Study On The Action And Toxicity Inhibition Mechanism Of Pb(Ⅱ)/Zn(Ⅱ)on Xanthate Degrading Bacteria

With the development of economy,the demand of mineral resources continues to increase.During the development of mineral resources,a large number of flotation wastewater containing heavy metals and flotation reagents are produced,which brings serious risk and harm to the environment.Xanthate is the most common mineral dressing agent in flotation reagents,and it has attracted all over the world’s attention.Aiming at the situation of flotation wastewater,this paper studied the effects of plumbum ion/zinc ion on the activity of xanthate degrading bacteria and the tolerance threshold of the xanthate degrading bacteria on the plumbum ions/zinc ions by the determination of the degrading rate of xanthate,COD and NH₃-N,and the influences of plumbum ion/zinc ion on the enzyme activity and extracellular polymer of the degrading bacteria by dehydrogenase,protein and polysaccharide;Scanning electron microscopy（SEM）,FTIR and XPS were used to observe the effects of plumbum and zinc ions on the morphology and functional groups of xanthate degrading bacteria.The following conclusions could be drawn from the results:（1）Pb²⁺had obviously toxic inhibition effects on the degrading bacteria of xanthate.Low concentration of Pb²⁺could inhibit the activity of the xanthate degrading bacteria.With the increase of Pb²⁺concentration,the removal rate of COD and NH₃-N gradually decreased,the activity of dehydrogenase was decreased either,the EPS secretion of the xanthate degrading bacteria was gradually reduced,and the protein and polysaccharide were as well as decreased;When Pb²⁺up to 10mg/L,the large granular colony of the degrading bacteria on the xanthate decreased and the number of channels increased.When the concentration of Pb²⁺reached 50mg/L,the surface of the degrading bacteria was more dense and the channels disappeared;the Pb²⁺could change the structure of the bacteria group and reduce the brightness of theβ-deformia,burktella and Xanthomonas decreased significantly,and the relative content of Pseudomonas aeruginosa decreased either.The results of FT-IR analysis showed that the addition of Pb²⁺had an obvious effect on the surface functional groups of the xanthate degrading bacteria.The Pb²⁺exceeding 10mg/L which had obvious damage to N-H,amides（-CONH-）and O-H in the carbohydrates.The results of XPS analysis showed that when the Pb²⁺was 10 mg/L,C-（O,N）was relatively contained.The relative content of C=O or O-C-O increased slightly,while the relative content of HO-C=O and RO-C=O was relatively stable,and the Pb²⁺of 50mg/L enhanced the toxicity of the xanthate degrading bacteria and destroyed the surface functional groups of the xanthate degrading bacteria.（2）With the increase of zinc concentration,the ORP and pH gradually decreased,and a small amount of Zn ions had a promotion effect on the xanthate degrading bacteria.When the concentration of Zn²⁺was 5mg/L,the degradation rate of xanthate,the removal rate of COD and NH₃-N were all increased,and the zinc ion of 5mg/L could promote the activity of dehydrogenase of the xanthate degrading bacteria,as well as the proliferation of the filamentous bacteria on the surface of the xanthate degrading bacteria,the increase of the pore structure,and the secretion of a large number of EPS by the xanthate degrading bacteria.When the concentration of Zn²⁺exceeded 20mg/L,the degradation rate of xanthate,COD and NH₃-N would be significantly inhibited,the protein and polysaccharide began to change,a amount of bacteria became inactivated at same time,and the concentration of protein and polysaccharide was significantly reduced.The main effects of the xanthate degrading bacteria was that Pseudomonas who played a major role.After adding zinc ions of20mg/L,Pseudomonas decreased significantly.If the concentration of Zn²⁺up to50mg/L,the filamentous bacteria were reduced and the pores were closed;FT-IR results showed that when the concentration of zinc ions was 5mg/L,the surface functional groups of the xanthate degrading bacteria secreted and proliferate,especially the groups of protein and polysaccharide.Besides,the relative content of C-（O,N）decreased,the relative content of C=O or O-C-O increased slightly,the relative content of HO-C=O and RO-C=O was relatively stable;when Zn ion concentration was 50mg/L,the surface functional groups of xanthate degrading bacteria were destroyed,the content of functional groups decreased,C-（O,N）,C=O or O-C-O,HO-C=O and RO-C=O could not peak basically.