Recovery of Metals from Electronic Waste-Printed Circuit Boards by Ionic Liquids, DESs and Organophosphorous-Based Acid Extraction

Abstract

The extraction of metals from waste printed circuit boards (WPCBs) with ionic liquids (ILs), Deep Eutectic Solvents (DESs) and organophosphorous-based acid (Cyanex 272) has been presented. The study was undertaken to assess the effectiveness of the application of the new leaching liquids, and the new method of extraction of metals from the leachate and the solid phase with or without the leaching process. Solvent extraction from the liquid leachate phase has been studied in detail with popular ILs, such as tetraoctylphosphonium bromide, {[P8,8,8,8][Br] and tributyltetradecylphosphonium chloride, [P4,4,4,14][Cl] using Aqueous Biphasic Systems (ABS) method. Trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate, [P6,6,6,14][Cyanex272], ([P6,6,6,14][BTMPP]), trihexyltetradecylphosphonium thiocyanate, [P6,6,6,14][SCN], methyltrioctylammonium chloride (Aliquat 336), as well as bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) were also used in the extraction of metals from the leachate. Two DESs (1) {choline chloride + lactic acid, 1:2} and (2) {choline chloride + malonic acid, 1:1} were used in the extraction of metals from the solid phase. The extraction behavior of metals with DESs was compared with that performed with three new bi-functional ILs: didecyldimethylammonium salicylate, [N10,10,1,1][Sal], didecyldimethylammonium bis(2-ethylhexyl) phosphate, [N10,10,1,1][D2EHPA], and didecyldimethylammonium bis(2,4,4-trimethylpentyl) phosphinate, [N10,10,1,1][Cyanex272]. The [P6,6,6,14][Cyanex272]/toluene and (Cyanex 272 + diethyl phosphite ester) mixtures exhibited a high extraction efficiency of about 50–90% for different metal ions from the leachate. High extraction efficiency of about 90–100 wt% with the ABS method using the mixture {[P8,8,8,8][Br], or [P4,4,4,14][Cl] + NaCl + H2O2 + post-leaching liquid phase} was obtained. The DES 2 revealed the efficiency of copper extraction, ECu = 15.8 wt% and silver, EAg = 20.1 wt% at pH = 5 from the solid phase after the thermal pre-treatment and acid leaching. The solid phase extraction efficiency after thermal pre-treatment only was (ECu = 9.6 wt% and EAg = 14.2 wt%). The use of new bi-functional ILs did not improve the efficiency of the extraction of metal ions from the solid phase. Process factors such as solvent concentration, extraction additives, stripping and leaching methods, temperature, pH and liquid/solid as well as organic/water ratios were under control. For all the systems, the selectivity and distribution ratios were described. The proposed extraction processes can represent alternative paths in new technologies for recovering metals from electronic secondary waste.

Recovery of Strategic Metals from Waste Printed Circuit Boards with Deep Eutectic Solvents and Ionic Liquids

“…The WPCB blend was used after the process of mechanical destruction. In the next step, the thermal pre-treatment at T = 1023 K for 7 h was carried out in a resistance chamber furnace (IZO), 16.1 kW, as described in our previous work [46] (see Figure 1). The high temperature helps to decompose the bonding force between particles of the material.…”

“…A new solvent extraction procedure has been proposed by many authors using thermal pre-treatment, different leaching procedures, and different ILs with different additives to recover Cu, Ag, Pd, Ni, Al, Au, Fe, and Zn from the solid material of WPCBs [3,5,[42][43][44][45][46]. In hydrometallurgical processes for recycling metals, different acids and alkalis are commonly used to extract metals such as copper, gold, silver, and palladium [5].…”

“…In our recent study, extraction with the IL, DESs and Cyanex 272 in the recovery of metals from WPCBs after thermal pre-treatment and leaching with different acids was proposed [46]. For the ILs, the aqueous biphasic system (ABS) method and DESs were used to extract metal ions from the leachate and the solid phase after leaching to the extent of 20-30 wt% of metals [46].…”

“…In our recent study, extraction with the IL, DESs and Cyanex 272 in the recovery of metals from WPCBs after thermal pre-treatment and leaching with different acids was proposed [46]. For the ILs, the aqueous biphasic system (ABS) method and DESs were used to extract metal ions from the leachate and the solid phase after leaching to the extent of 20-30 wt% of metals [46]. Various methods of recycling valuable metals have been developed with ILs and DESs with different additives, as well as using organophosphorusbased acids, and are presented in many works [14,19,47,48].…”

Green Deep Eutectic Solvents (DESs) for Sustainable Metal Recovery from Thermally Treated PCBs: A Greener Alternative to Conventional Methods

“…[30e] The use of green solvents for metal extraction from e-waste is a promising area of research with the potential to reduce the environmental impacts of traditional mining processes. Lactic acidÀ ChCl, [32] malonic acidÀ ChCl, [32] and ethylene glycolÀ ChCl [33] have been used to extract metals from WPCBs, covering limited aspects. However, no detailed study of formic acid-choline chloride and urea-choline chloride in metal extraction from WPCBs has been done in the past to the best of our knowledge.…”