FI84323C - FOERFARANDE FOER TILLVARATAGNING AV SILVER UR EN PB / AG-KAKA. - Google Patents

Description

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This invention relates to a process for recovering silver from a Pb / Ag cake generated in a hydrometallurgical zinc refining process, and more particularly to selectively recovering silver from a Pb / Ag cake by a flotation process using a sulfuric acid additive strongly acidic conditions prevail, with a sulfuric acid content of 10 to 70 g / l.

Zinc concentrate currently traded on the international market usually contains 48 to 53% Zn, 30 to 34% S, 2 to 12% Fe, 1 to 3% Pb and 50 to 500 g Ag / tonne Ag. . Of these, the value of silver at the current price level is about 15 5% of the value of the zinc contained in the zinc concentrate, and therefore silver is an important by-product and makes the processing of zinc, when sold in a suitable form, much more economically advantageous.

The hydrometallurgical refining of zinc consists of a roasting step of concentrate-20 known ore; an extraction step in which the roasted oxide ore is extracted into sulfuric acid to provide a zinc sulfate solution; a purification step of removing impurities from the zinc sulphate solution; and an electrolysis step in which metallic zinc is obtained from the pure zinc sulfate solution 25. The silver and lead contained in the zinc concentrate do not dissolve in the sulfuric acid solution during the extraction step, but remain as a residue called Pb / Ag cake. The composition of the Pb / Ag cake may vary depending on the composition of the zinc concentrate and the conditions of the extraction step, but generally contains 300 to 1,200 g silver / ton, 15-25% lead and / or other. Such a Pb / Ag cake is used as a raw material in a lead refining furnace or in an ISP (Imperial Smelting Process) furnace that simultaneously processes lead and zinc, but the cake has a low lead content and low energy value, so its exclusive use has been very limited 2 84323 . Japanese Mitsubishi Metal Co. tried a method for art-making silver and lead from a simple unmixed Pb / Ag cake in an electric oven, but rejected it for economic reasons.

5 Another way of reprocessing a Pb / Ag cake to increase its silver and lead content was intensively studied by Asturiana De Zink S.A. (F1 patent application 3,435/70). According to that patent application, the silver and lead components of the Pb / Ag cake were dissolved in the form of a chloride-bis salt in the presence of an oxidant in a chloride solution, and then the silver and lead were converted to silver sulfide and lead sulfide or a metal insoluble state and recovered. Not only does this process require large amounts of reagents, it also causes ai-15 placement problems in the effluent solution (water) in silver and lead recovery. For these reasons, this process is not commercially applicable in practice.

A unique and currently commercially successful method is to increase the silver and lead content of a Pb / Ag cake by foaming the cake. A method for raising the silver and lead content by the flotation process was proposed by the Spanish Asturiana De Zink S.A. EP patent application 411,058 (filed January 27, 1973), which describes the foaming of a ferrite-free Pb / Ag cake and the recovery of a silver-rich tea containing 14,000 g silver / tonne in the first stage, and a lead concentrate containing 55% lead, recovery in the second flotation stage. In the first flotation, the pH of the slurry to be flotated is adjusted to a range of 2 to 4.5, and a foaming agent such as xanthate, dithiophosphate or the like is added. The second flotation uses a sulfiding agent such as sodium sulfide and a defoamer such as xanthate or dithiophosphate. An example according to said invention shows that the silver recovery rate in the first flotation 35 is about 60%, and in the second flotation 3 84323 a degree of art recovery of about 91% is achieved.

JP Patent Publication No. 52-3519 / (Kokai), filed by Vielle Montagne on March 17, 1977, also discloses a method for treating residue 5 from zinc ore extraction. In this method, a Pb / Ag cake is treated under strongly acidic conditions at high temperature to completely remove ferrite, followed by a first flotation to obtain a silver concentrate containing 5,700 to 10,500 g of silver / -10 tons, and then a second flotation to give a lead concentrate with a lead content of 55 to 59%. In this method, too, the pH of the slurry to be foamed is adjusted to 1-5 in the first flotation and xanthate, alkyl or aryldithiophosphate, a mixture of alkyl and aryldithiophosphate or isopropylethylthiocarbamate is used as the foam collector (and about 10% sulfonate is added). In the second flotation, an alkyl or aryl complex complex salt (especially an inorganic salt) of pseudoic acid is used as the foam size. An example of said Kokai-pa-20 exam publication shows that the recovery rate of silver in the first flotation is 80-91% and the recovery rate of lead in the second flotation is 94%. This flotation process produces a fairly high quality, marketable ho-25 head and lead concentrate as the final product, and the recovery rate of silver and lead is satisfactorily high, but the disadvantage of the process is that to obtain a ferrite-free Pb / Ag cake, the residue from zinc extraction extracted with concentrated sulfuric acid solution. Thereafter, such Pb / Ag cake is diluted in the flotation process with a large amount of water to keep the cake in the pH range of 1 to 5 (or 2 to 4.5). Because the first and second flotation processes use a variety of materials, such as a blowing agent, a foam collector, and an activating agent, contamination of the large amount of water used to adjust the pH and solids content of the slurry also generates large amounts of wastewater.

