CA1288211C - Process for recycling sulphuric acid containing metal sulphate - Google Patents
Process for recycling sulphuric acid containing metal sulphateInfo
- Publication number
- CA1288211C CA1288211C CA 503907 CA503907A CA1288211C CA 1288211 C CA1288211 C CA 1288211C CA 503907 CA503907 CA 503907 CA 503907 A CA503907 A CA 503907A CA 1288211 C CA1288211 C CA 1288211C
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- Canada
- Prior art keywords
- process according
- filter cake
- filter
- sulphuric acid
- fil
- 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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-
- 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
-
- 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
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
- C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
- C22B3/08—Sulfuric acid, other sulfurated acids or salts thereof
-
- 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
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
- C22B3/22—Treatment or purification of solutions, e.g. obtained by leaching by physical processes, e.g. by filtration, by magnetic means, or by thermal decomposition
-
- 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
- C22B34/1259—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 treatment or purification of titanium containing solutions or liquors or slurries
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/36—Regeneration of waste pickling liquors
-
- 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
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Metallurgy (AREA)
- Life Sciences & Earth Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Geochemistry & Mineralogy (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Filtering Materials (AREA)
- Treatment Of Sludge (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Paper (AREA)
- Filtering Of Dispersed Particles In Gases (AREA)
Abstract
A process for recycling sulphuric acid containing metal sulphate ABSTRACT OF THE DISCLOSURE
The present invention provides a process for recycling used sulphuric acid containing metal sulphates by evaporating the dilute sulphuric acid containing the dissolved metal sulphates to a content of from 40 to 85%
of H2SO4, based on salt-free acid, separating the metal sulphates by filtration and rousing the separated sulphuric acid, the filtration taking place under excess pressure and compressed air being blown through the filter cake thereby formed for demoisturization.
Le A 23 661
The present invention provides a process for recycling used sulphuric acid containing metal sulphates by evaporating the dilute sulphuric acid containing the dissolved metal sulphates to a content of from 40 to 85%
of H2SO4, based on salt-free acid, separating the metal sulphates by filtration and rousing the separated sulphuric acid, the filtration taking place under excess pressure and compressed air being blown through the filter cake thereby formed for demoisturization.
Le A 23 661
Description
A process for recycling sulphuric acid containing me~al S sulphate The present invention relates to a process for re-cycling used sulphuric acid conLaining metal sulphates by evapora~ing the dilute sulphuric acid containing ~he dis-solved metal sulphates to a content of from 40 to 85% ofH250~, based on sal~-free acid, separating the metal sul-phates by filtration and reusing the separated sulphuric acid.
Metal sulphatP-cDntaining dilute acids, as occur in the production of TiO2 or as pickling acids, can be re-moved and supplied for reuse by evaporating these metal sulphate-containing sulphuric acids up to a concentration of the acid which is suitable for reuse or up to the con-centration at which the metal sulphates have a solubility minimum. Optionally after cooling the suspension, the metal sulphates are conven~ionally separa~ed by filtration frDm the sulphuric acid, which is ~hen recycled to the production prDcess DE-A 33 27 769, US 2 28D 5D8, US 2 098 056).
According to ~he prior art~ vacuum drum fil~ers are used for the filtration of these suspensions which gene-rally contain from 10 to 40X. ~y weight of solids material with grain sizes of predominantly from 5 to 100 ~m tUllmanns Encyklopadie d. techn. Chemie, Verl. Chemie, Weinheim, 4th Edition, 1972, Volume 2, p. 188 -190). The advantage of these apparatus lies in the simple and eco-nomical ccntinuous operation with low operatiDnal CDst5.
Le A Z3 6$1 The disadvan~ages o~ vacuum filtra~ion are ~ha~, depending on the grain size and proportional composi-ion of ~he me~al sulphates of ~he group of sulphates and hydrogen sulphates of iron, aluminum, magnesium, titani-um, manganese, chromium and vanadium, the filter cake tends to form cracks and i5 thixo~ropic The residual moisture of this filter cake is usually from 20 to 40% by weight, corresponding to from 12 to 25%
by weight of H2S04 This sulphuric acid is not only re-moved from the production process, but also makes the handling and safe removal of the metal sulphates substan-~ially more difficult In the case Df the ecologically op~imum removal of the metal sulphates by thermal decom-position a substantial proportion of the decomposition capaci~y is taken up by ~he residual moisture of the metal sulphates The use of this process by residual moisture i6, moreover, uneconomical, since it requires a specific energy of decomposition which is about 80% higher than in the case of metal =ulphate~
Many a~tempts have thus been made to reduce the residual moisture by additional demoisturizing of the fil~er cake obtained with vacuum drum filters A certain degree of success i5 achie~ed with compression s~rip filters, bu~ ~he technical cost for the double filtration is too high The object of the presen~ invention is thus ~o provide a process which does not suffer from the above-mentioned disadvanLages It has surprisingly now been found that an unex-pectedly good filtration with a minimum residual moisture Le A 23 661 382~
conten~ of the fil~er cake is possible by fil~ration in pressure filters which per~iLs uniform demoisturizina of the cake by blowing compressed air ~hrough ~he fil~er cake.
