Chelation of metal ions with citric acid in the ammoniation process of wet‐process phosphoric acid

Abstract A new process is proposed in which citric acid is added during the ammoniation process of wet‐process phosphoric acid (WPA) to chelate metal ions to produce fertilizer ammonium dihydrogen phosphate (MAP) containing medium trace elements. The parameters of the chelation reaction were studied systematically and the results show that the optimal reaction condition is pH 3.0, reaction time 60 minutes, temperature 50.0°C, and citric acid content 1.48%. The XRD patterns show that the water‐insoluble compounds are complex mixtures, and the composition of the water‐insoluble compounds are changed through the addition of citric acid. FTIR and XPS analyes further demonstrate that water‐insoluble compounds are complex mixtures. The XRD patterns of the MAP products indicate that the structure and morphology of the MAP were changed by the addition of citric acid. In addition, the contents of major elements, medium elements, and trace elements in the MAP product are 68.72%, 0.24%, and 0.50%, respectively, which is consistent with the relevant China national standard.