RU2847949C1 - Method for desorption of palladium with a selective silicate-based sorbent - Google Patents

Abstract

FIELD: hydrometallurgy of precious metals.

SUBSTANCE: invention can be used for the selective extraction of palladium from hydrochloric acid solutions. A hydrochloric acid solution containing palladium and other noble metals is passed through a silicate-based sorbent with a thioether functional group. The saturated sorbent is treated with a sodium phosphate buffer with a pH of 6.5-9 and a phosphate concentration of 1-5 M at a rate of 100-500 ml/h in a volume corresponding to the volume of the sorbent column. Then, desorption is carried out with a solution of ammonium hydrophosphate with a concentration of 1-5 M. Palladium is predominantly transferred to the desorbate.

EFFECT: selectivity of palladium recovery and elimination of premature formation of dichlorodiamminepalladium precipitate in the sorbent body.

6 cl, 1 dwg, 1 tbl, 6 ex

Description

Field of technology

The invention relates to the field of hydrometallurgy and can be used for the selective extraction of palladium from hydrochloric acid process solutions containing platinum group metals in various concentrations.

Prior art

The main method for extracting platinum and palladium is their precipitation in the form of poorly soluble salts of ammonium chloroplatinate and dichlorodiamminepalladium (Metallurgy of noble metals, textbook for universities / Maslenitsky I.N., Chugaev L.V., Moscow: -Metallurgy, 1987, pp. 414-415).

The disadvantages of this method include high residual contents of these metals (more than 100 mg/l for each metal), due to the solubility of these compounds. Also, cross-contamination of salts due to the co-precipitation of isostructural compounds (NH ₄ ) ₂ PdCl ₆ and (NH ₄ ) ₂ PtCl ₆ , Pd(NH ₃ ) ₂ Cl ₂ and Pt(NH ₃ ) ₂ Cl ₂ , which requires measures for additional recovery of platinum and palladium and additional purification of the resulting salts.

Sorption of platinum and palladium on ion-exchange and chelating sorbents allows for the almost complete extraction (desorption) of these metals. However, most known methods result in the combined sorption and desorption of platinum and palladium, necessitating their subsequent separation by salt precipitation. Therefore, the aforementioned shortcomings cannot be completely overcome.

A method is known for separating platinum and palladium using a selective sulfur-containing sorbent, in which a solution is brought into contact with a ligand containing sulfur and an electron-withdrawing group, said solution is removed from contact with a compound with which the desired ions have formed a complex, the compounds that have formed a complex with the desired ions are brought into contact with a volume of a receiving solution smaller than said first volume, having either a greater affinity for the desired ions than said compound, or a greater affinity for this compound than the desired ions, which breaks the complex between this compound and the desired ions, and the desired ions are restored in concentrated form in said smaller volume of the receiving solution (patent US5446182, published 08/29/1995).

A method for removing and concentrating desired ions, such as Pd2 ⁺ , even if they are present in low concentrations, from a feed solution containing a mixture of ions of these metals with ions that are undesirable to be removed is known, disclosed in application WO2013/168035A1, published 11/14/2013. The method comprises passing a feed solution enriched with desired ions through a separation device containing an ultrasonically treated MR resin with sulfur-form molecules and electron-withdrawing groups, resulting in the formation of Pd2 ⁺ complexes on the surface of the MR resin, subsequently removing the desired ions from the MR resin by contacting the MR resin with a smaller volume of eluent having a greater affinity for the desired ions than the sulfur- and electron-withdrawing group-containing ligand portion of the MR resin, and then extracting the desired ions from the receiving solution using known extraction methods.

The disadvantage of the described methods for palladium extraction is the following. Based on the structure of the sorbents used in the described methods, it is assumed that palladium sorption occurs through the formation of complexes with the functional groups of the sorbent according to the equation:

2 SiO ₂ -R ¹ -SR ² + [PdCl ₄ ] ^2- → (SiO ₂ -R ¹ (R ² )S) ₂ PdCl ₂ + 2Cl ^-

Platinum, however, practically does not form these complexes due to the low rate of ligand exchange and passes through the sorbent unchanged. Potassium sulfite is used for palladium desorption. In this case, desorption proceeds according to the equation:

(SiO ₂ -R ¹ (R ² )S) ₂ PdCl ₂ + (4-n)K ₂ SO ₃ → 2 SiO ₂ -R ¹ -SR ² + K _(6-n) [Pd(SO ₃ ) _(4-n) Cl _n ] + (2-n)KCl

The resulting palladium complex K _(6-n) [Pd( _SO3 ) _{(4-n) Cln} ] requires subsequent destruction to obtain pure palladium, i.e., time-consuming reactions requiring additional reagents and equipment. This, however, results in a low recovery rate (approximately 50%). Furthermore, the use of potassium sulfite leads to degradation of the silicate sorbent. All of this contributes to high operating costs for palladium recovery.

