LU87535A1 - PROCESS FOR THE TREATMENT OF MATERIALS CONTAINING HEAVY METALS BY ACID LIXIVATION - Google Patents

Description

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Patent No O * _ .. w _____ ^ ** BL 4237 ............. Minister of ___ - Economy and the Middle Classes

Title issued "Sÿ® Intellectual Property Service:

_e - 'Sô. · LUXEMBOURG

Invention Patent Application ► I. Application /

Center de Recherches Métallurgiques-Centrum voor Research _7 ^ 2) in de Metallurgie / Association sans but Ïucratif-Vereniging.

zonder winstoogmerkf 47 rueMontover B-1040 BRUSSELS______________________

Represented;; by ......: E.T ...... FREYLINGER & E. MEYERS, Inq. cons .__ in (3) ..2 ..-. 1 ,, .......... 3,2.1 ,,, ........ route ...... d'Arlo 'n - „; B ..... E ...-, l ________ ;, L = JB.Q, 0.1 ....... SIRZU5.SEN _____________________________ J____________________________________ deposit) this ___________ Twelve ...... juin mi 1 nine ...... one hundred ...... four ...... twenty ...... nine___________________ (4) at JULdPJP! - hours, at the Ministry of Economy and Middle Classes, at Luxembourg: 1. this request for obtaining a patent for an invention concerning: ----: -------------------- 1 ---- ---------------------------------------------------------- -1 — r —-------------------------------- (5) .. ".. Process .... .... of ........ treatment ...... of ...... materials ........ 5ont.e.nant ....... of. s ....... metals ........................................

..lQnr.ds ....... by ...... lixisiatiem ....... acid. ".................... .................................................. .................................................. ._................................................ ............_ 2. description in language .................. £ .§.ïl.tai§..§. ___________________________ the invention in triplicate; 3. ........................................ ± .......................... drawing boards, in triplicate; · 4. receipt of the fees paid to the Registration Office in Luxembourg , JL? j.ui n1989_; 5. the delegation of power, dated ................................ ......................... on ______? ...._ .. 1.ΗΪ?} ..... L ..? .. ?.? ____; 6. the successor document (authorization); declares (s) assuming responsibility for this declaration, that the inventor (s) is (are): (6) JOSIS Christian ZOBis Beauregard B-4050 ESNEUX (Belgium) ______ HISSEL ...... Joseph 4. Chemin de la Bruyère B-4801 STEMBERT (Belgium) eu (nt) for the above patent application the priority of one (s) application (s) of (7) _____ patent ...... of invention ____________ filed (s) in (8) Belgium_______________ i (9) _________ June 14 1988_________________________________________ under N ° (10) _____________________ Q88QQ-67J5 ____________________________________________________________ in the name of (11) Center de Recherches Métallurgiques _________________ élitfélisent) domicile for him (her) and, if designated, for his agent, ^ Luxembourg ___________________ .. 3.21., Route. „DlArlon_L .-. 8 ... 0..Q.1 ...... S.TRAS.SEÎJ .._______________________________ (12) seeks (s) the grant of a patent for the invention for the object described and represented in the abovementioned appendices, with postponement of this issue to ----------...--------------- / -------- -----------------------------------------------month. (13)

The depositor / mandatajire ^ ------------—____________________________________________________________________ (14) (\ Π. Minutes of Deposit

The above request for lin-tfl'inTintjqn has been filed with the Ministry of the Economy and the Middle Classes, Department of Property Intej ^ Â ^ f ^ * îft ^ l ^ ourg, dated: June 12, 1989 I ' '· 5! Pr. The Minister of the EcoAomie and the Average Qasses, at ... 1.5 .... 0.Û — hours I | · ’jfp. d.

