Calorimetric Determination of the PZC of Amorphous Aluminum Hydroxides: 1. Method Development.
(S02-kabengi909786-oral)
Authors:
N.J. Kabengi* - Univ. of Florida R.D. Rhue - Univ. of Florida S.H. Daroub - Univ. of Florida
Abstract:
A new method to measure the Point of Zero Charge (PZC) of amorphous aluminum hydroxides (AHO) has been developed using flow calorimetry. The rationale behind this method is that the heat of ion exchange is directly related to surface charge. When heats of both anion and cation exchange (AEC/CEC) are measured at different solutions pHs,the PZC is obtained. Using a flow calorimeter, Cl/NO3 and K/Na heats of exchange are measured at pHs of 5.75, 8.00 and 10.5. Solutions of 50 mM NaCl, NaNO3 and KCl are used and pHs are adjusted to the desired values with 1 mM
NaHCO3/Na2CO3 or KHCO3/K2CO3. Measurements of AEC and CEC along with calorimetrical data yield initial and final energies of exchange in KJ/mol. Molar heats of exchange for AEC and CEC are plotted against solution pH with the point of intersection representing the PZC. The PZCs of differently prepared batches of AHO determined calorimetrically were found to range between 8.9 and 9.5, values that agree with reported findings. This new way of determining the PZC offers several advantages over existing methods namely it is quicker, it gives better control over ionic strength of the background solution, and it allows one to simultaneously observe the effects of various treatments on both the PZC and a number of surface properties of the AHO.
Speaker Information: Nadine Kabengi, Univ. of Florida, Soil and Water Sciences Dept2169 McCarty Hall A, Gainesville, FL 32611; Phone: 352-392-1951 x 217; E-mail: [email protected]
Session Information: Thursday, November 6, 2003, 7:55 AM-10:15 AM Presentation Start: 10:00 AM
Keywords: Surface Charge; Point Of Zero Charge; Flow Adsorption Calorimetry; Heats of ion exchange reactions
