不同Ca/P比下碳酸根对磷酸钙沉淀反应回收磷的影响

以模拟污水处理厂污泥厌氧消化液为处理对象,进行磷酸钙沉淀除磷小试实验,考察了不同Ca/P物质的量比下碳酸根(CO2-3)对磷酸钙沉淀反应回收磷的影响;利用扫描电镜(SEM)、X射线衍射仪(XRD)和傅里叶变换红外光谱(FTIR)对沉淀产物进行表征。结果表明,磷酸钙沉淀反应是一个快速过程,CO2-3的存在并未改变这一显著特征。磷酸钙沉淀反应过程中,CO2-3的存在降低了磷的去除率,改变了沉淀物形貌、结构和组分;实验设定范围内,磷酸钙的过饱和度越高,越难形成晶体态羟基磷灰石((Ca5(PO4)3OH,HAP);当pH值为9.0,Ca/P比为1.67时,CO2-3取代HAP晶格中的PO3-4,形成碳磷灰石(CHAP);当pH值为9.0,Ca/P比为3.33和5.01时,CO2-3和PO3-4之间竞争,形成碳酸钙(CaCO3);增大Ca/P能有效提高磷的去除率,降低CO2-3对磷酸钙沉淀反应的抑制作用,但综合考虑实际效果,选择Ca/P比为3.33作为适宜的反应条件。

Effect of carbonate on calcium phosphate precipitation at different Ca/P ratios for phosphorus recovery

The effects of carbonate (CO₃^2-) on the reaction of calcium phosphate precipitation at different Ca/P ratios were investigated by using synthetic anaerobically digested supernatant as treatment target at bench-scale. The precipitates were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that calcium phosphate precipitation reaction was a fast process, irrespective of the existence of CO₃^2-. However, the existence of CO₃^2- could reduce the removal efficiency of P, and it had more effect on the morphology, structure and constituents of precipitate. In addition, it was more difficult to form hydroxyapatite (HAP) crystal with the increase of supersaturation of calcium phosphate in the experiment. The PO₄^3- in HAP crystal would be substituted by CO₃^2- and the carbonated hydroxyapatite (CHAP) was formed when pH value was 9.0 and Ca/P ratio was 1.67. However, CO₃^2- would compete against PO₄^3- and led to the formation of calcium carbonate when pH value was 9.0 and Ca/P ratio was 3.33 or 5.01. This research indicated that increasing the Ca/P ratio could improve the removal efficiency of phosphate and reduce the interference of CO₃^2-. It suggested that the Ca/P ratio of 3.33 would be an optimal reaction condition based on the comprehensive consideration.