. L * \ ^ xjgz Âjp The head of the service ^ Intellectual property,

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A68007 __ / τ / I_ EXPLANATIONS RELATING TO THE DEPOSIT FORM. / 1 / "'r (1) if applicable" Request for certificate of addition to the main patent, to main patent application No .. # .. of ........... . "- (2) enter the surname, first name, profession, address of the applicant, when the latter is an individual or your corporate name, legal form, address of the head office, when the applicant is a legal person- (3) register the name, first name, address of the authorized representative, industrial property attorney, with special powers, if applicable: "represented by ........... acting as agent" - (4) date of filing in all letters - (5) title of the invention - (6) enter the names, first names, addresses of the inventors or the indication "(see) separate designation {will follow)", when the designation is made or will be done in a separate document, or the indication "not to mention", when the inventor signs or signs a non-mention document to be attached to a designation "Autrée nnfeente nu nu futur" - / 71 patent certificate of addition, utility model, eunméenfCBÉl patent. international protection ÎPCTl-iei State in leauel DremierdéDôtaété i BL 4237

Claim to the priority of the patent application filed in Belgium on June 14, 1988 No 08800675 Descriptive memorandum filed in support of an invention patent application for: "Process for the treatment of materials containing heavy metals by acid leaching"

Metallurgical Research Center Centrum voor Research in de Metallurgie

Non-profit association Vereniging zonder winstoogmerk 47, rue Montoyer B-1040 BRUXELLES Belgium .κ - 1 -

Process for the treatment of materials containing heavy metals by acid leaching.

The present invention relates to the treatment of materials containing heavy metals, with a view to separating and recovering the metals which these materials contain and thus contributing to the protection of the industrial environment and to the economy of raw materials. It 5 relates in particular to the treatment of industrial residues, in particular steel residues, such as sludge and dust resulting from the dedusting of gas from blast furnaces and steelworks. Among the heavy metals targeted by the invention, mention may in particular be made of zinc and lead.

10

The description which follows will relate, by way of simple illustration, to the treatment of steel residues.

Already known, from patent BE-A-08800144, a process for the treatment of materials containing heavy metals by acid leaching by means of a spent pickling bath containing iron. This process includes in particular an operation in which the precipitation of this iron is carried out on the one hand in the form of insoluble compounds and on the other hand the dissolution, in the form of soluble compounds, of the heavy metals and of the elements alkali and alkaline earth present in these materials.

t - 2 -

In principle, this operation, which takes place in a single reactor, is particularly advantageous for re-treatment; iron and steel sidus such as, on the one hand, spent acid pickling baths and, on the other hand, sludges and dust from blast furnaces and steelworks. It makes it possible to: separate on the one hand the constituents of iron, which can then be reintroduced into the steel cycle, and on the other hand the non-ferrous constituents which it is also advantageous to recover.

10 Continuing his work in the context of this known process, the applicant then sought to specify the optimal operating conditions leading to good separation of the above-mentioned constituents. A few drawbacks appeared on this occasion.

If a weak chemical oxidizing agent, such as air, enriched air or even pure oxygen, is used, a medium is obtained in which the concentration of Fe is low; consequently, the redox potential of the medium is low and its pH is relatively high, that is to say of the order of 4. Such conditions ensure the formation of a goethite precipitate (Fe 00H) of excellent quality. However, this method leads to a decrease in the power of solubilization of zinc and lead, because of a too high pH, and it gives rise to a post-precipitation of metallic lead, due to a too redox potential. low.

25

If a more powerful chemical oxidizing agent, such as sodium hypochlorite, is used, an increase in the concentration - - +++, .... tion in Fe and consequently an increase in the potential of oxidation-reduction of the solution and a lowering of its pH to approximately 30 1, the suppression of the post-precipitation of lead and an improvement of the power of solubilization of zinc and lead. However, this also results in an increase in the cost of the reagents, in particular of the oxidizing agent, a degradation of the precipitation properties of iron, which no longer only precipitates in the form of goethite, as well as +++ 35 loss of iron from the made up of the largest proportion of Fe ions - remaining in solution.

