稀土冶炼废水除磷脱氮降镁深度处理与资源化利用集成技术研究

The treatment of ammonia nitrogen, phosphate and magnesium sulfate wastewater generated from rare earth hydrometallurgy is one of the problems hindering the sustainable development of the industry. To reach a satisfactory treatment result as well as cutting the cost in a large amount, we propose an integration technology based on chemical precipitation / biological methods to recycle the valuable elements in the three kinds of wastewater. The study plans to focus on the effects of essential factors on the removal rate of ammonia nitrogen, total phosphorus and total magnesium. The factors include the ratio of the three kinds of wastewater, the reaction system pH, dissolved oxygen, temperature, nutrients, microbial propagation and etc. Through intensive experiments, we aim to find a stable and suitable process conditions for wastewater treatment, probe the influence of coexisting components and their removal, and study the purity and application of recycled products. We expect the rates of cumulative denitrification, dephosphorization and demagnetization from three kinds of wastewater will be above 99%, 98% and 95%, respectively. The concentrations of ammonia, total phosphorus and total magnesium in the treated wastewater are lower than 15mg / L, 1mg / L, 100mg / L, respectively, so that the treated wastewater can reach the discharge standard. The process can maximize the removal rate of denitrification, phosphorus, magnesium. It can also remove and recycle multi-polluting components efficient and effectively at the same time in an economical way. These will have foreseeable economic and social benefits.

稀土湿法冶炼产生的氨氮废水、磷酸盐碱性废水、硫酸镁废水等的处理，成为制约着稀土产业可持续发展的问题之一。在确保处理效果的前提下，为了有效的降低废水处理成本，我们提出了以化学沉淀法/生物法为基础的集成技术，对上述三种废水中的有价元素进行资源化回收处理。重点研究三种废水样品配比、反应体系pH、溶解氧、温度、营养物质、微生物传代过程中降解率变化等因素，对氨氮、总磷、总镁去除率的影响。通过多次实验摸索，找到处理废水稳定的适宜工艺条件，探讨共存组分的影响及去除问题，研究回收产物的纯度及应用问题。预计该工艺对三种废水的累积脱氮、脱磷、脱镁率依次可达到99%、98%、95%以上，“出水”中氨氮、总磷、总镁浓度依次低于15mg/L、1mg/L、100mg/L,使处理后废水达标排放。该工艺最大程度的使废水脱氮、除磷、降镁，并实现多污染组分同步、高效、经济去除及资源化回收利用，它具有明显的经济和社会效益。

稀土湿法冶炼产生的氨氮废水、Na3PO4废水、MgSO4废水的治理，通常是采用物理、化学的方法，转化成固态物质回收处理，该过程往往需要消耗大量的能源，也会造成二次污染。本项目采用化学与生物法为基础的集成技术，对上述三种废水进行同步资源化处理，重点研究了酸度、物料比、加料顺序、共存组分、温度、盐度、碳源、氮源、氨氮浓度和接种量等因素，对废水处理的影响。初步找到了三种废水统一处理的适宜工艺条件，物料比为n(NH4+)：n(Mg2+)：n(PO43-)=1:1:1、加料顺序为氨氮废水与硫酸镁废水预先混合均匀，在搅拌下加入磷酸钠废水，期间使pH≤10，完全混合后调节pH=9.0；使沉淀反应完全，获得MAP白色晶型沉淀和上清液。测定上清液pH为8.3，组分浓度降低为氨氮91.35mg/L、Mg2+113.4 mg/L、PO43-168.7 mg/L，其去除率均达到97%以上。通过分离、纯化、筛选培养法，获得试验菌株MX（Bacillus megaterium），重点研究了其NH4+-N降解特性及降解动力学，对MX高效降解氨氮的适宜条件进行探讨。将MX 菌液（OD600=1.3）以5%的接种量投放于上清液中，按每升水样3.0g加入 NaAc，30℃好氧发酵72h，废水中氨氮浓度降低为11.05mg/L，氨氮降解率为87.9%，达到了《稀土工业污染物排放标准》对于氨氮浓度15 mg/L限值的排放标准要求。研究了MAP再利用，经测定MAP纯度达到96%以上，重金属元素浓度很低,可作为植物生长的缓释肥使用； MAP控温110℃焙烧4h，MAP发生分解可生成MHP和浓度为9%以上的氨水,MHP可作为处理氨氮废水的吸附剂使用，氨水回用于稀土生产。该方法充分利用化学沉淀法与生物法处理废水的技术优势，两者有机结合起到优势互补作用，与现有技术相比，达到以废治废、变废为宝、降低废水处理成本、保护环境的目的。