Application of Biomineralization to Noble Metals Recycling

提出了一种环境友好的方法，利用金属离子还原细菌希瓦氏藻和希瓦氏杆菌还原和沉积水溶液中的贵金属离子(铂(IV)、钯(II)、金(III))。以乳酸或氢气为电子供体，在室温和中性pH值为7的条件下，细菌静息细胞在30min内完成了贵金属纳米颗粒的还原和沉积。利用X射线吸收近边能谱(XANES)对细菌细胞中贵金属的形态进行了研究，结果表明细菌细胞中的可溶金属离子迅速还原为难溶金属。细菌细胞薄片的透射电子显微镜显示，5-10 nm的生源贵金属纳米颗粒位于细胞表面的周质空间，有利于生物纳米颗粒的回收。在H_2存在下，即使在pH=2和10的极端条件下，利用藻类静止细胞作为电子供体，也可以快速生物还原沉积金纳米颗粒。在pH值为2.8时，金纳米粒子沉积在细菌细胞上，大小为15-200 nm，生物纳米粒子呈现出包括三角形在内的各种形状。在溶液pH为2.0的条件下，金纳米粒子在细胞内沉积约20 nm，较大的金粒子在细胞内沉积约350 nm。溶液pH值是控制生物金颗粒形态和沉积位置的重要因素。此外，在Cu2+存在下，金的生物还原沉积是一个快速的过程。我们坚信，金属离子还原细菌对贵金属的生物矿化是从城市矿山电子废料浸出液中回收贵金属的一种非常有吸引力的方法。

An environmentally friendly method using the metal ion-reducing bacteria Shewanella algae and Shewanella oneidensis was proposed to reduce and deposit noble metal ions (Pt (IV), Pd (II), Au (III) ) in aqueous solutions. Microbial reduction and deposition of noble metal nanoparticles on the bacterial cells were achieved within 30 min at room temperature and neutral pH 7 using resting cells of the bacteria, when either lactate or H_2 was provided as the electron donor. Speciation of noble metal in bacterial cells by X-ray Absorption Near-Edge Spectroscopy (XANES) showed that soluble metal ions were rapidly reduced to insoluble metal in the bacterial cells. Transmission electron microscopy (TEM) of thin sections of bacterial cells revealed that the biogenic noble metal nanoparticles of 5-10 nm were located in the periplasmic space a preferable, cell surface location for easy recovery of biogenic nanoparticles.Fast bioreductive deposition of gold nanoparticles was also achieved even at the extremes of pH 2 and 10 using resting cells of S. algae in the presence of H_2 as the electron donor. At pH 2.8, gold nanoparticles of 15-200 nm in size were deposited on the bacterial cells, and the biogenic nanoparticles exhibited a variety of shapes that included triangles. At a solution pH of 2.0, gold nanoparticles about 20 nm in size were deposited intracellularly, and larger gold particles approximately 350 nm in size were deposited entracellularly. The solution pH was an important factor in controlling the morphology of the biogenic gold particles and the location of gold deposition. Furthermore, the bioreductive deposition of gold was a fast process in the presence of Cu(II) ions. We strongly believe that the biomineralization of noble metals by the metal ion-reducing bacteria is extremely attractive method for recovering noble metals from electronic scrap leachates in urbane mine.