γ-Alumina surfaces dehydrated at 450 and 700 °C were studied by using the conventional pyridine adsorption-DRFTIR technique. Three types of Lewis acid sites are present on the surface, and in each case pyridine adsorbed on them is concomitantly interacting with their adjacent OH groups. Because only three types of Lewis acid sites are present, only three hydrogen bonding bands were observed upon pyridine adsorption. From correlation of OH bands with hydrogen bonding bands, it is found that weak Lewis acid sites have type II66 or II64 OH groups as their neighbors, medium strong Lewis acid sites have type III OH groups near by, and strong Lewis acid sites have type I6 OH groups next to them. Dehydration at 700 °C generates more types of OH groups that also interact with pyridine. The reactivity of OH groups is not determined by their acidity and space restrictions, but rather by their proximity to Lewis acid sites. We assigned the three types of Lewis acid sites to five-, four-, and three-coordinate Al3+ ions.

The complexing capacity of a solution is a measure of the metal Ion blndlng ability of the dissolved ligands. The purpose of this study Is to evaluate dlalysls titration as a method of determlnlng the complexlng capacity of soil-derlved fulvic acld (SFA). In a prellmlnary experiment, we titrated 6.25 pM ethylenediaminetetraacetlc acld (EDTA) at pH 6 with Cu2+ and Cd2+ and obtained complexing capacity values within 2.4% of theoretlcal. Next, 15.5 pM SFA was titrated with Cu2+ or Cd2+ at pH 5, 6, and 7 during 30-day dialysis experiments. The SFA complexlng capacity values are greater for Cu2+ than for Cd2+ at the same pH and generally Increase for elther Cu2+ or Cd2+ as pH increases. We estimate that a maximum of 10% of the complexing capacity permeates the dialysis membrane. A statistical comparison of dlalysls and Cu2+ ISE results shows no dlfference in the abllity of the two techniques to measure complexing capacity.The complexing capacity of isolated humic matter (fulvic and humic acids) and humic matter dissolved in natural waters is its ability to complex free (hydrated) metal ions. The analytical difficulty inherent with complexing capacity measurements is to distinguish the free metal species from the complexed species, including labile complexed metal ions, and at the same time have minimal effect on the chemical equilibrium under study. In the past, researchers have employed biological and chemical techniques to make these exacting measurements. Biological methods often shift equilibria less than chemical methods but offer a smaller range of metal ions that can be studied (1-3). Chemical methods offer precision, convenience, sensitivity, and a greater number of metal ions that can be studied.It is convenient to place chemical methods in three categories: miscellaneous, electrochemical, and membrane separation or gel titration chromatography (GFC). The miscellaneous category includes a copper(I1) solubilization method (4, 51, a cobalt(II1) complexation method (6, 7), and chromatographic methods using MnOz (49) or Chelex-100 resinElectrochemical methods are especially popular. In particular, metal ion selective electrode (ISE) potentiometric titrations are commonly employed to determine complexing capacities (13)(14)(15)(16)(17)(18)(19). Many research groups use voltammetric titrations of measure metal ion complexing capacities (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), although this application of voltammetry is controversial because of potential interferences with the working electrode A group of analytical methods to determine metal ion binding capacities by separation use GFC (38-40), ultrafiltration (41), or dialysis (42-46) to segregate free metal ions from metal complexes during a titration. Then the researcher can determine concentrations of both metal species by various (31 -37).'Present address: Celanese Research Co., 86 Morris Av., Summit, NJ 07901. analytical techniques to meet detection limits and specify requirements for many metal ions, An advantage offered by dialysis is the ability t...

However, there are two unexpected findings. Firstly, the particle size distributions for the metals are generally coarser than might be anticipated from a foreknowledge of the corresponding particle sizes in ambient air, outside the industrial workplace. It is suggested that this phenomenon is due to the fact that, in the industrial case, small particles originating form combustion and condensation processes may be airborne in sufficiently high number concentrations to favor their coagulation.Secondly, it appears that lead oxides cannot be identified infallibly in the smelter environment by XRD. These compounds are almost certainly airborne in substantial proportions at a number of sites, e.g., the dross plant and the slagging floor of the ISF plant. We surmise that the lead oxides present in the works atmosphere have an amorphous or poorly crystalline structure. (In contrast, the ubiquitous presence of ZnO suggests that this compound occurs as a distinctly crystalline phase.) Generally, at each location, the phases identified in samples

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