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ARS Home » Midwest Area » Morris, Minnesota » Soil Management Research » Research » Publications at this Location » Publication #111860
Title: APPLICATION OF A GENERAL ENERGY MODEL FOR LIMITED SYSTEMS TO ADSORPTION

Author
item Olness, Alan
item Clapp, Charles
item HAYES, M - UNIVERSITY OF LIMERICK

Submitted to: International Humic Substances Society Conference
Publication Type: Abstract Only
Publication Acceptance Date: 7/29/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Adsorption of a molecule on a surface has been described by several models, many of which were developed to describe adsorption of small molecules on a rigid and stable surface. Flexible surfaces like humic substances may expose additional adsorption sites with increasing concentration of adsorbate. Adsorption isotherms for these substances appear as "stair step" curves when plotted as a function of concentration. Increasing rates of adsorption with increasing equilibrium concentration are poorly described by existing adsorption models. By combining the Arrhenius and Mitscherlich (1930) rate model concepts and integrating over time, a general energy model for limited systems (GEMLS) is described that accommodates adsorption on flexible surfaces (Olness, 2000). x/m = {sum}ai((e^k(C-Co) - e^-k(C-Co))/(e^k(C-Co) + e^-k(C-Co))) The coefficient ai represents the surface exposed at a given equilibrium concentration, C, and the sum of ai represents the total adsorption capacity. The coefficient of the equilibrium concentration, k, is a composite of all other energy forms affecting adsorption. The critical concentration, Co, is that point at which the rate of adsorption increases at a decreasing rate; for clean, homogeneous, rigid or invariant surfaces, Co = 0. The GEMLS describes increases in adsorption which occur at an increasing rate. Examples will be used to demonstrate the use of the model. The function coefficient represents the total adsorption capacity. By combining GEMLS functions, estimates of the change in surface area due to flexible rearrangement are obtained.