土壤铁锰结核中生命有关元素的化学地理特征

The chemicogeographic characteristics of life-relative elements in soil iron-manganese nodules

研究了我国亚热带、暖温带几种土壤铁锰结核中锰矿物的类型 ,探讨了它们形成的地球化学过程与特征。结果表明 :不同土壤铁锰结核锰矿物的类型及其含量不尽相同 ,但锂硬锰矿普遍存在且结晶程度较高 ;与土壤相比 ,土壤铁锰结核的化学组成仍以Si、Al、Fe为主 ,但Fe含量超过了Al,Mn含量远大于Mg、Ca ;结核中一些重金属富集顺序为Pb >Co >Ni>Cu >Zn >Cr ;揭示了土壤铁锰结核形成过程中存在着成核富集作用、成矿作用、专性吸附作用和轻度积钙作用。

Mn oxide minerals are very reactive components of soils. They could control the availability and toxicity of many life-relative elements. Meanwhile, Mn oxide minerals influence the fates of formation and transformation of organic materials, including humic substances, organic pollutants and humic acids, and affect the quantity and quality of crops. Ultimately, they make a notable impact on human health. As products of certain period of soil-forming processes, soil iron-manganese nodules are the main rich forms of Mn oxides. Studying on the mineral composition and geochemical characteristics of soil iron-manganese nodules can help us not only know the properties of soil iron-manganese nodules and Mn oxide minerals but also comprehend the soil-forming process and the ecological environmental conditions. The types and amounts of manganese minerals in several iron-manganese nodules in subtopical and warm-temperate zones were studied by means of X-ray diffraction and selective chemical dissolution. Their geochemical processes and characteristics were also investigated. The amounts and types of manganese mineral in different soils were distinct. Lithiophorite is a common mineral in all tested iron-manganese nodules with high degree of crystallinity. Compared with corresponding soils, Si, Al and Fe were still the main chemical elements in nodules. However, the increasing extent of iron content was higher than that of Al, and increasing extent of Mn content was higher than that of Mg and Ca. The enrichment order of some heavy metals was Pb>Co>Ni>Cu>Zn>Cr. During the processes of nodules formation, there exist nucleation and enrichment, mineral formation, specific adsorption and slight calcification.