應用高梯度磁分離技術回收磁性微奈米顆粒之研究

Abstract

本研究以高梯度磁分離機(high-gradient magnetic separator, HGMS)回收磁性微奈米顆粒。依不同實驗參數進行高梯度磁分離試驗，對於不同顆粒濃度、進流水之流率、磁場梯度及顆粒粒徑等參數下評估HGMS之分離效率、有效分離時間及分離室飽和時間，以期能將所得之資訊應用於實廠操作之參考。 本研究所使用之微奈米等級之磁性顆粒，主要為SM (SiO2/Fe3O4)及欲探討不同磁性顆粒粒徑所用之Fe3O4 (分別為5-20 nm、20-30 nm及40-60 nm)超順磁性顆粒。SM顆粒係以溶膠凝膠法所製備合成，其飽和磁化量為23.19 emu g-1，顆粒粒徑約為70-80 nm。 影響HGMS效能之重要操作參數包括：流體進流流率、磁性顆粒進流濃度、磁介質填充率及顆粒粒徑。流率越低則HGMS之有效分離時間越長，分離效率較佳。磁性顆粒進流濃度越低，磁介質之捕集半徑越大，有效分離時間越長，分離效率較佳。磁分離室所填充之磁介質於外加磁場作用下，產生高磁場強度與磁場梯度，對磁性顆粒有更強大的捕集能力。因此當基質填充率越高時，磁場梯度亦越大，其所能捕集之磁性顆粒能力越佳。磁性顆粒粒徑越大，越容易達到飽和，因此，使用HGMS時，必須考慮其所能捕集之顆粒粒徑範圍限制。 依實驗結果進行高梯度磁分離之模擬，可預測有效分離時間及最適流速(流率除以截面積)等操作參數。利用磁介質分離室之質量平衡模擬，可預測貫穿曲線模擬結果顯示，磁介質分離室之飽和容量與流量及濃度成反比，與磁場梯度成正比。所得模擬之結果，可應用於實廠操作上之參考，於較適合之時機進行磁場切換，以避免過多的磁性顆粒流失，進而造成環境上之二次汙染。

This study investigated the recovery of magnetic micro-nano particles using high-gradient magnetic separator (HGMS). The major system parameters examined, include: inlet concentration of magnetic particles (MP) in the solution (CLF,i), volumetric flow rate (QL), magnetic field gradient (▽H), particle size (dp) and other parameters, such as packing density of magnetic media filled in the magnetic separation chamber (ρF). The separation efficiency(ηM), effective separation time (tB) and saturation time of separation chamber by the system parameters were evaluate. The mainly target particles studied were superparamagnetic particles of SM (SiO2/Fe3O4). For exploring the effects of particle size ,the magnetic Fe3O4 particles with sizes of 5-20,20-30 and 40-60 nm were employed. The magnetic SM particles were prepared using the sol-gel method, yielding the saturation magnetization of 23.19 emu g-1and particle size of 70-80 nm. The results indicate that a lower QL offers a longer tB and a better ηM for the HGMS. Also, a lower CLF,i of MP allows a large capture radius of magnetic media (rCF), resulting in a longer and a better ηM.The magnetic separation chamber filled with the magnetic media with a high ρF, provides higher magnetic field strength H and magnetic field gradient ▽H for the external magnetic field, and thus a higher ηM. Further, the capture of magnetic particles size with larger tends to reach saturation more easily. Therefore, the limitation of particle size should be considered for the capture of MP using HGMS. The multi-wire dynamic model was employed to simulate the performances of HGMS. Comparisons of experimental data and prediction indicate satisfactory agreement. The model can be used to predict the tB, optimum QL and other operating parameters, as well as the breakthrough curves. The results illustrate that the saturated magnetic matrix capacity of separation chamber is inversely proportional to the QL and CLF,i, however, is proportional to the magnetic field gradient. In practice, the model can be applied to simulate the real plant operation. The results may be used for the proper control of switching the magnetic field, thus avoiding the excessive loss of magnetic particles, and the secondary pollution to the environment.