A Simple Primary Amide for the Selective Recovery of Gold from Secondary Resources

Abstract

Waste electrical and electronic equipment (WEEE) such as mobile phones contains aplethora of metals of which gold is by far the most valuable.Herein asimple primary amide is described that achieves the selective separation of gold from am ixture of metals typically found in mobile phones by extraction into toluene from an aqueous HCl solution;u nlike current processes,r everse phase transfer is achieved simply using water.P hase transfer occurs by dynamic assembly of protonated and neutral amides with [AuCl 4 ] À ions through hydrogen bonding in the organic phase,asshown by EXAFS, mass spectrometry measurements,a nd computational calculations,and supported by distribution coefficient analysis.The fundamental chemical understanding gained herein should be integral to the development of metal-recovery processes,i n particular through the use of dynamic assembly processes to build complexity from simplicity.Gold is avaluable metal resource,not only as jewellery and for investment, but increasingly in modern electronics, medicine,a nd chemical catalysis. [1] Thel ow abundance of gold in its ores,c ombined with economic and societal issues associated with mining and separation operations,means that e-waste streams are attractive sources of this metal. [2] The gold content of WEEE is estimated to be 80 times that found in primary mining deposits,r epresenting 3% of the world mine supply in 2007, and its recovery would decrease the environmental and societal footprint of mining along with potential savings of 17 000 t/t in carbon dioxide emissions. [3] Furthermore,current processes for the recovery of gold from WEEE are hazardous,asthey often use toxic chemicals such as cyanide.A ss uch, governments worldwide are developing waste-recycling strategies to exploit e-waste through "urban mining", [4] with the market forecasted to have ac ompound annual growth rate of 20.6 %between 2015 and 2020 from its USD 1.66 10 9 value in 2014. [5] These strategies combine metal-leaching,-separation, and -precipitation technologies which increasingly require the use of "green" materials, reagents,a nd processes for societal and economic acceptance. [6] Therecovery of metals using solvent extraction can offer significant environmental advantages over energy-and capital-intensive pyrometallurgical routes,e specially if as ingle metal is targeted. [7] Selectivity of extraction is achieved by designing areagent that favors the phase transfer of one metal from am ixed-metal aqueous leach solution to an organic phase. [8] Currently,2 5% of global Cu recovery is carried out by hydrometallurgy using phenolic oxime reagents, [8] the development of which relied on an understanding of the coordination and supramolecular chemistry of copper.In contrast, the chemistry that underpins the recovery of gold by solvent extraction is poorly understood. Commercial reagents such as MIBK (isobutyl methyl ketone), DBC (diethylene glycol butyl ether), and 2-EH (2-ethylhexanol) recover gold as its metalate [AuCl 4 ] À from aqueous HCl by solvent extraction [...

Bio-inspired nano-traps for uranium extraction from seawater and recovery from nuclear waste

“…Given the well-known strong interaction between the amidoxime group and uranyl in conjunction with its cost-effective synthesis 31 – 33 , as well as the excellent hydrogen bonding and electron donating capabilities of the amino group 34 , 35 , they were the coordinative site and reinforcing group of choice, respectively, to demonstrate the proof-of-concept. Considering the importance of spatial distribution of amine and amidoxime for their cooperation, a series of functionalized monomers with an amino substituent in different positions relative to amidoxime were designed to construct into hierarchical porous polymers.…”

Evaluation of Simple Amides in the Selective Recovery of Gold from Secondary Sources by Solvent Extraction

“…We recently reported that the simple primary amide L 1 (Figure 1) can strongly and selectively recover gold by solvent extraction from an aqueous mixture of metals representative of those found in WEEE. 32 The use of this reagent offers significant advantages over current commercial gold extractants through enhanced selectivity, efficiency, safety and overall mass-balance. It was seen that the primary amide L 1 extracts gold as supramolecular assemblies of the gold(III) chloridometalate AuCl4and combinations of L 1 and H(L 1 )2 + , e.g.…”

Pyridinethiol‐Assisted Dissolution of Elemental Gold in Organic Solutions

“…Thes tudy was initiated by conducting Au dissolution experiments using our previously published procedure: [18] A small amount of fine Au powder was added to a16mm EtOH solution of 4-PSH, and the mixture was stirred for 23 hunder 10 bar of O 2 at 22 8 8C. This resulted in only 14 %o fd issolved Au ( [3][4][5][6], showing that the dissolution efficiency correlates directly with the 4-PSH concentration. Importantly,q uantitative dissolution of the Au sample was achieved either with an extended reaction time and al ow 4-PSH concentration or within 25 min using a4 -PSH concentration of 203 mm (Table 1, entries 2a nd 7).…”