acids. Thus, concentration by evaporation to approximately 65% H2S04 in the liquid phase in submerged-burner evaporators (DE-A-l 173 074) or similar, directly heated systems is characterized by high energy consumption, high maintenance costs and emission problems. Multistage concentration by evaporation in forced-circulation vacuum evaporators has proved to be much more favorable in terms of energy and less expensive in terms of maintenance costs, temperatures of 80 to 120-C being preferred (EP-A-133 505).
In this case, however, problems can arise through the rela-tively low temperatures and sulfuric acid concentrations at which the metal sulfates crystallize on account of incrus-tation of the apparatus, particularly the heat-exchange surfaces, and on account of corrosion as a function of the particular acid concentration in the evaporation stages;
these problems are not observed where concentration by evaporation is carried out in submerged-burner evaporators (DE-A-1 173 074), in which the waste acid is directly con-centrated by evaporation in a single stage at around 150C
to form a suspension of metal sulfates, particularly iron sulfate monohydrate, in approximately 65% sulfuric acid.
According to DE-A-2 618 121, concentration of the wasteacid by evaporation is carried out, optionally in several Le A 27 318 , .
A PROCESS FOR THE RECOVERY OF SULFURIC ACID
This invention relates to a process for the recovery of sulfuric acid from wasteacids containing metal sulfates by concentration through evaporation and removal of the solid metal sulfates.
Sulfuric acid may be recovered from metal-sulfate-containing waste sulfuric acids, for example from spent pickling solutions or from thewasbe acid accumulating in the production of Tio2 by the sulfate method, by ~arious methods which can be attended by more or less serious tech-nical problems, according to the composition of the contam-inated waste acids. Thus, concentration by evaporation to approximately 65% H2S04 in the liquid phase in submerged-burner evaporators (DE-A-l 173 074) or similar, directly heated systems is characterized by high energy consumption, high maintenance costs and emission problems. Multistage concentration by evaporation in forced-circulation vacuum evaporators has proved to be much more favorable in terms of energy and less expensive in terms of maintenance costs, temperatures of 80 to 120-C being preferred (EP-A-133 505).
In this case, however, problems can arise through the rela-tively low temperatures and sulfuric acid concentrations at which the metal sulfates crystallize on account of incrus-tation of the apparatus, particularly the heat-exchange surfaces, and on account of corrosion as a function of the particular acid concentration in the evaporation stages;
these problems are not observed where concentration by evaporation is carried out in submerged-burner evaporators (DE-A-1 173 074), in which the waste acid is directly con-centrated by evaporation in a single stage at around 150C
to form a suspension of metal sulfates, particularly iron sulfate monohydrate, in approximately 65% sulfuric acid.
According to DE-A-2 618 121, concentration of the wasteacid by evaporation is carried out, optionally in several Le A 27 318 , .
2~30~
stages, by crystallization of the iron sulfate monohydrate in an evaporation stage in which the sulfuric acid concen-tration in the liquid phase is between 60 and 70%, whereas in optionally preceding evaporation stages concentration by evaporation is only continued to such an extent that no iron sulfate monohydrate crystallizes. This is said to im-prove the deposition of chromium sulfate with the iron sulfate.
On the other hand, it is pointed out in DE-A-2 807 380 that, in the concentration of the waste acid by evaporation, the deposition of CaSO4 and Tio2 on pipe walls and apparatus of the evaporation plants leads to considerable problems because the deposits in question are difficult to remove.
To avoid such deposits, it is proposed that concentration by evaporation be carried out in the presence of solid iron sulfate monohydrate in all evaporation stages, including those with low concentrations of sulfuric acid, any iron sulfate monohydrate deposited at relatively high concen-trations of sulfuric acid being recycled.
Now, the expert is confronted by the problem of recon-ciling these conflicting requirements which, in addition, are an obstacle to optimal process control in terms of energy. In addition, the last two processes mentioned above are designed for waste acids rich in iron sulfates of the type which accumulate in the processing of ilmenite as a titanium raw material. The relevance of the particular teaching to the working up of waste acid from processes in which titanium slag is used is questionable because the slag has only a very low FeSO4 content.
