乙二胺对CaSO_4·2H_2O-NH_3-CO_2-H_2O反应体系制备球霰石络合作用的研究

Complexation Effects of Ethylenediamine on Vaterite Preparation in CaSO_4·2H_2O-NH_3-CO_2-H_2O Systems

烟气CO_2与工业固废磷石膏(CaSO_4·2H_2O)在CaSO_4·2H_2O-NH_3-CO_2-H_2O多相复杂体系中生成碳酸钙与硫酸铵,反应体系中游离的Ca^(2+)浓度呈下降趋势,产物CaCO_3为方解石和球霰石混合晶型。研究以乙二胺为添加剂,在固定搅拌转速、CO_2流量、氨水浓度的条件下,研究乙二胺(EDA)对CaSO_4·2H_2O-NH_3-CO_2-H_2O反应体系制备球霰石的影响及作用机理。结果表明:添加剂乙二胺以钙络合剂的形式参与反应抑制结晶,将反应体系的诱导期延长至60 min,根据质量守恒定律和配位解离平衡模拟的硫酸根浓度理论值与硫酸根浓度实验值、钙元素浓度实验值之间的误差小于20%。钙以游离态或与乙二胺形成配合物的形式存在于溶液中,钙浓度呈先上升后下降趋势,上升阶段钙浓度大于20℃时CaSO_4·2H_2O-NH_3-CO_2-H_2O的溶解度15 mmol×L^(-1),获得单一形貌的碳酸钙产品球霰石。随着乙二胺浓度的升高,诱导期内体系中钙浓度增加。通过延长诱导期,将反应结晶过程中的溶解与结晶过程分离,为直接制备纯净球霰石提供理论和可行性方面的指导。

Calcium carbonate and ammonium sulfate can be produced by flue gas CO2 and industrial waste phosphogypsum in complex systems of CaSO4·2 H2 O-NH3-CO2-H2 O. Ca^（2＋）concentrations decrease in this reaction system and the products are polymorph CaCO3 including calcite and vaterite. Effects and mechanism of ethylenediamine（EDA） on the preparation of vaterite in CaSO4·2 H2 O-NH3-CO2-H2 O were studied under fixed agitation speed, CO2 flow rate and ammonia concentration. The results show that EDA participates in the reaction in a form of calcium complexant to prolong the induction period to 60 min and inhibit CaCO3 formation. The difference between calculated（via mass balance and coordinated dissolution equilibrium） and experimental SO4^（2-） concentrations is less than 20%. Calcium exists in forms of free Ca^（2＋） and EDA complexation in solution, and its concentration increases first and then decreases. When the calcium concentration increases and temperature is over 20℃, calcium solubility is over 15 mmol×L^（-1） and pure vaterite is formed. The increase of EDA in solution results in the increase of calcium concentration during induction periods. The dissolution and crystallization processes of the reaction system could be separated by prolonging induction period, and this result is helpful in preparing pure vaterite.