EP0244433A1

EP0244433A1 - Method for separation and recovery of metals from mixtures of metal sulfides such as lead ores

Info

Publication number: EP0244433A1
Application number: EP86905847A
Authority: EP
Inventors: Patrick Noual
Original assignee: Extramet SA
Current assignee: Extramet SA
Priority date: 1985-09-27
Filing date: 1986-09-26
Publication date: 1987-11-11
Also published as: FR2589885B1; BR8606886A; WO1987002068A1; AU6405186A; PT83433A; FR2589885A1; ES2001803A6; JPS63501023A; AU586507B2; MA20776A1; PT83433B

Abstract

On attaque le mélange de sulfures avec une solution aqueuse oxydante d'acide fluosilicique pour mettre en solution l'ensemble des métaux. A partir de la solution, on reprécipite le plomb, et éventuellement l'argent, à l'état de sulfates que l'on sépare du filtrat renfermant les autres métaux. On peut alors récupérer séparément les différents métaux par traitement, d'une part du précipité de sulfates et, d'autres part du filtrat, suivant des procédés classiques. On peut recycler les solutions d'attaque.The mixture of sulphides is attacked with an aqueous oxidizing solution of fluosilicic acid to dissolve all of the metals. From the solution, the lead, and possibly the silver, is reprecipitated in the form of sulphates which are separated from the filtrate containing the other metals. The different metals can then be recovered separately by treatment, on the one hand of the sulphate precipitate and, on the other hand of the filtrate, according to conventional methods. Attack solutions can be recycled.

Description

PROCESS FOR SEPARATING AND RECOVERING METALS FROM MIXTURES OF METAL SULFIDES SUCH AS LEAD ORES

The present invention relates to the metallurgical treatment of mixtures, natural or not, of metal sulfides. It relates more particularly to the extraction of lead and of the metals which accompany it in such mixtures of sulphides, in particular silver, copper, tin and zinc.

In hydrometallurgical treatments, one begins by oxidizing the sulphides by calcining them, or by dissolving them in an oxidizing medium. The metals are then recovered by chemical treatment or electrolysis. The two routes, dry and wet, have drawbacks linked, among other things, to pollution and energy consumption, as well as investments in equipment and space. In addition, implementation difficulties, mainly related to the control of the sulfur oxidation reaction, often appear.

An important improvement, aimed specifically at the selective recovery of lead has been brought to the wet process, in accordance with the process described in the French patent application published under No. 2,505,876.

In this case, a selective dissolution of the lead sulfide is ensured by attacking the mixture of sulfides by means of an oxidizing solution of fluosilicic acid where the oxidant is hydrogen peroxide.

In practice, this process is satisfactory insofar as the oxidant is hydrogen peroxide, under conditions where the dissolution of the sulphides is selective with respect to the lead sulphide. This selectivity makes it impossible to be able to dissolve effectively the sulfides of metals other than lead present in the mixtures of sulfides and, if therefore it is sought to recover these metals also, it is necessary to carry out a recovery of the attack residues mixtures of sulphides after the dissolution of lead sulphide to dissolve the metals and recover them, according to conventional treatments, the drawbacks of which are then found. The present invention relates to a new process for treating mixtures of metal sulfides which facilitates the recovery of different metals by selective precipitation, because it previously ensures the simultaneous dissolution of the different sulfides corresponding to a single operation.

It results from the observation that the simultaneous dissolution of the various sulfides can be obtained by attack with fluosilicic acid thanks to a particular choice of attack conditions, then unexpectedly giving an overall result diametrically opposite to the selective result of the process of French patent application 2,505,876.

From this point of view, the process according to the invention applies more particularly to the extraction of the various metals which accompany lead in natural sulphide ores, that is to say in particular in addition to lead, silver, copper, l tin, zinc. In this type of application, the method according to the invention makes it possible, by comparison with the previously applied hydrometallurgical treatments, to considerably reduce energy expenditure, pollution and investments. Thus, the volume of the installations necessary for the implementation of the method is only of the order of one fifth of the installations using methods hitherto known. The subject of the invention is a process for treating mixtures of metallic sulphides, in particular natural lead ores, with a view to the recovery of metals such as lead, silver, copper, tin, zinc, process comprising a step of attacking the mixture of sulphides with an aqueous oxidizing acid solution fluosilicon, characterized in that an oxidizing fluosilicon solution is used for said etching step, ensuring the dissolution of all the sulfides of the metals to be recovered and the precipitation of lead and silver in the state of sulfates , and in that one recovers, by operations in themselves conventional, lead and silver from said sulphates and the other metals from the solution remaining after separation of the precipitated sulphates.

