High-T_c superconducting high gradient magnetic separator using solid nitrogen cooling system for purification of CMP wastewater

This paper presents recent progress in the fabrication and test of a 3 T/60 mm room temperature bore high-T_c superconducting high gradient magnetic separator (HGMS) using a solid nitrogen (SN2) cooling system. The aim of the study was to develop an inexpensive, compact, and stable superconducting HGMS for the purification of chemical-mechanical-planarization wastewater in the semiconductor industry. The HGMS's magnet, which was cooled by SN2, was comprised of an assembly of 18 GdBCO double pancake coils, each of which was wound without turn-to-turn insulation. Cooling test results showed that the thermal stability of the high-T_c superconducting-HGMS magnet with SN2 was enhanced due to the large heat capacity of SN2. Moreover, in the filtration tests, the suspended solids value of filtrated wastewater at 2 T in a flow rate of 400 ml/min decreased to 1.6 mg/L, resulting in a 99.6% reduction in SS value compared to raw wastewater.