Microwave treatment of hazardous wastes : feasibility studies-mass balances

This laboratory has been developing processes for the remediation of soils contaminated with hazardous wastes using microwave treatment. The initial stage was to define situations in which microwave treatment could potentially have unique advantages, and to define the relevant physical chemical mechanisms. That having been accomplished, at the present stage, feasibility studies are being carried to determine whether or not on-site field testing is justified. To that end, mass balances on the processes are needed. In this study mass balance studies were carried out on the microwave assisted steam distillation of volatile organic chemicals (VOCs) and semi-volatile organics (SVOCs), respectively, from substrates. The substrates studied were sand, clay, humus, clay containing-magnetite, and soil, respectively. These substrates were impregnated with naphthalene. The naphthalene concentration in the substrate was 2000 ppm: taking into account the sample size, the total amount of naphthalene was 0.1 gram. It was assumed that the naphthalene, after treatment, would be in three possible states: a. In the substrate, and recoverable by extraction; b. Volatilized. c. In the substrate, but not extractable. For the first state, the substrate was subjected to Soxhlet extraction; for the second, the gases were trapped in methanol-containing wash bottles situated outside the microwave cavity; and for the potential non-extractables, the substrates were investigated by DRIFT (Diffuse Reflectance Fourier Transform Spectroscopy). It was found that approximately 85% of the naphthalene could be accounted for by extraction and trapping: no evidence for non-extractables in the substrates was found by DRIFT. Since the sample size was only 0.1 gram, the unaccounted material was approximately 0.015 grams. That amount could have easily been lost due to absorption on the tubes from the reaction vessel to the wash bottles or by diffusion through connections. It is concluded that mass balances can be carried out on this system in the manner developed in this study