Research On Producing High Purity CaCO₃by Phosphogypsum

Without effective treatment, most of the phosphogypsum were stored up which heavily polluted the environment. Throughout the effort of researchers, many utilizations of phosphogypsum were explored. It is one of the best influential utilization approaches for phosphogypsum to product sulfuric acid through decomposition of it. However, it will need a high temperature and lots of energies for the process which restrains it is application. It is large-scale resource utilization of phosphogypsum that has become the key of realizing sustainable development in phosphorous chemical industry. Based on the analysis of phosphogypsum, this paper provides a new way to acquire high quality CaCO3by phosphogypsum. With calculation of FactSage6.1, a series of experiments were developed to find the best conditions and control the crystal structure of CaCO31. A lot of thermodynamic calculation were taken by FactSage6.1to explore the effect of temperature. The analysis of phase diagram was taken to examine the transformation of products in every step. Both of the two major reactions are spontaneous and higher temperature restrains the reactions. Based on the analysis of FactSage6.1, this draft is theoretically viable.2. With the single factor experiments, the feasibility of this draft is proved. The best condition is phosphogypsum:H2O:NaOH=25:125:12, reaction time2h; phosphogypsum:HCl=5:7(edulcoration); gas:liquid=300:4,150mL/min. Based on the results of SEM,XRD, the CaCO3product are mainly vaterite with little calcite which have better heat stability, particle size1-10μm, purity98%, white96%.3. The by-products have good quality which could be utilized. The purity of Na2SO4and NH4CI are above85%and could be used as industrial addition directly. Based on the material calculation,It phosphogypsum can product0.45t CaCO30.75t Na2SO4and0.6t NH4Cl without pollution.4. As crystalline controller, citric acid, ethanol, H2SO4and NaOH were added during the carbonization process for examining the effect on the structure of CaCO3. Citric acid can promote the transformation from vaterite to calcite and lower the particle size of CaCO3. Ethanol can restrain the transformation from vaterite to calcite largely and lower the particle size of CaCO3. H2SO4can restrain the transformation from vaterite to calcite too and induce the whisker growing to chain. NaOH can control the product of calcite and induce the whisker growing to acicular.