分散元素硒的地球化学循环及其富集作用

本文概述了硒的物理、化学性质 ,形态和存在形式以及硒的地球化学循环和富集作用。硒呈四种主要的无机形态存在于自然界中 :硒化物 ( -2价 )、元素硒 ( 0价 )、亚硒酸盐 ( +4价 )和硒酸盐 ( +6价 )。不同硒形态的存在 ,很大程度上取决于 pH和Eh条件。硒的天然的、总的地球化学循环主要涉及壳岩源和海洋沉积物。次一级的循环涉及其它无机源和沉积物。另外 ,整个硒的壳循环 (岩石圈、生物圈、水圈和大气圈 )也强烈受到生物化学反应的影响 ,这些反应使硒在有机组分中固定或迁移。人类活动向环境中排放的硒极大地改变了硒天然的地球化学循环 ,主要是煤的燃烧、硫化物矿床的开采及工业上利用硒所产生的废料。岩浆期后热液活动阶段是硒最主要的活动、富集阶段 ,硒能大量地呈分散形式 (类质同像 )或独立矿物形式存在于这一阶段中 ;在火山及喷气活动产物 (有关热泉 )中硒的富集程度也很高。另外 ,硒在页岩特别是海相黑色页岩中的富集作用与生物活动有密切的关系。

DESPERSED ELEMENT SELENIUM: ITS GEOCHEMICAL CYCLE AND ENRICHMENT

This ppaper presents the physical and chemical properties of selenium, as well as its species, occurrence, geochemical cycle and enrichment. In the natural environment, four principal inorganic species exist: selenide (-2), element(0), selenite (+4), and selenate (+6). These species in a particular environment depend largely on the pH and Eh conditions. The natural, overall geochemical cycle of selenium mainly involves crustal rock sources and oceanic sediment sinks; in addition, the overall crustal cycle (including lithosphere, biosphere, hydrosphere and atmosphere) also is strongly influenced by biochemical reactions that mobilize or fix selenium in organic compounds. Human beings considerably modify this natural geochemical cycle by adding sources of selenium to the environment, principally by coal combustion, sulfide ore processing, and waste processing from the industrial use of selenium. Selenium was enriched mainly in the hydrothermal stage. Large amounts of dispersed forms (i.e., substituted forms in sulfides or adsorbed on carbonaceous matter) and independent selenium minerals occurred in this period. Selenium was accumulated to a higher extent in the products of volcanic activity and volcanic exhalation. In addition, its enrichment in shales, especially in oceanic black shales is chiefly related to biotic processes.;