FR2623489A1 - Process and apparatus for the continuous synthesis of an aqueous aluminium sulphate solution from an aluminium hydroxide sludge and apparatus for adjusting the temperature during this synthesis - Google Patents

Abstract

The process according to the present invention for the continuous synthesis of an aqueous aluminium sulphate solution from an aluminium sludge comprises the stages consisting in alternately introducing the aluminium sludge produced during a surface treatment operation of the aluminium, the residual sulphuric acid produced during the removal of a coating during the treatment and the aqueous sulphuric acid solution containing aluminium sulphate produced during the recovery of the sulphuric acid during the treatment into a plurality of reaction vessels, so as to subject these substances to a reaction in the vessels, respectively, while mixing them, stirring them and heating them at a temperature between 80 DEG C and the boiling point of the reaction solution, and, finally, in bringing part of the sulphuric acid solution containing the aluminium sulphate into at least one of the second to last vessels in order to adjust the pH value of the reaction solution in the last vessel to a level between 1.6 and 2.5.

Description

METHOD AND APPARATUS FOR CONTINUOUS SYNTHESIS OF A

  AQUEOUS SOLUTION OF ALUMINUM SULFATE FROM A

  ALUMINUM HYDROXIDE SLURRY AND APPARATUS FOR ADJUSTING

  TEMPERAPURE DURING THIS SYNTHESIS

  The present invention relates to a process for the continuous synthesis of an aqueous solution of aluminum sulphate from the separating aluminum sludge, in a state containing aluminum hydroxide as its main component, of the effluent formed during the aluminum treatment step carried out, for the production of Alumite (an aluminum product having an anticorrosion coating formed therein by anodization), by a processing company of aluminum, and it relates to a device to put

this process.

  During the Alumite treatment process, as a pretreatment, an alumina blank is etched with a caustic soda solutlon to remove scratches or other similar cracks affecting the surface of this blank and to equalize this surface. area. In addition, during the reprocessing operation (new coating) of a scrapable aluminum product, this product is treated with a caustic soda solution to remove the oxide coating. In addition, the aluminum blank is subjected to anodic oxidation treatment and electrolytic coloring treatment in a sulfuric acid solution. During these treatments, the Al ions from the aluminum preform dissolve in the mentioned solution and are entrained by the latter in a neighboring washing tank. The wastewater is sent to the wastewater discharge station. While the wastewater is subjected to a neutralization treatment,

  a white precipitate of aluminum hydroxide is produced.

  The residual liquid (suspension) which is produced accordingly generally results from the addition of a macromolecular flocculation agent of the acrylamide type.

  so as to form a flock in the strongly solid state.

  This fluff is hydrated to form an aluminum slurry (hereinafter simply referred to as "sludge") and this sludge is subjected to the following treatment (to be rejected or recovered). This sludge is generally composed of 83 to 87% of water, 8 to 12% of Al (OH) 3, and 6 to 3% of impurities (such as SI02 and organic substances). During the surface treatment of aluminum, an aqueous solution of sulfuric acid is used to remove the coating from the aluminum surface as well as the coating adhering to the surface of the mounting device. These coating removal operations give rise to residual sulfuric acid as the aging residue. This residual sulfuric acid is generally composed of 75 to 90% of H 2 O

free and from 2 to 0.5% of A12 (SO4) 3.

  To avoid environmental pollution and to conserve resources, sludge and sulfuric acid are generally used from aluminum surface

  the synthesis of the aqueous solution of aluminum sulphate

  minium. However, the reaction involved in the synthesis of aluminum sulphate takes place so rapidly that it is difficult to control the rate thereof. Further, since the pH value of the aluminum sulphate is set as the final product to be suitable for use of the product, the final pH value of the liquid to be used is adjusted. to the synthesis so that it is equal to the pH value of the aluminum sulphate. Since it is difficult to adjust this pH value, it was considered difficult to produce the aqueous solution of aluminum sulphate.

  the help of the synthesis process continues.

  To date, the aqueous aluminum sulfate solution has been synthesized from the sludge exclusively using the so-called intermittent process. generally, to pour into a tank for the synthesis a specific amount of residual sulfuric acid and to heat the contents of the tank with a determined quantity of the mud which therein

is introduced gradually.

  The aforementioned conventional process requires that the tank for synthesis is a material having excellent anticorrosion properties because the contents of the tank is composed mainly of residual concentrated sulfuric acid during the initial phase of the synthesis. For example, vats of the glass-lined type are now commonly used for synthesis. The tank formed of this material has the disadvantage of being expensive, resulting in maintenance work, repair and difficult verification, and tends to break easily. In addition, because the synthesis is performed discontinuously, the tank used for this synthesis is necessarily large, the power used for training is proportionally important and the equipment, as a whole, is bulky and occupies a large area of the ground. As a result, the synthesis entails a high cost in terms of the equipment and the capacity of the tank used for this synthesis can not be easily increased. In addition, as a result of batch production, the synthesis has the disadvantage that the operation involved is complicated and has an inferior efficiency and that the tank used for synthesis and heated by means of a jacket is called upon. subnr a gradual loss of thermal efficiency due to the phenomenon of tare and to cause a cost

of high exploitation.

