DE2342729C2 - Process for the precipitation and separation of arsenic from solutions containing copper - Google Patents

Description

40

The present invention relates to a method for Precipitation and separation of arsenic from arsenic and copper-containing solutions, as they are in processing of mining or metallurgical products are generated by hydrometallurgical methods. The solutions can in addition to copper and arsenic, any amount of other non-ferrous metals and, as anions, chloride or sulfate ions or mixtures of both.

Solutions containing arsenic and copper occur in the course of hydrometallurgical processing in numerous mining or metallurgical processes. For example, the processing of copper-containing, sulphidic flotation concentrates, in particular so-called bulk or medium concentrates, is increasingly being carried out by hydrometallurgical methods. In the case of oxidative pressure leaching or a combination of sulphating roasting with subsequent acid leaching, solutions are produced which, in addition to arsenic and copper, also contain zinc, iron and possibly other metals such as nickel, cobalt and others. Furthermore, for example, the removal of troublesome impurities from aqueous solutions of zinc sulfate, which are to be fed to a zinc electrolysis, is carried out in such a way that the solution is subjected to zinc dust cementation. In this case, arsenic (ASsO ₃ ) is added and a cementate is obtained which, in addition to excess zinc, contains all impurities that are electropositive with respect to zinc, in particular

Cu As Zn Ni Pb Fe 28.6% c «« 0 /
J, JJ / 0 21.8% 0.40% 8.8% 0.56%

In the case of lead smelting, in the course of the copper removal of the work lead, there is also a copper and arsenic-containing intermediate, which is referred to as so-called »copper slip«. Depending on the procedure (either direct separation of the copper or additional stirring in of sulfur) come the Analyzes of the copper slip, for example, as follows:

Cu As Zn Ni Pb Fe S. 30%
respectively.
19.3% 1.5%
1.3% 0.5%
4.90% 0.2%
0.15% 50%
55.7% 0.95%
0.56% 1.5%
7.85%

For the conversion of the last-mentioned product into an acidic, aqueous solution and the recovery of the Copper from this solution, a method has been proposed in DT-OS 2 036 391, which in principle also on similar materials, such as B. the aforementioned cementate sludge from zinc lye cleaning, can be applied. A method to remove arsenic or to reduce the As: Cu ratio is not specified in the mentioned OS. As a result, it is by reducing electrolysis in this process The copper obtained is very impure and has to be subjected to additional refining electrolysis will. Investment capital service and electricity costs must therefore be raised twice, what makes the profitability of this copper production appear doubtful.

A process for separating copper and arsenic by the wet route, which is useful for many purposes, has recently been proposed by Montecatini Edison (DT-OS 2 032 417). According to this process, solutions containing arsenic and copper are ^{mixed with Fe 2+} ions of any origin, with the redox equilibrium

Fe ² * + Cu ⁴ - = * = Fe ³⁺ + Cu *

an extensive reduction of the copper to the <* ^: valuable state occurs, in which form the copper remains in solution as a [CuCl ,,] complex in the solution containing chloride ions. If the solution is partially neutralized with any alkali, all arsenic, iron and any sulfate ions present in the solution are precipitated as iron arsenate or iron (III) hydroxide or gypsum at pH values of 3.0 to 3.5. From the solution purified in this way, the copper can be removed by known methods, e.g. B. by cementation with iron »as cement copper or by air oxidation as copper oxychloride.

This method, which is very elegant in itself, is subject to two essential restrictions, which affect its usability limit or impossible for the very important area of electrolytic copper extraction do:

7th

§ ■ ■. - ^{3 4}

A. 1. The process is based on substances that remove chloride solutions, such as pickling liquors, which crystallize out

f | f! restricts, since in purely sulphatic solutions no iron salts, e.g. B. from titanium white production, or

:. Cu + compounds are stable, but a foul sludge from caustic cleaning processes, too

ij Subject to disproportionation. This means that, when mixed with substances, it can be used. Lies

- - the procedure for copper-containing solutions, the 5 the iron in the said butts not yet in the

:: are to be fed to a copper electrolysis, the highest, trivalent oxidation state before, so is

·· not considered. Post-oxidation with one of the mentioned oxidation

2. In chloride solutions, the procedure on medium is required. The amount of iron added

'■ £ such relatively low copper contents are limited. must be stoichiometrically at least equal to the amount of in

"For the complex binding of the cuprous ion, 10 arsenic present in the solution, i.e. 56 kg Fe / 75 kg

which correspond to a crucial point of this verse. Appropriately, one turns

driving represents, are namely considerable, far a stoichiometric excess of 1.5 to

