WO1994008058A1 - Method for hydrometallurgical processing of zincky byproducts - Google Patents

Abstract

Zincky powder generated during the manufacture of steel is lixiviated in an alkaline solution to produce an alkaline zincky solution and an iron residue for separation. This solution is neutralized with acid to give a zincky precipitate and a salt solution for separation. The salt solution undergoes electrodialysis with bipolar membranes to regenerate the alkaline solution and the acid previously used. The zincky precipitate is intended for subsequent use as a neutralizing agent in a hydrometallurgical zinc plant.

Description

 PROCESS FOR HYDRO-ETALLURGICAL TREATMENT OF BY-PRODUCTS

ZINCIFERE?

The present invention relates to a process for the ydrometallurgical conversion of zinciferous dust, generated in the manufacture of steel and containing Fe, Ca, Zn and at least one of the elements Pb, Cu, Cd, into an iron residue leaner in non-ferrous metals than dust and in a zinc concentrate for further processing in a hydrometallurgical zinc plant, including the following steps

(a) treating the dust with a leaching solution so as to dissolve a substantial part of the Zn and of the Pb, Cu and Cd, if present, and to leave at least the major part of the iron undissolved, thereby producing a zinciferous solution containing Pb, Cu and / or Cd and said iron residue,

(b) the zinciferous solution of the iron residue is repaired,

(c) the Zn is precipitated together with the Pb, Cu and Cd, if present, in the form of compounds in the zinciferous solution, thereby producing a deglycated solution and said zinc concentrate,

(d) separating the demistered solution from the zinc concentrate,

(e) the leaching solution is regenerated from the demistered solution, and

(f) the leach solution produced in step (e) is reused in step (a).

Such a process is described in US Pat. No. 5,082,493 (EC Barrett et al.) And in the article "A hydrometallurgical process to treat carbon steel electric furnace dust" by EC Barrett et al., Hydrometallurgy, 30 (1992) 59-68. In this known process, we start with an example of a dust having the following composition in% by weight: 24.87 Zn, 19.73 Fe. 2.84 Pb, 0.10 Cd, 13.88 Ca, 3.41 Mg , 1.05 Na, 0.66 K, 5.53 other metals, 26.15 O and 1.78 Cl.

In step (a), the dust is leached with a 3M acetic acid solution and the major part of the Zn, Pb, Ca, Na, K and Mg and a minor part, for example 13.5%, are thus extracted, Fe as acetates. This gives a zinciferous solution containing Pb, Ca, Cu, Na, K, Mg and Fe and an iron residue, which is separated in step (b).

In step (c) the zinciferous solution is treated with a stream of H ₂ S so as to quantitatively precipitate Zn, Pb, Cd and Cu, thereby simultaneously precipitating a minor part of Fe, Mg and Ca. This gives a dezingue solution and a zinc sulphide concentrate, which are separated in step (d). The stripped solution mainly contains acetates and chlorides of Ca, Mg, Fe, Na and K.

Step (e), that is to say the regeneration of acetic acid from the dezingue solution, is carried out in several phases. In a first phase, the solution is treated with surface acid so as to reduce most of the Ca as gypsum, which Ion separates from the solution, and to transform most of the acetates into sulfates. The solution thus obtained mainly contains ions of Fe, Mg, Na and K, SO ₄ ^" and CI ^" and 135 g / l of free acetic acid. This solution is treated in a second phase by a very acidic cation exchanger so as to remove approximately 75% of the cations from the solution. The solution thus obtained is treated in a third phase with a weakly basic anion exchanger so as to remove from the solution 90% of the anions, except the acetate ion. A 2.5 M acetic acid solution is thus obtained, which is concentrated by distillation to 3M before recycling to step (a). The charged cation exchanger, obtained in the second phase, is regenerated with 8% sutfuric acid, and the charged anion exchanger, obtained in the third phase, with a 4% NaOH solution.

One consumes per 1001 of dust, 1.71 of acetic acid (100%), 12.9 1 of hydrogen sulfide, 35.9 1 of sutfuric acid (93%) and 6.71 of sodium hydroxide ( 50%), and per 1001 of dust 720 m ³ of effluent are produced following the regeneration of the ion exchangers. This effluent must pass through a wastewater treatment installation. before it can be rejected.

