Enhanced remediation of oil-contaminated mineral sand by the controlled release of a surfactant from calcium alginate capsules

The remediation of oil-contaminated soil poses significant environmental challenges, often necessitating innovative approaches for effective and sustainable solutions. This study focuses on the synthesis, characterisation, and application of biodegradable capsules loaded with surfactant for enhanced oil remediation of a clean sand. By controlling the release properties of capsules, the research aims to overcome the limitations of conventional surfactant-based remediation methods, such as rapid washout and reduced efficacy over time. The study outlines a systematic approach, beginning with the synthesis of capsules containing surfactant cargo using the ionic gelation technique, and charactering the capsules' physical attributes. Subsequently, laboratory washing tests were designed to evaluate the efficiency of capsules in enhancing the remediation of oil-contaminated sand, comparing their performance with conventional surfactant application methods. The results show that the capsules enhanced the efficiency of oil removal during the washing process by the controlled release of surfactants. With the use of capsules, oil removal rates of the contaminated sand increased from 29.56% (blank group) to 59.90%, 68.67%, and 76.72% (at 5%, 10%, and 15%, capsule content (mass of capsules by 100 g mass of sand), respectively). Compared to the direct use of surfactants, the capsule approach exhibited higher performance, which increased oil removal efficiency by 95.9%, 97.0%, and approximately 100%, respectively. A release mechanism of higher oil removal ability is proposed based on the measurement of the washing water's surface tension. The findings highlight the potential of polymeric capsules for oil remediation, paving the way for the development of self-remediation approaches in contaminated sands.