Overstoichiometric Cl ~ -concentrations require 3 Fe / '] As, i. H. 85 to 170 kg / Fe / 75 kg As, to the

similarly, as also from the examples given, residual solubility of arsenic in the subsequent fall can be seen. If the excess chloride is to be depressed. The precipitation of arsenic will low, then copper (I) chloride (CuCl) precipitates and by adding hydroxyl-ion-releasing substances such as proceed with the filtered iron and arsenic-lower alkali or alkaline earth hydroxide or carbonate blow lost. The procedure is thus taken down. For reasons of price and technology Limited copper concentrations, since the use of lime is preferable wherever higher concentrations the required ChIo- 20 in the case of a solution containing sulfate ions at the same time. Ride ion content not brought into solution or falling gypsum during the subsequent phase separation can be held. The practice is however from acting as a filter aid the precipitation of the arsenic economic reasons just as possible is done according to the equation interested in highly concentrated solutions.

as 2H ₃ AsO ₄ + 2Fe ⁸ + + 6OH- = 2FeAsO ₄ + 6H ₈ O In the following, a wet metallurgical process will now be described which, at the same time, is not subject to the above-mentioned restrictions and is practically quantitative

Separation of the arsenic from the valuable metals, regardless of Fe ³⁺ + 3 OH- = Fe (OH) ₃

depending on the As concentration of the solution, its 3 ° Addition as well as the type of anion permitted. or in a solution containing sulfate ions

The method of the invention for precipitation

and separation of arsenic from arsenic and copper-containing Fe ³⁺ + OH ~ + So; "= Fe (OH) SO ₄

Gen solutions, which may contain other non-ferrous metals, precipitated on wet metallurgical 35 as hydroxide or basic iron sulfate. Ways, is characterized in that the solution, If the precipitation is carried out with lime, then falls

to the extent that in their ions contained is not already in the same gypsum from corresponding present the equation highest oxidation state, with oxidizing agents to reach this state under the supervision Ca * + + SOF + 2H ₂ O = CaSO ₄ .2H ₂ O maintaining an pH ^ 1 treated, a 4 °

in relation to the arsenic overstoichiometric amount. The pH value is during the entire precipitation

Iron in the form of an acid-soluble iron salt must be strictly adhered to, the position of the precipitating pH and bringing it into solution, possibly post-oxidized, depending on the type of anion. In a solution containing chloride by adding alkali, preferably lime, the optimal value is exactly 1.9 to 2.0, pH value from 1.9 to 2.0 in chloride-containing or 45 in purely sulphatic solution is exactly 2.7 to 2.8. If the pH values are below the given pH values of 2.7 to 2.8 in purely sulphate-containing solutions, then the precipitated mixture, consisting of iron arsenate, remains in solution with slightly high arsenic contents. If they are exposed to excess iron hydroxide, possibly gypsum, the arsenic precipitation is complete and acid-insoluble residues of the feedstock are separated from the mother liquor, however, as the pH increases, rials are separated from the mother liquor and this is also precipitated in copper quantities, according to the known manner on copper and any other metals that may still be present. 4Cu ⁸⁺ + 2Ch + 60H "= 3Cu (OH), · CuCl,

The composition of the solution and its preparation or

future is arbitrary. It can be a Cu ⁸⁺ + 2 OH ″ = Cu (OH) ₈

Lye from the sulphating roasting of flotation 55

concentrates, the chlorinating roasting of gravel and go with the felled sludge that goes to the landfill, branden, the oxidizing dissolution of cementates, is lost. The precipitate contains iron-copper slip, copper lead stone or similar material arsenate, iron hydroxide or basic iron sulfate, open your to solutions for or from copper electrolysis gypsum and acid-insoluble residues of the operational activities. A possible treatment of the solution with 60 materials and the precipitant. He will do it in the usual way Oxiui tion agents, z. B. chlorine, oxygen, air or by filter presses, rotary filters o. Ä. From the mother-oxygen-air mixture, is necessary to safely separated caustic and this in a known manner on the to ensure that arsenic is present in a pentavalent valence state, iron in a trivalent valence state, copper, zinc, etc. it contains. If not worked out.

In some cases, enough iron is already available, 65 The result of the precipitation process according to the invention is iron in the form of one of its acid-soluble salts, in which arsenic and trivalent iron are largely, e.g. B. Fe (OH) ,, FeSO ₄ · 7H ₂ O 0, etc., added. Here copper, on the other hand, is practically not precipitated, it can be completely worthless and often even difficult to be astonishing insofar as it can be seen from the precipitation curves of

5 6

FeAsO ₄ and Cu oxychloride or hydroxide not As and 15.7 g / l Fe, which is a stoichiometric ratio

can be deduced Since you see the mentioned curve ratio Fe: As = 1 ^: 1 corresponds to the suspension

cut, there is strictly theoretically overwhelming none was diluted with water in the ratio 1: 1 and with

pH range in which both components are quantitatively a lime suspension up to a pH value of

can be separated. Precisely 2.0 precipitated by the 5 according to the invention. The filtrate contained 35.2 g / l Cu,

Method of setting a precisely defined pH 0.06 g / l As and 0.26 g / l Fe, the residue 1.19% Cu Value wild anyway a technologically satisfactory and 7.65% ace. Taking into account the solution A compromise between possible extensive As precipitation volume or the amount of residue is therefore As closed