The presen~ inven~ion ~hus provides a proce~s for recvcling used sulphuric acid con~aining metal sulpha~es 10 b~ evapora~ing ~he dilute sulphuric acid con~aining ~he :~
dissolved me~al sulpha~es ~o a con~en~ of from 40 to 85%
of H2S04, based on salt-free acid, separa~ing the me~al sulpha~es by filtration and reusing the separa~d sul-phuric acid~ the filtration taking placa under ~xcess pressure and compressed air being blown through the fil~er cake thereby formed for demoisturiza~iorl.
The filters used accordin~ to the invention sre con-ventionally used for separating very fine-grained solids materials and, owina ~o the discontinuous operation, for 2~ suspensions with a low solids contentt The suppliers are ~hus prejudiced against recommending such ~ypes of filter for the filtration of the metal sulphate-~ulphuric acid suspension which is high in solids material and relatively easy to filter. It i~ thus all the more ~urpri~ing that the residual moisture of the fil~er caka obtained with these types of filter, in contrast to ~he cake ob~ain2d on vacuum drum filters, can even be reduced by from 30 to 50%, so as ~o produce a correspondin~ increase in the yield of reusable sulphuric acid. In view of the above-described problems in ~he handling and ~sfe remo~al of the filter cake, the advanta~es of the me~hod of fil~ra~ion accordina to the invention are ex~remely great, particularly since the fil~er cake ob~ained accordina to : the invention is not thixotropic~ but crumbly and ::
35 apparently dry- ~
.
: Le A 23 661 , 8~11 In con~ras~ ~o ~he fil~ers oLherwise used, ~he ~iltra~ion ~akes place ba~chwise wi~h the ypes of fil~er according Lo ~he inven~ion.
I~ has been shown to be advan~ageous Lo carry out the fil~ra~ion according ~o Lhe invention until the thickness vf ~he ca~e is at least 1~ mm, preferably from 20 to 60 mm.
The demoisturizing of the filter cake takes place by blowing compressed air through the cake. The required pressure and dura~ion of blowing are ~hereby dependent on the thickness of ~he cake, the composition of ~he me~al lS sulphates mixture, the concen~ration of the sulphuric acid contained in ~he filter cake and the required residual mois~ure. The econDmical op~imum is easy ~o determine by tests. The ~se of hot air with ~empera~ures of at most 150C, preferably from 40 ~o 120C, is advantageous.
Compressed air is blswn ~hro~gh according to the invention for at least 2 minutes, preferably from 4 to 10 minutes.
The usefulness of the sulphuric acid is considerably influenced by its con~ent of dissolved metal sulphates.
To keep this salt con~ent low special conditions have to be observed during crys~alliza~ion (cf. EP 0 133 505). In addition, the salt content is influenced by the tempera~ure during the sulphate separation~ which is be-tween 40 and 70C. Although the dissolved sal~ content in the acid is lower at a low Lempera~ure ~han at a higher temperature, ~he filterability of the colder suspension is considerably poorer and after the demoisturization with compressed air subs~antially larger quantiLies of adheren~
mois~ure remain in the filter cake. A preferred embodimen~
of the ~S
Le A 23 661 process accordina ta ~he invenLion avoids Lhe disadvan-~ages of fil~ra~ion a~ a low ~empera~ure and of ~ha~ a~
a high ~empera~ure in such a wav ~hat ~he ruspension i5 fil~ered a~ a low ~empera~ure and ~he filLer cake i5 demois~urized wi~h ho~ compressed air.
A parLicularly preferred embodimen~ of the process accordine ~o ~he invenLion consists in carrying ou~ ~he fil~ra~ion aL a ~emperature of ~5 ~o 50C and blowing ~hrough compressed air having a tempera~ure of 70 ~o 12~C.
A no~iceable improvemen~ in relation ~o ~he conven-tional vacuum fil~ration can be achieved bv fil~ra~ion wi~h membrane fil~er presses. Still more favorable resulLs c~n be achieved wi~h pressure fil~ers of ~he car~ridge fil~er or pla~e fil~er types, which permit unexpec~edlv low residual mois~ure con~en~s in the fil~er cake. In this case, and in view of ~he simple cons~ruction of such fil~ers, subs~an~ial progress is ~hus made in overcoming ~he disposal problems.
