From trash to resource: a green approach to noble-metals dissolution and recovery

Abstract

Abstract:A process based on the lixiviant properties of organic mixtures of dihalogen/S,S-ligands, N,N′-dimethylperhydrodiazepine-2,3-dithione (Me 2 dazdt) and tetraalkylthiuramdisulphide (Et 4 TDS) in the presence of diiodine, for gold recovery from the non-ferrous metal fraction of real shredded waste electric and electronic equipment (WEEE), is presented here. Selective dissolution of metals is achieved through a sequence of three steps where the oxidation of different kinds of metals is achieved by using: (1) refluxing water solutions of HCl 1:5 under Ar atmosphere (Sn, Zn, etc.); (2) water solutions of NH 3 /(NH 4 ) 2 SO 4 mixtures in the presence of H 2 O 2 on the resting sample (Cu, Ag); and (3) acetone solutions of Me 2 dazdt or Et 4 TDS/ I 2 mixtures on the final residue (Au). Each step is followed by a further treatment for: (1) metal recovery, in the case of Au, Cu, Ag; and (2) inertization, in the case of heavy metals. As a whole, the process is very promising for effective recovery of gold and other valuable noble-metals and for using non harmful reagents in mild conditions.

Cooperative Ligands in Dissolution of Gold

“…Unfortunately, these methods require harsh reaction conditions or hazardous reagents, [5–7] or both, in addition they are also unselectively dissolving all metals simultaneously. Recently, a new approach based on organic solvents and reactive ligand systems has been introduced [8–25] . These methods are mainly based on S ‐donor ligands [8–13,17,18] such as dithioxamides, [10] tetraethylthiuram disulfides, [8–13] pyridinethiols, [17,18] and/or halides [19–24] .…”

Ionic liquids with trichloride anions for oxidative dissolution of metals and alloys

“…The results ( Fig. S3 in ESI †) showed that the imidazolium cations were attacked by chlorine gas, because new peaks were observed in the 1 Table 1), no changes in the NMR spectra were observed after transformation of the chloride into the trichloride ILs. ESI-MS spectra in the positive ionisation mode showed that the mass-to-charge ratios are in agreement with the cationic species in trichloride ILs (see ESI †).…”

Oxidative Dissolution of Metals in Organic Solvents

“…The mixture of Et 4 TDS and I 2 was also applied for gold recovery from real Waste Electrical and Electronic Equipment (WEEE) materials. 60 …”