FI65093B - FOERFARANDE FOER FRAMSTAELLNING AV EN VATTENHALTIG LOESNING AVINKSULFAT FOER ANVAENDNING SOM RAOMATERIAL I ELEKTROLYTI FSKAMSTAELLNING AV ZINK GENOM LAKNING AV ROSTAT MATERIAL - Google Patents

Description

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Patents · and Register Holders .... ........ ...___. _ * (44) Date of publication of the publication. -

Patent · och registrstyrelsen 7 AmMu uttajd oeh uti. * Krift * n publkund 30.ll.d3 (32) (33) (31) Pyri · »/ * Tuoik # ut — B * (ird prtorim 16.05.77

Netherlands i-Holland (NL) 7705371 * (71) Kempensche Zinkmaatschappij "Zincs de la Campine" BV, Hoofdstraat 1, Budel, The Netherlands i-Holland (NL) (72) Christian Xavier Dor, Budel, The Netherlands (NL) ( 7 ^) Oy Kolster Ah (5 ^) Method for preparing an aqueous solution of zinc sulphate for use as a raw material in the electrolytic production of zinc, by extraction of roasted material - av rostat material

The invention relates to a process for preparing an aqueous zinc sulphate solution for use as a feedstock in an electrolytic zinc production process, by extracting a material obtained by roasting zinc sulphide ore concentrate, the process comprising neutral extraction with a then the solid and liquid are separated and the zinc sulphate solution is recovered as a product stream by removing the liquid stream from the solid and liquid separation process after neutral extraction. The process is characterized in that the solid stream from the neutral extraction is passed to jarosite precipitation, the solids stream from jarosite precipitation is passed to the hot acid extraction step, the liquid stream from jarosite precipitation is returned to the 2,65093 neutral extraction step, and the hot acid extraction step is returned to the neutral extraction step.

Of the naturally occurring zinc ores, sulfide ores (zinc fluxes) today form the main source of raw materials for zinc metallurgy. In almost all cases, the zinc content of the ores is too direct for processing. They are therefore first removed by foaming most of the unusable side rock to obtain an ore concentrate. While the zinc content of the ore may be, for example, 4-9% by weight, the zinc content of the concentrate is generally between 48-62% by weight.

The next step in the production of zinc is the roasting of the ore concentrate with oxygen (air) during which the following main reaction takes place: 2ZnS + 302-> 2ZnO + 2SO2 · The zinc content of the product of this step, i.e. the "roasted product", is generally between 55-73% by weight.

The roasted material for the electrolytic production of zinc is treated with sulfuric acid to dissolve the zinc oxide:

ZnO + HoS0 .-> ZnSO. + H_0.

2 4 4 2 This is known as "firing" the roasted substance. The resulting aqueous solution of zinc sulfate is electrolyzed in electrolysis cells: 2ZnSO. + 2H-0-> 2Zn + 2 H ~ SO. + 0 ".

4 2 2 4 2

Zinc precipitates on the cathode and can be removed from it. As can be seen from the reaction equation, sulfuric acid is also formed during electrolysis. This acid is in the liquid that is drained away from the electrolysis cells at the end of the electrolysis. The acid content and its origin in electrolytic cells explain the term "battery acid", as this liquid is commonly said.

The electrolysis is generally started from a neutral zinc sulphate solution containing about 120-120 g zinc / l. "Battery acid" generally contains about 100-300 g t 1 SO 2 / l and 30-70 g zinc / l. Thus, not all of the zinc precipitates out of solution during electrolysis.

3,65093

Since the roasted material does not consist of ZnOr alone, the process is not as simple in practice as described above. The compounds contained in the roasted substance can be classified into the following groups.

1) Zinc compounds that are readily soluble in sulfuric acid. These primarily include ZnO. In addition, the roasted material may already contain some ZnSO 4.

2) Zinc compounds that are less readily soluble in sulfuric acid, i.e., that are soluble only in fairly old sulfuric acid at elevated temperatures. The main compound of this type is zinc ferrite, which can be represented by the formula ZnO.Fe 2 O 2 · Virtually all the iron in the ore concentrate is converted to zinc ferrite by conventional roasting methods.

3) Compounds insoluble in sulfuric acid. There are quite a lot of compounds of this type, such as PbSO 4, AgCl, SiO 2 and

CaSO ..