This known method has the following drawbacks. The consumption of reagents, in particular H ₂ S, H ₂ S0 ₄ and NaOH is very important, as is the production of effluent. There are many operations to perform to regenerate the leach solution.

Hydrogen sulfide is a toxic material with a very unpleasant odor and its use requires special precautions. The zinc concentrate produced must be fed later into the roasting furnace of a zinc factory, that is to say at the start of the zinc manufacturing process; it follows that its further treatment will cost as much as that of a natural zinc sulphide concentrate. The zinc concentrate produced is also contaminated with Fe, Mg and Ca, elements which are undesired in a zinc plant.

The object of the present invention is to provide a method as defined above, which avoids the drawbacks of the known method.

For this purpose, according to the invention, in step (a), an alkaline detergent is used as leaching solution, thereby producing an alkaline zinciferous solution which is essentially free of iron and calcium, the zinc concentrate is precipitated. in step (c) by neutralizing the alkaline zinc solution with an acid, thus producing a salt solution as a dezingue solution, the alkaline lye is regenerated in step (e) by subjecting the salt solution to an electrodialysis with bipolar membranes and by concentrating the alkaline detergent produced in this operation, by which the acid consumed in step (c) is simultaneously regenerated, and the regenerated acid in l is reused in step (c) '' step (e) This process is based on the following reactions (assuming that the dust contains both ZnO and ZnFe ₂ 0 ₄ and where a solution of NaOH is used as alkaline detergent and a solution of H ₂ S0 ₄ as acid ):

- step (a) MeO + 2NaOH → Na ₂ Me0 ₂ + H ₂ 0 (I) in which Me represents Zn, Pb, Cd, Cu and ZnFe ₂ 0 ₄ + 2NaOH + 2H ₂ 0 → Na ₂ Zn0 ₂ + 2Fe ( OH) ₃ Ψ (II)

- step (c)

Na ₂ Me0 ₂ + H ₂ S0 ₄ → Na ₂ S0 ₄ + Me (OH) ₂ vU (lu) • step (e) electrodialvse \, ___ „.

Na ₂ S0 ₄ + 2H ₂ 0 7 ₂ NaOH + H ₂ S0 ₄ (IV)

Iron is practically not dissolved according to (I) and calcium and magnesium, if present, are not at all: these elements are therefore found in the iron residue.

The elements Na, K and Cl, if present in the dust, are found in your unzipped solution and they are transformed into NaOH, KOH and HCI in step (e).

In this process, the consumption of reagents is theoretically zero and in practice very low: a little alkaline detergent and a little extra acid. Effluent production can be kept very low, as will be demonstrated below. The regeneration of the leaching solution takes place in only two operations: electrodialysis and concentration. We don't use toxic materials. The zinc concentrate produced, which essentially consists of a zinc oxide and / or hydroxide, is practically free of Fe, Mg and Ca and it can be used, in particular as a neutralizing agent, in an advanced stage of production. zinc.

It should be noted here that many processes for treating zinc dust by hydrometallurgy are already known, which, instead of targeting the recovery of a zinc concentrate for subsequent treatment in a zinc plant, are aimed at direct recovery zinc and possibly other elements in the form of a metal or a pure compound. These processes all have in common that they comprise several purification operations, which are not required in the process of the present invention and which substantially increase the investment costs relating to the operation of these processes, while the factories existing zinc are capable of processing substantial amounts of the zinc concentrate produced in the process of the present invention without making any investment. '

A process of this kind is described in the article "Zinc and lead recovery from EAF dusts by caustic soda process" by J. Frenay et al, published in "Disposai, recyciing and recovery of electπc furnace exhaust dust ", p. 171-175, published by Iron and Steel Society, AIME, 410 Commonwealth Drive, Wattendale, Pennsylvania 15085.USA, 1987. This process involves the following steps:

(1) alkaline leaching such as that carried out in step (a) of the process of the present invention;

(2) separating the leach solution from the residue;

(3) treatment of the leach solution with lime to precipitate the silicon present in the solution following the reaction

Na ₂ Si0 ₃ + Ca (OH) ₂ → 2NaOH + CaSiO _j (4) separation of CaSi0 ₃ from the solution;

(5) carburizing Pb and Cu present in the solution with zinc powder;

(6) separation of the cement from the solution;

(7) electrotysis of the solution to produce powdered zinc and regenerate the alkaline lye according to the reaction Na ₂ Zn0 ₂ 0 + H ₂ 0 → Zn - + / ₂ 0 ₂ f + 2NaOH

(8) the concentration of spent electrolyte; and

(9) the reuse of the spent electrolyte concentrated in step (1).

