LEI Liang-qi, SHI Zheng-huan, MO Jia, CHEN Si-nai，LIN Zhe-quong

 (Earth Science Faculty, Guilin University of Technology, Guilin 541004, China)

Abstract: The paper is focused on a carbonate type tailings rich in carbonate and sulfide, situated in Huangshaping Pb-Zn mine (Hunan Province, China). The characteristics and mechanism of acidification of the tailings were studied by analyzing the structure, mineral and chemical composition, paste pH values and acid neutralizing capacity (Carb-ANC) of a vertical profile of the tailing heap. Results show that there is a layer structure on the profile, namely a strong cementation layer/hardpan on the top of the profile, followed by a weak cementation layer, a sand-like layer and the bottom layer (near the water table of the tailings reservoir) successively. In the tailings, mineral neutralizing acid is calcite mainly; minerals producing acids are pyrite and pyrrhotite mainly, but pyrite is stronger than pyrrhotite in both oxidation resistance and acid generation. From the bottom to the top of the profile (or from early to late stage), associated with the gradual increasing oxidation degree, pyrrhotite oxidized (altered) prior to pyrite and gradually disappears. At this early stage, the acid neutralizing capacity of tailings is stronger, and the tailings remain near neutral circumstance. Since then, pyrite started to oxidize and produce acid, and calcite in the tailings was consumed in large quantities, resulting in decrease of the acid neutralizing capacity and the tailings generating acid. Up to the top of the profile, calcite in the tailings is consumed almost entirely, while pyrites alteration is further enhanced, resulting in acidification intensifying. Under stronger oxidizing circumstance at the top tailings, lepidocrocite (γ-FeOOH) precipitates largely and cement/enwrap the tailings particles (including calcite residual particles), so the hardpan forms.

Huangshaping carbonate type tailings, due to containing a lot of pyrite with strong antioxidant capacity and acid producing ability, have a great potential to release acid and heavy water and the release may last for a long time.

Keywords: carbonate type tailings; tailings fabric; acid neutralizing capacity; acidification

EARTH AND ENVIRONMENT Vol. 43, No.2, Tot No.304, 2015, Page 173-182