| Arsenic is a ubiquitous metal element.With the wide application of various arsenic compounds,a large number of arsenic enter the soil,water and atmosphere in various forms,posing a great threat to human security.Arsenic ingestion from sewage may lead to arrhythmia,severe muscle spasm,skin damage or cancer,and lead to arsenic poisoning in human and livestock.The serious harm caused by arsenic poisoning is increasingly emerging,which has become one of the issues of universal concern in the world.In this paper,Fe3O4 and CaO2 with simple preparation,low price,environment-friendly,good adsorption and oxidation performance are used as materials to prepare Fe3O4/CaO2 with different proportion and used to remove arsenic in water.The adsorption experiment shows that the adsorption capability is best when the molar ratio of Fe3O4 and CaCl2 is 1:5,so the composite material with this ratio is used as the research object in the subsequent experiments of this part.SEM and EDS showed that Fe3O4/CaO2 composite was successfully prepared.XRD analysis confirmed the composition of the adsorption material.VSM test shows that Fe3O4/CaO2 has good magnetic separation performance.XPS energy spectrum analysis showed that As(Ⅲ)was oxidized to As(Ⅴ)by CaO2 in the adsorption process,and the adsorption mechanism was the ligand exchange of hydroxyl group and arsenic on the adsorbent surface.A series of batch adsorption tests were conducted to find the conditions in which Fe3O4/CaO2 has the best adsorption performance.The experimental data reveal that Fe3O4/CaO2 showed the best property when pH was 6 and the amount of adsorbent was 2 mg/mL.In the process of adsorption,the adsorption rate of the material is fast,the interference of phosphate is insignificant,and it can show good adsorption performance at the initial concentration of 10-100ppb.The adsorption behavior of Fe3O4@DA/CaO2 was more consistent with the Langmuir model,and the maximum adsorption capacity was 56.35 mg/g.The adsorption kinetics study shows that the adsorption behavior of Fe3O4/CaO2 is more consistent with the pseudo-second order kinetics model,which shows that the adsorption of arsenic by Fe3O4/CaO2 occurs mainly through chemical adsorption.The results shows that Fe3O4/CaO2 not only has low cost,simple preparation method,but also has excellent adsorption performance in a wide range of pH and a great application prospect in removaling arsenic from wastewater.The above study found that the combination of Fe3O4 and CaO2 was not good,and the content of CaO2 in the product was only 8.5%.In order to improve the content of CaO2 in the adsorption material,the magnetic adsorption material with oxidation and adsorption ability was prepared by using dopamine(DA)modified Fe3O4 and then compounded with CaO2 by a simple coprecipitation method.Through the conditional feeding ratio,it is found that when the mass ratio of DA to Fe3O4 is 4:1,the modification effect is best.When the molar ratio of Fe3O4@DA and CaCl2 is 1:5,the adsorption performance of the material is the best.Therefore,the composite material of this ratio is used as the research object in the follow-up experiments of this part.Through the SEM characterization of Fe3O4@DA/CaO2 in different feed ratios,it was found that Fe3O4 modified with DA could be well combined with CaO2,and the products were homogeneous complexes;XRD and XPS define the composition of the adsorbent;VSM test confirmed that Fe3O4@DA has good magnetic separation performance.Batch adsorption experiments investigated the optimal adsorption conditions for Fe3O4@DA/CaO2,and evaluated the adsorption isotherms and adsorption kinetics.The experimental results show that when the pH was 7 and the adsorbent dosage was 2 mg/mL the adsorption effect of Fe3O4@DA/CaO2 was best.The adsorption rate of Fe3O4@DA/CaO2 is excellent.And it is only interfered by phosphate to a certain extent.Moreover,the adsorption performance of the material is good when the initial concentration is 10-100 ppb.The adsorption behavior of Fe3O4@DA/CaO2 was more consistent with the Langmuir model,and the maximum adsorption capacity was 46.26 mg/g.The adsorption kinetics study showed that the adsorption behavior of Fe3O4@DA/CaO2 was more consistent with the pseudo-second order kinetic model.It proves the adsorption is chemisorption.The results shows that Fe3O4@DA/CaO2 has a good utilization potentiality as arsenic adsorbentIn the above studies,the content of CaO2 in the adsorbed material was significantly increased,but the accumulation was relatively compact and there was no good three-dimensional structure.In order to make the material have a better structure,a multi-layer core-shell adsorption material was synthesised by combining Fe3O4 and CaO2 with halloysite as matrix after DA modification.SEM and TEM determined that the products were tubular composites.XRD and XPS confirmed the mechanism of adsorption was the ligand exchange of hydroxyl and arsenic on the adsorbent surface.Batch adsorption experiments investigated the optimal adsorption conditions of HNTs@DA/Fe3O4/CaO2,and evaluated the adsorption isotherms and adsorption kinetics.The experimental data reveal that HNTs@DA/Fe3O4/CaO2 showed the best property when pH was 6 and the amount of adsorbent was 5 mg/mL.In the adsorption process,the adsorption rate of HNTs@DA/Fe3O4/CaO2 is excellent.The material is subject to certain interference of phosphate.Moreover,the adsorption performance of the material is good when the initial concentration is 10-100 ppb.The adsorption behavior of HNTs@DA/Fe3O4/CaO2 was more consistent with the Langmuir model,and according to the Langmuir model,the theoretical maximum adsorption capacity was 152.26 mg/g;the adsorption kinetics study showed that the adsorption behavior of HNTs@DA/Fe3O4/CaO2 was more consistent with the pseudo-second order kinetic model.It proves the adsorption is chemisorption.The results shouws that HNTs@DA/Fe3O4/CaO2 not only has low cost,simple preparation method,but also has excellent adsorption performance in a wide range of pH and a great application prospect in removaling arsenic from wastewater. |
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