A novel process utilizing particle immobilization in alginate gels has been proposed for a solid-liquid separation of colloidal suspension. A mixture of sodium alginate aqueous solution and colloidal suspension is added to a calcium chloride aqueous solution, resulting in calcium alginate 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. The effect of the solution environment of the colloidal suspension on the process was studied. It was found that pH of the suspension does not affect the process, and sodium ions in the suspension also have little effect on the immobilization reaction. Calcium and aluminum ions in the suspension were found to interfere with the reaction, yielding metal-alginate gels before the sodium alginate solution and the colloidal suspension are mixed completely. For complete immobilization of colloidal particles, therefore, multi-valent ions in the suspension should be masked by use of a chelating agent.