大洋富钴结壳研究进展及展望

Formation of Oceanic Cobalt-rich Crust:Progress and Perspectives

富钴结壳是一种重要的海底矿产资源,具有独特的经济价值和科学意义,其不仅富含Mn、Co、Ni、Cu、PGE和REY等金属,而且在反演新生代以来古海洋环境记录等方面扮演着独特的角色。锰氧化物(MnO_(2)·xH_(2)O)和铁羟基氧化物(FeOOH)是构成富钴结壳的主要矿物,矿物颗粒十分微小(纳米级)。水羟锰矿和水钠锰矿具有层状结构且层电荷为负,通过吸附阳离子来补偿。前人通过连续浸出实验、元素相关性统计分析、吸附实验和拓展X射线吸收精细结构(EXAFS)光谱广泛研究了微量元素在矿物中的赋存状态,确定了微量元素在锰氧化物矿物中主要存在三种类型络合物:共六边(edge-sharing)、共双角(double-corner sharing)和共三角(triple-corner sharing)。综合研究表明,在最低含氧带之下铁锰氧化物(氢氧化物)从海水沉淀到周围海山坚硬基岩上形成富钴结壳的机制主要是无机胶体化学反应和矿物表面反应。最后针对已有的相关研究现状以及富钴结壳研究面临的挑战,富钴结壳的成矿物质来源及演化、微量元素富集机制、蕴含的古海洋信息等问题仍需要进一步深入探讨。

Cobalt-rich crust is an important seafloor mineral resource with unique economic value and scientific significance.Cobalt-rich crust is significantly enriched in Mn,Co,Ni,Cu,PGE(platinum group elements)and REY(rare earth elements+Y),and has special implications on the paleo-marine environmental records since the Cenozoic.Mn oxide(MnO_(2)·xH_(2)O)and Fe oxyhydroxide(FeOOH)are the dominant minerals that compose cobalt-rich crust,with most of them are nanoscale minerals.Vernadite and birnessite have a layer structure and a negative layer charge,which is compensated by cation sorption.The previous studies have extensively focused on the location of trace elements in minerals in the cobalt-rich crust,with the help of sequential leaching experiments,statistical analysis of element correlation,adsorption experiments and extended X-ray absorption fine structure(EXAFS)spectrum.Three main types of complexes in Mn oxide have been identified,i.e.,edge-sharing(E),double-corner sharing(DC)and triple-corner sharing(TC).Studies have shown that the process of hydrogenetic cobalt-rich crust precipitation is basically inorganic colloidal-chemical and surface-chemical.Finally,we proposed some suggestions for the future research directions in this field.