High-Temperature Chlorination of Nickel Oxide Using Calcium Chloride.

Attempts have been made to extract nickel from ores and nickel-containing wastes using the chlorination method. However, the use of gaseous chlorinating agents is limited due to their toxicity. High-temperature chlorination of nickel oxide using calcium chloride is analyzed in this study. The volatilization percentage is positively correlated to temperature and CaCl2 dosage and negatively correlated to oxygen partial pressure. The apparent activation energy is calculated to be 142.91 kJ/mol, between 1173 K and 1323 K, which suggests that the high-temperature chlorination of nickel oxide using calcium chloride is controlled by a chemical reaction.

Transport of graphene oxide nanoparticles in saturated sandy soil.

We examined the transport properties of graphene oxide nanoparticles (GONPs) in saturated sandy soil, under different solution chemistry conditions and flow velocities. GONPs exhibited high mobility in soil, even at 50 mM NaCl. While at relatively high ionic strength GONPs were less mobile in soil than in quartz sand, the differences were not significant. At a concentration of 0.5 mM, Ca(2+) significantly inhibited the transport of GONPs in soil, but only slightly inhibited the transport in quartz sand. This was because by complexing with the surface O-functionalities of both GONPs and soil components, Ca(2+) could enhance the aggregation of GONPs and bridge GONPs and soil grains. Increasing pH from 4 to 9 only slightly enhanced the transport of GONPs in soil, probably because the mobility of GONPs was already high at low pH. The presence of 10 mg L(-1) Suwannee River humic acid significantly enhanced the transport of GONPs in quartz sand at 35 mM, but only had a small effect for the transport in soil. This was possibly linked to the much smaller grain sizes and much more heterogeneous nature of the soil. Flow velocity had marked effects on the transport in soil, but essentially no effects on the transport in quartz sand. A two-site transport model incorporating both the blocking-affected attachment process and straining effects can effectively model the transport of GONPs. The high mobility of GONPs may have important implications for their environmental fate and effects.

Factors controlling transport of graphene oxide nanoparticles in saturated sand columns.

The authors conducted column experiments and a modeling study to understand the effects of several environmental factors on the aggregation and transport of graphene oxide nanoparticles (GONPs) in saturated quartz sand. The GONPs were negatively charged and stable under the test conditions (0-50 mM NaCl; pH 4.8-9.0), and the Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation indicated that deposition of GONPs was under unfavorable attachment conditions. The GONPs exhibited high mobility even at an ionic strength of 25 mM NaCl. The transport of GONPs was insensitive to the changes of pH (from 5.1 to 9.0), but the presence of 10 mg/L Suwannee River humic acid (SRHA) considerably enhanced transport at high ionic strength (35 mM NaCl), likely via enhanced steric repulsion and significantly inhibited stacking of GO flakes. Varying flow velocity also enhanced transport at high ionic strength. In general, GONPs exhibit greater mobility compared with other carbon nanoparticles because the aggregation and transport of GONPs are more resilient to changes in solution chemistry and hydrodynamic forces that favor aggregation and deposition of nanoparticles. A 2-site transport model incorporating both the blocking-affected attachment process and straining effects can effectively model the transport of GONPs. The high mobility of GONPs should be given full consideration in assessing their environmental risks.

Transport of fullerene nanoparticles (nC60) in saturated sand and sandy soil: controlling factors and modeling.

Understanding subsurface transport of fullerene nanoparticles (nC(60)) is of critical importance for the benign use and risk management of C(60). We examined the effects of several important environmental factors on nC(60) transport in saturated porous media. Decreasing flow velocity from approximately 10 to 1 m/d had little effect on nC(60) transport in Ottawa sand (mainly pure quartz), but significantly inhibited the transport in Lula soil (a sandy, low-organic-matter soil). The difference was attributable to the smaller grain size, more irregular and rougher shape, and greater heterogeneity of Lula soil. Increasing ionic strength and switching background solution from NaCl to CaCl(2) enhanced the deposition of nC(60) in both sand and soil columns, but the effects were more significant for soil. This was likely because the clay minerals (and possibly soil organic matter) in soil responded to changes of ionic strength and species differently than quartz. Anions in the mobile phase had little effect on nC(60) transport, and fulvic acid in the mobile phase (5.0 mg/L) had a small effect in the presence of 0.5 mM Ca(2+). A two-site transport model that takes into account both the blocking-affected attachment process and straining effects can effectively model the breakthrough of nC(60).

