Enhancing lead immobilization by biochar: Creation of "surface barrier" via bio-treatment. (June 2023)

• Record Type: Journal Article
• Authors: Hu, Huicong; Tang, Chao-Sheng; Shen, Zhengtao; Pan, Xiaohua; Gu, Kai; Fan, Xiaoliang; Lv, Chao; Mu, Wen; Shi, Bin
• Is Part Of: Chemosphere. Volume 327(2023)
• Publication Date: 2023-06
• Subjects: Lead immobilization -- Rice straw biochar -- Long-term effectiveness -- Bio-treatment -- Microbial induced carbonate precipitation (MICP) -- Surface barrier; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2023.138477
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: The long-term effectiveness of heavy metal immobilization is always a concern. This study proposes a completely novel approach to enhance the stability of heavy metals by combined biochar and microbial induced carbonate precipitation (MICP) technology, to create a "surface barrier" of CaCO3 layer on biochar after lead (Pb 2+ ) immobilization. Aqueous sorption studies and chemical and micro-structure tests were used to verify the feasibility. Rice straw biochar (RSB700) was produced at 700 °C, which shows high immobilization capacity of Pb 2+ (maximum of 118 mg g −1 ). But the stable fraction only accounts for 4.8% of the total immobilized Pb 2+ on biochar. After MICP treatment, the stable fraction of Pb 2+ significantly increased to a maximum of 92.5%. Microstructural tests confirm the formation of CaCO3 layer on biochar. The CaCO3 species are predominantly calcite and vaterite. Higher Ca 2+ and urea concentrations in cementation solution resulted in higher CaCO3 yield but lower Ca 2+ utilization efficiency. The main mechanism of the "surface barrier" to enhance Pb 2+ stability on biochar was likely the encapsulation effect: it physically blocked the contact between acids and Pb 2+ on biochar, and chemically buffer the acidic attack from the environment. The performance of the "surface barrier" depends on both the yield of CaCO3 and their distribution uniformity on biochar's surface. This study shed lights on the potential application of the "surface barrier" strategy combining biochar and MICP technologies for enhanced heavy metal immobilization. Graphical abstract: Image 1 Highlights: Biochar (RSB700) shows high immobilization capacity of Pb 2+ with poor stability. The stable fraction of Pb 2+ significant increased after MICP treatment. CaCO3 acts as a surface barrier to buffer environmental changes. Combining biochar and MICP for enhanced Pb 2+ immobilization in soil is feasible.