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Chinese Journal of Ecology ›› 2021, Vol. 40 ›› Issue (8): 2289-2301.doi: 10.13292/j.1000-4890.202108.007

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Geochemical characteristics of Fe-Mn nodules with different sizes in soils of high geological background areas.

JI Wen-bing1,2,3, YANG Zhong-fang3*, YIN Ai-jing1,2, LU Yuan-yuan1,2, YING Rong-rong1,2*, YANG Qiong3, LIU Xu3, LI Bo3, DUAN Yi-ren3, WANG Jue3, WANG Yi-zheng3, YU Tao4, WU Tian-sheng5, ZHANG Qi-zuan6   

  1. (1Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment, Nanjing 210042, China; 2State Environmental Protection Key Laboratory of Soil Environmental Management and Pollution Control, Nanjing 210042, China; 3School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China; 4School of Science, China University of Geosciences, Beijing 100083, China; 5GuangxiInstitute of Geological Survey, Nanning 530023, China; 6Guangxi Bureau of Geology & Mineral Prospecting & Exploitation, Nanning 530023, China).
  • Online:2021-08-10 Published:2021-08-10

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Abstract: Understanding the geochemical characteristics of different particle sizes of iron-manganese nodules in soils of high geological background areas is helpful to clarify the effects of iron-manganese nodules on the abnormal enrichment of heavy metals and the main controlling factors of heavy metal adsorption and fixation in soils in karst areas. The surface soil samples (0-20 cm) were collected in Nanning City and Daxin County in Chongzuo, Guangxi. The samples of iron-manganese nodules with different particle sizes (0.3-0.5, 0.5-1, 1-2, 2-4, 4-6, 6-8, and >8 mm) and corresponding soils (<2 mm) were screened out for chemical analysis. The main aims of this study were to examine the variation and controlling factors of heavy metals in iron-manganese nodules with different particle sizes, and clarify the distribution of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in iron-manganese nodules and corresponding soils. The results showed that Fe2O3 and Cr in iron-manganese nodules displayed synchronous dynamics, while MnO2 presented a synchronous dynamic with Cd, Cu, Ni, Pb, and Zn with changes of particle sizes. The characteristics of heavy metals with changes of particle sizes reflected the formation and growth process of iron-manganese nodules. Iron affects the geochemical behavior of Cr, while manganese affects the geochemical behaviors of Cd, Cu, Ni, Pb and Zn. We calculated the percentage of mass (PM) of iron-manganese nodules to the element concentrations in soil. The PM of iron nodules was in an order of Cr (47.76%) > Cd (24.91%) > Pb (18.44%) > Cu (16.26%) > Zn (14.77%) > Ni (10.41%), while the PM of manganese nodules was in an order of Cr (45.25%) > Cd (37.94%) > Pb (25.86%) > Cu (15.59%) > Zn (13.79%) > Ni (12.15%). Those results indicate that a large number of heavy metals in the soil of karst area are actually fixed by the nodules in the ironmanganese nodules, with quite low biological activities. Therefore, heavy metals fixed by the iron-manganese nodules in the total amount of soil should be deducted in the assessment of soil ecological risk in high geological background areas, which would be more scientific and accurate.

Key words: karst area, iron nodule, manganese nodule, geochemical behavior, heavy metal.