DE2620655A1 - PROCEDURE FOR THE REMOVAL OF CONTAMINATION FROM ZINC SULPHATE AND / OR CADMIUM SULPHATE SOLUTIONS - Google Patents

Description

"Process for removing contaminants from zinc sulphate and / or Cadmium Sulphate Solutions "The invention relates to a method for removing contaminants from zinc sulphate and / or cadmium sulphate solutions, in particular a method of removal of chlorine, manganese, cobalt, nickel and thallium from for the production Sulphate solutions determined by electrolyte zinc or electrolyte cadmium.

To remove the chlorine is known, such solutions with a To treat silver salt, whereby the forming silver chloride precipitate through Filtering is removed. The price of the silver salts and that of this treatment inevitable loss of part of the same result in a little economic Procedure.

In order to remove the manganese, it is known that that is present in the solution Zinc to fall with the help of a base like Ca (OH) 2, with the manganese in the solution remains, and that of a mixture of calcium sulfate and basic zinc sulfate existing precipitate to dissolve again in sulfuric acid.

This process is cumbersome and entails high investment and operating costs.

Aside from that. May usually be the rank of a zinc sulfate or Cadmium sulfate solution do not exceed one tenth of the zinc content; with a zinc content of, for example 150 g / l, this limit corresponds to a Mlangan content of 15 g / l, and removal a kg of manganese consequently results in the precipitation of 10 kg of zinc.

It is known to remove the cobalt and nickel in the solutions Enter zinc dust. This process is also costly because it is a very large one Excess zinc dust and further catalysts used and the solutions need to be heated to around 90 ° C. On the other hand, this procedure is at Solutions with cobalt and nickel contents above 50 mg / l cannot be used. Also included the cobalt-zinc and nickel-zinc complexes formed also cadmium, and its Redissolution is with a partial dissolution of the cobalt and nickel and which is returned to the circulation after the cadmium has been removed Solution causes an undesirable increase in the cobalt and nickel contents. To complete Removal of these two elements is not an enormously large excess regenerable zinc dust required.

The thallium can be obtained by adding sodium chromate in the form of Thallium chromate will be precipitated; however, this treatment leads to an undesirable one Enrichment of the solutions in sodium ions.

Another known method is to use a zinc sulfate or Treat cadmium sulfate solution with potassium permanganate; through this treatment you can the elements Mn, Co, Ni, Tl and Cl are removed, but it has the disadvantage Potassium ions in to bring the solution, and a lack of selectivity to bring all of the elements mentioned to precipitate at the same time; in some cases however, it is desirable to retain a certain residual level of manganese, which serves to do this during the lead electrolysis by forming a MnO2 layer on the lead anodes to extend their service life.

The present invention, through which the described disadvantages of known methods are overcome relates to a method for removing Impurities from zinc sulphate and Kadmiuz.-sulphate solutions, which is characterized by this is, dap the solution to be cleaned with a peroxysulfuric acid and preferably mj.t Peroxymonosulphuric acid, the so-called Caro's acid, is treated, whereby selective removal of the elements Cl, Mn, Tl, Co and Ni is made possible.

In the following description, the term persulphuric acid refers to generally refer to peroxydisulfuric acid H2S308, whose, among other things, by hydrolysis formed, derivatives and the corresponding salts, which separately or in mixtures can be used; among other things, apart from peroxydisulfuric acid, their salts such as Na2S2O8, K2S2O8, (NH4) 2S208; peroxymonosulphuric acid or Caro's acid H2SO5, its salts such as Na2SO5, K2S05, (NH4) 2SO5, as well as hydrogen peroxide H2O2 and mixtures of these compounds.

The peroxydisulfuric acid H2S208 is known to be formed by anodic oxidation of sulfuric acid on platinum anodes under high current density and decomposes by progressive hydrolysis according to the following scheme: As a result, peroxydisulfuric acid is practically pure and usually consists of a mixture of the three compounds H2S20a, H2S05 and H202, in which the contents of H2S05 and H202 depend on the duration of the hydrolysis.

