resumo
Precipitation processes, if selective, present a simple and economical alternative for the recovery of critical metals from primary and secondary ores including electronic wastes. In this work, the recovery of gold by precipitation from both mono-elemental solutions and real CPU leach solution was demonstrated using hydro-philic quaternary ammonium salts. The gold precipitation yield is shown to be dependent on the apolar volume of the precipitant, with the addition of tetrabutylammonium-based salts resulting in the recovery of over 90 % of gold from synthetic solutions. The origin of gold precipitation selectivity relative to common metal ions upon addition of tetrabutylammonium nitrate ([N4444][NO3]) was assigned by X-ray crystal structure to the formation of size selective apolar cavity between neighbouring [N4444]+ cation and the [AuCl4]- anion. Following opti-misation as a function of the gold to precipitant molar ratio, aqua regia concentration and time, approximately 70 % of gold could be recovered from waste CPU leach solution with a final purity of 91.4 % (mol/mol). [N4444] [NO3] proved to be a versatile gold extractant and could be further applied as part of an acidic aqueous biphasic system at higher aqua regia concentrations were precipitation yields decreased, ensuring a selective gold recovery across a range of leachate conditions. The disclosed results improve the circularity of gold by providing a new avenue for its simple recycling.
palavras-chave
EXTRACTION; SYSTEMS; PURIFICATION; ABSORPTION; SPECIATION; COMPLEXES; EXCHANGE; CHLORIDE; METALS; ANIONS
categoria
Engineering
autores
Nogueira, AFM; Carreira, ARF; Vargas, SJR; Passos, H; Schaeffer, N; Coutinho, JAP
nossos autores
Ana Rita Carreira
Colaborador
André Nogueira
Estudante de doutoramento
Helena Isabel Sousa Passos
Investigador Júnior
Nicolas Schaeffer
Investigador Auxiliar
Sílvia Juliana Rodriguez Vargas
Bolseiro de pós-DoutoramentoProjectos
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
CICECO - Aveiro Institute of Materials (UIDP/50011/2020)
Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)
agradecimentos
The authors would like to thank Dr. Paula Brandao and Maria C.C. Azevedo for help with the SCXRD and Raman data acquisition, respectively. This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC). H. Passos and A.R.F. Carreira acknowledge FCT, under the Scientific Employment Stimulus Individual Call (CEECIND/00831/2017) and Ph.D. grants SFRH/BD/143612/2019, respectively. N. Schaeffer acknowledges the national funds (OE), through FCT in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.