DE2632369C2 - Process for the selective separation of cobalt, nickel and cadmium from chlorideic zinc solutions - Google Patents

Description

45

The present invention relates to a method for the selective separation of cobalt, nickel and / or Cadmium and other metals, which are more noble than zinc, by means of sulphidating cementation from chlorideic Zinc solutions.

In general, metals that are more noble than zinc are separated from zinc-containing solutions by cementing these non-ferrous metals with zinc dust. So it is known that the non-ferrous metal ions Ag, Cu, As, Pb, Ni, Co, Cd can be reduced to metal by zinc dust. This cementation is used in the ( Cleaning of the zinc sulfate electrolyte for zinc electrolysis, in which to achieve high current densities Very low concentrations of the metals Cu, As, Ni, Co and Cd are required to succeed applied. Cementation takes place in a first stage with the addition of arsenic trioxide and copper sulphate of copper (up to <0.1 mg / 1), cobalt (up to <0.02 mg / 1), nickel (up to <0.2 mg / 1), arsenic and antimony have recently been used preferentially for cobalt precipitation with zinc dust antimony trioxide (instead of arsenic trioxide) (Mininiagazin,, uni .974 S ^ .6-429, and Mai, 975, S 342-347 U.S. Patent 3,672,868).

The separation of non-ferrous metals, which are more noble than zinc, from chloride-containing zinc solutions by cementation with zinc dust is very difficult because of the tendency to form chlorine complexes of some non-ferrous metals wherein in sulphatic solutions for nickel a high temperature of 90-95 C is required and has the Cadmiumzementation due easier redissolution, especially in chlor.dischen solutions, better at a temperature below 50 ⁰ C deposition conditions. Cobalt, on the other hand, only deposits very incompletely with zinc dust from chloride-containing solutions, even with a large excess, so that a different process is used for the separation of cobalt from chloride-containing zinc flakes. An example of this is the chloride-sulphatic solution that occurs during the processing of pebble burns through chlorinating rusting and leaching, which, in addition to copper and zinc, contains Co, Ni Fe Mn Pb, Cd and other metals as the main components. It is the state of the art to extract the copper from this lye by cementation with scrap iron, to separate the sulfate as sodium sulfate by crystallization and to remove the iron from the solution with lime.

It is also state of the art to use the chloric zinc lye obtained in this way with the aforementioned Β-sliding metals Co, Ni, Cd, Pb and Mn in small amounts of 0.1-2.0 g / l in addition to 40-60 g / l Working up Zn to obtain cobalt, cadmium and zinc. In a first stage, the cobalt is oxidized to Co ³⁺ _{with Cl 2} and a neutralizing agent, e.g. B. Ca (OH) ₂ or Zn (OH) ₂ , as Co (OH), precipitated. It cannot be avoided that the manganese present is also quantitatively precipitated _{as MnO (OH) 3 at the required pH value of ~ 4.} A previous Mn precipitation without substantial cobalt coprecipitation cannot be carried out. In contrast, existing nickel is only partially precipitated with complete cobalt precipitation.After cobalt precipitation, in a second stage, after cooling to <50 ° C, the cadmium is cemented out with a considerable excess of zinc dust.In a third stage, any nickel that may still be present is then removed possible from the chloride zinc solution by cementation at 90-95 ° C with zinc dust.

As an alternative to this third stage, the separation of nickel, an ion exchange process is proposed in DT-AS 21 60 632 in which complete nickel extraction is carried out by preferentially binding the nickel to chelate exchange resins with amino or imino acetic acid groups. The Ki obtained: "j, _c j_c | .j; j" g "contain zinc and, if the honey exchange was carried out before cobalt precipitation, additional cobalt content, so that further process steps are required to separate the metals in the eluate .

This process _for described as state of the art r separation of cobalt, cadmium> snd chloridic nickel from zinc solutions thus has the considerable disadvantage that three process steps are required, whereby in addition, apply heavily contaminated intermediates.

