Removal of calcium from phosphoric acid produced by the nitric acid process using solvent extraction with TCHDGA and stripping with water

The phosphoric acid produced by the nitric acid method cannot be used as an industrial-grade product as a result of the high calcium nitrate content. It can only be used for fertilizer production due to difficulty of complete removal of calcium nitrate. Herein, an efficient approach for the removal of calcium nitrate from the phosphoric acid produced by the nitric acid process was studied. The proposed process is based on solvent extraction with N, N, N′, N′-tetracyclohexyl-3-oxyglutaramide (TCHDGA). The effects of time, diluent, temperature, impurity ions, and the concentrations of extractant and nitric acid on the extraction of Ca2+ were considered. A series of characterization tests involving FT-IR spectroscopy, XPS analysis, slope analysis and X-ray single crystal diffracted analysis revealed that the stoichiometry of the complex is (Ca(NO3)2)(TCHDGA)3. The concentration of Ca2+ in phosphoric acid drops below 5 mg/L a three-stage cross-current extraction process. The stripping efficiency of calcium nitrate in the organic phase by water is above 99.9%. The extraction efficiency of Ca2+ by TCHDGA remained above 96.8% after ten extraction-stripping cycles, realizing the efficient removal of calcium nitrate in the phosphoric acid produced by nitric acid process without changing the traditional production conditions. •Efficient removal of calcium from phosphoric acid produced by HNO3-route.•Ca coordinates with nine oxygen donor atoms forming Ca(NO3)2·(TCHDGA)3.•TCHDGA could achieve high-efficient separation of Ca from Fe, Mg, and Al.•H2O could easily improve the reusability of TCHDGA.•TCHDGA exhibited high efficiency and prolonged reusability for the removal of Ca.