RU2861237C1 - Method for extracting rhodium, ruthenium and iridium from concentrate - Google Patents

Abstract

FIELD: non-ferrous metallurgy.

SUBSTANCE: invention relates to the refining of precious metals, specifically to a method for extracting target precious metals into solution – rhodium, ruthenium and iridium. The method includes carrying out a hydrochlorination operation. Preliminary leaching of the concentrate in a technical hydrochloric acid solution with a concentration of 200-210 g/l is carried out to obtain a leaching pulp. The obtained leaching pulp is sent for filtration, and the insoluble leaching residue obtained as a result of filtration is subjected to hydrochlorination using chlorine at a rate of 1.85 kg/kg of insoluble residue for 4-8 hours until a stable ORP value of 1020±20 mV is reached. The resulting hydrochlorination pulp is sent for further separation of the extracted metals.

EFFECT: increased selectivity of extracting rhodium, ruthenium and iridium from the concentrate and increased extraction thereof.

1 cl, 1 dwg, 3 tbl, 1 ex

Description

The present invention relates to the field of non-ferrous metallurgy, in particular to the field of refining precious metals, namely to a method for extracting target precious metals into a solution - rhodium, ruthenium and iridium.

Prior art, particularly patent application WO2014091456, describes a method for extracting platinum group metals (PGMs – ruthenium, rhodium, palladium, osmium, iridium, and platinum) and gold, as well as base metals (copper, nickel, and cobalt) from ores, concentrates, tailings, and secondary materials containing PGMs. The material is mixed with sodium or potassium chloride, added in an amount of 40–300% of its dry weight, and the mixture is treated with gaseous chlorine at 750–850°C, converting the metals into volatile chlorides, which are then leached with aqueous hydrochloric acid solutions.

Patent RU2398898 describes a method for the selective extraction of palladium, platinum, and rhodium from concentrates. The method involves sequential leaching with dissolution of each metal: palladium with a nitric acid solution, platinum with a mixture of nitric and hydrochloric acids, and rhodium with a solution containing hydrochloric acid, followed by the removal of each pregnant solution. The insoluble residue after platinum dissolution is leached with sodium hypochlorite in a solution of hydrochloric acid diluted with water. Leaching of all the metals is carried out with air bubbling through the reaction mixture from below through a porous membrane.

These methods have the following disadvantages:

WO2014091456 involves the use of pyrometallurgical methods, which can lead to losses (dust entrainment, absorption into the lining and/or container material), and additional equipment is required that is resistant to a chlorine environment at temperatures up to 850 ^° C, which entails additional costs and industrial safety risks.

RU2398898 involves the stepwise dissolution of precious metals with air bubbling. With an increase in the amount of dissolution at the head stages of the technological process, due to the properties of precious metals, the incompleteness of these dissolutions (without the use of oxidizing agents) with the sequential use of acids will lead to an additional need for additional enrichment of intermediate products and the possible spreading of precious metals throughout the technological scheme and, as a consequence, a drop in recovery at each stage. In addition, this method does not solve the problem of separating impurity non-target metals during the processing of complex raw materials containing a large number of impurities.

Thus, there is a need to develop a method that is free from the above mentioned disadvantages.

The proposed method allows for increasing the selectivity of extraction and reducing the content of the main impurity - copper in the material, as well as other impurities before the hydrochlorination operation, as a result, significantly reducing the mass of the material, as well as increasing the content of precious metals in the material before the hydrochlorination operation and increasing the extraction of rhodium, ruthenium and iridium.

The technical result of the proposed invention is

increasing the degree of selectivity of extraction of the following metals from concentrate: rhodium, ruthenium and iridium, as well as in obtaining a chloride solution of precious metals suitable for further refining.

It has been established that removing copper and other impurities by leaching has a beneficial effect on the subsequent hydrochlorination of the concentrate, reducing the yield of insoluble residue after hydrochlorination by more than 13% compared to direct hydrochlorination of the original concentrate. Leaching the concentrate in a hydrochloric acid solution before hydrochlorination reduces reagent consumption, reduces the mass of processed intermediate products, and increases the recovery of rhodium, ruthenium, and iridium.

The basic diagram of the claimed method is shown in Figure 1.

The method proposed in the present invention is carried out as follows.

Extraction of rhodium, ruthenium, and iridium from concentrate, the approximate composition of which is given in Table 1, involves hydrochlorination. The goal of this operation is to maximize the extraction of precious metals into solution. Along with the precious metals, the majority of impurities are also released into the solution. Hydrochlorination of the concentrate without prior preparation results in an increased yield of insoluble residue and decreased recovery of the target precious metals—rhodium, ruthenium, and iridium—into the final product, the solution.