In addition to the fact that it comprises two purification operations, which must be carried out with meticulous care so as not to compromise the quality of the zinc powder to be produced, this process has the disadvantage of requiring the operation of an installation for your electrolytic recovery of a powdered metal. Such an installation is, in fact, a large consumer of labor and its operation is particularly delicate because of the inevitable fluctuations in the concentration of Zn in the electrolyte, due to the large variations in the composition of the dust as a function of time. . Another method of the above kind is described in document DE-A-4033232. This process includes the following steps: (1 ') leaching the dust with a solution of NH ₄ CI to dissolve the elements Zn, Ca, Pb, Cd, Na, Cu (= Me) according to the reactions

MeO + 2NH ₄ CI → MeCI ₂ + H ₂ 0 + 2NH ₃ 'T MeC0 ₃ + 2NH ₄ CI → MeCI ₂ + H ₂ 0 + C0 ₂ + 2NH ₃ ^

MeOFe ₂ 0 ₃ + 2NH ₄ CI → MeCI ₂ + H ₂ 0 + Fe ₂ 0 ₃ + 2NH ₃ ^ (2 ') separation of the residue from the leaching solution; (3 ') the treatment of the leaching solution at pH 5.7-6.0 with recycled NH ₃ and CO ₂ so as to precipitate lead as carbonate according to the reactions

NH ₃ + C0 ₂ + H ₂ 0 → NH ₄ HC0 ₃

NH ₄ HC0 ₃ + NH, → (NH ₄ ) ₂ C0 ₃

PbCI ₂ - (NH ₄ ) ₂ C0 ₃ → PbC0 ₃ + NH ₄ CI (4 ') the separation of PbCO ₃ from the solution;

(5 ') the cementation of the Cd. Cu and Ni present αans ia unplugged solution with zinc powder; - (6 ') separation of the cement from the solution; 5 (7 ') treating the solution separated in step (6') at pH 6.0-6.5 with NH ₃ and CO ₂ recycled so as to precipitate the zinc as carbonate according to analogous reactions with those involved in the precipitation of lead; (8 ') ia separation of ZnC0 ₃ from the solution;

(9 ') the treatment of the dezingue solution at a pH greater than 6.5 with recycled NH ₃ and CO ₂ 10 so as to precipitate the calcium as carbonate according to reactions analogous to those involved in the precipitation of lead; (10 ') separation of CaCO ₃ from the solution;

(1) the reuse in step (V) of the solution separated in step (10 '); (2 ') washing the PbC0 ₃ separated in step (4') with an ammonia solution to remove the coprecipitated ZnC0 ₃ therefrom;

(13 ′) calcining the washed PbC0 ₃ so as to produce PbO and C0 ₂ for recycling, or alternatively dissolving the washed PbC0 ₃ in a mineral acid, eg in fluoboric acid, so as to produce C0 ₂ for recycling and a lead solution to be electrolyzed; (14 ') ia calcining the ZnC0 ₃ separated in step (8') so as to produce ZnO and

C0 ₂ for recycling, or the dissolution of ZnC0 ₃ in a mineral acid, eg in sutfuric acid, so as to produce C0 ₂ for recycling and a zinciferous solution to be electrolyzed; (15 ') caicination of CaCO ₃ separated in step (10') so as to produce CaO and CO ₂ for recycling.

Besides the impressive number of operations, which it involves and most of which must be carried out with meticulous care, this process still has the following drawbacks. It requires the use of ammonia, which implies taking special precautions. The recycling of gaseous NH ₃ and CO ₂ requires the presence of expensive storage means. The calcium and magnesium, if present, are dissolved together with the Zn, Pb and Cd; it would therefore be impossible to modify this process so that one can produce a zinc concentrate free of Ca and Mg, without being obliged to also produce a concentrate of Ca and Mg, the commercial value of which must be extremely low.

