This invention mainly consists of two processes: extration and purification. The phosphate is decomposed by sulfuric acid during the extraction process while silicon additive etc. are added. This process is carried out under negative pressure which helps to get rid of the harmful HF and SiF4 thoroughly and yield filtered acid of good characteristics, which is then subjected to concentration with conventional method. The purification process is carried on by passing in ammonia gas and the resulting sideproduct of ferric aluminium complex precipitated is then subjected to ageing and filtering, and phosphoric acid of super quality is obtainecd. The procedure for removing ferric and aluminium from phosphate is unnecessary, and P2O5 yielding is increased. |