晶种对磷酸铵镁法去除水中磷的影响

Effects of seed crystals on phosphorus removal by magnesium ammonium phosphate crystallization

磷酸铵镁(MAP)法去除并回收废水中的磷具有操作简单、反应迅速等特点,但该法因生成的晶体颗粒细小而导致固液分离困难。现提出在MAP沉淀过程中投加适当晶种,以期提高除磷率的同时便于固液分离。针对初始磷酸盐质量浓度为100 mg/L,摩尔比n(Mg)∶n(P)∶n(N)=1.3∶1∶1,p H=9.5的溶液体系,首先从投加的4种晶种(活化石英砂、活化沸石、石英砂、沸石)材料中筛选出最佳晶种,并考察晶种投加量、反应时间对除磷效果的影响,探究投加晶种对磷酸铵镁结晶除磷效能的机理,并运用SEM对沉淀产物、最佳晶种及晶种作用下的结晶产物进行表征分析。结果表明,在反应体系内投加活化石英砂能获得最佳的除磷效能;该溶液体系,在搅拌强度为150 r/min,投加粒径为100~120目的活化石英砂1.0 g/L,反应时间20 min,陈化时间30 min的条件下除磷率从未投加晶种的60.97%提高到80.97%。同时SEM表征结果表明,沉淀产物的晶形大致呈斜方形但晶体较分散且大小和粗细不均匀;而在加入活化石英砂晶种后,晶种周围存在大量的小斜方晶体,这说明沉淀产物确实有围绕晶种生长的趋势,从而增大了晶体粒径,便于固液分离。

Removal and recovery of phosphorus from wastewater by ammonium magnesium phosphate（ MAP） has the characteristics of simple operation and rapid reaction. However,this method is difficult to separate solid and liquid due to the small crystal particles. It is proposed to add appropriate seed crystals during MAP precipitation in order to improve the removal rate and to facilitate solid-liquid separation. In this paper,For a solution system of the initial phosphate concentrationwas 100 mg/L,the molar ratio of n（ Mg） ∶ n（ P） ∶ n（ N） = 1. 3∶ 1∶ 1 and p H = 9. 5,the optimal crystal species were selected from the four kinds of crystal（ activated quartz sand,activated zeolite,quartz sand and zeolite）,the effects of seeding dosage and reaction time on the phosphorus removal and the mechanism of seed crystals on phosphorus removal in magnesium ammonium phosphate crystallization were investigated. The crystallization products of precipitated products,optimal crystal species and crystalline species were analyzed by SEM. The results show that the addition of activated quartz sand in the reaction system can obtain the optimum phosphorus removal efficiency. Under the conditions of the stirring strength 150 r/min,the dosage of particle size of activated silica sand for 100 ~ 120 mesh 1. 0 g/L,reaction time 20 min,aging time 30 min,the phosphorus removal rate increased from 60. 97% to 80. 97%,which compared to the absence of the crystals. The results of SEM characterization show that the crystal shape of the precipitated products were obliquely square,but the crystal were dispersed and the size and thickness were not uniform. After adding the activated quartz sand,there are a lot of small oblique crystals around the seed crystal,which shows that the precipitated product does have the tendency to grow around the seed crystal,thus increasing thecrystal grain size and facilitating the solid-liquid separation.