去矿物前后碱萃取腐殖酸的化学组成与结构特征

本文采用改进的化学分离方法对Pahokee泥炭和稻田土壤中的腐殖酸进行了分离,得到了两类腐殖酸:去矿物前腐殖酸(HA-I)和去矿物后腐殖酸(HA-II),其中HA-II为前人未所顾及。然后采用元素分析、固体13C核磁共振、热解-色谱-质谱等技术对HA-I和HA-II的化学组成和结构进行了分析。结果显示HA-II在总腐殖酸中占有的比例分别是11.8%(泥炭)和37.1%(土壤)。HA-I和HA-II在化学组成和性质结构上有明显的差异,O/C原子比都表现为HA-IIH/CSSHA-I,表明从HA-I到HA-II,Pahokee泥炭和稻田土壤腐殖酸中的含氧基团都减少,Pahokee泥炭腐殖酸则脂族基团减少,而稻田土壤腐殖酸的脂族基团增加。这种HA-I和HA-II在结构性质上的变化在13C NMR和热解分析时也都得到了验证。另外热解分析还表明HA-I含有更多的易分解的结构组分,而HA-II则含有更多的难分解的结构组分。这些研究都说明HA-II与HA-I相比,在组成和结构特征上存在一些差异,含有更多的难分解的结构单元。本项研究结果对于理解土壤沉积物体系中腐殖酸的化学特征和地球化学过程与行为具有重要意义。

CHARACTERIZATION OF HUMIC ACIDS ALKALI-EXTRACTED FROM ORIGINAL AND DEMINERALIZED SOILS

Two kinds of humic acids were isolated from Pahokee peat(PP) and sandy paddy soil(SS) with an improved method for extraction of soil humic acids,including pre-demineralized humic acids(HA-I) and post-demineralized humic acids(HA-II),and HA-II hardly be considered previously.Then,HA-I and HA-II were characterized by elemental analysis,solid-state CP-MAS 13C nuclear magnetic resonance spectroscopy(13C NMR),and pyrolysis-gas chromatography-mass spectrometry(Py-GC-MS).The results showed that HA-II fraction accounts for 11.8% and 37.1% of the total humic acids in Pahokee peat and paddy soil,respectively.Distinct compositional and structural differences exist between HA-I and HA-II.The O/C atomic ratio decreases from HA-I to HA-II for peat HA and soil HA,while the H/C atomic ratio varies from HA-I to HA-II in order of H/CPPHA-II H/CSSHA-I.These trends suggested that the decreasing contents of oxygen-containing groups for peat HA and soil HA from HA-I to HA-II,and the decreasing contents of aliphatic groups for peat HA and the increasing contents of aliphatic groups for peat HA.These varieties of chemical composition and structures between HA-I and HA-II were also validated by CP-MAS 13C NMR and Py-GC-MS.Moreover,HA-I contains more labile structural contents than HA-II,whereas HA-II contains more refractory structural contents as indicated by the pyrolysis data.In summary,the study suggested that significant differences exist in chemical composition and structure between HA-I and HA-II,and that HA-II contains more refractory structural contents than HA-I.This study will greatly help us to precisely understand the chemistry of HA and its role in the geochemical cycles of carbon in soil/sediment systems.