| Atrazine(ATZ) and 2,4-dichlorophenoxyacetic acid(2,4-D),as common refractory organic pesticides,are widely used in the agricultural field.The detection amount in water environment is low,usually in the range of nanogram to microgram.ATZ is highly teratogenic and carcinogenic to organisms,and the neurotoxicity of 2,4-D is harmful to human health,which is difficult to be removed by conventional water treatment process.In this study,a kind of Portland cement particles with low cost,easy preparation,easy recovery and less secondary pollution was prepared as a catalyst to investigate the actual performance of its catalytic ozonation degradation of ATZ and 2,4-D,and to explore its reaction mechanism.Silicate particles were prepared by natural air drying at the mass ratio of Portland cement:quartz sand:Deionized water of"4:2:1".The silicate particles were characterized by SEM-EDS,bet and FT-IR,The average pore size,total pore volume and specific surface area of the catalyst are 33.8354 nm,0.083 cm~3/g and 14.847 m~2/g,respectively.The catalyst has uniform particle size and good dispersion.The surface of the catalyst is rich in acicular and thin ettringite,while the interior contains a large amount of calcium silicate polymer.The surface elements Al and Fe are evenly distributed.The catalyst still has good catalytic performance after 30 times of use.The removal efficiency of two kinds of organic pesticides by silicate particles catalytic ozonation is 25%higher than that by ozone alone.The effects of p H,temperature and other parameters on the activity of silicate catalyst were investigated.The results showed that the degradation rate of ATZ and 2,4-D was the highest in the static flow experiment when the dosage of silicate particle catalyst was 20 g/L,the initial p H was 9,and the reaction water temperature was 25℃;It was found that the degradation rate of ATZ and 2,4-D was affected by the dosage of carbonate alkalinity,and the degradation rate and reaction rate decreased with the increase of carbonate alkalinity.The purity of water distribution will affect the performance of silicate catalytic ozonation for the degradation of ATZ and 2,4-D.In this project,the mechanism of catalytic reaction of silicate particles was studied,and it was found that the addition of tert butyl alcohol decreased the catalytic effect and was not completely inhibited,which indicated that hydroxyl radical was the dominant active species in silicate particles/ozone system,and the direct interaction of ozone molecules also existed.Under the condition of continuous flow experiment,the catalytic oxidation system showed a high catalytic removal effect on ATZ/2,4-D when HRT was 25 min(ATZ)or 4.5min(2,4-D),ozone dosage was 1.8 mg/min,and the flow rate of ozonation gas was 0.6 L/min.It was found that the degradation rates of ATZ and 2,4-D decreased slightly with the increase of carbonate alkalinity,but the change range of water quality was smaller than that of the effluent in the static fluid system.In the range of p H 3～9,the degradation rates of ATZ and2,4-D increase with the increase of p H.when p H continues to rise to 11,the degradation rate decreases,and the effluent quality is stable between p H 7～9.In addition,with the decrease of water purity,the catalytic activity of ATZ and 2,4-D decreased significantly. |
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