Investigation of the adsorption-reduction mechanisms of hexavalent chromium by ramie biochars of different pyrolytic temperatures

Abstract We present petrographic and microthermometric evidence for precipitation of Au-Ag-Te–rich melt directly from hydrothermal fluids and subsequent entrapment as primary melt inclusions within pyrite from quartz veins of the Xiaoqinling lode gold district, southern margin of the North China craton. We propose the formation of Au-Ag-Te–rich melt through adsorption-reduction mechanisms on pyrite and subsequent growth of the melt nuclei via direct scavenging of metals from fluids. Because neither initial formation nor later growth of the melt require saturation of the ore fluid with respect to the constituent metals, this mechanism offers a new understanding of the enrichment of low-abundance ore components, such as gold. Our model may thus partly explain the discrepancy between the high gold solubilities reported from experimental studies and the much lower gold concentrations usually measured in natural fluids. This study also implies that Au-Ag-Te–rich melt has probably gone unrecognized in other lode gold deposits in which Au-Ag tellurides are present.

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Hexavalent Chromium Removal from Groundwater—A Low-Tech Approach

Environmental Sciences Proceedings ◽

10.3390/environsciproc2020002025 ◽

2020 ◽

Vol 2 (1) ◽

pp. 25

Author(s):

Samiotis Georgios ◽

Lefteri Lefteris ◽

Mavromatidou Charoula ◽

Tsioptsias Costas ◽

Trikilidou Eleni ◽

...

Keyword(s):

Hexavalent Chromium ◽

Low Cost ◽

Water Bodies ◽

Contaminated Water ◽

Chromium Removal ◽

Chromium Reduction ◽

Complete Understanding ◽

Pump And Treat ◽

Reduction Mechanisms ◽

The Creation

Chromium occurs in nature mainly in its trivalent or hexavalent form. Hexavalent chromium Cr(VI) is particularly toxic to humans, animals, and plants. The extensive pollution of groundwaters with Cr(VI) necessitates the complete understanding of natural chromium oxidation and reduction mechanisms, both for assessing the risk of hexavalent chromium formation and for the development of techniques for the reduction and removal of Cr(VI) from contaminated water bodies. In this work, the possibility of hexavalent chromium reduction by discarded or low-cost materials, which contain reducing compounds, is investigated regarding the creation of a compact, pump-and-treat filter for Cr(VI) removal from groundwater.

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Two-Dimensional Titanium Carbides (Ti3C2Tx) Functionalized by Poly(m-phenylenediamine) for Efficient Adsorption and Reduction of Hexavalent Chromium

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph17010167 ◽

2019 ◽

Vol 17 (1) ◽

pp. 167 ◽

Cited By ~ 4

Author(s):

Linfeng Jin ◽

Liyuan Chai ◽

Weichun Yang ◽

Haiying Wang ◽

Liyuan Zhang

Keyword(s):

Surface Charge ◽

Hexavalent Chromium ◽

In Situ Polymerization ◽

Interlayer Spacing ◽

Layer By Layer ◽

Negative Surface ◽

Negative Surface Charge ◽

Adsorption Reduction ◽

Titanium Carbides

Titanium carbides (MXenes) are promising multifunctional materials. However, the negative surface charge and layer-by-layer restacking of MXenes severely restrict their application in the field of anionic pollutants, including in hexavalent chromium (Cr(VI)). Herein, Ti3C2Tx MXenes was functionalized through in situ polymerization and intercalation of poly(m-phenylenediamine) (PmPD), then Ti3C2Tx/PmPD composites were obtained. Delightedly, Ti3C2Tx/PmPD composites exhibited positive surface charge, expanded interlayer spacing, and enhanced hydrophobicity. Furthermore, the specific surface area of Ti3C2Tx/PmPD composite was five and 23 times that of Ti3C2Tx and PmPD, respectively. These advantages endowed Ti3C2Tx/PmPD composite with an excellent adsorption capacity of Cr(VI) (540.47 mg g−1), which was superior to PmPD (384.73 mg g−1), Ti3C2Tx MXene (137.45 mg g−1), and the reported MXene-based adsorbents. The Cr(VI) removal mechanism mainly involved electrostatic adsorption, reduction, and chelation interaction. This study developed a simple functionalization strategy, which would greatly explore the potential of MXenes in the field of anionic pollutants.

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