4 4) Compounds (not zinc) that are soluble in sulfuric acid. These include compounds of numerous elements such as Co, Cu, Cd, Sb, As, Mg and Mn.

During the extraction treatment, the compounds mentioned in (1), (3) and (4) cause minor problems.

The compounds referred to in (1) are readily soluble.

The compounds referred to in (3) are insoluble and are removed as "extraction waste".

The compounds referred to in (4) are soluble and in solution in zinc sulphate. Compounds of certain elements (Mg, Mn) have little if any detrimental effect on electrolysis, while compounds of other elements (Co, Cu, Cd, Sb, As) are highly interfering. For this reason, in practice, a purification step between extraction and electrolysis is always used to remove interfering element compounds from the zinc sulphate solution. This known purification step does not need to be discussed here, as the invention relates to carrying out the extraction. In addition, the compounds referred to in (4) are of negligible significance.

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Problems in extraction arise from the compounds referred to in (2). If the extraction is carried out under relatively mild conditions in which the zinc oxide is soluble while the zinc ferrite is insoluble, the solid remaining after extraction ("extraction residue") still contains zinc, so that the "extraction efficiency" (i.e. the zinc present in the calcined substance and If the extraction is carried out under more severe conditions so that both zinc oxide and zinc ferrite are soluble, the latter

ZnO.Fe ^ O-, + 4 H „SO0-- ZnSO. + Feo (SO0, + Ho0 23 24 4 243 2, a solution is obtained which contains a relatively large amount of iron in addition to zinc. However, the zinc sulphate solution from which zinc must be prepared electrolytically should contain only a small amount of iron.

In the past, it was common to perform extraction under conditions in which the dissolution of zinc ferrite was reduced. This is achieved by extraction at low acidity (pH about 4 or higher).

This extraction is known as "neutral extraction". The acid used is usually "battery acid". If this acid is neutralized with zinc oxide, the resulting zinc sulfate solution automatically has the desired zinc sulfate content for electrolysis. At this low acidity, a small portion of the iron, which is nevertheless dissolved, precipitates as hydroxide. For this purpose, however, it is important that the iron be in the ferric form and not in the Ferro form. For this reason, some oxidant (usually air, sometimes manganese or even potassium permanganate) is usually added.

Neutral extraction is generally carried out at room temperature or at a slightly elevated temperature (usually not higher than about 60-70 ° C), in which respect it should be noted that raising the temperature can sometimes be advantageous for iron precipitation.

Neutral extraction can be carried out either batchwise or continuously and in one or more stages, in the latter case optionally according to the countercurrent principle.

Neutral extraction (and in the case of a multi-step process, optionally after each step) is followed by a solid-liquid separation, which can be carried out according to any desired method, but which in practice is most often carried out by one or more "thickening devices". The latter are vessels in which the solid / liquid mixture is placed and then the solid is allowed to settle. The top end of the thickener is drained of liquid. At the bottom of the thickener, the solid slurry in the liquid is removed downstream. Removing the sludge means that the solid / liquid separation is not complete. However, this has the practical advantage that the sludge can still be transported and pumped as a liquid. Of course, after use of the thickener, the separation can be further completed, for example by filtering or centrifuging the slurry. This is especially done when one component of the sludge is unusable (this unusable component may consist of, for example, solids that can be removed as a waste product), while the other component is valuable (such a valuable component is, for example, a liquid that is still usable and recyclable). in the process).

The liquid obtained in the solid / liquid separation is the desired aqueous zinc sulfate solution. The solids form a neutral extraction waste.

This extraction waste contains the insoluble compounds referred to in (3), insoluble zinc ferrite and some zinc oxide, because during neutral extraction it is always almost impossible to dissolve the zinc oxide quantitatively from the roasting feed. In addition, the extraction residue may contain some iron hydroxide precipitated during neutral extraction.

Previously, the neutral extraction treatment terminated the extraction process and the extraction residue was discarded.

Although it would be possible, as explained above, to dissolve the zinc ferrite by extraction under more stringent conditions, this would at the same time cause a fairly large amount of iron to dissolve.

If this iron is precipitated as FetOH in the above-mentioned manner, a large amount of bulky precipitate is obtained, the separation of which from the liquid encounters practically insurmountable difficulties.

