纳米钢渣硅钙肥对重金属复合污染酸性水稻土的修复机制与生态评估

With the rapid development of industry and agriculture, heavy metal contamination in acidic paddy soil is becoming more and more urgent problem in China. Steel slag is byproducts of steel and iron industries, containing large amounts of CaO and SiO2. It has been well documented that steel slag is a low-cost material of silicon-calcium fertilizer and acid soil amendment. However, The release speed of CaO and SiO2 from slag is very slow, which significantly impact the utilization efficiency of slag. In consideration of this problem and the advantages of nano-particles, we propose to produce nano-slag-based silicon fertilizer. In this work, firstly, we will choose one or two better methods to make nano-particles of slag, then analyze the morphology structure, elemental composition, and specific surface area of nano-slag. Secondly, we will study the adsorption characteristics of Cu2+, Cd2+ and Zn2+ by nano-slag and the main impact factors through Batch incubation experiments. Thirdly, we will investigate the immobilization efficiency of nano-slag in a multi-metal contaminated soil through rice pot experiments, using X-ray diffraction (XRD), scanning electron microscopy/energy spectrometer (SEM/EDS) to demonstrate the effects and mechanisms of CaO and SiO2 in slag on heavy metals contents and distributions in soil , rhizosphere soil and plant, as well as using multiscan spectrum and Polymerase Chain Reaction-Terminal Restriction Fragment Length Polymorphism (PCR-TRFLP) techniques to discuss the effects on enzymatic activity and microbial community structure in soil and rhizosphere soil. Lastly, we will test the residual effects of slag and stability of heavy metals in the late rice.

钢渣富含硅钙等氧化物，是低廉的硅钙肥原料和酸性土壤重金属钝化剂。但是钢渣中氧化物在土壤中释放缓慢，利用效率低。本项目针对钢渣农用存在的弊端，结合纳米颗粒的优势，拟筛选出纳米钢渣硅钙肥的适宜制备技术，并对其形貌结构、比表面积和元素组成进行表征。继而通过序批培养试验，探明纳米钢渣硅钙肥对水体中Cu2+、Cd2+和Zn2+的吸附特性和影响因素；进一步通过水稻盆栽试验，探讨纳米钢渣硅钙肥对重金属污染酸性水稻土的修复技术，利用X射线衍射（XRD）、扫描电镜/能谱仪（SEM /EDS）等仪器揭示钢渣中CaO、SiO2对土壤和根际土壤以及植物体内重金属形态变化的作用机理；借助酶标仪、聚合酶链反应-末端限制性片段长度多态性技术 (PCR-TRFLP) 揭示钢渣硅钙肥施用后对土壤酶活性和微生物群落结构的影响。最后，对纳米钢渣硅钙肥施用后在第二季的余效和对重金属的稳固性进行跟踪监测。

随着工农业的快速发展，酸性水稻土重金属污染问题日益严重。钢渣是钢铁厂的副产品，富含硅、钙等氧化物，是低廉的硅钙肥原料和酸性土壤重金属钝化剂。但是钢渣中硅、钙等氧化物在土壤中释放缓慢，利用效率低。本项目针对钢渣农用存在的弊端，结合纳米颗粒的优势，筛选制备高效纳米钢渣硅钙肥的，进一步通过水稻盆栽试验，探讨纳米钢渣硅钙肥对重金属污染酸性水稻土的修复技术。首先（1）对全国主要钢铁厂中钢渣搜集分析，发现不同钢渣中植物有效性硅含量差异很大。钢渣冷却方式对有效性硅含量影响显著，水淬渣有效性硅含量显著高于空气自然冷却钢渣有效硅含量。钢渣中有效性硅含量与全硅含量及电导率（EC）呈显著正相关系。（2）通过对3种不同的钢渣在不同介质中培养试验研究发现：钢渣在土壤溶液中培养，第一天的硅素释放量主要由钢渣冷却方式决定，而在以后的培养过程中主要受温度的影响，其次为钢渣粒径，冷却方式影响甚微。（3）通过对十种有效硅含量高的钢渣中重金属特性分析发现：部分钢渣中Cr总量超过国家粉煤灰农用的限定标准，部分钢渣TCLP浸提液中Cr浓度超过了美国环保局限定的最高浓度。钢渣的TCLP浸提液中测定的Cr浓度与钢渣中Cr全量浓度并不一致，Cr的环境风险性并不单由总量决定，更大程度上决定于化学存在形态。所有搜集钢渣都不存在Cd、Pb、Hg和As等重金属元素的污染的环境风险。含有有较高量的活性Fe和活性的Mn的钢渣，不适宜作为硅钙肥施用于酸性土壤。但是上述钢渣对于Fe/Mn和Si缺乏的土壤施用会有很好的效果，如钙质水稻土。（4）通过纳米钢渣硅钙肥盆栽试验究发现：在外源重金属污染酸性水稻土中，添加适宜用量的纳米钢渣硅钙肥施用可以有效提高酸性水稻土pH值，同时可以提高土壤有效硅的含量，改变土壤中Cu、Zn、Cd金属的赋存形态，降低土壤中Cu、Zn和Cd的活性，促进了水稻的生长发育，并降低了水稻体内重金属的吸收积累。另外，钢渣硅钙肥施用提高了重金属污染土壤中细菌群群落结构多样性。但pH较高的钢渣用量过大时为造成负面影响。