稀土矿区地下水“三氮”分布特征及迁移转化规律

三氮"浓度是稀土矿区地下水质量评价的重要指标,"三氮"污染特征的分析以及迁移转化规律的揭示对水环境监测和污染治理具有重要意义。以龙南离子型稀土矿区地下水为研究对象,通过钻孔取样和水质分析,探讨地下水中"三氮"的分布特征以及迁移转化规律。结果表明:1)龙南稀土矿区地下水中,"三氮"在松散岩孔隙水中的浓度略大于风化带裂隙水,NH₃-N浓度远超地下水Ⅲ类水标准,最大超标倍数48.42倍,超标率31.71%,NO₃-N、NO₂-N浓度较低,无明显超标现象。2)NH₃-N以浸矿区为中心,沿地下水径流方向迁移,水平迁移距离约3500m;"三氮"在松散岩类孔隙水中的迁移速度大于在风化带网状裂隙水,土体渗透系数越大,"三氮"迁移速度越快。3)"三氮"在地下水中的转化机制主要是硝化反应、反硝化反应以及NH4⁺的挥发作用和NO2^-的自分解反应,pH是影响矿区地下水中"三氮"富集以及相互转化的重要因素。

Distribution Characteristics and Migration and Transformation Rule of

Concentration of"three nitrogen"is an important index for groundwater quality evaluation in rare earth mining areas.Analysis of pollution characteristics of"three nitrogen"and revelation of migration and transformation rule are great significance for water environment monitoring and pollution control.Distribution characteristics of"three nitrogen"in groundwater and its migration and transformation rule were discussed through borehole sampling and water quality analysis in Longnan iontype rare earth mining area.The results show that:1)rare earth mining area groundwater in Longnan,"three nitrogen"in concentration of unconsolidated rock pore water is slightly greater than that of zone of weathering fissure water,concentration of NO₃-N far exceeds the groundwater classⅢwater standard,the largest excess multiple is 48.42 times with over standard rate of 31.71%,and NO₃-N and NO₂-N concentration is low and has no obvious exceed standard.2)NO₃-N migrates along the direction of groundwater runoff with leaching mining area as the center,and the horizontal migration distance is about 3500m.Migration rate of"three nitrogen"in pore water of loose rock is higher than that in fissure water of network of weathering zone.The big the permeability of soil is,the fast the migration rate is.3)Transformation mechanism of"three nitrogen"in groundwater mainly includes nitrification reaction,denitrification reaction,volatilization of NH4⁺and self-decomposition reaction of NO2^-.An important factor affecting enrichment and mutual transformation of"three nitrogen"in groundwater in mining areas is pH value.