| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 92 === Nano materials have drawn great attractions from scientists and engineers for their phenomena, syntheses, and applications all over our country. It can be foreseen that, within near future, there would be more nano-scale waste in our environment. For example, nanoparticles (e.g., SiO2) from chemical-mechanical polishing (CMP) process of the semiconductor industry are very small and highly charged; hence, they are very difficult to be separated from wastewaters. The purpose of this study is to use magnetic seeding aggregation to enhance the aggregation of silica nanoparticles, and as the consequence, to improve the removal efficiency of silica nanoparticles.
The collision frequency between commercial magnetite and silica nanoparticles might not be sufficient since the number of particles per unit weight of the commercial magnetite is very small due to its large size; therefore, magnetite nanoparticles are required to have efficient removal efficiency of the turbidity. Magnetite nanoparticles, whose saturated magnetic susceptibility and size were 55.6 emu/g and less than 300 nm, respectively, were synthesized by chemical co-precipitation of FeCl2•4H2O and FeCl3 in NaOH solution in this study. Synthesized magnetite nanoparticles were then used in the magnetic seeding aggregation of CMP wastewater. Influences of solution pH, salt concentration, G value, and application of an external magnetic field during sedimentation on the removal efficiency of nano silica were examined. It was found that when the solution pH is about 6, NaCl = 0 M, and G = 30 ~ 60 (1/sec), the removal efficiency of the turbidity is the highest, which is about 95% or even higher.
When magnetite-silica aggregates settled down in an external magnetic field, besides gravity, they also experienced magnetic forces, which enhance the settling velocity. Hence, high removal efficiency could be achieved in a much shorter time.
|
|---|
