NaCl溶液浓度对磷石膏制备α-半水石膏转晶行为的影响

Effect of NaCl solution concentration on transcrystallization behavior of α-hemihydrate gypsum from phosphogypsum

为提高湿法磷酸工艺排放的副产品磷石膏的利用率和附加值,采用常压水热合成法在NaCl溶液中制备α-半水石膏材料,研究了NaCl溶液浓度对α-半水石膏的结晶水含量、转晶行为、矿相组成和显微形貌的影响。研究结果表明,在温度为95℃质量分数为10.0%~20.0%的NaCl溶液中,磷石膏的结晶水含量均随着反应时间的延长逐渐降低,且降至约6%后将逐渐趋于平缓。结合XRD和SEM分析认为磷石膏在95℃质量分数为10.0%~20.0%的NaCl溶液中可脱水转晶形成稳定的六方柱状α-半水石膏。同时,磷石膏的脱水转晶速率呈现先缓慢上升而后快速升高,最后逐渐趋于平缓的变化趋势,属于典型的生长-成核动力学过程。随着NaCl溶液浓度的升高,α-半水石膏的诱导成核时间和晶体生长时间逐渐加快,总转晶时间逐渐缩短。其中,磷石膏在质量分数为20.0%的NaCl溶液中水热反应0.5 h后即可完全转变为α-半水石膏,与质量分数为15.0%的NaCl溶液相比缩短了1.38 h。因此认为,NaCl溶液浓度的提高有助于加快磷石膏的脱水转晶效率,这可为实际规模化生产α-半水石膏提供指导。

In order to improve the utilization rate and added value of phosphogypsum by-products discharged from wet phosphoric acid process,α-hemihydrate phosphogypsum materials were prepared in NaCl solution by the atmospheric pressure hydrothermal synthesis method,and the effects of NaCl solution concentration on crystal water content,crystallization behavior,mineral phase composition and microscopic morphology of α-hemihydrous phosphogypsum were studied.The results showed that the crystalline water content of phosphogypsum was gradually decreased with the prolongation of reaction time in 10.0%~20.0% NaCl solution at a temperature of 95 ℃ and leveled off after decreasing to about 6%.Combined with XRD and SEM analysis,it was concluded that phosphogypsum could be dehydrated and recrystallized to form stable α-hemihydrous gypsum with hexagonal columnar shape in 10.0%~20.0% NaCl solution at 95 ℃.At the same time,the dehydrated transcrystallization rate of phosphogypsum was increased slowly at first,then rapidly,and finally gradually tended to be gentle,which was a typical growth-nucleation dynamic process.With the increase of NaCl concentration,the induced nucleation time and crystal growth time of α-hemihydrous phosphogypsum were gradually accelerated,and the total crystallization time was gradually shortened.Among them,the completely dehydrated transcrystallization time of phosphogypsum in 20.0%NaCl solution was only 0.5 h,and which was shortened by 1.38 h compared with 15.0%NaCl solution.Therefore,it was concluded that the increase of NaCl solution concentration accelerated the dehydration and crystallization efficiency of phosphogypsum,which could provide guidance for the actual large-scale production of α-hemihydrate gypsum.