Abstract: A method for preventing scale from precipitating and an apparatus for producing deionized water are disclosed. The acidic water produced by electrolysis in the electrolysis unit (30) is introduced into a concentrating compartment (19) in the continuous deionization unit (10). The pH of the concentrated water in the concentrating compartment decreases, thereby preventing scale from precipitating.

Abstract: Provided is a method of removing particles having a size of less than 10 .mu.m from an aqueous solution. The pH of the aqueous solution is first adjusted to be less than 9 and then the aqueous solution is passed through an absorbent of mineral fiber, containing 35 to 65 wt % of SiO.sub.2 and 65 to 35 wt % of at least one oxide selected from the group consisting of MgO, CaO, Al.sub.2 O.sub.3 and FeO. The particles in the aqueous solution adhere to the absorbent and are separated from the aqueous solution. The absorbent is regenerated by passing a descaling solution having a pH greater than 10 through the absorbent. The particles are recovered as a concentrated solution.