PURPOSE: To manufacture high purity graphite by immersing fine granular natural graphite after flotation in a soln. contg. hydrofluoric acid to remove the impurity made of clay mineral by leaching.
CONSTITUTION: Natural graphite ore is crushed to fine granules having ≤ about 6 mesh size and subjected to flotation. The granular graphite refined in some degree is immersed in an aqueous soln. contg. hydrofluoric acid. The soln. is an aqueous soln. of hydrofluoric acid having about 46% concn. as HF to 35.37% which is the concn. of the azeotropic mixture with water, and an aqueous soln. of a mixture of hydrofluoric acid with various kinds of mineral acids is also preferably used as said soln. The preferred mineral acids are nitric acid, hydrochloric acid and sulfuric acid, and an about 1:1 mixture of one of the mineral acids with water is mixed with about 46% hydrofluoric acid in about 1:1. The clay mineral composed chiefly of silica, alumina and iron oxide is removed by leaching for several min W several hr. The treated graphite is washed and dried to obtain a refined product.
OKAMURA TAKEO
TAKEUCHI YOSHIMITSU
SASAKI SHIGEO
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