Removal of PCBs and HCB from contaminated solids using a novel successive self-propagated sintering process

Mechanochemical treatment of hexachlorobenzene-contaminated soil with additives

The use of mechanochemistry for the remediation of hexachlorobenzene (HCB)-contaminated soil was investigated. Additives such as alkaline materials, neutral materials, natural minerals, and solid waste were studied to explore their effect on the degradation of hexachlorobenzene in soil with single or combined addition by mechanochemical method. The best combination of materials were determined based on HCB destruction percentage by considering the impact on soil quality, the treatment cost, and the availability of additives. Scanning electron microscope (SEM) images and X-ray photoelectron spectrometer (XPS) analysis were conducted for the mechanism studies. The combination of albite and ferric oxide (Fe₃O₄) was found to achieve the best performance in the degradation of HCB with the destruction percentage from 74.3 to 92.5% after 2-h and 6-h reaction, respectively. The developed fracture structure and complex compositions of albite provided abundant reaction sites for mechanochemical degradation of HCB in soil.

Recent advances in PCB removal from historically contaminated environmental matrices

Despite being drastically restricted in the 1970s, polychlorinated biphenyls (PCBs) still belong among the most hazardous contaminants. The chemical stability and dielectric properties of PCBs made them suitable for a number of applications, which then lead to their ubiquitous presence in the environment. PCBs are highly bioaccumulative and persistent, and their teratogenic, carcinogenic, and endocrine-disrupting features have been widely reported in the literature. This review discusses recent advances in different techniques and approaches to remediate historically contaminated matrices, which are one of the most problematic in regard to decontamination feasibility and efficiency. The current knowledge published in the literature shows that PCBs are not sufficiently removed from the environment by natural processes, and thus, the suitability of some approaches (e.g., natural attenuation) is limited. Physicochemical processes are still the most effective; however, their extensive use is constrained by their high cost and often their destructiveness toward the matrices. Despite their limited reliability, biological methods and their application in combinations with other techniques could be promising. The literature reviewed in this paper documents that a combination of techniques differing in their principles should be a future research direction. Other aspects discussed in this work include the incompleteness of some studies. More attention should be given to the evaluation of toxicity during these processes, particularly in terms of monitoring different modes of toxic action. In addition, decomposition mechanisms and products need to be sufficiently clarified before combined, tailor-made approaches can be employed.

Static decontamination of oil-based drill cuttings with pressurized hot water using response surface methodology

Separating organic pollutants from oil-based drill cuttings (OBDC) is the current trend for its safe disposal. In this study, pressurized hot water extraction (PHWE) was adapted to decontaminate OBDC for the first time. Two typical OBDC samples, i.e., diesel-based drill cuttings (OBDC-A) and white oil-based drill cuttings (OBDC-B), were statically extracted in a homemade batch autoclave. Response surface methodology (RSM) with a central composite design (CCD) was applied to investigate the effects and interactive effects of three independent operating parameters (temperature, extraction time, and water volume) and to ultimately optimize the PHWE process. The results suggested that temperature is the dominant parameter, followed by water volume and extraction time. Interactive effects among the three parameters are present in the PHWE of OBDC-A but absent in the PHWE of OBDC-B. The suitable conditions for the effective PHWE of OBDC-A were found to be a temperature of 284-300 °C, water volume of 15-35 ml, and extraction time of 20-60 min. The corresponding conditions were 237-300 °C, 15-35 ml, and 20-60 min for the PHWE of OBDC-B. These different phenomena are caused by the different characteristics of the two OBDC samples. All of the polynomial models obtained from the RSM experiments are very valid and can adequately describe the relationship among the three independent operating parameters and responses. The experimental results also confirmed that PHWE is a more efficient separation technique for decontaminating OBDC than single organic solvent extraction or low-temperature thermal desorption because PHWE integrates the advantages of both these processes.

Dechlorination of Hexachlorobenzene in Contaminated Soils Using a Nanometallic Al/CaO Dispersion Mixture: Optimization through Response Surface Methodology

Hexachlorobenzene (HCB) contamination of soils remains a significant environmental challenge all over the world. Reductive stabilization is a developing technology that can decompose the HCB with a dechlorination process. A nanometallic Al/CaO (n-Al/CaO) dispersion mixture was developed utilizing ball-milling technology in this study. The dechlorination efficiency of HCB in contaminated soils by the n-Al/CaO grinding treatment was evaluated. Response surface methodology (RSM) was employed to investigate the effects of three variables (soil moisture content, n-Al/CaO dosage and grinding time) and the interactions between these variables under the Box-Behnken Design (BBD). A high regression coefficient value (R² = 0.9807) and low p value (<0.0001) of the quadratic model indicated that the model was accurate in predicting the experimental results. The optimal soil moisture content, n-Al/CaO dosage, and grinding time were found to be 7% (m/m), 17.7% (m/m), and 24 h, respectively, in the experimental ranges and levels. Under optimal conditions, the dechlorination efficiency was 80%. The intermediate product analysis indicated that dechlorination was the process by stepwise loss of chloride atoms. The main pathway observed within 24 h was HCB → pentachlorobenzene (PeCB) → 1,2,3,4-tetrachlorobenzene (TeCB) and 1,2,4,5-TeCB. The results indicated that the moderate soil moisture content was crucial for the hydrodechlorination of HCB. A probable mechanism was proposed wherein water acted like a hydrogen donor and promoted the hydrodechlorination process. The potential application of n-Al/CaO is an environmentally-friendly and cost-effective option for decontamination of HCB-contaminated soils.

Hydrodehalogenation of hexachloro- and hexabromobenzene by metallic calcium in ethanol, in the presence of Rh/C catalyst

Both hexachlorobenzene and hexabromobenzene were successfully hydrodehalogenated to the monohalogenated derivative and ultimately to benzene (which was subsequently reduced to cyclohexane) using a mixture of metallic Ca, ethanol, and Rh/C, by simple stirring in diethyl ether, at room or mild temperature (60 °C). Various experiments were performed in order to assess the role of the solvent and Rh/C catalyst, as well as for elucidating the reaction pathway.

Application of microwave irradiation for the removal of polychlorinated biphenyls from siloxane transformer and hydrocarbon engine oils

The removal of polychlorinated biphenyls (PCBs) both from siloxane transformer oil and hydrocarbon engine oil was investigated through the application of microwave (MW) irradiation and a reaction system based on polyethyleneglycol (PEG) and potassium hydroxide. The influence of the main reaction parameters (MW irradiation time, molecular weight of PEG, amount of added reactants and temperature) on the dechlorination behavior was studied. Promising performances were reached, allowing about 50% of dechlorination under the best experimental conditions, together time and energy saving compared to conventional heating systems. Moreover, an interesting dechlorination degree (up to 32%) was achieved for siloxane transformer oil when MW irradiation was employed as the unique driving force. To the best of our knowledge, this is the first time in which MW irradiation is tested as the single driving force for the dechlorination of these two types of PCB-contaminated oils.