Research On Spatial Distribution And Formation Mecharism Of Heavy Metals And Arsenic Species In Guangxi Diaojiang River

Mining exploitation is one of the important resources of heavy metals pollution, heavy metals from mining activity migrate with surface runoff easily and pollute vicinal river. Diaojiang River, a mining polluted river was selecited as a tapical regional to carrying out research. Sequential extraction method and X ray absorption near edge structur were used to investigate arsenic (As) species and its distribution in sediments from Diaojiang River. Spatial and seasonal distributions of arsenic (As), zinc (Zn) and lead (Pb) in dissolvedand particulate fraction, and the distribution of the heavy metals were investigated in river flows and sediments in Diaojiang River. It was shown that Diaojiang River was seriously polluted by the 3 heavy metals. Sediments in downstream which was 200km away from mining areas were also seriously polluted. Chehe mining area contributed more As and less Pb than Dachang mining area for Diaojiang River basin pollution. The occurrence form of heavy metals in river flow varied among elements. Lead in particulate form contributed greater for its pollution in river flow than dissolved Pb, while it was reversed for As and Zn. Higher Pb presented in particulate form in river flow might due to that Pb was mainly presented in smaller size fraction of sediments trended to be re-suspend, and Pb sulfide mineral was more stable than As and Zn. Seasonal variety showed that the proportions of particulate heavy metals in river flow were significantly higher in wet season than that in dry season.The distributions of the heavy metals in different size fraction were investigated in river flows and sediments in Diaojiang River. The particle size distribution of sediments and its effect on heavy metals partitioning were also analyzed. Heavy metals was found to be highly concentrated in 63～170μm size fraction in bottom sediment, while it mainly hosted in <63μm size fraction in floodplain sediments.Sequential extraction method and X ray absorption near edge structure (XANES) were used to investigate arsenic (As) fractionations in sediments from Diaojiang River. Arsenic sediments mainly presents as arsenoprite, arsenate and arsenite (Fe-As, Ca-As) forms. High proportion arsenoprite in sediments showed the typical mining tailing contamination in the river. The bottom sediment had relatively high proportion of arsenoprite, which was mainly concentrated in 63～170μm size fraction, while the proportion of arsenoprite in floodplain sediment at flood water level were lower. It might due to the variety of sulfide arsenic oxidization in different exposure environments between sediments. The result of sequential extraction showed that in the middle and lower reaches of the river, the proportion of Res-As in sediments in the bottom and median water level floodplain decline downstream, while Fe-As showed a reverse change pattern.All the analysis indicated that the arsenopyrite riched tailings transport and deposit in Diaojiang River was the direct reason lead to Diaojiang River pollution.