The fil~ers par~icularly preferred according to ~he inven~ion are thus car~ridge fil~ers. Particularly good results are achieved when several fil~er tubes are used, ~he minimum spacing be~ween ~he fil~er car~ridges being from 100 to 150 mm, preferably from 120 ~o 1~0 mm and the minimum spacing between ~he car~ridges and the fil~er housing being from 70 ~o 100 mm.
~ The inven~ion is explained below by means of non-limi~ ng Examples. In ~hese Examples ~ons means me~ric tons and m3 of air means cubic me~ers under s~andard condi~ions.
Metal sulphatP-cDntaining dilute acids, as occur in the production of TiO2 or as pickling acids, can be re-moved and supplied for reuse by evaporating these metal sulphate-containing sulphuric acids up to a concentration of the acid which is suitable for reuse or up to the con-centration at which the metal sulphates have a solubility minimum. Optionally after cooling the suspension, the metal sulphates are conven~ionally separa~ed by filtration frDm the sulphuric acid, which is ~hen recycled to the production prDcess DE-A 33 27 769, US 2 28D 5D8, US 2 098 056).
According to ~he prior art~ vacuum drum fil~ers are used for the filtration of these suspensions which gene-rally contain from 10 to 40X. ~y weight of solids material with grain sizes of predominantly from 5 to 100 ~m tUllmanns Encyklopadie d. techn. Chemie, Verl. Chemie, Weinheim, 4th Edition, 1972, Volume 2, p. 188 -190). The advantage of these apparatus lies in the simple and eco-nomical ccntinuous operation with low operatiDnal CDst5.
Le A Z3 6$1 The disadvan~ages o~ vacuum filtra~ion are ~ha~, depending on the grain size and proportional composi-ion of ~he me~al sulphates of ~he group of sulphates and hydrogen sulphates of iron, aluminum, magnesium, titani-um, manganese, chromium and vanadium, the filter cake tends to form cracks and i5 thixo~ropic The residual moisture of this filter cake is usually from 20 to 40% by weight, corresponding to from 12 to 25%
by weight of H2S04 This sulphuric acid is not only re-moved from the production process, but also makes the handling and safe removal of the metal sulphates substan-~ially more difficult In the case Df the ecologically op~imum removal of the metal sulphates by thermal decom-position a substantial proportion of the decomposition capaci~y is taken up by ~he residual moisture of the metal sulphates The use of this process by residual moisture i6, moreover, uneconomical, since it requires a specific energy of decomposition which is about 80% higher than in the case of metal =ulphate~
Many a~tempts have thus been made to reduce the residual moisture by additional demoisturizing of the fil~er cake obtained with vacuum drum filters A certain degree of success i5 achie~ed with compression s~rip filters, bu~ ~he technical cost for the double filtration is too high The object of the presen~ invention is thus ~o provide a process which does not suffer from the above-mentioned disadvanLages It has surprisingly now been found that an unex-pectedly good filtration with a minimum residual moisture Le A 23 661 382~
conten~ of the fil~er cake is possible by fil~ration in pressure filters which per~iLs uniform demoisturizina of the cake by blowing compressed air ~hrough ~he fil~er cake.
The presen~ inven~ion ~hus provides a proce~s for recvcling used sulphuric acid con~aining metal sulpha~es 10 b~ evapora~ing ~he dilute sulphuric acid con~aining ~he :~
dissolved me~al sulpha~es ~o a con~en~ of from 40 to 85%
of H2S04, based on salt-free acid, separa~ing the me~al sulpha~es by filtration and reusing the separa~d sul-phuric acid~ the filtration taking placa under ~xcess pressure and compressed air being blown through the fil~er cake thereby formed for demoisturiza~iorl.
The filters used accordin~ to the invention sre con-ventionally used for separating very fine-grained solids materials and, owina ~o the discontinuous operation, for 2~ suspensions with a low solids contentt The suppliers are ~hus prejudiced against recommending such ~ypes of filter for the filtration of the metal sulphate-~ulphuric acid suspension which is high in solids material and relatively easy to filter. It i~ thus all the more ~urpri~ing that the residual moisture of the fil~er caka obtained with these types of filter, in contrast to ~he cake ob~ain2d on vacuum drum filters, can even be reduced by from 30 to 50%, so as ~o produce a correspondin~ increase in the yield of reusable sulphuric acid. In view of the above-described problems in ~he handling and ~sfe remo~al of the filter cake, the advanta~es of the me~hod of fil~ra~ion accordina to the invention are ex~remely great, particularly since the fil~er cake ob~ained accordina to : the invention is not thixotropic~ but crumbly and ::
35 apparently dry- ~
.
