Search

Revised legislation and bans on imports of waste electrical and electronic equipment (WEEE) into many Asian countries for treatment are driving the need for more efficient WEEE fractionation in Europe by expanding the capacity of treatment plants and improving the percentage recovery of materials of economic value. Data from a key stakeholder survey and consultation are combined with the results of a detailed literature survey to provide weighted matrix input into multi-criteria decision analysis calculations to carry out the following tasks: (a) assess the relative importance of 12 process options against the 6 industry-derived in-process economic potential criteria, that is, increase in product quality, increase in recycling rate, increase in process capacity, decrease in labour costs, decrease in energy costs and decrease in disposal costs; and (b) rank 25 key technologies that have been selected as being the most likely to benefit the efficient sorting of WEEE. The results indicate that the first stage in the development of any total system to achieve maximum economic recovery of materials from WEEE has to be the selection and application of appropriate fractionation process technologies to concentrate valuable components such as critical metals into the smallest possible fractions to achieve their recovery while minimising the disposal costs of low-value products. The stakeholder-based study has determined the priority for viable technical process developments for efficient WEEE fractionation and highlighted the economic and technical improvements that have to be made in the treatment of WEEE. [ABSTRACT FROM AUTHOR]

The strategic metal indium is recovered from solutions containing tin and lead that are typical of those obtained from leach solutions of metal component fractions of electronic waste including the leach solutions from indium tin oxide thin film conductive layers that contain only indium and tin. Almost total recovery of the metals can be achieved from nitric, perchloric and acetic acid leach solutions using a novel cylindrical mesh electrode electrolysis cell under appropriate conditions. The optimum separation of indium from tin and lead is achieved by a novel three-stage process from nitric acid media in the presence of SCN − as a complexing agent. Lead is removed from dilute indium-tin-lead solutions in the first stage from 0.1 mol L −1 nitric acid solution by electrodeposition over an 8 h period in the absence of SCN − to give a residual solution containing a maximum of 2 mg L −1 of lead (97% recovery). Tin is removed in the second stage by electrodeposition over an 8 h period from the solution after addition of 0.02 mol L −1 SCN − to give a maximum residual electrolyte tin concentration of 3 mg L −1 (94% recovery). In the third stage indium is recovered at the anode of the cylindrical mesh electrode cell as an oxy-hydroxide phase by increasing the SCN − concentration to 0.1 mol L −1 and carrying out the electrolysis for a period of 24 h to give a residual solution containing 1 mg L −1 of indium (98% recovery). [ABSTRACT FROM AUTHOR]

Phosphors and optoelectronic thin film electronic device layers contain critical metals including lanthanides and indium that should be recycled. Solvent impregnated resins (SIRs) containing (i) DEHPA (ii) DODGAA and (iii) DODGAA with the ionic liquid [C 4 mim][Tf 2 N] are investigated in extraction chromatography methodologies to recover and separate critical metals from dilute solutions that model those leached from thin films. Optimum adsorption of metals occurs at pH 1.5–3.5 but is highest on DODGAA-[C 4 mim][Tf 2 N]. The recovery and separation of adsorbed metal species on the DODGAA-[C 4 mim][Tf 2 N] SIR resin from solutions containing the glass matrix ions, Ca(II) and Al(III), along with In(III) and Sn(IV) or lanthanide ions is achieved by elution with HNO 3 . Ca(II) and Al(III) are completely eluted with 0.1 M HNO 3 retaining the target critical metal species on the resin. Separation of In from Sn is achieved by elution of In(III) with 2.5 M HNO 3 and Sn(IV) with 5 M acid. La is separated from the other lanthanides by elution of La(III) with 2.5 M HNO 3 and the remaining lanthanides with 5 M acid. The SIR resins can be reused over a series of at least five cycles of loading, stripping, and rinsing to reduce reagent costs and achieve economic critical metal recovery by extraction chromatography. [ABSTRACT FROM AUTHOR]