|dc.description.abstract||CMP(chemical mechanical polishing) is an important process in semiconductor industry. Both of polishing slurry and post cleaning result in high turbidity of CMP wastewater. CMP particles are in nano scale and have high zeta potentials, which are difficult to remove by coagulation and flocculation. In this study, chemical coagulation treatment of mixing silica and alumina oxide CMP wastewater was studied.
The wastewater was prepared by diluting silica and aluminum oxide (Al2O3) slurries to 200 times. Effects of mixing ratio on coagulation were examined by 100% silica, 70% silica and 30% Al2O3, and 50% silica and 50% Al2O3. It was found that the residual turbidity was the lowest when the solution pH was 7 and increased with increasing pH. Also, when the solution pH was 7 and PACl was 600 ppm, the residual turbidity increasing with increasing amount of Al2O3, which is because the Al2O3 slurry had much higher turbidity.
Effects of the mixing ratio of cationic and anionic polymers on the removal of turbidity, suspended solids (TSS), chemical oxygen demands (COD),and particle size distribution were also investigated. It was found that the dosing of cationic and anionic polymer was greatly dependent on the ratio of silica and Al2O3. The TSS was higher when there were more Al2O3 nanoparticles, which was because the particle size of Al2O3 was larger than the pore size of the filter (0.1 m) and the density of Al2O3 was higher than that of silica.
In general, higher ratio of Al2O3 leaded to higher residual turbidity though the removal efficiencies for three mixing ratio of silica and Al2O3 were similar. It is suggested that when there are two different CMP nanoparticles in wastewater, 70% silica and 30% Al2O3 would have better coagulation performance.||en_US|