Accordingly, the problem addressed by the invention was to provide a process which would enable waste acids both from the processing of titanium slag and from the proces-sing of ilmenite to be worked up to produce a sulfuric acid which could be reused in the digestion of titanium raw material. At the same time, the energy and maintenance Le A 27 318 2 '' I . , ~ :
~ : ' : :
~ o ~
costs involved in the evaporation process were to be as low as possible.
Surprisingly, this problem was solved by the process according to the invention.
The present invention relates to a process for the recovery of sulfuric acid from waste sulfuric acid contain-ing metal sulfates by concentration through evaporation and removal of the solid metal sulfates, the waste sulfuric acid being concentrated by evaporation to a concentration of 26 to 32% by weight HzSO4 in an evaporation stage 1, the acid obtained is then concentrated by evaporation in a steam-heated evaporation stage 2 to such an extent that water-soluble metal sulfates are suspended in solid form in the acid concentrated by evaporation, preferably in a quantity of at least 1% by weight, the vapors from evapora-tion stage 2 being used as heating medium in an evaporation stage 3 in which the suspension from evaporation stage 2 is concentrated by evaporation to a concentration of 60 to 75%
by weight H2SO4. ~
One particular embodiment of the process according to the invention is characterized in that, without preliminary removal of the solid metal sulfates, the suspension dis-charged from evaporation stage 3 is concentrated by evapor-ation in a steam-heated evaporation stage 4 to a concentra-tion of 72 to 85% by weight sulfuric acid.
In evaporation stage 1, the waste sulfuric acid is preferably concentrated by evaporation at temperatures below 100C and preferably at temperatures below 90C.
In evaporation stage 2, the waste sulfuric acid is preferably concentrated by evaporation at 120 to 165C to a sulfuric acid concentration of 40 to 50% by weight.
In another particular embodiment, the vapors produced in evaporation stage 2 are partly used for concentration of the waste sulfuric acid by evaporation in evaporation stage 1.
Le A 27 318 3 2030~
The acid from evaporation stage 1 is preferably fed into the circulation pipe of evaporation stage 2 on the pump pressure side.
The wasteacid is thus brought to a concentration of 60 to 75% by weight by the three-stage evaporation process de-scribed above. The sulfuric acid may optionally be further concentrated to 85% by weight in a fourth evaporation stage. According to the invention, 10 to 26% waste acids are concentrated in an e~aporation stage 1 to a concentra-tion of at most 32% by weight H2S04 (based on the liquid asa whole) at-temperatures below 100C and preferably at tem-peratures below 9ooc. It has been found that, under these conditions, only small quantities of CaS04 are deposited from the usual waste acids and that this CaS04 is easier to remove from walls of pipes and apparatus than CaS04 which has been deposited at higher temperatures. The concentra-tion by evaporation may take place in a vacuum evaporator heated with steam or with part of the vapors from evapora-tion stage 2 or may be carried out by one of the known ad-vantageous processes which utilize various types of wasteprocess heat (DE-A-2 529 708, DE-A-2 529 709, EP-A-313 715).
The wast*acid concentrated by evaporation to a concen-tration of 26 to 32% by weight H2S04 in evaporation stage 1 is concentrated by evaporation to a concentration of 40 to 50% by weight H2S04 (expressed as salt-free sulfuric acid) in an evaporation stage 2, but in any event to such an ex-tent that the metal sulfates are partly suspended in solid form in the sulfuric acid. In evaporation stage 2, evapo-ration of the water takes place under an absolute pressureof 1 to 4 bar, so that the vapors may advantageously be used for further concentrating the sulfuric acid containing dissolved and solid metal sulfates by evaporation to a con-centration of 60 to 75% by weight H2S04 in an evaporation stage 3 in which evaporation of the water takes place at 80 Le ~ 27 318 4 ~' ~: -2~3~
to 140C under a pressure of 40 to 300 mbar.
The suspension of metal sulfates in 60 to 75% sulfuric acid flowing off from evaporation stage 3 may be suitably cooled (for example in accordance with EP-A-133 505). A
reuseable sulfuric acid may then be separated off from the solid metal sulfates.