A method for separating non-ferrous metals from one another, which is fundamentally different from zinc dust cementation, is sulphide precipitation. This is based on the different solubility products of the individual sulphides. It is known that from a sulphatic solution with about 19 g / l Co, 10 g / l Zn and 8 g / l Ni with H ₂ S, the zinc is separated as zinc sulphide as the first element without any noticeable co-precipitation of cobalt and nickel can (Erzmetall, Vol. 22, 1969, supplement, pp. 81-86).

On the other hand, it is known that nickel and cobalt, dissolved as chlorides, can be separated from FeCl ₂ -containing solutions by H ₂ S precipitation without significant iron co-precipitation, with the addition of a neutralizing agent such as. B. iron powder (Tr. Kaz. Politekh. 1967, vol. 26, pp. 452-456) or Fe ₂ O ₃ or NHj (DT-OS 22 64 541).

These publications show that cobalt and nickel can be separated from chloride solutions by means of H ₂ S precipitation, but that in the presence of zinc this is not possible without significant co-precipitation of this element or, if there is a high zinc excess, mainly zinc sulfide is precipitated first.

In addition to the two processes already mentioned above for the separation of nickel and cobalt, namely the Cementation with zinc dust and the hydrogen sulfide precipitation, it is state of the art, nickel from To remove cobalt-containing sulphate or chloride solutions, by means of a sulphidizing Cementation. This takes place with the addition of cobalt and / or iron powder or fine-grain substances that contain these metals in a finely divided state, with the simultaneous addition of elemental sulfur vigorous stirring of the suspension for several hours at 90.degree. There are also proportions of cobalt liked, z. B. when using iron powder as the cementing metal, the amount being a function the Co / Ni ratio and their concentrations in the cobalt starting liquor (L'lndustrie Chim. Beige, 20, 1955, pp. 532-536; l'lndustrie Chim. Beige, Suppl. I (1959), pp. 697-703, 813-815 and 816-821; U.S. Patent 2,651,562). From the 2nd publication (p. 814) also shows that in the presence of zinc the removal of nickel from cobalt solutions is made more difficult; at 15 g / l Zn z. B. the precipitation product consists mainly of zinc sulfide with a little nickel and cobalt.

The joint precipitation of nickel, cobalt and copper from sulphatic iron solutions by means of sulphidating Cementation, with the addition of finely divided metallic iron and elemental sulfur, these elements are precipitated as sulfides, the sulfur being treated with an alkali metal sulfide solution is described in U.S. Patent 3,1 03,414.

From the prior art cited above, it can be said in summary that no process is known, in a technically simple manner, cobalt, nickel, optionally also from chloride zinc solutions Cadmium to be separated in one step and at the same time other interfering elements present in the zinc solution, the are more noble than zinc, to be removed at the same time.

The inventive method of sulfiding

Cementation for the selective (compared to zinc) separation of cobalt, nickel, cadmium and possibly Silver, copper, lead and arsenic from chloridic zinc solutions now consist in that one of the solutions finely divided metallic zinc and elemental sulfur powder at elevated temperature adds to the suspension Stirring for a long time and then separating the precipitated metals from the zinc solution. The sulfur can, as is known, also wholly or partially by reactive sulfides, eg. B. ZnS or FeS replaced will.

The cemented metals are formed by the action of elemental sulfur via intermediately formed H ₂ S or of suitable sulfides, e.g. B. ZnS, completely or partially converted into the sulfides.

It is also possible to replace the finely divided zinc with iron powder. The use of iron powder however, it has significant disadvantages. These are: a slow reaction process, use of a higher temperature (above 90 ° C), a higher stoichiometric excess and bringing in an additional Foreign element. In contrast, the use of zinc has the advantage of a rapid reaction process, the use of lower temperatures, preferably between 60 and 80 ° C, and a lower one stoichiometric excess.