- <When the zinc dust to be treated by the process of the present invention contains water-soluble halides such as NaCI, KCI and CaCI _{2 for example} , it is advantageous to separate them from the dust by washing with hot or cold water, before subjecting the dust to alkaline leaching. Otherwise, the acid regenerated in step (e) would be enriched more and more halide ions and would contaminate with these ions the zinc concentrate precipitated in step (c), which is to be avoided.

Instead of washing the dust, it is also possible to practice a bleeding on the acid regenerated in step (e) or possibly on the unzipped solution to avoid an excessive accumulation of halide ions in the circuit. We could also combine the two techniques: washing and bleeding.

Washing would normally produce an effluent volume of about 0.5-1.5 πrvVtonne of dust, and bleeding, for example of the unzipped solution, an effluent volume of about 0.3-1.5 m ³ / ton of dust.

When the dust to be treated contains both ZnO and ZnFe ₂ 0 ₄ , the alkaline leaching can be carried out in different ways.

The alkaline leaching can be carried out under moderate conditions, for example with NaOH at 240 g / l for 1.5 hours and at 95 ° C., so that the ZnO dissolves and the ZnFe ₂ 0 ₄ remains in the residue.

It is also possible to carry out the alkaline leaching under more severe conditions, for example with NaOH at 450 g / l for 4 hours and at 95 ° C., so that the oxide and the ferrite dissolve.

If it is possible to split the dust by one or the other technique, p. ex. by magnetic separation, in a first fraction containing the oxide and a second fraction containing the ferrite, we can then apply this technique and release the first fraction in moderate conditions and the second fraction in severe conditions, as also provided in the article by J. Frenay et al discussed above. If ZnFe ₂ 0 ₄ is present, the dust can also be subjected to a reducing mesh before your leaching in order to transform the ferrite into a more easily soluble substance, as mentioned in the following articles: "The Caron zinc process" by JW van Put et ai appeared in "Production and processing of fine particles, 1988, 27th Annual Conference of Metallurgists of CIM, August 28-31", p. 691-700; "Techno-economic feasibility of zinc and lead recovery from electric arc furnace baghouse dust * by JG Eacott et al published in CIM Bulletin, September 1984, p. 75-81; and" Recovery of heavy metals from electric arc furnace steel making dusts " by E. Radha Krishnan, 1984 ASM Metals Congress, Detroit, Michigan 15-20 September 1984, paper 8402-002.

When choosing among these different possibilities, several factors will play a role, such as the ZnFe ₂ 0 _{4 content} of the dust and the specifications concerning the composition of the residue.

When your dust contains silicon soluble in alkaline medium and that consequently the alkaline zinciferous solution contains silicate, we can precipitate the silicon of the solution together with Zn, Pb, Cd ... in stage (c), but we could also, before moving on in step (c), remove the silicon from the alkaline zinc solution by precipitating it as CaSi0 ₃ with CaO or Ca (OH) ₂ and separating the CaSi0 ₃ from the solution.

In step (c) normally sutfuric acid will be used, because a sulphate solution is used in the production of zinc by hydrometallurgical means. It will already be understood that it is not at all indicated to use hydrochloric acid there.

It may however be useful to neutralize in step (c) with C0 ₂ , for example by blowing blast furnace gas into the solution, because carbonates are then precipitated and the carbonates, such as for example zinc carbonate are very often easier to filter than the corresponding hydroxides, for example zinc hydroxide, which are obtained by neutralization with sutfuric acid. The salt solution, which is obtained by neutralizing with CO _2, is a carbonate solution, for example a sodium carbonate solution, when leached in step (a) with NaOH, or a solution of potassium carbonate, when leached with KOH. Such a carbonate solution may be less suitable for electrodialysis with bipolar membranes than, for example, a solution of sulfate, chloride or nitrate. This is why it may be useful, in the event of neutralization with C0 ₂ in step (c), to convert between steps (d) and (e) the carbonate solution to a solution of sulfate, chloride or of nitrate, preferably a solution of sulfate, and of electrodiatysing this solution in step (e). The C0 ₂ , which is released during the conversion of the carbonate solution, can optionally be recycled to step (c) and the acid, which is regenerated in step (e), can be reused to convert from the carbonate solution.

