广东凡口Pb-Zn尾矿中重金属的表生地球化学行为及其对矿山环境修复的启示

Heavy metal geochemistry behavior during the oxidation of the Fankou Pb-Zn minetailings in Guangdong province and the implications for environmental remediation of the mines

通过分级提取实验 ,结合矿物成分和化学成分分析 ,对广东凡口铅锌尾矿的新尾矿和 1号尾矿库不同氧化程度尾矿的矿物组成、重金属含量及其形态进行了研究和对比 .新尾矿中的黄铁矿含量很高 (约 3 1% ) ,铅锌的含量分别高达 0 7%和 1 2 %以上 ,重金属元素主要赋存于金属硫化物中 .1号尾矿库样品中的黄铁矿含量 <10 % ,重金属元素也明显低于新尾矿 .在表层氧化带 (硬化层 ) ,硫化物的快速氧化导致大量次生矿物沉淀 ,锌大量吸附于 (氢 )氧化铁表面 ,可迁移性大 ;铅则主要形成次生难溶矿物 (如铅矾 ) ;次氧化带以硫化物的缓慢淋溶作用为主 ,难以形成次生矿物 ,Pb、Zn的流失比例大于 70 % .常用于矿山环境治理的尾矿覆盖方法往往使尾矿处于次氧化环境 .上述研究结果表明 ,这些方法不一定能够阻滞污染元素的迁移 .此外 ,本次研究采用Dold提出的分级提取法 ,发现方铅矿的溶解主要发生在第 2步 (提取液 :pH =4 5 ,1moL L- 1 NH4 Ac) ,而其它硫化物的溶解主要在第 6步 ,这可能是Ac- 与Pb2 + 的络合作用所造成的 ,表明提取液中含Ac-

The mineral constituent, content and configuration of heavy metals in newly released tailings and in the profiles of tailings site 1 were studied in the Fankou Zn-Pb mining field, China, by using mineralogical and chemical analysis as well as sequential extraction experiment. The concentration of Pb, Zn was rather high in the oxidized zone (indurated layer), and that in the underlying sub-oxidized zone decreases to levels that are unbelievably low for Pb-Zn mine tailings. Calculations indicated that the amount of Zn and Pb leached out from the oxidized and sub-oxidized zones was more than 30% and 70%, respectively. These observations suggested that the heavy metals released from metal sulfides should be re-immobilized by secondary minerals in the oxidized zone, rather than primary minerals, and they could be leached out from the sub-oxidized environment due to the low rate of oxidative dissolution, which prevented the precipitate of secondary minerals in significant amount. Thus, cover scenarios which established a sub-oxidized environment under the cover layer might not be effective in preventing heavy metal release from mine tailings. Sequential extraction and mineralogical studies indicated that, in addition to heavy metal leaching, oxidation of the mine tailings increased the mobility of residual Zn and Cu, while Pb remained immobile due to the formation of insoluble secondary minerals such as anglesite (PbSO_4). By using (the seven-step extraction technique developed by Dold, galena dissolved in significant amount at step 2, which was most probably due to the strong complexing force of Pb^(2+) with Ac^-. Meanwhile other metal sulfides dissolved at step 6, which indicated that extraction techniques in which Ac^--bearing solutions might not be appropriate to evaluate the mobility of lead in nature.