Application of Biomineralization to Noble Metals Recycling

提出了一种利用金属离子还原菌海藻希瓦氏菌（Shewanella algae）和奥奈氏希瓦氏菌（Shewanella oneidensis）在水溶液中还原并存款贵金属离子（Pt（IV）、Pd（II）、Au（III））的环境友好方法。在室温和中性pH 7条件下，以乳酸或H_2为电子供体，利用细菌的静息细胞，在30 min内实现了贵金属纳米粒子在细菌细胞上的还原和沉积。用X射线吸收近边光谱法（XANES）对细菌细胞中贵金属的形态进行了分析，结果表明可溶性金属离子在细菌细胞中迅速还原为不溶性金属。透射电子显微镜（TEM）观察发现，5-10 nm的贵金属纳米粒子主要分布在细菌细胞的周质间隙中，这是一个易于回收的较好的细胞表面位置，即使在pH为2和10的极端条件下，也能实现金纳米粒子的快速生物还原沉积。在H_2为电子供体的条件下，在pH 2.8时，15-200 nm大小的金纳米颗粒沉积在细菌细胞上，并且生物纳米颗粒表现出包括三角形在内的各种形状。在pH为2.0的溶液中，大小约为20 nm的金纳米颗粒沉积在细胞内，而大小约为350 nm的较大金颗粒沉积在细胞内。溶液pH值是控制生物金颗粒形貌和金沉积位置的重要因素。此外，在Cu（II）离子的存在下，金的生物还原沉积是一个快速的过程。利用金属离子还原菌对贵金属进行生物矿化是一种极具吸引力的从城市矿山电子废弃物浸出液中回收贵金属的方法。

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.