离子型稀土矿区小流域氨氮污染物地表迁移特征

离子型稀土原地浸矿工艺大量使用硫酸铵作为浸矿剂，矿体中残留的氨氮等化学物质随流域汇水过程迁移，引起矿区水土环境的严重污染。为了揭示矿区氨氮污染在流域尺度上的地表迁移特征，本研究选择赣南某离子型稀土矿区小流域，在流域汇水过程最为强烈的雨季开展实地采样，借助GIS水文分析等手段研究了矿区流域氨氮和硝态氮的地表迁移分布特征。结果表明：矿区土壤和泥沙中氨氮和硝态氮含量排序为：沉积泥沙>崩塌浸矿山体表土>原状浸矿山体表土，且沉积泥沙中氨氮含量与细颗粒物质含量呈正相关。流域主沟道的氨氮平均浓度为95.12 mg/L，出口处为115 mg/L，超过国家标准（GB 26451—2011）6.7倍，局部矿区支沟最高超标达24.5倍。矿体紧邻的支沟径流氨氮浓度随累计汇水面积呈指数型增加趋势，而主沟道沿程径流氨氮浓度则随矿区支沟的汇入呈突增和衰减交替的波动趋势。综合考虑主沟道沿程水流距离、支沟汇水面积和汇入点浓度构建了氨氮迁移估算模型，模型有效系数达0.79。以上研究初步揭示了离子型稀土矿区小流域雨季氨氮污染物的地表迁移分布特征，可以为评价流域水土污染风险和制定生态治理方案提供依据。

Transport of Ammonia Nitrogen Pollutants in Ionic Rare Earth Mining Small Watershed

Ammonium sulfate is widely used as leaching agent for the in-situ leaching mining of ionic rare earth. The residual leaching chemicals such as ammonia nitrogen might migrate along with the catchment process, causing serious pollution of soil and water environment in mining area. In order to reveal the surface migration characteristics of ammonia nitrogen pollution at the basin scale, field sampling was conducted in a small basin of an ionic rare earth mining area in southern Jiangxi during the rainy season when the catchments were most intense. The surface migration and distribution characteristics of ammonia nitrogen and nitrate nitrogen in the mining basin were studied by means of GIS hydrological analysis and other means. The results showed that the contents of leaching agent in the channel sediment and surface soils were sorted as:channel deposits > collapsed hillslope > natural hillslope. The content of residual leaching agent in the channel deposits was positively correlated with the finer particle composition. On average, the ammonia nitrogen concentration in the main channel of the watershed was measured as 95.12 mg/L with the outlet value of 115 mg/L, which has exceeded the standard by 6.7 times. For some branch gullies in the mining area, the ammonia nitrogen could exceed the standard by as high as 24.5 times. A typical branch gully illustrated an exponential increasing leaching agent concentration in runoff with the accumulative flow area. On the other hand, the runoff leaching agent concentration in the main channel showed a fluctuation trend composed by sudden increase and steady attenuation. An estimation model of ammonia nitrogen concentration along the main channel was established by comprehensively considering the inflow of both the contaminated and natural water, and it was proved to be reliable by the model efficiency of 0.79. The above results preliminarily clarified the migration and distribution of the residual leaching agent in the small watershed of ionic rare earth mining area in rainy seasons, and in turn it could be helpful for evaluating water and soil pollution risk in the watershed and guiding the ecological restoration measurements.