It is an object of the present invention to provide a novel method for recovering silver from a Pb / Ag cake and in particular to minimize the disadvantages of said known methods according to ES patent application 411 058 and JP patent publication 52-35197 (Kokai).

The features and advantages of the present invention are achieved by 10 new flotation methods for recovering silver concentrate from a Pb / Ag cake from a hydrometallurgical zinc refining process, in which flotation of the Pb / Ag cake is performed using sulfuric acid as a reagent under strongly acidic conditions (sulfuric acid content corresponds to a pH of 0.9 to 0.1) or by adding a small amount of sulphidating agent to the slurry to be foamed.

The process according to the invention is preferably carried out by adding recycled liquid (filtrate from a filtration press, supernatant from a centrifugal separator), water and sulfuric acid to the Pb / Ag cake so that the solids content of the slurry to be foamed is 100-300 g / l and the acidity is H2SO4. - 70 g / l (corresponding to a pH of 0.1 to 0.1). The resulting slurry 25 is subjected to a flotation process and the silver is flotated using air, or a sulfiding agent such as H 2 S, Na 2 S and / or NaSH is further added to the resulting slurry and the slurry is subjected to a flotation process and the silver is floted using air. The silver (and a small amount of lead) is collected as a foam and the resulting foam is washed, filtered and recovered as a silver concentrate. The silver concentrate contains 8,000 to 12,000 g of silver / tonne of concentrate and this figure corresponds to a recovery rate of 80 to 90%.

Although in the present invention the acidity of the Pb / Ag cakes is within certain limits, the acidity of the different cakes varies. For this reason, the addition of recyclable liquid and concentrated sulfuric acid is adjusted so that the sulfuric acid content of the slurry to be foamed is 10 to 70 g / l.

In fact, the sulfuric acid 5 used as a reagent consists of the sum of the sulfuric acid contained in the Pb / Ag cake itself and the amount of sulfuric acid added to the slurry device and the conditioning device. Related to the present invention is that the Pb / Ag cake itself contains a large amount of sulfuric acid and that the acidity of the liquid to be recycled is also high.

10 For this reason, the amount of sulfuric acid actually added is relatively small.

The present invention relates to a flotation process in which flotation is carried out using sulfuric acid alone as a reagent, and also to a flotation process in which flotation 15 is carried out without the addition of a flotation agent by adding only a sulfiding agent to the slurry to be flotated.

During foaming, 0.2 to 4.0 g / l of, for example, H2S, Na2S and / or NaSH can be added to the slurry as sulphating agent. By adding a sulfidating agent, the invention achieves an improvement in the recovery rate of more than 5% compared to not adding a sulfiding agent.

The air feed to the flotation process is controlled to flotate the entire recoverable silver content, and generally the preferred feed rate is about 700 m3 (NTP) / ton of Pb / Ag cake.

The present invention features a simple and easy process that involves the use of sulfuric acid alone or the addition of a sulfiding agent, and a unique process that makes it easy to recycle the filtrate.

If necessary, the flotation process according to the invention can be carried out in several steps, and a washing step, a solid-liquid separation, etc. can be connected to the process.

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Other advantages are achieved by the invention when the range of acidity useful in the foaming process is extended. The acidity used in the process itself is flexible and within easy reach. Pb / Ag-kak-5 could be used directly, without water purification or neutralization, as a raw material in the flotation process. For this reason, no neutralization tanks or dilution water are required, resulting in a reduction in water consumption.

Figure 1 schematically illustrates the flow of a process according to the present invention.

As shown in Fig. 1, the Pb / Ag cake 1 used as a raw material is efficiently mixed in a slurry device 5 with a recyclable filtrate 15 20 from a filter press, a supernatant 19 from a centrifugal separator, water 3 and sulfuric acid 2. The solids content of the slurry at this stage is 300 to 600 g / l and the sulfuric acid content is 50 to 120 g / l. This slurry is fed to a conditioning device 6, where further water and residues from the purification cell 12 are added to adjust the sulfuric acid content to a range of 10 to 70 g / l. If necessary, sulphidating agents are added to the slurry at 0.2 to 4.0 g / l, and the solids content of the slurry is finally adjusted to a range of 100 to 300 g / l.

