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Hazardous heavy metal-laden coal combustion byproducts exposed to precipitation or surface/groundwater are of environmental concern. This study analyzed fly ash (FA) and desulfurization gypsum (FGD gypsum) samples obtained from 16 coal-fired power plants in Guizhou Province, China. A combination of field and laboratory studies was used to investigate the binding forms of lead (Pb), cadmium (Cd), and chromium (Cr) and their leaching characteristics under natural storage conditions. The results showed that there were significant proportions of residual states of these elements in FA (84–99% for Pb, 83–91% for Cd, and 73–97% for Cr), indicating a lack of migration to other environmental media. FGD gypsum contained high proportions of metals in migratable states, but the environmental risks were low due to their very low concentrations. The release of Pb, Cd, and Cr from FA and FGD gypsum into extracts varied according to pH. This is related to the form of each element in the solid and the series of reactions that occurs during the leaching process. However, aside from Cr in FA, all heavy metals in FA and FGD gypsum samples were present in concentrations below the relevant standards for landfill leachate, indicating very low release rates. The Cr levels (206–273 μg/L) in some of the FA extracts were higher than the limits for water pollution from domestic landfill, indicating that Cr in FA poses a leaching risk. The results of field leachate sampling and indoor simulated rainfall experiments further validated these findings, indicating that the release of Cr from stockpiled coal FA is a cause for concern.

Disclosing the fate of lead (Pb) and cadmium (Cd) during the cement production process is the key to control their atmospheric emissions, which have not attracted much attention yet. In this study, three precalciner cement plants (CPs) using different raw materials in Guizhou Province in Southwest China were investigated. It showed that the concentrations of Pb and Cd in different raw materials and the associated total metal input of these materials were different among CPs; the behavior of Pb and Cd were almost the same during the clinker production process that there has been no accumulation of these two elements inside the system, and nearly all input of Pb and Cd were discharged by the clinker. Although the temperature of clinkerization was pretty high of 1450 °C, the atmospheric emission ratio of both metals was negligible (<0.006% for Pb and <0.002% for Cd of the total output, respectively); the main reason might be that the two elements were incorporated into the minerals of clinker, either as silicate or sulfate. The long-term environmental impacts of some high Pb-and Cd-laden clinkers and cement need to be monitored and evaluated.

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Mercury (Hg)-laden coal fly ash is an environmental concern when it is exposed to precipitation or surface/groundwater under natural conditions. In this study, fly ash samples collected from fifteen coal-fired power plants in Guizhou province of southwest China were subjected to examine the different Hg binding forms. The results showed that total Hg in fly ash from these CFPPs ranged from 30 to 870 ng/g. The percentage of different Hg binding forms in coal fly ash decreased in the following order: strong complexed form (64%–91%) &gt; acid-soluble form (1%–25%) and sulfide form (3.4%–14.8%) &gt; ion-exchangeable form (0.01%–8.1%), and water-soluble form (0.01%–4.4%). The low proportion of water-soluble and ion-exchangeable forms indicated that Hg was not easily removed under natural conditions. Furthermore, fly ash samples from three out of fifteen CFPPs were carried out the leaching experiments to disclose the leachability of Hg and the transmedia migration potential of this element. The results indicated pH dependence of Hg leachability, with more than 4-times fold higher Hg been leached out under acidic (pH &lt; 5.5) and strong alkaline (pH &gt; 13) conditions than under neutral and weakly alkaline conditions (pH = 7–12). In addition, Hg was leached out more in higher liquid/solid ratio than lower ratios. Nevertheless, Hg concentration in extract (&lt;7 ng/L) of these three CFPPs under all conditions was well below the applicable regulation limits, and less than 0.11% of total Hg was leached out. This study demonstrated that Hg in the CFPP fly ashes was more stable under natural conditions when exposed to surface/groundwaters and had a negligible Hg leachability.

Atmospheric emission of heavy metals from different anthropogenic sources is a great concern to human beings due to their toxicities. In order to disclose the emission levels and the distribution patterns of zinc (Zn) in the modern cement industry with respect to its low boiling point (~900 °C) comparing to the high-temperature (1450 °C) clinker production process, solid samples representing the input and output flow of Zn during the entire production process in two preheater–precalciner cement plants (CPs) were collected and analyzed. For the first time, it was found that the behaviour of Zn inside different precalciner CPs was similar despite a huge difference in the Zn inputs to the CPs; namely, almost all the Zn input was output in clinker, which was then mixed with different additives and retarder to make cement products. The high-temperature clinkerisation process would incorporate Zn into the aluminosilicate of clinker. As a result, there was no enrichment of Zn during clinker production and the atmospheric emission factor was relatively low at 0.002%, or 1.28–9.39 mg Zn·t−1 clinker. Our result for the atmospheric Zn emissions from CPs was much lower than most previous reports, implying the CPs were not a crucial Zn emission source. However, the higher load of Zn in some raw/alternative materials—like nonferrous smelting slag with a Zn content of ~2%—could greatly increase the content of Zn in clinker and cement products. Therefore, further investigation on the environmental stability of Zn in such Zn-laden cement and concrete should be carried out.