合成条件对粉煤灰合成沸石除磷特性的影响

利用不同钙含量的3种粉煤灰采用碱熔融-水热法合成沸石,研究了不用合成条件对3种粉煤灰合成沸石除磷性能的影响,并分析了除磷机理。3种粉煤灰合成沸石中沸石的种类各不相同,低钙粉煤灰合成沸石主要以NaP1型沸石为主,中钙粉煤灰合成沸石主要以一种无名沸石为主,高钙粉煤灰合成沸石则主要以加藤石为主,沸石含量几乎为零。碱灰比、熔融时间、熔融温度、固液比、结晶时间等合成因素中,对3种粉煤灰合成沸石固磷能力影响相对较大的是碱灰比和熔融时间。3种合成沸石的除磷能力顺序依次为高钙粉煤灰合成沸石> 中钙粉煤灰合成沸石> 低钙粉煤灰合成沸石,并且3种沸石的固磷能力与初始原料粉煤灰中的CaO含量成正比。固磷机理是合成沸石溶于水后向水中释放Ca2+,释放出来的Ca2+即可与磷酸根生成磷酸钙沉淀,从而达到固磷的目的。合成的沸石最大固磷能力为92.24 mg/g。

Effect of synthetic conditions on characters of phosphorus removal using synthetic zeolite from fly ash

An alkaline fusion method was adopted to synthesize zeolites from low-calcium, middle-calcium, and high-calcium fly ashes. The effects of different synthesis conditions on the phosphorus immobilization capacity of the synthesized zeolites were studied, and the phosphorus immobilization mechanism was also analyzed. The main crystals of the three synthesized zeolites from low-calcium, middle-calcium, and high-calcium fly ashes are NaP1 zeolite, Na6(AlSiO4)6·4H2O, and katoite, respectively. The effects of the NaOH/fly-ash mass ratio and the melting time on the phosphorus uptake of the synthesized zeolites are relatively larger than the solid-liquid ratio, melting temperature, and crystallization time. The phosphorus uptake capacity of the three synthesized zeolites is in the following order:high-calcium zeolite> middle-calcium zeolite> low-calcium zeolite. The capacity of synthetic the synthesized zeolites for phosphorus removal is proven to be proportional to the calcium content of the different raw materials. After the synthesized zeolites were added into the solution, the Ca2+ in the zeolite was leached into the solution and its was then precipitated with PO3-4 to produce calcium phosphate. The maximum adsorption capacity for phosphorus obtained is 92.24 mg/g.