[New pretreatment method for detecting petroleum hydrocarbons in soil: silica-gel dehydration and cyclohexane extraction].

Oil is a primary source of energy worldwide. However, the use of oil produces large amounts of pollutants, which are detrimental to the environment. The presence of petroleum hydrocarbons in soil is a critical marker of environmental pollution and safety. Rapid on-site detection technology has been broadly used in emergency tracking, offering critical information support for effective reactions to environmental emergencies. Thus, it is expected to play an increasingly critical role in environmental remediation efforts. The current approach for petroleum hydrocarbon detection in soil mainly involves Soxhlet extraction with a combination of solvents, including acetone and n-hexane. The samples are then analyzed after rotary evaporation, dehydration with anhydrous sodium sulfate, and purification using a magnesium silica-type adsorbent. Unfortunately, this approach requires sample analysis to be performed in the laboratory, which is tedious and time consuming, and consumes large amounts of solvents. Moreover, the rotary evaporator is not portable. Therefore, this method is not appropriate for the rapid on-site detection of petroleum hydrocarbons. In this study, a rapid on-site detection method based on silica-gel dehydration and cyclohexane extraction was developed for the extraction and pretreatment of petroleum hydrocarbons (C10-C40) in soil. First, an appropriate amount of silica gel was added to the soil, and the mixture was completely ground to eliminate moisture. Next, petroleum hydrocarbons were extracted with 40 mL of cyclohexane, and the extract was cleaned by Florisil solid-phase extraction (SPE) column elution. Finally, the samples were analyzed by gas chromatography (GC) to evaluate the above method. The silica gel exhibited optimal adsorption properties compared with anhydrous sodium sulfate, calcium oxide, and molecular sieves, with recovery of 87.5%. The effects of different soil water content (5%, 10%, and 20%) and silica gel (1, 3, 5, and 10 times the moisture content) dosage on the extraction of petroleum hydrocarbons were investigated. The recoveries of petroleum hydrocarbons increased from 74.0% to 103.8% after 15 min of invasive extraction (relative standard deviation, RSD, <10.1%) when silica gel amounting to 10 times the moisture content was used. Five types of silica gels with different properties were purchased from four manufacturers, and the effects of these silica gels on the dehydration and extraction efficiency of petroleum hydrocarbons in soil were assessed. The results showed that amorphous silica gel led to low recoveries (<60%), spherical silica gel achieved extraction efficiencies of approximately 70%-90%, and alkaline silica gel produced recoveries with poor precision. Therefore, neutral spherical silica gel was used for further experiments. The fingerprints of petroleum hydrocarbons with different carbon numbers are an important reference for identifying pollution sources. Thus, ensuring good recoveries throughout the entire carbon range is necessary to ensure the accuracy of the fingerprint analysis results. The proposed method showed good recoveries for petroleum hydrocarbons of all carbon numbers (75%-101%). The findings above indicate that the developed method could be an efficient means to extract petroleum hydrocarbons from soil for both total quantity and fingerprint analyses. Compared with standard methods, the proposed method requires lower solvent dosages and features simpler processing steps. Another advantage of this method is that it does not require the use of highly toxic halogenated solvents; thus, it does not contribute to environmental pollution. It can be applied to the laboratory analysis of soil petroleum hydrocarbons and coupled with other rapid on-site detection techniques for soil petroleum hydrocarbons, such as infrared spectroscopy and portable GC. However, because it does not include a concentration process, the developed method exhibits relatively low sensitivity. In the future, we plan to develop a simple and flexible on-site sample-concentration system to further improve various indicators of this method.

[PCDD/Fs formation from pentachlorobenzene under the catalysis of CuO].

The formation processes of PCDD/Fs from pentachlorobenzene catalyzed by CuO under heating conditions were investigated. The results showed that, the amount of the formed PCDD/Fs increased with the temperature from 200 degrees C to 350 degrees C, and then decreased with futher increase of temperature from 350 degrees C to 450 degrees C. PCDD/Fs homologue pattern varied significantly according to the reaction temperature. At the lower temperature (200-250 degrees C), the major PCDD/Fs products were highly chlorinated ones; but at the higher temperature (400-450 degrees C), the low chlorinated PCDD/Fs predominated in the PCDD/Fs products. The change of temperature did not cause a systematical variation in the isomer distributions in each PCDD/Fs homologue. By comparing the formation of PCDD/Fs from pentachlorobenzene with the dechlorination of OCDD/F both under the catalysis of CuO at 400 degrees C, the precursor mechanism of PCDD/ Fs formation from pentachlorobenzene was speculated. Low chlorinated PCDDs mainly came from the dechlorination of highly chlorinated PCDDs which were formed from the pentachlorobenzene, whereas PCDFs could be mainly formed by the direct condensation of dechlorination products of pentachlorobenzene.

