Pamela K. Cody-Longmire, 1997, The Influence of fine-fraction carbonate content of Ohio tills on adsorption of total chromium, copper, nickel, and zinc.

ABSTRACT

Till deposits representing the full range of carbonate content (~0% to >40%) found in Ohio were subjected to simulated landfill leachate. Batch adsorption techniques were employed to assess the affect of calcareous material on metals in solution. The metals of interest in this study were copper (Cu), zinc (Zn), nickel (Ni), and chromium (Cr). Atomic adsorption spectroscopy was used to determine the chemical concentration remaining in solution after twenty-four hour contact between soils and solutes. The attenuation of metal over the full range of carbonate content was 98% (Cu), 84% (Zn), 55% (Ni), and 2.7% (Cr). The mathematical relation for metal attenuation as a function of carbonate content was found to be nonlinear. The data was fitted employing polynomial curves of order three (Cu), five (Zn), four (Ni), and six (Cr). The variability, or measure of the proportion of the total variation about the mean explained by the regression, was 70.1% (Cu), 85.6% (Zn), 66.3% (Ni), and 65.9% (Cr). This variability suggests that other variables were operative. A linear relationship was observed for Cr attenuation as a function of the percent change of Ca in solution. Ni attenuation as a function of the percent change of Mg in solution exhibited a linear relation. For Cu, Ni, and Zn there is a strong linear relationship between adsorption and solution pH. Solution pH is controlled by carbonate content, dissolution of CaCO results in an increase in pH. For carbonate content in excess of five percent pH is 7.4. Thus 5% carbonate content represents the minimum amount of carbonate needed to buffer the system and promote precipitation of metals as hydroxides. Chromium, however, did not correlate with pH, an alternate mechanism must be responsible for its removal. The alternate mechanism is probably cation exchange with calcium.