: Le A 23 661 , 8~11 In con~ras~ ~o ~he fil~ers oLherwise used, ~he ~iltra~ion ~akes place ba~chwise wi~h the ypes of fil~er according Lo ~he inven~ion.
I~ has been shown to be advan~ageous Lo carry out the fil~ra~ion according ~o Lhe invention until the thickness vf ~he ca~e is at least 1~ mm, preferably from 20 to 60 mm.
The demoisturizing of the filter cake takes place by blowing compressed air through the cake. The required pressure and dura~ion of blowing are ~hereby dependent on the thickness of ~he cake, the composition of ~he me~al lS sulphates mixture, the concen~ration of the sulphuric acid contained in ~he filter cake and the required residual mois~ure. The econDmical op~imum is easy ~o determine by tests. The ~se of hot air with ~empera~ures of at most 150C, preferably from 40 ~o 120C, is advantageous.
Compressed air is blswn ~hro~gh according to the invention for at least 2 minutes, preferably from 4 to 10 minutes.
The usefulness of the sulphuric acid is considerably influenced by its con~ent of dissolved metal sulphates.
To keep this salt con~ent low special conditions have to be observed during crys~alliza~ion (cf. EP 0 133 505). In addition, the salt content is influenced by the tempera~ure during the sulphate separation~ which is be-tween 40 and 70C. Although the dissolved sal~ content in the acid is lower at a low Lempera~ure ~han at a higher temperature, ~he filterability of the colder suspension is considerably poorer and after the demoisturization with compressed air subs~antially larger quantiLies of adheren~
mois~ure remain in the filter cake. A preferred embodimen~
of the ~S
Le A 23 661 process accordina ta ~he invenLion avoids Lhe disadvan-~ages of fil~ra~ion a~ a low ~empera~ure and of ~ha~ a~
a high ~empera~ure in such a wav ~hat ~he ruspension i5 fil~ered a~ a low ~empera~ure and ~he filLer cake i5 demois~urized wi~h ho~ compressed air.
A parLicularly preferred embodimen~ of the process accordine ~o ~he invenLion consists in carrying ou~ ~he fil~ra~ion aL a ~emperature of ~5 ~o 50C and blowing ~hrough compressed air having a tempera~ure of 70 ~o 12~C.
A no~iceable improvemen~ in relation ~o ~he conven-tional vacuum fil~ration can be achieved bv fil~ra~ion wi~h membrane fil~er presses. Still more favorable resulLs c~n be achieved wi~h pressure fil~ers of ~he car~ridge fil~er or pla~e fil~er types, which permit unexpec~edlv low residual mois~ure con~en~s in the fil~er cake. In this case, and in view of ~he simple cons~ruction of such fil~ers, subs~an~ial progress is ~hus made in overcoming ~he disposal problems.
The fil~ers par~icularly preferred according to ~he inven~ion are thus car~ridge fil~ers. Particularly good results are achieved when several fil~er tubes are used, ~he minimum spacing be~ween ~he fil~er car~ridges being from 100 to 150 mm, preferably from 120 ~o 1~0 mm and the minimum spacing between ~he car~ridges and the fil~er housing being from 70 ~o 100 mm.
~ The inven~ion is explained below by means of non-limi~ ng Examples. In ~hese Examples ~ons means me~ric tons and m3 of air means cubic me~ers under s~andard condi~ions.
3~
Le A 23 661 ' -. ~
Exam~le 1 (Compara~ive Example) In this and ~he foll~wing Examples, a me~al sulphate-con~aining 65% sulphuric acid is used, which i~ obLained by evapora~ing a waste acid from the production of Tio2.
This me~al sulpha~e suspension has the following composi-tion ~data in % by weight):
FeS04 H2010.6 Fe2(54~3 H2504 . 8 H20 1.1 Fe2H2~S04)3 . H20 11.4 Al2(504)3 H2SOq 8 H20 ~954 ~ H203.6 TiOS04 2.9 MnS04 H200.7 VOS04 0-3 H2504 43-4 H20 23.3 The particle size of these sulphates, as far as can be seen with a microscope, is from 5 to 120 ~m, predomi-nantly from 15 to 80 ~m. The temperature is 55C.
When filtering with a vacuum drum cell filter (drum diameter = 2.2 m, rotational speed = 0.3 min 1) an 8 to 10 mm thick filter cake i5 obtained. The thixotropic filter cake contains 28.2X by weight of mois~ure, corresponding to 18.3% by weight of H2504.
540 kg of reusable 65% sulphuric acid and 460 kg of filter eake are Dbtained per ton of suspension.
Example 2 The suspension described in Example 1 is filter~d with a membrane filter press (Pressfilter-Automat P of Hoesrh g Sohne, Duren~ up to cake thickness of 25 mm.
