CHEMICAL LEACHING CHARACTERISTICS OF STONEWARES IN KOREA

Stones are processed widely for cooking utensils such as cookers, broilers, kettles, and others in Korea. Dominant rock types of commercialized stonewares are pyroxenite, breccia and biotite diorite. Pyroxenite and biotite diorite which are relatively abundant in mafic minerals have higher specific gravities of 3.0 than breccia of 2.5. Breccia shows the highest absorption (2.9%) among the three stones and the pH values of three stone types are in the alkaline range of 9.7 to 9.9. Among the studied stones, biotite diorite is the most durable against abrasion and has the highest strength and therefore, it is expected to be used effectively for the longest time except for other specific causes. Crushed stone grains of about 0.8 to 4.8mm in size were selected and heated in deionized neutral water and acidic water for the chemical leaching test. Macrominerals (Ca, P, Mg, K, Na) are leached from stones preferably in acidic conditions regardless of rock types. Ca and Na are leached extremely from breccia, K from biotite diorite, and P from pyroxenite, which can be expected in relation with modes and rock-forming mineral compositions of stones. Standard criteria of leached heavy metals and macrominerals should be studied thoroughly to utilize stones for cooking utensils of high quality which are harmless to the human body. Also it is required to examine more detailed abiochemical properties of various stone types used presently for cooking utensils.