铅和铬污染包气带及再释放规律的实验研究

Study on the migration and release of lead and chromium and in the vadose zone

利用有机玻璃柱模拟包气带,研究了Pb2+和Cr6+在污染包气带时的迁移转化规律,以及雨水淋洗受污染包气带中重金属再释放规律.结果表明:包气带受重金属污染过程中,铅和铬在粗砂包气带中的迁移速率分别为7.25cm/d和0.4cm/d,远大于其在细砂包气带中的迁移速率4.46cm/d和0.36cm/d,且Cr2O72-形式存在的六价铬在包气带中的迁移速率比的铅离子迁移速率大10倍以上;在模拟实验中,溶液在通过包气带区域时六价铬还原为三价铬的反应很弱,通过包气带的水样中三价铬未检出,并且包气带介质中三价铬含量(0.006mg/kg)几乎为零;雨水淋洗铬和铅污染的粗砂和细砂包气带模拟研究中铅淋洗溶出率为0.056%和0.112%,铬淋洗溶出率为62.33%和40.36%.因此,Cr2O72-在砂质包气带中的迁移性很强且容易从介质表面淋洗去除,而铅在介质中的迁移性较差且很难从介质中淋洗去除掉.

Sand-column simulations were designed to investigate charateristics of migration and transformation of Pb^2＋and Cr^6＋and their releasing mechanism flushed by rain water in the vadose zone. Experimental results indicated that the migration rate of hexavalent chromium was ten times more than that of lead in the vadose zone;and the migration rate of lead and hexavalent chromium was 7.25cm/d and 0.4cm/d in the coarse sand and 4.46cm/d and 0.36cm/d in the fine sand, respectively. Reduction reaction of hexavalent chromium was not a dominant process in the vadose zone; the trivalent chromium was not detected in the water, and the content was 0.006mg/kg in the vadose media. The removal efficiency of Pb^2＋was 0.056%and 0.112%, and Cr2O7^2-was 62.33%and 40.36%for fine sand and coarse sand columns flushed by rain water, respectively. Therefore, the mobility of Cr2O7^2-was high in the vadose zone and prone to removing from vadose media by rain flushing, Pb^2＋showed a reverse trend compared with Cr2O7^2-.