滇中富碱斑岩风化剖面中重金属元素地球化学特征和环境风险评价

Geochemical Characteristics and Environmental Risk Assessment of Heavy Metals in Weathering Profiles of Alkali-enriched Porphyry in Central Yunnan

中国西南地区发育大规模富碱斑岩带,通常具有重金属高背景值的特征,岩石风化是重金属的重要来源,土壤重金属污染是全球性关注的热点问题。在云南水热条件充足、成土作用强烈的条件下,为了查清富碱斑岩成土过程中重金属元素地球化学行为特征以及可能带来的一系列生态环境问题。本文选择滇中姚安富碱斑岩岩石风化剖面为研究对象,采用电感耦合等离子体质谱/发射光谱法(ICP-MS/OES)、原子荧光光谱法(AFS)、X射线荧光光谱法(XRF)、容量法等方法测定岩石和土壤样品中As、Cd、Cr、Cu、Hg、Ni、Pb、Zn、Al_(2)O_(3)、TFe_(2)O_(3)、CaO、Na_(2)O、K_(2)O、MgO、SiO_(2)、有机碳等主微量元素含量和pH值,利用多元统计学方法和质量迁移系数研究风化剖面中重金属元素分布特征、迁移富集规律及影响因素,探讨富碱斑岩风化成土过程中重金属地球化学特征,揭示重金属元素迁移富集机制及可能带来的生态环境问题。结果表明:①富碱斑岩各风化层元素分布特征继承了基岩的特征,在风化成土过程中,As、Cr、Cu、Hg和Cd、Pb、Zn具有相似的地球化学行为,相对于Ti,重金属迁移能力强弱顺序为:Cd>Zn>Pb>Hg>Cu>As>Ni>Cr;②Cu、Cr、Ni、Hg受其自身化学性质和脱硅富铝铁作用的影响,随风化最终富集于黏土矿物与Al、Fe氧化物/氢氧化物中,As与Fe、Al结合成难溶性的化合物而显著富集,土壤层迁移系数均值为7.64,Cd、Pb、Zn在酸性和强淋溶条件下显著地淋失迁移,土壤层迁移系数均值分别为−0.67、−0.45、−0.59。与大部分铅锌矿区相似,As受富铝铁作用影响原地次生富集,Cd、Pb、Zn受自身活泼的化学性质和pH影响大量淋失;③研究区土壤生态环境可能存在As、Pb污染的风险,Pb的大量淋失可能随地表径流迁入蜻岭河,应加强对富碱斑岩上覆土壤中As、Pb和流经富碱斑岩区河流中Pb、Zn的监测。

BACKGROUND:The contents of many heavy metals in soil in many areas of southwest China are much higher than the national soil background value,and related studies show that most heavy metals in soil are in a state of“high background and low activity”,which is closely related to the special geological process in the area.Most scholars have concentrated more on the weathering process and post-weathering heavy metals of granite,basalt,carbonate rocks and other geological bodies with high background value of heavy metals in southwest China.However,alkali-enriched porphyry also has the characteristics of high background value of heavy metals,and the geochemical behavior characteristics of heavy metals in the weathering process of alkali-enriched porphyry are less studied.The ecological and environmental effects of heavy metal element migration and transformation during weathering are still unclear.There is a large-scale alkali-enriched porphyry belt located in southwest China.Most of the alkali-enriched porphyry areas have precious metals such as gold and silver,and polymetallic deposits such as copper,lead and zinc.Therefore,soil in alkali-enriched porphyry areas usually has the characteristic of high background value of heavy metals.