Characterization of arsenic biogenic minerals by SEM-EDS and Raman

Abstract

The data set contains the SEM-EDS analysis raw data generated to characterize biogenic arsenic sulfides obtained from two arsenate/sulfate-reducing reactors operated in fed- batch mode for 6 cycles (14 d each), fed with simulated groundwater containing 10 mM lactate and 5 mM arsenate, using sediment as the packing material and inoculum. High rates of arsenate (1.9 mmol/L·d) and sulfate (1.0 mmol/L·d) reduction were achieved, reaching 91-99 % arsenic removal efficiencies (last 42 d). Primarily, alacranite (As8S9) and uzonite (As4S5) formed, but once incorporated into the bed, sediment mineralogy masked their signals. The samples analyzed originated at the top of the reactors once yellow precipitates formed, and some solid attached to the glass wall of the reactors was recovered for analysis. The samples consisted of a mixture of sediment and biogenic precipitates and were dried (40 °C) and pulverized in an agate mortar. Finally, the dried samples were characterized by scanning electron microscopy coupled with X-ray Energy-Dispersive Spectroscopy (SEM- EDS) (UHR FEI Helios NanoLab 600, Hillsboro, OR, USA). The data in the CSV files correspond to the signals generated by the Electronic Microscope during the analysis of Zones A and B highlighted in the SEM image file 1ER_SE_0004.tif. The images 1ER_SE_0004_EDS Zona A.tif and 1ER_SE_0004_EDS Zona B.tif correspond to the raw EDS spectra generated for zones A and B, respectively. Files 1 ER_SE_004_EDS Zona A.csv and 1 ER_SE_004_EDS Zona B.csv contain the raw data of the EDS raw X-ray counts of zones A and B, for the yellow precipitate (arsenic sulfide), respectively. To generate the EDS spectrum, it is necessary to graph X-ray intensity on the Y axis against X-ray energy (Kiloelectron volts, keV) on the X axis. Files 1 ER_SE_004_EDS Zona AQ.csv and ER_SE_004_EDS Zona BQ.csv contain the raw data of the weight (wt. %) and atomic (At. %) percentages of the elements detected in the samples for zones A and B, respectively. File 3BP-E_633-2.txt contains the data used to generate the Raman spectrum. A standard Raman spectrum is plotted with Raman Intensity counts on the Y-axis against Wavenumber (cm-1) on the X-axis.