风化壳淋积型稀土矿闭矿场铵盐淋出液化学沉淀脱氮

Nitrogen Removal of Ammonium Leaching Solution from Weathered Crust Elution-Deposited Rare Earth Ore Tailing by Chemical Precipitation

铵盐浸取风化壳淋积型稀土矿后残留大量铵盐,对稀土矿闭矿场淋出液进行脱氮处理是解决氨氮污染的有效手段。采用化学沉淀法脱除稀土矿闭矿场淋出液中氨氮,研究了沉淀条件对氨氮去除率的影响,利用响应面法优化沉淀工艺参数,通过溶液化学计算、XRD与SEM等分析化学沉淀脱氮过程及机理。结果表明:在pH=7.0、n(N)/n(P)=1.0/1.1、25℃、反应时间240 s的条件下,氨氮去除率可达86.87%;响应曲面拟合结果表明,各因素对氨氮去除率的影响次序为:NaOH的用量(pH)>n(N)/n(P)>反应时间,优化条件下氨氮去除率高达98.02%,化学沉淀后淋出液氨氮浓度<15 mg/L,达到国家排放标准;沉淀产物主要为MgNH4PO4·6H2O及少量MgHPO4·3H2O、Mg(OH)2和Mg3(PO4)2固体,呈表面粗糙的空心棒状结构。

A large amount of ammonium salt remains after leaching the weathered crust elution-deposited rare earth ore.Denitrification of leachate from rare earth tailings is an effective method to solve ammonia nitrogen pollution.The ammonia nitrogen was removed from the leachate of rare earth ore tailings by chemical precipitation method and effects of precipitation conditions on ammonia nitrogen removal rate were studied.The response surface method was used to optimize the precipitation process parameters, and the chemical precipitation denitrification process and mechanism were analyzed by solution chemical calculation, XRD and SEM.The results show that under the conditions of pH=7.0,n(N)/n(P)=1.0/1.1,25 ℃,reaction time of 240 s, the ammonia nitrogen removal rate could reach 86.87%.The results of response surface fitting show that the sequence of influence of each factor on ammonia removal rate is NaOH dosage(pH),n(N)/n(P),and reaction time.Under the optimized conditions, the ammonia removal rate is up to 98.02%,and the ammonia concentration of leachate after chemical precipitation is less than 15 mg/L,which meets the requirement of national emission standard.The precipitated products are mainly MgNH4PO4·6 H2O and a small amount of MgHPO4·3 H2O,Mg(OH)2and Mg3(PO4)2solids with rough surface and hollow rod-like structure.