【作者】 姜学钧；

【导师】 翟世奎； 姚德；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2008， 博士

【摘要】 成岩型结核和水成型结壳作为海洋铁锰沉积物的两种主要类型,含有丰富的过渡金属元素、碱金属和碱土金属元素以及稀土元素。本文选择了东太平洋赤道附近的系列铁锰结核（壳）样品,应用X-射线衍射仪确定了样品中的矿物相;再用化学上的两种相态分析手段——选择性提取实验和吸附实验,按照海洋铁锰沉积物中的主要矿物相或/和氧化物相,用选择性提取实验把海洋铁锰沉积物中元素分为可溶态、锰氧化物态、非晶态铁氧化物态、结晶态铁氧化物态和硅酸盐态;用等离子体光谱仪和等离子体质谱仪测定了各个相态中的元素;然后利用提取以后的样品吸附特定的离子;借助地球化学、晶体化学和矿物学手段对过渡金属元素、碱金属和碱土金属元素以及稀土元素在海洋铁锰氧化物沉积物中的赋存状态、与沉积物组成矿物之间的关系,以及组成矿物对这些元素的吸附机制进行了系统的研究,以期了解海洋铁锰沉积物与海水中上述元素的相互作用机理并得到如下的结果:由于Fe3+和Mn4+之间晶体化学特点差别很大,因此在两种成因的铁锰沉积物中各自形成了自己独立的氧化物而相互之间没有发生广泛的类质同象,即在成岩型结核中形成了10（?）-水锰矿和无定形铁的氧化物/氢氧化物,在水成型结壳中则形成了δ-MnO2和无定形铁的氧化物/氢氧化物。Cu和Ni可以进入10（?）-水锰矿中并使其结构变得稳定,因此成岩型结核中相对富集Mn、Cu和Ni。Ti在水成型结壳中的富集则是由于其中大量的无定形铁的氧化物/氢氧化物的吸附和络合,Co在水成型结壳中的存在则是Co和其中δ-MnO2中Mn之间的类质同象代替,因此水成型结壳相对富集Fe、Ti和Co。碱金属和碱土金属在两种成因的海洋铁锰沉积物中的存在都主要与其中的锰氧化物有关。在成岩型结核中,碱金属和碱土金属进入其主要组成矿物―10（?）-水锰矿中并成为其结构的重要组分,虽然由于10（?）-水锰矿的结构原因导致其中的大半径阳离子钠、钙和小半径离子镁、锂在10（?）-水锰矿中占的位置不同,但是碱金属离子特别是钠离子对于10（?）-水锰矿结构的稳定性起到了非常重要的作用,结构中钠离子的缺失会导致10（?）-水锰矿结构的坍塌,在坍塌以后10（?）-水锰矿转变成7（?）-水锰矿。镁离子同过渡金属离子Cu、Ni在支撑10（?）-水锰矿的结构使其结构稳定的方面起到了同等重要的作用,而不仅仅是Cu和Ni等过渡金属元素。锂元素在成岩型结核中不是以锂硬锰矿的形式存在,而是与镁离子相同,存在于10（?）-水锰矿中,10（?）-水锰矿可以看作是锂元素在海水中的吸附剂,并且成岩型结核也许对于锂元素在海水中的平衡起到了重要作用（Jiang et al., 2007）。水成型结壳中的碱金属和碱土金属是由于δ-MnO₂对这两类离子的吸附作用,只是吸附在了δ-MnO₂的表面上,对于δ-MnO₂的结构没有大的影响,推测只是对于δ-MnO₂平衡其自身的电荷有一定的作用。而锂元素在水成型结壳中的存在则可能是由于其中的粘土矿物的吸附作用。稀土元素在成岩型结核和水成型结壳中的富集都是由于其中无定形铁的氧化物/氢氧化物对于海水中稀土元素的较强的络合作用。无定形铁的氧化物/氢氧化物对稀土元素的络合作用要强于10（?）-水锰矿、δ-MnO₂对稀土元素的络合作用。无定形铁的氧化物/氢氧化物对稀土元素比碳酸根对稀土元素有着更强烈的络合作用,可以从稀土元素的碳酸盐络合物中争取到稀土元素离子与之络合而形成络合物,而10（?）-水锰矿和δ-MnO₂则只络合海水中稀土元素的络合物,这表明10（?）-水锰矿和δ-MnO₂对稀土元素的络合能力要小于碳酸根对稀土元素的络合。水成型结壳中Ce正异常并不是由δ-MnO₂把可溶性的Ce3+氧化成不溶性的Ce4+而发生沉淀所导致,也不是无定形铁的氧化物/氢氧化物的氧化作用,这可能与水成型结壳生长的氧化环境有关,因此,Ce的异常仍具有一定的指示氧化还原环境的作用。此外,磷酸盐或磷灰石对于REE在海洋铁锰氧化物沉积物中的富集起到的作用也是有限的,远小于铁氧化物的影响。更多还原

