Determination of Calcium Diffusion Coefficients as an Estimator of the Long-Term Dissolution Potential of Phosphogypsum:Cement:Lime Composites

Guo, Tingzong; Hawke, and Autumn S.; Rusch, Kelly A.

doi:10.1021/es981116m

Cited by 10 publications

(4 citation statements)

References 5 publications

(6 reference statements)

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“…The effective diffusion coefficients obtained during this experiment are 1-2 orders of magnitude smaller than those estimated for PG:portland type II cement:lime composites (10 -13 -10 -14 m 2 s -1 ) of similar cement content (25). It must also be noted that no stable CaCO3 coating was observed on any of the PG:portland type II cement:lime composites, which exhibited severe deterioration within 2 months of saltwater submergence (25). The PG:class C fly ash:portland type II cement composites had effective diffusion coefficients that approached those of the 70%:30% PG:portland type II cement composites (mean De ) 10 -16 m 2 s -1 ), which survived saltwater submergence for more than 1 yr (11).…”

Section: Resultscontrasting

confidence: 55%

Section: Resultsmentioning

confidence: 54%

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Stabilized Phosphogypsum:Class C Fly Ash:Portland Type II Cement Composites for Potential Marine Application

Guo

Malone²,

Rusch³

2001

Environ. Sci. Technol.

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Phosphogypsum (PG, CaSO4 x H20), a byproduct of phosphoric acid manufacturing, contains low levels of Ra226. PG can be stabilized with portland type II cement and class C fly ash for use in marine environments, thus eliminating the airborne vector of transmission for radon gas. An augmented simplex centroid design with pseudocomponents was used to select 10 PG:class C fly ash:portland type II cement compositions. The 43 cm3 blocks were fabricated and subjected to a 1.5-yr field submergence test and a 28-d saltwater dynamic leaching study. All field composites survived with no signs of degradation. Dynamic leaching resulted in effective calcium diffusion coefficients ranging from 0.21 to 7.5 x 10(-14)m2 s(-1). Effective diffusion depths, calculated for t=1 and 30 yr, ranged from 0.4 to 2.2 mm and from 2.0 to 11.9 mm, respectively. Scanning electron microscopy and wavelength dispersive microprobe and X-ray diffraction analyses of the leached composites identified a 40-60-microm calcite layer that was absent in the control composites. This suggests that a reaction between the composites and the saltwater results in the precipitation of calcite onto the block surface, encapsulating the composites and protecting them from saltwater attack and dissolution.

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Section: Resultscontrasting

confidence: 55%

Section: Resultsmentioning

confidence: 54%

Stabilized Phosphogypsum:Class C Fly Ash:Portland Type II Cement Composites for Potential Marine Application

Guo

Malone²,

Rusch³

2001

Environ. Sci. Technol.

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“…So, the effects of these stacks on the environment consist primarily of groundwater contamination with trace amounts of heavy metals and air pollution for radionuclides, the most threatening being Ra 226 and its daughter product Rn 222 [1,[4][5]. Consequently, the presence of some U-series radionuclides in phosphate rock and its impact on the environment requires alternative ways of disposal of this kind of residue.…”

Section: Introductionmentioning

confidence: 99%

Valorization of phosphogypsum waste as asphaltic bitumen modifier

Cuadri

Navarro

García‐Morales

et al. 2014

Journal of Hazardous Materials

116

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The accumulation of phosphogypsum wastes from the fertilizer industries, which remain in regulated stacks occupying considerable land resources, is causing significant environment problems worldwide. In that sense, the scientific community is being pressured to find alternative ways for their disposal. In this research, we propose a novel application for phosphogypsum wastes, as a modifier of bitumen for flexible road pavements. Viscous flow tests carried out on bitumen modified with a phosphogypsum waste and doped with sulfuric acid demonstrated an extraordinary increase in viscosity, at 60 ºC, when compared to a counterpart sample which had been modified with gypsum, the main component of phosphogypsum. Similarly, a significant improvement in the viscoelastic response of the resulting material at high temperatures was also found. FTIR (Fourier transform infrared spectroscopy) scans provided evidences of the existence of chemical reactions involving phosphorus, as revealed by a new absorption band from 1060 to 1180 cm -1 , related to C−O−P vibrations. This result points at phosphorus contained in the phosphogypsum impurities to be the actual "modifying" substance. Furthermore, no C-O-P band was observed in the absence of sulfuric acid, which seems to be the "promoting" agent of this type of bond.

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“…A one-dimensional diffusion model based on Fick's second law of diffusion with a zero surface concentration at the solid-solution interface is generally used to describe the leaching process (10,13,18). This simple model, which assumes no reaction occurs for the leaching contaminants, can be solved analytically (13) and used to calculate the effective diffusion coefficients for a host of constituents in stabilized waste systems (6,18,(23)(24)(25). Since calcium is the major element in most stabilized matrixes, effective calcium diffusion coefficients can also be used to predict the longterm stability of stabilized wastes based on short-term leaching measurements (21,(25)(26)(27)(28).…”

Section: Introductionmentioning

confidence: 99%

Identification of Dynamic Leaching Kinetics of Stabilized, Water-Soluble Wastes

Guo

Deshpande

Rusch

2003

Environ. Sci. Technol.

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A one-dimensional diffusion model based on Fick's second law with a non-zero surface concentration at the solid-solution interface was developed to calculate effective calcium and sulfate diffusion coefficients of composites placed in saltwater. A regression method was used to identify the leaching kinetics. The regression method decomposes the stabilized PG leaching processes into diffusion, surface wash-off, and immediate and long-term precipitation. The immediate surface precipitation of both calcium and sulfate ions occurred only in three of the PG composite combinations. The effective diffusion coefficients of calcium (2.58-4.68 x 10(-13) m2 s(-1)) and sulfate (2.77-5.02 x 10(-13) m2 s(-1)) obtained from the regression method are similar to those obtained from methods of cumulative flux and daily flux associated with the simple diffusion model, provided that the leaching processes do not deviate significantly from that of the diffusion. The ratio (1.13) of effective sulfate to calcium diffusion coefficients obtained using the regression analysis is statistically consistent with the theoretical value (1.31), which further justifies the regression method. The research also implies that the leaching processes of calcium and sulfate ions stop after a certain period of time (300-900 d for calcium and 80-170 d for sulfate) and that the precipitations of calcium and sulfate affect the leaching processes. The regression method can be used to identify the leaching mechanisms and to predict the long-term stability of the stabilized wastes.

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Determination of Calcium Diffusion Coefficients as an Estimator of the Long-Term Dissolution Potential of Phosphogypsum:Cement:Lime Composites

Cited by 10 publications

References 5 publications

Stabilized Phosphogypsum:Class C Fly Ash:Portland Type II Cement Composites for Potential Marine Application

Stabilized Phosphogypsum:Class C Fly Ash:Portland Type II Cement Composites for Potential Marine Application

Valorization of phosphogypsum waste as asphaltic bitumen modifier

Identification of Dynamic Leaching Kinetics of Stabilized, Water-Soluble Wastes

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