In the processing of waste acid from the digestion of titanium slag, it is of particular advantage directly to concentrate the sulfuric acid/metal sulfate suspension flowing off from evaporation stage 3 to a concentration of 72 to 85% H2S04 in an evaporation stage 4 without prelimin-ary separation of the solid metal sulfates. In this evapo-ration stage 4, which is heated with fresh steam, the con-centration by evaporation takes place at 120 to 150C under a pressure of 40 to 200 mbar.
Forced-circulation evaporators are preferably used for the concentration of waste acid by evaporation in evapora-tion stages 2 to 4 by the process according to the inven-tion.
It has been ~ound that the known corrosion problems which are caused by the chloride in the waste acid (E.
Schmoll, Escher Wyss Mitteilungen 2/1978-1/1979, pages 17 to 20) can be avoided if the 26 to 32% waste acid from evap-oration stage 1 is fed into evaporation stage 2 after the circulation pump, pre~erably in the circulated acid stream be~ore or a~ter the steam-heated heat exchanger.
The process according to the invention affords the ~ollowing particular advantages over the prior art:
a) low steam consumption through multistage evaporation utilizing the vapors from evaporation stage 2, b) low consumption of cooling water through multistage evaporation at a high temperature, c) brie~ stoppage times ~or the removal of deposits be-cause the deposits formed in evaporation stage 1 are minimal and relatively soft while the deposits formed Le A 27 318 5 203~5~
in evaporation stages 2 to 4 can be removed by flush-ing with water, d) elimination of corrosion problems caused by the chlo-ride in the wasteacid.
The following ~E~les are intended to illustrate the process according to the invention without limiting it in any way.
Example 1 (Comparison Example) Waste acid of the following composition was wor~ed up according to the prior art (EP-A-133 505) (all quantities in % by weight):
24.5 % HzSO4 0.15 ~ VOSO4 6.62 % FeSO4 o.o9 % Cr2(S04) 3 1.84 % Al2(SO4)3 1.42 % MeSO4 2.20 % MgSO4 63.18 % H2O
(Me z Mn, Ti, Ca, Na etc.) Evaporation stage 1 was operated with waste heat from the sulfuric acid plant in accordance with DE-A-2 529 708. Concentration by evaporation to 28~ H2S04 took place at 73C. Further concentration by evaporation to a concen-tration o~ 68% H2S04 ~expressed as salt-free acid, corre-sponding to IOO-H2S04:(H2S04 + H20) - % H2S04) took place in a ~orced-circulation vacuum evaporator.
~he acid was ~ed into the steam-heated first evapora-tion stage of this evaporator in which concentration by evaporation took place at 110C under a pressure of 760 mbar to a concentration of 41.5% H2SO4 ~salt-free). The acid passing into the second evaporation stage from the first evaporation stage contained all the metal sulfates except CaSo4 in dissolved form.
In the second evaporation stage, which was heated with the vapors from the first evaporation stage, concentration Le A 27 318 6 ~ . "-. .
2 ~ 3 ~
by evaporation took place at 76C/50 mbar to a concentra-tion of 59% H2S04.
The suspension of metal sulfates in 59% sulfuric acid discharged from the second evaporation stage had to be further concentrated by evaporation at 90C/50 mbar in a third steam-heated evaporation stage to obtain the desired concentration of 68% H2S04. The vapors from the second and third evaporation stages were directly condensed with cooling water and removed.
After the suspension discharged from evaporation stage 3 had been cooled from 90C to 54~C over a period of 22 h in a stirred cascade, the solid metal sulfates were sepa-rated off by pressure filtration. The filtrate had the following composition:
65.15 % H2S04, corresp. to 68.1% salt-free 0.005 ~ VOS04 0.19 % FeS04 0.08 % Cr2 ( S04 ) 3 2.1 ~ Al2( S04 ) 3 0 . 3 % MeS04 1.7 % MgS04 30.58 % H20 The evaporator was cleaned monthly, deposits in the thlrd and second evaporation stages being easy to remove with water. In the first evaporation stage, the deposits consisted essentially of calcium sulfate and could not be completely removed with hi~hly pressurized water- The stoppage time required to clean the evaporator was between 20 and 50 hours.
