Study On The Heavy Metal Of Mn, As And Pb In Waste Manganese Rock:Chemical Speciation,Leaching Characteristics And Mechanism

In the long-term activities of manganese mining,it produced a large of manganese ore waste rock with toxic and harmful.These manganese waste rocks not only occupy a large of land area,but also global pollutants like manganese and its associated heavy mentals,which dissolved and released under the condiction including shearing,impact and leaching from rainfall,snowing and weathering.Under such conditions,a typical point pollution source with complex heavy metals is formed,which causes serious damage to humans and the surrounding ecosystem,brings a series of environmental problems.The manganese waste rocks at Hongqi Mining in Xiangtan City,Hunan Province(China's manganese capital with a century-old reputation),as the research object for this paper.In this paper,the content of elements in waste rock,chemical speciation of major heavy metals(Mn and Pb),the release law of heavy metals(Mn,Pb and As)in leaching and its release kinetic model were systematically studied by field sampling,simulation experiment in laboratory,measurement and characterization methods.Come to the following conclusion:(1)The content of basic elements,phase composition and chemical speciation of Mn and Pb in manganese waste rock have been research by Inductively Coupled Plasma Optical Emission Spectrometer(ICP-OES),X-Ray Diffraction(XRD)and Tessier Extraction Methods.The results show that the content of Mn and associated heavy metals(such as:As,Pb,Cr,Cu,etc.)is high,and the total contents of Mn,As and Pb exceed the soil background values of Hunan Province by 26.7,8.5 and 2.6 times,respectively.Manganese waste rock mainly contains alkaline minerals(such as:quartz),so that the pH value of contaminated stream is maintained at 6.05~8.0;Similar to the results of XRD analysis,Mn and Pb present in the residue form and the other less,but there will be speciation transformation between different forms due to environmental changes..(2)The effects of stir,solid-liquid ratio(S/L)and particle size were studied on dissolution test about Mn,As and Pb.The results show that the stir can increase the concentration gradient of heavy metals in the leachate,the strength of hydraulic shear and particle collision probability,which contribute to the dissolution and release of heavy metals;The small particle size were significantly higher than large in the leaching concentration and dissolution rate of heavy mentals,especially Mn and As;the leaching concentration and dissolution release rate of Mn and Pb did not effect much in S/L,but As was higher than other conditions when the solid-liquid ratio was 1:20.It indicates that the effect of solid-liquid ratio is affected by the heavy metal itself.(3)The effects of rainfall intensity,pH value of rainfall and rainfall duration were studied on leaching test about Mn,As and Pb.Under the experimental conditions,rainfall intensity has little effect on the dissolve and release of Mn and Pb,at the same time the light rainfall(80 mL/h)was benefited of the release of Mn and Pb in early time,but the rainfall intensity(200 mL/h)was benefited of the release of As;Under different pH value of rainfall,the alkaline condition(low pH value)was benefited of the release of Mn,the acidic condition(high pH value)was benefited of the release of Pb,and the pH value had little effect with the release of As.In the alternating natural environment of drg and wet,the three heavy metals react differently to rainfall(rainfall duration),and heavy rainfall(long-rainfall duration)is more conducive to heavy metal dissolution and release.In particular,in the early time,the long rainfall duration contributed to the increase of the total release of heavy metals.(4)In the leaching test,the high-conductivity mixed-type pollution stream in the leaching are mainly composed of Mn and its associated heavy metals(As,Pb,Cr,Cu and Zn)and Na,K,Ca and others.Under the combined action of the mineral-liquid-solid,the sulfide and alkaline minerals(predominant)in the manganese waste rock play a good buffering role,so that the leaching solution can be maintained neutral or alkaline regardless of the initial pH value.During the migration process,the main loss of Mn during leaching is exchangeable form,and some exchangeable form of Mn released under hypoxia and alkaline conditions in the lower layer will be transformed into carbonate form and organic-sulfide form.(5)The fitted kinetics model of heavy metal release show that,the data are fitted by Elovich-equation model,the Double-constant-equation model and the S-curve-DoseResp equation model in the toxic leaching test,as the fitted results:the double constant equation is more suitable for Mn,the Elovich equation is more suitable for Pb,the results of the two equations are similar to As.the release rate of Mn,Pb and As slows down at about the 8th,3th and 6th days by DoseResp equation.In the leaching test of drg and wet,the cumulative equations are quadratic function and R~2>0.98,which is more consistent with the relationship between cumulative release of heavy metals and rainfall in the absence of apex.