| The sulfide in tailings in natural environment would be oxidized by the air,microbe and water,with the formation of acid mine drainage(AMD)and release of heavy metals.The AMD could be transported into rivers,lakes as well as soils through the runoff and agricultural irrigation,caused severe pollution problems in groundwater,surface water and soils,destroyed ecosystems,and even affected human health.A good understanding on the oxidation of sulfides in tailings is a foundation for the prevention,control and restoration of mine pollution.In this study,sediment profiles of S and SP were collected from a copper tailing of Shuimuchong tailing in Tongling City,Anhui Province.The physical and chemical proxies,sulfur species,sulfur isotope of sulfate and secondary mineral composition in each layer subsamples were analyzed to study the change of sulfur species and secondary minerals during the oxidation of sulfides.The main results were showed as follows.1.Both S and SP profiles show an obvious oxidation in the upper layers.They were general acidic,with a pH value of 2.59?6.12 and 3.50?6.27,respectively,which showed an obvious decreasing trend from bottom to top.The oxidation-reduction potential(Eh)of S and SP increased obviously from the bottom up,with an Eh value of 66?457mV and-37?307mV,respectively.It was proved that oxidation and acidity of the profiles increased significantly from bottom to top.2 The content of acid volatile sulfur(AVS)in S and SP profile was 0-62.36 mg/g and 0-3.44 mg/g,while the pyrite sulfur(CRS)was 0.70?32.30 mg/g and 0.17?5.39 mg/g,respectively.The content of AVS and CRS in these two profiles showed a similar decrease trend from the bottom up,and AVS was oxidized earlier than CRS,The content of elemental sulfur(ES)in S and SP profiles was 0-8.83 mg/g and 0?3.62 mg/g,without clear trend in depths.The content of sulfate was 8.44?66.34 mg/g and 8.48?29.87 mg/g,respectively,they decreased from bottom-up in these two profiles.The hardpan(iron hvdroxide)at 11.5?16.5 cm and 18?54 cm in S and SP blocked the transport of oxygen and water from the top down,slowed the oxidation of sulfide in down layers,and formed a sulfate-rich zone.The total sulfur(TS)of these two profiles was 9.18?109.69 mg/g and 12.38?37.72 mg/g,respectively,and the lower values in up layers were likely due to the surface leaching.Generally,the content of TS and sulfur species in SP profile was lower than those in S,suggested more intense leaching.The proportion of reducing sulfur at the bottom of S profile was higher than that of SP profile,which indicated that the oxidation degree of SP profile was high er than that of S profile.3.The ?34S of sulfate in S and SP was-3.32‰?13.43‰ and-3.08‰?1.80‰,respectively.An exceptional ?34S of 13.43‰o in S-9 layer suggested a source of anhydrite,while others indicated a source of sulfide.4.The mineral compositions of S and SP profile were similar in basically.The results from XRD analysis showed that some minerals such as pyrite,pyrrhotite and calcite decreased gradually or even disappeared from bottom to top while secondary minerals such as jarosite and goethite formed;the results from XPS analysis showed that the sulfur and iron species changed significantly from bottom to top,suggested effects from the transformations of sulfur species during the oxidations. |
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