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- Title
Formation and properties of inorganic Si-contaminant compounds.
- Authors
Stein, Mathias; Rennert, Thilo; Gudat, Dietrich; Georgiadis, Anna
- Abstract
Contamination of soil with inorganic contaminants such as lead (Pb), copper (Cu)and cadmium (Cd) is a major environmental issue, especially concerning food andgroundwater security. Various studies demonstrate positive effects of Si regardingresilience of some crops towards these inorganic contaminants. One reason could be acomplexation reaction of Si and the metal cations. However, this process has not yet beensystematically investigated. Thus, our research contributes to reducing the mobility of Cd,Cu and Pb in contaminated soils and to decreasing their transfer into aquifers orplants. The main goal of this study is to elucidate the extent and the mechanisms of theinteractions between Pb2+, Cd2+ and Cu2+ and silicic acid, including the long-term kinetics,and to investigate whether the metals are bound by silicic acid. In order to understand theseprocesses a series of precipitation experiments was performed in aqueous solution at roomtemperature. Tetraethoxysilane (TEOS) as Si source and Pb(NO3)2, Cd(NO3)2 and Cu(NO3)2 withan initial concentration of 10 mmol l−1were used for synthesis. Selectivity of Sitowards the metals was tested in an equimolar solution of all three salts and TEOS.Time-dependency of particle growth was examined at sixteen different dates usingdynamic light scattering (DLS) and transmission electron microscopy (TEM). The Siand metal concentration in the dialyzed aliquots were measured using microwaveplasma-atomic emission spectroscopy (MP-AES). Spectroscopic analysis of thedialyzed and freeze dried solid phase, was performed using FTIR and 29Si-NMRspectroscopy. DLS and TEM analyses showed that the metals had a positive effect on thepolymerization reaction of silicic acid [Cu2+ > (Cu2+, Pb2+, Cd2+) > Cd2+ > Pb2+].Initial formation of nanoparticles through homogenous nucleation was followed by particlegrowth. Particle growth of the control synthesis (TEOS in aqueous solution) stoppedafter 124 days at a size of 34 nm (Z-Average). Particles in the syntheses with themetals kept growing until the experiment was completed after 211 days reaching afinal size of 260 nm for Cu-, 96 nm for Pb- and 196 nm for the Cd-variant. Finalconcentrations of up to 15 μmol l−1 of Cu, 10 μmol l−1 of Pb and 13 μmol l−1of Cd remained in the dialyzed aliquots. The Si concentrations in these aliquotsincreased continuously until an equilibrium was reached after 112 days at differentconcentrations (Cu: 7.3 mmol l−1, Pb: 6.9 mmol l−1, Cd: 4.8 mmol l−1). The FTIR spectrashowed a shift of the Si-O stretching vibration by 10 to 32 cm−1 towards lowerwavenumbers, which could indicate an incorporation of the metals in the polymericnetwork of the silicic acid. The 29Si-NMR relaxation experiments will show ifand how Cu is incorporated. That will be the first analysis to show such structuralincorporation of Cu, which might reduce the transfer of Cu into plants and aquifers.
- Subjects
INORGANIC compounds; INORGANIC soil pollutants; SILICON compounds; SILICIC acid; SOIL pollution; EMISSION spectroscopy; LIGHT scattering
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article