Dec 14 2018
尽管缺乏有效且环境良性的过程，但事实证明，“城市采矿”或从二手电子小工具中回收贵金属的回收都比以往任何时候都重要。
©Wiley-VCH
Currently, an international research team has taken a deep look into gold dissolution, particularly how organic thiol-containing compounds help dissolve elemental gold. The fast, selective, and convenient thiol-assisted gold leaching processes have been proposed in their study published in the journalAngewandte Chemie.
Melting is the conventional method used for recycling gold “waste.” Dental gold and jewelry can be recycled about 100%; however, recycling of precious metals in computers, smartphones, and other electronic gadgets is much more difficult, and the recovery quote is even low. Although they are abundant in electronic devices, their relative content is still very low to enable really economical urban mining.
Hydrometallurgical cyanide leaching is the conventional mining method for gold and it produces a large amount of hazardous waste while being comparatively unselective. Many of the latest concepts are based on the complexation of gold in organic solutions as it forms soluble complexes with sulfur-containing reagents. However, the processes must be viable on a large scale and still prevent the formation of hazardous or toxic compounds. Currently, Timo Repo from the University of Helsinki, Finland, and his team have deeply examined the details of selective gold extraction in organic solution. They put forward an efficient gold recovery method from electronic waste using the chemical dimethyl formamide as organic solvent, pyridinethiols and hydrogen peroxide as reagents, and, optionally, elemental sulfur to minimize the reagent load.
吡啶硫醇是吡啶，一种含氮的芳环，带有硫醇基，Sh，附着在其环上。该试剂结合元素金以形成可溶性复合物，此外，该复合物具有由两个吡啶硫醇分子在金原子的两侧产生的有利的线性结构。氧化后，它变为有机溶液中稳定的含阳离子金的产物。这种具有两个配体的复合物形成是金的独特特征，促进了溶解和氧化的能量。结果，作者报告了20分钟的提取时间后，金几乎定量溶解了膜，粉末或电子板。
但是，如何将溶解与其他贵金属的溶解呢？与具有单电子氧化的黄金不同，钯和铂需要两电子氧化，因此无法使用此技术。相反，铜和银与吡啶硫醇形成复合物，尽管不如黄金有效。因此，在将黄金从“金指”区域溶解在印刷电路板上之前，研究人员首先提取了用氨和含硫酸盐的溶液提取的银和铜，这是传统方法。
通过分析硫醇辅助金溶解的确切机制，研究人员发现了多种含硫的副产物。其中一些似乎对于继续进行氧化反应至关重要，例如S8，一种元素硫的常见形式。这也被证明是一种资产：当外部S8is added, it was possible to reduce the ligand load, according to the authors. Their extraction technique could mark a new beginning for more efficient urban mining.