For the execution of step (e), known techniques can be used such as for example the AQUATECH ^* "system from Allied Corporation, 7 Powderhorn Drive, Mt. Bethel,

NJ 07060, marketed in Europe by the firm Corning. Information on the AQUATECH ¹ system "is given in the catalogs of these two companies. More general information on the recovery of acids and bases from salt solutions by electrodialysis with bipolar membranes can be found in the following articles:" AQUATECH ™ membrane technology for recovery of acid / base values from sait streams "KN Mani et al., Desaiination, 68 (1988), p. 149-166;" Bipolar membranes for purification of acids and bases "YC Chiao et al., Journal of Membrane Science, 61 (1991), p. 239-252; "Application of n-exchange membranes to hydrometallurgy" Toshikatsu Sata, Extraction Metallurgy '89, p. 977-1001, Proceedings of an IMM Conférence, London 10-13 7/1989; and "Solution purification" DS Flett, Hydrometallurgy, 30 (1992) p. 327-344. The following is a description of a possible embodiment of the method according to the invention. This description is given by way of nonlimiting example and is illustrated by the attached diagram.

This embodiment comprises a leaching step 1, a first solid-liquid separation step 2, a neutralization step 3, a second solid-liquid separation step 4, an electrodialysis step 5 in which the lye is recovered. alkaline and acid from a salt solution, a concentration step by evaporation 6 in which the alkaline detergent recovered in 5 is concentrated, two washing steps 7 and 8 in which the solid material separated in the step 2 is washed and a washing step 9 in which the solid material separated in step 4 is washed.

Dust 10, produced in the manufacture of steel in an electric arc furnace and containing approximately 20% Zn, 4% Pb, 22% Fe, 9% Ca and possibly small amounts of Cd and Cu, is leached in 1 with an alkaline detergent 11 containing approximately 300g NaOH / l at 95 ° C and for 2h. A pulp 12 is thus obtained consisting of an alkaline zinciferous solution and an iron residue 13, which is separated from the puipe in 2.

The residue 13 is washed in 7 with part 14 of the regenerated alkaline detergent, concentrated in 6. The alkaline detergent 11 consists of washing detergent 15 and the other part 16 of the regenerated alkaline detergent, concentrated in 6. The residue 17, washed with alkaline detergent, is washed in 8 with fresh water 18 and with part 19 of the water recovered in 6. The residue 20, washed with water, consists essentially of oxide iron, zinc ferrite and calcium oxide; this residue can possibly be recovered later in the blast furnace of a steel plant, where Zn, Ca and Mg (if present) will be scorified. The washing water 21 is used in the neutralization step 3.

The alkaline zinciferous solution 22 originating from stage 2 and containing approximately 40 g ZrVI is neutralized in 3 with the acid solution 23, which leaves stage 5 and which contains approximately 100g H ₂ S0 ₄ / l and 150 g Na ₂ S0 ₄ / l. at the same time, the alkaline zinc-containing solution 22 is diluted in 3 with water 24, this water being composed of the washing water 21, the washing water 25 coming from step 9 and a part 26 of the water recovered in 6, which is recycled directly in 3. A pulp 27 consisting of Na ₂ S0 _{4 solution} and precipitate is obtained in 3; this precipitate 28 is separated from the pulp 27 at 4.

The precipitate 28 is washed at 9 with fresh water 29 and with part 30 of the water recovered at 6. The washed precipitate 31, which essentially consists of hydroxide and / or zinc oxide and which contains more lead and possibly small amounts of Cd and Cu in the form of hydroxide and / or oxide, can subsequently be used as neutralizer in the purification circuit of the zinc sulphate solution of a electrolytic zinc, this in place of calcine (roasted blende): the zinc present in the precipitate will ultimately be found in refined zinc, while the other constituents of the precipitate (Zn, Pb, Cd) will be found in the cements and residues, by example the copper cement and the residue of lead sulphate, which is produced in an electrolytic zinc plant anyway. The washing water 25 is used in step 3, as already mentioned above.

