School of Environment and Chemical Engineering, North China Electric Power University , Beijing 102206, P.R. China.
Environ Sci Technol. 2014 Nov 18;48(22):13138-45. doi: 10.1021/es503570y. Epub 2014 Nov 5.
The formation of mixed metal precipitates has been identified as a significant mechanism for the immobilization and elimination of heavy metal ions. Silicate is present in natural systems ubiquitously, which may interfere with metal uptake on the mineral surface and thereby influences the solubility of the precipitate. Herein, kinetic sorption and dissolution experiments combined with extended X-ray absorption fine structure spectroscopy (EXAFS) were performed to elucidate the effect of silicate on the formation of Ni precipitates at the γ-Al2O3 surfaces. The uptake of Ni on γ-Al2O3 decreased with increasing amounts of silicate coated onto the γ-Al2O3 surface. Results of EXAFS analyses suggested the formation of Ni-Al layered double hydroxide (LDH) phases. The surface coating of silicate on γ-Al2O3 reduced Al release and finally resulted in a high Ni:Al ratio due to a lower extent of Al substitution into the precipitates. The presence of silicate prevented the growth of the precipitates and led to the formation of less stable Ni-Al LDH. The influence of silicate on the precipitate formation provided the evidence for the growth relationship between the precipitate and mineral substrate in the real environment. Increased rates of proton-promoted dissolution of Ni surface precipitates were mainly attributed to higher Ni:Al ratios in Ni-Al LDH precipitates formed in the presence of silicate.
混合金属沉淀物的形成已被确定为固定和消除重金属离子的重要机制。硅酸盐在自然系统中普遍存在，它可能会干扰矿物表面的金属吸收，从而影响沉淀物的溶解度。在此，通过动力学吸附和解吸实验以及扩展 X 射线吸收精细结构光谱（EXAFS）研究了硅酸盐对γ-Al2O3 表面形成 Ni 沉淀物的影响。随着覆盖在 γ-Al2O3 表面的硅酸盐量的增加，Ni 在 γ-Al2O3 上的摄取量减少。EXAFS 分析结果表明形成了 Ni-Al 层状双氢氧化物（LDH）相。硅酸盐在 γ-Al2O3 上的表面涂层减少了 Al 的释放，最终由于 Al 取代进入沉淀物的程度较低，导致 Ni:Al 比值较高。硅酸盐的存在阻止了沉淀物的生长，导致形成了不太稳定的 Ni-Al LDH。硅酸盐对沉淀物形成的影响为实际环境中沉淀物和矿物基质之间的生长关系提供了证据。在存在硅酸盐的情况下形成的 Ni-Al LDH 沉淀中 Ni:Al 比值较高，主要归因于促进了 Ni 表面沉淀物的质子促进溶解。
