Abstract
Waste electrical and electronic equipment (WEEE) has increased in recent decades due to the continuous advancement of technology in the modern world. These residues have various metals that are found in concentrations that make their recovery profitable. A group of metals of interest are the rare earths such as europium and yttrium, as well as semiconductors such as indium. Yttrium was recovered from cathode ray tubes that were manually dismantled. The resulted powder was leached with HNO3, and then the solution was submitted to solvent extraction with di-(2-ethylhexyl) phosphoric acid (DEHPA) using n-heptane as a diluent. For re-extraction, HNO3 was used again, and yttrium was precipitated by adding four times the stoichiometric amount of oxalic acid, reaching 68% yttrium purity. Indium was recovered from the liquid crystal display (LCD) screens for which the pulverized material was leached with H2SO4. Then, the indium sulfate was subjected to solvent extraction using DEHPA as an extractant, and diesel as a diluent. The re-extraction was carried out again with H2SO4, and the obtained acid solution was evaporated until the indium precipitated, reaching a recovery of 95%. The investigations that were carried out show that it is feasible to recover these metals in the form of oxides or phosphates with high commercial value.
Highlights
During the last decades, there has been a vertiginous development of the technological industry, which has caused a significant increase in electronic waste
The following substances were employed in the development of this research: Nitric acid (HNO3 ), 68% Panreac; sulfuric acid (H2 SO4 ), 98% Mallinckrodt; hydrochloric acid (HCl), 37% Panreac; hydrofluoric acid (HF), Merck; n-hexane, 99.9% JT Baker; n-heptane, 99.9% Merck; di-(2-ethylhexyl) phosphoric acid (DEHPA), 99.9% Merck; tributyl phosphate (TBP), 97%, Fluka AG; methyl trioctyl ammonium chloride (Aliquat 336), 90% Merck; oxalic acid dehydrate, 99% Merck; and diesel premium and sodium hydroxide (NaOH), technical grade
From the analysis of crystalline phases performed by X-ray diffraction (XRD), it was found that the main constituent compounds of the coating powder were: zinc sulfide (ZnS) and yttrium oxysulfide (Y2 O2 S)
Summary
There has been a vertiginous development of the technological industry, which has caused a significant increase in electronic waste. The electronic waste that is generated due to the continuous advance of the technology is stored in deposits as scrap. Many of these WEEE have high value-added metals in their structure in concentrations that are much higher than those within minerals [2]. It is estimated that 14 kg of WEEE per year are generated per person, and this tendency grows exponentially each year [4]. Despite this trend, there are no regulations or provisions for the proper disposal of WEEE in undeveloped countries due to economic constraints. In the case of Europe, it is known that the amount of WEEE is approximately 7.5 million tons, and the annual growth of this trend ranges between
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