Biofuel Ash Aging in Acidic Environment and Its Influence on Cd Immobilization

Area of Science:

• Environmental Science
• Soil Science
• Geochemistry

Background:

• Biofuel ash (BFA) shows potential for immobilizing heavy metals like cadmium (Cd) in soil.
• The long-term effectiveness of BFA for Cd immobilization, particularly after aging, requires further investigation.

Purpose of the Study:

• To investigate the effects of natural and artificial aging on the physicochemical properties of BFA.
• To evaluate the influence of BFA aging on its capacity and mechanisms for immobilizing Cd in soil.

Main Methods:

• BFA was subjected to natural aging in southern China soil (BFA-N) and artificial acid aging (BFA-A).
• Physicochemical properties and Cd adsorption capacities of aged and unaged BFA were analyzed using Langmuir and pseudo-second-order models.
• Cd immobilization mechanisms (adsorption and precipitation) and changes in chemical composition (e.g., Ca content) were assessed.

Main Results:

• Both natural and acid aging reduced the Cd adsorption capacity of BFA, with acid aging showing a more pronounced decrease.
• Cd immobilization by BFA is primarily driven by adsorption, with precipitation playing a minor role.
• Aging led to calcium (Ca) loss in BFA, correlating with reduced Cd adsorption, suggesting Ca is key to Cd immobilization.

Conclusions:

• The primary mechanism for Cd immobilization by BFA, both before and after aging, is linked to calcium content.
• Aging alters the specific adsorption mechanisms (electrostatic interaction, ion exchange, hydroxyl complexation) of BFA for Cd.
• The long-term efficacy of BFA as a Cd immobilizer may be reduced by aging processes, necessitating careful consideration of its application.