The recovery of metals from electronic waste : a review

Abstract: Waste electric and electronic equipment, or electronic waste, has been taken into consideration not only by the government but also by the public due to their hazardous material contents. In the detailed literature survey, value distributions for different electronic waste samples were calculated. It is showed that the major economic driver for recycling of electronic waste is from the recovery of precious metals. The state of the art in recovery of precious metals from electronic waste by pyrometallurgical processing, hydrometallurgical processing, and biometallurgical processing are highlighted in the paper. Pyrometallurgical processing has been a traditional technology for recovery of precious metals from waste electronic equipment. However, state-of-the-art smelters are highly depended on investments. Recent research on recovery of energy from PC waste gives an example for using plastics in this waste stream. It indicates that thermal processing provides a feasible approach for recovery of energy from electronic waste if a comprehensive emission control system is installed. In the last decade, attentions have been removed from pyrometallurgical process to hydrometallurgical process for recovery of metals from electronic waste. In the paper, hydrometallurgical processing techniques including cyanide leaching, halide leaching, thiourea leaching, and thiosulfate leaching of precious metals are detailed. In order to develop an environmentally friendly technique for recovery of precious metals from electronic scrap, a critical comparison of main leaching methods is analyzed for both economic feasibility and environmental impact. It is believed that biotechnology has been one of the most promising technologies in metallurgical processing. Bioleaching has been used for recovery of precious metals and copper from ores for many years. However, limited research was carried out on the bioleaching of metals from electronic waste. In the review, initial researches on the topic are presented. In addition, mechanisms and models of biosorption of precious metal ions from solutions are discussed

Thermodynamic effects of temperature during roasting of chromite for sodium chromate salts formation

This paper aims to assess the potential effects of roasting temperature on the formation of sodium chromate (Na2CrO4). To perform this task, chromite samples were complexed with NaCl at temperatures ranging from 900 °C to 1 200 °C in the presence of excess oxygen. These experimental conditions were set and assessed based on the predicted phase transformations using Facstage as a prediction tool. The scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) have revealed the roasting behaviour of chromite to be governed by a fully reacted outside layer and an unreacted core. As per the x-ray diffraction (XRD) results, at lower temperature settings, mineral phases such as hematite and chromium oxide reported as an indication of predicted oxidation of chromite. The key results indicate that the addition of NaCl reduces the equilibrium temperature, thereby fully decomposing the stable and refractory spinel structure of chromite at 1 200 °C

Thermodynamic effects of temperature during roasting of chromite for sodium chromate salts formation

This paper aims to assess the potential effects of roasting temperature on the formation of sodium chromate (Na2CrO4). To perform this task, chromite samples were complexed with NaCl at temperatures ranging from 900 °C to 1 200 °C in the presence of excess oxygen. These experimental conditions were set and assessed based on the predicted phase transformations using Facstage as a prediction tool. The scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) have revealed the roasting behaviour of chromite to be governed by a fully reacted outside layer and an unreacted core. As per the x-ray diffraction (XRD) results, at lower temperature settings, mineral phases such as hematite and chromium oxide reported as an indication of predicted oxidation of chromite. The key results indicate that the addition of NaCl reduces the equilibrium temperature, thereby fully decomposing the stable and refractory spinel structure of chromite at 1 200 °C

Wettability of graphite by synthetic and industrial PGM-furnace matte

Wettability of SGL's RN-graphite by synthetic and industrial PGM (Platinum Group Metal)-furnace matte (CuFeNiS) was investigated using a sessile drop configuration. This work was done to determine the compatibility of a graphite refractory with liquid PGM-furnace matte. Direct measurements of interfacial contact angles were used to determine wettability. In inert conditions, graphite was poorly wetted by synthetic and industrial PGMfurnace matte (CuFeNiS), the contact angles were > 90° for all tested matte types. No correlation was observed between the sulphur content of the matte and its wetting behaviour. The granulated matte expanded by up to 25 volume % during melting.</p