마이크로웨이브를 이용한 납석 내 Fe 불순물 제거 및 세라믹 분리막 활용방안

Abstract

Ceramic membrane is superior to existing polymer membranes in chemical and wear resistance, preservation of physical and chemical properties under high temperature and pressure and utilization for extreme environment conditions such as strong acidic and alkalic wastewater treatment. However, although ceramic membrane has an excellent potential of water treatment, most of it depends on import from foreign countries and as its cost is very high, its utilization rate for wastewater treatment is very low due to high cost. Therefore, development of alternate material is desperately needed. The physical and chemical properties of pyrophyllite are similar to those of alumina and the raw material is available in very low price. It is suggested that utilization of the pyrophyllite-based ceramic membrane will increase as it can maintain the function of pyrophyllite-based ceramic membrane and the raw material can be supplied with low price. However, impurities have to be completely removed from pyrophyllite to supply raw material of the pyrophyllite-based ceramic membrane as such impurities cause weakness in strength, low quality of final product due to coloring and low malfunction of the membrane. Accordingly, this study selectively removed impurities from pyrophyllite using microwave heating while maintaining its physical-chemical properties of raw pyrophyllite. And then, this study made the pyrophyllite-ceramic membrane with impurities removed and investigated whether the physical functional potential as the ceramic membrane is available. To check impurities contained in raw pyrophyllite, this study carried out the following analyses: polarization microscope, XRD, XRF and SEM-EDS analyses. Then, this study confirmed impurities removal efficiency to remove the impurities from the raw pyrophyllite. Microwave heating and magnetic separation were also performed to remove impurities from raw pyrophyllite. This study measured impurities removal efficiency according to microwave radiation time and magnetic power through the XRF analysis. This study examined mineralogical features of raw pyrophyllite and discovered that it was composed of pyrophyllite, quartz, and diaspore, and its chemical contents were presented as follows : 57.48~78.65 wt.% of SiO2, 15.12~32.38 wt.% of Al2O3, and 0.16~3.03 wt.% of Fe2O3. As a result of the SEM-EDS analysis, it was discovered that hematite was contained in the raw pyrophyllite. When the raw pyrophyllite sample was heated in a microwave, the heating temperature reached to 788℃ in 30 min. and the temperature remained constant during 60 min. Through magnetic separation of the producted material obtained from microwave heating, non-magnetic fraction was obtained. The results of the XRF analysis of the material were presented as follows: the Fe2O3 content ranged from 0.09 to 0.05 wt.% and the impurity removal efficiency was over 98% and the Al2O3 content ranged from 15.54 wt.% to 17.88 wt.%. Using the pyrophyllite sample with impurities removed, this study fabricated the pyrophyllite-based ceramic membrane with the use of an extrusion method. When flexural rigidity and porosity of this ceramic membrane was measured, the former ranged from 5.57 to 16.25 MPa at 1200℃ and from 24.09 to 34.96 MPa at 1300℃. It increased as temperature increased. And the porosity ranged from 28.12 to 36.71% at 1200℃ and from 20.44 to 25.79% at 1300℃. The porosity rate decreased as temperature increased. Accordingly, the results of this study satisfied requirements of functional conditions for pyrophyllite-based ceramic membrane such as strength, density and porosity. However, if the problem of low porosity caused by the mineralogical characteristics of pyrophyllite is overcome, the pyrophyllite- based ceramic membrane can be effectively utilized in various fields for water treatment.