Research on simultaneous removal and recovery of phosphorus from sewage by tobermorite induced crystallization
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摘要: 通过水热法合成雪硅钙石晶体，利用扫描电镜、X射线衍射仪和傅里叶变换红外光谱对晶体进行表征；以模拟厌氧消化液为处理对象，分析合成雪硅钙石作为晶种诱导磷酸钙结晶法去除污水中磷的效率，并对该晶种减轻反应过程中CO3 2−影响的作用进行研究。结果表明，合成的雪硅钙石纯度较高，且具有较强的pH和钙离子析出能力，在超纯水和自来水中分别投加2 g/L晶种后，溶液pH最终达到11.7和9.1，Ca2+浓度达到43和30 mg/L；体系中含有CO3 2−时，合成雪硅钙石诱导磷酸钙结晶反应符合晶体生长界面控制模型，且结晶反应仍符合二级方程（n=2）；CO3 2−的存在会抑制磷酸钙结晶反应过程中的除磷效率；但投加合成雪硅钙石晶种后，CO3 2−的抑制作用减轻，磷酸钙结晶反应效率和速率大幅提高，在试验设定CO3 2−浓度最大条件下，磷的去除率由4.6%大幅升至76.7%，速率常数（k）由0.76 L/(mol·min)提高至67.74 L/(mol·min)；合成雪硅钙石重复利用4次之后，对磷的去除效果仍然高于未投加合成雪硅钙石时磷的去除效果，表现出良好的可重复利用性。Abstract: A synthetic tobermorite crystal was obtained by hydrothermal method and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FTIR). Taking the simulated anaerobic digestion liquid as the treatment object, the performance of synthetic tobermorite-induced crystallization in removing phosphorus from wastewater was analyzed, and the effect of the seed crystal on CO3 2− reduction was studied. The results showed that the purity of synthetic tobermorite was high, resulting in higher pH and the release of a large amount of Ca2+ in the water. After adding 2 g/L seed crystals into ultra-pure water and tap water, respectively, pH of the solutions could reach 11.7 and 9.1, with the concentration of Ca2+ reaching 43 and 30 mg/L, respectively. The Interface-controlled crystal growth model well described the removal process of phosphorus by synthetic tobermorite-induced calcium phosphate crystallization, and the reaction conformed to the second-order equation (n=2). The presence of CO3 2− could inhibit the performance and rate of phosphorus removal in the crystallization reaction of calcium phosphate. However, it was found that the phosphorus removal rate and reaction rate were improved quickly after adding synthetic tobermorite seed, which had a certain eliminate with the interference of CO3 2− in the precipitation reaction of calcium phosphate. Under the condition of maximum CO3 2− concentration, the phosphorus removal rate increased significantly from 4.6% to 76.7%, and the rate constant k increased from 0.76 L/(mol·min) to 67.74 L/(mol·min). Moreover, after the synthetic tobermorite was reused for four times, the phosphorus removal efficiency was still higher than that without adding synthetic tobermorite, thus showing its good reusability.
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图 1 水热法合成的雪硅钙石晶体性能表征
Figure 1. Performance characterization of the synthetic tobermorite crystal synthesized by hydrothermal method
图 2 合成雪硅钙石对不同水体pH和Ca2+浓度变化影响
Figure 2. Effects of synthetic tobermorite on pH and Ca2+ concentration in different water bodies
图 3 合成雪硅钙石投加量对磷去除及体系pH的影响
Figure 3. Effect of different dosages of synthetic tobermorite on phosphorus removal and pH
图 4 不同反应体系中磷的去除效果
Figure 4. Phosphorus removal efficiency in different reaction systems
图 5 CO3 2−浓度为20 mmol/L时不同初始pH条件下投加晶种后反应过程中pH变化
Figure 5. pH changes during the reaction after adding crystal seeds under different initial pH at CO3 2− concentrations 20 mmol/L
图 6 不同CO3 2−浓度对合成雪硅钙石除磷反应动力学的影响
Figure 6. Effects of different CO3 2− concentrations on phosphate removal reaction kinetics of synthetic tobermorite
图 7 不同CO3 2−浓度下合成雪硅钙石重复使用对磷去除效果的影响
Figure 7. Effect of synthetic tobermorite recycle numbers on phosphate removal ratio at different CO3 2− concentrations
表 1 磷剩余浓度和沉淀速率常数(k)
Table 1. Residual phosphorus concentrations and precipitation rate constant ( k)
晶体投加
量/（g/L）碳酸根浓度/
(mmol/L)磷剩余浓度/
(mmol/L)k/
〔L/(mol·min)〕0 20 0.52 0.76 2 0 0.01 386.29 5 0.07 140.53 10 0.12 67.74 20 0.15 54.33 
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