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Type: Journal article
Title: Pyrohydrolysis of CaCl₂ waste for the recovery of HCl acid upon the synergistic effects from MgCl₂ and silica
Other Titles: Pyrohydrolysis of CaCl(2) waste for the recovery of HCl acid upon the synergistic effects from MgCl(2) and silica
Author: Zhou, S.
Qian, B.
Hosseini, T.
De Girolamo, A.
Zhang, L.
Citation: ACS Sustainable Chemistry and Engineering, 2019; 7(3):3349-3355
Publisher: ACS Publications
Issue Date: 2019
ISSN: 2168-0485
Statement of
Song Zhou, Binbin Qian, Tahereh Hosseini, Anthony De Girolamo, and Lian Zhang
Abstract: In this paper, an efficient HCl acid recovery method from the mixture of alkaline-earth-metal chlorides waste was demonstrated via co-pyrohydrolysis in a laboratory-scale horizontal furnace in a temperature range of 700–1000 °C, and fixed additions of SiO₂ and steam. The synergistic effect of MgCl₂ on the HCl recovery from CaCl₂ was explored intensively. A double-sided effect was revealed. For the reaction temperatures below 1000 °C, the MgCl₂ addition delayed the HCl release through competing with CaCl₂ for the inclusion into silica matrix. In contrast, once the chloride mixtures were subjected to 1000 °C with a noticeable residence time (e.g., 2 h) and at a minimum molar ratio of 0.5 of MgCl₂ to CaCl₂, the MgCl₂ addition promoted the HCl release remarkably, via promoting the conversion of Ca₃(SiO₄)Cl₂ into Ca₈Mg(SiO₄)₄Cl₂. A portion of Mg²⁺ derived from the early decomposition of MgCl₂ substituted the Ca(I) site in Ca₃(SiO₄)Cl₂, thereby resulting in the formation of weak Mg–Cl bond that is in favor of the HCl release. Additionally, the remaining Mg²⁺ consumed the excessive SiO₂ so as to cause the skeleton of [SiO₄]⁴⁻ to be fully affiliated and balanced by cations to form Ca₈Mg(SiO₄)₄Cl₂ in which the weaker ionic polarization between Ca²⁺ and adjacent anions further enhanced the breakage of the Ca–Cl bonds.
Keywords: Pyrohydrolysis; alkaline-earth-metal chlorides; HCl regeneration; Cl release; silica
Rights: © 2019 American Chemical Society
RMID: 1000015252
DOI: 10.1021/acssuschemeng.8b05513
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Appears in Collections:Chemical Engineering publications

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