- 3 -

The object of the present invention is to propose a method which makes it possible to remedy the various abovementioned drawbacks and thereby to ensure good separation of iron on the one hand and heavy metals on the other hand, while limiting the cost of operation and making possible 5 Individual separation of the various Heavy metals.

According to the present invention, a process for treating materials containing Heavy metals by acid leaching using an acid solution rich in Fe +++ ions and poor in Fe ++ ions is characterized by the following successive operations: (a) on brings together said acidic solution and said materials containing heavy metals, and causes on the one hand the hydrolysis and precipitation of at least part of the Fe +++ of said acidic solution and on the other hand the dissolution of said heavy metals , which produces a second solution; (b) the pH of said second solution is measured at regular intervals and the addition of said materials is interrupted when said pH is substantially equal to 2; (c) said second solution is collected, its pH is adjusted to a value between 3 and 5 by addition of an alkaline substance, the residual Fe is oxidized to Fe using an oxidizing agent, and precipitation is brought about selective residual iron in solution; (d) the solid phase resulting from said selective precipitation is separated from the liquid phase containing said soluble components; (e) adding to said liquid phase, either simultaneously or successively, at least one reagent causing the formation and precipitation of an insoluble compound of at least one of said heavy metals from said corresponding soluble compound present in said phase Liquid; (F) after each precipitation operation of an insoluble compound, the residual liquid phase and the solid phase containing said insoluble compound are separated.

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In the context of the present process, step (a) above can be carried out by means of any acid solution rich in Fe ions. In particular, it would not be departing from the scope of the invention for the process to include a preliminary step consisting in subjecting to an oxidation operation an acid solution rich in Fe ++ ions, in order to oxidize them and produce a acid solution rich in ions _ +++

Fe

In accordance with this variant, it is particularly advantageous, with a view to recovering steel residues, to use a spent acid pickling bath. As is known, these baths are rich in Fe ++ ions.

According to the invention, the oxidation operation carried out during this preliminary step can be carried out by introducing into the bath an appropriate oxidizing agent, either gaseous such as air or pure oxygen, or liquid such as hydrogen peroxide, or sodium hypochlorite, is still solid such as potassium monopersulfate. It goes without saying that the oxidizing agents mentioned here constitute only examples of agents which can be used in the context of the invention. This oxidation can also advantageously be carried out electrochemically.

Also according to the invention, the redox potential and the pH of the solution are measured during the leaching operation (a), the measured values are compared to predetermined reference values and the addition of 'Fe +++ ions, respectively of materials containing heavy metals, as a function of the difference between the measured values and the reference values of the po-30t redox potential, respectively of the pH.

It is known that the content of Fe ions and the redox potential of the solution are linked; this potential must be high enough to avoid post-precipitation of lead; however, it should not be raised excessively in order to limit the content of Fe +++ in the solution, ferric iron which would then be lost for the leaching of heavy metals.

Materials containing heavy metals are alkaline in nature and uncontrolled addition would cause the pH of the solution to increase excessively. In this regard, the pH of the solution should remain below 2, and preferably be below 1, which provides the solution with excellent power to dissolve materials containing heavy metals.

10

According to an interesting feature of the invention, the solution is stirred and maintained at a temperature below 90 ° C during the leaching step (. Step ··· a).

It is also advantageous to continuously measure the pH of said second solution, in step (b).

According to a particular variant embodiment of step (d), the zinc and the lead are precipitated simultaneously in the form of hydroxides.

It has been found to be advantageous to carry out this precipitation in the form of hydroxides by the addition of a hydroxide, in particular calcium hydroxide, to said liquid phase.

25

According to another alternative embodiment of step (d), the zinc and the lead are precipitated simultaneously in the form of sulphides.

In this case, it has been found to be advantageous to produce this precipitation in the form of sulphides by introducing a sulphide compound into said liquid phase.

In this respect, it is advantageous to use the hydrogen sulfide present in the gas from coke ovens, which makes it possible to ensure partial desulfurization of this gas.