  As one of the various kinds of waste products occurring during aluminum surface treatment operations, a dilute aqueous solution of sulfuric acid produced, in a state containing aluminum sulphate (hereinafter referred to briefly as "sulfuric alum") during the recovery of sulfuric acid from an electrolyte, itself constitutes an annoying by-product in addition to the above-mentioned sludge and residual sulfuric acid. The aqueous solution of sulfuric acid containing this sulfuric alum has not appeared to an appreciable extent so far, and therefore it has been coped with sufficiently with the help of water treatment residual. In recent years, various processes for the treatment of electrolytes, such as the process using ion exchange resins for separation and the method using diffusion-diffusion membranes for separation, have made progress. As a result of the progress of these processes, the volume of the aqueous solution of sulfuric acid containing sulfuric acid has increased rapidly. In carrying out the process using an ion exchange resin for separation, for example, a part of the electrolyte containing the sulfuric acid present in the electrolytic cell is subjected to ion exchange treatment. for the anodic oxidation treatment or the AC coloring treatment. Although the sulfuric acid recovered by this ion exchange treatment is returned to the electrolytic cell, this treatment gives rise to

  treated water containing a part of the sulfuric acid

  only and sulfuric alum. In addition, during the implementation of the method using a membrane of

  transmission-diffusion, some of the electricity is

  trolyte in the electrolytic cell with the transmission-diffusion membrane. Although the sulfuric acid recovered by this treatment is returned to the electrolytic cell, this treatment produces treated water containing a portion of sulfuric acid and sulfuric alum. The dilute aqueous solution of sulfuric acid containing sulfuric alum generally contains 3-6% H2SO4 and 7-9% A12 (SO4) 3. In recent years, because the number of facilities for the treatment of electrolytes has increased in relation to the improvement of the quality of the surface treatment of aluminum, the volume of this dilute aqueous solution of sulfuric acid has become more important. In these circumstances, the question of how to safely dispose of the dilute aqueous solution of sulfuric acid

  pushed the industry concerned to solve this problem.

  One can possibly imagine using this solution for the aforementioned discontinuous synthesis of an aqueous solution of aluminum sulphate. The Applicant of the present invention itself partially uses the solution for this synthesis. Since the above-mentioned sulfuric acid aqueous solution of sulfuric acid is a dilute liquid, the use of this solution in one

  increased volume inevitably translates into a diminished

  reaction rate. Moreover, the synthesis taking place in a discontinuous way, it does not lend itself to

industrialization.

  The present invention has therefore been designed with the aim of overcoming the disadvantages described above that

  presents the prior art. An object of the invention

  It is intended to provide, on the one hand, a process for the continuous synthesis of an aqueous solution of aluminum sulphate by efficient use of the sludge, the residual sulfuric acid and the aqueous sulphate solution. sulfur-aluminum containing alumina that are produced during surface treatment operations of aluminum and pose serious problems for the industry concerned with respect to their safe disposal and, on the other hand, distined to be used to implement this method. Another object of the present invention is to provide, on the one hand, a method for the synthesis of

  continuous aqueous solution of aluminum sulfate.

  this process being excellent in the production of

  handling, safety, etc. and being implemented with relatively inexpensive equipment and allowing production with high efficiency, and, on the other hand, an apparatus for implementing

this process.

  Another object of the present invention is to provide, on the one hand, a method for performing the continuous synthesis of an aqueous solution of aluminum sulphate with a high energy efficiency and a low operating price and, another, a device

to implement this method.

  To achieve the objects described above the Applicant has designed, according to the present invention, a method for continuous production of a solution

  aqueous aluminum sulphate from a sub-

  product collected during the aluminum surface treatment operation, which process is characterized by the steps of feeding an aluminum slurry produced during the aluminum surface treatment operation and consisting mainly of of aluminum hydroxide, of residual sulfuric acid produced during the removal of a coating during

  of the surface treatment operatlon referred to above

  and an aqueous solution of sulfuric acid containing aluminum sulphate and produced during the recovery of sulfuric acid during

  the surface treatment operation mentioned above

  above to a reaction vessel consisting of a plurality of tanks, namely from first to nth tanks, to flow the substances successively supplied from the first to the nth tank (last tank) to undergo them. reactions under temperature conditions between 80 ° C and the boiling point of the reaction solution and at the same time to bring part of the aforementioned aqueous solution of sulfuric acid containing aluminum sulphate up to at least one of the second to last tanks, and to adjust the pH value of the reaction solution in the last

  tank at a level between 1.6 and 2.5.

