Study On Nano-zero-valent Iron Loaded Spent Bleaching Earth Carbon Mediated Removal Of Typical Cl-PhACs From Water

Spent bleaching earth（SBE）is an industrial waste produced after the bleaching of crude oil in the vegetable oil refining industry.SBE was pyrolyzed under anaerobic conditions to obtain spent bleaching earth carbon（SBE@C）,and on this basis,magnetic spent bleaching earth carbon（n ZVI/CTAB-SBE@C and S-n ZVI/CTAB-SBE@C）were prepared.Diclofenac（DCF）,a drug compound widely existing in water,was removed.Through the characterization and analysis of the material,the reaction mechanism was determined.Reuse of resources for SBE had realized the use of waste to treat waste,which had good environmental benefits.The specific research results are as follows:（1）SBE was treated by pyrolysis to obtain SBE@C,which was modified with cetyltrimethylammonium bromide（CTAB）to obtain CTAB-SBE@C,and nano-zero valent iron was loaded by liquid-phase reduction method to prepare n ZVI/CTAB-SBE@C.The effects of CTAB concentration,Fe⁰ loading,n ZVI/CTAB-SBE@C dosage and initial p H on the removal efficiency of DCF were investigated.The results showed that under the conditions of CTAB concentration of 30 mmol/L,Fe⁰ loading of 25%,initial p H value of 5,and material dosage of 2.0 g/L,the removal efficiency of DCF could reach up to 87.0%.This indicated that the strong adsorption of the material and the degradation of n ZVI could achieve efficient removal of DCF.The adsorption mechanism was mainly hydrogen bonding,π-πinteraction and electrostatic interaction,and the degradation mechanism was the reduction of n ZVI and the oxidation of?OH and O₂^?-.Based on the detected reaction intermediates,four possible degradation pathways for DCF were deduced.Furthermore,the toxicity assessment of DCF and its intermediates revealed that the degradation of DCF by n ZVI/CTAB-SBE@C was a process of gradual dechlorination and reduced toxicity.（2）On the basis of CTAB-SBE@C,the nanomaterial S-n ZVI/CTAB-SBE@C was obtained by loading sulfided nano-zero-valent iron on CTAB-SBE@C by liquid-phase reduction method.The effects of Fe/S ratio,S-n ZVI/CTAB-SBE@C dosage and initial p H on the removal efficiency of DCF were investigated.When the Fe/S ratio was 5/1,the initial p H was 5,and the dosage of S-n ZVI/CTAB-SBE@C was 2.0 g/L,the removal efficiency of DCF was up to 83.3%,and the degradation efficiency was 80.2%.The core-shell structure of S-n ZVI/CTAB-SBE@C slowed down the corrosion rate of Fe⁰ and greatly improved the degradation efficiency of DCF.The free radicals that had a major impact on the reaction were mainly O₂^?-,SO₄^?-and?OH had relatively minor effects.The toxicity assessment of DCF and its intermediates showed that the acute toxicity of most intermediates was significantly reduced after DCF degradation,the degree of bioaccumulation was reduced,and they were transformed into developmentally non-toxic substances.DCF and all products had negative mutagenicity.（3）Based on the above studies,the removal of clofibric acid（CA）and DCF coexisted by n ZVI/CTAB-SBE@C was investigated.The effects of reaction time,dosage,temperature,actual wastewater,humic acid and coexisting ions on the removal of DCF and CA were investigated.Compared with the single DCF system,the removal efficiency of DCF in DCF+CA was higher,indicating that the presence of CA had a promoting effect on the removal of DCF.When K⁺,Mg²⁺and Al³⁺coexisted in the system,the presence of K⁺had the most significant inhibitory effect on the removal of DCF,and the inhibitory effect of Mg²⁺was less than that of K⁺.The presence of Al³⁺could promote the removal of DCF.According to the 16 intermediate products in the DCF degradation process detected by HPLC-MS,five possible degradation pathways were deduced:decarboxylation reaction,dechlorination reduction reaction,hydroxyl addition reaction,demethylation and hydroxyl substitution reaction.By evaluating the toxicity of DCF and its intermediates,the acute toxicity of most intermediates was significantly reduced after DCF degradation,and the product P16 was actually non-toxic.DCF and all products were negatively mutagenic and the bioaccumulation of most products was reduced.However,in addition to P8 and P16,the products generated during the reaction were still developmental toxicants and might require deeper degradation.