- 6 -

It is also possible, in the context of step (d) of the process of the invention, to individually precipitate and separate the heavy metals from their soluble compounds contained in said liquid phase.

5

In particular, lead precipitation, in the form of metallic lead, can be carried out by carburizing with Fe ++ ions, these 4 * + ions.

Fe being supplied by any suitable source and preferably by a spent pickling bath.

10

After separation of this lead precipitate, a new liquid phase is obtained, to which it is possible, for example, to add an alkali hydroxide to cause precipitation of zinc hydroxide. For this purpose, the pH of the alkaline solution is preferably between 7 15 and 7.5.

Other particularities and advantages of the present invention will appear on reading the detailed description, given below by way of example, of a preferred variant of implementation of the method; 20 this description refers to the single appended figure, which schematically illustrates the sequence of operations according to the variant of step (d) where lead and zinc are separated individually and successively.

25 The figure illustrates the use of a spent bath from a hydrochloric acid steel pickling installation A1, for the treatment of materials consisting of sludge and dust, rich in lead and zinc, produced in an A2 oxygen steelworks and in an A3 blast furnace. The spent pickling bath is symbolized by B1, the 30 sludge and dust from the steelworks by B2 and that from the blast furnace by B3.

Typically, a pickling bath with hydrochloric acid, rejected at the rate of 25 l / ton of rolled steel, contains 144 g / l, ie 2.58 35 moles / l of ferrous ions (Fe ++), 2 g / l or 0.036 moles / l of ferric ions (Fe +++) and 205 g / l or 5.77 moles / L of chloride ions (Cl). These 9 - 7 - contents are given for information only and can in no case constitute any limitation of the process of the invention.

In addition, the main constituents of steel residues 5 are iron (30 - 60%), zinc (1 - 10%), lead (0-5%), carbon (1 - 35%), calcium ( 1 - 5%) and magnesium (0-3%). The values mentioned in parentheses give, by way of indication only, the weight contents commonly encountered for these constituents. The effective contents of these constituents can therefore vary quite widely depending on the origin of the residues, in particular depending on whether they come from an oxygen steelworks, an electric steelworks or a blast furnace.

In the variant implementation illustrated in the figure, the spent bath B1 is introduced into a first reactor C1 to undergo electrochemical oxidation of ferrous ions (Fe ++) to ferric ions (Fe + * +). To this end, the reactor C1 is divided into an anode compartment 1, containing an anode 2, and a cathode compartment 3, containing a cathode 4. The spent bath B1 is introduced into the anode compartment 20 1, where the ferrous ions are oxidized , in an acid medium, depending on the reaction:

Fe ++ —- Fe +++ + 1 e "(1)

The two compartments are separated by a membrane 5 with selective permeability, which prevents the iron ions from going to reduce at the cathode, but which on the contrary allows the anions to migrate, in particular the Cl and OH. The solution contained in the anode compartment is therefore enriched with ferric ions Fe +++.

The cathode compartment 3 of reactor C1 is supplied with an aqueous solution of salts such as alkali or alkaline earth chlorides; this solution is generally arbitrary, but it is preferably constituted by the brine obtained after the separation of iron and heavy metals, as will be seen below.

- 8 -

In this cathode compartment, there is a reduction in the water molecules, with evolution of hydrogen and formation of OH ions, giving the cathode solution an alkaline character. The reaction at the cathode is written: 5 H-0 + 1 e ~ _ * - 1_ H2 + 0H ‘(2).

2

The anodic and cathodic solutions are strongly agitated. In particular, the anode 2 and / or the cathode 4 can be rotating.

The solution rich in ferric ions Fe is transferred in 6, from the anode compartment 1 to a second reactor C2, where it is brought into contact with the steel residues B2, B3, which have an alkaline character. The reactor C2 is equipped with an agitator 7 and a heating element 8 intended to agitate and, if necessary, to heat the resulting bath 15.