  In the process described above, the adjustment of

  the pH value of the reaction solution is itself

  even one of the important factors for the efficiency of the desired continuous synthesis. Therefore, according to the present invention, the Applicant has designed an apparatus 1'C for the continuous production of the aqueous solution of aluminum sulphate, this apparatus being arranged so that the adjustment of the pH value is carried out. appropriately. This apparatus is characterized in that it comprises: a reaction vessel consisting of first to eighth vessels adapted to allow, respectively, continuous reactions of the aluminum sludge produced during the surface treatment operation of

  aluminum and consisting mainly of hydro-

  aluminum oxide, waste sulfuric acid produced during removal of the coating during the above-mentioned surface treatment operation and an aqueous solution of sulfuric acid containing aluminum sulphate produced during the recovery of the sulfuric acid during the above-mentioned surface treatment operation; a first supply line for supplying the aforementioned aqueous solution of sulfuric acid containing aluminum sulphate to the first aforementioned tank; a supply duct denoting (n designating an integer of a value at least equal to 2) for bringing the aforementioned aqueous solution of sulfuric acid containing aluminum sulphate to at least one of the second and other following tanks;

  a first indication-setting device

  pH recording arranged inside the first and second tanks above a first control valve in mutual connection

  with the first indication, control and

  pH adjusting and recording device adapted to control the flow volume inside the aforementioned first supply duct:

  a nieae device of indication-setting-enregls-

  trement (n denoting an integer of a value at least equal to 2) disposed in at least one of the second and other following tanks above; and a nieme control valve (n designating an integer having a value at least equal to 2) relée

  mutually with the umpteenth indication device-

  adjustment-recording aforesaid and adapted to control the volume of flow inside the umpteenth duct

aforementioned feed.

  In addition, in the aforementioned method, controlling the temperature of the reaction solution itself is also another important factor for the efficiency of the desired continuous synthesis. Therefore, according to the present invention, the Applicant has devised an apparatus for controlling the reaction temperature arranged so as to allow a continuous production of the aqueous solution of aluminum sulphate from by-products collected during the course of the process. surface treatment operation of aluminum, this apparatus being characterized in that it comprises: the precleaned reaction vessel consisting of first to nth tanks; a first heat exchanger for effecting a heat exchange between the final aqueous aluminum sulphate solution exiting the aforesaid reaction vessel and having a boiling point approximating the boiling point of the reaction solution and the aforementioned aqueous solution of sulfuric acid containing aluminum sulphate; a first steam duct disposed within the first aforementioned tank;

  a first indication-setting-recording device

  very temperature disposed inside the first aforementioned tank; a first temperature control valve

  connected to the first aforementioned device for

  temperature setting-recording and adapted to control the flow of water vapor inside the first aforementioned water vapor duct; a niece conducts water vapor (n denoting an integer with a value of at least 2) and an uth temperature indicating and recording device (n designating an integer of at least equal value at 2) disposed within at least one of the following second and further vessels; and a nlime temperature control valve (n

  designating an integer of at least equal value -

  21 connected to the nth aforementioned device for indicating and recording temperature and adapted for manual or automatic control of the flow of water vapor inside the nth device preclte

  indicating and recording temperature.

  The present invention will now be described with reference to the accompanying drawings in which: FIG. 1 is a block diagram illustrating a typical apparatus suitable for continuous synthesis

  an aqueous solution of aluminum sulphate according to

  to the present invention; Fig. 2 is a partial block diagram illustrating another embodiment of the present invention; and FIG. 3 is a partial longitudinal sectional view of another reaction vessel which can be

  used in the apparatus according to the present invention.

  In the present invention, an aqueous solution of aluminum sulphate is continuously synthesized by reacting successively in a plurality of reaction tanks an aluminum sludge resulting from the surface treatment operation of the aluminum, waste sulfuric acid occurring during the removal of a coating during the above-mentioned surface treatment operation, and an aqueous solution of sulfuric acid containing aluminum sulphate produced during the recovery of sulfuric acid during the above-mentioned surface treatment operation. The synthetic aluminum sulphate solution obtained at the end of these reactions is subjected to filtration and concentration to produce aluminum sulphate as the final product. The qualities of the final product depend on the final pH value of the synthetic aluminum sulphate solution, and it is ensured that it is within a range of

  determined to be appropriate for the particular purposes of

  final product. In the present invention, the dilute aqueous solution of sulfuric acid containing sulfuric acid is used for the adjustment of the

  pH value of the reaction solution.

  The reaction for the synthesis of aluminum sulphate is represented by the following formula (1) and the reaction formula, for calculation reasons,

  is represented by the following formula (2).

  2A1 (OH) 3 + 3H2S04 + A12 (SO4) 3 + 6H20 (1)

  A1203 + 3H2S04 + A12 (S04) 3 + 3H20 (2)

  The reaction rate constant in the aforementioned reaction as well as the effect of pH in the reaction were studied using sludge, spent sulfuric acid and a dilute aqueous solution of sulfuric acid containing sulfuric acid. sulfuric alum having the respective compositions indicated in

Table 1 below.

