Study On The Performance And Mechanism Of Tetracycline Antibiotics Degradation Based On Steel Slag/persulfate Syste

Steel slag is one of the main solid wastes produced in iron and steel industry.According to statistics,every 3 tons of steel products produced will produce about 1ton of steel slag.However,the comprehensive utilization rate of steel slag in China is less than 30%,and the stock has exceeded 1 billion tons.A large number of steel slags are still stored or buried,which will not only occupy a large amount of land resources,but also cause soil pollution due to the seepage of high-alkaline components contained in it.In addition,a large amount of antibiotics will flow into the natural environment along with biological metabolism and sewage treatment system,and the hidden danger to the ecosystem cannot be underestimated.At present,the main treatment methods of antibiotic wastewater include biological method,adsorption method and advanced oxidation method（AOPs）.Compared with traditional adsorption method,AOPs can oxidize antibiotic molecules into organic intermediates with smaller molecular weight or mineralize them into inorganic substances,fundamentally solving the problem of antibiotic pollution.Persulfate advanced oxidation technology is a new advanced oxidation technology.The oxidizer persulfate used by it has better chemical stability than H₂O₂ in the traditional Fenton oxidation technology,which is convenient for storage and transportation.In addition,the sulfate radical(SO₄^·-)produced by its activation has stronger oxidation capacity and longer life than the hydroxyl radical（·OH）.Based on this,this paper proposed to use steel slag with high alkali characteristics,grinding steel slag powder to obtain steel slag powder（SSP）as a cheap alkali source to activate persulfate to degrade tetracycline antibiotics.It was found that due to the asymmetry of molecular structure of peroxymonosulfate（PMS）,the high alkaline environment produced by steel slag could activate PMS to produce reactive oxygen species and efficiently remove tetracycline（TC）,but did not activate peroxdisulfate（PDS）effectively.In SSP/PMS system,the removal rate of 50 mg/L TC was as high as93.64%,but the total organic carbon（TOC）removal rate was only 30.50%.TC was not completely mineralized and existed in the form of organic intermediates.Inorganic anions CO₃^2-,H₂PO₄^-and organic humic acid（HA）inhibited the degradation process to a certain extent.Radical quenching experiment and electron paramagnetic resonance（EPR）showed that the main reactive oxygen species generated in this system were superoxide free radical(O₂^·-)and singlet oxygen（¹O₂）,and the degradation pathways mainly included demethylation,dehydroxylation,hydroxylation and deamidation.SSP/PMS system not only has excellent TC removal performance,but also has good removal effect on common organic dyes such as methylene blue and congo red.In order to further activate more stable and cheaper PDS with steel slag and improve the mineralization rate of antibiotics,salicylic acid modified steel slag（SA-SSP）was obtained by modifying salicylic acid which selectively dissolves calcium-containing components in steel slag and acts as the catalyst for activating PDS.By SEM-EDS,XRD,FT-IR and XRF characterization,it was found that the calcium content of modified steel slag decreased significantly,the content of Ca O decreased from 36.33%before modification to 20.54%after modification,and more transition metals Fe and Mn with catalytic activity were exposed at the same time.The conversion of low-priced Fe（Ⅱ）to high-priced Fe（Ⅲ）in SA-SSP is the main way to activate PDS,and the main reactive oxygen species produced are·OH and ¹O₂.In the SA-SSP/PDS system,the removal rates of aureomycin hydrochloride（CTC）and TOC were 93.42%and 46.05%,and the degradation process was also inhibited by CO₃^2-,H₂PO₄^-and HA.The degradation pathways of CTC mainly include dechlorination and demethylation.In addition,SA-SSP has a certain degree of reuse and magnetic,easy to separate and recycle.