DE2406394C3 - Hydrometallurgical process for the extraction of zinc, copper and cadmium from their ferrites - Google Patents

Description

is acid washed (Norwegian patent 123 248). The thickened jarosite sludge is used in sulfuric acid or electrolytic reverse acid added as appropriate; the dissolution;, relationships become chosen so that they correspond to those of the ferrite dissolution level. This leads to the dissolution of the Most of the ferrites contained in the sludge, while the jarosite remains undissolved.

The jarosite process can thus include four additional stages in addition to the neutral dissolution: Dissolution of the Ferrites, neutralizing the excess acid. Precipitation of iron as jarosite and acid washing of the precipitated jarosite sludge. Each of these stages requires its own control and monitoring system as well as a considerable number of reactors and Thickener (Fig. 1).

It is also possible to use iron in an autoclave without neutralization either at a higher temperature (180 to 220 C) than a mixture of hematite and hydronium jarosite or in the presence of NH ₄ N Na ⁺ and K ⁺ ions at a slightly lower temperature (140 up to 180 C) as ammonium, sodium and potassium jarosite (USA, patent 3493 365: Canadian patent 7 87 853).

In both processes outlined above, the ferrites are dissolved and the iron is precipitated separate stages. In the first process in its most general form - the precipitation stage includes a pretreatment (pre-neutralization) and a post-treatment stage (acid washing). In the latter process, the iron is precipitated in an autoclave, which is much more difficult than that in terms of process and system technology Working under atmospheric conditions.

The present invention now offers the possibility - even under atmospheric conditions
to achieve the same result in a single step as in the processes outlined above in all the steps following the neutral resolution together (e.g. in the atmospheric process, Fig. 1, steps 2 to 5), ie almost ferrite-free iron sludge (iron precipitate ) to achieve.

The invention results in a simple, reliable process, which is also over the previous Process gets by with much less complex systems.

In the following the invention is described in detail with reference to the accompanying drawings. In the drawings, F i g. 1 shows the flow diagram of the known jarosite process, FIG. 2 shows, as an example, the solubility of an ammonium jarosite at 95 ° C. as a function of the H ₂ SO ₄ concentration, and FIGS. 3 and 4 show the flow diagrams of preferred embodiments of the invention.

Before actually describing the method according to the invention, however, there are some considerations On the one hand, the dissolution rate of the ferrites and the precipitation rate of the jarosile and the other basic iron salts to employ other influencing factors.

The dissolution rate of ferrites satisfies the following equation:

or written in integrated form

1 - Il - .ν) ¹ - ¹ = Ki. (2)

whereby

K = ykS _u .

The change in the specific surface area during the dissolution process takes place according to the formula

d.v

d /

= kS "( 1 - .ν) ² '· ¹

In equations (1-4):

.v = degree (advanced) of resolution,
S ₀ = original specific surface area in ² / g)

the ferrites.
S _A. = specific surface area for the values of the

Degree of solution x (irr / g),
ί = solution time (min),
K = dependent on the specific surface

Solution constant (min " ¹ ),
k = dissolution rate constant independent of the specific surface area

(g x min " ¹ x m" ² ).

The values of the reaction rate conslants k are in the order of magnitude of 3 -6 · 10 " ^-1 g · min"'· m " ² .

The rate of dissolution of zinc ferrites is primarily a function of the specific surface area, the temperature and the sulfuric acid concentration. The rate of dissolution is strongly influenced by changes in the specific surface area. However, this cannot generally be changed by regulating the roasting ratios, but can be viewed as a characteristic variable of the respective roasted material, which comes from the structure of the concentrate. The temperature also has a considerable influence on the rate of the reaction. It is essential to operate in the temperature range from 70 to 100 ^° C., or better still in the range from 90 to 100 ° C., when dissolving. With regard to the influence of the sulfuric acid concentration, it can be stated that the rate of dissolution is at least

• in the range from IO to 100 g / l there is an almost linear relationship to the sulfuric acid concentration. If the temperature is in the range from 95 to 100 ° C., the reaction rate constant k has a value that is sufficiently large for the process to be described below even at H ₂ SO _{4 concentrations of less than 30 g / l.}
The rate of iron precipitation is in turn determined by the Fe ³ ^ concentration, the H ₂ SO ₄ content, the NH ₄ ⁺ , Na ⁺ and K n 'ion concentrations and the temperature.

