Initially, it was shown that the physical method for calcium reduction in rock phosphate digestion solutions containing nitric acid was subject to absolute limits, which are set by the particular crystallisation characteristics. The BASF Odda process approaches these limits very closely with the required energy costs and capital costs. Compared with other processes for the production of compound fertilisers, this method therefore provides an economical process for the production of nitrophosphate with good product properties, as described in the last section of the paper.

L Diehl, K F Kummer and H Oertel, BASF Aktiengesellschaft, 67056 Ludwigshafen, Germany

27 pages, 20 figures.