Nippon Electric Co., Ltd.

Naotaka Sakakibara

Shigeru Ohno

Shigeki Shimizu

A method is provided for treating waste water containing solids of difficultly-soluble compounds of at least one heavy metal, the method comprising the steps of adding an amount of ferrous ions to said waste water corresponding on a molar basis to about 2 to 100 times the total molar amount of heavy metal present in said waste water, adding an alkaline substance to said waste water in an amount corresponding to about 0.9 to 1.2 equivalent of free acid present in said waste water, and stirring the waste water without aeration at a temperature of at least about 40.degree. C., whereby insoluble ferrite crystals are precipitated having said heavy metal incorporated therein.

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Tokyo, Japan

Naotaka Sakakibara