云浮硫铁矿区土壤剖面的磁学性质研究

广泛分布的硫铁矿在开采利用过程中可通过多种途径对矿区及周边环境产生严重影响,污染物产生的机制和迁移途径等成为学术界关注的焦点。近年来,环境磁学以其快速、经济、无损等优点被广泛应用于环境污染、物源分析等研究领域。本文对云浮硫铁矿矿区附近一个菜地土壤剖面进行详细的磁学测试,得到低频磁化率、频率磁化率、非磁滞剩磁磁化率、饱和等温剩磁及S比值等一系列磁学指标结果,并分析这些指标的剖面变化特征及指标间的相关关系,探讨影响土壤剖面磁学性质变化的主要因素,结果表明：低频磁化率、非磁滞剩磁磁化率和饱和等温剩磁在剖面底部（30 cm以下）基本稳定并且其值保持在较低的水平,其平均值分别为5.32×10-8m3·kg-1、13.70×10-8m3·kg-1和3.66×10-3Am2·kg-1;上述指标在表层30 cm的平均值分别为32.97×10-8m3·kg-1、86.21×10-8m3·kg-1和5.39×10-3Am2·kg-1,土壤剖面30 cm以上部分土壤明显受外来细颗粒磁性矿物的影响,磁性被显著增强。不同深度土壤中磁性矿物种类存在明显区别,剖面中部的高SIRM/χ值（70～100 kA·m-1）指示有胶黄铁矿等铁硫化物的存在。磁学参数之间的相关分析发现,剖面土壤中的铁硫化物及其中的单畴磁性颗粒是影响土壤磁学性质的主要因素。由于磁性矿物可通过吸附、共沉积、晶格置换等多种形式使多种重金属在土壤中富集,较大范围、多手段针对多种环境介质的磁学深入研究有望为硫铁矿周边重金属污染的产生机制和迁移路径研究开拓新途径。

Study of magnetic properties for a soil profile from the Yunfu pyrite zone

The mine and utilization of widespread pyrite can produce serious impacts on mining area and the surrounding environment through various ways. The producing mechanism and transportation route of pollutants have been becoming a focus of pollution research for pyrite areas. Recently, environmental magnetism has been widely used in many research fields such as environmental pollution and provenance analysis due to its advantages of rapid, economic and nondestructive. Detailed magnetic investigation was performed for a soil profile covered by vegetables within the Yunfu pyrite zone in the present study. Analytical results of magnetic parameters low frequency magnetic susceptibility （χlf）, frequency dependent magnetic susceptibility （χfd）, anhysteresis remanent magnetic susceptibility （χARM）, saturation isothermal remanent magnetization （SIRM） and S-ratio were acquired for all soil samples. Both vertical variation and correlationship of these parameters were analyzed. Main influencing factor for magnetic vertical variation was discussed for the studied soil profile. The results showed that low frequency magnetic susceptibility, anhysteresis remanent magnetic susceptibility and saturation isothermal remanent magnetization were basically stable and remained low level at the bottom of the soil profile （below 30 cm）. The average values of these parameters were 5.32×10-8 m3·kg-1,13.70×10-8 m3·kg-1 and 3.66×10-3 Am2·kg-1, respectively. However, the average values of the mentioned parameters for the upper 30 cm increased to 32.97×10-8 m3·kg-1,86.21×10-8 m3·kg-1and 5.39×10-3 Am2·kg-1, respectively. Upper 30 cm of the soil profile was obviously influenced by external fine particles of magnetic minerals. As a result, magnetic properties of upper 30 cm were significantly enhanced. Magnetic mineral composition within soils differed through different depths. The high SIRM/χvalues （70-100 kA·m-1） of middle part of the soil profile indicated the presence of iron sulfide such as greigite. Correlation analysis of magnetic parameters indicated that single-domain iron sulfides predominates the magnetic properties through the soil profile. Detailed magnetic study of large scale and multi means for various environmental media is expected to provide an effective approach for the generation mechanism and migration path of heavy metal pollution for pyrite zone and its surrounding area since heavy metal can be enriched in soil through adsorption, co-deposition and lattice displacement by magnetic minerals.