Humic acid-mediated transport of tetracycline and pyrene in saturated porous media.

The authors observed that humic acid (HA) mediates transport of tetracycline and pyrene in saturated porous media via distinctively different mechanisms. The presence of HA (20-80 mg C/L) in the influent consistently enhances the transport of tetracycline, whereas for pyrene a critical HA concentration exists (about 10 mg C/L), below which transport is inhibited but above which transport is enhanced. The difference in the HA effect stems from the difference in relative sorption affinity to HA and sand between these two compounds. Because sorption of pyrene is driven primarily by hydrophobic effect, pyrene exhibits much stronger sorption to HA than on sand. Accordingly, pyrene in the influent (or mobile phase) is predominantly associated with HA, and its transport is controlled by the partition of HA between mobile phase and sand. For the polar, ionic, and highly hydrophilic tetracycline, sorption is driven mainly by surface complexation and ligand exchange, so tetracycline exhibits relatively strong adsorption on sand, but has much weaker sorption to HA than pyrene does. For tetracycline, the effect of HA on transport is likely the competition of HA for the available adsorption sites on sand. In addition, tetracycline and pyrene exhibit markedly different breakthrough profiles, both in the presence and in the absence of HA; this can be attributed to the greater degree of adsorption nonequilibrium of tetracycline on sand.

Facilitated transport of 2,2',5,5'-polychlorinated biphenyl and phenanthrene by fullerene nanoparticles through sandy soil columns.

The potential environmental implications of buckminsterfullerene (C60) and its derivatives have received much attention. In this study, we investigated facilitated transport of 2,2',5,5'-polychlorinated biphenyl (PCB) and phenanthrene by nC60 (a stable aqueous-phase aggregate of C60) through two sandy soil columns. We found that low-level (from 1.55 to 12.8 mg/L) nC60 could significantly enhance the mobility of PCB and phenanthrene. However, none of the three model dissolved organic matters (DOMs)-a humic acid, a fulvic acid, and a bovine serum albumin-had a noticeable effect on the transport of PCB when these DOMs were present at concentrations equivalent to approximately 10-11 mg/L organic carbon. We propose that the contaminant-mobilizing ability of nC60 is a result of irreversible adsorption of a fraction of nC60-associated PCB/phenanthrene (whereas DOM-associated PCB is readily desorbable). Additionally, slow desorption kinetics of nC60-adsorbed PCB/phenanthrene is another possible mechanism. The findings in this study indicate that nC60 in the subsurface environment can greatly enhance the mobility of nonionic, highly hydrophobic organic contaminants, which typically exhibit very low mobility. Such effects should be taken into account when assessing the potential environmental risks of engineered carbonaceous nanomaterials.

Simulation of nonlinear sorption of N-heterocyclic organic contaminates in soil columns.

The transport of organic contaminants in porous media is frequently influenced by nonequilibrium sorption and/or nonlinear sorption. In this study, sorption of coal tar related contaminants with different sorption properties, i.e., toluene, quinoline, quinaldine, and benzotriazole, was studied in column experiments using a European reference soil and compared with batch sorption results in order to quantify the governing sorption features. The breakthrough curves (BTCs) were simulated with a versatile 1-D reactive transport model using a one-site first-order sorption approach. Some differences in fitted parameters from batch and column experiments were found and discussed in terms of different sorption mechanisms in different aqueous concentration ranges, effects of solution properties (e.g., pH) and differences in solid-to-solution ratio and accessible sorption sites. The modeling results show that the fitting results were not sensitive to mass transfer coefficients and that a local equilibrium assumption provides excellent agreement with BTCs in our designed column when Damkohler numbers were greater than 20. Nonequilibrium sorption resulting from intraparticle diffusion thus was negligible in the column experiments. Tailing of BTCs nevertheless occurred and was primarily attributed to nonlinear sorption due to specific interactions in the sorption processes rather than to sorption nonequilibrium. Our study demonstrates how column experiments with different concentrations and flow velocities can be designed to obtain reliable sorption parameters for polar solutes with nonlinear sorption isotherms from modeling.