TY - JOUR
T1 - Pyrohydrolysis of CaCl2 waste for the recovery of HCl acid upon the synergistic effects from MgCl2 and silica
AU - Zhou, Song
AU - Qian, Binbin
AU - Hosseini, Tahereh
AU - De Girolamo, Anthony
AU - Zhang, Lian
PY - 2019/2/4
Y1 - 2019/2/4
N2 -
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 SiO
2
and steam. The synergistic effect of MgCl
2
on the HCl recovery from CaCl
2
was explored intensively. A double-sided effect was revealed. For the reaction temperatures below 1000 °C, the MgCl
2
addition delayed the HCl release through competing with CaCl
2
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 MgCl
2
to CaCl
2
, the MgCl
2
addition promoted the HCl release remarkably, via promoting the conversion of Ca
3
(SiO
4
)Cl
2
into Ca
8
Mg(SiO
4
)
4
Cl
2
. A portion of Mg
2+
derived from the early decomposition of MgCl
2
substituted the Ca(I) site in Ca
3
(SiO
4
)Cl
2
, thereby resulting in the formation of weak Mg-Cl bond that is in favor of the HCl release. Additionally, the remaining Mg
2+
consumed the excessive SiO
2
so as to cause the skeleton of [SiO
4
]
4-
to be fully affiliated and balanced by cations to form Ca
8
Mg(SiO
4
)
4
Cl
2
in which the weaker ionic polarization between Ca
2+
and adjacent anions further enhanced the breakage of the Ca-Cl bonds.
AB -
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 SiO
2
and steam. The synergistic effect of MgCl
2
on the HCl recovery from CaCl
2
was explored intensively. A double-sided effect was revealed. For the reaction temperatures below 1000 °C, the MgCl
2
addition delayed the HCl release through competing with CaCl
2
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 MgCl
2
to CaCl
2
, the MgCl
2
addition promoted the HCl release remarkably, via promoting the conversion of Ca
3
(SiO
4
)Cl
2
into Ca
8
Mg(SiO
4
)
4
Cl
2
. A portion of Mg
2+
derived from the early decomposition of MgCl
2
substituted the Ca(I) site in Ca
3
(SiO
4
)Cl
2
, thereby resulting in the formation of weak Mg-Cl bond that is in favor of the HCl release. Additionally, the remaining Mg
2+
consumed the excessive SiO
2
so as to cause the skeleton of [SiO
4
]
4-
to be fully affiliated and balanced by cations to form Ca
8
Mg(SiO
4
)
4
Cl
2
in which the weaker ionic polarization between Ca
2+
and adjacent anions further enhanced the breakage of the Ca-Cl bonds.
KW - Alkaline-earth-metal chlorides
KW - Cl release
KW - HCl regeneration
KW - Pyrohydrolysis
KW - Silica
UR - http://www.scopus.com/inward/record.url?scp=85061081792&partnerID=8YFLogxK
U2 - 10.1021/acssuschemeng.8b05513
DO - 10.1021/acssuschemeng.8b05513
M3 - Article
AN - SCOPUS:85061081792
VL - 7
SP - 3349
EP - 3355
JO - ACS Sustainable Chemistry & Engineering
JF - ACS Sustainable Chemistry & Engineering
SN - 2168-0485
IS - 3
ER -