Exam~le 2 Waste ~cid (composition as in Example 1) was concen-trated by evaporation to 28.3$ H2S04 (salt-containing) in an evaporation stage 1 in accordance with DE-A-2 529 708 and fed into the evaporation stage 2 of a forced-circulation evaporator in accordance with the present invention. The acid was fed into the circulation pipe on the pump pressure Le A 27 318 7 side by way of a heat exchanger which was heated with part of the vapors from evaporation stage 2 and in which the acid was heated to 107C. In the steam-heated evaporation stage 2, the acid was concentrated by evaporation to a con-centration of 47% H2S04 (expressed as salt-free acid) at 150C/2.2 bar (absolute). Part of the iron sulfate crys-tallized out. The vapors were passed into the preheating heat exchanger and the heat exchanger of evaporation stage 3.
In evaporation stage 3, the suspension discharged from evaporation stage 2 was concentrated by evaporation to a concentration of 68% ~2S04 at 107C/lOo mbar and directly discharged into the stirred cascade. The vapors from evap-oration stage 3 were condensed by indirect cooling with cooling water. The specific cooling water demand amounted to approximately 65% of the demand in Comparison Example 1.
The suspension was cooled and filtered as in Example 1. However, the filtration rate was approximately 30%
higher than after concentration by evaporation in accord-ance with Example 1. The composition of the 68% sulfuricacid obtained as filtrate was identical with that in Ex-ample 1 within the limits of analytical accuracy. The monthly cleaning intervals were maintained. However, the deposits in evaporation stage 2 were relatively easy to remove with water, so that the overall stoppage time for cleaning could be shortened to 15 to 20 hours.
Example 3 Concentration of the waste acid (composition as in Example 1) by evaporation took place as in Example 2, except that the suspension of metal sulfates in 68% sul-furic acid discharged from evaporation stage 3 was not passed into the stirred cascade, but instead into an evaporation stage 4.
In the steam-heated evaporation stage 4, further con-Le A 27 318 8 ,: ..: ~
, - ' ~ ~ ,., :
, ~ . ,. . ~.
2 ~
centration by evaporation took place at 140C/40 mbar. The suspension discharged was cooled from 140C to 90C in a heat exchanger and introduced into the stirred cascade in which it was cooled to 50C over a period of 25 hours. The suspension was readily filtrable. The sulfuric acid ob-tained as filtrate had the following composition:
79.5 % H2S04, corresp. to 82.3% salt-free 0.008 % VOS04 0.24 % FeS04 0.08 % Cr2(So4)3 1.8 % Al2(S04) 3 0.4 % MeS04 0.9 % MgS04 17.1 % H20 It will be appreciated that the instant specification ls set forth by way of illustration and not limitation, and that various modifications and changes may be made without departin~ from the spirit and scope of the present invention.
Le A 27 318 9
stages, by crystallization of the iron sulfate monohydrate in an evaporation stage in which the sulfuric acid concen-tration in the liquid phase is between 60 and 70%, whereas in optionally preceding evaporation stages concentration by evaporation is only continued to such an extent that no iron sulfate monohydrate crystallizes. This is said to im-prove the deposition of chromium sulfate with the iron sulfate.
On the other hand, it is pointed out in DE-A-2 807 380 that, in the concentration of the waste acid by evaporation, the deposition of CaSO4 and Tio2 on pipe walls and apparatus of the evaporation plants leads to considerable problems because the deposits in question are difficult to remove.
To avoid such deposits, it is proposed that concentration by evaporation be carried out in the presence of solid iron sulfate monohydrate in all evaporation stages, including those with low concentrations of sulfuric acid, any iron sulfate monohydrate deposited at relatively high concen-trations of sulfuric acid being recycled.
Now, the expert is confronted by the problem of recon-ciling these conflicting requirements which, in addition, are an obstacle to optimal process control in terms of energy. In addition, the last two processes mentioned above are designed for waste acids rich in iron sulfates of the type which accumulate in the processing of ilmenite as a titanium raw material. The relevance of the particular teaching to the working up of waste acid from processes in which titanium slag is used is questionable because the slag has only a very low FeSO4 content.
Accordingly, the problem addressed by the invention was to provide a process which would enable waste acids both from the processing of titanium slag and from the proces-sing of ilmenite to be worked up to produce a sulfuric acid which could be reused in the digestion of titanium raw material. At the same time, the energy and maintenance Le A 27 318 2 '' I . , ~ :
~ : ' : :
~ o ~
costs involved in the evaporation process were to be as low as possible.
