Catalytic Treatment Of Xanthate Wastewater Through Advanced Oxidation Processes Catalyzed By Bentonite-based Bismuth Ferrites Activated Via Mechanical Activation

In the flotation process,xanthate is the most common sulfide mineral collector,which can collect all heavy metal sulfide minerals.In the process of mineral flotation,after flotation of iron,copper,lead,zinc and other metals,a large number of toxic alkyl xanthates remain in mineral processing wastewater,which can cause serious pollution to the environment of mining areas.If the toxic flotation wastewater containing alkyl xanthates is not treated in time,the ecological environment of many mining areas will further deteriorate,and water and soil will be seriously polluted,which will cause great harm to human health,agricultural production and fishery.Thus,it is of significance to develop efficient treatment methods of xanthate wastewater and study the degradation law of xanthate for mineral processing wastewater treatment and environmental protection.The traditional treatment methods of mineral processing wastewater containing xanthate have some shortcomings such as high cost,long treatment time and low degradation efficiency.However,the advanced oxidation processes（AOPs）exhibit the advantages of high efficiency,simple operation and no secondary pollution.Hence,it is of great practical significance to develop advanced oxidation technology for degrading xanthate in mineral processing wastewater.In this work,the activated bentonite-based bismuth ferrites（A-BiFe/Bent）,modified by mechanical activation,was used as catalyst,and ethyl xanthate（EX）was used as the model pollutant.High-efficient and economic AOPs,including photo-Fenton,the three-dimensional electrode electro-Fenton under visible-light（Vis-3D/EF）and persulfate-based advanced oxidation process,were applied to degrade EX.Main research contents and results are as follows:using A-BiFe/Bnet as catalyst,the degradation of EX via the photo-Fenton process under visible light has been studied.The optimum conditions for EX degradation in the photo-Fenton process were as follows:natural p H（6.82）,catalyst dosage 0.4 g·L^-1,H₂O₂dosage 33.67 mg·L^-1and reaction temperature 30°C.Under the optimum conditions,it was found that the degradation efficiency of EX at 120 min and the removal percentage of COD_Crat 300 min was 98.43%and 86.01%,respectively.According to the UV-Vis,¹H NMR,LC-MS analyses,it could be found that EX molecules were firstly transferred into some intermediates,including ethyl perxanthate（EPX）,ethanol and thiosulfate.And then the intermediates were further degraded to inorganic small molecules as per the FT-IR analysis.Moreover,the XPS analysis proved that EX molecules were adsorbed on the A-BiFe/Bent surface by Bi-S and Fe-S bonds.The toxicity test demonstrated that the toxicity of degraded EX solution evidently reduced compared with that of initial EX solution.In photo-Fenton degradation of EX,A-BiFe/Bent composite exhibited high settleability,good magnetism,great reusability and low Fe leaching,which provided the necessary conditions for A-BiFe/Bent used in real xanthate wastewater treatment.The effects of co-existing substances in mineral processing wastewater containing xanthate on the degradation of EX in photo-Fenton were investigated.The results show that Na⁺,K⁺,Mg²⁺and Ca²⁺exhibited relatively weak negative effect on the photo-Fenton degradation of EX.A certain concentration of Cu²⁺and Pb²⁺could promote the degradation of EX.Whereas,excess Cu²⁺and Pb²⁺would cause the elimination of hydroxyl radicals（·OH）,resulting in the decrease of the the degradation efficiency of EX.Anions such as CO₃^2-,HCO₃^-,S^2-,SO₄^2-,Cl^-and NO₃^-had inhibiting effect on the degradation of the EX degradation and the inhibiting effect of S^2-was strongest among these anions.Terpenic oil had no obvious effect on the degradation of EX in photo-Fenton process.The effective removal of n-butyl xanthate and isopropyl xanthate was achieved in this photo-Fenton reaction catalyzed by A-BiFe/Bent.A-BiFe/Bent as particle electrodes were employed to degrade ethyl xanthate（EX）in a 3-dimensional Electro-Fenton system under visible light（Vis-3D/EF）.The optimum conditions for EX degradation in the Vis-3D/EF reaction system were as follows:electrolyte of Na₂SO₄0.10mol/L,A-BiFe/Bent 1.0 g/L,applied voltage 10 V,aeration intensity 3.5L/min,and natural p H（ca.6.82）.Under the optimum conditions,the degradation efficiency of EX and the COD_Crremoval efficiency respectively reached 97.85%and 93.50%at 150 min.The degradation product of EX in the Vis-3D/EF system catalyzed by A-BiFe/Bent particle electrodes was comprehensively explored by UV-Vis,¹H NMR,LC-MS and FTIR techniques.It was found that EX was directly degraded into CO₂,H₂O and SO₄^2-during the photoelectrocatalytic degradation.Based on the analysis results of XPS,quenching experiment and ESR,the possible mechanism for the photoelectrocatalytic degradation of EX in the Vis-3D/EF system catalyzed by A-BiFe/Bent particle electrodes was proposed.The reasons for the highly oxidative capacity of Vis-3D/EF reaction system catalyzed by A-BiFe/Bent were mainly attributed to the high-efficient generation of H₂O₂,multiple generation sources for active species,and participation by all active species（·OH,h⁺and·O₂^-）.The results of comparative experiment and kinetics indicate that a significant coupling effect between photocatalytic action and 2-dimensional electrode reaction existed in the Vis-3D/EF system.A-BiFe/Bent presented good recycling efficiency and high stability during the photoelectrocatalytic degradation of EX.Photo-assisted activation of persulfate by using A-BiFe/Bent（Vis-A-BiFe/Bent-PS）process was applied to degrade EX.The optimum conditions for EX degradation in the reaction system were as follows:PS concentration 0.006 mol/L,catalyst dosage 0.8 g/L,30°C of reaction temperature and natural p H（ca.6.82）.At the optimum conditions,the degradation efficiency of EX and the COD_Crof degradation efficiency of EX reached 98.67%and 97.88%,respectively.The inhibiting effect of different anions increased in the order of SO₄^2-<NO₃^-<Cl^-<HCO₃^-.In the presence of the above anions,corresponding the kinetics constants were 0.0495 min^-1,0.0286 min^-1,0.0279 min^-1,0.0210 min^-1,respectively.Also,with the increase of above concentration of anions,the inhibiting effect of these coexisting anions gradually increased.According to the results of UV-Vis spectrum,COD_Crmeasurement,quenching experiment and ESR analysis,possible degradation mechanism of EX in Vis-A-BiFe/Bent-PS reaction system was proposed.Besides,EX could be effectively degraded in this Vis-A-BiFe/Bent-PS system in media of laboratory tap water and Bihu water.Under the same reaction conditions,the degradation efficiency of isopropyl xanthate and butyl xanthate reached 99.78%and 99.84%,respectively.