Contaminant Sorbent Aggregation Index based on Cadmium Sorption Capacity

Abstract

Mixture rules that enable the estimation of the characteristics of composite mixtures using data on the characteristics of their components are useful in reducing the frequency and cost of material testing for construction quality assurance prediction of barriers in waste containment systems. Different components of a mixture have characteristics that may not always be represented in direct proportion to their contents in the composite mixture. In this paper, the interaction effects of such mixtures are scaled in terms of an aggregation index. This index is formulated on the basis of metal sorption capacity measurements and used to investigate four mix designs, covering different weight proportions of four materials (Ottawa sand, fly ash, diatomaceous earth and Ca-montmorillonite). Computations using test data obtained through cadmium sorption tests indicate an increase in aggregation by up to 50% for mixtures with high clay content (10%). Also, values of aggregation index were found to be less than 1 for mixtures with low clay content, indicating an increase in cadmium sorption beyond theoretical levels that are based on mix component proportions and their sorption capacities. Presumably, textural changes after material mixing increased the measured specific surface of the composite materials relative to the theoretically computed value. This result is attributed to disruption of cohesion in the clay fraction.

Keywords:

• sorbent
• aggregation
• contaminant
• barriers
• waste containment

Notes

*These values are calculated based on the sorption measured for individual components and their mass fraction in the mixture.