Study On Alkali Melting And Chlorination Roasting Of Polymetallic Iron Tailings

The excessive production of tailings comes from the unreasonable development and utilization of mineral resources.With the rapid development of society and technology,a large amount of tailings containing a variety of valuable elements had gained re-use value.The recovery of valuable elements from tailings by new technology not only can turn waste into treasure and obtain enormous economic benefits,but also tackles the environmental pollution problem.In according to the basic characteristics of iron tailings from the mine in Guangdong Province,based on the analysis of main components and mineral composition of iron tailings using X-ray fluorescence analysis,X-ray diffraction and scanning electron microscope,this paper adopted the alkali melting-water leaching method to remove and recover the impurity elements Si and Al from iron tailings.The effect of holding time,melting temperature and the addition ratio of Na OH/iron tailings on the enrichment effect of Fe in iron tailings was studied,and the response surface method was used to optimize the process.In addition,the heavy metal element Cr,Ni,Pb,Zn,Cu,in iron tailings were recycled by chlorination and thermal treatment.The effect of different chlorinating agents on the removal of heavy metals at different temperatures was studied,and the leaching toxicity of roasting residue was tested.Finally,the decomposition methods of different chlorinating agents were analyzed.The influence of tailings mineral composition on the chlorination effect of heavy metals was explored.The main research results are as follows:The main elements in the iron tailings samples were Fe,Si,and Al,which were mainly in the form of hematite(Fe₂O₃),quartz(Si O₂),and kaolinite(Al₂Si₂O₅(OH)₄).The chlorine content from iron tailings was only 0.0196%.The analysis results of heavy metal content showed that the contents of Pb,Zn,Cu,Ni,Cr were 1429.0 mg·kg^-1,1434 mg·kg^-1,3005.2mg·kg^-1,22.7 mg·kg^-1,48.8 mg·kg^-1.Through single factor test and response surface optimization test,the best reaction conditions of alkali melting were determined:the holding time was 60 min,the melting temperature was 800°C,the addition ratio of Na OH/iron tailings was 1.20:1.By this time,the Fe₂O₃ content was 89.08%,which was close to the model prediction value of 90.97%.The leaching experiment results showed that the leaching concentration of heavy metal Cr?Ni?Pb?Zn?Cu in roasting residue could meet the regulatory limit of leachate(GB5085.3-2007 Identification standards for hazardous wastes general specifications and the fifth-order index of GB3838-2002 Environmental quality standards for surface water).The alkali melting-water leaching method could achieve the separation of Si,Al and Fe elements in iron tailings,which provided basic data support for the subsequent utilization of iron tailings.The study of chlorination roasting showed that when Al Cl₃?6H₂O as chlorinating agent was added,the highest volatilization ratios of heavy metals Cr,Ni,Pb,Zn,and Cu was lower than 30%due to the prior decomposition of Al Cl₃?6H₂O at 135°C.With the addition of Na Cl,the volatilization ratios of Pb,Zn,Cu achieved above 90%,but only 16.2%of Cr and30.0%of Ni were removed from tailings.The addition of Ca Cl₂ exhibited the best volatilization effect compared to Na Cl and Al Cl₃?6H₂O.The hazardous Pb,Zn and Cu were reduced significantly(97.5%of Pb,99.0%of Zn,93.3%of Cu)at 900°C,and the maximum volatilization of Ni and Cr was 31.9%and 49.5%at 1000°C.The volatility of heavy metals in iron tailings was:Pb>Zn>Cu>Ni>Cr.Adequate chlorine could ensure a higher volatilization ratios of Pb and Zn.The volatilization ratios of Cu was affected by the evaporation rate of Cu chloride,and increasing the temperature could increase the volatilization ratios of Cu.The higher the temperature,the higher the volatilization ratios of Cr and Ni,but the formation of spinel structures such as Fe Cr₂O₄hindered the volatilization of Cr and Ni.The leaching concentration of heavy metals in roasting residue after the addition of Ca Cl₂ and Na Cl could meet the regulatory limit of leachate(GB5085.3-2007 Identification standards for hazardous wastes general specifications and GB16889-2008 Standard for Pollution Control on the Landfill Site of Municipal Solid Waste).The chlorination and thermal treatment could effectively remove heavy metals from polymetallic iron tailings,which provided new strategies for the harmlessness and resource utilization of polymetallic iron tailings.