Narrow Results

The polyacrylamide surface grafted poly(vinyl chloride) (PAM-PVC) film was successfully prepared via a facile copper-mediated surface-initiated atom transfer radical polymerization (SI-ATRP) of acrylamide (AM) from the surfaces of the PVC thin film with their surface labile chlorines as initiation sites. Graft reaction was first-order kinetic with respect to the polymerizing time in the low monomer conversion stage, this being typical for ATRP. A percentage of grafting (PG) of 32.1% was achieved in 6 h, calculated from the elemental analysis results. The surface morphology of the product was characterized with scanning electron microscopy (SEM). The sorption property of the grafted film toward Hg(II) ion was also preliminarily investigated.

The kinetic behavior of gas phase mercury sorption on ZSM-5 supported cerium- and lanthanum-based composite oxides in the temperature range of 120–240^∘C is investigated. The Hg⁰ sorption abilities all first increase and then decrease with the elevation of the temperatures, the cerium-based composite oxides show better Hg⁰ sorption abilities than that of the lanthanum-based composite oxides. CeO₂–Mn₂O₃/ZSM-5 performs the best Hg⁰ sorption ability with Hg⁰ removal efficiency of nearly 100% at 180^∘C. Doping Cu or Mn into La₂O₃ lattice causes the decrease in the Hg⁰ removal efficiency of the lanthanum-based composite oxides due to the formation of perovskite or perovskite-like compounds. The sorption of elemental mercury over metal oxides is governed both by diffusion processes as well as chemical reactions, and the sorption of elemental mercury on the cerium- and lanthanum-based composite oxides are chemisorption processes.

Sorption of meso-tetrakis(4-sulfonatophenyl)porphyrin (H₂tpps) onto chitosan has been investigated in aqueous medium. Kinetic and isotherm studies were carried out by considering the effects of various parameters, such as pH, initial concentration of H₂tpps solution, and temperature. The kinetic data obtained from different batch experiments were analyzed using pseudo first-, second-order, intraparticle, and film diffusion kinetic models. The equilibrium sorption data was analyzed by using Tempkin, Langmuir and Freundlich models. The best results were achieved with the pseudo second-order kinetic, Langmuir and Freundlich isotherm models. The intraparticle diffusion and film diffusion are the rate limiting steps. The amount of sorbate adsorbed at equilibrium (q_e) increased with increasing the initial concentration of H₂tpps solution, showing maximum sorption capacity of 445.21 μmol.g^-1. The activation energy (E_a) of sorption kinetics was found to be 19.47 kJ.mol^-1. Thermodynamic parameters such as change in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were evaluated by applying the Van't Hoff equation. Thermodynamic activation parameters such as change in enthalpy of activation (ΔH^‡), entropy of activation (ΔS^‡), and free energy of activation (ΔG^‡) were also calculated. The thermodynamics of H₂tpps sorption onto chitosan in aqueous medium indicates its spontaneous and endothermic nature.

The chapter outlines the main provisions of the proposed model of competitive sorption of a microelement by a sorbent placed in a suspension of contaminated material. The simulation results were used to create a new sorption technique for cleaning radioactively contaminated material, in which competitive partitioning of microelements between material suspension and a selective sorbent is coupled with membrane separation of the contaminated material and sorbent. The above coupling is realized in the construction of a minireactor (MR), which consists of a closed container made of a semi-permeable membrane material, inside which there is a suspension of the adsorbent. As an example, the results of an experimental study of the statics and kinetics of material purification from trace amounts of Cs(I) ions pre-sorbed by the material are presented. Silica gel and soil samples in the form of an aqueous suspension were taken as materials contaminated with cesium ions. It was found that the limiting stage of sorption mass transfer of cesium ions from the material to the sorbent (particles of the suspension of Prussian blue, PB, separated from the suspension of the material by the wall of the membrane MR) is diffusion inside the pores of the membrane. The distribution of Cs(I) ions between the material, the aqueous solution, and the sorbent is determined using the difference in the chemical potentials of cesium ions in the material and the sorbent. It is found that the flow of Cs(I) ions from the suspension of the material inside the MR can be regulated by changing the pore diameter of the membrane, the size of the membrane surface of the MR, and the composition of the solution, including pH and the concentration of humic acids. The construction of the membrane MR allows its simple mechanical separation from suspensions. By using this property, it is shown that the ratio between the equilibrium concentrations of Cs(I) ions in an aqueous solution and in each of the solid phases represented by the material and the competing sorbent is additive in nature and can be described by the sum of two Langmuir isotherms for the material (silica gel, the soil reference sample, SRS) and for the sorbent (PB). In conclusion, the methods of controlling the mass transfer of sorbed ions inside a MR with a sorbent and the possibility of scaling up the technique of sorption purification of materials using sorbent-filled MRs as part of future technologies for directed and autonomous remediation of radioactively contaminated areas are discussed.

Mercury in the aquatic environment is a neurotoxin with several known adverse effects on the natural ecosystem and the human health. Mathematical modeling is a cost-effective way for assessing the risk associated with mercury to aquatic organisms and for developing management plans for the reduction of mercury exposure in such systems. However, the analysis of mercury fate and transport in the aquatic environment requires multiple disciplines of science ranging from sediment transport and hydraulics, to geochemistry and microbiology. Also, it involves the knowledge of some less understood processes such as the microbial and diagenetic processes affecting the chemical speciation of mercury and various mechanisms involved in the mass-exchange of mercury species between the benthic sediments and the overlying water. Due to these complexities, there are many challenges involved in developing an integrated mercury fate and transport model in aquatic systems. This paper identifies the various processes that are potentially important in mercury fate and transport as well as the knowns and unknowns about these processes. Also, an integrated multi-component reactive transport modeling approach is suggested to capture several of those processes. This integrated modeling framework includes the coupled advective-dispersive transport of mercury species in the water body, both in dissolved phase and as associated to mobile suspended sediments. The flux of mercury in the benthic sediments as a result of diffusive mass exchange, bio-dispersion, and hyporheic flow, and the flow generated due to consolidation of newly deposited sediments is also addressed. The model considers in addition the deposition and resuspension of sediments and their effect on the mass exchange of mercury species between the top water and the benthic sediments. As for the biogeochemical processes, the effect of redox stratification and activities of sulfate and iron-reducing bacteria on the methylation of mercury is discussed, and the modeling approach is described. Some results for the application of the model to the Colusa Basin Drain in California are presented. At the end of the paper, the shortcomings of our current knowledge in predicting the fate of mercury in water-sediment systems, the potential improvements, and additional complexities required to make the model more realistic, are discussed.