The iron precipitation in the ammonium- and alkali-free system Fe ₂ O, - SO, - H ₂ O is dealt with in the following article: J. Rast as, S. Fuglcberg. TL. Huggare; Treatment of Iron Residues in the Electrolytic Zinc Process: The Metallurgical Society 102nd AIME Annual Meeting in Chicago, Illinois.

If the solution contains alkali or NH ^ ions, the equilibrium shifts in a favorable direction for mixed jarosites (A., H, 0, _ J [Fe ₁ (SO ₄ MOH) ₆ ]), as was explained in the last-named article

is. Parts of the stability range can be found in the literature of the more general system

A ₂ O

Fc ₂ O, -SO, -H ₂ O

(A = NH ₄ , Na or K), but detailed and clear stabilization diagrams are not available to our knowledge.

In Fig. 2 is to explain the invention The solubility line of a mixed jarosite in the system

H ₂ SO ₄ -Fe ₂ (SO ₄ ), - (NH ₄ I ₂ SO ₄ -

^L H ₂ O- (NH ₄ ) _V (H, O), _ JFe ₃ (SO ₄ J ₂ (OH) ₁ J (s), ₅

shown. The curve corresponds to the following situation: pure —— NH ₄ —H ₃ O -jarosite precipitated under procedural conditions was dissolved in dilute sulfuric acid; the system has been given enough time to adjust to equilibrium. If the point corresponding to the composition of the lye lies above (Fig. 2) the curve, this means that the trivalent iron in the lye precipitates as mixed jarosite; the rate of precipitation depends on it, among other things. how much Fe ^{1 +} concentration is above the equilibrium value corresponding to the curve: is.

From Fig. 2 and from what has been said above about the dissolution of ferrites is evident that the point corresponding to the composition of the solution stage lies above the equilibrium line (Festsloff-Stabililätsbereich), the possibility ge give is. at the same time and under atmospheric conditions to dissolve ferrites and to extract iron fall. The present invention, the main features of which emerge from claim I, establishes sicr in principle that the valuable metals contained in the ferrite-containing solids in a single Reaction stage as sulfates in the solution stage and the iron contained in the ferrites in solid basic salt are transferred. The following reaction takes place at this stage:

3MeO · Fe ₂ O ₃ (S) + (7 - x) H ₂ SO ₄ (aq) + vA ₂ SO ₄ (aq) + (2 - 2.v) H, O
^ 2A ₁ H ₃ O ₁ .. _v [Fe ₃ (SO ₄ ) ₂ (OH) ₍ ,] (s) + 3MeSO ₄ (aq)

(Me = Zn, Cu. Cd; A = Na. K. NH ₄ )

In principle, this reaction can be seen as a combination of the one that characterizes the ferrite dissolution reaction

3MeO ■ Fe ₂ O ₃ (S) + 12H ₂ SO ₄ (aq) = ^ 3MeSO ₄ (aq) + 3Fc ₂ (SO ₄ ) ₃ (aq) + 12H ₂ O (6)

and the reaction representing iron precipitation

3Fe ₂ (SO ₄ ) ₃ (aq) + xA ₂ SO ₄ (ag) + (14 - 2.X) H ₂ O = * = 2Α _Λ H, O, _ _v [Fe, (SO ₄ ) ₂ (OHy (s) + (5 + x) H ₂ SO ₄ (aq)

understand, but it is noticeable that in the transformation reaction (5) with a smaller amount of sulfuric acid - and thus with smaller streams of liquor - than with the separate implementation of the Reactions (6) and (7).

If so much ferrous sulphate liquor is fed into the reforming stage. that the reaction (7) released The amount of sulfuric acid is equivalent to the amount of sulfuric acid required for reaction (6), so one obtains

as a total reaction (8) = (~~ p J ■ (6) + (7).

I *

MeO · Fe ₂ O ₃ (S) + ( ₄ -) Fe ₂ (SO ₄ ) ₃ (aq) + .vA ₂ SO ₄ (aq) + (9 - 3.V) H ₂ O
= * = 2A _x H ₃ O ₁ . . [Fe ₃ (SO ₄ I ₂ (OHy (S) + (-J-) MeS0 ₄ (aq)
(Me = Zn, Cu, Cd; A = Na.K, NH ₄ )

In principle, there is the possibility, at all points above the equilibrium line (Fig. 2), to dissolve ferrites and to precipitate iron at the same time. But now there is the speed of the solution the ferrites decrease with decreasing acidity of the solution (lye) and on the other hand the proportion of unprecipitated Iron in the lye increases as the acidity of the lye increases, these are the operating conditions in practice to be chosen so that one works in the optimal acid concentration range, wherein then a maximum by minimizing the costs associated with circulation iron and treatment times Yield of zinc and other valuable metals can be achieved.