In a hydrolysis of peroxydisulfuric acid at 220C were dependent the hydrolysis time the concentrations listed in table 1 (in mol / l) measured: TABLE 1 hydrolysis content of content of content of permanent H2S2O8 H2SO5 H2O2 (in hours) 0 1.45 0.00 0.00 0.17 1.27 0.1 0.00 0.5 1.10 0.35 0.00 1 0.96 0.51 0.00 1.5 0.81 0.71 0.00 2 0.64 0.87 0.010 3 0.37 1.07 0.015 5 0.15 1.30 0.030 6 0.095 1.35 0.040 7 0.05 1.37 0.050 10 0.015 1.39 0.080 25 0.00 1.23 0.20 A Another method for producing Caro's acid is to add oleum to react at low temperature with hydrogen peroxide. By converting oleum (with 25 percent by weight SO3) with 70 percent by weight H2O2 in a molar ratio S03 / H202 between 1.8: 1 and 2: 1, a mixture of the following is obtained, for example Composition (in percent by weight): H2SO5 43% H2S2O8 1.6% H2O2 1% H2SO4 44% 1120 Residual salary.

This method therefore also gives one of the three connections Mixture containing H2SO5, H2S2O8 and H2O2, in this case Caro's Acid is the main component alongside sulfuric acid.

Treatment of a zinc sulfate or cadmium sulfate solution which contains chlorine, manganese, nickel, cobalt and thallium ions as impurities, with such a mixture containing H2S208, H2SO5 and H2O2 leads to a Oxidation of these elements in a form in which they can be easily removed.

The chlorine compounds undergo one of the following oxidation reactions: both of which lead to the formation of gaseous chlorine, which can easily be eliminated from the solution by blowing in air.

The remaining elements are converted into one by the peroxydisulfuric acid insoluble form oxidizes as shown in the following table: TABLE 2 Before which after oxidation by treatment 1125208 in solution precipitated as Mn ++ Mn4 + Mn (OH) 4 Ni ++ Ni3 + Ni2O3 Co ++ Co3 + Co (OH) 3 Tl + Tl3 + Tl (OH) 3 It was found that the chlorine selectively from acidic, in the extraction of electrolyte zinc or electrolyte cadmium solutions obtained can be removed by treatment with a persulfuric acid can if the manganese (IV) salts contained in these solutions before this treatment be reduced in manganese (II) salts.

The method according to the invention therefore provides such Solutions before adding the persulfuric acid with a reducing agent, for example an Fe (II) salt and preferably with ferrous sulfate until it is completely discolored to treat; the amount of reducing agent to be used is in the Usually 100 to 200 mg / l.

@@ Mentioned above, a partially hydrolyzed one is preferred Peroxydisulfuric acid used for the treatment according to the invention; have performed the tests show that a hydrolysis of 10 to 14 hours at 200C to optimal levels leads to CarQ acid.

The stoichiometric amount of mentioned in the following examples Persulfuric acid understands the sum of the in the form of H2S208, 112505 and H202 as Oxidizing agents added compounds and corresponds to the theoretically necessary Amount to convert the chlorine into gaseous Cl2 and the other existing elements Mn, To convert Ni, Co and Tl into the oxidation stages indicated in Table 2.

EXAMPLE 1 A sulfuric acid obtained in an electrolytic cell Zinc sulphate solution with the following composition: Zn 50 gil H2SO4 170 g / l Cl 495 mg / l is treated with 145 mg / l ferrous sulfate, and the complete transition of the manganese (IV) - in manganese (II) salts is confirmed by the discoloration of the solution.

The solution is then added all at once, heated to 400C stoichiometric amount of persulphuric acid, which leads to the release of chlorine in gaseous form Shape is needed. The released chlorine gas is made up by blowing in air the solution removed.

The amount of chlorine removed and the residual content of the solution depend on chlorine from @ the duration of treatment.

The solution treated according to the present example with an initial chlorine content of 495 mg / l has the following residual chlorine levels depending on the duration of treatment: after 1 hour: 300 mg / l "2 hours: 240 mg / l" 3 ": 210 mg / l" 4 ": 175 mg / l 5 5 ": 170 mg / l; as a result, 66Só of the total chlorine content are eliminated after 5 hours.

