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

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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.