In connection with the electrolytic zinc production process, what has been described above can be used Method z. B. apply in the following way:

After the neutral dissolution, the ferrite-containing solid material (thickening, filtering) is deposited and the Um conversion stage supplied. The required sulfur acid - according to reaction 5 - is in the form of back acid and / or concentrated before electrolysis! Sulfuric acid added (the amount of concentrated sulfuric acid is determined by the sulfate balance de; Process determined; Jarosite Process boosts Zinc World Mining. Sept. [1972], 34 to 38). The cheapest Conditions exist when the temperature is close to the lye boiling point and the alkali and / or ammonium content is as high as possible.

(ο

By regulating the acid concentration it becomes On the one hand, the degree of ferrite solution, on the other hand, the ferric iron content remaining in the lye is optimized.

This treatment of the ferrites can either be in the form of a continuous process or in batches respectively. As soon as the valuable metals have dissolved in the desired quantities, will Lye and solids separated from each other The lye is returned to the neutral stage while subjecting the solid to conventional treatment (i.e. washing the solid with water and taken out of the process). Only one if possible gets into the conversion stage scarce amount of lye, provided the ferrite sludge is free of acidic zinc oxide.

This condition can be resolved by a two-stage counter-current neutral of the roasted food. A typical flow diagram in this regard is shown in FIG. 3b shown. With this switching method, the raw lye (solution) of the zinc extraction process is from the first neutral stage supplied, the pH is usually so high that the ferric iron completely precipitated is (pH 3.5 to 5.0). Under these conditions, a certain amount of ZnO always remains undissolved (if also roasted material is used for final neutralization). This excess oxide can be used in a second "neutral" stage are dissolved, in which case the pH value is kept in a range in which the Dissolve oxides, but the ferrites remain undissolved from a practical point of view.

If you provide a somewhat larger reactor volume for the conversion stage and take it a somewhat more extensive iron circulation in purchase, so you can do without the second neutral stage. Such a circuit is shown in FIG. 3 a shown.

The following is a comparison of the method according to the invention - the conversion process with the jarosite process described at the outset are given. The circuit diagram of the latter process is shown in FIG. In F i g. 1 and F i g. 3 shows the approximate calculated solution flows for the jarosite and the conversion process; Calculation basis: 100,000 t Zn year, concentrate with 52% Zn and 10% Fe. The neutral level (pH 4.5) is the same in all three cases (85% of the Zn oxide contained in the roasted material dissolves), as does the addition of strong acid. at The calculation of the reactor capacity was based on the assumption that in both processes the the same yield of valuable metals is achieved. The calculations are based on by the patent applicants experiments carried out. As can be seen from the comparison, you come yourself when working with only one neutral stage (3a) in the conversion process with a smaller reactor volume than in the jarosite process.

The regulation of the conversion process is different from the regulation of the one shown in FIG. 1 The process is significantly easier, because (1) the number of stages is lower, (2) the infeed of the roasted food takes place only at a single point and (3) the regulation takes place with the help of alkalis (solutions). Furthermore, the conversion level is self-regulating for the time being and only requires a relatively "rough" Regulation.

In the jarosite process, there is in principle the possibility of using the Pb and Ag-containing, when dissolving in stronger Separate acid accumulating solution residue and feed processes that the extraction of this Metals serve. In practice, however, it is generally used because of the low Ag content of the concentrate seldom proceeded in this way, but the aforementioned residue is used together with the iron sludge taken out of the process. This is also the case with the conversion process, provided that it accesses the in F i g. 3 is performed. Recommend it But now, because of the high Pb and Ag content of the

ίο Concentration the above solution backlog Door to separate, this is also possible in the conversion process, with the relevant level under Utilization of the reaction (8) z. B. on in F i g. 4 can be switched into the process.