Le A 23 661 ~ ~Je ~k The filter cake is then pressed by pre~sirg ~he mem-branes wi~h 16 bar and compressed air (5 bar) i5 blown ~hrough for lO minuLes for demoisturizaLion. Ihe residual moisture of the resulting cake is 20.3% by weight, corres-ponding to 13.2% by weigh~ of H2504.
With a pressure of 8 bar during pressing the mem-~ branes, a residual mois~ure of 18.9X. by weight, corres-ponding tD 12.3~/. by weighL of H2504, i5 produced. The ne-cessary blowing air (50C) corresponds to a requirement of 194 m3 per ton of filter cake.
ExamDle ~
The suspension from Example 1 i5 filtered wi~h 3 tube filter (Fundabac (R) - Filter of DrM, Mannedorfl Switzer-land~.
The filter i5 fitLed wi~h 8 ~ubes wi~h a ~o~al area of filter cloth of 2.2 m2. The minimum spacing between the tubes is 50 mm. With an excess pressure of 3 bar, filter-ing is carried out for 30 seconds and compressed air (5C) i5 blown through the filter cake for 5 minutes to remove the residual moisture. The air pressure within the filLer thereby falls from Z.8 to 2.1 bar. The filter cake (86 kg) delivered from Lhe filter has a ~hickness of about 20 mm and a moisture content of 18.0% by weight, corresponding to 11.7% by weight of H2504.
ExamDle 4 Analogously to Example 3, filtering is carried DUt under 3 bar for 30 seconds and compressed air (55C) is Le A 2~ 661 s~
blown ~ro~gh ~he fil~er cake for 5 minu~es The residual mois~ure is ~hereaf~er 14 6% by weigh~, corresponding Lo eight of H2504 610 kg of 65% sulphuric acid (6l 9/ H2S04, 3~ 3% H30, 4 8% dissolved sulpha~es~ are separa~ed per ~on of suspension (compared wi~h 540 kg/~on under vacuum fil~ra~ion corresponding to Example 1) The fil~er cake (390 kgl~on Df suspension) has not thixo~ropic proper~ies, bu~ is an apparen~ly dry powder For dry-blowing 84 kg of filter cake, 40 m3 of pressurised air are required, corresponding to 476 m31ton of filter cake ExamDle S
In order ~o ob~ain a greaLer cake ~hickness, 6 filter tubes are removed from the Fundabac(R) - Filter and only ~he central filter tubes is u6ed for the fur~her experi-ments The fil~er ~0 31 m2 fil~er surface) is charged for 80 sec under an excess pressure of 5 bar with ~he suspen-sion correspJnding to Example 1 After emptying the pulp, dryblowing is carried out for 10 minutes wi~h compressed air ~emperature 5~C, pressure falling from 4 7 ~o 3 7 bar) 2~ kg of fil~er cake are ob~ained wi~h a moi 5 -~ure con~ent of 15 9% by weigh~ corresponcling ~o 10 3% bv weigh~ of H2S04. The average cake ~hickness is 45 mm Exam~le 6 Fil~ering i5 carried ou~ wi~h a filter equipped wi~h one tube (analogously ~o Example 5) for 8D seconds and, ~5 Le A 23 661 af~er emptyin~ ~he pulp, dry-blowing is carried ouL for 5 minutes wi~h compressed air (tempera~ure 55C, pressure falling from 4.5 ~o 3.2 bar). The fil~er cake obtained has a residual moisture content of 14~3% by weight, correspon-ding to 9.3% ~y weight of H2504. For dry-blowing 27 kg of fil~er cake, 6 m3 of air are required, corresponding to ~ 222 m31~on of filter cake.
ExamDle 7 Filtering is carried out for 80 seconds analogously to Example 6 and dry-blowing is carried out for 8 minutes with compressed air (temperature 75C, pressure 3.3 bar).
The residual mois~ure content of the fil~er cake obtained (27.5 kg) is 13.5% by weight, corresponding to 8.8% by weight of H2504. The air consump~ion is 7 m3, correspon-ding to 255 m3~on of fil~er cake.
Exam~le 8 The suspension according to Example 1 was cooled in the course of 5 hDurs frDm 55C to 42C and fil~ered with a tube filter as in Example 6. Eiltra~ion was carried out for 60 seconds under a pressure of 5 bars and af~er remov-ing the slurry ~he filter cake was air-blown for 10 mi-nutes using compressed air (40C 4.2 bars). The filtrate contained 62.9% of H2504, 33.8% of H20 and 3.3% of dis-solved sulphates (cf. example 4). 16.4 kg of a filter cake containing 26.7~/. by weigh~ of residual moisture, corres-pDnding to 10.9% by weight of H2S04, were discharged. The Le A 23 661 8~il air consumpLion was 8.3 m3, corresponding ~o 506 m3/ton of fil~er cake.
