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固液分离难过滤胶体悬浮液的新技术。该过程的基本方面进行了研究，使用钠基膨润土/PMMA作为实验材料。将藻酸盐-膨润土/PMMA混合物滴加到氯化钙溶液中，得到藻酸钙凝胶。胶体颗粒被固定在凝胶中。凝胶悬浮液通过重力脱水，然后机械挤压凝胶颗粒。在挤出过程中，胶体颗粒保留在凝胶中，并且挤出的液体是澄清的。然后丢弃挤出的滤饼。当液滴中的藻酸盐浓度高于1000 ppm时，亚微米颗粒完全包埋在藻酸钙凝胶中。减小混合物的液滴尺寸加速凝胶化，因为钙离子扩散到液滴中决定了凝胶化反应的速率。降低凝胶中的藻酸盐含量加速膨润土/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;即，在藻酸钠溶液和胶体悬浮液完全混合之前，它们产生金属-藻酸盐凝胶。为了使胶体颗粒完全固定，胶体悬浮液中的多价离子应通过使用螯合剂来掩蔽。胶体悬浮液的pH不影响该过程。

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.