Surprisingly, this problem was solved by the process according to the invention.
The present invention relates to a process for the recovery of sulfuric acid from waste sulfuric acid contain-ing metal sulfates by concentration through evaporation and removal of the solid metal sulfates, the waste sulfuric acid being concentrated by evaporation to a concentration of 26 to 32% by weight HzSO4 in an evaporation stage 1, the acid obtained is then concentrated by evaporation in a steam-heated evaporation stage 2 to such an extent that water-soluble metal sulfates are suspended in solid form in the acid concentrated by evaporation, preferably in a quantity of at least 1% by weight, the vapors from evapora-tion stage 2 being used as heating medium in an evaporation stage 3 in which the suspension from evaporation stage 2 is concentrated by evaporation to a concentration of 60 to 75%
by weight H2SO4. ~
One particular embodiment of the process according to the invention is characterized in that, without preliminary removal of the solid metal sulfates, the suspension dis-charged from evaporation stage 3 is concentrated by evapor-ation in a steam-heated evaporation stage 4 to a concentra-tion of 72 to 85% by weight sulfuric acid.
In evaporation stage 1, the waste sulfuric acid is preferably concentrated by evaporation at temperatures below 100C and preferably at temperatures below 90C.
In evaporation stage 2, the waste sulfuric acid is preferably concentrated by evaporation at 120 to 165C to a sulfuric acid concentration of 40 to 50% by weight.
In another particular embodiment, the vapors produced in evaporation stage 2 are partly used for concentration of the waste sulfuric acid by evaporation in evaporation stage 1.
Le A 27 318 3 2030~
The acid from evaporation stage 1 is preferably fed into the circulation pipe of evaporation stage 2 on the pump pressure side.
The wasteacid is thus brought to a concentration of 60 to 75% by weight by the three-stage evaporation process de-scribed above. The sulfuric acid may optionally be further concentrated to 85% by weight in a fourth evaporation stage. According to the invention, 10 to 26% waste acids are concentrated in an e~aporation stage 1 to a concentra-tion of at most 32% by weight H2S04 (based on the liquid asa whole) at-temperatures below 100C and preferably at tem-peratures below 9ooc. It has been found that, under these conditions, only small quantities of CaS04 are deposited from the usual waste acids and that this CaS04 is easier to remove from walls of pipes and apparatus than CaS04 which has been deposited at higher temperatures. The concentra-tion by evaporation may take place in a vacuum evaporator heated with steam or with part of the vapors from evapora-tion stage 2 or may be carried out by one of the known ad-vantageous processes which utilize various types of wasteprocess heat (DE-A-2 529 708, DE-A-2 529 709, EP-A-313 715).
The wast*acid concentrated by evaporation to a concen-tration of 26 to 32% by weight H2S04 in evaporation stage 1 is concentrated by evaporation to a concentration of 40 to 50% by weight H2S04 (expressed as salt-free sulfuric acid) in an evaporation stage 2, but in any event to such an ex-tent that the metal sulfates are partly suspended in solid form in the sulfuric acid. In evaporation stage 2, evapo-ration of the water takes place under an absolute pressureof 1 to 4 bar, so that the vapors may advantageously be used for further concentrating the sulfuric acid containing dissolved and solid metal sulfates by evaporation to a con-centration of 60 to 75% by weight H2S04 in an evaporation stage 3 in which evaporation of the water takes place at 80 Le ~ 27 318 4 ~' ~: -2~3~
to 140C under a pressure of 40 to 300 mbar.
The suspension of metal sulfates in 60 to 75% sulfuric acid flowing off from evaporation stage 3 may be suitably cooled (for example in accordance with EP-A-133 505). A
reuseable sulfuric acid may then be separated off from the solid metal sulfates.
In the processing of waste acid from the digestion of titanium slag, it is of particular advantage directly to concentrate the sulfuric acid/metal sulfate suspension flowing off from evaporation stage 3 to a concentration of 72 to 85% H2S04 in an evaporation stage 4 without prelimin-ary separation of the solid metal sulfates. In this evapo-ration stage 4, which is heated with fresh steam, the con-centration by evaporation takes place at 120 to 150C under a pressure of 40 to 200 mbar.