However, methods were later invented for the selective precipitation of iron from solutions, in addition to zinc, which contain quite large amounts of iron in the form of a precipitate which can be easily separated from the liquid. One of these methods is the selective precipitation of iron as jarosite. This "jarosite method" is described in the article "Die Eisenfällung als Jarosit und Ihre Anwendung in der 6 65093

Nassmetallurgie des Zinks "(precipitation of iron as jarosite and its use in zinc liquid metallurgy) by G. Steintveit in" Erzmetall "23 (1970), pages 532-539. However, it is now possible to treat the neutral extraction residue with both concentrated sulfuric acid and zinc ferrite The zinc oxide and iron hydroxide present are then treated with an excess of fairly concentrated sulfuric acid at an elevated temperature (usually at 80-110 ° C, preferably at about 95 ° C) and the concentration of this sulfuric acid should be about 180-250. g H2SC> 4/1, but in practice it has been found that it is sufficient to use sulfuric acid with a concentration of about 130 to 250 g H2SO4 / 1, for which purpose "battery acid" may be used, if desired, supplemented with fresh concentrated sulfuric acid. the liquid should still be quite strongly acidic, according to the above-mentioned literature about 80-120 g H2SO4 / 1 should still be present, but in practice it has been found that about 40-120 g H2SO4 / 1 is sufficient. This treatment is known as "hot acid extraction", a term that is explained by high temperature and high acidity. As with neutral extraction, hot acid extraction can be performed either batchwise or continuously and in one or more stages.

Hot acid extraction is followed by solid / liquid separation as well as neutral extraction. Solids can be removed as extraction waste. The liquid contains dissolved sulphates of zinc and iron and an unused excess of sulfuric acid.

The liquid is now subjected to "jarosite precipitation". wherein the iron is selectively precipitated as jarosite at an elevated temperature (approximately the same temperature as in the hot acid extraction). Jaroite has the formula X2 / Feg (SO4) 4 (OH) .2, where X is an ammonium or alkali metal ion. It immediately follows that ammonium or alkali metal ions should generally be added during jarosite precipitation, for example in the form of a salt or base. In the case where ammonium ions are added in the form of ammonia, the reaction equation can be written as follows: 3Fe2 (SO4) 3 + 2 NH4OH + 10 H2O-> (ΝΙφ 2 / Feg (SO4) 4 (OH) 1 2 5 H2SC> 4

In order not to contaminate the liquid unnecessarily, no more ammonium or 7,65093 alkali metal ions are added than are required to form jarosite. It is possible to use less than an equivalent amount. Some of the iron then precipitates (H, 0) _ / Fe - (SO.). (OH). "7: na.

6 Z o 4 4 U

In this case, however, precipitation occurs more slowly.

The given reaction equation shows that sulfuric acid is formed during the reaction. In addition, the liquid contains an excess of sulfuric acid which was not consumed during the hot acid extraction. This total amount of sulfuric acid is too high for good jarosite precipitation. In order to precipitate the iron as quickly and completely as jarosite (and therefore to achieve the lowest possible iron content in the remaining liquid, it is generally guaranteed that the precipitation will finally cease at a pH of about 1.0 to 1.5, although it is also possible to work with a slightly higher final acidity, depending on the time available). and / or an acceptable iron content in the residual liquid, however, in all cases it is necessary to add a basic neutralizing agent.A basic zinc compound is used to avoid acid loss.

Pure ZnO would be ideal, but it is too expensive to use a roasted substance in practice.

Optionally, the jarosite precipitation can be divided into two parts, namely “pre-neutralization” and the actual jarosite-precipitation. ”In pre-neutralization, part of the calcined substance required as a neutralizing agent is then added to the liquid so that the pH is already close to the desired value. roasted material and ammonium or alkali metal ions are added.

Jarosite precipitation is followed by a second solid / liquid separation. (If jarosite precipitation is divided into pre-neutralization and the actual jarosite precipitation, it is of course possible that both steps are followed by a solid / liquid separation, whereby the residue of pre-neutralization can be returned to hot acid extraction).

The liquid is an aqueous solution of zinc sulphate, the pH of which indicates that it still contains some acid during jarosite precipitation. This liquid is usually returned to neutral extraction where the acid is neutralized.

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The solid is known as a "jarosite residue". It contains mainly precipitated jarosite. However, it also contains other ingredients derived from the roasted material that was added as a neutralizing agent during jarosite precipitation. Of this roasted material, mainly only zinc oxide has dissolved (though not quantitatively) during jarosite precipitation, whereas the zinc ferrite in the roasted material has remained largely insoluble and the insoluble constituents have, of course, remained insoluble. All these insoluble substances are therefore present in the jarosite residue.

