Peroxymonosulfate assisted mechanochemical remediation of high concentration DDTs contaminated soil

Mechanochemical remediation of contaminated soil: A review

Mechanochemical techniques have been garnering growing attention in remediation of contaminated soil. This paper summarizes the performance, mechanism, influential factors, and environmental impacts of mechanochemical remediation (MCR) for persistent organic pollutants (POPs) contaminated soil and heavy metal(loid) s (HMs) contaminated soil. Firstly, in contrast to other technologies, MCR can achieve desirable treatment of POPs, HMs, and co-contaminated soil, especially with high-concentration pollutants. Secondly, POPs undergo mineralization via interaction with mechanically activated substances, where aromatic and aliphatic pollutants in soil may go through varied degradation routes; inorganic pollutants can be firmly combined with soil particles by fragmentation and agglomeration induced by mechanical power, during which additives may enhance the combination but their contact with anionic metal(loid)s may be partially suppressed. Thirdly, the effect of MCR primarily hinges on types of milling systems, the accumulation of mechanical energy, and the use of reagents, which is basically regulated through operating parameters: rotation speed, ball-to-powder ratio, reagent-to-soil ratio, milling time, and soil treatment capacity; minerals like clay, metal oxides, and sand in soil itself are feasible reagents for remediation, and alien additives play a crucial role in synergist and detoxification; additionally, various physicochemical properties of soil might influence the mechanochemical effect to varying degrees, yet the key influential performance and mechanism remain unclear and require further investigation. Concerning the assessment of soil after treatment, attention needs to be paid to soil properties, toxicity of POPs' intermediates and leaching HMs, and long-term appraisement, particularly with the introduction of aggressive additives into the system. Finally, proposals for current issues and forthcoming advancements in this domain are enumerated in items. This review provides valuable insight into mechanochemical approaches for performing more effective and eco-friendly remediation on contaminated soil.

Green mechanochemical activation of solid persulfate to remove PAHs in soil: Performance and mechanism

Due to the high biotoxicity and persistence of polycyclic aromatic hydrocarbons (PAHs), the remediation of PAHs-contaminated soil becomes an intractable problem. Persulfate-based advanced oxidation processes are widely used to degrade PAHs in aquatic environment. However, they are not convenient for used in soil due to the heterogeneity and complexity of soil matrix. In this study, a green and convenient ball milling process is introduced to activate persulfate for the remediation of PAHs-contaminated soil. About 82.5% PAHs were removed with 10% wt. Na2S2O8 (PS) addition and ball-milling for 2 h under 500 r/min. The degradation of PAHs is attributed to the attack of radicals (SO4·- and·OH) generated from the activation of PS by mechanochemistry. Moreover, stable Si-O bonds were disrupted during ball-milling process, and formed free electron on the surface of soil particles. This facilitates the electron transfer from oxidants to contaminants. The particle size, surface element composition, functional group, and thermogravimetric analysis confirmed the slight disturbance of ball-milling-assisted PS process on the physical and chemical properties of soil. Therefore, ball-milling assisted PS approach would be a promising technology for the remediation of PAHs-contaminated soil.

Mechanochemical degradation performance of lindane in different types of soils: The effects of soil properties and elemental components

Although mechanochemical remediation of organic-contaminated soil has received substantial attention in recent years, the effects of soil properties on soil remediation performance are not clear. In this work, the properties and elemental components of 16 soils were tested, and the mechanochemical degradation performance of lindane in these soils was investigated through experiments. Most importantly, the relationships between soil variables and the mechanochemical degradation rates of lindane in the additive-free and CaO systems were elucidated. The results showed that the mechanochemical degradation efficiencies of lindane in the 16 soils were significantly different without additives, with a range of 31.0 %-97.2 % after 4 h. The mechanochemical degradation rates of lindane in the 16 soils varied from 0.7 h-1 to 15 h-1 after the addition of 9 % CaO. Correlation analysis, redundancy analysis and the partial least squares path modeling results clearly showed that the main factors affecting the reaction rate (k1) without additives were organic matter (-) > clay (+) > bound water (-) > Si (+). After the addition of 9 % CaO, the order in which the main factors affected the reaction rate (k2) was organic matter (-) > bound water (-) > Ti/Fe/Al (-) > pH (+) > clay (+). The established and corrected multiple nonlinear regression equations can be used to accurately predict the mechanochemical degradation performance of hexachlorocyclohexanes in actual soils with and without additives.