Pyrolysis kinetics and environmental risks of oil-based drill cuttings at China's largest shale gas exploitation site.

Chongqing Fuling shale gas field, the largest shale gas exploration site in China, produces a large amount of oil-based drill cuttings (OBDC) every year, which is a hazardous waste. Traditional treatment methods such as solidification/stabilization did not recycle the valuable components such as petroleum hydrocarbons. Pyrolysis is proven to be an efficient method that can recover those components. This study firstly investigated the pyrolysis kinetics by two different methods on the basis of detailed material characterization, and then taking the workers and the surrounding ecological environment as the analysis object, the human health risk assessment (HHRA) and ecological risk assessment were evaluated respectively before and after pyrolysis. The results showed that the pyrolysis of OBDC was divided into three stages, and the cracking of light hydrocarbons stage was the key control step for pyrolysis process. The activation energy E increased gradually during the pyrolysis progress. The HHRA results showed that pyrolysis could greatly reduce the non-carcinogenic risk, carcinogenic risk and ecological risk by 59.6 %, 62.8 % and 75 % respectively. However, the carcinogenic risk after pyrolysis was still higher than the critical value 10-6.

Temporal and Spatial Distribution Analysis of Atmospheric Pollutants in Chengdu-Chongqing Twin-City Economic Circle.

In order to study the temporal and spatial distribution characteristics of atmospheric pollutants in cities (districts and counties) in the Chengdu-Chongqing Twin-city Economic Circle (CCEC) and to provide a theoretical basis for atmospheric pollution prevention and control, this paper combined Ambient Air Quality Standards (AAQS) and WHO Global Air Quality Guidelines (GAQG) to evaluate atmospheric pollution and used spatial correlation to determine key pollution areas. The results showed that the distribution of atmospheric pollutants in CCEC presents a certain law, which was consistent with the air pollution transmission channels. Except for particulate matter with an aerodynamic diameter equal to or less than 2.5 µm (PM2.5) and ozone (O3), other pollutants reached Grade II of AAQS in 2020, among which particulate matter with an aerodynamic diameter equal to or less than 10 µm (PM10), PM2.5, sulfur dioxide (SO2), nitrogen dioxide (NO2) and carbon monoxide (CO) have improved. Compared with the air quality guidelines given in the GAQG, PM10, PM2.5, NO2 and O3 have certain effects on human health. The spatial aggregation of PM10 and PM2.5 decreased year by year, while the spatial aggregation of O3 increased with the change in time, and the distribution of NO2 pollution had no obvious aggregation. Comprehensive analysis showed that the pollution problems of particulate matter, NO2 and O3 in CCEC need to be further controlled.

Co-sintering MSWI fly ash with electrolytic manganese residue and coal fly ash for lightweight ceramisite.

The MSWI fly ash (FA) is classified as hazardous waste and electrolytic manganese residue (EMR) as the harmful industrial waste. FA, water-washed FA (WFA), EMR and coal fly ash (CFA) were co-recycled to form lightweight MFCE ceramisites. The effects of FA, WFA and mixed MSWI fly ash on ceramisites were discussed. The approach to mixing FA and WFA increased the recycling amount of MSWI fly ash. The optimal mixture of 34.5% EMR, 24.1% CFA, 20.7% FA and 20.7% WFA sintered at 1160 °C for 12 min with a procedural heating rate (10 °C/min) and belonged to Class 800 artificial lightweight aggregate (GB/T 17431.1-2010); the quantity of MSWI fly ash in ceramisite was as high as 41.4%. Volatilization rates of Cd, Pb, Cu, Zn, Mn and Cr for ceramisite were higher 75.0, 24.2, 62.7, 133, 343 and 764% than FA respectively, attributed to the co-existence of chlorides and sulfates. The remained Zn, Cu, Pb, Mn and Cr were exchanged with Mg2+/Ca2+/Al3+ of diopside and wollastonite to form residual fractions. Our findings provided a feasibility method of co-recycling MSWI fly ash and electrolytic manganese residue to produce green lightweight aggregates.

Characterization of typical heavy metals in pyrolysis MSWI fly ash.

Thermal treatment methods are used extensively in the process of municipal solid waste incineration fly ash. However, the characterization of heavy metals during this process should be understood more clearly in order to control secondary pollution. In this paper, the content, speciation and leaching toxicity of mercury (Hg), plumbum (Pb), cadmium (Cd) and zinc (Zn) in fly ash treated under different temperatures and time were firstly analysed as pre-tests. Later, pilot-scale pyrolysis equipment was used to explore the concentration and speciation changes in the heavy metals of fly ash. Finally, the phase constitution and microstructure changes in fly ash were compared before and after pyrolysis using X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. The results showed that (a) The appropriate processing temperature was between 400°C and 450°C, and the processing time should be 1 h. (b) The stability of heavy metals in fly ash increased after pyrolysis. (c) XRD and SEM results indicated that phase constitution changed a little, but the microstructure varied to a porous structure similar to that of a coral reef after pyrolysis. These results suggest that pyrolysis could be an effective method in controlling heavy metal pollution in fly ash.

Co-disposal of MSWI fly ash and electrolytic manganese residue based on geopolymeric system.

MSWI fly ash (MSWI FA) and electrolytic manganese residue (EMR) were successfully co-disposed by use of a geopolymeric system. Alkaline products of MSWI FA and NaOH were used to elicit chemical reactions to promote solidification. The best performing formulation of EMR-based geopolymer for immobilization of heavy metals was composed of 75 wt% MSWI FA and 25 wt% EMR with NaOH solution (7.5 M)/solid of 0.5. Solidification was most effective for the heavy metals: Pb > Cu > Cr > Zn > Mn, respectively. The EMR-based geopolymer had high structural stability likely due to the high ratio of SiO2/Al2O3. The Solidification/Stabilization (S/S) mechanism for heavy metals of geopolymers is likely due to alkaline conditions and geopolymeric encapsulation, highlighting the utility and feasibility of this approach.

Heavy metal pollution of oil-based drill cuttings at a shale gas drilling field in Chongqing, China: A human health risk assessment for the workers.

With the flourish of shale gas industry in China, the characteristic hazardous waste, oil-based drill cuttings (OBDC), was also produced in large quantities. Unlike traditional petroleum industry, shale gas exploitation covers a wider area and there are more well sites, the adverse effects of OBDC piled up around well sites are even greater. This study investigated the pollution status and leaching toxicity of eight heavy metals (Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn) in OBDC of shale gas exploitation, and evaluated the health risks of the drilling workers. The results showed that heavy metal pollution in OBDC was moderate, and the leaching toxicity was far below the standard value. Non-carcinogenic and carcinogenic risks of drilling workers were within an acceptable range. Meanwhile, in order to reduce the health risks of drilling workers, some suggestions are proposed to reduce the exposure risks of workers and the content of heavy metals in OBDC.