Table 1

Acid Aqueous solution of acid

  Composition Sulfuric mud of sulfuric containing residual of sulfuric alum

Al (OH) 3 9.5% -

H20 86.8%

) 9.4%) 85.8%

  Other substances (such as 3.7% micro-molecular flocculating agent)

H2SO4 - 90.0% 5.3%

A12 (SO4) 3 _0.6% 8.7%

  Since it has been experimentally demonstrated that the reaction of the above-mentioned three materials can be considered as a second-order homogeneous reaction, the reaction rate constant was determined by means of a batch test. . According to the results of this test, it has been found that the constant

  velocity at 90'-100 C was 0.12 - 0.671 L / Al 2 O 3 .mol.

  dry. The results of the various tests of the test performed using the three materials in various mixing ratios indicate that the appropriate value of the rate constant must exceed at least 0.01.

  ú / Al2O3.mol.sec. In the context of industrial exploitation

  triune of synthesis, the highest allowed limit

  the speed constant is 2.0 ú / AlzO3.mol.sec.

  If the pH value is excessively high, that is,

  to say if the quantity of free H2zSO4 is excessively low, the reaction rate is too low for the synthesis to be possible industrially. In view of the fact that the final pH value of the synthetic solution is adjusted, it is therefore most desirable, in the case of a continuous reaction, to control this continuous reaction of manner. such that the pH value of the reaction solution in the first of the reaction vessels is lowered to enhance the reaction rate and that the pH values of the reaction solutions in the following vessels are gradually increased successively in order to adjust. the final pH value of the synthetic solution finally reaches the prescribed level. As a result of a test conducted by the present inventors, it has been found that when the sludge, the spent sulfuric acid and the dilute aqueous solution of sulfuric acid containing sulfuric acid are fed in a continuous in a determined gravimetric ratio in a multi-stage reaction vessel (3 to 6 stages), the constituent stages of which respectively have determined volumes proportional to the desired volumes treated at the respective determined temperatures (in the range from 80 C to boiling point of the reaction solution, preferably 90 ° C up to the boiling point), the synthetic solution of the reaction vessel is continuously obtained from the final stage of the reaction vessel. aluminum sulphate having a pH value (of the order of 1.6 to 2.5, preferably

  from 1.8 to 2.0) as a result of completion of the reaction.

  The dilute solution of sulfuric acid containing sulfuric alum is charged in such a way that the pH values of the reaction solutions in the constituent vessels are maintained at the respective prescribed levels. In order to increase the reaction rate thereby producing the aqueous aluminum sulfate solution with increased yield, it is desirable to set the pH value in the first reaction vessel in the range of 0.1 to 1. , 0. For an industrial exploitation of the synthesis, it is enough to fix this value of the pH in the range of 0,1 to

2.0.

  The present invention will now be described in detail with reference to exemplary embodiments of the present invention shown in FIG.

the attached drawings.

  Fig. 1 is a block diagram illustrating a typical apparatus suitable for performing continuous synthesis of an aqueous solution of aluminum sulphate using the parallel flow type reaction.

  in a multistage tank according to the present invention.

  In the drawing, reference numeral 1 denotes a belt conveyor for transporting a sludge whose main component is aluminum hydroxide, reference 2 a mixing vessel, reference 3 a reaction vessel consisting of first In the same tanks, the reference 4 is a tank for containing a dilute aqueous solution of sulfuric acid containing sulfuric alum and reference 5 an acid tank.

su furlque residualre.

  The reaction vessel illustrated in FIG. 1 represents a case in which n = 5, that is to say using 5 constituent vessels. The first tank Ri and the second tank R2 are separated by a barrier-like partition 8a and erected vertically so as to allow an overflow. The second tank R2 and the third tank R3, the third tank R3 and the fourth tank R4, and the fourth tank R4 and the fifth tank R5 are individually separated by respective partitions 8b suspended from the top so as to form openings in their lower parts. These constituent tanks are each provided with an agitator 9 adapted to be rotated by an electric motor M. The sludge and fed to the mixing tank 2

  by being conveyed on the belt conveyor 1.

  Meanwhile, the dilute aqueous solution of sulfuric acid containing sulfuric acid, maintained at normal room temperature in the tank 4 of dilute sulfuric acid solution, is sent by a pump 10 via a feed line 11, at a first heat exchanger to the solution is heated to a temperature of between about 65 and 70 C by heat exchange with the solution of synthetic aluminum sulphate produced whose temperature is about C. and is then sent to a second heat exchanger 7 where the solution is heated to an even higher temperature of between about and 100 ° C. by heat exchange with water vapor at boiling point, then sent to a mixing tank 2 by

  via a first feed duct 12.

  Part of the heated solution is sent to the fourth tank R4, preceding the last tank, by

  via a second feed conduit 13.

