Extraction of silver from alkaline cyanide solutions

FIELD: metallurgy.

SUBSTANCE: invention relates to hydrometallurgy of noble metals and can be used for silver extraction from alkaline cyanide solutions by cementation. Proposed method comprises cementation by aluminium as 0.1-2.0 mm thick chips. Cementation is carried out at specific solution feed rate of 1-4 m3/m2·h at concentration of sodium hydroxide of 1.0-10.0 g/l.

EFFECT: higher yield and quality.

3 tbl, 3 ex

 

The invention relates to the field of hydrometallurgy of precious metals and can be used, in particular, to extract silver from cyanide solutions by cementation.

Known methods of extraction of precious metals from cyanide solutions by cementation using as reagent precipitator zinc or zinc dust(1).

Zinc dust and chips in the air undergo oxidation, which complicates their use.

There is also known a method of extracting silver from cyanide solutions by cementation, in which the reagent precipitator used aluminum powder (2).

Aluminum powder consists of particles with a size of 5-20 μm, has a very developed surface, so that when in contact with air rather intensively oxidized, resulting after cementation receive precipitation containing 20-30% aluminum. Such precipitation before receiving ingots (fuse) require additional operations (alkaline or acid). In addition, in view of the difficulties associated with the wetting of the dust, need a special form of agitator. In campaign mode because of the developed surface of the aluminum dust is unacceptable dissolves quickly. In the process of campaigning because of the good contact of the solution with air, there is intense saturation of the solution with oxygen, which slows down the process of deposition, in addition, the precipitate of silver, formed by deposition of aluminum dust, then quickly dissolves (3).

The disadvantage of this method is the low velocity of the deposition of silver on the reason for the slow wettability of aluminum dust cyanide solutions. In addition, this method is associated with high consumption of aluminum resulting from unproductive dissolution of the last lye.

The task, which is aimed by the invention is the provision of improved performance of silver extraction from alkaline solutions and reducing the consumption of the precipitator.

The task is solved by the technical result, which is in the choice of optimal conditions cementation, namely due to the optimal size of the precipitator, the concentration of sodium hydroxide and the optimal flow rate of the deposition of silver.

The technical result is achieved in that in the method of extracting silver from alkaline cyanide solutions, including cementation aluminum, which is carried out with the use of aluminum in the form of chips with thickness of 0.1-2.0 mm while maintaining the concentration of sodium hydroxide 1-10 g/l to passing the solution with the specific rate of 1-4 m3/m2PM

The difference of the proposed technical solutions from the prototype is the use of aluminum the form of chips with thickness of 0.1-2.0 mm, ensuring the concentration of sodium hydroxide 1-10 g/l with a specific velocity cementation 1-4 m3/m2PM

When using aluminum shavings in the process of cementation aluminum actively interacts with alkali (NaOH) is one of the components of cyanide solutions. Upon contact of aluminum with such solutions containing silver, there are two main reactions:

the reaction cementation

3Ag(CN)2-+Al+4OH-=3Ag+AlO2-+6CN-+2H2O(1)

the reaction of dissolution of aluminum in an aqueous solution of alkali

2Al+2OH-+2H2O=2AlO2-+3H2 (2)

As you can see, the more developed the surface precipitator, the more it is spent on interaction with the alkali with hydrogen gas, causing it to unproductive consumption, i.e. this reaction is parasitic.

The method consists in the following. Chip thickness less than 0.1 mm is quickly dissolved in alkaline cyanide solutions, which leads to increased consumption of aluminum, and the use of chip thickness greater than 2.0 mm due to the smaller contact surface of the precipitant solution slows down the cementation process and decrease, as a consequence, the degree of extraction of silver.

The prior art is not identified technical solutions that have the signs consistent with the distinctive features of the present invention, therefore, can be considered that the proposed solution meets the criterion of "inventive step".

The method is illustrated by the following examples.

Example 1. The study was carried out in campaign mode with loading precipitator 15 g/l NaOH concentration of 1 g/l for 120 min with a selection of solutions for the analysis of silver for the extraction residue. The results of the experiments are shown in table 1.

the table 1
The results of the deposition of silver from solutions.
Time, minutesThe concentration of silver in solution (mg/l) when the chip thickness (mm)
0,050,12,02,5Al the dust
02120,02120,02120,02120,02120,0
3050,078,034,233,532,0
6078,22,11,62,968,1
1206740,020,012,7524,0

As can be seen from table 1, the best results on the deposition of silver obtained on the aluminum flakes with thickness of 0.1-2.0 mm, while its extraction amounted to more than 99.99%, and the prototype is 75,3%.

Example 2. The study was carried out in campaign mode with a load of 15 g/l of aluminum shavings in the thickness of 1.0 mm for 120 minutes With a selection of solutions for the analysis of silver for the extraction residue. The results of the experiments are shown in table 2.

Table 2
The results of the deposition of silver from solutions of Table 2.
Time, minutesThe concentration of silver (mg/l) in solution at a concentration of sodium hydroxide (g/l)
0,51,05,010,0to 12.0
02120,02120,02120,02120,02120,0
3092,075,031,729,549,2
6075,05,12,11,7 a 12.7
120150,00,040,010,019,2

As can be seen from table 2, the best results on the deposition of silver obtained when the concentration of sodium hydroxide and 1.0-10.0 g/l, the extraction of silver amounted to more than 99.99%.

Example 3. Studies were performed in columns with a diameter of 0.05 m and a height of 0.25 m with a load of chips 150 g, the concentration of the silver solution of 920 mg/l, NaOH - 5.0 g/l and the specific rate of the transmittance of the solution is from 0.5 to 4 m3/m2h, chip thickness 1,0 mm the results of the experiments are given in table 3.

Table 3
The results of the deposition of silver from solutions (Table 3).
Time minThe extraction of silver in solution (%) specific velocity (m3/m2h)
0,51,02,03,04,04,5
3020,130,5 35,840,145,140,6
6040,869,775,1an 80.285,674,2
12065,6a 94.296,798,199,090,5
18075,999,999,999,999,996,1
22090,1----96,8

As can be seen from table 2, the best results are obtained when the specific speed transmission solution from 1 to 4 m3/m2h, thus removing 180 min amounted to 99.9%.

Sources of information

1. Metallurgy of noble metals (foreign experience). Meretukov M.A., Orlov A.M. - M.: metallurgy, 1991, pagination 126-131.

2. Metallurgy of noble metals. Malinetskii I.N., The Chugai is L.V. - Ed. Metallurgy, 1987, 182-185.

3. Metallurgy of noble metals. Textbook for high schools (Malinetskii I.N., Chugaev L.V., Borbat VF and others). Edited tchugaev L.V. - 2nd ed., revised and enlarged extra - M.: metallurgy, 1987, p.189 (prototype).

The method of extracting silver from alkaline cyanide solutions, including cementation aluminum, characterized in that the cementation is carried out with the use of aluminum in the form of chips with a thickness of 0.1-2.0 mm, while maintaining the concentration of sodium hydroxide and 1.0-10.0 g/l to passing the solution with the specific rate of 1-4 m3/m2PM



 

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