[PCDD/F emission characteristics in different waste incineration facilities and evaluation of 23478-PeCDF as I-TEQ indicator of PCDD/F in flue gases].

The emission characteristics of PCDD/F from different waste incineration facilities in China, the correlations of different PCDD/F isomers with I-TEQ and the linear regression analysis of 23478-PeCDF with I-TEQ were reported in this article. Statistical analysis of the homologue patterns of PCDD/F in different incineration facilities will provide valuable information in environmental survey to find the contamination sources. PCDD/F congener patterns were almost constant among municipal and hazardous waste incineration facilities with only very small variations, but those patterns in medical waste incineration facilities were slightly different from medical and hazardous waste incineration facilities. It was found that the major contributors to the toxic PCDD/F concentrations were OCDD and 1234678-HpCDF contributing for 12.3%-23.0% and 15.0%-19.7% respectively. However, the largest contributor to I-TEQ was 23478-PeCDF and 33.1%-34.5% of I-TEQ was the presence of this congener. Correlation analysis showed that:23478-PeCDF posed the best the correlation relationship with I-TEQ, R2 0.93-0.99. The most toxic 2378-TCDD only posed weak correlation with I-TEQ, R2 0.29-0.49. The correlation coefficient between the most abundant OCDD and I-TEQ was only 0.03-0.12. However, another abundant congener 1234678-HpCDF posed better correlation with I-TEQ, R2 0.62-0.87. Linear regression analysis showed that even I-TEQ fell into the concentration range of 5-6 orders of magnitudes, the linear relationship between 23478-PeCDF and I-TEQ was still excellent. The slopes of that lines, in different waste incineration facilities, were in the range of 1.16-1.40 and R2 0.94-0.97.

[Patterns of PCDD/Fs, PCBs and PCNs homologues in fly ash from cement kilns].

The concentrations and toxic equivalent (TEQ) values of PCDD/Fs, PCBs and PCNs in fly ash collected from three types of cement kilns (vertical shaft kiln, wet-process rotary kiln and dry-process rotary kiln) and two types of waste incinerators were determined, and the patterns of homologues and congeners were compared. The results showed that the total TEQ of PCDD/Fs, PCBs and PCNs in cement kiln fly ash, which were in the range of 4.0-62, 0.069-3.9 and 0.47-2.8 ng x kg(-1) respectively, were much lower than that of fly ash from waste incinerators. In cement kiln fly ash, the predominating PCDD/Fs homologues were TCDFs, and the chief 2, 3, 7, 8-PCDD/Fs congeners were OCDD, 2, 3, 7, 8-TCDF and 1, 2, 3, 4, 6, 7, 8-HpCDF. The patterns of PCBs homologues in cement kiln fly ash were similar to those of waste incinerators in which TeCB were predominating homologues. PCB77, PCB105, PCB118 were at higher concentrations than other co-polar PCBs. Different types of cement kiln fly ash presented similar PCNs homologue patterns. The predominant homologues were TeCN, whereas OcCN were not detected. PCN 66/67 which has dioxin like toxity was the most abundant congener in all fly ash.

[PCDD/F formation and its mass balance in a MSW incineration system].

