Removal process of colloidal particles from colloidal suspensions by use of particle immobilization in calcium alginate gel

提出了一种利用水凝胶中颗粒固定化的新技术，用于难以过滤的胶体悬浮液的固液分离。以钠基膨润土/PMMA为实验材料，研究了该工艺的基本原理。将海藻酸盐-膨润土/PMMA混合物滴加到氯化钙溶液中，得到海藻酸钙凝胶。胶体颗粒固定在凝胶中。凝胶悬浮液在重力作用下脱水，然后进行凝胶颗粒的力学表达。在表达过程中，胶体颗粒保留在凝胶中，表达液清澈。然后将表达好的蛋糕丢弃。当水滴中的海藻酸盐浓度超过1000ppm时，亚微米颗粒被海藻酸钙凝胶完美地包裹住。由于钙离子在液滴中的扩散决定了凝胶反应的速率，因此减小混合物的液滴尺寸加速了凝胶反应。降低凝胶中海藻酸盐的含量会加速膨润土/PMMA凝胶的表达。胶体悬浮液中的单价金属离子不影响固定化反应。胶体悬浮液中的二价和三价金属离子干扰固定化反应；也就是说，在海藻酸钠溶液和胶体悬浮液完全混合之前，它们产生海藻酸金属凝胶。为了完美地固定胶体颗粒，胶体悬浮液中的多价离子应使用螯合剂来掩盖。胶体悬浮液的pH值不影响工艺。

A novel technique utilizing particle immobilization in hydrogels has been proposed for a solid-liquid separation of difficult-to-filter colloidal suspensions. Fundamental aspects of this process are investigated using sodium bentonite/PMMA as experimental materials. The alginate-bentonite/PMMA mixture is added dropwise to a calcium chloride solution, resulting in calcium alginate gels. Colloidal particles are immobilized in the gels. The gel suspension is dehydrated gravitationally, followed by mechanical expression of the gel particles. During the expression, the colloidal particles remain in the gels and the expressed liquid is clear. The expressed cake is then discarded. When an alginate concentration in the droplets is above 1000 ppm, submicron particles are perfectly entrapped in calcium-alginate gels. Decreasing the droplet size of the mixture expedites gelation since the diffusion of calcium ions into the droplets determines the rate of gelation reaction. Reducing the alginate content in the gels accelerates expression of the bentonite/PMMA gels. Monovalent metal ions in a colloidal suspension do not affect the immobilization reaction. Divalent and trivalent metal ions in a colloidal suspension interfere the immobilization reaction; i.e., they yield metal-alginate gels, before the sodium alginate solution and the colloidal suspension are mixed completely. For the perfect immobiUzation of colloidal particles, multi-valent ions in the colloidal suspension should be masked by use of a chelating agent. pH of colloidal suspension does not affect the process.