~xam~e 9 As in ~xample 8 ~he susDension was fil~.ered for ~ 80 seconds under a pressure of 5 bars and a~ a ~emperature of 42C. Af~er removal of ~he slurry the filter cake was air-blown for 8 minu~es using compressed air which had a ~empera~ure of 110C and a pressure of 4.2 bars. The filtrate contained 62.8% of H2504, 33.8% of H20 and 3.4%
~5 of dissolved sulpha~es. 20.9 kg of a filter cake having a tempera~ure of 55C and containing 13.8% by weight of residual moisture, corresponding to 9.0% by weigh~ of H2504, were discharged. The air consump~ion was 5.5 m3, corresponding to 26.3 m3/ton Df fil~er cake.
Le A 23 661
Le A 23 661 ' -. ~
Exam~le 1 (Compara~ive Example) In this and ~he foll~wing Examples, a me~al sulphate-con~aining 65% sulphuric acid is used, which i~ obLained by evapora~ing a waste acid from the production of Tio2.
This me~al sulpha~e suspension has the following composi-tion ~data in % by weight):
FeS04 H2010.6 Fe2(54~3 H2504 . 8 H20 1.1 Fe2H2~S04)3 . H20 11.4 Al2(504)3 H2SOq 8 H20 ~954 ~ H203.6 TiOS04 2.9 MnS04 H200.7 VOS04 0-3 H2504 43-4 H20 23.3 The particle size of these sulphates, as far as can be seen with a microscope, is from 5 to 120 ~m, predomi-nantly from 15 to 80 ~m. The temperature is 55C.
When filtering with a vacuum drum cell filter (drum diameter = 2.2 m, rotational speed = 0.3 min 1) an 8 to 10 mm thick filter cake i5 obtained. The thixotropic filter cake contains 28.2X by weight of mois~ure, corresponding to 18.3% by weight of H2504.
540 kg of reusable 65% sulphuric acid and 460 kg of filter eake are Dbtained per ton of suspension.
Example 2 The suspension described in Example 1 is filter~d with a membrane filter press (Pressfilter-Automat P of Hoesrh g Sohne, Duren~ up to cake thickness of 25 mm.
Le A 23 661 ~ ~Je ~k The filter cake is then pressed by pre~sirg ~he mem-branes wi~h 16 bar and compressed air (5 bar) i5 blown ~hrough for lO minuLes for demoisturizaLion. Ihe residual moisture of the resulting cake is 20.3% by weight, corres-ponding to 13.2% by weigh~ of H2504.
With a pressure of 8 bar during pressing the mem-~ branes, a residual mois~ure of 18.9X. by weight, corres-ponding tD 12.3~/. by weighL of H2504, i5 produced. The ne-cessary blowing air (50C) corresponds to a requirement of 194 m3 per ton of filter cake.
ExamDle ~
The suspension from Example 1 i5 filtered wi~h 3 tube filter (Fundabac (R) - Filter of DrM, Mannedorfl Switzer-land~.
The filter i5 fitLed wi~h 8 ~ubes wi~h a ~o~al area of filter cloth of 2.2 m2. The minimum spacing between the tubes is 50 mm. With an excess pressure of 3 bar, filter-ing is carried out for 30 seconds and compressed air (5C) i5 blown through the filter cake for 5 minutes to remove the residual moisture. The air pressure within the filLer thereby falls from Z.8 to 2.1 bar. The filter cake (86 kg) delivered from Lhe filter has a ~hickness of about 20 mm and a moisture content of 18.0% by weight, corresponding to 11.7% by weight of H2504.
