摩尔配比对MAP沉淀法回收模拟废水中磷的影响

以磷浓度50mg/L的实验室模拟废水为研究对象,考察了以鸟粪石(MAP)形式回收磷的最佳摩尔配比,并借助X-衍射(XRD)对不同摩尔配比条件下得到的沉淀物进行分析。试验结果表明,在pH=9.5时,以鸟粪石形式回收磷的最佳Mg:N:P=4:1.6:1。对沉淀物的XRD分析发现,在pH=9.5,当固定Mg:P=1.6时,N:P=1时沉淀物中基本不含MAP,当N:P=2时,生成的沉淀物中混有少量的副产物Mg(3PO)42,当N:P2时则生成较纯的MAP;当固定N:P=4时,Mg:P=2是生成较纯的MAP的临界值,超过此比例则生成副产物Mg(3PO)42;当反应按照理论配比投加氨氮和镁盐时,所得产物基本不是MAP,而是副产物Mg(3PO)42。故鸟粪石沉淀结晶反应中应尽量提高氨氮配比,并避免投加过量的镁盐,以保证回收产物的纯度。

Molar Ratio Effect on Phosphorus Recovery by MAP from Simulative Wastewater

Phosphorus recovery by struvite from simulative wastewater with phosphorus concentration of 50mg/L was studied under the condition of molar ratio. X-ray diffraction (XRD) was used to analyze the identity of the precipitate produced under different molar ratio. Results showed that at pH 9.5,the optimum Mg : N : P is 4 : 1.6 : 1. XRD results showed that the precipitate weren't struvite basically at pH 9.5 and Mg:P 1.6, when N : P 1; when N : P at 2, the precipitate contained a little outgrowth of Mg_3(PO_4)_2; when N : P>2, that were almost only struvite. When pH 9.5 and N : P at 4, the critical molar ratio of Mg : P for purer precipitate was 2;when Mg : P molar ratio was higher than 2, the outgrowth of Mg_3(PO_4)_2 would be produced. With stoichiometric concentration of three ions, the precipitate wasn't struvite but outgrowth Mg_3(PO_4)_2. Therefore, increasing the ammonium concentration and avoiding excess magnesium would increase the purity of the precipitate on struvite crystallization.