It is also advantageous that iron and manganese as accompanying elements in the zinc solution do not interfere, since they do not go into the precipitate. Compared to the previously mentioned oxidizing precipitation of Co (OH) ₃ together with MnO (OH) ₂ , the process according to the invention thus represents a separation of the metals mentioned from manganese To achieve high nickel deposition, with only small amounts of cobalt being cemented, the process according to the invention, ie the addition of sulfur powder, results in a nickel and cobalt precipitation of over 90% even at temperatures of 60-70 ° C with a short reaction time of 20-30 minutes economically justifiable excess zinc dust achieved. The cadmium precipitation reaches values of 70-90% depending on the excess zinc dust.

Another advantage is that other accompanying elements such. B. silver, copper, lead and arsenic, almost quantitatively with being precipitated, since they are even more easily than nickel and cobalt by the mechanism the sulphidating cementation can be deposited. For these metals, the process also provides a highly effective zinc lye cleaning.

In the zinc lye, it appears during the reaction pH of 5.0-5.5. This high pH range favors the cobalt deposition but has through Hydrolysis results in the precipitation of basic zinc salts. However, it is sufficient to slightly re-acidify the Suspension, preferably with HCl, to a pH of 4.0-4.2, to remove the basic zinc salts from the sulphide precipitate to bring it back into solution. In order to avoid that precipitated cadmium is dissolved in the process is known to have to be avoided afterwards exposure to air or a longer residence time.

Through continuous sulphidating cementation in the countercurrent of zinc lye and precipitated sludge the excess Zn + S can be in a two- or; multi-stage cascade with the interposition of Thickening can be achieved that with reduced consumption of precipitants a high output of the metals to be separated is achieved and at the same time in

The basic zinc salts which have precipitated out are dissolved again in the initial stage by the fresh zinc solution will. The precipitants are expediently metered in in the last stage of the cascade.

To explain the process according to the invention, a two-stage countercurrent precipitation is shown in the drawing shown as an example.

The following examples are intended to explain the process according to the invention without restricting it thereto.

example 1

To a zinc solution (in g / l) 40 Zn, 1,2Ni and 1,2Co as chlorides and a pH of 3.6 is zinc powder in a four-fold and flowers of sulfur in threefold stoichiometric excess, based on Ni and Co, at 70 ⁰ C stirred in. The suspension is stirred for 30 minutes while avoiding strong exposure to air, the pH value rises to 5.3. The basic zinc salts, which are formed by hydrolysis in the sulphide precipitate, are then dissolved again by careful acidification with HCl to pH 4 and the precipitate is filtered off. The filtrate contains 46.2 g / l Zn, 0.06 g / l Ni and 0.11 g / l Co, which corresponds to a separation of 95% of the Ni and 92% of the Co. Due to the higher reaction ^{temperature at 90 °} C. and 20% more zinc dust, the Co deposition also increases to 95% and the Ni deposition to 98%.

Example 2

The sulphidating cementation of the accompanying elements Co, Ni and Cd takes place in a zinc chloride solution, which was obtained during the processing of pyrite burns by chlorinating roasting, after Cu by cementation with Fe, Na ₂ SO ₄ by crystallization with the addition of NaCl and iron had been deposited by precipitation with lime. The zinc solution contains in g / l: 38 Zn, 0.7 Mn, 0.79 Co, 0.3Ni, 0.11 Cd and <0.1 Pb and Cu. The pH of the solution is 3.5.

A by-product of a pyrometallurgical zinc extraction process is now added to 10 l of the solution Zinc dust with 45% metallic Zn added; the amount of Zn corresponds to 4.5 times Stoichiometry based on the sum of Co + Ni. The amount of sulfur powder added is threefold Chosen stoichiometry with respect to Co + Ni.

The suspension is stirred well ^{at 70 ° C. for 1 hour}

and then lowered the pH from 5.5 to 4.2 by carefully adding hydrochloric acid to dissolve precipitated basic zinc salts. After separation

^The solution of the precipitated product and the solution are contained in the filtrate (in mg / 1): 27 Co, 20 Ni and 18Cd. The separation of the accompanying metals reaches 91% for Co, 93.5% for Ni and 84% for Cd, while Pb and the remaining Cu are> 3 and <1 mg / 1, respectively. Mn is not in precipitation

ίο included.