ExamDle 4 Analogously to Example 3, filtering is carried DUt under 3 bar for 30 seconds and compressed air (55C) is Le A 2~ 661 s~
blown ~ro~gh ~he fil~er cake for 5 minu~es The residual mois~ure is ~hereaf~er 14 6% by weigh~, corresponding Lo eight of H2504 610 kg of 65% sulphuric acid (6l 9/ H2S04, 3~ 3% H30, 4 8% dissolved sulpha~es~ are separa~ed per ~on of suspension (compared wi~h 540 kg/~on under vacuum fil~ra~ion corresponding to Example 1) The fil~er cake (390 kgl~on Df suspension) has not thixo~ropic proper~ies, bu~ is an apparen~ly dry powder For dry-blowing 84 kg of filter cake, 40 m3 of pressurised air are required, corresponding to 476 m31ton of filter cake ExamDle S
In order ~o ob~ain a greaLer cake ~hickness, 6 filter tubes are removed from the Fundabac(R) - Filter and only ~he central filter tubes is u6ed for the fur~her experi-ments The fil~er ~0 31 m2 fil~er surface) is charged for 80 sec under an excess pressure of 5 bar with ~he suspen-sion correspJnding to Example 1 After emptying the pulp, dryblowing is carried out for 10 minutes wi~h compressed air ~emperature 5~C, pressure falling from 4 7 ~o 3 7 bar) 2~ kg of fil~er cake are ob~ained wi~h a moi 5 -~ure con~ent of 15 9% by weigh~ corresponcling ~o 10 3% bv weigh~ of H2S04. The average cake ~hickness is 45 mm Exam~le 6 Fil~ering i5 carried ou~ wi~h a filter equipped wi~h one tube (analogously ~o Example 5) for 8D seconds and, ~5 Le A 23 661 af~er emptyin~ ~he pulp, dry-blowing is carried ouL for 5 minutes wi~h compressed air (tempera~ure 55C, pressure falling from 4.5 ~o 3.2 bar). The fil~er cake obtained has a residual moisture content of 14~3% by weight, correspon-ding to 9.3% ~y weight of H2504. For dry-blowing 27 kg of fil~er cake, 6 m3 of air are required, corresponding to ~ 222 m31~on of filter cake.
ExamDle 7 Filtering is carried out for 80 seconds analogously to Example 6 and dry-blowing is carried out for 8 minutes with compressed air (temperature 75C, pressure 3.3 bar).
The residual mois~ure content of the fil~er cake obtained (27.5 kg) is 13.5% by weight, corresponding to 8.8% by weight of H2504. The air consump~ion is 7 m3, correspon-ding to 255 m3~on of fil~er cake.
Exam~le 8 The suspension according to Example 1 was cooled in the course of 5 hDurs frDm 55C to 42C and fil~ered with a tube filter as in Example 6. Eiltra~ion was carried out for 60 seconds under a pressure of 5 bars and af~er remov-ing the slurry ~he filter cake was air-blown for 10 mi-nutes using compressed air (40C 4.2 bars). The filtrate contained 62.9% of H2504, 33.8% of H20 and 3.3% of dis-solved sulphates (cf. example 4). 16.4 kg of a filter cake containing 26.7~/. by weigh~ of residual moisture, corres-pDnding to 10.9% by weight of H2S04, were discharged. The Le A 23 661 8~il air consumpLion was 8.3 m3, corresponding ~o 506 m3/ton of fil~er cake.
~xam~e 9 As in ~xample 8 ~he susDension was fil~.ered for ~ 80 seconds under a pressure of 5 bars and a~ a ~emperature of 42C. Af~er removal of ~he slurry the filter cake was air-blown for 8 minu~es using compressed air which had a ~empera~ure of 110C and a pressure of 4.2 bars. The filtrate contained 62.8% of H2504, 33.8% of H20 and 3.4%
~5 of dissolved sulpha~es. 20.9 kg of a filter cake having a tempera~ure of 55C and containing 13.8% by weight of residual moisture, corresponding to 9.0% by weigh~ of H2504, were discharged. The air consump~ion was 5.5 m3, corresponding to 26.3 m3/ton Df fil~er cake.
Le A 23 661
Claims (12)
1. A process for recycling used sulphuric acid con-taining metal sulphates by evaporating the dilute sulphu-ric acid containing the dissolved metal sulphates to a content of from 40 to 85% of H2SO4, based on salt-free acid, separating the metal sulphates by filtration and reusing the separated sulphuric acid, wherein the filtra-tion takes place under excess pressure and compressed air is blown through the filter cake thereby formed for de-moisturizaion.
2. A process according to claim 1, wherein the filtration takes place batchwise.
3. A process according to claim 1, wherein the filter cake has a thickness of at least 10 mm.
4. A process according to claim 1, wherein com-pressed air is blown through the filter cake for at least 2 minutes.
5. A process according to claim 1, wherein the com-pressed air used for blowing through the filter cake has a temperature of at most 150°C.
6. A process according to claim 1, wherein the filtration is carried out at a temperature of 35 to 50°C
and in that the compressed air blown through the filter cake has a temperature of 70 to 120°C.
Le A 23 661
and in that the compressed air blown through the filter cake has a temperature of 70 to 120°C.
Le A 23 661
7. A process according to claim 1, wherein tube filters are used as the filter.
8. A process according to claim 7, wherein the minimum distance between the filter tubes is 100 to 150 mm and the minimum distance between the tubes and the filter housing is 70 to 100 mm.
