Volatilization characteristics of high-lead slag and its influence on measurement of physicochemical properties at high temperature

Abstract

Volatilization causes measurement deviations of physicochemical properties for volatiles-containing slag at high temperature. Hence, investigating the degree of volatilization and identifying the volatilization mechanism and deviation rules are crucial to improve the accuracy of the measured properties. Here, PbO-FeOx-CaO-SiO2-ZnO slag system was selected as a research subject. The volatile characteristics and non-isothermal intrinsic kinetic models of high-temperature volatilization for lead slag were established by thermogravimetric analysis (TGA), and the volatilization mechanism and deviation in the measured properties were determined by analyzing the phase and chemical composition of the residues. In addition, experimental measurements of the melting temperature/ viscosity were compared with theoretically calculated results. The volatilization of PbO decreased the lead-containing phase, but increased the amount of precipitated spinel phase, which led to the deviation in the measured physicochemical properties of the studied slags. The volatilization kinetics for PbO in the slags followed three-dimensional diffusion. The diffusion of PbO gas from PbO-FeOx-CaO-SiO2-ZnO slag was the restrictive step of volatile reaction, and mechanism function was g(?)=1-(1-?)1?3. Moreover, during the slag properties measurement at high temperatures, a high heating rate and protective gas can be used to reduce volatilization of lead slag and avoid consequent properties deviation.

Evaporation and its Effects on Physico-Chemical Properties of PbO-containing Slag

“…Our group measured the weight loss of PbO slag with TG-DSC. It is detected that the weight loss (i.e., evaporation) to slag with initial PbO content (determined in slag sample preparing) of 21.54 % and 43.09 % can reach to 21.62 % and 38.69 %, respectively, at temperature between 736 °C to 1450 °C [17]. Thus, in the physicochemical property measurement of slag at high temperature, the evaporation is absolutely not neglectable.…”

“…Thus, in the physicochemical property measurement of slag at high temperature, the evaporation is absolutely not neglectable. The traditional slag property measurement method in not fit these slags again [5,6,17]. Then how much the evaporation effect is?…”

“…The weight loss of some PbO and ZnO containing slag were measured at high temperature as listed in table 1 and figure 1 [17]. To avoid the effect of moisture in the samples, only the weight loss at higher temperature, i.e.…”

Volatilisation Behaviour and Mechanism of Lead-Containing Slag during Physical Property Tests

“…For example, the oxygen potential not only affects the existence of volatiles but also affects the activation energy of volatilisation reactions [4], which may lead to nonlinear variations in the rate of volatilisation reactions. Moreover, the contents and diffusion conditions of volatiles also significantly impact the volatilisation rate [10]. In physical property tests, including slag melting temperature and viscosity tests, continuous volatilisation will change the composition and properties of the slag, thereby adversely affecting the test results.…”

“…However, as an intermediate product of volatilisation reactions, the proportion of PbO has a great effect on the total volatilisation. Yaru Cui et al [10] investigated the volatilisation characteristics of high-lead slag during physical property tests. Their study revealed that when the temperature exceeded 900 • C, the volatilisation proportion of PbO(s) exceeded 50%, and diffusion conditions were the main influencing factor.…”