Improved adsorption capacity and applicable temperature of gaseous PbCl2 capture by modified montmorillonite with combined thermal treatment and acid activation

The emission of semi-volatile heavy metals during the thermal utilization of various fuels has been a huge threat to the environment. In this study, the montmorillonite modified by thermal treatment and hydrochloric acid activation was evaluated for the PbCl2 adsorption performance. The optimum adsorption temperature of sorbents increased with the thermal treatment temperature (<500 C) for the increased amount of reactive sites caused by the removal of interlayer water and hydroxyl, while a higher treatment temperature will collapse the lamellar structure of montmorillonite and greatly inhibit the PbCl2 adsorption. Besides, the hydrochloric acid activation can help inhibit the melting of sorbents during the adsorption process by removing the impurities and promote the PbCl2 vapor to contact with more reactive sites at higher temperatures. By comparing different sorbents, montmorillonite was found to exhibit better adsorption performance at 600-700 degrees C, while the sorbent thermal -treated at 500 degrees C and then acid-activated got the highest adsorption efficiency at 900 degrees C, which was 17.83% higher than that of montmorillonite. This study provided an environmental-friendly modification method to capture more heavy metals at high-temperature conditions, which can be partly realized by the recycling of montmorillonite used for the removal of normal gas pollutants in lower temperatures conditions or acid wastewater treatment.

Automated summary

The emission of semi-volatile heavy metals during fuel utilization poses a significant threat to the environment. This study investigated the sorption performance of montmorillonite modified by thermal treatment and hydrochloric acid activation for PbCl2. The optimal sorption temperature of the sorbents increased with thermal treatment temperature (<500 C) due to the removal of water and hydroxyl groups, but higher treatment temperatures led to the collapse of lamellar structure and hindered PbCl2 adsorption. Additionally, hydrochloric acid activation helped inhibit sorbent melting and enhanced PbCl2 adsorption at higher temperatures.