From reaction (8) it can be seen that about 50% of the iron entering the process is interposed via this Level can come without this in any way affecting the conversion level affects.

example 1

The conversion stage was carried out as a batch process. Analysis of the solid containing zinc ferrite resulted in the following values:

Zn 20.8%

Fe 38.0%

NH ₄ 0.26%

Cu 0.47%

Cd 0.19%

Pb 3.5%

1 kg of the above-mentioned solid was added to the conversion stage, and 6.6 l of reverse zinc electrolysis acid was added to this stage. The temperature in the conversion stage was about 95 ° C., and the H ₂ SO ₄ content was kept in the range between 22 and 25 g / l by adding sulfuric acid. After 24 hours, the solid and the alkali (solution) were separated from one another. The washed and dried solid had a weight of 1100 g and the following composition:

Zn 3.6%

Fe 30.5%

NH ₄ 2.3%

Cu 0.08%

Cd 0.02%

Pb 3.2%

The H ₂ SO ₄ , Fe and NH ₄ concentrations of the lye (solution) were found to be 22.0 5.4 and about 5 g / l, respectively.

The zinc yield in the lye was 81% in the conversion stage, the iron yield in the Schlamrr (Rainfall) was 88.5%.

With a zinc and iron content of 60.3 and 12.4% in the roast, this means that 97.9% of the zinc: were transferred from the roast to the lye (solution).

Example 2

The experiment was carried out as in Example 1, but the H ₂ SO ₄ level in the convection stage was now kept in the range between 28 and 33 g / l

609 617/29

The washed and dried solids shed Weight of 945 g and the following composition:

Zn. .
Fc ...
NH ₄ .
Cu. .
Cd ..
Pb ..

2.9 '/ «
31.0%
2.2%
0.06%
0.01%
3.7%

The H ₂ SO ₄ , I ⁷ C and Nl! ,, - concentrations of the alkali (solution) were 33.0, 11.4 and about 5 g / l, respectively.

The zinc yield in the solution was 87%, the iron yield in the sludge was Ti%. The total yield of zinc from the soot into the lye (solution) was 98.6%.

Example 3

The conversion stage took place as. continuous process. The zinc ferrite-containing solid was the same material as in Example 1, which was fed into a three-part series reactor at a rate of 150 g / h. The zinc electrolysis rheumatoid acid was fed in at a rate of 1 l / h. The temperature in the conversion stage was about 95 ° C. and the sulfuric acid supply was regulated so that the H ₂ SO ₄ content at the end of the stage was 35 to 36 g / l. The total residence time was 24 hours. In the individual parts (chambers) of the series reactor, the lye (solution) has the following H ₂ SO ₄ or Fe concentration:

10

H ₂ SO ₄ , g / I about 30 32 34

IV \ g / l 14 15

35 36

I 1

At the low end of the stage, the washed Feslstol had a zinc content of 2.0% and a sugar content of voi 29.9%.

The zinc bulge in the liquor was 91.0% in the conversion stage, the total yield from the Roasted in the liquor amounted to 99.0%. In the conversion stage, 78% of the iron went into the Mud over.

B c i s ρ i e 1 4

The experiment was carried out as described in Example 1, but the H ₂ SO ₄ content in the conversion stage was kept at 65 to 70 g /, and the solid matter was separated from the lye after just 8 hours. The washed and Gelrock Nete solid had a mass of 980 g and the following composition:

Zn

Fe

Cu

CD

Pb

1.3%
6.5%

3.6%

The FI ₂ SO ₄ , Fe and K concentrations of the liquors at the end of the experiment were 69, 10.8 and 2.4 g / l, respectively.

The yield of zinc in the liquor was 93.9% and the yield of iron in the sludge was 81%. Total all in all, 99.3% of the zinc contained in the roasted material went; into the lye (solution).

For this purpose 4 sheets of drawings

Claims (3)