PCDD/F distributions in a two-stage reciprocating grate municipal solid waste (MSW) incinerator under two kinds of operating conditions were investigated by sampling the ashes, flue gases and bottom ashes at different positions, and the mass balance was calculated. At the boiler outlet, the concentration of PCDD/F in the flue gas is 2.602 ng x m(-3) and 1.236 ng x m(-3) under operating condition 1 (RUNI) and operating condition 2 (RUN2), respectively. A significant formation of PCDD/F was found in the sections of semi-dry scrubber (SDS) and cyclone precipitator (CP), in which the temperature of flue gas was in the range of 260-180 degrees C. Compared with PCDD/F level measured at the boiler outlet, the total concentration of tetra-to octa-CDD/F measured at the CP outlet increased 82.2% and 17.6% under RUN1 and RUN2, respectively. At the bag filter (BF) section, about 90% of PCDD/F was removed from the flue gas by the precipitation of fly ash. The PCDD/F homologue patterns were almost similar for the boiler ash, CP ash, BF ash and the flue gases. The higher O2 content in flue gas led to a larger PCDD/F yield, but the variation of O2 level did not give rise to a systematical change of PCDD/F homologue pattern. Under RUN1, 10.4%, 3.2%, 9.3%, 64.1% and 13.0% of formed tetra-to octa-CDD/F were distributed into bottom ash, boiler ash, CP ash, BF ash and emission gas, respectively. The corresponding values were 8.6%, 8.0%, 9.4%, 66.7% and 7.3% for RUN2, respectively.

Influence of variation in the operating conditions on PCDD/F distribution in a full-scale MSW incinerator.

Optimizing the operating parameters to minimize polychlorodibenzo-p-dioxins and polychlorodibenzofurans (PCDD/F) emission is the common interest of the municipal solid waste (MSW) incineration industry. In this study, we investigated the distribution of tetra- to octa-CDD/F along the flue gas line in a full-scale reciprocating grate incinerator and evaluated the effects of temperature control and O(2) level on PCDD/F formation. Six runs were laid out and all performed under sufficient burning conditions, in which the combustion efficiency of MSW was more than 99.9%. The total concentration of tetra- to octa-CDD/F measured at the boiler outlet showed an increasing tendency with the increase of boiler outlet temperature (T(B)) from 214 degrees C to 264 degrees C. When flue gas ran across the semi-dry scrubber and cyclone precipitator, in which the temperature varied from 264 degrees C to 162 degrees C, the concentrations of the lower chlorinated dioxins and furans were significantly raised, especially for the TCDF. Increasing O(2) supply from 6.0% to 10.5% essentially led to a higher yield of tetra- to octa-PCDD/F, suggested that under sufficient burning conditions the lower O(2) level was favorable for reducing PCDD/F formation and emission. The variation of O(2) level did not give rise to a systematical change of PCDD/F homologue pattern. For all measurements, the isomer distributions of tetra- to hepta-PCDD/F were more or less the same, nearly independent of variations in the operating conditions and sampling positions. Only the significant increase of the sum of 1,3,7,8-TCDF and 1,3,7,9-TCDF was found in the zone after the boiler section.

[Stabilization of heavy metals in municipal solid waste incineration fly ash with the thiol collectors].

Three kinds of thiol collector, sodium diethyldithiocarbamate (DDTC), potassium ethyl xanthate (EXT) and ammonium dibutyl dithiphosphate (DDTP), were adopted to stabilize heavy metals from municipal solid waste incineration fly ash (MSWI fly ash). The concentration of the three thiol collectors was all 62.5 micromol x g(-1) fly ash. Scanning electron microscopic observation shows that, the thiol collectors evenly cover on the surface of fly ash which makes the angles of mineral crystal ambiguous. Furthermore, the leaching characteristics of heavy metal Cu, Pb, Cd, Cr and Zn in fly ash were analyzed according to the toxicity characteristic leaching procedure (TCLP) and the horizontal vibration method. Comparing with Na2S, thiol collectors present better stabilization effects for Cu and Pb when the extractant is 0.1 mol x L(-1) acetic acid. DDTC stabilizes almost all the acid-extractable Cu, and DDTP stabilizes 69.2% of acid-extractable Pb. When extracted by water, the stabilization ratios of the five heavy metals by DDTC, EXT and DDTP are 72.6%, 73.5% and 76.8%, respectively, significantly higher than that by Na2S (52.4%). The affinity preference of the thiol collectors for the five heavy metals is generally in the order of Cu > Pb > Cr > Cd > Zn. Also, over 60% of the collector participates in the chelating reaction with the acid-extractable heavy metals. Under neutral and alkali condition (pH > 6) the chelators of heavy metal-thiol collector are steady, but partly dissolved under acid condition (pH < 6). Evidently, in order to obtain better heavy metal stabilization effects, it is important to maintain the acid buffer capacity of stabilized fly ash at a higher level.