Department of Chemical Engineering, University of São Paulo, Rua do Lago, 250, P.O. Box 61548, São Paulo, SP, Brazil 05424-970.
Environ Technol. 2011 Oct;32(13-14):1615-25. doi: 10.1080/09593330.2010.545440.
Contaminated sediments provide the main source of mercury for methylation by bacteria in lakes and waterways. In situ capping has been used to remediate these sediments, but traditional reactive materials have very low affinity for Hg(II). This study investigated the mercury uptake by biogenic silica modified with L-cysteine, as a potential material to be used for in situ remediation technologies. The adsorbent was obtained from rice hull ash by extraction as sodium silicate and acid hydrolysis through the sol-gel process; it was then modified with L-cysteine by impregnation from aqueous solution. The unmodified and modified biogenic silica showed structural and chemical properties suitable for mercury sorption from aqueous medium. The cysteine affected the structural properties of the unmodified silica, decreasing the specific surface area and pore volume by eightfold. On the other hand, cysteine increased the silica adsorption capacity, resulting in mercury uptake similar to that of the unmodified silica. The Hg(ll) specific adsorption by unmodified and modified silica was 0.20 mmol/g and 0.19 mmol/g SiO2, respectively, from an aqueous solution of 1 mmol/L Hg(II). The pH range of 3-7did not have an effect on Hg(II) adsorption. However, the presence of chlorine, added as HgCl2, seems to have limited the mercury adsorption, especially at high concentrations of Hg(II). The mercury adsorbed on the silica surface could not be recovered using HCl even from concentrated solutions.
受污染的沉积物为湖泊和水道中细菌将汞甲基化提供了主要来源。原位覆盖已被用于修复这些沉积物，但传统的反应性材料对 Hg(II) 的亲和力非常低。本研究调查了经 L-半胱氨酸修饰的生物硅石对汞的吸收，作为一种潜在的原位修复技术材料。该吸附剂是从稻壳灰中提取的，方法是通过溶胶-凝胶工艺将其制成硅酸钠并进行酸水解；然后通过水溶液浸渍将其用 L-半胱氨酸进行修饰。未修饰和修饰的生物硅石均表现出适合从水介质中吸附汞的结构和化学性质。半胱氨酸影响未修饰二氧化硅的结构特性，使比表面积和孔体积降低了八倍。另一方面，半胱氨酸增加了二氧化硅的吸附能力，导致对汞的吸收与未修饰的二氧化硅相似。从 1mmol/L Hg(II)的水溶液中，未修饰和修饰的硅石对 Hg(ll)的特异性吸附分别为 0.20mmol/g 和 0.19mmol/gSiO2。pH 值范围在 3-7 之间对 Hg(II)的吸附没有影响。然而，添加的氯（以 HgCl2 的形式）似乎限制了汞的吸附，尤其是在 Hg(II)浓度较高时。甚至从高浓度的溶液中，用 HCl 也无法回收吸附在硅石表面的汞。