Patent claims: 1. Hydrometallurgical process for the extraction of zinc, copper and cadmium from their Ferrites by treatment with a solution containing sulfuric acid in the presence of potassium, Sodium or ammonium ions at a temperature of 85 to 105 "C, characterized in that that the treatment in a single stage by regulating the sulfuric acid or Ferris sulfate addition equivalent to the compressed or filtered amount of ferrite added to this stage and by further reducing the sulfuric acid content to a value that is sufficient for one Ensuring rapid progress of the reaction is carried out, after which the solid from the alkali is washed separately and thoroughly with water, and the lye as well as the washing water in the Neutral solution stage are fed back, in which part of the acid and the entire amount of roasted material be fed in. 2. The method according to claim 1, characterized in that with a sulfuric acid content of Lye of 15 to 80 g / l is used. 3. The method according to claim 1 or 2, in which the lead, silver and gold-rich zinc roasted material is separated is dissolved in alkali containing sulfuric acid, ferric acid and zinc sulfate, that the zinc oxide and the Ferrites of the roasted goods go into solution almost in their entirety and the lead, silver and gold-containing solid is separated from the lye, characterized in that the ferrisulfate-containing Lye is fed to a treatment cycle corresponding to claim 1 or 2. The present invention relates to a hydrometallurgical process for the extraction of zinc, copper and cadmium from iron compounds of these metals in oxide form. The invention is suitable is particularly suitable for use in connection with the hydrometallurgical extraction of zinc. In the electrolytic zinc production process, the main starting material is roasted material, made of sulphide Zinc concentrate oxidic product produced by roasting, processed in which the zinc is used Mostly as oxide (80 to 90%), to a considerable extent as ferrite (5 to 15%), to some extent also as sulphate (2 to 5%) and in small amounts as unroasted sulphide, silicate and aluminate is included. The Rösigut, the zinc content of which is generally between 50 and 65%, contains up to 12% iron, about 1% lead and silicon oxide and a few tenths of a percent copper, cadmium, manganese, Magnesium, barium and aluminum. In addition, small amounts of silver can be found in the rosy material (H) to KM) ppm) and gold (<I ppm). The iron in the roast is almost exclusively in ferrite form, mainly as zinc ferrite ZnFe ₂ O ₄ . The ferrites are of crucial importance with regard to the further processing of the roasted material. Almost to this day, the roasted food has been selectively dissolved in diluted ingredients Sulfuric acid in the form that the oxides are dissolved while the ferrites are largely undissolved stay This procedure was chosen because it was difficult to collect the large amounts of iron from dissolving the ferrites in an easily filterable Form "to precipitate. The one at this resolution The resulting solution residue is therefore mainly composed of ferrites, reveals but also insoluble sulfates and other insoluble, o compounds, such as. B. Silicates. For the further treatment of this remote solution residue and for the recovery of the contained therein valuable substances, among other things, a hy- " Drometallureic process developed. A closer one Description of this procedure is given in the Norwegian Patent specification 1 08 047 and in the article by G S (a (veil »Die Eisenfallung als Jarosit und their application in the wet metallurgy of zinc ". Erzmetall 23 (1970), 532-539 In the jarosite process, the ferritic solution residue is dissolved in zinc electrolysis return liquor at a sufficiently high temperature (90 to 95 C), whereby the majority of the ferrites are dissolved (PbSO ₄ , CaSO ₄ , BaSO ₄ ), the majority of the silicon (in the form of SiO ₂ ) as well as the gold and silver, can be separated from the lye and fed to processes that facilitate the separation and recovery of the valuable substances it contains ( Pb, Ag, Au) serve. If the Pb, Ag and Au concentrations are low, such a separation is not necessary and the lye, including solids, can be fed directly to the iron precipitation process, as is usually the case today. In connection with the dissolution of the ferrites, a solution is formed, the iron and sulfur contents of which are usually within the limits of 20 to 35 g / l and 40 to 80 g / l, and which is fed to the iron precipitation either directly or after a pre-neutralization. In order to neutralize the excess sulfuric acid released during the precipitation reaction, zinc rosin was added to this iron precipitation stage. In general, efforts were made to keep the pH in the precipitation stage of the jarosite process at 1.2 to 1.4. Since sodium and ammonium salts are also added to this stage, the iron is precipitated in the form of sodium or ammonium _{jarosite (A [Fe 3} (SOJ ₂ (OH) ₆ ]; A = Na, NH ₄ ) Properties of the ferric ion, in the presence of NH ₄ ⁺ , Na ⁺ and K ⁺ ions under atmospheric conditions in acidic solutions, form poorly soluble basic sulfates (JG Fairchild, Amer. Min. 18 [1933] 543 to 547; GP Br ο ph y, ES Scott, R. A Snellgrove, Amer. Min. 47 [1962], 112 to 126 NW S ζ is ζ hi η. Zap. Ws. Min. Obszcz. 79 [1950] 94 to 102, NW Sziszhin, HA Krogius PA L w ο wics, Zap. Ws. Min. Obszcz. 87 [1958] 682 to 686; Z. H arada, M. Gο tο, Kobutsugaki Zasshi 1 [1954], 344 to 355, Ref Chem. Abstr. 51 [1957], 143 h). The ferritic component of the roasted material used for the neutralizing egg dissolves in the precipitation stage does not rise, but merges into the iron sludge. For this reason, the jarosite process has not been used a step attached, in which the Jarositschlamtr