| Summary: | 碩士 === 國立成功大學 === 資源工程學系碩博士班 === 98 === A tremendous amount of sericite deposit is located 2 kilometers northwest of Li-dao Village, Hai-duan Borough, Taitung County. The recoverable amount is estimated to be about 15,000,000 tons. This sericite deposit belongs to a sericite-pyrophyllite-quartz schist-type deposits and is one of the most economically valued industrial minerals in Taiwan. After hydraulic classification, the particle size of finished sericite powder is smaller than 400 mesh. The major mineral compositions are sericite and pyrophyllite.
In this study, ＜2 μm parts of the saled sericite powder were separated by sedimentation and used in the synthesis of analcime via hydrothermal routes. In the hydrothermal synthesis, the mineralizer was 4M Na2SiO3, S/L ratio was 1/10 and the reactions were carried out at 250℃ for 4 hr.
The adsorption experiments of Ni2+, Mn2+, Cr3+ and Sr2+ on the synthesized analcime were performed. The adsorption behaviors were investigated by analyzing the ion concentration of solutions, using atomic absorption spectrometry, before and after each adsorption test. The factors detailedly studied were ion species, equilibrium time, ion concentration, adsorption amount, removal percentage and adsorption mechanism. The following conclusions can be drawn.
1.In solutions of 0.01M concentration, the times required for adsorption to reach equilibrium are for Mn2+ about 10 hr, and for Ni2+, Cr3+ and Sr2+ about 24 hr.
2.For varied ion concentrations, the adsorption of Cr3+ is always the largest, while Ni2+, Mn2+ and Sr2+are smaller and almost similar. This may be due to that Cr3+ has highest valence, so that the polarity is the highest and the replacement is the largest.
3.With the increasing of ion concentrations, the adsorption amount of Ni2+, Mn2+, Cr3+ and Sr2+ also increases. The adsorption becomes saturated for Ni2+ at 0.0001M, Mn2+ at 0.001M, Sr2+ at 0.005M, and Cr3+at 0.01M, respectively.
4.The ion removal percentage decreases with the increasing of ion concentrations. This is because the total adsorption sites are fixed for a limited amount of analcime. When the ion concentration increases, the total number of ions exceeds the total number of sites, eventually reduces the removal percentage. Similarly, with the increasing of S/L ratio, removal percentage increases proportionally. Because increasing the solids is equivalent to increasing the adsorption sites, so the removal percentage can be increased.
5.The adsorption behaviors of Ni2+, Mn2+, Cr3+ and Sr2+ conform to the Langmuir isotherm model. This means, the sites on the analcime surface are equivalent and have the same adsorption energy. Each adsorption site only adsorbs one ion (i.e. monolayer adsorption). There is no interaction between adsorbed ions.
6.The adsorption of Ni2+, Mn2+, Cr3+ and Sr2+, thus the reduction in concentrations of these ions, was accompanied by the increase of the Na+ concentration. This means, the removal of ions by analcime is via the mechanism of ion exchange. However, the total charge of Na+ is less than the total charge of adsorbed Mn+, suggesting that other mechanisms should also in exist.
7.In the range that the zeta potentials of analcime are negative, the adsorption of ions (e.g. Ni2+ and Cr3+) decreases the absolute value of zeta potential. The larger the adsorption, the smaller the absolute value of zeta potential becomes. For [Ni2+]≧0.01M and [Cr3+]≧0.001M, the zeta potential even changes to positive. Therefore the adsorption of ions on analcime must also be via the mechanism of physical adsorption.
8.The valence of ions and ionic radius are closely related to the adsorption and desorption behaviors of ions on analcime. The Cr3+ ion has the highest valence and smallest radius (0.62?), it is found that Cr3+ is most strongly adsorbed, and the desorption is almost none. The adsorption of divalent ions are in the order of, from high to low, Ni2+(0.69?) ＞Mn2+(0.83?)＞Sr2+(1.18?). While the desorption is arranged reversely.
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