Pyrohydrolysis of CaCl₂ waste for the recovery of HCl acid upon the synergistic effects from MgCl₂ and silica

9^th World Convention on Waste Recycling and Reuse

March 11-12, 2019 Singapore

Song Zhou, Binbin Qian, Tahereh Hosseini, Anthony De Girolamo and Lian Zhang

Monash University, Australia

Scientific Tracks Abstracts: Adv Recycling Waste Manag

Abstract :

An efficient HCl acid recovery method from the mixture of alkaline earth metal chlorides waste was demonstrated via co-pyrohydrolysis in a lab-scale horizontal furnace at a temperature range of 700-1000ºC 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 1000ºC, 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 1000ºC with a noticeable residence time (e.g. 2 hours) 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.

Biography :

Song Zhou is currently a PhD student at Monash University. He is a Member of Clean Solid Fuel Laboratory (CSFL). His present research interest is mainly on chloride waste treatment and atomic structure analysis based on X-ray Adsorption Fine Spectroscopy (XAFS) analysis.

E-mail: song.zhou@monash.edu