Abstract
The freezing acidolysis solution of the nitric acid-phosphate fertilizer process has a high calcium content,which makes it difficult to produce fine phosphate and high water-soluble phosphate fertilizer products.Here,based on the potential crystallization principle of calcium sulfate in NH4NO3-H3PO4-H2O,the deep decalcification(i.e.calcium removal)technology to achieve α-high-strength gypsum originated from freezing acidolysis-solutions has been firstly proposed and investigated.Typically,calcium can be removed from the factory-provided freezing acidolysis-solution by neutralizing it with ammonia,fol-lowed by the addition of ammonium sulfate solution.As a result,the formation of calcium sulfate in the reaction system undergoes the nucleation and growth of CaSO4·2H2O(DH),as well as its dissolution and crystallization into short columnar α-CaSO4·0.5H2O(α-HH).Remarkably,with the molar ratio of SO24-/Ca2+at 1.8,the degree of neutralization(NH3/HNO3 molar ratio)at 1.7,the reaction temperature of 94 ℃,and the reaction time of 300 min,the decalcification rate can reach 86.89％,of which the high-strength α-CaSO4·0.5H2O(α-HH)will be obtained.Noteworthy,the deep decalcification product meets the standards for the production of fine phosphates and highly water-soluble phosphate fertilizers.Consequently,the 2 h flexural strength of α-HH is 5.3 MPa and the dry compressive strength is 36.8 MPa,which is up to the standard of commercial α-HH.
基金项目
National Key Research and Development Program of China(2018YFC1900206-2)
Science &Technology Plan Projects of Guizhou Province(Qiankehe Service Enterprises[2018]4011)
Science and Technology Support Plan Project of Guizhou Provincial(Qiankehe Support[2021]General 487)
NETL
NSTL
万方数据