  The mixture formed inside the mixing tank 2 by the sludge and the aqueous solution of sulfuric acid containing sulfuric acid is then in a state maintained at a high temperature of between about 70 'and 80 ° C. C, and stirred by the stirrer 9 and then sent to the first reaction vessel R1. Meanwhile, the residual sulfuric acid maintained inside the residual sulfuric acid tank 5 is sent by a pump 14 to a residual sulfuric acid receiving tank 15, is stripped of the floating substances by a sieve 16 disposed inside the receiving tank 15 and is then sent to the first tank of

R1 reaction by a pump 17.

  In the reaction vessel 3, the reaction solution formed inside the first tank Ri of the sludge mixture, spent sulfuric acid and an aqueous solution of sulfuric acid containing sulfuric alum flows. from the first tank R1 to the fifth final tank R5 being kept stirred by the stirrer 9 and sublt reactions represented by the formula (1) mentioned above. As a result, the synthetic aluminum sulphate solution is obtained at a temperature of about 100.degree. C. from the fifth tank Rs. This solution is sent by a pump 18 via a line 19 of solution produced and the first heat exchanger 6 to a filtration and purification unit (not shown). The control system will now be described below. Firstly, as regards the adjustment of the pH value of the reaction solution, the pH value of the reaction solution is fixed in the first tank Ri and in the second tank R2 at a level of about 0. 8. If the actual amount of the sludge input falls below the theoretical amount supplied, the amount of residual sulfuric acid is increased in proportion with the result that the pH value moves away from the set level. PH = 0.8, towards the acid side (up to pH = 0.2, for example). By

2623489-

  therefore, in this case, the pH value must be set.

  This adjustment of the pH value is done using

  of a first device (PHICR) 20 indication-setting-

  pH regulation which is arranged inside the second tank R2. When the pH value indicated by the first pH setting-setting indicating device is less than 0.8 (strongly on the acidic side), a first control valve 21, disposed in the premlet 12 for supplying dilute aqueous solution sulfuric acid containing sulfuric alum and releted to the aforementioned device 20, closes. Conversely, when the indicated pH value is greater than 0.8, the first control valve 21 opens. Thus, the pH value of the initial reaction solution is automatically set to 0.8 by appropriate control of the supplied amount of dilute aqueous acid solution.

  sulfuric acid containing sulfuric alum.

  The adjustment of the pH value in the first tank is normally performed as described above. If the actual sludge supply increases beyond the prescribed level, for example when the operation of the apparatus resumes after a shutdown or when the pH value in the first tank is significantly altered from the prescribed level, It follows naturally that the pH value of the first tank Ri deviates from the prescribed level. In order to bring the pH value back to the fixed range, the residual sulfuric acid having a pH value (strongly acidic side! less than that of the above dilute aqueous sulfuric acid-containing sulfuric acid solution may be used in place of the diluted aqueous solution just mentioned When the pH value indicated by the first device 20 d If the indicated pH value is higher, then the supply of residual sulfuric acid is stopped by stopping the pump 17 of the receiving tank 15 of residual sulfuric acid.at 0.8, the pump 17 is started and its capacity is increased (by opening the valve) so that the sending of sulfuric acid waste to the first tank R1 begins. The value

  The pH value is automatically set to 0.8.

  The appropriate increase or decrease in the input of residual sulfuric acid with a low

  pH is advantageous for pH adjustment, especially

  when the pH value varies greatly due to the fact that the time required for the pH value to return to the fixed range is smaller than in the case where the dilute aqueous solution of acid

  sulfuric acid containing sulfuric alum is used.

  Those skilled in the art will readily understand that this pH adjustment can be accomplished by using both the dilute aqueous sulfuric acid solution containing

  alum and residual sulfuric acid.

  It is possible to have, at choice, the first pH-adjusting-indlcation-regulating device inside the first tank Ri and adapting it to detect the pH value on the outlet side of the first tank Ri. As the reaction proceeds, the pH value of the reaction solution

  increases and deviates to the weak side acid.

  When the pH value of the synthetic aluminum sulphate solution in the fifth (bottom) tank R5 falls, on the strongly acidic side, below the prescribed level (1.6 to 2.5, preferably 1 to , 8 to 2.0), the detector of a second device (RPHCRi 22 indication setting-recording pH has inside the fifth tank Rs detects this variation of the pH value and closes a second control valve 23 arranged in the second conduit 13 for feeding dilute aqueous solution of acid

  sulfuric acid containing sulfuric alum. When, inver-

  In this case, the pH value increases above the prescribed level, the aforementioned detector automatically opens the second control valve 23. It is possible to connect the supply ducts conveying the dilute aqueous solution of sulfuric acid containing alum. sulfuric respectively to the constituent tanks

  by arranging the indicating-regulating devices

  recording of pH respectively in the constituent vessels, and to fine-tune the pH values of the reaction solution in the constituent tanks using the procedure described above. In any case, since the adjustment of the pH value of the reaction solution is effected by controlling the supply of dilute aqueous sulfuric acid solution containing sulfuric alum and / or the addition of the sulfuric acid is dual, and because, furthermore, the pH value of the reaction solution is not less than 0.8 and the conversion rate in the first tank is about 90% and that the pH value in the second tank can not fall below the aforementioned level, it suffices to use stainless steel of about SUS 316 JIL quality as material for the first tank and steel quality stainless steel about SUS 316 L as a material for

  the second and other following tanks.

