The refining method of palladium is mainly a combination of chloropalladium acid precipitation and ammonia complexation.
The solution containing palladium 40-50g/L is oxidized by chlorine or, for example, hydrogen peroxide, and a deep red (NH4)2PdCl6 crystal is precipitated by adding ammonium chloride with a theoretical excess of 10%-15%:
H 2 PdCl 4 +2NH 4 Cl+Cl 2 ====(NH 4 )2PdCl 6 ↓+2HCl
It was isolated by filtration after an impurity base metals, palladium salts of boiling water method for the reduction of palladium soluble alkylene ammonium chloride:
(NH 4 )2PdCl 6 +H 2 O====(NH 4 ) 2 PdCl 4 +HCl+HClO
The oxidative precipitation was repeated 2-3 times to completely separate the ruthenium metal. Palladium solution is heated to 80 ° C plus ammonia to complex palladium:
H 2 PdCl 4 +4NH 4 OH====[Pd(NH 3 ) 4 ]Cl 2 +4H 2 O+2HCl
Control pH8~9, filter out other precious metal impurity precipitates, light-colored [Pd(NH 3 ) 4 ]Cl 2 solution is acidified to pH 0.5-1 with hydrochloric acid at room temperature to form yellow [Pd(NH 3 ) 2 ]Cl 2 precipitation:
[Pd(NH 3 ) 4 ]Cl 2 +2HCl====[Pd(NH 3 ) 2 ]Cl 2 ↓+2NH 4 Cl
After filtration, it is complexed with ammonia water, acidified with hydrochloric acid, and repeated 2-3 times to obtain pure dichlorodiamine chromium palladium salt. The combined method can refine 80-99% crude palladium into 99.99% pure palladium with a direct yield of 97%-98%.
The preparation of pure metal palladium has a satin burning method and a direct reduction method.
(1) Calcination method Pure (NH 4 ) 2 PdCl 6 or [Pd(NH 3 ) 2 ]Cl 2 is placed in a porcelain crucible and capped, dried in a dedicated muffle furnace, and then heated to 500-600 ° C. The metal palladium is calcined, but part of the palladium is oxidized to form PdO. It needs to be hydrogen-reduced at 500-600 ° C in a tube furnace. After cooling to 100 ° C, it is protected by an inert atmosphere to room temperature to obtain sponge metal palladium:
(2) The direct reduction method may use two reducing agents of formic acid and hydrazine hydrate.
Reduction of metal palladium by direct recovery from weakly basic palladium-containing pure solution with formic acid:
H 2 PdCl 4 +HCOOH=====Pd↓+4HCl+CO 2 ↑[next]
The fine palladium powder produced by the reduction of formic acid adsorbs a large amount of gas, and requires high-temperature hydrogen reduction and cooling under an inert atmosphere to obtain metal palladium.
The metal palladium is produced by reduction of hydrazine hydrate directly from the palladium ammine complex.
Restore from solution:
2Pd(NH 3 )4Cl 2 +N 2 H 4 ·H 2 O=====2Pd↓+4NH 4 Cl+3N 2 ↑+H 2 O
Restore in suspension:
2Pd(NH 3 )2Cl 2 +N 2 H 4 ·H 2 O====2Pd↓+4NH 4 Cl+N 2 ↑+H 2 O
The metal palladium produced by the reduction of hydrazine hydrate is relatively dense, with less adsorbed gas and no need for high temperature hydrogen reduction.
The Chinese metal palladium product standard (GB1420-89) is shown in the table.
China Metal Palladium Product Standard ( GB1420-89 ) /% | ||||||||||||
species | Pd | Pt | Rh | Ir | Au | Cu | Fe | Ni | Al | Pb | Si | Total impurity |
HPdt-1 | 99.99 | 0.003 | 0.002 | 0.002 | 0.002 | 0.001 | 0 | 0 | 0 | 0.001 | 0.003 | 0.01 |
HPd-2 | 99.95 | 0.02 | 0.02 | 0.02 | 0.02 | 0.005 | 0.01 | 0.01 | 0 | 0.005 | 0.005 | 0.05 |
HPd-3 | 99.9 | 0.03 | 0.03 | 0.03 | 0.05 | 　 | 0.01 | 0.01 | 0 | 0.01 | 0.01 | 0.1 |
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