Printed circuit boards (PCBs) are difficult to recycle because of the layered structure of non-metal (i.e., epoxy resin, glass fiber) and copper. In this work, we conducted a systematic investigation to effectively recover copper from PCB. A thermal treatment was employed for improving the crushing performance of PCB and conducted by varying the temperature and the gas. Then, the mechanical strength, degree of liberation (DL), and copper separation efficiency of the heat-treated and untreated PCBs were investigated. After heat treatment under a 300 °C air atmosphere, the mechanical strength of PCB decreased from 386.36 to 24.26 MPa, and copper liberation improved from 9.3% to 100% in the size range of a coarser size fraction (>1400 μm). Accordingly, when electrostatic separations were performed under these conditions, a high-Cu-grade concentrate and high recovery could be obtained. The results show that the change in the physical properties of the PCBs leads to an improvement in the DL following thermal decomposition at 300 °C in air. Our study elucidates the physical properties of PCBs and the DL under various heat treatment conditions. Furthermore, it shows that the heat treatment condition of 300 °C in air is ideal for recovering copper from the PCB.
We investigated the hydrolytic precipitation process with regard to purification of low-purity vanadium pentoxide (V2O5) to obtain high-purity vanadium electrolyte (VE) of a vanadium redox flow battery (VRFB). The lowest purities of VE and V2O5 for VRFB, which were reviewed through the purity analysis of commercial VE, were found to be 99.98% and 99.8%, respectively. The hydrolytic precipitation process applied to V2O5 powder with 99.7% and 98.3% purity resulted in V2O5 powder with a purity higher than 99.8%. However, the V2O5 powder contained impurities such as Fe and Ga. To further improve the purity, a two-step process comprising red cake precipitation was applied. However, this process exhibited a low vanadium recovery rate; therefore, development of a new single purification process with a high vanadium recovery rate is required.
The glycothremal reaction of a stoichiometric mixture of aluminium isopropoxide and yttrium acetate in 1,4-butanediol (1,4-BG) at 300 ºC directly yielded crystalline yttrium aluminium garnet (YAG) with the crystallite size of 28 nm. The crystallization of YAG in 1,4-BG takes place as follows: An intermediate, HO(CH2)4-O-Al<, is formed by the alkoxyl exchange reaction between aluminium isopropoxide and glycol. The cleavage of the CO bond in HO(CH2)4-O-Al< yielding protonated tetrahydrofuran and aluminate ion is facilitated by participation of the intramolecular hydroxyl group. Ease in the cleavage of the CO bond seems to be the prime factor for the formation of crystalline YAG. On the other hand, the gelatinous product was formed in glycothermal reaction in ethylene glycol because CO bond of ethylene glycol is more difficult to be cleft than that of 1,4-BG. Rietveld analysis of YAG synthesized by glycothermal reaction in 1,4-BG indicated the presence of Al vacancies in the 24d sites and oxygen vacancies in the 96h sites, and partial substitution of Al ions in the 16a sites with Y ions was also suggested. Rapid crystal growth in the glycothermal reaction and the absence of mechanisms for elimination of defects, such as the dissolution-crystallization mechanism operated in hydrothermal reactions, are the reasons for the formation of defects. Al vacancies in the 24d sites and oxygen vacancies disappeared for YAG calcined at 1000 ºC but the ratio of substitution of Al ions in the 16a sites with Y ions increased as compared with as-synthesized YAG. Although the solid solution of YAG did not appear in the stable phase diagram, YAG with Y-rich composition could be synthesized by glycothermal reaction.
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