  Ensuring that the temperature of the slurry mixture and the dilute aqueous sulfuric acid solution containing sulfuric alumina within the mixing vessel 2 is controlled by controlling the temperature of the reaction solution, increases to a level between 70 ° and 80 ° C due to the addition of a dilute aqueous solution of sulfuric acid containing sulfuric alum which has a temperature between about 95 and 100 C. The dilute aqueous solution sulfuric acid containing sulfuric acid, maintained at room temperature inside the tank 4 of dilute sulfuric acid, is heated, as described above, to a level between 65 and 70 '. C (detected by a temperature indicating-recording device 24) by means of the first heat exchanger and then raised to a level of between about 95 and 10 ° C. by means of the second exchanger 7. This temperature is det ected by a temperature control-monitoring-recording device (TRC) 25 disposed behind the second heat exchanger 7 in the feed pipe conveying the solution.

  diluted sulfuric acid containing sulfuric alum.

  When the temperature thus detected is less than the prescribed level, a valve 27 for controlling the passage of water vapor, disposed in a conduit 26 for supplying water.

  water vapor and connected to the aforementioned device 25, opens.

  When the detected temperature is higher than the prescribed level, the valve 27 for controlling the passage of water vapor reduces its opening. By adjusting the amount of water vapor entering the second heat exchanger 7, the temperature is automatically adjusted to the prescribed level. To the reaction tanks are connected steam supply ducts. A first steam supply duct is immersed in the form of a coil or a flat plate in the reaction solution contained in the first tank R: and then leads to a channel of

  discharge 32 so as to effect a heat exchange.

  A second steam supply duct 29, a third steam supply duct 30 and a fourth water supply duct 31 are respectively connected to the second to fourth tanks.

  in order to perform a steam introduction.

  The temperature of the reaction solution inside the first tank Ri is regulated by a first device (TRC) 33 of temperature setting-recording and temperature control valve 34 arranged in the first aforesaid conduit 28. supply of water vapor and connected to the aforementioned device 33. When the temperature of the reaction solution in the first tank R1 is greater than the prescribed level, the first valve 34 for reducing temperature control

  its opening. The temperature is automatically set

  only at the prescribed level. Third and fifth temperature indicating-recording devices (TR) 35 and 36 are respectively connected to the third and fifth tanks R3 and Rs.

  detected by these devices 35 and 36 of indication-

  temperature recording, the temperature is manually adjusted by opening or closing

  second to fourth control valves 37 to 39.

  Optionally, it is possible to adjust the temperature of the reaction solution by arranging temperature regulation / indicating devices respectively in the constituent vessels and connecting these devices to the respective temperature control valves of the steam supply ducts. of water. If the system is designed in such a way that the temperature is raised by introducing water vapor into the constituent tanks, the reaction solution is diluted and, consequently, involves the use of additional energy during subsequent operation. of purification. Therefore, it is desirable to increase the temperature of the reaction solution by means of a heat exchange between the steam supply duct and the

  reaction solution, as shown in the diagram.

  In addition, in FIG. 1, reference numeral 40 designates a liquid level indication-setting device (LC) in the residual sulfuric acid receiver vessel 15 to prevent empty rotation of the pump motor 17. The device automatically actuates the pump 14 when the level of the residual sulfuric acid liquid in the waste sulfuric acid receiver tank falls below a determined benchmark and it stops the operation of the pump when the liquid level rises. above this mark. Reference numeral 41 designates a liquid level indicating-setting device (LICA) equipped with an alarm and adapted for

  adjust the level of the liquid in the reaction vessel 3.

  This device automatically reduces the opening of the control valve 42 when the level of the reaction solution falls below the determined mark and it opens the control valve 42 when the level rises above this mark. The reference 4 $ designates a cumulative flow indication device (FIQ) adapted to display the flow rate or quantity supplied of dilute aqueous solution of sulfuric acid containing sulfuric alum. Gold has carried out the continuous synthesis of an aqueous solution of aluminum sulphate with the apparatus

  of Figure 1 under the following conditions.

