Alum Residual Floc Interactions with an Advancing Ice/Water Interface

Parker, Philip J.; Collins, Anthony; Dempsey, J. P.

doi:10.1061/(asce)0733-9372(1998)124:3(249)

Cited by 17 publications

(11 citation statements)

References 11 publications

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“…Thereby, the HFO crystallites are pushed together to form dense aggregates. With increasing freezing rate, the progressing ice front changes from smooth to dendritic [17], thereby entrapping HFO aggregates between prograding ice needles, ultimately leading to the formation of smaller HFO aggregates.…”

Section: Discussionmentioning

confidence: 99%

“…Later studies investigated dense aggregates of various metal oxyhydroxides as a sorbent material for heavy metals and radionuclides [15]. Several attempts have been made to make the technique available in water treatment plants, notably for the reduction of alum sludges [9,16,17]. Driehaus et al [18] proposed the use of HFO aggregates in fixed bed reactors for the purification of natural waters contaminated with arsenic.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of the pores in hydrous ferric oxide aggregates formed by freezing and thawing

Hofmann¹,

Pelletier

Michot

et al. 2004

Journal of Colloid and Interface Science

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Hydrous ferric oxides (HFO) are efficient sorbents for inorganic and organic pollutants and therefore have great potentials in environmental science and engineering applications. Freezing and thawing of HFO suspensions leads to the formation of dense HFO aggregates. It facilitates the handling and increases the drying rate of HFO. In this study, we used a combination of pycnometry, gas adsorption (N 2 gas, water vapor), and small-angle neutron scattering (SANS) to characterize the porosity and pore size distribution of dense HFO aggregates formed by freezing dialyzed HFO suspensions at −25 • C and thawing them at room temperature. The crystallinity of the HFO, which was a 2-line ferrihydrite, was not affected by this treatment. Wet sieving and laser diffraction analysis showed that the dense HFO aggregates had a unimodal size distribution with an average diameter of 235 ± 35 µm. Increasing the freezing rate by cooling with liquid N 2 (−196 • C) resulted in much smaller aggregates with an average diameter of 20 µm. Adding NaNO 3 electrolyte to the HFO suspensions prior to freezing also resulted in the formation of smaller aggregates. The dense HFO aggregates formed at −25 • C had a porosity of 0.73 ± 0.02 l l −1 . SANS revealed a unimodal size distribution of pores, with an average pore diameter of 2.0 nm. The diameter of the HFO crystallites was estimated by transmission electron microscopy to be 1.9 ± 0.5 nm. Geometrical considerations taking into account the unit particle and average pore size suggest that the crystallites retain 1-2 layers of hydration water during the coagulation induced by freezing. Analysis by N 2 gas adsorption showed that drying the dense HFO aggregates induced a reduction in porosity by about 25% and shifted the pore size distribution to smaller diameters. Rewetting during water vapor adsorption did not induce significant changes of the aggregate structure. The specific surface area of the dry HFO aggregates was between 320 and 380 m 2 g −1 .

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Characterization of the pores in hydrous ferric oxide aggregates formed by freezing and thawing

Hofmann¹,

Pelletier

Michot

et al. 2004

Journal of Colloid and Interface Science

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“…Ice spikes grow as tiny cracks in a radial direction from the core margin towards the center of the core, where spikes increase in size (maximum length of 6 mm) and decrease in number. Parker et al () stated that ice spikes can grow into the still unfrozen sludge in the direction of freezing at high freezing rates (> 21 μ m s −1 ), generally bypassing the sludge flocs, apparently without moving or altering them (Parker et al ). The occurrence of ice spikes (Fig.…”

Section: Resultsmentioning

confidence: 99%

Laboratory and field investigations on freeze and gravity core sampling and assessment of coring disturbances with implications on gas bubble characterization

Dück

Lorke

Jokiel

et al. 2019

Limnology & Ocean Methods

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The quantification of greenhouse gas emissions from aquatic ecosystems requires knowledge about the spatial and temporal dynamics of free gas in sediments. Freezing the sediment in situ offers a promising method for obtaining gas‐bearing sediment samples, unaffected by changes in hydrostatic pressure and sample temperature during core withdrawal and subsequent analysis. This article presents a novel freeze coring technique to preserve the in situ stratigraphy and gas bubble characteristics. Nondestructive X‐ray computed tomography (CT) scans were used to identify and characterize coring disturbances of gravity and freeze cores associated with gassy sediment, as well as the effect of the freezing process on the gas bubble characteristics. Real‐time X‐ray CT scans were conducted to visualize the progression of the freezing process. Additional experiments were conducted to determine the freezing rate to assess the probability of sediment particle/bubble migration, and gas bubble nucleation at the phase transition of pore water to ice. The performance of the freeze coring technique was evaluated under field conditions in Olsberg and Urft Reservoir (Germany). The results demonstrate the capability of the freeze coring technique for the preservation of gas‐bearing sediments and the analysis of gas bubble distribution pattern in both reservoirs. Nevertheless, the obtained cores showed that nearly all gravity and freeze cores show some degree of coring disturbances.

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“…Vesilind and Martel [2] hypothesized that the floc would increase in size at low freezing speeds because of floc-floc contact at the freezing ice front, which is of planar shape. Parker et al [12] claimed that the floc would decrease in size since the dendrite formed at high freezing speeds could pierce and fragment the floc. At intermediate freezing speeds, a "rough" ice front was noted to engulf and fragment part of the sludge flocs.…”

Section: Introductionmentioning

confidence: 99%