Interaction Of Heavy Metals In Tailings With Cyanobacteria And Natural Alga-bacteria Biofilm

Large amount of tailings were produced in mining and smelting,the ecological environment problems caused by soluble heavy metals are increasingly prominent.The open-air stacking of tailings causes its soluble heavy metals to leach and migrate,causing serious pollution to the surface environment around the mining area.Cyanobacterias were used as experimental materials to study the toxic effects of leachate on cyanobacteria photosynthesis in four typical tailings Xinjiang tailings,such as Pb-Zn,Cu-Ni,Cu-Mo,Au,such as the reaction center activity of the photosynthetic system and the photosynthetic oxygen rate of leaves.In order to further explore the mechanism of heavy metals and cyanobacteria in the tailing filtrate,the biological membrane of the algae in the natural water environment was used as the experimental material to study the mechanism of the biofilm and the heavy metal,and the removal efficiency of the heavy metal AS and Hg by the biofilm.In this study,the complex coordination of 5 kinds of heavy metal ions in the algae biofilm EPS（extracellular polymer）and the lead zinc tail slag in the natural lakes of arid areas were studied by using the three-dimensional fluorescence spectroscopy.The adsorption of AS and Hg by biofilm and the removal of typical heavy metals in the tailing filtrate were studied by shaking flask experiments.The results show that:（1）The heavy metal elements in the four tailings leaching filtrate determined were Cr,Co,Ni,Cu,Zn,Cd,Pb,As and Hg.The contents of Cd,Co,Ni,Zn,Pb,As and Hg in tailings all exceeded the reference values of GB 15618-1995 soil environmental quality standards（2）In Pb-Zn,Cu-Mo,Cu-Ni,under three kinds of tailing leaching filtrate stress significantly lower blue-green fluorescence value,PSII function was damaged,and the zinc content in the Au ore than other tailings leaching filtrate content is higher,enhance algae body PSII physiological activity,cyanobacteria PSII function has not been damaged.（3）Under the stress of tailings leaching filtrate,the photosynthetic action of algal was weakened,and the changes of photosynthetic oxygen release rate and chlorophyll fluorescence parameter Fv/Fm were consistent,with different degrees of reduction.（4）Two fluorescence peaks can be detected from EPS fluorescence spectra of algal biofilms,all of which are derived from aromatic protein tyrosine substances.（5）Heavy metals in the lead-zinc tailings leachate mainly include Pb,Co,Ni,Zn,Hg,Cu,As and Cd,and these 8 metal ions can effectively extinguish the fluorescence of EPS.（6）Fluorescence quenching titration test results:Hg²⁺and EPS have the strongest complexation ability,the maximum complexing constant is 8.1605,the maximum number of binding sites is 1.4291,the complexing ability of Cd²⁺and EPS is the weakest,the maximum complex constant is 1.9571,the maximum number of binding sites is 0.6848,and the complexing ability of Co²⁺,Ni²⁺,Zn²⁺,Pb²⁺,As³⁺and Cu²⁺is similar to EPS.The study shows that the effect of the fluorescent groups in the biofilm EPS on the metal ions is related to the type of metal ions.Complexation and coordination of the two can affect the chemical morphology,migration,bioavailability and ecotoxicity of heavy metals in water environment.Therefore,algal biofilms and their EPS have certain effects on the removal of typical heavy metals in the tailings filtrate.（7）In the range of 0-350 mg/L concentration,two adsorption isotherms of Freundlich（F）and Langmuir（L）can well describe the adsorption of As³⁺and Hg²⁺by biomembrane.The adsorption capacity of algal biofilm for two heavy metal ions was found to be As³⁺>Hg²⁺.These two heavy metal ions conformed to the two level kinetics characteristics.The adsorption of As³⁺and Hg²⁺by biofilms reached equilibrium within a few hours.（8）The results of scanning electron microscopy showed that the typical heavy metal elements in the tailings were absorbed by the algae or could be complexed by the extracellular polymer（EPS）of the algae and removed from the aqueous solution.（9）The concentration of As and Hg in the supernatant continued to decrease,while the accumulation of biofilm continued to rise,and the amount of As and Hg accumulated in the biofilm showed the opposite change with the concentration in the supernatant.This indicates that As and Hg have certain toxic effects on the biofilms of the bacteria.