| The environmental pollution of non-ferrous metal smelting sites is serious,especially Cd,Zn and other heavy metals pollution.At present,microbial remediation of heavy metal pollution is a research hotspot,but it has problems such as long remediation period and poor adaptability of bacteria to high-concentration pollution.FCC waste slag,a kind of industrial solid waste slag,has the potential of high-capacity adsorption of heavy metals,which can be used as a passivator for high-concentration heavy metal pollution,buffer the pressure of microbial remediation,provide an advantageous environment for microbial remediation,and greatly improve the efficiency of microbial remediation.This study takes a nonferrous smelting site in Guangxi as the research object,investigates and analyzes the characteristics of heavy metal pollution in the soil of a non-ferrous smelting site,and explores the remediation effect of Cd and Zn in soil and key influencing factors in the three stabilization systems,including sulfate-reducing bacteria(SRB),FCC waste slag and FCC waste slag enhanced SRB.And the remediation mechanism has been deeply explored.The main contents and results are as follows:In this paper,the sources,distribution characteristics,pollution degree and leaching toxicity of heavy metals in non-ferrous smelting site were systematically studied by correlation analysis and principal component analysis.The study showed that that there are many heavy metal exceeding standards in the soil of the smelting site,among which the leaching toxicity of heavy metals is only Cd and Zn exceeding the standard,with the maximum exceeding multiples are 697.36 times and 33.81 times respectively.The groundwater also showed the problem of heavy metals exceeding the standard.The excessive elements were Cd and Zn,with the maximum exceeding multiples were 13.30 times and 19.60 times respectively.Therefore,Cd and Zn pollution in the smelting site needs to be treated urgently.The effects of electron donor and environmental factors on SRB stabilization of Cd and Zn were comprehensively analyzed,and the optimal experimental parameters of SRB remediation was obtained:sodium lactate with 1.82 g/L,temperature of 30℃,initial Ph of 6.5 and inoculation amount of 10%.The mechanism of SRB on the stabilization of Cd and Zn pollution was further discussed by means of SEM,TEM,EDS and other characterization methods,which mainly included the adsorption of Cd and Zn by proteins,polysaccharides and lipids on the surface of SRB and the induction of Cd and Zn sulfide precipitation by SRB.Zinc cadmium sulfide(Cd0.22Zn0.78S)with definite crystal structure was found in the precipitated products.The isothermal adsorption,kinetic process and mechanism of Cd and Zn adsorption by FCC were systematically discussed.The results showed that the FCC waste slag could efficiently adsorb Cd and Zn.The maximum adsorption capacity of Cd and Zn in single system was 87.95 mg/L and 101.12 mg/L,respectively.The maximum adsorption capacity of Cd and Zn in composite system was 66.55 mg/L and 71.92 mg/L,respectively.The main mechanism of Cd and Zn adsorption by FCC waste slag is the ion exchange of Na+.The adsorption of Cd by FCC waste slag was monomolecular chemisorption,while the adsorption of Zn was monomolecular chemisorption and multilayer physicochemical adsorption.Compared with other solid waste stabilization materials,the leaching toxicity of Cd and Zn with high concentration in soil reduced by 92.49%and 89.09%,respectively,with only 0.8%addition of FCC,which significantly reduced the capacity enhancement ratio of stabilization and provided data support for enhancing SRB remediation.The effects of soil leaching and remediation by SRB,FCC waste slag and SRB enhanced by FCC waste slag were comprehensively compared,and the migration and transformation law and mechanism of Cd and Zn in soil in the remediation process of SRB enhanced by FCC were deeply studied.The results showed that the remediation effect ofSRB enhanced by FCC waste slag was the best.After 28 days of action,the Cd and Zn concentration in the soil leaching solution would reduced and maintained below the groundwater(Class Ⅳ)standard limit for a long time,and the permeability of the contaminated soil would greatly reduced.And the migration of Cd and Zn were significantly inhibited.,as the proportion of residual Cd and Zn in soil increased.In addition,by strengthening the regulation of SRB through the FCC,the soil microbial community structure was reshaped,the abundance of Desulfitobacterium was significantly increased,and the growth of acid-producing microorganisms was significantly inhibited.The reduction of soil permeability and the stable growth of the dominant bacterium Desulfitobacterium can maintain the soil reduction atmosphere and inhibit the oxidative dissolution of the reduced metal sulfide precipitation products.The remediation mechanism of SRB enhanced by FCC waste slag was that the FCC waste slag absorbed Cd and Zn with high concentrations in the solution through ion exchange,promoted the growth of SRB and provided a suitable remediation environment.Then,the S2generated by reducing SO42-by SRB first reacted with free Cd and Zn,and then reacted with Cd and Zn adsorbed by the FCC waste slag to form metal sulfide precipitates,and gradually formed a mineral film to realize the stabilization of all Cd and Zn in the system.In this study,on the basis of using SRB to remediate Cd and Zn pollution in soil of non-ferrous smelting site,the method of using FCC waste slag with high adsorption capacity and low-capacity enhancement ratio to strengthen SRB stabilization of Cd and Zn was proposed,so as to improve the remediation efficiency of single technology,reduce soil permeability,and increase the dominant ratio of SRB and other remediation bacteria.It is expected to provide theoretical basis and technical support for low-cost and efficient treatment of soil heavy metal pollution in non-ferrous smelting sites,and provide a new application approach for resource utilization of industrial solid waste-FCC waste slag. |
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