【作者】 谭文峰；

【导师】 李学垣； 刘凡；

【作者基本信息】 华中农业大学 ， 土壤学， 2000， 博士

【摘要】 用X-射线衍射（XRD）、透射电镜（TEM／ED／EDS）、扫描电镜（SEM／EDS）、X射线光电子能谱（XPS）和全量分析、化学选择溶提等技术，研究了我国几类土壤铁锰结核的形态构造、氧化锰矿物类型与形貌、物质组成、对重金属离子的吸附和Cr（Ⅲ）的氧化，探讨了铁锰结核和所含氧化锰矿物的性质、形成机制及其与土壤环境条件的关系。 1、本文提出的方法—用样液比1:100、pH3.0的0.1mol／L HAHC处理样品2小时，能从铁锰结核中分别溶提出80.6～86.3％、1.9～3.8％和＜0.36％的锰、铁和铝，说明将此方法用于分离、测定铁锰结核中的锰、铁、铝是可行的。 2、与土壤相比，铁锰结核中的MnO₂、Pb、Cd、Ba、Co、Ni、Cu、Zn强烈富集，Fe₂O₃明显富集，CaO、P₂O₅、Na₂O稍有富集，SiO₂、Al₂O₃、K₂O、MgO、TiO₂有所减少。结核中Ba、Cd、Co、Cu、Ni、Pb、Zn含量与MnO₂含量显著相关；而土壤中的Cd、Cu、Ni、Pb、Zn含量与Fe₂O₃，含量显著相关。因子分析表明铁锰结核中的元素可分三组：第一组为SiO₂、Al₂O₃、K₂O、MgO、CaO、Na₂O、TiO₂、Sr，代表硅酸盐矿物的元素组合；第二组为MnO₂、Ba、Cd、Co、Cu、Li、Ni、Pb、Zn，它们的富集与氧化锰矿物有关；第三组为Fe₂O₃、P₂O₅、Cr，其富集与氧化铁矿物有关。XPS分析表明铁锰结核中的锰为+3、+4价。 3、SEM下的铁锰结核背散射电子（BSE）图像表明，从南到北，结核内环带构造由清晰到模糊；Mn、Fe的环带分布逐渐减弱，Ca的增强。SEM／EDS分析表明：①MnO₂、Fe₂O₃在结核剖面上呈波形曲线分布，二者含量交替上升或下降，波形变化由南向北更加频繁，结核的环带构造逐渐由厚变薄；②红壤、黄棕壤铁锰结核剖面上MnO₂含量的变异系数比砂姜黑土、棕壤的高，Fe₂O₃的则相反；③酸性-微酸性土壤中铁锰结核的Ca、Ba、Co、Ni、Pb富集于氧化锰矿物，微碱性-碱性土壤中铁锰结核的Ca、Ba富集于氧化锰矿物，Co、Ni、Pb主要沉淀富集于结核。铁锰结核的生长可分为土壤渍水与贫水两个阶段，环带构造可能是在较大全球气候变化或新构造运动中引起地形、土壤环境巨大波动的条件下形成的。 4、土壤的层状硅酸盐矿物由南到北逐渐从以1:1型高岭石为主过渡到以2:1型矿物为主；1.4nm过渡矿物转变成蛭石，蒙脱石从无到有，三水铝石从有到无；铁锰结核从南到北的变化与相应土壤的一致，但不含三水铝石，1.4nm矿物为蛭石，2:1型矿物含量比相应土壤的高，高岭石含量则相反。随着铁锰结核颗粒增大，高岭石含量减少、水云母含量增加，层状硅酸盐矿物与土壤间的差异增大。铁锰结核中氧化铁的活化度与游离度比相应土壤的大，从南到北由针-赤混合型向针铁矿过渡，针铁矿比例增加，赤铁矿比例逐渐减少直至消失，与土壤的变化一致，但G／（G+H）比值比土壤的高，针、赤铁矿的铝同晶替代量比相应土壤的低。 5、砂姜黑土铁锰结核的锰矿物以钙锰矿与狸硬锰矿为主，其它土壤的均以理硬锰矿为主。黄褐土、武汉黄棕壤铁锰结核中还含水钠锰矿、水羟锰矿，宜章红壤、武汉黄棕壤、砂姜黑土还含锰钡矿，桂阳红壤有少量锰铅矿；铁锰结核中的锰矿物类型与其所含特征元素的地球化学特性相符。TEMffeDffiDS的观察与分析表明，桂阳红壤、黄褐土、棕壤铁锰结核中理硬锰矿的结晶颗粒为500urn～1000nm，呈片状或板块状，衍射花样清晰；武汉黄棕壤的水钠锰矿和砂姜黑土的钙锰矿在TIM明场下都为微晶集合体；前者的单个晶粒不易分辨，只在暗场像下显示出10urn—30urn极细小晶体颗粒，电子衍射花样呈多晶衍射环，后者多呈纤维状、长片状或针状，电子衍射花样呈较清晰的多晶衍射环。 6、pHS．5下，土壤铁锰结核对不同重金属离子的吸附顺序为：Ph＞Cn＞Zfi＞C。＞M＞C山 对这些重金属离于吸附力大小的顺序为：＊5－1＞＊2－1＞N个1＞N卜1，这与其所含的主要氧化锰矿物类型有关。 7、N4－l、NZ－l、NS－l中氧化锰对k（Im的最大氧化量分别为 723．6、627．l、打8．6m。1／陌（枷0。）。铁锰结核对k（皿的氧化百分率：（1）随出 升高而降低； ＊）随离子强度增加而略有升高：u）随样品c人P吸附量增加的变化较小；随Ph吸附量的增加而降低，Ph吸附量大于100nunol爪g时，降幅减弱、趋于稳定。铁锰结核的氧化锰矿物对Cr皿)的氧化，仅限于吸附在Stern层的Cr（ill），对其它Cr（Ill）的氧化机率很小，并受PH、竟争吸附阳离子种类、氧化锰矿物类型、锰的价态及表面位点亲和性的影响。更多还原

