无石膏复合水泥固化处理Pb(Ⅱ)、Cr(Ⅵ)的研究

Experiments on Solidification/Stabilization of Divalent Lead,Hexavalent Chromium Using Composite Cement Without Gypsum

实验发现采用无石膏复合水泥固化处理溶解态Pb(Ⅱ)、Cr(Ⅵ)的效果很理想,虽然搅拌水中Pb(Ⅱ)或Cr(Ⅵ)的浓度高达4 000 mg/L,但其28 d龄期固化体粉碎样浸提液中的Pb(Ⅱ)或Cr(Ⅵ)的浓度均能降低至0.2 mg/L,达到了废水的排放标准。此外,在掺加Na2CrO4后复合水泥的水化反应加快,凝结时间缩短,各龄期固化体的抗压强度也明显提高。与此相反,掺Pb2+后复合水泥净浆的凝结时间明显延长,胶砂的流动度明显增大,早期强度也明显降低,分析认为这主要是水化过程中形成了含Pb沉淀物,它们包裹着水泥颗粒,形成致密的不透水层而使水泥水化受阻所致。

Experiments showed that divalent lead or hexavalent chromium in wastewater were effectively solidified by composite cement without gypsum. Although the concentration of Pb（Ⅱ ） or Cr（ Ⅵ） in mix water got to 4 000 mg/L, they both became low down to 0.2 mg/L in leachate from 28 d old powdered mortar-sand cubes and also meet the standard of drainage of wastewater into environment. Furthermore, the hydration of cement was accelerated and the compressive strengths of hard cement mortar-cubes also increased significantly after they were blended with .sodium chromate. On the contrary, the setting time of the composite cement slurry delayed greatly and their fluidity were increased significantly after blended with lead nitrate. The unconfined compressive strength of hardened motar-sand cubes at early stage of hydration was aiso greatly reduced. The main reason was that lead-containing compound forms a dense impervious coat around cement particles when they deposited on their surface, thus hinder the reaction between cement and water.