The 25 Pb / Ag cake slurry, the sulfuric acid content and solids content of which have been finally adjusted, is further fed to the flotation cell (7, 8 and 12), where flotation takes place. The flotation process is usually carried out by blowing air with a feed rate of 600 to 800 30 m3 (NTP) / tonne of Pb / AG cake. The flotation cell is not special in construction, but conventional flotation equipment is useful. In order to increase the recovery rate of the silver obtained as a final product, the first flotation is carried out in a coarser cell (pre-flotation cell) 35 7, and the residues from this cell are re-flotated in the rescue cell 8. for. The foam 17 from the cleaning cell 12 is separated from the solids and liquid in the settling tank 13 and the centrifugal separator 14, whereby a silver concentrate is obtained as the final product and the residues are returned to the slurry device 5 to recover the remaining silver.

The residues from the rescue cell 8 are collected in a waste tank 9, the solid and liquid are separated in a filter press 10 and the residue 22 remaining from the residues is discarded as waste and the filtrate is partially recycled.

A typical Pb / Ag cake used as a raw material in the process of this invention contains about 3 to 15% Zn, 3 to 13% Fe, 15 to 35% Pb, 12 to 18% S, and 200-1,500 g Ag / ton.

The silver concentrate obtained by the flotation process contains about 6,000 to 12,000 g of silver / ton of concentrate, which corresponds to a recovery rate of 20 to 80 to 90%.

The following examples illustrate this invention.

Example 1 2 kg (dry weight) of a Pb / Ag cake with a composition of 6.2% zinc, 6% iron, 20.5% lead, 15.5% sulfur and 25,802 g silver / tonne were mixed with 9 liters of water and 350 g of sulfuric acid for 5 minutes to give a slurry having a solids content of 200 g / L and an acidity expressed as H 2 SO 4 of about 50 g / L.

The resulting slurry was placed in a laboratory-sized flotation cell and foamed by blowing air into it for 10 minutes, and the foam was collected. After washing the foam with water and separating the solid and liquid, 140 g of silver concentrate were obtained; the residue formed from the flotation residues was 1,820 g.

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The composition of the silver concentrate and the composition of the flotation residue were as follows:

Silver concentrate Foaming residue 5 _weight ratio_____weight ratio___

Zn 6.8 4.3

Fe 2.2 5.3

Pb 17 22.1 S 55 10.3 10 Ag______9 452 (g / t) ________________ 154 (g / t) ___

The silver art ratio was 82.5%.

Example 2 2 kg of Pb / Ag cake, the same as used in Example 1, were mixed with 9.5 liters of water and 50 g of sulfuric acid for 3 minutes to obtain a slurry with a solids content of 200 g / l and an acidity of H 2 SO 4. expressed as a concentration of about 17 g / l. Then 200 ml of 3% NaSH was added as sulfiding agent and stirring was continued for another 3 minutes.

The resulting slurry was placed in a laboratory-sized flotation cell and foamed by blowing air, and the foam was collected. After washing the foam and separating the solid and liquid, 148 g of silver concentrate were obtained. 1,859 g of a flotation residue were also formed. The composition of the silver concentrate and the composition of the flotation residue were as follows:

Silver concentrate Foaming residue 3 0 _weight ratio___weight ratio_

Zn 6.9 4.7

Fe 2.0 5.2

Pb 16 22.3 S 56.4 10.3 35 Ag_9 429 (g / t) __ 112 (g / t) _

The silver art rate was 87%.

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Example 3 3 kg (dry weight) Pb / Ag cake with a composition of 9.5% Zn, 8.8% Fe, 19.5% Pb, 14.2% S and 704 g AG / ton, mixed with 20 liters of water and 250 g of sulfuric acid for 5 minutes to give a slurry with a solids content of 150 g / l and an acidity, expressed as H 2 SO 4, of about 30 g / l.

The resulting slurry was placed in a laboratory-sized flotation cell and floted by blowing IL-10 soil into it for 10 minutes. The collected foam was washed and the solid and liquid were separated to give 195 g of silver concentrate. 2,765 g of a flotation residue was also formed. The composition of the silver concentrate and the composition of the flotation residue were as follows: 15 _______

Silver concentrate Foaming residue residue _weight ratio__weight ratio_

Zn 10.2 7.8

Fe 6.5 8.0 20 Pb 15.5 19.8 S 56.9 13.9

Ag 8 803 (q / t) __ 143 (g / t) _

The silver recovery rate was 81.3%.

Claims (3)

Foaming method for recovering silver from a Pb / Ag cake, characterized in that the foaming 5 is carried out using sulfuric acid as the blowing agent or using sulfuric acid and a sulphidating agent under strongly acidic conditions, with a sulfuric acid content of 10 to 70 g / l and a slurry concentration of 100 to 300 g / l . Process according to Claim 1, characterized in that 0.2 to 4.0 g of H 2 S, Na 2 S and / or 1 liter of NaSH are added to the slurry as sulphating agent. Process according to Claim 1, characterized in that the sulfuric acid consists of the total sulfuric acid initially contained in the Pb / Ag cake, the sulfuric acid to be added to the slurry and the sulfuric acid contained in the recyclable liquid consisting of the filtrate from the filter press and the supernatant from the centrifugal separator. K 11 84323