Nowadays Light Emitting Diodes (LEDs) are widely utilized. They are applied as backlighting in Liquid Crystal Displays (LCD) and TV sets or as lighting equipments in homes, cars, instruments and street-lightning. End of life equipments are containing more and more LEDs. The recovery of valuable materials -such as Ga, Au, Cu etc. -from the LEDs is essential for the creating the circular economy. First task is the development of a proper recycling technology. Most of the researchers propose fully chemical or thermal-chemical pathway for the recycling of LEDs.In the meantime our approach based on the thorough investigation of the structure and composition of LEDs, and shown in this paper, is the combination of mechanical and chemical techniques in order to recover more valuable products, as well as to facilitate the mass transfer. Our laboratory scale experiments are introduced, the final aim of which is Ga recovery in accordance with our above approach. It was experimentally proved that the LED chips contain Ga and can be recovered by mechanical processes along with copper-product. Ga is presented on the surface of the chips in GaN form. Mechano-chemical activation in high energy density stirred medium mill and the following acidic leaching resulted in the enrichment of 99.52% of gallium in the pregnant solution.
Landfill mining is a prospective tool for the recycling of valuable materials (waste-to-material) and secondary fuel (waste-to-energy) from old, therefore more or less stabilised municipal solid waste landfills. The main target of Horizon 2020 ‘SMARTGROUND’ R&D was improving the availability and accessibility of data and information from both urban landfills and mining dumps through a set of activities to integrate all the data – from existing sources and new information retrieved with time progress – in a single EU database. Concerning urban landfills, a new sampling protocol was designed on the basis of the current Hungarian national municipal solid waste analysis standards, optimised for landfill mining. This protocol was then applied in a sampling campaign on a municipal solid waste landfill in Debrecen, Hungary. The composition and parameters of the landfilled materials were measured as a 12-year timescale. The total wet and dry mass of the valuable components possible for utilisation was estimated.
Present paper deals with the development of geopolymer foam prepared from ground F class power station fly ash. The effect of the fly ash fineness on the rheology of the geopolymer paste and the foam properties have been investigated. The raw fly ash was ground in a ball mill for various duration, 5, 10, 20, 30, 60 and 120 min. Geopolymer paste was prepared from the raw and ground fly ash with NaOH -sodium silicate mixture as alkaline activator. Geopolymer foam production was made using H 2 O 2 as foaming agent. Additionally, the geopolymer material structure was investigated by Fourier transform infrared spectrometer, the foam cell structure was monitored using optical microscopy. The rheological behaviour of the geopolymer paste changed due to the grinding of fly ash (from Bingham plastic to Newtonian liquid). Grinding of fly ash has a significant effect on the physical properties as well as on the cell structure of the geopolymer foam.
The behavior of slurries and suspensions made by mixing solid particles and liquids is very important for various industrial applications. The latest accidental failure events at tailings facilities (Kolontár, Baia Mare) have focused public interest into this field. Nowadays, environmental practice is turning to use dry deposition techniques or at least as high concentration slurries or pastes as possible, to avoid large spills in case of an accidental failure of an embankment. High concentration slurries are becoming widely accepted in many environmentally related operations such as underground backfilling or simple tailings deposition. However, the hydraulic transport of pastes or high density slurries requires higher energy input via pumps, and, in addition, the energy requirement or pressure loss calculation methods are also different because the rheology of pastes differs from that of dilute slurries. At the University of Miskolc, Institute of Raw Materials Preparation and Environmental Processing, Miskolc, Hungary, this topic has been studied for many decades. The fine suspension – coarse mixture flow model was introduced, and it has been determined that the flow behavior of fine suspensions made of solid particles smaller than a limit particle size can be measured and interpreted in almost the same way as for single phase clear liquids. Based on these measured rheological parameters of fine suspensions, the frictional energy loss can be calculated. The aim of this paper is to give a summary and data base about the rheological behavior of different industrial materials based on pilot scale hydraulic loop measurements. An Anton-Paar rotational viscometer and a tube viscometer with three measuring pipe sections,– developed by our institute – were used for testing. The results of measurements of various granular materials, such as sands, fly ashes, perlite, tailings and red mud are presented in connection with environmental applications. Based on these results, empirical relationships are presented, where the parameters are determined by simple function fitting into the data of measurements carried out at discrete concentration values. The rheology of fine suspensions of any concentration up to the measured maximum can be calculated by these relationships.
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