Can torrefaction be a suitable method of enhancing shredder fines recycling?

Effective recycling of metallic waste and end-of-life vehicles (ELVs) is of crucial importance. Currently used separation and sorting techniques result in the formation of fine residue (usually below 10-20 mm) called shredder fines. Shredder fines contain the so-called 'fluff' (i.e., foam, wood and textile fibres) with metal particles entangled in it. This 'fluff' interferes with sorting techniques and thus reduces the metal recycling rate. For this reason, presently, shredder fines are primarily landfilled, which is not covered by the greater objective of the circular economy; therefore, the need for their recycling emerged. Low-temperature pyrolysis (torrefaction) increases the 'fluff' fragility and thus liberates the metal particles without their substantial oxidation, thereby enabling their recycling. For that reason, in this article, shredder fines torrefaction was performed at the temperature range of 250-450 °C. The process products were comprehensively characterised using, among others, MicroGC (non-condensables), GC/MS (condensables), and ICP-SFMS (char). The possible application of the torrefied shredder fines after the metal sorting was discussed as well. Torrefaction was identified as a promising way of shredder fines recycling, and the torrefied shredder fines after metals sorting have the potential to be used as an ingredient of a raw material mix for cement kilns.

Investigations into Recycling Zinc from Used Metal Oxide Varistors via pH Selective Leaching: Characterization, Leaching, and Residue Analysis.

Metal oxide varistors (MOVs) are a type of resistor with significantly nonlinear current-voltage characteristics commonly used in power lines to protect against overvoltages. If a proper recycling plan is developed MOVs can be an excellent source of secondary zinc because they contain over 90 weight percent zinc oxide. The oxides of antimony, bismuth, and to a lesser degree cobalt, manganese, and nickel are also present in varistors. Characterization of the MOV showed that cobalt, nickel, and manganese were not present in the varistor material at concentrations greater than one weight percent. This investigation determined whether a pH selective dissolution (leaching) process can be utilized as a starting point for hydrometallurgical recycling of the zinc in MOVs. This investigation showed it was possible to selectively leach zinc from the MOV without coleaching of bismuth and antimony by selecting a suitable pH, mainly higher than 3 for acids investigated. It was not possible to leach zinc without coleaching of manganese, cobalt, and nickel. It can be concluded from results obtained with the acids used, acetic, hydrochloric, nitric, and sulfuric, that sulfate leaching produced the most desirable results with respect to zinc leaching and it is also used extensively in industrial zinc production.

Conversion of microwave pyrolysed ASR's char using high temperature agents.

Pyrolysis enables to recover metals and organic feedstock from waste conglomerates such as: automotive shredder residue (ASR). ASR as well as its pyrolysis solid products, is a morphologically and chemically varied mixture, containing mineral materials, including hazardous heavy metals. The aim of the work is to generate fundamental knowledge on the conversion of the organic residues of the solid products after ASR's microwave pyrolysis, treated at various temperatures and with two different types of gasifying agent: pure steam or 3% (v/v) of oxygen. The research is conducted using a lab-scale, plug-flow gasifier, with an integrated scale for analysing mass loss changes over time of experiment, serving as macro TG at 950, 850 and 760 °C. The reaction rate of char decomposition was investigated, based on carbon conversion during gasification and pyrolysis stage. It was found in both fractions that char conversion rate decreases with the rise of external gas temperature, regardless of the gasifying agent. No significant differences between the reaction rates undergoing with steam and oxygen for char decomposition has been observed. This abnormal char behaviour might have been caused by the inhibiting effects of ash, especially alkali metals on char activity or due to deformation of char structure during microwave heating.

Recycling of automobile shredder residue with a microwave pyrolysis combined with high temperature steam gasification.

Presently, there is a growing need for handling automobile shredder residues--ASR or "car fluff". One of the most promising methods of treatment ASR is pyrolysis. Apart of obvious benefits of pyrolysis: energy and metals recovery, there is serious concern about the residues generated from that process needing to be recycled. Unfortunately, not much work has been reported providing a solution for treatment the wastes after pyrolysis. This work proposes a new system based on a two-staged process. The ASR was primarily treated by microwave pyrolysis and later the liquid and solid products become the feedstock for the high temperature gasification process. The system development is supported within experimental results conducted in a lab-scale, batch-type reactor at the Royal Institute of Technology (KTH). The heating rate, mass loss, gas composition, LHV and gas yield of producer gas vs. residence time are reported for the steam temperature of 1173 K. The sample input was 10 g and the steam flow rate was 0.65 kg/h. The conversion reached 99% for liquids and 45-55% for solids, dependently from the fraction. The H(2):CO mol/mol ratio varied from 1.72 solids and 1.4 for liquid, respectively. The average LHV of generated gas was 15.8 MJ/Nm(3) for liquids and 15 MJ/Nm(3) for solids fuels.