Regulation Mechanism Of Trichoderma Viride On Pb²⁺ Sorption Onto Mica Minerals

As migrating into the soil,heavy metals（HMs）might undergo physical,chemical,and biological reactions with soil fractions,such as adsorption/desorption,precipitation/dissolution,oxidation/reduction,and biomineralization process.These complex reactions dominate the migration,transformation,and fate of HMs in the soil.Hence,the micro-interface process of HMs in the soil has been a research hotspot and frontier field of environmental science,which has scientific guiding significance for the evaluation and treatment of HMs pollution.Clay minerals and fungal are widely present in the soil and have a vital impact on the environmental chemical behavior of HMs.However,the regulation mechanism of fungal on the HMs enrichment at the clay-water interface is still unclear.In this study,lead Pb²⁺,micas and Trichoderma viride（T.viride）are employed to explore the regulation mechanism of T.viride on Pb²⁺enrichment at the mica-water interface.This study has maintained the following research progress and understanding:（1）Sorption behavior of Pb²⁺on micas is explored.Muscovite,biotite and phlogopite can fix Pb²⁺by sorption and block the migration of Pb²⁺in the soil.The order of sorption capacity for Pb²⁺is:Phlogopite>Biotite>Muscovite,which is related to cation exchange capacity（CEC）of the corresponding mica.The sorption of Pb²⁺by micas increases with the increasing p H（3.3-7.4）,indicating that inner-sphere complexes（ISCs）is an important mechanism for Pb²⁺sorption on micas.Ionic strength also has a significant effect on Pb²⁺immobilization by biotite and phlogopite,confirming that outer-sphere complexes（OSCs）and ion exchange are also the mechanism for Pb²⁺sorption.FT-IR reveals that active groups such as O-H,Si-O and Al-O on micas participate in Pb²⁺sorption.XRD shows that Pb²⁺can enter and expand the interlayer of biotite and phlogopite,and occupy its interlayer sites,which in turn leads to a higher sorption of Pb²⁺on biotite and phlogopite.XPS further indicates that ISCs and OSCs are the main mechanism of Pb²⁺sorption on micas,which is consistent with the results of sorption experiments.（2）Sorption behavior of Pb²⁺on T.viride mycelium is investigated.Sorption experiments show that T.viride mycelium can effectively immobilize Pb²⁺.The Pb²⁺sorption on T.viride mycelium is stronger than that on micas,which is related to the higher surface area and abundant active groups on the surface of T.viride mycelium.FT-IR and XPS further confirm that active groups such as O-H,-NH₂,C=O and P-O participate in Pb²⁺sorption.Moreover,Pb²⁺sorption on T.viride mycelium obviously depends on p H,but is weakly affected by ionic strength,indicating that the ISCs is the main mechanism for Pb²⁺sorption on T.viride mycelium.SEM-EDX and XRD results reveal that Pb²⁺is mineralized as lead phosphate minerals during the interactions with T.viride mycelium,which is also an important way for T.viride mycelium fixing Pb²⁺.（3）Pb²⁺exposure to T.viride is studied.The results show that Pb²⁺exposure can significantly inhibit and delay spores’germination and mycelium growth of T.viride,and the toxic effects increase with the increasing Pb²⁺.Pb²⁺exposure also significantly affects the morphology of the T.viride mycelium.With the increasing Pb²⁺,the diameter of T.viride mycelium becomes larger,and the morphology of T.viride mycelium becomes curled,folded,swollen,and damaged,and even mycelium is cut into irregular particles.The intracellular and extracellular secretions of T.viride also changed with increasing Pb²⁺.Further,the relative content of Pb²⁺loaded on the T.viride mycelium increases with the increasing Pb²⁺in the system,and it is mainly distributed on the cell membrane.The active groups such as O-H,-NH₂,C=O and P-O on the surface of T.viride cells participate in the biosorption and enrichment of Pb²⁺.SEM-EDX,XRD and XPS show that Pb²⁺is mineralized as lead phosphate minerals in the process of biosorption and enrichment,and part of Pb²⁺was reduced to elemental lead.（4）Pb²⁺sorption on the mica-T.viride complex is carried out.The results show that the filamentous branching growth habit and chemical organic nutrition metabolism of T.viride can not only make T.viride colonize on micas,but also make micas weather and cause changes in structure,Zeta potential and CEC.The mica-T.viride complex can effectively adsorb Pb²⁺.The order of the sorption capacity for Pb²⁺is:Phlogopite-T.viride complex>Biotite-T.viride complex>Muscovite-T.viride complex,which is greater than that of corresponding mica.The Pb²⁺sorption on the mica-T.viride complex is obviously affected by p H,but weakly depends on the ionic strength,indicating that ISCs is the main mechanism for mica-T.viride complex adsorbing Pb²⁺.FT-IR and SEM-EDX show that the active groups of T.viride and the weathering of mica co-contribute to the high sorption of Pb²⁺by the mica-T.viride complex.XRD shows that T.viride can accommodate and accelerate the entry of Pb²⁺to the interlayer of biotite and phlogopite,and the biomineralization of Pb²⁺also contributes to the Pb²⁺sorption on the mica-T.viride complex.Moreover,XPS shows that the synergistic effects of T.viride and micas are contributing to Pb²⁺sorption through forming the ISCs and biomineralization.In summary,micas and T.viride in the soil can interact with Pb²⁺,block the migration of Pb²⁺,and effectively attenuate the entry of Pb²⁺into other environmental system.Further,T.viride can accelerate the weathering of micas and influence chemical behavior and occurrence state of Pb²⁺in soil environment.The results of this study can provide an important theoretical basis for accurately and effectively evaluating and predicting the diffusion,migration,retardation,transformation,temporal and spatial distribution and evolution of Pb²⁺in the soil.Also,it can provide important technical support in the prevention,control,treatment,and restoration of the soil environment.