Atmospherically stable NZVI (nanoscale zero-valent iron) particles were produced by modifying shell layers of Fe(H2) NZVI particles (RNIP-10DS) by using a controlled air contact method. Shell-modified NZVI particles were resistant to rapid aerial oxidation and were shown to have TCE degradation rate constants that were equivalent to 78% of those of pristine NZVI particles. Fe(H2) NZVI particles that were vigorously contacted with air (rapidly oxidized) showed a substantially compromised reactivity. Aging of shell-modified particles in water for one day resulted in a rate increase of 54%, implying that depassivation of the shell would play an important role in enhancing reactivity. Aging of shell-modified particles in air led to rate decreases by 14% and 46% in cases of one week and two months of aging, respectively. A series of instrumental analyses using transmission electron microscopy, X-ray diffractography, X-ray photoelectron spectroscopy, and X-ray absorption near-edge structure showed that the shells of modified NZVI particles primarily consisted of magnetite (Fe(3)O(4)). Analyses also implied that the new magnetite layer produced during shell modification was protective against shell passivation. Aging of shell-modified particles in water yielded another major mineral phase, goethite (alpha-FeOOH), whereas aging in air produced additional shell phases such as wustite (FeO), hematite (alpha-Fe(2)O(3)), and maghemite (gamma-Fe(2)O(3)).

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We developed a novel mixed binder of MgO (magnesia) and supplementary cementitious materials that can solidify sediments contaminated with heavy metals as well as store CO2 through mineral carbonation reactions. The optimal MgO‐based binder consisted of MgO, lime (L), fly ash (FA), and blast furnace slag (BFS) with a formula of MgO0.5–(L0.1–(FA0.4BFS0.6)0.9)0.5. The binder exhibited a compressive strength of 11.9 MPa, which was similar to that of Portland cement. Sequential extraction of treated sediments showed that the stabilization capacity of the MgO‐based binder for heavy metals (Cu, Cd, Ni, Pb, and Zn) was two times higher than that of PC. Results also show that more than 50% of the stabilized heavy metals existed within very persistent solid phases that were not disintegrated during the final step of the sequential extraction procedure using a HNO3/HClO4/HF solution. The hydration products of MgO that contributed to strength development and metal stabilization included brucite (Mg(OH)2), magnesium–silicate–hydrates (M–S–H), and lansfordite (MgCO3 · 5 H2O). Lansfordite was a major carbonation product in the treated sediments. By use of thermogravimetric analyses, we found that 58 kg of CO2 could be sequestrated within the solidified sediment when a ton of dredged sediment was treated.

Two types of river sediments with contrasting characteristics (anoxic or oxic) were resuspended and the release of heavy metals and changes in water chemistry were investigated. During resuspension of the anoxic sediment, the dissolved oxygen (DO) concentration and redox potential of the water layer decreased abruptly within the first 1 min, followed by increases toward the end of the resuspension period. Heavy metals were released rapidly in the first 6 h, probably due to the oxidation of acid volatile sulfide (AVS) of the anoxic sediment, and then the aqueous phase concentrations of the heavy metals decreased due to resorption onto the sediment until the 12-h point. During resuspension of the oxic sediment, the DO concentration and redox potential remained relatively constant in the oxic ranges. The heavy metals were released from the oxic sediment gradually during a 24-h resuspension period. The temporal maximum concentrations of Ni, Cu, Zn, and Cd in the aqueous phases in both experiments frequently exceeded the USEPA water quality criteria or the water quality guidelines of Australia and New Zealand. This suggests that a resuspension event could bring about temporal water quality deterioration in the two sediment environments.

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We previously described a MgO-based binder for treating fine sediment and simultaneously store CO. Here, we describe a study of the physical/mechanical characteristics and carbonation reactions of the MgO-based binder used to solidify/stabilize fine sediment in atmospheres containing different CO concentrations. Carbonation of the sediment treated with the MgO-based binder at the atmospheric CO concentration markedly improved the compressive strength of the product. The compressive strength was 4.78 MPa after 365 days of curing, 1.3 times higher than the compressive strength of sediment treated with portland cement. This improvement was caused by the formation of carbonation products, such as hydromagnesite, nesquehonite, and lansfordite, and the constant high pH (~ 12) of the specimen, which favored the growth of hydration products such as calcium silicate hydrates and portlandite. Very low compressive strengths were found when 50 and 100% CO atmospheres were used because of excessive formation of carbonation products, which occupied 78% of the specimen depth. Abundant carbonation products increased the specimen volume and decreased the pH to 10.2, slowing the growth of hydration products. The absence of brucite in specimens produced in a 100% CO atmosphere indicated that MgO carbonation is favored over hydration at high CO concentrations.

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