As suggested in Steintveit's above-mentioned article, it is possible to further improve the extraction efficiency by re-treating the jarosite residue with sulfuric acid to dissolve the zinc ferrites. This "jarosite acid wash" is performed under conditions that are somewhat milder than those in hot acid extraction.

After solid / liquid separation, a predominantly zinc-free solid is obtained, which can be discarded, and an acidic liquid containing iron and zinc sulfates. Iron must be removed from this liquid, which, of course, is more easily accomplished by returning the liquid to jarosite precipitation.

In this way, therefore, it is achieved (at least in theory) that no residue which still contains soluble zinc is discarded from the process.

In Fig. 1, the above-mentioned most advanced known method is schematically shown as a continuous process. In this figure, neutral extraction is denoted by I and, for the sake of simplicity, shown as a one-step process. It is fed with fresh roasted material via line 1, sulfuric acid via line 2 and air via line 3. The product of neutral extraction passes along line 4 to thickener II, where it is separated into a zinc sulphate solution and a slurry of solids. The zinc sulphate solution is removed via line 5 as an overflow from the thickener II. The slurry is removed via line 6 downstream of the thickener II and passes to a hot acid extraction labeled III and, for simplicity, shown as a one-step process. It is fed with sulfuric acid due to 7. The product of the hot acid extraction passes in a pipe 8 to a thickening device IV, where it is separated into a liquid and 9,65093 into a slurry of solids. The liquid is removed from the thickener IV via line 9 as an overflow and passes through a jarosite precipitation marked V and, for simplicity, shown as a one-step process. Sludge is removed from the thickener IV downstream via line 10. This slurry passes to a filter VI where it is separated into a precipitate and a liquid. The separated precipitate is subjected to a secondary wash treatment with a filter through water 11, which is then removed via line 12. All the liquid from the filtrate is conveyed in line 13 to jarosite precipitation V. Ammonia is fed to jarosite precipitation via line 14 and roasted material via line 15. The product of the jorosite precipitation passes in line 16 to a thickener VII, where it is separated into a liquid and a solid slurry. The liquid is removed from the thickener VII as an overflow in line 17 and returns to neutral extraction. The slurry is removed from the thickener VII downstream through line 18 and passes to a jarosite acid wash labeled VIII and, for simplicity, shown as a one-step process. Sulfuric acid is fed through line 19. The product of the jarosite acid wash passes in line 20 to a thickener IX, where it is separated into a liquid and a solid slurry. The liquid is removed from the thickener IX upstream through the pipe 21. The slurry is removed downstream of the thickener IX via line 22 and passes to filter X where the slurry is separated into a solid and a liquid. The separated solid is subjected to a secondary wash with a filter which is fed through line 23 and then removed via line 24. All the liquid coming from the filter is connected via line 25 with the liquid from line 21. the combined liquid stream in line 26 returns to jarosite precipitation V.

The sulfuric acid used in practice is mainly "battery acid", but the addition of fresh sulfuric acid (in some other form of tisulphate ions) is necessary to maintain the sulphate balance in the system because sulphate (in the form of jarosite) is continuously removed from the system. This is most effectively done by adding fresh concentrated sulfuric acid to the hot acid extraction.

The present invention is now based on the principle that it is possible to omit the jarosite-acid wash and nevertheless achieve the same extraction efficiency, provided that the entire jarosite residue is returned to the hot acid extraction. The zinc compounds present in the jarosite waste dissolve during the hot acid extraction. The jarosite itself redissolves only in a very small amount, so that almost a larger part of the jarosite can be removed with the residue.

It has been found that no problems occur with the presence of small amounts of metallic impurities.

The method according to the invention is schematically shown as a continuous process in Figures 2 and 3. With regard to the markings in the figures, reference is made to the above description of Figure 1.

The improvement obtained according to the invention (introduction of the neutral extraction residue not into hot acid extraction but into jarosite precipitation) is shown in Figure 2. This improvement is based on the fact that the neutral extraction residue still contains zinc oxide and some FeiOH). · When this material is not transported in hot acid extraction sulfuric acid than in known methods. By transporting these substances to jarosite precipitation, it is necessary to add less roasted substance as a neutralizing agent to jarosite precipitation. As a result of these measures, less liquid circulates in the circuit III-IV-V-VII in Fig. 2 than in the method known in the corresponding circuit, so that in the case of Fig. 2 less equipment is required, and the method becomes more advantageous.