The addition of the solution rich in Fe +++ ions, of an acidic nature, is subject to a measurement, in 9, of the redox potential of the bath, while the addition of residues is subject to a measurement, in 10, of the pH of this bath.

The pH is preferably close to 1, so as to ensure, to a satisfactory extent, the dissolution of the residues, in particular lead and zinc, but also of the alkali metals (Na, K, etc.) and of the 25 a lino-earthy Ica (Ca, Mg, ...). The oxidation-reduction potential must be high enough to avoid post-precipitation of lead while remaining at levels that limit the escape of iron, which would be lost for leaching.

In such an acidic medium (pH ^ 1), the iron preferably precipitates in the form of a gelatinous, colloidal ferric hydrate, from which it is difficult to decant.

The sludge resulting from the reactions taking place in the reactor C2 is then transferred at 11, to a third reactor C3, for post-oxidation and precipitation of the iron in the form of hydroxides - 9 - various Fe ( OH) and oxides.

λ Π

To favor this oxidation and this precipitation of iron, one operates in an oxidizing medium with a pH close to 4.

5

PH ·? 4 can be obtained by adding any alkaline solution; in the illustrated variant, it is obtained by means of the alkaline solution produced by reaction (2), in the cathode compartment 3 of reactor C1. This addition can be controlled by a pH measurement at 12.

The oxidizing medium is obtained by introduction of a chemical oxidizing agent, B4, such as air, air enriched with oxygen or even pure oxygen, for example also from the A2 steelworks. The quantity 15 of oxidizing agent introduced can be controlled by measuring the redox potential at 13. Finally, the bath can also be agitated, for example by means of a propeller 14.

The solution resulting from these reactions is transferred, by 15, to a first separator D1, where a solid-liquid separation is carried out, for example by decantation, by filtration or by centrifugation. A solid phase is thus obtained, which essentially contains hydroxides Fe (OH) n and iron oxides (FeO, Fe ^ O ^, Fe ^ O ^), as well as other insoluble substances such as carbon (C) and silica C Si 02>, and a liquid phase, of an acidic nature, essentially containing chlorides.

The solid and liquid phases can undergo the treatments described in the aforementioned document BE-A-08800144, with a view to their recycling in suitable industrial processes. There is no need to reproduce here the description of these treatments.

In the illustrated variant, the solid phase S1 obtained in the separator D1 receives washing water at 16, then, after washing and dehydration at E1, this solid phase having the composition qualitatively recalled in the figure, is directed towards the agglomeration of iron ores G1, where it is recycled. This operation is analogous to that of the aforementioned document BE-A-08800144.

The liquid fraction collected in 17 is mixed with the liquid phase 5 L1 coming from the separator D1; this liquid phase L1 essentially contains chlorides and has an acidic character.

The resulting mixture is directed to a reactor C4, equipped with a stirrer 18, where it receives an addition of a solution rich in ferrous ions Fe, coming for example from a spent pickling bath such as B1.

In this C4 reactor a reaction of cementation of lead by Fe ions takes place, which is written: 15 2 Fe ++ + Pb ++ - ► 2 Fe +++ + Pb | and which causes the precipitation of lead in metallic form.

The bath is transferred through 19 to a second separator D2, from where the solid phase, consisting essentially of lead is, after washing and conventional dehydration in E2, recycled to G2 in the non-ferrous metal industry.

The liquid fraction 20 is in turn mixed with the liquid phase L2 and the resulting mixture is introduced into a reactor C5, equipped with a stirrer 21. In this reactor C5, an alkaline solution is introduced at 22 in order to obtain a pH of the order of 7. This alkaline solution is arbitrary, but it preferably comes from the cathode compartment of reactor C1.

The precipitation of zinc is thus caused by the reaction:

Zn ++ + 2 0H _— ^ Zn (0H> 2l The insoluble zinc hydroxide is then separated in a separator D3 then, after conventional washing and dehydration in E3, it is recycled to G3 in the non-ferrous metal industry.

