Effect of Temperature and Flow on the Volatilization of Elemental Lead and Cadmium

ABSTRACT

The volatilization characteristics of lead and cadmium were investigated by a series of experiments and theoretical analysis. The experimental part of the research included heating small amounts (approximately 3 gms) of pure metal samples to volatilization temperatures in a laboratory scale furnace and capturing the vapors by condensation and absorption. Temperatures as high as 900°C were attained during experiments. Experiments were conducted with a carrier gas flow rate between 2 lpm and 6 lpm, corresponding to mean velocities of 1.7 to 5 cm/sec. The study showed that temperature, speciation, gas flow velocity over the waste matrix, and the amount of oxygen in the gas flow were the crucial factors affecting the metal volatilization in an incinerator-like environment.

Equilibrium calculations were performed to predict the lead vaporization using the chemical equilibrium code, CET89 (1). The theoretical analysis also included modeling the metal vaporization using a transport phenomena approach. The theoretical analyses were compared with experimental results.

Based on the experimental analysis it was found that the volatility of cadmium depended strongly on its oxidizing environment; it volatilized more quickly when it was heated in an inert environment than in an oxidizing environment. Further, the volatility of cadmium increased when the rate of flow of the carrier gas was increased. The amounts of lead volatilized with either air or nitrogen carrier gas were below the analytical detection limits of 20 mg/l in the sample solution even with minimum dilution of the collected sample. This corresponds to a maximum of 4 mg lead vaporization during the 15 minute experimental duration.