| The organic sulfhydryl compounds is one of the most commonly used collector agent in sulfide flotation.Sodium diethyldithiocarbamatre (DDTC) is a kind of effective sulphur flotation capture reagent. Most DDTC will react with sulfide mineral and elect the useful metal, and water residue DDTC can cause great harm to the water environment. In the meanwhile, "Lead-zinc industry emission standards"(GB25466-2010) implemented in 2012 has higher requirements to control the water pollution of Pb-Zn flotation wastewater. In order to effectively remove the residual DDTC in the environment, it is very important to explore its degradation behavior and mechanism.This study used ozonation methods to treat the DDTC in simulation wastewater. The migration characteristics of carbon, sulfur and nitrogen in simulation wastewater were studied. The products of ozonation were analyzed. In the meanwhile, the ozone oxidation degradation pathways and mechanisms of DDTC was studied.Firstly, the experiment investigated the decomposition of 100 mg/L DDTC simulation wastewater by 5 g/h of ozone. The results demonstrated that after 15 min, the removal rate of DDTC could reach to 100%. However, the removal rate of TOC were 20.79%. It is shown that DDTC is not mineralized completely in the ozonation process, and generated small stable molecule organic matter in water. The pH in simulation wastewater was decreased from 8.47 to 3.18.Secondly, the migration characteristics of carbon, sulfur and nitrogen in DDTC during ozonation were analyzed by TOC analyzer, Ion Chromatography and methods for chemical analysis. When DDTC was decomposed completely,80.07% of the carbon and 53.4% of the sulfur were determined in the liquid phase system,19.93% of the carbon and 46.6% of the sulfur were determined in gas phase system, and 100.00% of nitrogen was determined in the liquid phase system. The carbon and sulfur in liquid phase system is in form of TOC and SO42-, the nitrogen in liquid phase system is in form of NH4+-N (31.29%)、 NO3-N (8.34%) 'DON-N(60.37%)It can speculate that, at the beginning of the reaction, the HO2,·O2- and H+ are generated by indirect reaction of ozone in the wastewater. The HO2 and ·O2- are reacted with thiol preferentially and generate SO42-. The rest of H+ make the pH decrease. In addition, intermediate can also lead to lower pH, Such as 1,1-diethyl amino carbonyl formic acid. Hydroxyl free radical inhibitors (HCO3- and HSO4-) inhibited the indirect reaction of ozone in aquatic, resulting in the late reaction of pH tend to be stableThirdly, the ozonation products were determined by GC/MS and LC/MS. Then its oxidative decomposition approach and mechanism were derived. The results showed that the DDTC was dissociated into C5H10NS2- and Na+ in liquid phasehe before ozone oxidation treatment. And free C5H10NS2- could be combined with C5H10NS2S2NHi0C5(TETD). When O3 was bubbled into the system, its direct oxidation and indirect oxidation were combined, organic chemical bonds were destroyed, finally,DDTC was oxidized into N, N-diethyl formamide (C5H11NO). In addition, there could be SO42-,NO2-, NO3- and NH4+ in the liquid phase,Finally, the deep purification test of flotation wastewatera from a certain lead-zinc mine in guangxi by ozone-coagulation sedimentation method was discussed, and then the related mechanism was discussed. The results showed that most of the organic phosphorus could be transformed into inorganic phosphorus by ozone oxidation and then be removed by coagulation sedimentation. The total phosphorus (TP) in tailings discharged wastewater concentrations dropped from 1.4-1.7mg/L to 0.2-0.4mg/L, which is significantly lower than the "lead and zinc industry pollutant discharge standard" (GB25466-2010) of 1.0 mg/L emission standards. |
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