- 11 -

The final liquid phase, L3, mixed with the liquid fraction from E3, contains low-polluting salts and can, for example, be - discharged directly into the sea or into a stream with a high flow rate.

If the discharge of this final liquid phase is only possible in a stream with a low flow rate, it is also recommended, according to the invention, to include a step of desalination of this liquid phase.

The solid products obtained by this desalination operation 10 can in particular be used as snow-removing salts.

The final rejection is symbolized by the reference 64, and the possible desalination step is not shown in the figure.

As indicated above, the final liquid phase L3 can also, at least in part, be returned to the cathode compartment of the first reactor C1, where it constitutes the electrolyte necessary for the alkalinization reaction.

The process which has just been described and illustrated can be applied directly to sludge and dust from blast furnaces and oxygen steelworks. However, it is preferably intended for concentrates enriched in zinc and lead, resulting from primary treatment operations.

25

It therefore makes it possible to consider this type of steel residue on the one hand as an iron ore recyclable in the urban area and on the other hand as a source of zinc and lead likely to interest the non-ferrous metal industry.

30

Another major advantage of the process of the invention is to combine in a single process the treatment of a large type of steel waste and the recovery of spent pickling baths with hydrochloric acid. It makes it possible to advantageously use the poten-tial acidity and the considerable complexing power of these spent and iv baths ”- 12 - thus avoiding the regeneration of these spent baths which, in certain cases, can increase the price of l hydrochloric acid to a degree * reaching 30%.

5 It goes without saying that the invention is not limited to the description which has just been given. In particular, it would not be departing from the scope of the invention to apply the process using spent sulfuric acid pickling baths, subject to the adaptation, obvious to a person skilled in the art, of the reagents used in your various stages. 10 of the process.

&

Claims (10)

20 ce) at least one reagent causing said formation and precipitation of an insoluble compound of at least one of said heavy metals from said corresponding soluble compound present in said liquid phase is added to said liquid phase, either successively or successively ; 25 Cf) after each precipitation operation of an insoluble compound, the residual liquid phase and the solid phase containing said insoluble compound are separated. 2. Treatment method according to claim 1, characterized in that, in a preliminary step, said acid solution rich in Fe ions is produced by oxidation of at least part of the Fe ions contained in an acid solution rich in Fe ++ ions. , particularly in a spent steel pickling bath. A - 14 - ψ t 3. Treatment method according to either of Claims 1 and 2, characterized in that the potential is measured - redox, respectively the pH of the solution during the leaching operation (step a), in that the 5 measured values of these parameters are compared with predefined reference values, and in that the addition of Fe ions, respectively of materials containing heavy metals, is regulated, as a function of the difference between the measured values and the reference values of the redox potential, respectively of the pH, of the said solution. 10 4. Treatment process according to either of Claims 1 to 3, characterized in that the solution is kept at a temperature below 90 ° C during the leaching operation (step a). 15 5. Treatment method according to either of claims 1 to 4, characterized in that in step (e), a reagent is used which causes said heavy metals to precipitate in the form of hydroxides. 20 6. Treatment method according to claim 5, characterized in that Said reagent is calcium hydroxide. 7. Treatment method according to either of claims 1 to 4, characterized in that in step (e), a reagent is used which causes said heavy metals to precipitate in the form of sulfides. 8. Treatment method according to claim 7, characterized in that said reagent is hydrofluoric acid. 9. Treatment method according to either of claims 1 to 4, characterized in that in step (e), a reagent containing Fe ++ ions is used and the precipitation of a first f - - heavy metal, such as lead, by carburizing using said Fe ++ ions. you 10. Treatment method according to claim 9, characterized in that the solid phase containing the precipitate of said first heavy metal is separated, and the liquid phase containing in particular the soluble compounds of the other heavy metals, in that one adding to said liquid phase a reagent causing precipitation of at least one second heavy metal, such as zinc, in the form of hydroxide, and in that the solid phase containing said precipitate is separated from the residual liquid phase .