[Pollution Source Apportionment of Heavy Metals in Cultivated Soil Around a Red Mud Yard Based on APCS-MLR and PMF Models].

In order to explore the characteristics and sources of heavy metal pollution in cultivated soil around a red mud yard in Chongqing， the content and spatial distribution characteristics of eight heavy metal elements （Cd， Cr， Hg， Ni， Pb， As， Cu， and Zn） in the soil were analyzed， and the single factor pollution index method and Nemerow comprehensive pollution index method were used to evaluate the characteristics of heavy metal pollution in soil. On the basis of correlation analysis， the APCS-MLR and PMF models were used to quantitatively analyze the sources of heavy metals. The results showed that the average contents of the other seven heavy metal elements were higher than the background values of Chongqing soil， except for that of Cr. The heavy metals Cd， Hg， and As were moderately polluted， and Pb， Cu， Ni， and Zn were mildly polluted. The spatial distribution pattern of Cr， Ni， Pb， Cu， and Zn in the soil was similar， and there was a very significant positive correlation between them （P < 0.01）. The spatial distribution characteristics of Cd， Hg， and As were significantly different， and there was no significant correlation between them （P > 0.05）. The source apportionment showed that the sources of heavy metals in the soil in the study area were relatively complex， and the APCS-MLR and PMF models could identify the same four pollution sources， namely red mud yard percolation emission and natural sources， thermal power generation emission sources， agricultural activities and natural sources， and non-ferrous metal smelting emission sources. There was little difference in the results of source apportionment between the two models. The contribution rates of the four pollution sources in the APCS-MLR model were 51.8%， 18.0%， 15.9%， and 14.3%， respectively， whereas those in the PMF model were 45.9%， 12.8%， 21.5%， and 19.8%， respectively.

Heavy metal pollution in agricultural soils from surrounding industries with low emissions: Assessing contamination levels and sources.

The potential for heavy metal (HM) pollution in agricultural soils adjacent to industries with elevated HM emissions has long been recognized. However, industries with relatively lower levels of HM emissions, such as alumina smelting and glass production, may still contribute to the pollution of surrounding agricultural soils through continuous, albeit low-level, emissions. Despite this, this issue has not garnered adequate attention thus far. Therefore, this study aimed to assess the extent of HM pollution in agricultural soils adjacent to an alumina smelting and a glass production factory, identifying contamination levels and potential sources through the analysis of input fluxes, isotope fingerprints, and receptor models. Results showed moderate cadmium (Cd) contamination in surface soil, exceeding standards at a rate of 86.36 %. Further analysis revealed that atmospheric deposition was the primary route for Cd input in both paddy fields (89.20 %) and dryland soils (91.61 %). Additionally, the δ114/110Cd values in surface soils indicated that dust played a role in influencing Cd levels in distant surface soils, while raw materials and slags were identified as primary sources near the factory. Industrial sources were considered the primary contributors of Cd in soil accounting for approximately 73.38 % and 82.67 %, respectively, according to the positive matrix factorization model (PMF) and absolute principal component scores-multiple linear regression model (APCS-MLR). Overall, this study underscores the importance of monitoring HMs from industries with relatively low emissions and provides a scientific basis for effectively managing HMs pollution in agricultural soils, ensuring the preservation of agricultural soil quality.

[Characteristics of Mercury Emissions from Modern Dry Processing Cement Plants in Chongqing].

Three typical modern dry processing cement plants in Chongqing were chosen to investigate mercury emission characteristics and its source and fate through a mercury mass balance method by analyzing mercury contents in all input and output materials. The results showed that limestone was the main source of mercury in three cement plants followed by coal, and their mercury concentrations were (0.025±0.001)-(0.032±0.002) mg·kg-1and (0.080±0.002)-(0.110±0.012) mg·kg-1, respectively. The highest mercury level in all required input materials was (0.447±0.007)-(0.525±0.009) mg·kg-1 for gypsum, while the mercury content of other raw materials were very low. Most of the mercury released from these cement plants entered into flue gas, and the mercury of gypsum entered into cement. The mercury emission fluxes were calculated to be (73.42±8.10)-(215.18±10.75) g·d-1 in these three selected plants. The mercury emission factors for clinke and cement (EFclinker and EFcement) were (0.016±0.001)-(0.049±0.001) g·t-1 and (0.011±0.000)-(0.036±0.001) g·t-1, respectively, which were significantly lower than that employed in cement industry according to the foreign mercury emission factors in the past.

[Characteristic of Mercury Emissions and Mass Balance of the Typical Iron and Steel Industry].

To preliminarily discuss the mercury emission characteristics and its mass balance in each process of the iron and steel production, a typical iron and steel enterprise was chosen to study the total mercury in all employed materials and estimate the input and output of mercury during the steel production process. The results showed that the mercury concentrations of input materials in each technology ranged 2.93-159.11 µg · kg⁻¹ with the highest level observed in ore used in blast furnace, followed by coal of sintering and blast furnace. The mercury concentrations of output materials ranged 3.09-18.13 µg · kg⁻¹ and the mercury concentration of dust was the highest, followed by converter slag. The mercury input and the output in the coking plant were 1346.74 g · d⁻¹ ± 36.95 g · d⁻¹ and 177.42 g · d⁻¹ ± 13.73 g · d⁻¹, respectively. In coking process, mercury mainly came from the burning of coking coal. The sintering process was the biggest contributor for mercury input during the iron and steel production with the mercury input of 1075. 27 g · d⁻¹ ± 60.89 g · d⁻¹ accounting for 68.06% of the total mercury input during this production process, and the ore powder was considered as the main mercury source. For the solid output material, the output in the sintering process was 14.15 g · d⁻¹ ± 0.38 g · d⁻¹, accounting for 22.61% of the total solid output. The mercury emission amount from this studied iron and steel enterprise was estimated to be 553.83 kg in 2013 with the emission factor of 0.092 g · t⁻¹ steel production. Thus, to control the mercury emissions, iron and steel enterprises should combine with production practice, further reduce energy consumption of coking and sintering, or improve the quality of raw materials and reduce the input of mercury.