A simple process for the recovery of palladium from wastes of printed circuit boards

Abstract

An efficient process for the recovery of palladium from waste printed circuits boards (PCBs) is detailed. Palladium is employed as an electrode material in multi-layer ceramic capacitors (MLCCs). These components can be easily removed from PCBs by desoldering. As palladium is alloyed with silver, its dissolution is readily achieved using dilute nitric acid. As a result, a solution containing palladium along with base metals, mostly copper and iron, is obtained. This solution is then processed through solvent extraction (SX) with a solvent based on N,N'-dimethyl,N,N'-dibutyltetradecylmalonamide (BDMA), a robust extracting molecule previously developed in the frame of the reprocessing of waste nuclear fuel. The volume of effluents generated during the SX sequence is limited: iron scrubbing is operated with a very low aqueous to organic phase volume ratio, no specific metal chelator is required for palladium stripping, and no shift from acidic to basic media is required. Finally, a ca 1 g/L Pd(II) aqueous solution with 99,4% purity is obtained, from which palladium is directly isolated as dichlorodiammine palladium(II) salt (Pd(NH 3 ) 2 Cl 2 ) after precipitation with ammonia. Overall, palladium is quantitatively recovered from the leaching solution, and no palladium was detected in the remaining solid residue. Purity is high, as no contaminating metal could be detected in the final palladium salt. The proposed approach is simple and complementary to existing hydrometallurgical processes dedicated to gold and copper recovery.

From Electronic Waste to Suzuki−Miyaura Cross‐Coupling Reaction in Water: Direct Valuation of Recycled Palladium in Catalysis

“…The use of a solvent extraction process has two further key features: it enables Pd concentration (up to 10‐fold concentration between leaching solution and surfactant solution for catalysis) and separation of Pd from the nitric acid employed for leaching (initially 3 M aqueous solution). The amount of waste generated by the proposed process is very low (only 10 % of the volume of the organic phase employed), and especially in comparison with previously performing processes developed at our laboratory, which are already very well positioned . It is key to mention that, without surfactant, back extraction of Pd from a BESO based organic phase requires the use of a specific aqueous layer, which has then to be processed in order to isolate Pd, usually by precipitation after addition of ammonia followed by hydrochloric acid.…”

“…Washing of the organic phase with a small amount of water (volume phase ratio organic/aqueous of 10) is possible without measurable loss of Pd from the organic layer (less than 1 %), and enables to bring concentrations of unwanted metals below limit of detection (LoD) in the case of BESO (Table ). In the case of MA, there is still a small amount of Fe and Cu (Table ), which removal could be envisioned using a second washing with dilute nitric acid, albeit with 4 % Pd loss, as observed during our previous studies, and which was not attempted here …”

“…It is preferable to perform the concentrating extraction stepwise, i. e. working with moderate A/O during extraction, and with A/O below unity during the back extraction (Table , entries 1 and 3). The Pd that is not found in the final aqueous micellar solution remains in the organic phase after incomplete back extraction, and is not lost: it is possible to recycle the organic phase containing a small Pd hold‐up, as it is not deleterious to its extraction properties . When using recycled Pd, in order to keep the Pd quantity constant relative to cross‐coupling reaction reagents, it was necessary to adapt the amount of surfactant solution employed in the cross‐coupling reaction, that is, to increase the volume of aqueous solution employed in order to reach the 1.1 mol% Pd amount required.…”

“…This operation leaves most Au and Cu on the residual naked board, along with a chemical desoldering bath, the regeneration of which has been previously studied . Thus, Pd present in WEEE can be easily available as Pd II in a relatively simple aqueous nitrate solution, which contains base metals such as Cu, Ni, Co, Zn, La, Fe or Al (Figure ) . We previously reported the selective extraction of Pd from this mixture, using either a sulfoxide (bis(2‐ethylhexyl)sulfoxide, BESO) or a diamide ( N , N ’‐dimethyl, N , N ’‐dibutyltetradecylmalonamide, MA) extractant (see Figure S1 in the Supporting Information for chemical structures) .…”

Electrochemical recovery of low concentration of palladium from palladium(II) chloride of electroplating wastewater

“…Performance of the electrogenerative system is on a par with other Pd recovery processes from e-waste. [39][40][41][42][43][44][45]…”