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
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

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.