Particle containing alkali

Alkali agent-containing particles comprising (a) particles containing an alkali agent and having an average particle size of from 150 to 1000 μm, and a layer of (b) clay mineral particles exhibiting a water impregnation capacity of 200% by mass or more as calculated according to the following method and having an average particle size of from 1 to 200 μm, the layer being formed on a surface of the respective particles (a):

• Method for calculation of water impregnation capacity:
• A dispersion of the clay mineral particles (b) obtained after measuring a swelling power of the particles (b) according to a Standard Testing Method of Japan Bentonite Manufactures Association “Swelling Test Method for Bentonite (Powder)” (JBAS-104-77) (volumetric method) is subjected to suction filtration (under 0.5 MPa for 2 h;
• filter paper:
• “Type No. 4A” having a diameter of 90 mm available from Advantec Toyo Kaisha, Ltd.) using a Buchner funnel to measure a mass (A) of a residue of the clay mineral particles (b) on the filter paper;
• the clay mineral particles (b) are dried according to a drying method of a sample prescribed in JIS K0068 “Method for Measuring Water Content of Chemical Products;
• 7:
• Loss-on-Drying Method” to measure a mass (B) of the dried clay mineral particles (b);
• and a water impregnation capacity of the clay mineral particles (b) is calculated from the thus measured mass (A) and mass (B) according to the following formula:
• Water impregnation capacity (%)=[(A−B)/B]×100.