9. A process according to claim 1, wherein the filter cake has a thickness of from 20 to 60 mm.
10. A process according to claim 1, wherein com-pressed air is blown through the filter cake for from 4 to 10 minutes.
11. A process according to claim 1, wherein the compressed air used for blowing the filter cake has a temperature of from 40 to 100°C.
12. Process according to claim 8, wherein the mini-mum distance between the filter tubes is 120 to 130 mm.
Le A 23 661
Le A 23 661
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3509069 | 1985-03-14 | ||
| DEP3509069.3 | 1985-03-14 | ||
| DEP3511479.7 | 1985-03-29 | ||
| DE19853511479 DE3511479A1 (en) | 1985-03-14 | 1985-03-29 | METHOD FOR RECIRCULATING SULFURIC ACID CONTAINING METAL SULFATE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1288211C true CA1288211C (en) | 1991-09-03 |
Family
ID=25830288
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 503907 Expired - Lifetime CA1288211C (en) | 1985-03-14 | 1986-03-12 | Process for recycling sulphuric acid containing metal sulphate |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0194544B1 (en) |
| CA (1) | CA1288211C (en) |
| DE (2) | DE3511479A1 (en) |
| FI (1) | FI89875C (en) |
| NO (1) | NO167970C (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2634751B1 (en) * | 1988-07-29 | 1991-02-08 | Metaleurop Sa | |
| EP0362428B1 (en) | 1988-10-06 | 1992-12-23 | KRONOS TITAN-Gesellschaft mbH | Process and apparatus for the treatment of a sulfuric-acid solution containing ferrous sulfate |
| DE3927751A1 (en) * | 1989-08-23 | 1991-02-28 | Bayer Ag | METHOD FOR CONCENTRATING SULFURIC ACID CONTAINING METAL SULFATE |
| DE4015538A1 (en) * | 1990-05-15 | 1991-11-21 | Bayer Ag | METHOD FOR PRODUCING TITANIUM DIOXIDE |
| FR2663860B1 (en) * | 1990-07-02 | 1994-03-04 | Sollac | FILTER FOR USE IN SEPARATING SILICIC COMPOUNDS CONTAINED IN AN ACIDIC BATH, METHOD AND DEVICE FOR SEPARATING SAID SILICIC COMPOUNDS. |
| ES2049127B1 (en) * | 1991-06-13 | 1994-10-01 | Tioxide Espa A S A | CORRECTOR OF MICROELEMENTS LAWS FOR AGRICULTURAL SOILS AND PROCEDURE FOR ITS PREPARATION. |
| DE19829592C1 (en) * | 1998-07-02 | 1999-12-09 | Umweltanalytisches Zentrum Gro | Mineral acids containing metals from pickling plants are processed and recovered |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1500285A (en) * | 1965-09-19 | 1967-11-03 | Polysius Ag | Pasta drying process |
| US3743484A (en) * | 1969-12-30 | 1973-07-03 | Daido Chem Eng Corp | Regeneration of sulfuric acid pickling waste |
| DE3128768A1 (en) * | 1981-07-21 | 1983-02-10 | Werner Prof. Dr. 6740 Landau Stahl | Filter press |
| DE3327769A1 (en) * | 1983-08-02 | 1985-02-14 | Bayer Ag, 5090 Leverkusen | METHOD FOR THE TREATMENT OF THICK ACID |
| DE3327770A1 (en) * | 1983-08-02 | 1985-02-14 | Bayer Ag, 5090 Leverkusen | METHOD FOR PROCESSING SULFURIC ACIDS CONTAINING METAL SULFATE |
-
1985
- 1985-03-29 DE DE19853511479 patent/DE3511479A1/en not_active Withdrawn
-
1986
- 1986-02-26 NO NO860712A patent/NO167970C/en not_active IP Right Cessation
- 1986-03-03 EP EP19860102765 patent/EP0194544B1/en not_active Expired - Lifetime
- 1986-03-03 DE DE8686102765T patent/DE3681470D1/en not_active Expired - Lifetime
- 1986-03-12 CA CA 503907 patent/CA1288211C/en not_active Expired - Lifetime
- 1986-03-12 FI FI861017A patent/FI89875C/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| NO860712L (en) | 1986-09-15 |
| FI89875B (en) | 1993-08-31 |
| FI861017A (en) | 1986-09-15 |
| DE3681470D1 (en) | 1991-10-24 |
| EP0194544B1 (en) | 1991-09-18 |
| FI89875C (en) | 1993-12-10 |
| NO167970C (en) | 1992-01-02 |
| DE3511479A1 (en) | 1986-09-18 |
| FI861017A0 (en) | 1986-03-12 |
| NO167970B (en) | 1991-09-23 |
| EP0194544A2 (en) | 1986-09-17 |
| EP0194544A3 (en) | 1988-09-21 |
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