The Na ₂ S0 ₄ 32 solution leaving step 4 is subjected in 5 to an electrodialysis with bipolar membranes and it is thus decomposed into solution 23 already mentioned above, which contains approximately 100 g H ₂ S0 ₄ / l and 150 g Na ₂ S0 ₄ / l, and in a solution 33 which contains approximately 150 g NaOH / l.

The solution 33 is concentrated to 6 by evaporation to approximately 300 g NaOH / l: the concentrated alkaline detergent and the recovered water are recycled as described above.

For the conversion of one tonne of dust per hour, the various streams of material have approximately the following hourly flow rates:

Leaving aside the small losses of reagents, which inevitably occur in each process operated in a closed circuit, in this case in particular by entrainment with residue 20 and with precipitate 31, the only "reagent", which is consumed in the mode of realization that we have just described, is water, and this at the rate of 0.111 πWtonne of dust / hour.

It might however be advisable to practice a bleeding, for example a bleeding of 2 to 10%, on stream 32, in particular when the dust 10 contains chloride and it is not possible to remove all of this chloride by washing dust or for some reason it is preferred not to wash the dust beforehand. In this case, there would obviously be a consumption of reagents, but this would still be low.

It is obvious that zinciferous dust of any origin can be treated by the process of the present invention, when their composition is analogous to that of the dust produced in the manufacture of steel.

A variant of the process of the invention consists in replacing the zinciferous dust with zinciferous cement containing nickel and / or cobalt, by-product of the purification of zinc sulphate solutions in the manufacture of zinc by electrolytic means. A nickel and / or cobalt residue is then produced in step (a) and a zinc concentrate in step (c).

Claims

1. Process for the hydrometallurgical conversion of zinciferous dust, generated in the manufacture of steel and containing Fe, Ca, Zn and at least one of the elements Pb, Cu and Cd, into an iron residue leaner in non-metals - ferrous as dust and as a zinc concentrate for further processing in a hydrometallurgical zinc plant, comprising the following steps (a) treating the dust with a leaching solution so as to dissolve a substantial part of the Zn and of the Pb, Cu and Cd, if present, and to leave at least the major part of the iron undissolved, thereby producing a zinciferous solution containing Pb, Cu and / or Cd and said iron residue, (b) the zinciferous solution is separated from the iron residue, (c) the Zn is precipitated together with the Pb, Cu and Cd, if present, in the form of compounds in the zinciferous solution, thereby producing a lozenge solution and said zinc concentrate, (d) separating your lozenge solution from the zinc concentrate, (e) the leaching solution is regenerated from the unzipped solution, and (f) the leaching solution produced in step (e) is reused in step (a), this process being characterized in that in step (a) an alkaline detergent is used as the leaching solution , thereby producing an alkaline zinc-containing solution which is substantially free of calcium iron, which precipitates the zinc concentrate in step (c) by neutralizing the alkaline zinc-containing solution with an acid, thereby producing a solution of salt as a dezingue solution, which the alkaline lye is regenerated in step (e) by subjecting the salt solution to an electrodialysis with bipolar membranes and concentrating the alkaline lye produced in this operation, by which the l acid consumed in step (c), and which is reused in step (c) the acid regenerated in step (e). 2. Method according to ia claim 1, characterized in that a solution of NaOH or KOH is used as leaching solution. 3. Method seion claim 1 or 2, characterized in that neutralizes the alkaline zinc solution with a solution of sutfuric acid. 4. Method according to claim 1 or 2, characterized in that neutralizes the alkaline zinciferous solution by insufflation of C0 ₂ gas, thereby producing a carbonate solution as a salt solution. 5. Method according to claim 4, characterized in that the caibonate solution is transformed into a sulfate, chloride or nitrate solution, that this solution is electrodialysis in step (e) and that r acid thus regenerated for the transformation of carbonate solution. 6. Variant of the method according to any one of claims 1-5, characterized in that the zinciferous dust is substituted for zinciferous cement containing nickel and / or cobalt, thereby producing a residue of nickel and / or of cobalt in step (a) and a zinc concentrate in step (c).