In the implementation of the method according to the invention, the conditions suitable for the dissolution of all the metals to be recovered, in particular in the treatment of natural lead ores, are met in particular the oxidizing nature of the attack solution is provided by the redox couple suitably chosen from the known redox couples.

According to one of the embodiments of the invention, the attack on the mixture of sulfides is advantageously carried out with an aqueous solution of fluosilicic acid and nitric acid, the redox couple being

NO ₃ - / N0-

In another embodiment of the method, the mixture of sulfides is attacked with an aqueous solution of fluosilicic acid and a ferric salt such as ferric sulfate or fluosilicate, the redox couple then being the ferric iron couple / ferrous iron Fe3 + / Fe2 +.

After the step of precipitating lead and, possibly silver, in the sulphate state, it is practical to treat the precipitated sulphates with an aqueous solution of calcium chloride and fluosilicic acid, to obtain a solution containing lead and possibly silver, which is separated, by filtration, from the rest of the residue resulting from the attack of the initial mixture of sulphides and of the calcium sulphate formed.

We can rush any money in the filtered solution, by displacement using lead powder, then recover by filtration the silver precipitated from the lead solution. From the redissolution solution, it is then possible to recover the lead, by electrolysis according to the methods and with the conventional equipment. The solution of the exhausted cathode compartment (catholyte) is advantageously recycled to redissolve lead and silver sulfates precipitated and filtered during the process which is the subject of the invention.

As regards the other metals which may be present in the initial mixture of sulphides, it is in particular possible to successively extract the copper, iron and zinc from the sulphide attack filtrate, by proceeding by displacement using iron and / or metallic zinc to precipitate the copper, possibly present, then after filtration, by precipitation of the iron possibly present in the filtrate, with sodium hydroxide and air bubbling then, after filtration of the goethite formed, by precipitation with sulphide sodium or hydrogen sulphide of the zinc possibly present and filtration of the zinc sulphide formed. The hydrogen sulfide used there can be obtained from the residue.

After exhausting the dissolved metal filtrate, it can advantageously be recycled to attack a new mixture of sulphides according to the process which is the subject of the invention.

The best results are generally obtained with the process which is the subject of the invention, if the attack solution of the mixture of sulphides contains a minimal amount, even a trace, of hydrochloric acid, and if for a sulphide concentration of 90 to 100 g / l for example, it contains from 80 to 100 g / l of fluosilicic acid and 30 to 40 g / l of nitric acid, 10 to 50 g / l of ferric iron.

Thus the process which is the subject of the invention makes it possible to recover all of the metals present in the mixtures sulphides in a minimum of operations, and therefore with a reduced apparatus and a lower energy consumption, which considerably reduces the time and the cost of the treatment compared to the processes hitherto known.

The description of the invention is illustrated by the appended drawings, in which:

- Figure 1 is a block diagram of the method according to the invention;

- Figure 2 is a diagram showing a dissolution of sulfides as a function of time.

The succession of the different stages of the process, completed in a particular implementation mode, is illustrated by FIG. 1. The leaching stage is shown diagrammatically in 1, at which level a sulfur concentrate to be treated is admitted in 2. , in 3 the oxidizing agent, with recirculation, in 4 an aqueous hydrochloric acid solution and in 5 air, optionally enriched in oxygen. Fluosilicic acid is recycled at this stage in 6. In 7, a precipitate is recovered by filtration. which is subjected in 8 to a step of dissolution with a hydrochloric solution of fluosilicic acid and of calcium chloride recirculated in 9. In 10 the precipitate formed is separated, which contains calcium sulphate, sulfur and residues d attack of sulphides, the assembly being eliminated at 11. The collected solution is subjected at 12 to a displacement step with lead introduced at 13 and the precipitated silver is collected at 14. The remaining filtrate is treated by electrolysis at 15 so as to collect the lead at 16, while the electrolysis is recycled to the dissolving step at 8. For its part, the filtrate separated from the sulfates at 7 is treated at 17 by displacement of the copper by means of iron and / or zinc introduced in 18, according to methods which are in themselves conventional, the precipitated copper being recovered in 19. The filtrate is then subjected to a precipitation step in 20 by means of a solution of soda 21, under air bubbling 22, which makes it possible to cause the precipitation of iron by techniques in themselves conventional, which is collected at 23. A subsequent precipitation, carried out at 24 by means of hydrogen sulfide at 25, allows the precipitation of zinc, collected at 26 in the form of zinc sulfide. The filtrate is reused in leaching step 1.