Example 3
(Drawing)

ι s With the zinc solution mentioned under Example 2 takes place continuous countercurrent precipitation in a laboratory apparatus with two reaction vessels and two Laboratory thickener with a throughput of 8 l / h. The zinc solution is in the reaction vessel 1 with the Pretreated cement slurry from vessel 2. After separation of solid and solution in the thickener El The solution flows into the reaction vessel 2, where, with the addition of Zn and S powder, the remaining sulfidating Cementation at a residence time of 1/2 hour, one

: s temperature of 75 -8O ⁰ C and a final pH-value is carried out of 5.4. After the solids and the solution have been separated in the thickener E 2 , the overflow contains the purified zinc solution. The thickened sludge is pumped back into vessel 1 for pre-cementation. In vessel 1, excess zinc and excess sulfur react with the more easily cementable accompanying metals Cu, Pb and Ni. The precipitated basic zinc salts are dissolved again by the fresh liquor flowing in; it turns out to be a pH of -4.2 in

; ö of the suspension. When using zinc dust with only 3.5 times and sulfur of only 2.5 times stoichiometry, based on Co and Ni, were -90% of the Co 96% of the Ni and 83% of the Cd separated, while Ph and Cu are precipitated to more than 98%. One Exposure to atmospheric oxygen, which in particular has a negative effect on Cd precipitation, since it is chloridic Solution, which tends to redissolve cadmium at higher temperatures, is avoided. In the felling product In addition to sulfur, it also contains 13% Zn, 8.2% Co, 9.0% Ni, 2.8% Cd and less than 2% Pb and 1% Cu. The ratio of the accompanying elements to Zn is

In the solution
In the precipitation

Co: Zn

0.0076
0.63

Ni: Zn

0.0079 0.69 Cd: Zn

0.0029
0.21

Cu: Zn

<0.0026
0.15

Pb: Zn

<0.0026
0.08

Compared to zinc, the accompanying elements Co, Ni and Cd are deposited in the precipitate enriched with the following factors:

Co around 83, Ni around 87, Cd around 74

For this purpose I HUitl Zciclinunucn

Claims (7)

Patent claims: 1. A process for selective Abu ing of cobalt, nickel and / or cadmium ι a ande ^r en metals more noble than zinc, by sulfidizing cementation of chloridic zinc solutions, characterized in that, in the solutions of metallic zinc and elemental sulfur in finely divided form Increased temperature ι adds, the suspension is stirred for a long time and then separates the precipitated metals from the zinc solution. 2. The method according to claim 1, characterized in that in addition to cobalt, nickel in the zinc solution and / or other metals still present in cadmium, e.g. B. silver, copper, lead and / or arsenic, to be liked. 3. The method according to claims 1 and 3, characterized in that the sulfidizing cementation at temperatures between 50 and 100 ° C, preferably between 60 and 80 ⁰ C, is carried out. 4. Process according to claims 1-3, characterized in that the metallic portion of the Cementing agent zinc-containing intermediates or dusts in which the zinc is at least partially present metallic, used. 5. Process according to claims 1-4, characterized in that instead of sulfur powder fully or partially reactive sulfides, e.g. B. that of zinc and / or iron used. 6. The method according to claims 1-5, characterized in that the reaction in one pH range from 4.0-5.5, preferably from 5.0-5.5, and then with a mineral acid, preferably with HCl, reduced to a pH of 4.0-4.2. 7. The method according to claims 1-6, characterized in that the sulphidating cementation carried out in steps in countercurrent, the precipitation reagents being metered into the last stage and the precipitation product including the excess precipitant continuously in countercurrent with the brings fresh solution into contact. IHIS <002mg / l) with zinc dust at 90-95 ⁰ C. In the! wide stage, the Cadrniumkonzentration at 80 ° C mU zinc dust with the addition of copper sulfate as activator to below 1.0 mg / 1 reduced (for example we in of Metals, Vol. Aug. 18, 1966, pp. 947-956,