  Conditions of the synthesis Sludge: déblt - 1,429 kg / hour composition Al (OH) 3 9,5% in weight impurities 3,7% in weight H20 86,8% in weight Residual sulfuric acid: flow - 72,6 liters / hour composition - Hz free S04 90.0% by weight A12 (SO4) 3 0.6% by weight specific gravity - 1.804 (25 C) Aqueous solution of sulfuric acid containing sulfuric alum: flow rate - 3.112 liters / hour composition - free H2SO4 5.3% by weight A12 (SO4) 38.9% by weight H20 the balance specific weight - 1.134 (12: C) reaction temperature: 99 to 100 ° C pH value in the first tank: approximately 0.8 pH value in the fifth tank: about 2.0 As a result, the aqueous solution of aluminum sulphate could be synthesized continuously with a conversion rate of about 98%. The aqueous aluminum sulphate solution thus obtained was subjected to a filtration test under the following conditions, namely 300 ml as the amount of synthetic solution used. C filtration temperature, vacuum filtration (without filter aid) as filtration, 95 cm 2 as the available filter surface, No. 2 filter paper of Toyo Roshi Co., Ltd., and 166 mbar as the filtration pressure (degree of vacuum). The test revealed no problem with regard to the filtration properties

of the solution.

  FIG. 2 illustrates another typical apparatus for the continuous synthesis of an aqueous solution of aluminum sulphate according to the present invention, this figure showing only the parts in which this apparatus differs from FIG. 1. The devices (such as eg the waste sulfuric acid tank and heat exchangers), measuring instruments (such as

  for example, indicating-regulating devices

  pH control), and supply lines (such as, for example, the sulfuric acid aqueous sulfuric acid solution supply line) which are not shown in FIG.

  are identical to those shown in FIG.

  The apparatus illustrated in FIG. 1 is disposed in mixing vessel 2. This mixing vessel is arranged as shown, for the simple reason that a reaction vessel can not be installed below the belt conveyor when adopts the existing device in its unmodified state. This installation of the mixing tank is not always necessary. As illustrated in FIG. 2, the three aforementioned raw materials can be directly

  sent to the first tank Ri of the reaction vessel 3.

  In the apparatus of Figure 2, the sludge is advanced by a pump through a conduit 44 of sludge feed. Of course, it could be advanced by a conveyor belt as in the apparatus of Figure 1. In the reaction vessel 3 illustrated in Figure 2, the constituent tanks Ri to R5 are separated, alternately, by partitions 8a and 8b, similar to dams and suspended so as to prevent any shortened passage of the reaction solution which otherwise could take place. In order to more effectively prevent a shortened passage of the reaction solution, it is possible to

  dispose inside the constituent tanks

  baffle 53, as shown in FIG.

  The adjustment of the temperature of the reaction solution in the first tank R is carried out automatically, in a manner similar to that carried out by the apparatus of FIG. 1, in that the

  first indication-setting-register

  temperature controller controls the first temperature control valve 34 disposed in the first conduit

  28 supplying steam. In this respect, the temperatures

  The reaction solution in the second to fourth tanks R2 to R4 are automatically adjusted by means of second to fourth temperature control devices (TRC) 45 to 47 and arranged in the respective component vessels and second - fourth temperature control valves 48 to 50 disposed respectively in the second to fourth water supply conduits 290 to 31. In addition, temperatures of the constituent tanks are regulated by heat exchange between the parts of the reaction solution located inside the constituent tanks and the second to fourth submerged water vapor supply ducts in the form of 'a coil or a flat plate in the solution of

reaction.

  The apparatus illustrated in FIG. 2 is provided with a synthetic solution circulation line 52 which exits the discharge side of the pump 18 to discharge the synthetic solution and return it to the first tank Ri. This circulation pipe 52 comprises a manual valve 51. With this device, the aqueous solution of aluminum sulphate can be returned to the first tank Ri by opening the manual valve 51 when the second device (PHICF! 22 <Fig.! ) setting-pH setting to display the pH value of the synthetic solution displays a normal value (outside the prescribed range). Of course, the apparatus of Figure 1 may be provided with a circulatilon conduit.

  We see, from the description given above,

  that the present invention provides the effects and

following advantages.

  (a) Since the synthesis of the aqueous aluminum sulphate solution is carried out continuously by the parallel type reaction in a multi-stage vessel, the production capacity is significantly improved with respect to conventional synthesis carried out discontinuously and for a given production volume, the device allows a significant reduction in size. The device, if

  need is, can be installed inside a local.

  (b) Since the adjustment of the pH values of the reaction system is effected by using the dilute aqueous solution of sulfuric acid containing sulfuric acid, the pH adjustment can easily be obtained and the concentration of H2S04 free in the first tank is weak. Therefore, by adjusting the pH values of the reaction solution in the component vessels such that these values are between 0.8 and 2.5, stainless steel reaction vessels can be used safely. The reaction tanks can, for example,

  Therefore, receive the necessary maintenance by welding.

  repair and inspectcin appropriate. The cost of the equipment is therefore low. Because the apparatus operates in a continuous manner, the pH value of the solutonr. The reaction time can be adjusted continuously without the need to switch on or off the valves, pumps, agitators, ect. The device can therefore be easily automated. It is also effective in improving the

  maneuverability and security.

