Long-term leaching scenarios for cement-based waste forms

Abstract

Cement-based waste forms (solidified wastes) are used for the long-term land disposal of industrial hazardous wastes. A cement-based waste form can be prepared by mixing a hydraulic cement and, if needed, a bulking agent with an aqueous waste to cause it to solidify. This article presents eight long-term leaching scenarios based on various properties of waste forms and contaminants as well as different hydraulic regimes and characteristics of groundwater. Each scenario takes the form of a simplified mathematical model used to predict leaching rates for periods of up to 100 years. The analysis demonstrates the importance of chemically fixing the contaminants in the matrix and illustrates the advantages of avoiding situations where ground-water flows through the waste. In situations where advective transport is negligible, leaching rates are limited by pore diffusion and tend to decrease with time.