Yu Jie, Sun Lushi, Ma Chuan, Qiao Yu, Xiang Jun, Hu Song, Yao Hong
State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 430074 Wuhan, Hubei, China.
State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 430074 Wuhan, Hubei, China.
Waste Manag. 2016 Mar;49:124-130. doi: 10.1016/j.wasman.2015.12.015. Epub 2015 Dec 31.
This work aims to study the mechanism of heavy metals vaporization by MgCl2⋅6H2O. Firstly, the decomposition mechanism of MgCl2⋅6H2O was investigated by thermodynamic equilibrium calculations, XRD and TG. Upon heating, MgCl2⋅6H2O went through the processes of dehydration and hydrolysis simultaneously accompanied by the release of HCl between 150 and 500°C. At temperature higher than 500°C, Mg(OH)Cl gradually release part of HCl. MgCl2⋅6H2O followed the similar processes of decomposition at both oxidative and reductive atmospheres. In oxidative atmosphere, vaporization of Zn and Cu was significantly accelerated by MgCl2⋅6H2O. However, in inert atmosphere, vaporization of Cu was not promoted since copper chloride was only stable in oxidative atmosphere. Under slow heating condition, vaporization of heavy metals were close to that under fast heating condition. This may be partially attributed to that most heavy metals already reacted with HCl forming metal chlorides below 500°C, which can be vaporized at higher temperature. Moreover, the Mg(OH)Cl contributed to release HCl up to 800°C. At such high temperature, the metal chlorides continue to be formed and then vaporized. After treatment, the leaching concentration of heavy metals from treated fly ashes were much lower than that from raw fly ash and met the regulatory limit of leachate. Since a large amount of MgSiO3 were formed during thermal treatment, the fly ash treated with MgCl2⋅6H2O can be used as raw materials for glass-ceramics production.
本工作旨在研究MgCl₂⋅6H₂O对重金属蒸发的作用机制。首先，通过热力学平衡计算、XRD和TG对MgCl₂⋅6H₂O的分解机制进行了研究。加热时，MgCl₂⋅6H₂O在150至500°C之间同时经历脱水和水解过程，并伴有HCl的释放。在高于500°C的温度下，Mg(OH)Cl逐渐释放部分HCl。MgCl₂⋅6H₂O在氧化和还原气氛中均遵循类似的分解过程。在氧化气氛中，MgCl₂⋅6H₂O显著加速了Zn和Cu的蒸发。然而，在惰性气氛中，由于氯化铜仅在氧化气氛中稳定，Cu的蒸发未得到促进。在缓慢加热条件下，重金属的蒸发与快速加热条件下相近。这可能部分归因于大多数重金属在500°C以下已与HCl反应形成金属氯化物，这些金属氯化物可在较高温度下蒸发。此外，Mg(OH)Cl在800°C之前都有助于HCl的释放。在如此高的温度下，金属氯化物继续形成然后蒸发。处理后，处理后的飞灰中重金属的浸出浓度远低于原飞灰，且符合渗滤液的监管限值。由于热处理过程中形成了大量的MgSiO₃，用MgCl₂⋅6H₂O处理的飞灰可作为微晶玻璃生产的原料。
