Separation and enrichment of arsenic(V) with composite resin beads containing magnetite crystals.

The adsorption of arsenic(V) was investigated using macroporous resin beads containing magnetite crystals. Arsenic(V) was favorably adsorbed at pH 2-9, where the distribution coefficients were larger than 10(3). The maximum capacity was 0.050 mmol/g. Metal cations including Ca(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and La(III) did not give serious interference at 10(-4) M level. Diluted arsenic(V) was collected with a packed column, and the retained arsenic(V) was quantitatively eluted out with 1 M NaOH.

Effect of exchangeable cation on the swelling property of 2:1 dioctahedral smectite--a periodic first principle study.

We used both localized and periodic calculations on a series of monovalent (Li+, Na+, K+, Rb+, Cs+) and divalent (Mg2+, Ca2+, Sr2+, Ba2+) cations to monitor their effect on the swelling of clays. The activity order obtained for the exchangeable cations among all the monovalent and divalent series studied: Ca2+ > Sr2+ > Mg2+ > Rb+ > Ba2+ > Na+ > Li+ > Cs+ > K+. We have shown that, in case of dioctahedral smectite, the hydroxyl groups play a major role in their interaction with water and other polar molecules in the presence of an interlayer cation. We studied both type of clays, with a different surface structure and with/without water using a periodic calculation. Interlayer cations and charged 2:1 clay surfaces interact strongly with polar solvents; when it is in an aqueous medium, clay expands and the phenomenon is known as crystalline swelling. The extent of swelling is controlled by a balance between relatively strong swelling forces and electrostatic forces of attraction between the negatively charged phyllosilicate layer and the positively charged interlayer cation. We have calculated the solvation energy at the first hydration shell of an exchangeable cation, but the results do not correspond directly to the experimental d-spacing values. A novel quantitative scale is proposed with the numbers generated by the relative nucleophilicity of the active cation sites in their hydrated state through Fukui functions within the helm of the hard soft acid base principle. The solvation effect thus measured show a perfect match with experiment, which proposes that the reactivity index calculation with a first hydration shell could rationalize the swelling mechanism for exchangeable cations. The conformers after electron donation or acceptance propose the swelling mechanism for monovalent and divalent cations.

2,3,7,8-Tetrachloro dibenzo-p-dioxin can be successfully decomposed over 2:1 dioctahedral smectite-a reactivity index study.

2:1 Dioctahedral smectite family has shown its capability to decompose 2,3,7,8-tetrachloro dibenzo-p-dioxin (TeCDD) using the active hydroxyl hydrogen attached with the central octahedral aluminum, as monitored using density functional theory (DFT). From the values of the local softness and the charge on the hydrogen atom of the bridging/structural (occurring on the surface) hydroxyl attached to octahedral/tetrahedral metal site present in smectite used as a first approximation to the local hardness, it is concluded that the local acidities of the inorganic material systems are dependent on several characteristics which are of importance within the framework of hard-soft acid-base (HSAB) principle. The first step in this process of decomposition is the abstraction of chlorine bound to TeCDD using surface hydrogen of smectites. This results in non-chlorinated dibenzo-p-dioxin (NCDD), which is less toxic than TeCDD. The second step is the formation of a dative bond between oxygen of NCDD and hydroxyl proton of smectite, with the breaking of Cz.sbnd;O bond of NCDD. The reaction mechanism is postulated within the helm of DFT using Fukui functions for all possible chlorinated and non-chlorinated dioxin varieties along with clay clusters. The material is identified to act for the decomposition of dioxin.