This pH reached over 99% in the residue was separated during

The value lies in solutions containing chloride ions, of which more than 97% of Cu remained in the solution.

there are also other anions, e.g. B. auji sulfai- _. . . .

ions, can contain, at exactly \ $ up to 2.0, in pure JJ e ι s ρ ι e ι ζ

solutions containing sulfate ions at 2.7 to 2.8. This 1.5 kg of a cement as in Example 1 were in

The finding is with the lower level of complexation - 201 a CuCly solution (38.8 g / l Cu ³⁺ ) suspended,

the ζ of the SOf ions, compared to CrMons, in 15 With the addition of dilute sulfuric acid and

good match. Maintaining a pH of about 0.5 was made

Finally, it should be pointed out that the other suspension oxidizes with air until all of the copper

In the case of FällschJämme, the arsenic was present in landfill friend in a bivalent form. The suspension

Licher form included. The precipitated compound contained 65.0 g / l Cu and 5.4 g / l As. This mixture

FeAsO ₄ · 2 H _e O (scorodite) indicates from all known ao it was further precipitated with sulfuric acid and iron gypsum Arsenic compounds with sludge up to a molar ratio of Fe: As = 2: 1

τ _ _ ο ο in- «offset.

1-FeAsO ₄ - Aö · lu _{After the fanning} J ₁₁ J _{1 contained lime at pH β 2)} o

(Chuklantev, J. Anal. CH. [Russ.], 11 [1956], the solution 63.6 g / l Cu, 0.026 g / l As and 0.185 g / l Fe,

529) has the lowest arsenic solubility. In a 35 the residue 0.71% Cu and 4.10% As.

Work by G. Z ί η 11 in »Erzmetall«, 26 (1973), 2, S. 141 to 147, the landfill harmlessness example i

convincingly demonstrated this connection. 10 kg of a copper slip with 56.7% Pb, 28.3%

The following examples are intended to use Cu according to the invention, 1.45% As, 4.45% Zn and Sb, Sn, Fe, Ni, Ag Explain procedures without restricting them to these. 3 ° and other ingredients were diluted in 501 Sulfuric acid (17%) entered at 8O ⁰ C. Under Example 1 vigorous stirring was technical oxygen (approx

10 kg of a cementate sludge with 37.7% Cu, 90%) until the copper dissolves quantitatively

7.85% As and 10.4% Zn (i. Tr.) Were introduced in 501. The easily filterable residue contained this

suspended in dilute sulfuric acid (85 g / l H ₂ SO _4). 35 total lead as PbSO ₄ as well as the total contents

The suspension was ^{stirred at 6O 0} C and elements Sb, Sn, Ag and part of the arsenic. The solution

tares chlorine with 800 l / h up to the occurrence of the chlorine contained 99 g / l Cu and 1.25 g / l As. Subsequently was

potentials of 1800 mV (with thalamide electrode the solution with about 0.5 kg of one from pickling waste liquor

measure). The solution contained 76.5 g / l Cu-derived iron sulfate heptahydrates (FeSO ₄ · 7H ₈ O)

and 17.2 g / l As. Then 40 were added and the iron was oxidized to the trivalent stage.

Stirring and addition of sulfuric acid a total of 6 kg of the Fe: As molar ratio was about 1.9: 1. To

wet iron gypsum precipitation sludge (about 50% H ₂ O, e.g. precipitation with hydrated lime suspension at pH 2.75

24% Fe (i. Tr.), About 30% CaO (i. Tr.) Stirred in. the solution contained 94.3 g / l Cu, 0.014 g / l As, 0.11 g / l

The suspension then contained 71.1 g / l Cu, 14.0 g / l Fe, which corresponds to an As separation of over 99%.

Claims (3)

Claims; 1. Process for the precipitation and separation of arsenic from copper-containing solutions, if necessary can also contain other ferrous metals, in a wet-Jlurgischem way, thereby characterized in that the solution, as far as the ions it contains are not already in the the highest level of valency, with oxidizing agents until this state is reached treated while maintaining a pH value of 2 £ 1, one that is overstoichiometric in relation to the arsenic Adds amount of iron in the form of an acid-soluble iron salt and brings it into solution, optionally post-oxidized, by adding alkali, preferably lime, a pH of 1.9 to 2.0, in chloride-containing or from 2.7 to 2.8 in purely sulphate-containing solutions, the Precipitated mixture consisting of iron arsenate, excess iron hydroxide, possibly gypsum and acid-insoluble residues of the feedstock, separated from the mother liquor and these processed in a known manner on copper and any other metals that may still be present. 2. The method according to claim 1, characterized in that the iron salts used are waste materials such. B. Pickling liquor, crystallized iron sulfate heptahydrate or preferably trivalent iron hydroxide used from caustic cleaning or precipitation processes. 3. Process according to Claims 1 and 2, characterized in that one is used as the oxidizing agent Chlorine, oxygen, air or an oxygen-air mixture are used. Copper, nickel, lead and others, in metallic or arsenide Contains shape. Such a cementate has the following analysis, for example: