The deposit of gypsum, a by-product from wet phosphoric acid process, are drawing more and more attention over world. In China, the gypsum deposit has been a severe environmental problem accompanying with the production of phosphate or phosphorus-based complex fertilizer. Using ammonium carbonate aqueous solution to convert gypsum to CaCO3 and (NH4)2SO4 is an effective way to reuse gypsum which can significantly reduce the gypsum deposit. But impurities in gypsum by product greatly influence the crystalliza...