Disclosure of invention

The technical problem is the creation of a simple, economical and technologically advanced method for desorbing palladium from a selective silicate-based sorbent, ensuring the highest yield of desorbate and, accordingly, an increase in the degree of extraction of pure palladium, and using alternative reagents in the desorption process that are free from the disadvantages described above.

The technical result consists in eliminating the premature formation of dichlorodiamminepalladium precipitate in the sorbent body, as well as increasing the selectivity of desorption while simultaneously increasing the degree of extraction to 50% in 8 fractions.

The technical result is achieved in that in the method for desorbing palladium from a selective silicate-based sorbent containing a thioether functional group, according to the invention, the sorbent is pre-treated with a sodium phosphate buffer with a pH in the range from 6.5 to 9, and desorption is carried out with ammonium hydrogen phosphate.

In particular embodiments of the method:

• the preferred pH range of sodium phosphate buffer is 7.5-8.5;

• buffer treatment is carried out at a rate of 100-500 ml/h;

• and/or buffer treatment is carried out by passing it through a column with a sorbent in a volume corresponding to the volume of the column;

• and/or buffer treatment is carried out with a phosphate concentration from 1 M to 5 M;

• and/or desorption is carried out with a concentration from 1 M to 5 M.

Pretreatment of the sorbent ensures a pH level that prevents premature precipitation of dichlorodiamminepalladium. Subsequent desorption with ammonium hydrogen phosphate, which has a pH similar to that of the pretreatment solution (pK _a2 = 7.21), allows for the highest yield of desorbate, while maintaining a high degree of stability, enabling long-term storage while maintaining easy reprocessing by any known method.

Palladium can be desorbed using ammonium salt solutions after adjusting the pH to 8–8.5. Desorption can be described by the following equation:

(SiO ₂ -R ¹ (R ² )S) ₂ PdCl ₂ + 4NH ₄ ⁺ → [Pd(NH ₃ ) ₄ ]Cl ₂ + 4H ⁺

During the reaction, the solution is acidified by the resulting protons, which leads to a decrease in pH below 5.5 and the formation of a precipitate of dichlorodiamminepalladium in the body of the sorbent:

[Pd(NH ₃ ) ₄ ]Cl ₂ + 2H ⁺ → [Pd(NH ₃ ) ₂ Cl ₂ ]↓+ 2NH ₄ ⁺

To prevent premature formation of dichlorodiamminepalladium precipitate, it is recommended to use salts of acids with buffering properties in the pH range of 6-8 (i.e., with a pKa in the same range). Among the widely available compounds, ammonium hydrogen phosphate ( _pKa2 = 7.21) can be used for this purpose. When using it, the overall desorption equation is described by the following equation:

(SiO ₂ -R ¹ (R ² )S) ₂ PdCl ₂ + 4(NH ₄ ) ₂ HPO ₄ → 2SiO ₂ -R ¹ -SR ² + [Pd(NH ₃ ) ₄ ]Cl ₂ + 4NH ₄ H ₂ PO ₄

Dichlorodiamminepalladium can be easily obtained from the resulting desorbates by adding hydrochloric acid to a pH of 1-3. Using a low-cost ammonium hydrogen phosphate solution for desorption is economical, and the desorbates obtained with this solution are highly stable and can be easily processed into dichlorodiamminepalladium using known methods.

Brief description of the drawings

The invention is explained by graphic materials, where Fig. 1 shows a graph of the cumulative curves of palladium desorption according to the prototype method and the claimed method (the curves according to examples 4, 5 and 6 are superimposed on each other).

