含砷矿区河流沉积物粒径组成及砷赋存特征

矿区河流沉积物是重金属污染物的迁移载体。研究了某含砷矿区河段沉积物砷含量分布、赋存形态及粒径对沉积物中砷水力传输的影响机制。结果表明:矿区河流沉积物中砷污染问题突出;沉积物颗粒大小不仅影响砷在沉积物组分中的分配与赋存形态,还会影响水环境中砷的传输。在矿区上游和中上游河段,沉积物均以粗砂、中砂组分为主,上游河段沉积物中砷含量为18.53 mg/kg,主要来源于原生矿物,以结晶水合铁铝氧化物结合态和残渣态等稳定形式存在。中上游河段沉积物中砷含量达到3492 mg/kg,主要来源于采矿活动导致矿石中砷的氧化溶出和部分原生矿物,粗砂、中砂组分(73.90%)中砷以弱结晶水合铁铝氧化物结合态和残渣态为主,分别占总砷含量的83.71%和83.82%,细砂、极细砂、粉砂中砷主要以专性吸附态和弱结晶水合铁铝氧化物结合态存在,分别占总砷含量的58.72%、58.51%和73.10%。在距离矿区2,4 km处的中游、下游河段沉积物砷含量仍有371,247 mg/kg,以细砂、极细砂、粉砂为主,其中专性吸附态和弱结晶水合铁铝氧化物结合态砷是主要形态;沉积物<0.25 mm(细砂、极细砂、粉砂)组分中砷含量是粗砂组分的1.5倍,<0.25 mm细颗粒沉积物对砷的水力传输起主导作用。因此,应加强废弃含砷矿区河流生态治理和水土保持,防止细泥沙入水;同时,加强下游河段沉积物生态疏浚和修复治理,防止沉积物中砷的再释放。

PARTICLE SIZE AND OCCURRENCE CHARACTERISTICS OF ARSENIC IN RIVER SEDIMENTS OF ARSENIC-BEARING MINE AREAS

River sediments are the transporters of pollutants. In this study, the effects of sediments particle size on hydraulic transport, content distribution, and speciation of arsenic in arsenic-bearing mine river were studied. The results showed that arsenic pollution was prominent in river sediments of the mine area; particle size affected not only the distribution and speciation of arsenic in various sediment particle size fractions but also their transport in water environment. The sediments were mainly composed of coarse sand and medium sand in the upstream and middle and upper reaches. In the upstream reaches, arsenic content in the sediments was 18.53 mg/kg, which mainly came from the primary minerals and existed in stable forms, such as well-crystallized hydrous Fe and Al oxides and residual. The content of arsenic reached 3492 mg/kg in the middle and upper reaches, which mainly came from oxide dissolution of arsenic-bearing ore and some original mineral. The amorphous and poorly-crystalline hydrous oxides of Fe and Al and residual were the main existing forms in coarse sand and medium sand components(73.90%), accounting for 83.71%, 83.82% of the total arsenic content, respectively. In fine sand, very fine sand and silty sand, the specific adsorption and amorphous and poorly-crystalline hydrous Fe and Al oxides were the main constituents, accounting for 58.72%, 58.51% and 73.10% respectively. The arsenic contents were still 371, 247 mg/kg in the sediments from middle and lower reaches of 2 km and 4 km away from the mine. The sediments existed mainly in fine sand, extremely fine sand and silt-sand, and predominant forms of arsenic were the specific adsorption and amorphous and poorly-crystalline hydrous Fe and Al oxides. Arsenic in the component less than 0.25 mm(fine sand, very fine sand, silted sand) was 1.5 times of that of the coarse sand component, and fine grain sediments played a leading role in the hydraulic transmission of arsenic. Therefore, the ecological control and soil and water conservation in the upper and middle reaches and the ecological dredging and rehabilitation of sediments in the downstream reach should be strengthened.