太平洋徐福海山富钴结壳稀土元素和铂族元素赋存状态研究

Occurrence phases of rare earth elements and platinum group elements in cobalt-rich crusts from the Seamount Xufu in the Pacific

利用等离子体发射光谱法、等离子体质谱法以及相态分析手段,对太平洋徐福海山富钴结壳稀土和铂族元素地球化学特征、赋存状态及富集机制进行研究。结果表明,富钴结壳稀土和铂族元素明显富集,其稀土总量为1842~2854μg/g,铂族总量为144~1180 ng/g,老壳层中稀土和铂族元素含量明显高于新壳层,这可能与老壳层发生磷酸盐化作用有关。轻稀土元素含量明显高于重稀土元素含量,呈现Ce正异常而Eu无异常,具有明显Ce富集特征。铂族元素之间发生了明显分异作用,PPGE含量明显高于IPGE,表现出明显Pt正异常而Pd负异常,具有明显Pt富集而Pd亏损特征。稀土元素赋存状态显示,新壳层中稀土元素主要赋存于铁氧化物相,其富集比例为65.40%~70.05%,老壳层中稀土元素主要赋存于残渣态,富集比例为62.27%~65.77%,这可能与残渣态中磷酸盐有关。铂族元素赋存状态显示,新壳层和老壳层中铂族元素都主要赋存于铁氧化物相,其富集比例为63.66%~69.51%,残渣态(29.20%~34.68%)对铂族元素也有一定的富集能力。富钴结壳稀土和铂族元素的富集推测为铁氧化物胶体粒子的吸附作用,受海水氧化性环境影响,可溶性Ce^(3+)和Pt^(2+)分别被氧化成不溶性Ce^(4+)和Pt^(4+),沉淀被吸附到铁氧化物相中,从而造成富钴结壳稀土和铂族元素的富集。

The geochemistry,occurrence phase and enrichment mechanism of REE and PGE were studied in cobalt-rich crusts from the Seamount Xufu in the Pacific by ICP-OES,ICP-MS and phase analysis methods.The results showed that,REE and PGE were enriched in cobalt-rich crusts,REE contents were 1842−2854μg/g,and PGE contents were 144−1180 ng/g.REE and PGE contents in the old layers were higher than that in the new layers,and the phosphatization in the old layers might play an active role in the REE and PGE enrichment.Moreover,LREE contents were more than HREE contents,and REE diagrams showed the positive Ce anomalies and no Eu anomalies,so Ce was enriched in cobalt-rich crusts.Meanwhile,there was an obvious contrast between PGE,and PPGE contents were more than IPGE contents.PGE diagrams showed the positive Pt anomalies and negative Pd anomalies,so Pt was enriched and Pd was poor in cobalt-rich crusts.In addition,REE in the new layers were mainly enriched in the iron oxide phase,and the enrichment ratios were 65.40%−70.05%.While REE in the old layers were mainly enriched in the residual phase,and the enrichment ratios were 62.27%−65.77%,because it might be related to the phosphate.Meanwhile,PGE in the new or old layers were mainly enriched in the iron oxide phase,and the enrichment ratios were 63.66%−69.51%,and also the residual phase ranged from 29.20%to 34.68%had an impact on PGE enrichment.Therefore,REE and PGE enrichment were presumed to the iron oxide colloid particles adsorption.In the marine oxidative environment,the soluble Ce^(3+) and Pt^(2+) were oxidized to insoluble Ce^(4+) and Pt^(4+) respectively,and the precipitates were adsorbed into the iron oxide phase,so REE and PGE were enriched in cobalt-rich crusts.