The invention will be better understood on reading the practical examples which follow of embodiments of the method which is the subject of the invention.

EXAMPLE 1

In a double-jacketed glass reactor, heated by circulation of water in a thermostatic bath and equipped with a stirring device by propeller and counter-current vane, 200 g of a sulphide ore concentrate are introduced beforehand. pulverized by grinding to a particle size between 50 to 500 microns, which is suspended in a mixture comprising: - 400 ml of fluosilicic acid (H _2SiF6 ) at 31%

(density 1.29),

- 10 ml of 1N hydrochloric acid (HCl), and 200 ml of water.

200 ml of 65% nitric acid (HNO ₃ ) are added at 65% (density 1.4) and the temperature is maintained at approximately 70 ° C. at ambient atmospheric pressure while stirring for approximately 3 hours to complete the leaching.

Air, or oxygen, or oxygen-enriched air is bubbled during leaching to entrain the nitrous vapors formed, and recover them for reinjection, in the attack solution, after transformation into acid nitric. The precipitate containing the lead and silver sulfates and the residue are recovered by filtration. of the sulfide mixture, and it is treated with an aqueous solution containing 150 grams per liter of fluosilicic acid (H2SiF6), 320 g / l of calcium chloride (CaCl ₂ ) and 71 g / l of hydrochloric acid (HCl). After one hour of treatment under the conditions of pressure, temperature, stirring, leaching and in a similar reactor, the sulfates are dissolved, however, a precipitate of calcium sulfate, of sulfur is formed. This precipitate is removed by filtration, which also contains the residues of the attack by sulphides. The silver is then moved from the solution in a conventional manner by lead shot and, after filtration of the shot and the precipitated silver, the lead is extracted from the filtrate by electrclyse with a two-cell electrolysis cell . The spent electrolyte is reused, after verification and readjustment of the calcium chloride and fluosilicic acid content, for the dissolution of a new batch of sulfates, lead and silver, obtained in a new attack attack. a mixture of sulfides as before.

Furthermore, the filtrate separated from the precipitate of sulfates is taken up in order to extract the copper from it by displacement with iron and / or zinc, in a conventional manner.

It is filtered to recover the precipitated copper and then a solution of NaOH sodium hydroxide solution is added to the filtrate while bubbling air through it to precipitate the iron.

In the filtrate, hydrogen sulfide (H _2S ) is bubbled until complete precipitation of the zinc in the sulfide state.

The filtrate is recovered which is reused after verification and possible addition of the necessary supplements of constituents, as an attack solution for a new batch of mixture of sulphides.

Finally the process allows the extraction of 89% copper, 55% zinc, 73% lead and 72% silver.

EXAMPLE 2

50 g of a sulphide ore containing 27.6% lead, 8.55% copperi and 40% iron are attacked at 80 ° C with an aqueous solution of ferric sulfate ((SO ₄ ) _3Fe2 ) in l fluosilicic acid containing 44 g of Fe3 + ions and 80 g / 1 of fluosilicic acid (H _2SiF6 ), and with stirring.

The progress of the reaction is checked by taking samples after 30, 60, 90, 120 and 240 minutes.

Analysis of the sample solution gives the following results:

Time mn 30 60 90 120 240

Pb g / l 1.12 3.62 2.9 0.6 0.6 Cu g / l 1.2 1.6 2 2 2

After moving the copper with the zinc powder, the etching solution contains only 0.17 g / l of copper.

In the solution thus depleted of copper, but still containing iron ions, oxygen is bubbled for 1 hour at 85 ° C., adding sodium hydroxide, to precipitate the iron in the form of goethite.

