Structure,Composition And Interfacial Properties Of Iron Sulfides Synthesized By Sulfate-reducing Bacteria (SRB)

Recent years,more attention has been paid to the application of nanoparticles in oil reservoirs due to their progress in improving oil recovery.Nanoparticles can not only be used as surfactant,but also compete with surfactants absorbed at the oil-water layer to make them more closely packed,which further reduces the oil-water IFT compared with pure surfactants.Nanoparticles which have the high surface free energy were dispersed not well in the oil-water layer with aggregation.On the other hand,these nanoparticles tend to adsorb amphiphilic compounds such as surfactants in aqueous media,leading to a change of their surface wettability,dispersion stability,particle diameter size and distribution.It is of great significance for considering how to decrease the IFT of oil-water.Sulfate-reducing bacteria(SRB)widely exists in crude oil gathering and injection-production systems.SRB can reduce sulfate to S(II)and react with iron sources to produce iron sulfides.Iron sulfides which have greater specific surface area adsorbing oil droplets form colloidal particles to have oil emulsified.The emulsion process makes oil-water separation difficult and increases the treatment of oil-bearing wastewater.Adsorption of iron sulfides colloid particles at the plate of electric dehydra resulting in the electric field disproportion on the surface makes the electric dehydrator unable to work.At the same time,cottony or lump bacteria adsorb heavy oil particles,mechanical impurities and other small substances together floating between oil and water posing a serious threat to the safe and reliable operation of crude oil dehydration process.The existence of iron sulfides seriously affects the quality of crude oil and reduces the crude oil production rate.Therefore,it is necessary to study the influence of iron sulfides on the interfacial performance of oil/water with surfactants.The main contents are as follows:1.Sulfate-reducing bacteria(SRB)isolated from Daqing oilfield sewage were isolated and purified.Using Fourier transform infrared spectroscopy(FTIR)to identify the SRB.The growth curve of SRB and the adsorption ability of extracellular polymeric substances(EPS)to the Fe²⁺were combined to explore iron sulfides generation.X-ray diffraction(XRD)results showed that different species of SRB produce iron sulfides,mainly composed by Mackinawite.The growth characteristics of SRB affected the formation of iron sulfides and had a negative charge.Various SRB growth trends was different.The growth of the bacterium in an exponential phase or log phase can be described by the greater concentration of inoculation.And smooth growth trend were contribute to the formation of FeS.At the same time,sulfur-rich,like FeS2,was easily formed when S^2-(or S2^2-)played a major role compared with the protein and polysaccharide functional groups in the negatively charged EPS at the process of Fe²⁺adsorption.2.The biological iron sulfides(SRB-Iron Sulfides),which were prepared using sulfate-reducing bacteria(SRB)seprarated from Daqing oilfield wastewater.Non-biologically iron sulfides(Iron Sulfides)and Synthesis of modification iron sulfides(ABS-SRB-Iron Sulfides and ABS-Iron Sulfides)were prepared by crushing crush the bacteria and using Sodium alkyl benzene sulfonate(ABS)to modificate,respectively.They had different surface properties.The physicochemical characteristics such as composition and morphology were characterized by XRD and SEM.The results show that SRB,belonging to the Desulfovibrio,was used to synthesize various biogenic iron sulfides mainly composed of mackinawite.The pyrolysis process of water,organic matter,organic sulfur and iron sulfides in O2 is more complex than that in N2 and the weight loss drops noticeably.ABS is adsorbed on the surface of particles to obtain modified iron sulfides.SRB-Iron Sulfides containing a large number of polar protein peptide bonds(i.e.amide bonds)and polar hydroxyl groups(polysaccharides and oligosaccharides)on the surface of SRB show hydrophilicity.After SRB removal,the hydrophilicity of Iron Sulfides particles decreases due to the presence of organic S in the surface.Therefore,the surfaces of Iron Sulfides are coated by oleophilic long alkyl chain and sulfonate ions is far from the surface through van der Waals force,which resulting in the zeta potential absolute value decrease and good dispersion in water after modification.3.The effects of iron sulfides on the DIFTs of ABS were investigated by the spinning drop methods.The results show that excellent dispersing performance of the modified iron sulfides is presented due to electrostatic repulsion and steric hindrance.Different iron sulfides added to the oil phase effectively reduced the interfacial tension(IFT),and the dynamic interfacial tensions(DIFTs)curves presented the“L”shape.which is followed the adsorption mechanism controlled by diffusion.For iron sulfides,the synergism with ABS is intensive,and a more stable and dense adsorption layer can be formed,leading to the lower IFT.