PbCl₂ Capture by Kaolin and Metakaolin under Different Influencing Factors of Thermal Treatment

Abstract

With dramatically increasing emission of heavy metals and chlorinated compounds from thermal treatments of fuels and wastes, kaolin, one of the widely used materials in the industry, was researched to control these pollutants in recent years. To investigate the retention of lead chloride (PbCl2) by kaolin and metakaolin obtained from thermal activation of kaolin, the PbCl2 adsorption experiment in a two-stage furnace was conducted from 600 to 900 °C under N2, H2O, and O2. Furthermore, the toxicity leaching procedure was also utilized to evaluate the leachability of Pb from used sorbents. The results showed that the capture efficiency of PbCl2 by the sorbents and leachability of Pb from the used sorbents were closely related to the increase of the experimental temperature. The retention of Pb by raw kaolin was superior to that by metakaolin; however, the leachability of Pb from the used metakaolin was totally lower. Adding H2O in the adsorption experiment can obviously increase the retention of Pb by the sorbents and decrease the leachability of Pb from the used sorbents. Besides, the effects of adding O2 on promoting the retention of Pb by kaolin and reducing the leachability of Pb from used kaolin were also noticeable due to the influence of adding O2 on enhancing chemical adsorption and melting behavior of kaolin. The maximum capture efficiency of Pb by kaolin and the minimum ratio of leachability from the used kaolin can reach 74.01% and 1.60%, respectively, with the addtion of O2 in the adsorption experiment at 900 °C.

Green production of a novel sorbent from kaolin for capturing gaseous PbCl2 in a furnace

“…To clarify into which species the adsorbed lead was captured by could reveal its adsorption behaviour, so a leaching test was conducted and these results are shown in Figure 6(b). The proportions of leached form lead for all sorbents decreased with increasing temperature, which means the diffusion of lead from the sorbent surface into the silicates lattice was accelerated by heating (Yu et al, 2020). Moreover, all partition values were below 0.1 at 900 °C, where the apparent melting phenomenon occurred in SEM images for all samples, indicating that most of the lead in the sorbents at high temperature was stabilised and removed to a limited extent by leaching from the adsorption product (Zha et al, 2018).…”

“…No peak representing lead content was detected in XRD curves, which could be due to the little mass of sorbate used in the test, while PbSi2Al2O8 has been reported as a product of reaction between kaolin and lead in some literature (Linak et al, 1993;Yu et al, 2020), following these reaction equations:…”

“…The detailing temperature control procedures are available in Table S2. It should be noted that in our previous work (Yu et al, 2020), the sorbent and sorbate were heated simultaneously so that the sorbent might adsorb gaseous heavy metal below the set point during the rising temperature, which could lead to different results.…”

“…The presence of moisture or hydroxylation, which can be regarded as a mineralizer, helps kaolin eutectic melting so that the adsorbed metal can be diffused into the liquid phase and the surface remains active (Yu et al, 2020;Temuujin et al, 1999;Linak et al, 1993). Metakaolin can also adsorb gaseous metal chlorides without the presence of moisture, but its adsorption ability is reduced without water vapour being present (Yu et al, 2020;.…”

In-Furnace Control of Arsenic Vapor Emissions Using Fe2O3 Microspheres with Good Sintering Resistance

“…This indicated that NO and SO 2 in flue gas could be transformed into nitrate and sulfate under the catalysis of Fe 2 O 3 . 31,32 Based on this fact, some valuable conclusions could be gained. The formed sulfate occupied the active sites on the surface of the adsorbent and further limited the fixation of arsenic, while the generated nitrate possessed oxidizability and could facilitate the transformation of As(III) in flue gas to As(V), 33 which explained why NO promoted arsenic capture at 1000 °C, as shown in Figure 9.…”