Products Compositions and Release Rates from Intense Thermal Treatment of Soil

Abstract

Yields, compositions, and global release rates of major products from heating a synthetic soil matrix under conditions pertinent to current and emerging thermal remediation technologies are reported. The soil specimens were mixtures prepared for the U.S. EPA to reflect certain attributes of soils from U.S. Superfund sites. Because this study focuses on determining how soil decomposition itself may affect thermal cleanup, exogenous contaminants were not added to the soil. The experiments involved heating 49−54 mg batches of 63−125 μm neat soil particles, thinly spread on a 0.001 in. thick stainless steel foil, at nominal rates of 1000 °C/s, to temperatures in the 350−1050 °C range, under 3 psig of helium. Above 500−600 °C the total weight loss increased strongly with increasing temperature. Devolatilization exceeded 21 wt % when soil was heated to 1033 °C and then maintained at this temperature for 5 s before cooling. For this heating regimen, CO2, CO, and tars were the major volatile products, material and carbon balances were good, but oxygen balances were only fair and hydrogen balances were poor, possibly because yields of chemical water were not quantified. A single first-order reaction kinetics model well describes the global release rates of most gaseous volatiles except CO2, which, because of apparent step-like evolution, is better fitted by a model consisting of two independent parallel first-order reactions. A multiple independent parallel first-order reaction kinetics model provides a good fit to the soil weight loss data.