Long-term behavior of a portland cement-electroplating sludge waste form in presence of copper nitrate

The microchemistry and microstructure of a waste form containing a synthetic electroplating sludge in portland cement (OPC) in the presence of various amounts (2%, 5%, and 8%) of copper nitrate were studied over a period of eight years. The electroplating sludge, dewatered to 25% solids, contained 86.2 mg g of Ni, 84.1 mg g of Cr, 18.8 mg g of Cd, and 0.137 mg g of Hg. The OPC to sludge ratio was 0.3:1. A waste form without copper nitrate was prepared as control. The microstructure and microchemistry were studied by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffractometry, thermal analysis and Fourier-transform infrared spectroscopy. Increasing amounts of copper nitrate effected significant changes in crystallinity, porosity and phase chemistry. The principal copper-bearing phase in the presence of copper nitrate was CuO·3H O, whose appearance was both time- and concentration-dependent. Some amount of copper was also trapped in the newly formed crystalline calcium silicates. At the same copper nitrate level, subtle changes in the microchemistry occurred over time, but the microstructure remained qualitatively unchanged. Some of the sludge heavy metal phases disappeared with increasing copper nitrate concentration but others were not affected. -1 -1 -1 -1

Solidification/stabilization of arsenic salts: Effects of long cure times

Leachability of As(III) and As(V) from various solidification-stabilization (S/S) binders has been studied over a period of four years. Type I portland cement (OPC), both alone and mixed with a number of additives, results in toxicity characteristic leaching procedure (TCLP) leachabilities of ≤ 3 mg l for arsenite and 12 mg l for arsenate. There is no appreciable change in leachability after 3 years of cure, compared with 28 days of cure. The combination of OPC and Class F fly ash as a binder results in substantially degraded performance, as measured by TCLP leachability. Furthermore, the OPC-FA-As mixtures show increasing leachability with time. These solidified products have been studied using powder X-ray diffraction (XRD), derivative thermal gravimetry (DTG) and solid-state magic angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR). The As(V) salt, NaCaAsO ·7.5H O, is identifiable by XRD in many of these samples, particularly when sodium arsenate is the model As waste, but even when sodium arsenite is the original form of As. The OPC-FA mixtures show substantial respeciation during long curing times. There is evidence for formation of stratlingite from XRD, and there is substantial conversion of octahedrally coordinated aluminum, which is the predominant form at 28 days, to tetrahedrally coordinated aluminum at longer cure limes, as shown by NMR. These matrix changes are correlated with increased leachability, although direct cause and effect cannot be established. These results emphasize the importance of long-term testing to identify specific combinations of S/S binders and wastes that are prone to undergo respeciation, and consequent leachability changes, after long cure times. -1 -1 4

The effect of sodium sulfate on solidification/stabilization of a synthetic electroplating sludge in cementitious binders

The effect of sodium sulfate on the solidification/stabilization of a large quantity of a synthetic electroplating sludge in cementitious binders was s. © 1992

Synchrotron X-ray microtomography and solid-state NMR of environmental wastes in cement

Synchrotron X-ray microtomography shows vesicular structures for toluene/cement mixtures prepared with 1.22 to 3.58 wt% toluene. Three-dimensional imaging of the cured samples shows spherical vesicles with diameters ranging from 20 to 250 microns; a search with electron microscopy for vesicles in the range of 1-20 microns proved negative. However, the total vesicle volume, as computed from the microtomography images, accounts for less than 10% of initial toluene. Evidence for toluene in the cement matrix comes from 29Si MAS NMR spectroscopy, which shows a reduction in chain silicates with added toluene. Also, 2H NMR of d8-toluene/cement samples shows high mobility for all toluene and thus no toluene/cement binding. A model that accounts for all observations follows: For loadings below about 3 wt%, most toluene is dispersed in the cement matrix, with a small fraction of the initial toluene phase separating from the cement paste and forming vesicular structures that are preserved in the cured cement. Furthermore, at loadings above 3 wt%, the abundance of vesicles formed during toluene/cement paste mixing leads to macroscopic phase separation

Solid-State Deuterium NMR Spectroscopy of d\u3csub\u3e5\u3c/sub\u3e-Phenol in White Portland Cement: A New Method for Assessing Solidification/Stabilization

We have developed a new NMR-based procedure for studying waste/cement interactions. This is the first use of deuterium NMR spectroscopy to study waste solidification/stabilization (S/S). The main feature of deuterium NMR spectroscopy is the ability to monitor molecular reorientations over a wide range of reorientation rates. This technique allows one to determine if a particular deuterated organic waste is effectively solidified/stabilized and to determine the lower limit of the bond strength between the waste and the cement matrix. Comparison of the predicted and experimental deuterium NMR spectra show that phenol is mainly dissolved in pore waters and, thus, poorly immobilized by white portland cement, at least for cure times up to 1 year. After evaporation of the pore water from the cement matrix the 2H line shape and T1 were measured at 230–360 K; the maximum activation energy for the 180° ring flip process is 5.5 kcal/mol. Hence, the lower limit of the bond strength between phenol and the cement matrix is approximately 5.5 kcal/mol. © 1993, American Chemical Society. All rights reserved