Table 1 - Approximate composition of the concentrate

Concentrate containing rhodium, ruthenium, iridium Content, % Pt Pd Rh Ir Ru Au Ag Cu Ni Se Te 0.1
-
0.4 0.3
-
3.0 7.0
-
20.0 0.2
-
2.0 3.8
-
8.0 Less
0.15 Less
6.0 5.0
-
27.0 Less
0.5 0.15-
1.0 Less than 11.0 Fe As Pb Co Sb Cr Sn 0.1
-
0.3 Less
0.20 Less
0.30 Less
0.1 Less
0.05 Less
0.05 Less
1.2

The proposed method for extracting rhodium, ruthenium and iridium from concentrate involves preliminary leaching of the concentrate in a hydrochloric acid solution, converting most of the impurity elements into a dissolved form.

Leaching of the concentrate is carried out in a hydrochloric acid solution with a concentration of 200-210 g/l.

The following example does not limit the scope of the invention; a person skilled in the art will understand that variations of the method are possible.

Example of the method implementation

A reaction apparatus with a working volume of 45-55 ^dm3 is filled with 18.5 ^dm3 of water, 9.5 kg of concentrate are loaded, the mixing device is turned on, and 18.5 ^dm3 of hydrochloric acid (technical 35%, GOST 857-95, grade A) is poured in portions of 1-2 ^dm3 over 15-20 minutes. After adding the acid, the reactor heating is turned on, and the pulp is kept under stirring for 3 hours, maintaining a temperature of 70-90°C. Upon completion of leaching, the reactor cooling is turned on, and when the pulp temperature reaches below 45°C, it is unloaded into a Nutsche filter filled with polyester or polypropylene fabric. The Nutsche filter is connected to a vacuum, and the pulp is filtered off. The insoluble residue is washed on the filter with water to displace the solution.

The filtrate is pumped into prepared containers. The insoluble precipitate (IS) is removed from the Nutsche filter into prepared containers. All containers are subject to preliminary mass determination.

In order to increase productivity, it is possible to use a reaction apparatus of a larger volume, while maintaining the proportions of the input of concentrate, hydrochloric acid, and water.

Table 2 below shows the results of the concentrate leaching operation with hydrochloric acid.

Table 2 - Results of the concentrate leaching operation with hydrochloric acid

Product Units of measurement Pt Pd Rh Ir Ru Au Ag Initial concentrate % 0.16 0.99 14.55 1.13 3.84 0.02 0.30 Extraction into leaching solution % 3.95 2.67 14.23 7.34 11.70 <0.53 6.42 Product Units of measurement Cu Ni Fe Pb As Se Te Sn Initial concentrate % 26.80 0.02 0.14 0.01 0.48 0.15 2.28 1.19 Extraction into leaching solution % 80.86 39.46 ~100.0 63.21 14.82 5.26 31.77 11.52

The yield of insoluble residue is on average 43.6%.

Hydrochlorination

Hydrochlorination of the insoluble leaching residue is carried out in a reaction apparatus. In the first stage, water is added and the insoluble residue is loaded at a liquid:solid ratio of 2, taking into account the moisture contained in the insoluble leaching residue. Next, the mixing device is turned on and hydrochloric acid (technical 35%, GOST 857-95, grade A) is added in a volume equal to the amount of water (taking into account the moisture contained in the insoluble residue). After adding hydrochloric acid, the heating of the reaction apparatus is turned on and the pulp is heated to a temperature of 60-70°C. Once the temperature is reached, the heating is turned off and chlorine is added at a rate of 1.85 kg/kg of insoluble residue for 4-8 hours until a stable ORP value of 1020 ± 20 mV is achieved. The pulp is sent for further separation of precious metals.

Table 3 – comparative indicators of extraction into the target solution

Element Extraction into the target solution, % With direct hydrochlorination of concentrate During hydrochlorination of the insoluble residue after preliminary leaching of the concentrate Pt 66.8 51.59 Pd 89.3 65.67 Rh 37.3 53.76 Ir 30.9 52.42 Ru 2.1 49.39 Au 78.2 50.54 Ag 5.6 70.89

Thus, the method proposed in accordance with the present invention allows for a more than 50% reduction in the amount of feedstock required for the hydrochlorination step, thereby reducing the consumption of the most expensive reagent—chlorine—proportionally. The method also increases the recovery of target precious metals contained in the concentrate from the hydrochlorination step when leaching the concentrate in hydrochloric acid prior to the hydrochlorination step: rhodium, ruthenium, and iridium are recovered by 16.46%, 21.52%, and 47.29%, respectively.

Claims (1)

A method for extracting rhodium, ruthenium and iridium from concentrates, including a hydrochlorination operation, characterized in that the concentrate is preliminarily leached in a solution of technical hydrochloric acid with a concentration of 200-210 g/l and a leaching pulp is obtained, which is sent for filtration, and the insoluble leaching residue obtained as a result of filtration is subjected to hydrochlorination using chlorine at a rate of 1.85 kg/kg of insoluble residue for 4-8 hours to a stable ORP value of 1020±20 mV, the resulting hydrochlorination pulp is sent for further separation of the extracted metals.