The recovery of the attack precipitate, consisting mainly of lead sulphate (Pb SO ₄ ) with calcium chloride in a fluosilicic acid medium gives a solution containing 25 g / l of lead, which can be treated for recovery of lead , especially by electrolysis.

The kinetics of the reaction show a first phase of dissolution of the lead sulphide in the attack solution followed by an oxidation with precipitation of the lead sulphate that the diagram of FIG. 2 shows, where the percentages of copper, of iron and lead dissolved in the attack solution, in relation to the initial ore content, are indicated as a function of the attack time of the ore.

EXAMPLE 3 The lead dissolved in a solution is extracted

CaC12 / H2SiF6 By electrolysis in a conventional installation with two separate compartments with, in one a graphite anode, in the other a stainless steel cathode.

As electrolysis aids, gelatin and phosphoric acid (H3PO4) are added to the solution

In the cathode compartment the solution contains 112.5 g / l of dissolved lead, 80 g / l of fluosilicic acid and 320 g / l of calcium chloride. The anode compartment contains only an aqueous solution containing 400 g / l of fluosicilic acid.

Electrolysis is carried out at 30 ° C. at 3.29 volts and 0.27 amperes with a stainless steel cathode of

5.8 cm2.

Naturally, the invention is in no way limited by the features which have been specified in the foregoing or by the details of the particular embodiments chosen to illustrate the invention. All kinds of variations can be made to the particular embodiments which have been described by way of examples and to its constituent elements without thereby departing from the scope of the invention. The latter thus include all the means constituting technical equivalents of the means described as well as their combinations.

Claims

1. Process for treating mixtures of metal sulfides, with a view to recovering metals such as lead, silver, copper, tin, zinc, process comprising a step of attacking the mixture of sulfides with a aqueous oxidizing solution of fluosilicic acid, characterized in that, for said attack step, an oxidizing fluosilicic solution is used which dissolves all the sulphides of the metals to be recovered and the precipitation of lead and silver , which are collected in the form of sulphates, and in that we recover, by operations in themselves conventional, lead and silver from said sulphates and the other metals from the solution remaining after separation of precipitated sulfates.

2. Method according to claim 1, characterized in that one attacks the mixture of sulfides with an aqueous solution of fluosilicic acid and 'nitric acid, the redox couple being NO ₃ - / NO.

3. Method according to claim 1, characterized in that one attacks the mixture of sulfides with an aqueous solution of fluosilicic acid and ferric sulfate or fluosilicate, the redox couple being Fe3 + / Fe2 +.

4. Method according to any one of claims 1 to 3, characterized in that the sulfates precipitated are treated with an aqueous solution of calcium chloride, and fluosilicic acid, optionally with hydrochloric acid, to obtain a solution containing lead and possibly silver, which is separated by filtration from the etching residue of the mixture of sulphides.

5. Method according to claim 4, characterized in that the silver possibly present in the filtered solution by displacement with metallic lead, and in that the silver is recovered by filtration precipitated in the solution which contains the lead extracted from the sulphides.

6. Method according to one of claims 4 and 5, characterized in that the lead is recovered by electrolysis of the solution from which the silver has been withdrawn, by operating in a cell with two compartments.

7. Method according to claim 6, characterized in that the electrolytic solution from which the lead has been extracted is recycled to dissolve new precipitated lead and silver sulfates.

8. Method according to any one of claims 1 to 7, applied to the treatment of natural lead ores and characterized in that the copper, iron and zinc which are optionally present in the sulphide attack filtrate are successively recovered by displacement with metallic iron and / or zinc to precipitate the copper, possibly present, then after filtration, by precipitation of the iron possibly present in the filtrate, with sodium hydroxide and air bubbling, then, after filtration, by precipitation with l hydrogen sulphide of the zinc possibly present and filtration of the zinc sulphide formed.

9. Method according to claim 8, characterized in that the filtrate is recycled, after recovery of the various possible metals by precipitation, to attack a new mixture of sulphides.

10. Method according to any one of claims 1 to 9, characterized in that a minimal amount of hydrochloric acid is introduced into the etching solution of the mixture of sulphides.

11. Method according to claim 2 and any one of claims 4 to 10, characterized in that the attack solution, for a concentration of 90 to 100 g / l, contains from 80 to 100 g / l of acid fluosilicic and 30 to 40 g / l of nitric acid, 10 to 50 g / l of ferric iron.