ABSTRACT
The term nitrophosphate is used to designate various complex fertilizer grades, usually obtained when phosphate rock is digested with nitric acid. Sometimes, authors or technical publications enlarge the scope of the term to include digestion with an acidic mixture in which at least one component is nitric acid (the others being sulfuric acid, phosphoric acid, or even carbon dioxide). This meaning of the term is usually to be found in older publications [ 1-3]. Today, this term is generally used when nitric acid is the only agent for phosphate rock digestion. The process is rather complex, including many distinct steps, a wide variety of reaction media, and a wide range of working temperatures (for this type of process), so that multiple environmental pollution problems are generated, whose solution requires very sophisticated engineering and designing work. In such a plant the resulting liquid effluents are of complex chemical composition, including almost all the harmful components common to the fertilizer industry, such as NOx-, NH4 +, P 20 5 , F, S04 2-, Si02, and sometimes even Cl-or various types of insoluble matter.