Implementation of the invention

The claimed method for desorbing palladium from a silicate-based selective sorbent is illustrated by the examples below. Each example used the same saturation solution (a palladium-containing solution), the composition of which is shown in Table 1.

Example 1 (Prototype)

Palladium was desorbed using a column containing 60 ml of a silicate-based sorbent with a thioether functional group. The column was pre-saturated by passing a palladium-containing solution through it. The sorbent was then washed with 180 ml of 1 M HCl to remove the saturated solution from the column and with 180 ml of water to remove the acid solution. Palladium was desorbed using a 1 M K ₂ SO ₃ solution acidified to pH 4. The desorbate from the column outlet was fractionated in 30 ml portions. Aliquots of the resulting solutions were mixed with an equal volume of 6 M HCl and analyzed by inductively coupled plasma atomic emission analysis. The fraction compositions (after accounting for dilutions) are presented in Table 1.

Example 2

A column containing 60 ml of a sorbent similar to that in Example 1 was used for palladium desorption. The sorption column was pre-saturated by passing a palladium-containing solution through it. Palladium was desorbed using a 1 M solution of (NH ₄ ) ₂ HPO ₄ . During the experiment, a longer desorption time was also observed (Fig. 1) and the formation of a certain amount of dichlorodiamminepalladium precipitate in the desorbate and the column with the sorbent (which dissolved by the end of desorption). For analysis, a 5 ml aliquot was mixed with 25 ml of 6 M HCl. The resulting dichlorodiamminepalladium precipitate dissolved upon further heating. The resulting solution was made up to 50 ml with water and submitted for analysis.

Example 3

A column containing 60 ml of a sorbent similar to the one in Example 1 was used for palladium desorption. The sorption column was pre-saturated by passing a palladium-containing solution through it. Palladium was desorbed using a 2 M solution of (NH ₄ ) ₂ HPO ₄ . This prevented the formation of dichlorodiamminepalladium in the desorbate and in the column.

Example 4

A column containing 60 ml of a sorbent similar to the one in Example 1 was used for palladium desorption. The sorption column was pre-saturated by passing a palladium-containing solution through it. Then, 60 ml of sodium phosphate buffer with a pH of 8 and a phosphate concentration of 1 M was passed through the column at a flow rate of 300 ml/h. Palladium was desorbed using a 1 M solution of (NH ₄ ) ₂ HPO ₄ . No precipitation of dichlorodiamminepalladium was observed.

Due to treatment with phosphate buffer, chloride ions were replaced in the sorbed palladium complexes:

(SiO ₂ -R ¹ (R ² )S) ₂ PdCl ₂ + 2Na ₂ HPO ₄ → (SiO ₂ -R ¹ (R ² )S) ₂ Pd(OH) ₂ + 2NaH ₂ PO ₄ + 2NaCl

After removal of chlorides from the sorbent, desorption occurs without the formation of dichlorodiamminepalladium, even at an ammonium hydrogen phosphate concentration of 1 mol/l:

(SiO ₂ -R ¹ (R ² )S) ₂ Pd(OH) ₂ + 2(NH ₄ ) ₂ HPO ₄ → 2SiO ₂ -R ¹ -SR ² + [Pd(NH ₃ ) ₄ ](H ₂ PO ₄ ) ₂ + H ₂ O

Example 5. Differs from example 4 in that before desorption, 60 ml of sodium phosphate buffer with pH 7 was passed through the column with the sorbent. During desorption, the formation of dichlorodiamminepalladium precipitate was not detected, but desorption lasted longer than in example 4.

Example 6. Differs from example 4 in that before desorption, 60 ml of sodium phosphate buffer with pH 9 was passed through the column with the sorbent. During desorption, no differences from example 4 were detected.

