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Most Pb/Zn smelter contaminated sites in China are often encountered natural phenomenon known as freeze-thaw (F-T) cycles and acid rain. However, the coupled effects of F-T cycles and acidification on the release behavior of potentially toxic elements (PTEs) from soils remains unclear. A mechanistic study on PTEs release from soils was conducted by revealing the physicochemical weathering characteristics of minerals under F-T cycles combined with acidification. The results from F-T test indicated that among F-T parameters, F-T frequency were the more important factors influencing PTEs release, with the corresponding contribution ranges of 21.20-94.40 %. As pH decreased, the leaching concentrations of As, Cd, Cu, Mn, Pb and Zn did not increase under the same F-T frequency. As F-T frequency increased, the leaching concentrations of these studied PTEs also did not increase under the same pH condition. Microstructure characteristics revealed that the soils were a complex system with multi-mineral aggregates, which had experienced complex physicochemical weathering after F-T combined with acidification treatment. Combined with geochemical modeling results, PTEs release was found to be mainly influenced by the microstructure damage and proton corrosion of minerals, while little affected by their precipitation and dissolution. The mutual coupling relationships of mineral weathering and PTEs release were conducive to the better understanding of the migration behavior of PTEs in contaminated sites under complex environment scenarios. The present study results would provide theoretical instruction and technical support for the longevity evaluation of multi-metal stabilization remediation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Chromium (Cr) is a highly toxic element, which is widely present in environment due to industrial activities. One of most applicable technique to clean up Cr pollution is chemical reduction. However, the Cr(VI) concentration in soil increases again after remediation, and meanwhile the yellow soil would appear, which is commonly called as "yellowing" phenomenon. To date, the reason behind the phenomenon has been disputed for decades. This study aimed to introduce the possible "yellowing" mechanism and the influencing factors based on the extensive literature review. In this work, the concept of "yellowing" phenomenon was explained, and the most potential reasons include the reoxidation of manganese (Mn) oxides and mass transfer were summarized. Based on the reported finding and results, the large area of "yellowing" is likely to be caused by the re-migration of Cr(VI), since it could not sufficiently contact with the reductant under the effects of the mass transfer. In addition, other driving factors also control the occurrence of "yellowing" phenomenon. This review provides valuable reference for the academic peers participating in the Cr-contaminated sites remediation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Since lager quantities of the zinc (Zn) smelting slags were traditionally dumped at the indigenous Zn smelting sites, the release characterization of potentially toxic elements (PTEs) from the Zn smelting slags under various environmental conditions were of great significance for an environmental risk analysis. The acidification of the Zn smelting slags to pH= 4 and 6 would result in the leaching concentrations of Cd and Mn exceeding the fourth-class standard of surface water quality standard in China (GB3838-2002). Notably, most metals exhibited an amphoteric leaching pattern, where the highest leached concentrations of As, Cd, Cu, Mn, Pb, and Zn were 4.15, 4.21, 140.0, 78.1, 156.9 and 477.0 mg/L, respectively. In addition, the highest release of toxic metals within 96 h reached 0.17 % of As, 3.50 % of Cd, 2.77 % of Cu, 6.92 % of Mn, 0.13 % of Pb, and 2.57 % of Zn, respectively. The combined results of various characterization techniques suggested that the PTEs remobilization effected by rhizosphere-like organic acids were mainly controlled by the precipitation of newly formed Fe, Mn and Al (hydr) oxides and the complexation of organic ligands. The present study results could provide valuable insights into the long-term leaching behaviors of PTEs from the Zn smelting slags to reduce ecological hazard., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Smelting slags is a well-known industrial solid waste, while there were limited studies on the key factors controlling the potential health risks caused by these smelting slags. In this work, the metal bioaccessibility in the size fractionated-zinc smelting slags was examined using various In vitro assays, in combination with multidisciplinary methods. The results indicated that the bioaccessible fractions of heavy metals showed a significant difference, but no statistical difference among different particle sizes of the zinc smelting slags. The bioaccessible metal fractions in the gastric (GP) and gastrointestinal (GIP) phases were 0 (Cr) - 91.39% (Cd)) and 0 (Cr) - 47.80% (Ni). Among the studied metals, Cd, Cu, Mn, Pb and Zn were the most bioaccessible to human. The Pearson correlation analysis showed that the carbonate bound phases of heavy metals were responsible for their bioaccessibility in GP and GIP. Moreover, the combined results of multidisciplinary characterization also further implied that the solubility behaviors of toxic elements in the smelting slags were dominated by soluble metal bearing- mineral phases and absorbable Fe, Mn and Al-rich minerals and metal bearing-precipitates during SBRC extractions. Therefore, these study results provide a insight into the potential controls of metal bioaccessibility in the zinc smelting slags, which was of great significance from the aspects of their resource recycling and risk management., (Copyright © 2021 Elsevier B.V. All rights reserved.)

This study comprehensively investigated the potential roles of soil mineralogy identified by the automated mineral liberation analysers (MLA) in the prediction of geochemical behavior of toxic metals in the smelter polluted soils. The results from modal mineralogy revealed that the non-reactive silicate phases such as quartz (42.05%) and biotite (40.43%) were the major mineralogical phases. The element deportment showed that fayalite, lead oxide, apatite, galena and wollastonite were identified as the dominant As, Cd, Pb and Zn bearing minerals. Furthermore, MLA analysis also confirmed that Pb was most concentrated in the smaller particles of lead oxide, which significantly enhanced Pb release in reaction with the chemical extractant during chemical kinetic tests. The results from pH-dependent leaching tests indicated that the leaching concentrations of As, Pb and Zn increased at low and high pH values, but were lowest at the neutral pH range. In addition, the results from the kinetic study demonstrated that the second order model provided the best description for the release patterns of the main metal contaminants in the bioavailability and bioaccessibility tests. The integrated geochemical analysis demonstrated that among these studied elements, As showed a typical geochemical pattern, which was predominantly controlled by 90.09% of fayalite. The above study results would have significant implications for soil remediation and risk management of smelter contaminated sites., (Copyright © 2021 Elsevier B.V. All rights reserved.)