Forced-circulation evaporators are preferably used for the concentration of waste acid by evaporation in evapora-tion stages 2 to 4 by the process according to the inven-tion.
It has been ~ound that the known corrosion problems which are caused by the chloride in the waste acid (E.
Schmoll, Escher Wyss Mitteilungen 2/1978-1/1979, pages 17 to 20) can be avoided if the 26 to 32% waste acid from evap-oration stage 1 is fed into evaporation stage 2 after the circulation pump, pre~erably in the circulated acid stream be~ore or a~ter the steam-heated heat exchanger.
The process according to the invention affords the ~ollowing particular advantages over the prior art:
a) low steam consumption through multistage evaporation utilizing the vapors from evaporation stage 2, b) low consumption of cooling water through multistage evaporation at a high temperature, c) brie~ stoppage times ~or the removal of deposits be-cause the deposits formed in evaporation stage 1 are minimal and relatively soft while the deposits formed Le A 27 318 5 203~5~
in evaporation stages 2 to 4 can be removed by flush-ing with water, d) elimination of corrosion problems caused by the chlo-ride in the wasteacid.
The following ~E~les are intended to illustrate the process according to the invention without limiting it in any way.
Example 1 (Comparison Example) Waste acid of the following composition was wor~ed up according to the prior art (EP-A-133 505) (all quantities in % by weight):
24.5 % HzSO4 0.15 ~ VOSO4 6.62 % FeSO4 o.o9 % Cr2(S04) 3 1.84 % Al2(SO4)3 1.42 % MeSO4 2.20 % MgSO4 63.18 % H2O
(Me z Mn, Ti, Ca, Na etc.) Evaporation stage 1 was operated with waste heat from the sulfuric acid plant in accordance with DE-A-2 529 708. Concentration by evaporation to 28~ H2S04 took place at 73C. Further concentration by evaporation to a concen-tration o~ 68% H2S04 ~expressed as salt-free acid, corre-sponding to IOO-H2S04:(H2S04 + H20) - % H2S04) took place in a ~orced-circulation vacuum evaporator.
~he acid was ~ed into the steam-heated first evapora-tion stage of this evaporator in which concentration by evaporation took place at 110C under a pressure of 760 mbar to a concentration of 41.5% H2SO4 ~salt-free). The acid passing into the second evaporation stage from the first evaporation stage contained all the metal sulfates except CaSo4 in dissolved form.
In the second evaporation stage, which was heated with the vapors from the first evaporation stage, concentration Le A 27 318 6 ~ . "-. .
2 ~ 3 ~
by evaporation took place at 76C/50 mbar to a concentra-tion of 59% H2S04.
The suspension of metal sulfates in 59% sulfuric acid discharged from the second evaporation stage had to be further concentrated by evaporation at 90C/50 mbar in a third steam-heated evaporation stage to obtain the desired concentration of 68% H2S04. The vapors from the second and third evaporation stages were directly condensed with cooling water and removed.
After the suspension discharged from evaporation stage 3 had been cooled from 90C to 54~C over a period of 22 h in a stirred cascade, the solid metal sulfates were sepa-rated off by pressure filtration. The filtrate had the following composition:
65.15 % H2S04, corresp. to 68.1% salt-free 0.005 ~ VOS04 0.19 % FeS04 0.08 % Cr2 ( S04 ) 3 2.1 ~ Al2( S04 ) 3 0 . 3 % MeS04 1.7 % MgS04 30.58 % H20 The evaporator was cleaned monthly, deposits in the thlrd and second evaporation stages being easy to remove with water. In the first evaporation stage, the deposits consisted essentially of calcium sulfate and could not be completely removed with hi~hly pressurized water- The stoppage time required to clean the evaporator was between 20 and 50 hours.
Exam~le 2 Waste ~cid (composition as in Example 1) was concen-trated by evaporation to 28.3$ H2S04 (salt-containing) in an evaporation stage 1 in accordance with DE-A-2 529 708 and fed into the evaporation stage 2 of a forced-circulation evaporator in accordance with the present invention. The acid was fed into the circulation pipe on the pump pressure Le A 27 318 7 side by way of a heat exchanger which was heated with part of the vapors from evaporation stage 2 and in which the acid was heated to 107C. In the steam-heated evaporation stage 2, the acid was concentrated by evaporation to a con-centration of 47% H2S04 (expressed as salt-free acid) at 150C/2.2 bar (absolute). Part of the iron sulfate crys-tallized out. The vapors were passed into the preheating heat exchanger and the heat exchanger of evaporation stage 3.
