EFFECT OF TEMPERATURE AND FLOW ON THE VOLATILIZATION OF ELEMENTAL LEAD AND CADMIUM

The volatilization characteristics of lead and cadmium were investigat ed by a series of experiments and theoretical analysis. The experiment al part of the research included heating small amounts (approximately 3 gms) of pure metal samples to volatilization temperatures in a labor atory scale furnace and capturing the vapors by condensation and absor ption. Temperatures as high as 900 degrees C were attained during expe riments. Experiments were conducted with a carrier gas flow rate betwe en 2 lpm and 6 lpm, corresponding to mean velocities of 1.7 to 5 cm/se c. The study showed that temperature, speciation, gas flow velocity ov er 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 t he lead vaporization using the chemical equilibrium code, CET89 (1). T he theoretical analysis also included modeling the metal vaporization using a transport phenomena approach. The theoretical analyses were co mpared with experimental results. Based on the experimental analysis i t was found that the volatility of cadmium depended strongly on its ox idizing environment; it volatilized more quickly when it was heated in an inert environment than in an oxidizing environment. Further, the v olatility of cadmium increased when the rate of flow of the carrier ga s was increased. The amounts of lead volatilized with either air or ni trogen 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.