Immobilization by sulfuration of waste heavy metals

本文研究了一种新的固定和沉积垃圾焚烧飞灰中重金属的方法。有毒重金属如铅和锌在飞灰中以可溶化合物的形式存在，如金属氯化物和氧化物。这项研究是基于这样一个事实，即重金属自然以不溶于水的硫化物的形式存在，而且沥青是憎水的。在加热温度为403-523K的双轴捏合机中，通过混合沥青、硫磺和碱性试剂氢氧化钠和氢氧化钙，对废重金属进行了物理和化学固定。对Gibbs自由能的计算表明，重金属的硫化是硫磺与碱性试剂反应生成硫化钠或硫化钙的结果。对含有硫磺和碱性试剂的可溶性金属化合物的X射线衍射分析结果也表明，只有在初始形成硫化钠或硫化钙的情况下，可溶金属化合物才能转化为不溶的金属硫化物。研究发现，在403K下向飞灰中加入硫磺和氢氧化钠会导致重金属的硫化。同样，硫和氢氧化钙在523K下的加入也导致了重金属的硫化。对所提出的固定化方法处理后的飞灰进行了淋溶试验，结果表明，处理后的飞灰中重金属的淋溶是可抑制的。

The present study is concerned with a novel method to immobilize and deposit heavy metals contained in fly ash from waste incineration facilities.The toxic heavy metals such as lead and zinc are present as soluble compounds in fly ash such as metal chlorides and oxides. This study was based on the fact that heavy metals naturally exist as insoluble sulfides and that asphalt is water-repellent. We propose the physical and chemical immobilization of waste heavy metals by mixing with asphalt, sulfur and alkaline agents-sodium hydroxide and calcium hydroxide, in a bi-axial kneader heated at 403-523K.Calculations on the Gibbs' free energies showed that sulfuration of heavy metals resulted from the formation of either sodium sulfide or calcium sulfide via the reaction of sulfur with alkaline agents. Experimental results from XRD analysis of soluble metal compounds mixed with sulfur and alkaline agents also indicated that soluble metal compounds were convertable to insoluble metal sulfides only if either sodium sulfide or calcium sulfide is initially formed. It was found that the addition of sulfur and sodium hydroxide into fly ash at 403K led to the sulfuration of heavy metals. Similarly, the addition of sulfur and calcium hydroxide at 523K brought about sulfuration of heavy metals. The results of the leachability test for the treated fly ash by the proposed immobilization method indicated that leaching of heavy metals in fly ash was suppressible.