【Abstract】 The structure, mineralogy, elemental geochemistry of Fe-Mn nodules, and heavy metals adsorbed and Cr(III) oxidized by them were studied. Formation and elemental accumulation mechanisms of Fe-Mn nodules, relationship between composition of nodules and soil environment, interaction of ion adsorption and redox on Mn oxide minerals were discussed.1 The method-pH3.0 of 0.1 moI/L NH2OH HC1 solution (sample:solution = 1:100) treatment with 2h-proposed by the paper could dissolve 80.6%-86.3% of total Mn, 1.9%-3.8% of total Fe and < 0.36% of total Al in Fe-Mn nodules. The method could effectively separate Mn, Fe and Al oxide minerals from Fe-Mn nodules in soil and estimate their content.2 Comparison with soils, Mn02, Ba, Cd, Co, Cu, Ni, Pb, Zn and Sr were strongly accumulated, Fe2O3 were obviously accumulated, CaO, P2O5, Na2O were slightly accumulated, and SiO2, A12O3, K2O, MgO, TiO2 were reduced in Fe-Mn nodules. There was remarkable positive correlation between the contents of Ba, Cd, Co, Cu, Ni, Pb, Zn and MnO2 in Fe-Mn nodules, whereas there was remarkable negative correlation between the contents of Cd, Cu, Ni, Pb, Zn and Fe2O3 in soils. The chemical elements could be divided into three groups according to factor analysis: (1) Si, K, Mg, Ca, Na, Ti and Sr which were elemental composition of phyllosilicate, (2) Mn, Ba, Cd, Co, Cu, Li, Ni, Pb and Zn which were related to Mn oxide minerals, (3) Fe, Cr and P which were related to Fe oxide minerals. The results of XPS showed that valences of Mn in Fe-Mn nodules were +3 and +4.3 From south to north, the band structure of Fe-Mn nodules was from clear to obscure, the extent of banded Mn and Fe decreased, whereas the extent of banded Ca increased in backscattered electron image (BSE) of SEM. The line distribution of MnO2 and Fe2O3 contents in Fe-Mn nodule profile was wave-like curve, and the content of Fe203 increased when the content of MnO2 declined or the content of Fe203 decreased when the content of Mn02 increased. With the latitude increasing, the wave-like curve of Fe2O3 and MnO2 contents changed frequently, and the thickness of band was from thick to thin. The coefficient variation (C.V.%) of MnO2 content in Fe-Mn nodules profile of red soil and yellow-brown soil were higher than that of Shajiang black soil and brown soil, but C.V.% of Fe2O3 content of them was reverse. Ca, Ba were accumulated in Mn oxide minerals regardless of soil types. However, Co, Ni, Pb were accumulated in Mn oxide minerals of acid-slight acid soils, and precipitated in Fe-Mn nodules of alkaline-slight alkaline soils. The alkaline micro-region model of Mn-Fe nodule in soil was proposed. Two periods for growth of Fe-Mn nodules in soils were flooding-water and lacking-water. The band structures of Fe-Mn nodules wouldprobably form when the landscape and soil environment experienced greatly change which were affected by global climate change, neotectonics and so on.4 From red soil to Shajiang black soil and brown soil, the main phyllosilicate composition of soils changed from 1:1 kaolinite to 2:1 minerals, from 1.4 nm intergrade mineral to vermiculite, montmorillonite from none to present, and gibbsite was only in red soil. The phyllosilicate composition of their Fe-Mn nodules was similar to the corresponding soil. However, Fe-Mn nodules contained no gibbsite, no 1.4 nm intergrade mineral. The content of 2:1 minerals in nodules was higher than that in soils, whereas the content of kaolinite in them was reverse. With the increasing of diameter of nodules, the content of kaolinite decreased, whereas the content of hydromica increased, and the differences of phyllosilicate composition between nodules and soils were increasing. The ratios of Feo/Fed and Fed/Fet of soils were lower than that of Fe-Mn nodules. From south to north, the composition of Fe oxide minerals changed from goethite-hematite mixture type to goethite (G) type, and the contents of goethite were increased as the contents of hematite (H) were decreased in soils. The changes of types and content更多还原