  (c) Based on the experimental data for the reaction rate constant, the production capacity can be increased at the cost of

minor modification of the device.

  (d) The system used in the present invention for controlling the temperature of the reaction, causes practically no loss of thermal efficiency due to tilting, because the heating is carried out using heat exchanger devices installed in a manner independent of the reaction tanks. In addition, the temperature setting can be performed automatically. Due to the ease of setting the temperature associated with the effect of continuous operation, the apparatus has a high energy efficiency and low energy consumption.

  as well as a low operating cost.

  Other benefits and effects of this

  inventior. appear in the above description of

the invention.

Claims (2)

  i. Process for the continuous production of a   aqueous solution of aluminum sulphate from   products collected during the surface treatment of aluminum. this process being carczerlsed by the steps of bringing an aluminum slurry produced during the surface treatment operation of aluminum and preferably comprising aluminum hydroxide. residual sulfuric acid produced during the removal of a coating during said surface treatment operation, and an aqueous solution of sulfuric acid containing aluminum sulphate and produced during the recovery of the sulfuric acid at during said surface treatment operation to a reaction vessel consisting of a plurality of tanks, namely from first to nth tanks, to flow said substances brought successively from the first to the nth tank (last tank) to undergo reactions under conditions of temperature between 80 ° C and the boiling point of the reaction solution and, at the same time, to bring part of the aqueous solution of sulfuric acid containing aluminum to at least one of the second to last tanks and adjust the pH value of the reaction solution in the last tank to a level between 1.6 and 2.5.   2. Process according to revendzcation 1, characterized by the fact that a part of the aqueous solution of aluminum sulphate exiting the final tank is returned to the reaction vessel when the pH value of the reaction sclution in the final vat deviates of: a prescribed range.   Process according to Claim 2, characterized in that part of the aqueous solution of aluminum sulphate leaving the final tank is returned to the first tank.   4. Process according to any one of   Claims 1 to 3, characterized in that the   pH value of the reaction fraction in the first or second vessel is adjusted to be understood between 0.1 and 2.0.   5. Method according to claim 4, characterized in that the adjustment of the pH value of the reaction solution is carried out by adjusting the amount of aqueous sulfuric acid solution containing aluminum sulphate introduced into the first tank.   6. Process according to any one of   1 to 5, characterized in that the   adjusting the temperature of the reaction solution in the reaction vessel is carried out by introduction   water vapor in said reaction solution.   7. Process according to any one of   1 to 5, characterized in that the   Adjusting the temperature of the reaction solution in the reaction vessel is effected by heat exchange between said reaction solution and a steam line immersed in this reaction solution. 8. Process according to any one of   Claims 1 to 7, characterized in that the   aqueous solution of sulfuric acid containing aluminum sulphate and heated to a high temperature is introduced into the first tank.   9. Apparatus for the continuous production of a   aluminum sulphate solution from sub-   products occurring during the aluminum surface treatment operation, this apparatus being characterized in that it comprises: a reaction vessel (3) consisting of first to nth adapted tanks (R ... Rn) to respectively allow continuous reactions of an aluminum sludge produced during the surface treatment operation. aluminum and consisting mainly of aluminum hydroxide, waste sulfuric acid produced during the removal of a coating during said surface treatment process, and an aqueous solution of sulfuric acid containing aluminum sulphate produced during the recovery of sulfuric acid during the surface treatment operation; a first supply duct (12) for supplying the aqueous sulfuric acid containing aluminum sulphate in the first tank (Ri): a feed line (n denoting an integer of equal value); at least 21) to bring the aqueous sulfuric acid solution containing aluminum sulphate into at least one of the following second and further vessels;   a first device (PHICR) (20) for indicating   pH setting-recording disposed within the first and second tanks; a first control valve (21) connected to said first pH setting-adjusting-recording indicia and adapted to control the flow rate in the first supply line;   an umpteenth indication-setting device   pH control (n denoting an integer of a value at least 2) disposed in at least one of said second and subsequent vessels; and an umpteenth control valve (n denotes an integer having a value at least equal to 2) connected to the nth indicating-setting-recording device and adapted to control the flow rate in the nth supply duct. 10. Apparatus according to claim 9, characterized in that the uième feed duct serves to bring the aqueous solution of sulfuric acid containing aluminum sulfate to the tank immediately precede the last tank, the umpteenth disputed positive indication-setting-recording pH being arranged in the final tank and the nth eezan control valve: - sdsée in said supply conduit. 11. Apparatus according to claim 9 or 10, characterized in that the reaction vessel is divided into nth tanks by partitions (8b) suspended so as to form an opening in the portion -r4 = The reaction vessel and / or dam-like bulkheads (s) are erected vertically to allow overflow to occur. the solci.on de r atro :.   2. A device according to claim 11, 13 characterized by the fact that a baffle forming a baffle (53) da_pe, for shortening of the _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ of acne is rsosée in minus one these _ _ _.