Comparative experiment If, on the other hand, a solution of the above composition treated with persulphuric acid without first reducing the manganese (IV) salts, the elimination of chlorine proceeds as follows: Duration of treatment: t hour Residual chlorine content: 375 mg / l: 2 hours 372 mg / l 3 1E 370 mg / l: 4 "364 mg / l: 5" 362 mg / l, that is, that after five hours of treatment only eliminates 27% of the total chlorine content of 495 mg / l have been.

By reducing the manganese (IV) - to manganese (II) salts beforehand the chlorine excretion is more than doubled as a result.

EXAMPLE 2 One obtained in the manufacture of electrolytic zinc Zinc sulphate solution with the following contents: Zn 52 g / l 112504 169 g / l Cl 700 mg / l are added to reduce the manganese (IV) salts 125 mg / l ferrous sulfate; three equal parts of it are then treated as follows: Part 1: in one Sometimes the stoichiometric amount required to remove the chlorine is fresh added prepared H2S208; 228 Part 2: Addition of the same starting amount H2S208, but after hydrolysis for ten hours at 120C; Part 3: encore the same initial amount of H2S208, but after a previous 42-hour hydrolysis at 12 ° C.

Depending on the duration of the treatment, the three differently treated partial solutions the following chlorine levels (starting chlorine level 700 mg / l each): TABLE 3 part 1 Part 2 Part 3 Residual chlorine content after 1 hour: 452 295 400 2 2 hours: 400 238 295 "3": 350 212 275 "4": 312 175 252 "5 I1: 270 165 252 Chlorine excretion after 5 hours of the initial content): 61.43 76.43 64.

A comparison of these results shows that there is a maximum excretion of chlorine is obtained when peroxydisulfuric acid is used, which by corresponding Hydrolysis has a maximum content of Caro's acid.

It was found that a maximum removal of the manganese in the range of pH values 2 to 5> 5 and with a persulfuric acid with the largest possible Caro's acid content is reached, and furthermore, the filtering of the precipitated product, the easier the higher the precipitation temperature.

EXAMPLE 3 A zinc sulphate solution with a zinc content of 140 g / l and a manganese content of 10 g / l becomes one for 12 hours in the course of 30 minutes Addition of persulphuric acid solution hydrolyzed at 150C with the following contents: H2SO5: 175 g / l; H2S2O8: 1.5 gil; HO .; + 1.5 g / l, with the temperature at 500C and the pH is kept at 4.5 by adding ZnO.

After all the persulphuric acid solution has been added, the nangan content is reached reduced to 0.5 g / l; after a further 3 hours of treatment, the manganese content is only 0.38 g / l. As a result, the nangan excretion amounts to over 96% of the Starting salary.

Comparative experiment A Oxidized under the conditions just described the manganese contained in an identical zinc sulfate solution in Mn4 + by adding a freshly prepared persulfuric acid solution with the following contents: H2S2O8 : 307.5 g / l H2S05: 26.5 g / l H2O2: O After the addition is complete, the manganese content is another 8 g / l and during the following 3 hours the same oscillates, depending on the Sampling precision, between 7.8 and 8.2 gll; the manganese excretion is thus limited to 18 to 22% of the starting salary.

Comparative experiment B The persulfuric acid solution for the oxidation of the Manganese in an identical zinc sulphate solution under the conditions described is hydrolyzed for 5 days at 20-22 ° C. At the time of its use it has the following contents: H2S05: 60 gil H2S20E: 0.1 gil H2O2: 28.3 gil.

After the addition, within 30 minutes, the.

Nangan content (starting content: 10 g / l) still 8.7 g / l, and after more 3 hours it has increased again to 9.6 g / l.

The manganese excretion is under 5% des under these conditions Starting salary.

The results obtained in these 3 experiments prove that it is beneficial is, a persulphuric acid solution with a maximum content of Caro's acid and to use a minimum content of hydrogen peroxide; if the H202 concentration is too high some of the precipitated manganese (IV) hydroxide goes into solution again.

EXAMPLE 4 Experiment A of a sulfuric acid zinc sulfate solution with the following Content: Zn 140 g / l; Mn 10 g / l, Co 13.9 mg / l; Ni S, 5 mg / l; Cl 909 mg / l, is used for Oxidation of Mn ++ in Mn4 + within 30 minutes the stoichiometric narrow one hydrolyzed persulphuric acid solution with the following contents: H2SO5: 290 g / l; 112S208 and H2O2: 1.5 gll, the pH value being kept at 4.5 by adding ZnO will.