Table 1 - Composition of the saturation solution and desorption fractions

Faction number Solution composition, mg/l Degree of desorption (from the first 4 fractions), % Pt Pd Rh Ir Ru Au Ag Saturation solution 252.3 1,037.9 7.9 1.1 1.7 1.9 1.7 Desorption according to example 1 (prototype) 1 1.0 31.6 <0.2 <0.2 <0.2 <1.0 <0.2 58 2 7 122 <1 <1 <1 <5 <1 3 8 11,250 <1 <1 <1 32 <1 4 8 6,200 <1 <1 <1 48 3 5 5 1,002.3 <1 <1 <1 20 3 6 5 148.8 <1 <1 <1 16 2 7 4 8.0 <0.2 <0.2 <0.2 6 1 8 3 2.5 <0.2 <0.2 <0.2 2 1 Desorption according to example 2 1 1.0 18.2 <0.2 <0.2 <0.2 <1.0 10.8 81 2 3 138 <1 <1 <1 <5 <1 3 4 5 299 <1 <1 <1 <5 <1 4 5 17,488 <1 <1 <1 42 2 5 5 11,634 <1 <1 <1 82 2 6 5 5 229 <1 <1 <1 42 3 7 5 2,663 <1 <1 <1 21 9 8 5 733 <1 <1 <1 9 3 Desorption according to example 3 1 1.0 46.4 <0.2 <0.2 <0.2 <1.0 <0.2 86 2 2 14,732 <1 <1 <1 <5 1 3 3 23,763 <1 <1 <1 56 1 4 4 6,548 <1 <1 <1 56 1 5 4 601 <1 <1 <1 18 8 6 3.4 86.4 0.6 <0.2 <0.2 6.0 14.2 7 2.6 31.0 0.4 <0.2 <0.2 2.8 22.4 8 2.0 18.6 0.4 <0.2 <0.2 1.6 26.8 Desorption according to example 4 1 0.8 40.8 <0.2 <0.2 <0.2 <1.0 <0.2 99 2 1 17,400 <1 <1 <1 <5 1 3 4 24,018 <1 <1 <1 16 1 4 6 7 114 <1 <1 <1 58 <1 5 1 1,041.4 <1 <1 <1 18 4 6 0.8 155.8 0.2 <0.2 <0.2 7.0 7.2 7 0.6 9.2 0.2 <0.2 <0.2 1.8 12.4 8 0.4 2.0 <0.2 <0.2 <0.2 1.2 14.8 Desorption according to example 5 1 1.0 35.8 <0.2 <0.2 <0.2 <1.0 <0.2 98 2 2 12,632 <1 <1 <1 <5 <1 3 3 23,100 <1 <1 <1 32 <1 4 3 5,600 <1 <1 <1 48 1 5 3 970.0 <1 <1 <1 20 1 6 1 210.0 <1 <1 <1 5 <1 7 0.7 9.0 <0.2 <0.2 <0.2 3.5 0.7 8 0.7 2.0 <0.2 <0.2 <0.2 1.2 0.5 Desorption according to example 6 1 1.0 39.1 <0.2 <0.2 <0.2 <1.0 <0.2 97 2 2 18,300 <1 <1 <1 <5 <1 3 5 22,150 <1 <1 <1 32 <1 4 4 5,000 <1 <1 <1 48 1 5 3 960.6 <1 <1 <1 20 1 6 1 180.9 <1 <1 <1 5 <1 7 0.8 8.9 <0.2 <0.2 <0.2 3.5 0.7 8 0.6 2.0 <0.2 <0.2 <0.2 1.2 0.5

During the tests conducted using the stated methods, no degradation of the silicate sorbent in an alkaline environment was observed.

Thus, the claimed method ensures the highest yield of stable desorbate from a selective silicate-based sorbent by eliminating the premature formation of dichlorodiamminepalladium precipitate in the body of the sorbent during the reaction, which generally determines the simplicity, cost-effectiveness and technological effectiveness of this method for extracting palladium.

Claims (6)

1. A method for desorbing palladium from a selective silicate-based sorbent containing a thioether functional group, characterized in that the sorbent is treated with a sodium phosphate buffer with a pH in the range from 6.5 to 9, and desorption is carried out with ammonium hydrogen phosphate. 2. The method according to claim 1, characterized in that the preferred pH range of the sodium phosphate buffer is 7.5-8.5. 3. The method according to paragraph 1, characterized in that the treatment with buffer is carried out at a rate of 100-500 ml/h. 4. The method according to paragraph 1, characterized in that the treatment with the buffer is carried out by passing it through a column with a sorbent in a volume corresponding to the volume of the column. 5. The method according to paragraph 1, characterized in that the treatment with buffer is carried out with a phosphate concentration of 1 to 5 M. 6. The method according to paragraph 1, characterized in that desorption is carried out with a concentration of 1 to 5 M.