Si3 N4 production from silicon wastes and fluorate effluents

A process to obtain silicon nitride from siliceous and fluoride industrial wastes, primarily from the uranium purification process was developed. The reaction of these wastes with sulphuric acid produces a vapor which is absorbed by an organic solvent and precipitated with ammonium gas. The final product identified by X-rays diffractometry was (N H4)2 Si F6. That material was further mixed with graphite in the ratio of 1:2 (m/m) and heat treated at 1300 deg C under N2 atmosphere. α-Si3 N4 was determined as a major phase presented afterwards. (author)