In evaporation stage 3, the suspension discharged from evaporation stage 2 was concentrated by evaporation to a concentration of 68% ~2S04 at 107C/lOo mbar and directly discharged into the stirred cascade. The vapors from evap-oration stage 3 were condensed by indirect cooling with cooling water. The specific cooling water demand amounted to approximately 65% of the demand in Comparison Example 1.
The suspension was cooled and filtered as in Example 1. However, the filtration rate was approximately 30%
higher than after concentration by evaporation in accord-ance with Example 1. The composition of the 68% sulfuricacid obtained as filtrate was identical with that in Ex-ample 1 within the limits of analytical accuracy. The monthly cleaning intervals were maintained. However, the deposits in evaporation stage 2 were relatively easy to remove with water, so that the overall stoppage time for cleaning could be shortened to 15 to 20 hours.
Example 3 Concentration of the waste acid (composition as in Example 1) by evaporation took place as in Example 2, except that the suspension of metal sulfates in 68% sul-furic acid discharged from evaporation stage 3 was not passed into the stirred cascade, but instead into an evaporation stage 4.
In the steam-heated evaporation stage 4, further con-Le A 27 318 8 ,: ..: ~
, - ' ~ ~ ,., :
, ~ . ,. . ~.
2 ~
centration by evaporation took place at 140C/40 mbar. The suspension discharged was cooled from 140C to 90C in a heat exchanger and introduced into the stirred cascade in which it was cooled to 50C over a period of 25 hours. The suspension was readily filtrable. The sulfuric acid ob-tained as filtrate had the following composition:
79.5 % H2S04, corresp. to 82.3% salt-free 0.008 % VOS04 0.24 % FeS04 0.08 % Cr2(So4)3 1.8 % Al2(S04) 3 0.4 % MeS04 0.9 % MgS04 17.1 % H20 It will be appreciated that the instant specification ls set forth by way of illustration and not limitation, and that various modifications and changes may be made without departin~ from the spirit and scope of the present invention.
Le A 27 318 9
Claims (8)
1. In the recovery of sulfuric acid from waste sulfuric acid containing metal sulfates by concentration through evaporation and removal of the solid metal sulfates, the improvement which comprises concentrating the waste sulfuric acid by evaporation to a concentration of 26 to 32% by weight H2SO4 in an evaporation stage 1 and concentrating the acid obtained by evaporation in a steam-heated evaporation stage 2 to such an extent that the water-soluble metal sulfates are partly suspended in solid form in the acid concentrated by evaporation, the vapors from evaporation stage 2 being used as heating medium in an evaporation stage 3 in which the suspension from evapora-tion stage 2 is concentrated by evaporation to a concentra-tion of 60 to 75% by weight H2SO4.
2. A process as claimed in claim 1, wherein without preliminary separation of the solid metal sulfates, the suspension discharged from evaporation stage
3 is concentrated by evaporation to a concentration of 72 to 85% by weight sulfuric acid in a steam-heated evapora-tion stage 4.
3. A process as claimed in claim 1, wherein concentration of the waste sulfuric acid by evaporation in evaporation stage 1 takes place at a temperature below 100°C.
3. A process as claimed in claim 1, wherein concentration of the waste sulfuric acid by evaporation in evaporation stage 1 takes place at a temperature below 100°C.
4. A process as claimed in claim 1, wherein in evaporation stage 2 the waste sulfuric acid is concentrated by evapor-ation to a sulfuric acid concentration of 40 to 50% by weight at 120 to 165°C.
Le A 27 318
Le A 27 318
5. A process as claimed in claim 1, wherein the vapors produced in evaporation stage 2 are partly used for concentrating the waste sulfuric acid by evaporation in evaporation stage 1.
6. A process as claimed in claim 1, wherein the acid from evaporation stage 1 is fed into a circulation pipe of evaporation stage 2 on a pump pressure side.
