Toxic Elements Behavior during Plasma Treatment for Waste Collected from Power Plants

Abstract

The subject of this work is the treatment of solid waste collected from power plants using thermal plasma technology. Inductively coupled plasma (ICP), X-ray fluorescence (XRF), and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the waste before and after the treatment. The results show that waste is formed essentially from carbon, but it also contains sulfur and toxic elements like lead, cadmium, zinc, and arsenic. For this reason, a plasma reactor was used to separate carbon from the heavy metals by a pyrolysis/combustion plasma system. After the plasma treatment, the mass of the waste was reduced by more than 85% and the metals were collected in the filter bag. A computer code was used to study the toxic element volatility during the treatment. With this code, the effects of plasma temperature, confinement matrix, and the composition of the carrier gas on the volatility of lead and arsenic were determined. The code results show that arsenic remains in the liquid phase for temperatures less than 2000 K, whereas for temperatures beyond 2100 K, arsenic becomes very volatile. For lead, any increase in temperature increases its vaporized quantity and its vaporization speed. The addition of oxygen in the carrier gas leads to the heavy metal incorporation in the confinement matrix. The increase of the quantity of Ba in the containment matrix strengthens the confinement of as in the matrix.