Selenium Sorption in a Sedimentary rock/saline Groundwater System and Spectroscopic Evidence

Abstract

Sorption of selenium (Se) was studied by batch technique by using sedimentary rock samples andcorresponding saline groundwater from Horonobe underground research laboratory (URL)site under reducing condition. Spectroscopic analyses were performed by X-ray absorption near-edge structure (XANES) afterthe sorption experiments to identify the oxidation states of Se on the sedimentary rock. It issuggested thatthe dominant parameters affecting the Se sorption are iron-bearing minerals, especially exchangeable Fe and pyrite, and organic matters. Most of the Se sorbed on the sedimentary rock was Se(0) inthe case of natural saline groundwater, at least at relatively high Se concentration, while only part of the Se was Se(0) in caseof the synthetic groundwater, which contains no organic matters. Incorporationinto pyrite could be the sorption mechanism of Se(0).

Sorption Behavior of Selenium(−II) on Rocks under Reducing Conditions

“…Naveau et al 31) and Breynaert et al 32) reported that the sorption mechanism of Se(IV) onto pyrite was a redox reaction with sulfur but not iron, supporting the interpretation by Xia et al 15) and Liu et al 30) Although it is not clarified whether Se can be incorporated into pyrite, it seems not to occur easily because the crystalline system of ferroselite (FeSe 2 ; orthorhombic) is different from that of pyrite (FeS 2 ; cubic). 20) Thus, the sorption mechanism of selenide onto pyrite is probably a local redox reaction with sulfur at the surface, as shown in Eq.…”

“…The K d values obtained for sandy mudstone were compared to previously reported ones for mudstone and shale 10,[14][15][16] (Fig. 8).…”

“…Xia et al 15) carried out sorption experiments of Se(ÀII)/Se(0) on sedimentary rock samples containing pyrite under reducing conditions. Selenium(IV) in a test solution was reduced to Se(ÀII)/Se(0) by a mixed gas (H 2 (4.9%) + N 2 ) in the presence of a platinum (Pt) catalyst.…”

“…The K d values obtained in the previous study by the authors 16) using the same types of groundwater and rock samples under higher ionic strengths (0.1 to 1 mol dm À3 ) and higher Se(ÀII) concentrations (1:2 Â 10 À5 to 3:4 Â 10 À5 mol dm À3 ) agree with the results in this study. Xia et al 15) carried out the sorption experiments for Se using 4 types of mudstone/shale. The K d values varied according to the rock type ((A)-(D) in Fig.…”

“…Although a considerable amount of Se sorption data has been obtained under aerobic conditions, [7][8][9][10][11][12][13][14] where selenite and selenate species are dominant, the data obtained under reducing conditions are limited. [12][13][14][15][16] In particular, the sorption data for Se(ÀII) species in alkaline groundwater are scarce.…”