【Abstract】 As the two dominant types of the marine ferromanganese oxide deposits, both diagenetic nodules and hydrogenic crusts are enriched in transitional elements, alkaline metals and alkaline earth metal elements as well as rare earth elements. Distribution of above-mentioned elements in the ferromanganese oxide deposits, relationship between the elements and the compositional minerals of the deposits as well as the factors to control the enrichments of the elements in the deposits were investigated systematically in terms of the selective dissolution experiments and adsorption experiments as well as geochemistry, crystal chemistry and mineralogy by using the ferromanganese oxide deposit samples recovered near the equatorial east Pacific.Manganese and iron are present as 10（?）-manganates and ferric oxides in diagenetic nodules, respectively, while they are present asδ-MnO₂ and ferric oxides in hydrogenic crusts, respectively. Little substitution occurred between Fe and Mn in the ferromanganese oxide deposits due to their different crystal chemistry. The diagenetic ferromanganese nodules are relatively rich in Mn, Cu and Ni, because Cu and Ni can enter into the structure of 10（?）-manganates and stabilize the structure. The 10（?）-manganates can be considered as the scavenger of Cu and Ni in the seawater. On the other hand, hdyrogenic crusts are rich in Fe, Co and Ti. The enrichment of Ti in the hdyrogenic crust is attributed to the adsorption and combination of Ti by amorphous ferric oxide/hydroxide, while the enrichment of Co is attributed to the substitution of Co for Mn ofδ-MnO₂. About three factors control the enrichments of Cu, Co, Ni, Ti and Zn in the ferromanganese oxide deposits as follows: 1) chemistry and crystal chemistry of minerals in the marine ferromanganese deposits; 2) states of the transitional elements in the seawater; 3) biological productivity and sedimentation rate of the environments in which the marine ferromanganese oxide deposits formed. The former two factors determine the present phases of the transitional elements in the deposits and the latter one controls the amounts enriched in the deposits.Enrichments of alkali elements and alkali earth elements in marine ferromanganese oxide deposits are mainly attributed to the absorbability of manganese oxides. Alkali and alkali earth elements can enter into the structure of 10（?）-manganates of diagenetic nodules as important constituents despite the fact that different ions occupy varying positions in the structure due to their different effective ionic radius. Sodium ions can make the structure of 10（?）-manganates stable because the absence of sodium ions results in the collapse of 10（?）-manganates to turn into 7（?）-manganates. In addition, it is assumed that magnesium ions also play an important role to brace the structure of 10?-manganates as the transitional elements, such as Cu²⁺, Co²⁺ and Ni²⁺ do. Lithium in the diagenetic nodules is present in the 10（?）-manganates phase rather than in the lithiophorite phase. 10（?）-manganates can be considered as the scavenger of lithium in the seawater and it may play a important role in the mass balance of lithium in the oceans. The enrichments of alkali and alkali earth elements in hydrogenic crusts are different from that of diagenetic nodules. It is assumed that alkali and alkali earth elements ions are adsorbed on the surface ofδ-MnO₂ rather than into its structure, therefore the alkali and alkali earth elements ions is unimportant for the structure ofδ-MnO₂. On the other hand, the alkali and alkali earth elements ions may play a role in the charge balance ofδ-MnO₂ to some extent.The enrichments of rare earth elements （REE） in marine ferromanganese oxide deposits of different origin are attributed to the strong complexing of amorphous ferric oxide/hydroxide for REE in seawater. Rare earth elements in seawater can be more strongly combined by amorphous ferric oxide/hydroxide than by 10（?）-manganates andδ-MnO₂. The amorphous ferric oxide/hydroxide of marine ferromanganese deposits can combine the REE which are complexed by carbonate and bicarbonate in seawater, while 10（?）-manganates andδ-MnO₂ just combine the complex of REE and carbonate/bicarbonate directly from seawater. The pronounced positive Ce anomalies in hydrogenic crusts are not attribute to the oxidation of Ce from soluble Ce³⁺ to insoluble Ce⁴⁺ by eitherδ-MnO₂ or amorphous ferric oxide/hydroxide. The oxidative environments in which the hydrogenic crusts are formed may result in the pronounced positive Ce anomalies. Therefore, the Ce anomaly can be can be used to infer redox conditions. Apatite contribute less to the enrichments of REE in marine ferromanganese oxide deposits than amorphous ferric oxide/hydroxide.更多还原