2020同步年報

Environmental and Earth Science 071 Figure 1 displays XANES spectra at the Sb K-edge, Fe K-edge and S K-edge taken from solid minerals after reac- tion for 4 h under simulated sunlight irradiation and dark conditions. The Sb 2 S 3 standard exhibited a signal at 30490 eV (feature A in Fig. 1(a) ); Sb 2 O 3 and Sb 2 O 5 standards showed distinct signals at 30493 and 30495 eV, respec- tively. The Sb 2 S 3 species was unchanged after dissolution, as evident from linear-combination-fitting (LCF) results of 100% Sb 2 S 3 , consistent with S K-edge XANES spectra ( Fig. 1(b) ). Minor 5% Sb 2 O 3 was observed in a mixed Sb 2 S 3 and FeS 2 system under sunlight irradiation ( Fig. 1(a) ), indicating the adsorption of dissolved Sb species. The normalized S K-edge XANES spectrum of solid pyrite shows two obvious signals at 2469 (feature B) and 2481 eV (feature C in Fig. 1(b) ), corresponding to 48% FeS 2 and 52% SO 4 2- species. From the LCF results of S K-edge XANES spectra for samples in a mixed Sb 2 S 3 and FeS 2 system, ratio 50% Sb 2 S 3 and 48% FeS 2 was derived. The normalized Fe K-edge XANES spectrum of solid pyrite exhibited three signals at 7114 eV (feature D), 7121 eV (feature E), and 7136 eV (feature F in Fig. 1(c) ). Feature D is assigned to the transition from a 1 s core state to a hybrid state of 3 d and 4 p (1 s →3 d , 4 p ); feature E corresponds to a transition from 1 s to 4 p state (1 s →4 p ), and feature F is interpreted as a multiple scattering resonance of Fe p -like states in the continuum. Notably, for samples in a mixed Sb 2 S 3 and FeS 2 system, the heights of features D and E increased, but decreased for feature F ( Fig. 2(a) ), indicating the occupation of electrons in p states in the continuum. The accumulation of electrons on the Fe species resulted in Fe(III) reduction. The ratio of Fe(III) oxide, which was best fitted as ferrihydrite in the XANES spectra, decreased Fig. 2 : (a) Fe K-edge XANES spectra for samples in a mixed Sb 2 S 3 and FeS 2 system. (b) Reaction mechanisms of Sb 2 S 3 oxidative dissolution and sequestra- tion on FeS 2 . (1) Sb(III) oxidation by •OH radicals that were generated with Fe 2+ /Fe 3+ cycling; (2) Sb(III) oxidation by O 2 •- radicals on FeS 2 surface under light. (3) Sb(III) oxidation by •OH radicals in solution. The solid arrow presents reactions on the surface; the dashed arrow shows the dissolu- tion. [Reproduced from Ref. 1] from 47% to 26% in darkness, and further to 14% under sunlight ( Fig. 1(c) ). Correspondingly, a FeS 2 ratio increased from 53% to 74% in darkness and to 86% under light was observed. The heterogeneous electron transfers from Sb 2 S 3 to FeS 2 hence promoted Sb(III) oxidation and Fe(III) reduc- tion on the surfaces. In summary, Jing used XAS measurements to reveal hetero- geneous electron transfers between Sb 2 S 3 and FeS 2 interfaces. The electron transfers from Sb 2 S 3 to FeS 2 separated photo- generated hole (h + ) and electron (e - ) pairs, facilitating the generation of hydroxyl radicals (•OH) on Sb 2 S 3 and FeS 2 , and superoxide radicals (O 2 •- ) on FeS 2 , contributing to the oxidative dissolution of Sb 2 S 3 ( Fig. 2(b) ). The knowledge of the reactions and mechanisms gained from this work is crucial for an understanding of the environmental fate of sulfide minerals and the generation of acid mine drainages. (Reported by Ting-Shan Chan) This report features the work of Chuan-Yong Jing and his col- laborators published in Environ. Pollut. 262 , 114309 (2020). TLS 01C1 SWLS – EXAFS TLS 16A1 BM − Tender X-ray Absorption, Diffraction • XANES • Environmental Science, Chemistry Reference 1. L. Yan, T. S. Chan, C.-Y. Jing, Environ. Pollut. 262 , 114309 (2020).