After the addition of the hydrolyzed persulphuric acid solution is the manganese content 0.315 g / l; with prolonged treatment it can be up to 0.16 g / l are pressed, resulting in a manganese excretion of more than 9850 of the initial content is equivalent to.

The residual contents found for the other elements are: CO: 5.75 mg / l; Ni: 3.55 mg / l and Cl: 750 mg / l.

Experiment B If experiment A is repeated under identical conditions is, with the exception of the pH, which is kept at 3 with the help of ZnO the manganese excretion 90.5% of the initial content.

Residual content after the addition of persulfuric acid is complete: 0.95 g / l; after a further three hours of contact: 0.94 g / l residual content of the other elements: Co 4.25 mg / l Ni 2.80 mg / l Cl 785 mg / l.

Experiment C If, under the conditions given above, the pH is kept at 1.5 by adding ZnO, the following results are obtained: residual manganese content after addition of persulfuric acid: 2.7 g / l = manganese excretion of 73% (also remains unchanged after three hours of treatment); Co - residual content: 2 mg / l Ni - residual content : 2.3 mg / l Cl - residual content: 720 mg / l.

The comparison of the results obtained in experiments A, B and C. proves that manganese precipitation is favored by a higher pH value, and that the precipitation of cobalt and nickel has little influence on the precipitation pH, however, it is slightly improved at higher acidity.

EXAMPLE 5 For the oxidation of manganese, cobalt, nickel and thallium ions, As indicated in Table 2, a cadmium sulfate solution with the following contents: Cd : 170 g / l; Mn: 4.9 g / l; Co: 82.5 mg / L; Ni: 755 mg / l; Tl: 2.3 g / l; Cl: 178 mg / l, after heating them to 50 ° C and maintaining a pH value between 4 and 4.5 by adding calcium carbonate, all at once the stoichiometric Amount of a persulphuric acid solution hydrolyzed for 12 hours at 200C was added.

One hour after the addition of the hydrolyzed persulfuric acid solution the following residual contents and the following excretion rates are determined: residual content Elimination (% of the initial content) Im. 10 mg / l 99.80 Co: 15 mg / l 81.22 Mi: 110 mg / l 85.43 Tl: 48 mg / l 97.91 Cl: 150 mg / l 15.73.

These results prove that the process according to the invention There is a possibility of zinc sulphate and cadmium sulphate solutions, which are produced by the elements Mn, Co, Ni and Tl are contaminated, these contaminants are advantageously used and way to remove together.

- patent claims -

Claims (7)

P A T E N T A N S P R U C H E 1. Process for removing impurities of zinc sulphate and cadmium sulphate solutions, characterized in that the Solution with a hydrolyzed peroxydisulfuric acid and preferably with Caro's Acid is treated. 2. The method according to claim 1, characterized in that the dap for Treatment of the solution to be cleaned related hydrolyzed peroxydisulfuric acid solution mainly Caro's acid 112505 and only minor ones to peroxydisulfuric acid 1125308 and hydrogen peroxide H202. 3. The method according to any one of claims 1 and 2, characterized in that that the persulfuric acid used to treat the solution to be cleaned by Reaction of oleum with hydrogen peroxide is prepared. 4. The method according to any one of claims 2 to 3, characterized in, The treatment with persulfuric acid promotes the removal of the chlorine Reduction of the manganese (IV) in manganese (II) salts precedes which reduction with the help of a reducing agent such as an E: isene (II) salt and preferably ferrous sulfate in a sulfuric acid medium with a sulfuric acid content of over 10 g / l he follows. 5. The method according to any one of claims 1 to 3, characterized in, dap the excretion of manganese by adding persulfuric acid at a pH value takes place between 2 and 5.5. 6. The method according to any one of claims 1 to 3, characterized in that that the precipitation of cobalt, nickel and thallium by adding Persulphuric acid in a sulfuric acid medium with a residual sulfuric acid content of 15 g / l and a pH value below> takes place. 7. The method according to any one of claims 1 to 6, characterized in that that the persulfuric acid is a peroxydisulfuric acid hydrolyzed at 20 ° C. for 10 to 14 hours is used.