Figure 3 shows the method of Figure 2 in another form. Figure 3 shows more clearly the simplicity of the method.

EXAMPLE

In this example, reference is made to Figure 2 or 3. Neutral extraction (60 ° C, average residence time 2 hours) is fed: via line 1: 22.8 t / h of roasted material (containing 59% by weight of Zn, 11% by weight of Fe and 1.8% by weight of % S04), via line 2: 72.7 m3 / h "battery acid" (contains 159 g H2SC> 4/1, 52 g Zn / l.) And 25 m3 / h zinc-containing waste liquid from different sections of the zinc plant (contains 53.1 g H2SO4 / 1 and 100 g Zn / l) and via line 3: air.

li 3 11 65093

A 200 m / h neutral zinc sulphate solution (containing 139.5 g Zn per liter) is removed upstream of the thickener II via line 5. A slurry comprising 30 m / h of liquid and 12.152 kg / h of solids passes downstream through line 6. This solid contains 29.6% by weight of Zn and 22.55% by weight of Fe.

This slurry passes to jarosite precipitation (95 ° C, average residence time 3.8 hours), to which 200 kg / h of ammonia (in gaseous form) is also fed in line 14 and 7 tonnes / h of roasted material via line 15.

Thickening device VII discharges 3 145 m / h of acidic zinc sulphate solution (containing 110 g of 3+ 2 +

Zn per liter, 6.5 g I / SO 2 / l, 1 g Fe / l and 0.6 g Fe / l). This solution returns to neutral extraction. A slurry of 40 m / h of liquid and 18.270 kg / h of solids passes downstream through pipe 18. This solid contains 13.79% by weight of Zn, 29.20% by weight

Fe and 15.65% by weight SO 2.

This slurry is subjected to hot acid extraction (95 ° C, average residence time 3 hours), to which 83.3 m / h "battery acid" and 1.419 l / h fresh 96% by weight sulfuric acid are also fed via line 7. 87 m ^ / h of liquid (containing 50.8 g H-SO./l, 81.0 g Zn / l, 15.7 g 3+ ^ 4) is removed from the thickener IV via line 9.

Fe / 1). This liquid passes into jarosite precipitation. Slurry is removed from the thickener IV via line 10 downstream, which. 3 comprises 50 m / h of liquid and 11,500 kg / h of solids. This solid contains 1.34% by weight of Zn, 28.24% by weight of Fe and 24.79% by weight of SO2.

This slurry passes to a filter VI, where the separated solid is subjected to a secondary wash by spraying 23 m 2 / h of water fed through line 11. Line 12 removes 11,500 kg / h of solids from the process. This solid is further irrigated with 3 5 m / h of liquid (containing 11.8 g of HSO2./l, 28 g of Zn / 1, 6 g of 3 + λ 4 FEJ / 1).

3

Filter VI gives 68 m / h of a liquid containing 36.5 g of II (SO2 / 1, 57.5 g of Zn / 1, 11.1 g of Fe (+ + / 1). This liquid passes through line 13 to jarosite precipitation.

The extraction efficiency is 98.3%.

Claims (1)

12 65093 A process for preparing an aqueous zinc sulphate solution for use as a feedstock in an electrolytic zinc production process by extracting a material obtained by roasting a liquid zinc sulphide ore concentrate, the process comprising separating the zinc sulphate solution as a product stream by removing the liquid stream from the solid-liquid separation process after neutral extraction from the process, characterized in that the solid stream obtained from neutral extraction is passed from the the fluid flow is returned to the stage precipitation or neutral extraction step. Fertilization for the production of zinc sulphate in the production of zinc sulphate by the production of zinc sulphide malformation, In the case of pure-cut solutions, which can be separated from the product, the colors of the material must be separated from the material and process, känneteck-n at därav, att den frän neutrallakningen erhällna fastämnes-strömmen leds account jarositutfällningen, den frän jarositutfäll -ingen erhällna fastämnesströmmen leds account hetsyralakningssteget, den frän jarositutfällningen erhällna väh hetsyralakningssteget erhällna vätskeströmmen äterförs account jarositutfällningen eller neutrallakningssteget.