Viability of adding gypsum and calcite for remediation of metal contaminated soil: laboratory and pilot plant scales
Supplementary material
Materials and methods
Main sample parameters
The pH was measured in Milli-Q water using a solution-to-soil ratio of 2.5 mL g-1. The total content of trace elements in the soils and materials was determined using X-ray fluorescence. The final suspension was shaken at 30 rpm for 16 h at room temperature, centrifuged, and then the water extract was filtered and maintained at 4 °C before the analyses. The particle size distribution was determined using the pipette method (Burt 2004). The concentration of major anions in the water extracts was determined using the USEPA standard 9056 method, which is based on anionic chromatography using a conductivity detector, a Waters IC-Pack Anions column and a mobile phase formed by boric acid, sodium gluconate, acetonitrile and glycerin. The major cation and trace element contents of the samples were determined as described in the “Determination of major and trace elements in the extracts”.
pH titration test
The neutralisation capacity of the samples within a pH range of 2 to 12 was examined using a pH titration test (Kosson et al. 2002; CEN/TS 2006a). First, the initial pH of each sample (2 g) was measured in deionised water (200 mL). Then, after consecutive additions of 200 μL of HNO3 or NaOH, the pH of the suspension was measured after 20 min of stirring. The acid and base addition was repeated until the pH range of 2 to 12 was covered.
Structural analyses of the samples
The samples were ground before being analysed using X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX). The minerals were qualitatively analysed using XRD with a Bruker D8I instrument. This instrument operates with Ni-filtered Cu Ka radiation at 40 kV and 40 mA. The diffractograms were obtained from 3 to 70° 2q at a scan step of 0.05° 2q with a counting time of 3 s. The morphology and chemical composition of the samples were analysed using JEOL JSM 5400 and JEOL 6460LV scanning electron microscopes that were operated at an acceleration voltage of 20 kV. Both instruments were equipped with a probe for energy dispersive X-ray spectroscopy measurements. The samples were coated with a gold film before analysis.
The specific surface area of the materials was determined using N2 adsorption measurements in liquid nitrogen with a Micromeritics ASAP 2010. The samples were degassed for 2 h at 150 ºC in vacuum before analysis.
References
Burt R (2004) Soil survey laboratory methods manual. Investigations Report No 42. Version 4.0. Natural Resources Conservation Service, USDA. Washington
Table S1 Main sample characteristics in samples from the pilot plant (mg kg-1, mean values; n= 3; RSD <5%)
ALJ2_PP / 2.6 / 158000 / 9400 / 6900 / 810 / 34 / 3100 / 1320 / 11600 / 1120 / 12
Table S2 Extraction yields under acidic, basic and medium pH conditions in samples from the pilot plant (%; mean values; n = 2-6; RSD <5%)
ALJ2_PP / 12.5 / 1.5 / <0.5 / <0.5 / <0.5 / <0.5 / <0.5 / <0.5 / <0.5 / <0.5 / <0.5
5.9 / 57 / 100 / <0.5 / 0.6 / <0.5 / <0.5 / <0.5 / <0.5 / <0.5 / <0.5
1.4 / 90 / 100 / 17 / 34 / 26 / 18 / 23 / <0.5 / 29 / <0.5
ALJ2+GC_PP / 12.6 / 2.1 / <0.5 / <0.5 / <0.5 / <0.5 / <0.5 / <0.5 / 4.6 / <0.5 / <0.5
6.0 / 24 / 96 / <0.5 / <0.5 / <0.5 / 1.2 / <0.5 / <0.5 / <0.5 / <0.5
1.6 / 31 / 100 / 5.7 / 7 / <0.5 / 6 / 7 / 1.6 / <0.5 / <0.5
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Fig. S1 XRD pattern (a), SEM micrographs (b) and EDX mapping (c) of the ALJ2 soil. Q= quartz (PDF 00-46-1045), A= anglesite (PDF 01-89-3750), G=gypsum (PDF 04-10-9409) and P=pyrite (PDF 01-73-8127)
Fig. S2 XRD pattern and SEM micrographs of gypsum (gypsum: PDF 04-10-9409)
Fig. S3 XRD pattern and SEM micrographs of calcite (calcite: PDF 00-05-586, veterite (*): PDF 01-74-1867 and plombierite (^):PDF 00-29-0331)
Fig. S4 pH titration curves and ANC values (meq kg-1). The horizontal line indicates initial pH
Fig. S5 XRD pattern of mixtures of ALJ2 with gypsum, calcite and gypsum+calcite: initial (a, e and i); after leaching at the initial pH (b, f and j); after leaching at an acid pH (c, g and k); and after leaching at a basic pH (d, h and l). Q= quartz (PDF 00-46-1045), A= anglesite (PDF 01-89-3750), G=gypsum (PDF 04-10-9409), C=calcite (PDF 00-05-586) and P=pyrite (PDF 01-73-8127)
Fig. S6 pH titration curves and ANC values (meq kg-1) for pilot plant samples. The horizontal lines indicate initial pH
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