Efficient removal of foam agent in shield muck by modified biochar materials with controlled bimetallic crystalline...

Anionic surfactant sodium alcohol ether sulphate (AES) is widely used as the core component of foam agent in shield construction, which can cause soil contamination and impede the resource utilisation of shield muck. In this study, bimetallic modified biochar materials, Enstatites/BC and Amphiboles/BC, were prepared via acidic and alkaline coprecipitation method followed by pyrolysis, respectively. Their adsorption performance on AES in the filtrate and shield muck, as well as the underlying mechanism, was investigated in detail. The results showed that the maximum equilibrium adsorption of AES by Enstatites/BC and Amphiboles/BC was 224.15 and 267.15 mg/g, respectively (1.88 and 2.24 times higher than that of unmodified biochar). The Enstatites/BC was primarily subjected to metal ion modification to enhance positive charge density and electrostatic attraction to AES. At the same time, the Amphiboles/BC relied on their high ionic strengthen to enhance electrostatic interaction and ion exchange with the AES. The optimal dosage of Enstatites/BC and Amphiboles/BC for the stabilisation of AES in soil was found to be 5 % and 3 %, which could effectively reduce AES leaching from soil by 96.9 % and 98.6 %, respectively. More dosage might lead to the opposite effect due to charge shielding failure, particle agglomeration, or pore blockage. Furthermore, higher pH and electrical conductivity (EC) facilitated the adsorption of AES within soil. This study reveals the key influence of modulating the crystalline configuration in modified biochar on the adsorption performance of AES, which provides a theoretical basis and technical support for the efficient removal of AES from the filtrate and the restoration of shield muck.