7. A process as claimed in claim 1, wherein in evapora-tion stage 2 the acid is concentrated by evaporation to such an extent that the acid concentrated by evaporation contains at least 1% by weight water-soluble metal sulfates in solid form.
8. A process as claimed in claim 1, wherein concentration of the waste sulfuric acid by evaporation in evaporation stage 1 takes place at a temperature below 90°C, the waste sulfuric acid is concentrated by evaporation to a sulfuric acid concentration of 40 to 50% by weight at 120 to 165°C, the vapors produced in evaporation stage 2 are partly used for concentrating the waste sulfuric acid by evaporation in evaporation stage 1, the acid from evaporation stage 1 is fed into a circulation pipe of evaporation stage 2 on a pump pressure side, and in evaporation stage 2 the acid is concentrated by evaporation to such an extent that the acid concentrated by evaporation contains at least 1% by weight water-soluble metal sulfates in solid form.
Le A 27 318
Le A 27 318
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3938915A DE3938915C1 (en) | 1989-11-24 | 1989-11-24 | |
| DEP3938915.4 | 1989-11-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2030655A1 true CA2030655A1 (en) | 1991-05-25 |
Family
ID=6394110
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002030655A Abandoned CA2030655A1 (en) | 1989-11-24 | 1990-11-22 | Process for the recovery of sulfuric acid |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0429933B1 (en) |
| JP (1) | JPH03177305A (en) |
| CA (1) | CA2030655A1 (en) |
| DE (2) | DE3938915C1 (en) |
| ES (1) | ES2057333T3 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4403841C2 (en) * | 1994-02-08 | 1997-12-04 | Bayer Ag | Process for evaporating used sulfuric acid |
| DE19741511A1 (en) * | 1997-09-20 | 1999-04-01 | Metallgesellschaft Ag | Process for concentrating thin acid by utilizing process heat in a forced circulation evaporator system |
| GB9816464D0 (en) * | 1998-07-30 | 1998-09-23 | Tioxide Group Services Ltd | Process for the concentration of dilute sulphuric acid solutions |
| KR20020046285A (en) | 1999-09-28 | 2002-06-20 | 고마즈 교우이찌 | Triazolopurine derivatives, drug compositions containing the same and adenosine a3 receptor affinitive agents |
| CN101891161A (en) * | 2010-06-29 | 2010-11-24 | 上海华谊微电子材料有限公司 | Preparation method of ultra-pure sulfuric acid |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2352701A1 (en) * | 1973-10-20 | 1975-06-12 | Hoechst Ag | PROCESS FOR CONCENTRATING SALTY, DILUTED SULFUR ACID |
| DE2618121A1 (en) * | 1976-04-26 | 1977-11-10 | Kronos Titan Gmbh | Sulphuric acid demetallisation in titanium dioxide pigment mfr. - by continuous addn. to metal salt suspension in conc. acid and evapn. |
| EP0022181B1 (en) * | 1979-06-13 | 1983-10-12 | Bayer Ag | Process and apparatus for regenerating sulfuric acid |
| DE3327769A1 (en) * | 1983-08-02 | 1985-02-14 | Bayer Ag, 5090 Leverkusen | METHOD FOR THE TREATMENT OF THICK ACID |
| DE3632623A1 (en) * | 1986-09-25 | 1988-03-31 | Bayer Ag | METHOD FOR CONCENTRATING SULFURIC ACID |
-
1989
- 1989-11-24 DE DE3938915A patent/DE3938915C1/de not_active Expired - Lifetime
-
1990
- 1990-11-10 ES ES90121560T patent/ES2057333T3/en not_active Expired - Lifetime
- 1990-11-10 EP EP90121560A patent/EP0429933B1/en not_active Revoked
- 1990-11-10 DE DE9090121560T patent/DE59002095D1/en not_active Revoked
- 1990-11-20 JP JP2312966A patent/JPH03177305A/en active Pending
- 1990-11-22 CA CA002030655A patent/CA2030655A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| DE59002095D1 (en) | 1993-09-02 |
| ES2057333T3 (en) | 1994-10-16 |
| JPH03177305A (en) | 1991-08-01 |
| EP0429933A1 (en) | 1991-06-05 |
| EP0429933B1 (en) | 1993-07-28 |
| DE3938915C1 (en) | 1991-05-08 |
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