Adsorption of Pb(II) and Cu(II) on α-quartz from aqueous solutions: influence of pH, ionic strength, and complexing ligands

Adsorption of aqueous Pb(II) and Cu(II) on α-quartz was studied as a function of time, system surface area, and chemical speciation. Experimental systems contained sodium as a major cation, hydroxide, carbonate, and chloride as major anions, and covered the pH range 4 to 8. In some cases citrate and EDTA were added as representative organic complexing agents. The adsorption equilibria were reached quickly, regardless of the system surface area. The positions of the adsorption equilibria were found to be strongly dependent on pH, ionic strength and concentration of citrate and EDTA. The addition of these non-adsorbing ligands resulted in a competition between chelation and adsorption. The experimental work also included the examination of the adsorption behavior of the doubly charged major cations Ca(II) and Mg(II) as a function of pH.

The theoretical description of the experimental systems was obtained by means of chemical equilibrium-plus-adsorption computations using two adsorption models: one mainly electrostatic (the James-Healy Model), and the other mainly chemical (the Ion Exchange-Surface Complex Formation Model). Comparisons were made between these two models.

The main difficulty in the theoretical predictions of the adsorption behavior of Cu(II) was the lack of the reliable data for the second hydrolysis constant(*β_2) The choice of the constant was made on the basis of potentiometric titratlons of Cu^(2+)

The experimental data obtained and the resulting theoretical observations were applied in models of the chemical behavior of trace metals in fresh oxic waters, with emphasis on Pb(II) and Cu(II).

Pulse NMR in solids : chemical shift, lead fluoride and thorium hydride

Part one of this thesis consists of two sections. In the first section the fluorine chemical shift of a single crystal CaF_2 has been measured as a function of external pressure up to 4 kilobar at room temperature using multiple pulse NMR techniques. The pressure dependence of the shift is found to be -1.7 ± 1 ppm/kbar, while a theoretical calculation using an overlap model predicts a shift of -0.46 ppm/kbar. In the second section a separation of the chemical shift tensor into physically meaningful "geometrical" and "chemical" contributions is presented and a comparison of the proposed model calculations with recently reported data on hydroxyl proton chemical shift tensors demonstrates, that for this system, the geometrical portion accounts for the qualitative features of the measured tensors.

Part two of the thesis consists of a study of fluoride ion motion in β-PbF_2 doped with NaF by measurement of the ^(19)F transverse relaxation time (T_2), spin lattice relaxation time (T_1) and the spin lattice relaxation time in the rotating frame (T_(1r)). Measurements over the temperature range of -50°C to 160°C lead to activation energies for T_1, T_(1r) and T_2 of 0.205 ± 0.01, 0.29 + 0.02 and 0.27 ± 0.01 ev/ion, and a T_(1r) minimum at 56°C yields a correlation time of 0.74 μsec. Pressure dependence of T_1 and T_2 yields activation volumes of <0.2 cm^3/g-mole and 1.76 ± 0.05 cm^3/g-mole respectively. These data along with the measured magnetic field independence of T_1 suggest that the measured T_1's are not caused by ^(19)F motion, but by thermally excited carriers.

Part three of the thesis consists of a study of two samples of Th_4H_(15), prepared under different conditions but both having the proper ratio of H/Th (to within 1%). The structure of the Th_4H_(15) as suggested by X-ray measurements is confirmed through a moment analysis of the rigid lattice line shape. T_1 and T_2 measurements above 390 K furnish activation energies of 16.3 ± 1.2 kcal/mole and 18.0 ± 3.0 kcal/mole, respectively. Below 350 K, T_(1r) measurements furnish an activation energy of 10.9 ± 0.7 kcal/mole, indicating most probably more than a single mechanism for proton motion. A time-temperature hysteresis effect of the proton motion was found in one of the two samples and is strongly indicative of a phase change. T_1 at room temperature and below is dominated by relaxation due to conduction electrons with the product T_1T being 180 ± 10 K-sec. Using multiple pulse techniques to greatly reduce homonuclear dipolar broadening, a temperature-dependent line shift was observed, and the chemical shift anisotropy is estimated to be less than 16 ppm.

Kinetics and mechanisms of adsorption of Escherichia coli bacteriophage T_4 to activated carbon

A study was conducted on the adsorption of Escherichia coli bacteriophage T₄ to activated carbon. Preliminary adsorption experiments were also made with poliovirus Type III. The effectiveness of such adsorbents as diatomaceous earth, Ottawa sand, and coconut charcoal was also tested for virus adsorption.

The kinetics of adsorption were studied in an agitated solution containing virus and carbon. The mechanism of attachment and site characteristics were investigated by varying pH and ionic strength and using site-blocking reagents.

Plaque assay procedures were developed for bacteriophage T₄ on Escherichia coli cells and poliovirus Type III on monkey kidney cells. Factors influencing the efficiency of plaque formation were investigated.

The kinetics of bacteriophage T₄ adsorption to activated carbon can be described by a reversible second-order equation. The reaction order was first order with respect to both virus and carbon concentration. This kinetic representation, however, is probably incorrect at optimum adsorption conditions, which occurred at a pH of 7.0 and ionic strength of 0.08. At optimum conditions the adsorption rate was satisfactorily described by a diffusion-limited process. Interpretation of adsorption data by a development of the diffusion equation for Langmuir adsorption yielded a diffusion coefficient of 12 X 10^-8 cm²/sec for bacteriophage T₄. This diffusion coefficient is in excellent agreement with the accepted value of 8 X 10^-8 cm²/sec. A diffusion-limited theory may also represent adsorption at conditions other than the maximal. A clear conclusion on the limiting process cannot be made.

Adsorption of bacteriophage T₄ to activated carbon obeys the Langmuir isotherm and is thermodynamically reversible. Thus virus is not inactivated by adsorption. Adsorption is unimolecular with very inefficient use of the available carbon surface area. The virus is probably completely excluded from pores due to its size.

Adsorption is of a physical nature and independent of temperature. Attraction is due to electrostatic forces between the virus and carbon. Effects of pH and ionic strength indicated that carboxyl groups, amino groups, and the virus's tail fibers are involved in the attachment of virus to carbon. The active sites on activated carbon for adsorption of bacteriophage T₄ are carboxyl groups. Adsorption can be completely blocked by esterifying these groups.