Effects Of Typical Heavy Metals Release And Microbial Community In Mercury-thallium Mining Waste Slag During The Combined Application Of Fish Manure And Natural Minerals

The Lanmuchang mercury-thallium mine in Southwest Guizhou Province,China,is characterized by rich sulfur and arsenic,and often coexists with toxic heavy metals such as As,Sb,and Hg and accumulates in the sulfides of these elements.Continuous mining since the 1990s(now stopped)have allowed heavy metals to accumulate in the environment,causing problems such as local soil,water,and air pollution,the area has become one of the most seriously thallium-polluted areas.Strong acidity,high toxicity,low nutrition and polymetal combined pollution are the most significant characteristics of the mine yard.Due to the special polluted environment,it is difficult for a single remediation method to achieve the ideal remediation effect,and the combined remediation technology has a more prominent effect on the remediation of heavy metal compound contaminated mining area.In conventional ecological restoration,natural organic matter is often used for nutrient improvement,and chemical heavy metal passivators are added to improve the p H of mining area and reduce the bioavailability of heavy metals.On this basis,vegetation restoration and ecosystem reconstruction are carried out.Therefore,in this study,we amended mercury-thallium mining waste slag with nitrogen-and phosphorus-rich natural organic matter(fish manure)and calciumand phosphorus-rich natural minerals(carbonate and phosphate tailings)as heavy metal passivators to increase the nutrient content,regulate the p H,inhibit the mobility of heavy metals and determine the optimal adding ratio of the modifier.What’s more,we used indoor simulation experiment and pot experiment respectively to study the effect of the combination of fish manure and natural minerals on the migration of heavy metals in mercury-thallium waste slag,the composition characteristics and evolution process of microbial community in the system,and discussed the relevant mechanism.The results of the study are as following,(1)The combined use of fish manure and natural minerals improved the basic characteristics and nutrient status of mercury-thallium mine waste slag.Compared with CK,the p H changed from acidic(p H=3.9～4.44)to moderately alkaline(p H=6.9-7.97),and Eh decreased(from 6.9-7.97 to-52.88 m V ～-20.44 m V)significantly.The average content of organic matter in waste slag increased from 1.01 g/kg to 4.18 g/kg,the average available nitrogen increased from 34.30 mg/kg to 131.22 mg/kg,the average available phosphorus increased from 5.46 mg/kg to 52.99 mg/kg,and the average available potassium increased from 31.52 mg/kg to 332.60 mg/kg.(2)Use of fish manure and natural minerals alone or in combination significantly reduced the biotoxicity of the mining waste slag,in which the combination was more efficient.And the luminescence of the bacteria was negatively related to leaching of As from the waste slag and the proportion of P.When the ratio of fish manure,carbonate,and phosphate tailings was 7:3:0,the relative luminescence intensity of bacteria was the highest,and the leachates from the waste slag had the lowest toxicity..(3)The release of Tl and As from mercury-thallium mine waste slag treated with the combination of fish manure and natural minerals is opposite.In indoor simulation experiment,sterile treatments promoted the release of As but inhibited the release of Tl.In pot experiment,the combination of fish manure and natural minerals inhibited the release of Tl and Hg in the surface and deep mercury-thallium waste slag at the 15 th day.And different treatments promoted the release of Tl and Hg on the 45 th and 75 th day,while As and Sb were released in each time period.On this basis,carbonate and ryegrass further promoted the release of As and Sb,simultaneously inhibits the release of Tl and Hg.The combination of fish manure and natural minerals with the slag can promote Tl dissolution in the order of JF > JFD > JFDZ > MF > MFD > MFDZ(abbreviations mean different treatments),and the promotion effect of As is MFDZ >MFD > MF > JFD > JFD > JF.On the whole,the release laws of Hg and Tl are similar,Sb and As are the samer,while the release laws of Tl and As are opposite.(4)The release of heavy metals from mercury-thallium mine waste slag was significantly affected by non-sterile and sterile treatments.In indoor simulation experiment,addition of fish manure and natural minerals to the non-sterile treatments promoted the release of As and Tl,resulting in an increase in As and Tl concentrations in the tailing lixiviums from 0.57 to 2.38-6.37 μg/L and from 69.92 to 107.51-157.21μg/L,respectively.Sterile treatments promoted the release of As(from 0.28 to 49.88-104.18 μg/L)and inhibited the release of Tl(from 94.53 to 27.60-34.50 μg/L).In pot experiment,the Tl content in the leaching solution was reduced by 63.32-74.20% under the treatment of non-sterile fish manure,and by 87.96-91.31% under the treatment of sterile fish manure at the 15 th day.Sterile treatments had a stronger effect on Tl fixation.(5)The dissolution of minerals in and the release of heavy metals from the slag were closely related to microorganisms after the addition of amendments and passivators.XRD analysis showed that the intensities of the typical peaks of kaolinite and jarosite in the non-sterile treatments were reduced or disappeared,indicating that microorganisms in unsterilized fish manure changed the mineral morphology in the waste slag.(6)Different growth time,different treatments(sterilized and non-sterilized)and different environmental factors significantly affected the diversity and the community structure of microorganisms.The functional microorganisms in the mercury-thallium waste slag treated with fish manure and natural minerals are generally resistant to heavy metals,mainly including organic degrading bacteria and heavy metal tolerant bacteria in Proteobacteria,Actinobacteriota,Firmicutes,Bacteroidota and Chioroflexi.In addition,a large number of sulfur metabolism genes,iron metabolism genes,and heavy metal resistance genes were found in core functional bacteria.Under natural conditions,the microbial composition of each treatment tended to concentrate to some dominant strains with the increase of time,and Actinobacteriota replaced Proteobacteria as the absolute dominant strains after 75 days.