Ultrafiltration based on various polymeric membranes for recovery of spent tungsten slurry for reuse in chemical mechanical polishing process

Membrane separation based on ultrafiltration for the recovery of spent tungsten slurry from chemical mechanical polishing (CMP) process has been investigated. Five polymeric membranes with different molecular weight cut-off (MWCO) i.e. 10 kDa PES, 30 kDa PES, 100 kDa PES, 50 kDa PS and 50 kDa PVDF were successfully applied. Flux analysis was conducted to study the fouling phenomena and the fouling effects on membrane surface were elucidated by means of SEM and AFM analyses. Almost steady fluxes were reached after about 60 min of filtration process. Meanwhile, the membrane fouling was mainly due to the formation of cake layer on the membrane surface leading to blockage of membrane pores. On top of that, 50 kDa PS membrane showed the highest potential in filtrating and concentrating the CMP spent tungsten slurry with 92% retention of silica particles and 42% retention of tungsten. Furthermore, it also achieved the lowest mean size particle of 126 nm in the retentate which were significantly different from that of the original spent tungsten slurry.