Study On The Adsorption Performance Of Composite Mineral Adsorbents For Arsenic And Selenium

Municipal sewage sludge will be obtained after the dewatering treatment of urban sewage.Due to the wide range of sewage sources,the substances contained in urban sewage sludge are also diverse.The harmful substances arsenic and selenium contained in the sludge will be enriched in the fly ash in the gaseous form of AS2O3 and SeO2 when the sludge is incinerated.If it is directly discharged into the atmosphere,it will cause great harm to humans and the environment.Therefore,it is very important to study how to remove arsenic and selenium in fly ash better and more effectively.This article is processed by using minerals to adsorb arsenic and selenium.The adsorbents studied include CaCO3,Fe2O3,Al2O3 and molecular sieves,the effects of temperature and SO2 concentration on the adsorption of arsenic and selenium were also explored.The adsorption of arsenic and selenium was studied by the method of experiment in a vertical furnace,and the experimental results were characterized.The reaction mechanism was analyzed and discussed,which provided reference value and pointed out the research direction for further research on the adsorption of arsenic and selenium in the sludge incineration process.The adsorption performance of CaCO3 and Fe2O3 on AS2O3 and SeO2 volatilized during sludge incineration was studied through vertical furnace experiments,and explored the adsorption performance of the composite adsorbent to As2O3 and SeO2 when CaCO3 and Fe2O3 are mixed according to different mixing ratios.Research indicates:The adsorption of AS2O3 and SeO2 by CaCO3 and Fe2O3 is mainly chemical adsorption.CaCO3 and As2O3 react to form Ca3(AsO4)2,CaCO3 and SeO2 will react to form CaSeO3 and CaSeO4 depending on the temperature.Fe2O3 and As2O3 react to form FeAsO4,Fe2O3 and SeO2 react to form Fe2(SeO3)3.And the adsorption performance of CaCO3 is stronger than Fe2O3.The composite adsorbent itself will undergo a chemical reaction to form Ca2Fe2O5 and CaFe2O4,and adsorb As2O3 and SeO2 simultaneously.The adsorption effect of composite adsorbent will be better than that of single adsorbent.And when the mixing ratio of CaCO3 and Fe2O3 is 3:1,the adsorption effect is the best.The effects of temperature and SO2 concentration on the adsorption of arsenic and selenium were also studied.The results of the study showed that:When CaCO3 is used as the adsorbent,the best adsorption temperature is 900℃,and the addition of SO2 will inhibit the adsorption of As2O3 and SeO2 by CaCO3.When Fe2O3 is used as the adsorbent,the best adsorption temperature is 800℃,and the addition of SO2 will promote the adsorption of Fe2O3 to As2O3 and SeO2.Al2O3 and molecular sieve have larger specific surface area and pore structure,which can provide more adsorption sites for the adsorption of arsenic and selenium.Therefore,the adsorption performance of Al2O3 and molecular sieves on As2O3 and SeO2 was studied,and Al2O3 and molecular sieves were metal loaded.The supported metal ions are Ca2+and Fe3+,to study the adsorption performance of Al2O3 and molecular sieve metal support on As2O3 and SeO2.The adsorption performance of Ca2+and Fe3+when loaded in a ratio of 3:1 was also explored.Research indicates:The adsorption of As2O3 and SeO2 by Al2O3 and molecular sieves is mainly physical adsorption.In the adsorption process after metal loading,chemical adsorption and physical adsorption will occur simultaneously.And as the concentration of Ca2+and Fe3+increases,the adsorption capacity of As2O3 and Se02 by the adsorbent gradually increases.After the concentration reaches a certain value,the adsorption will tend to be saturated.When Ca2+and Fe3+are loaded in a ratio of 3:1,the adsorption capacity will be between the adsorption capacity when Ca2+and Fe3+are separately loaded.At this time,the blending of the two metal ions will have no obvious promoting effect.The performance of SO2 on the adsorption of As2O3 and SeO2 on Al2O3 and molecular sieve metal support was also studied.The results of the study showed that:SO2 has a certain inhibitory effect on the adsorption of As2O3 and molecular sieve-loaded Ca2+,and has a certain promotion effect on the adsorption of As2O3 and molecular sieve-loaded Fe3+.Use molecular sieve loaded Ca2+adsorbent to simultaneously adsorb As2O3 and SeO2,change one of the concentrations to study its adsorption,the results of the study show:When the adsorbent adsorbs As2O3 and SeO2 at the same time,there will be a certain competitive relationship between As2O3 and SeO2,and As2O3 is more easily adsorbed.When the concentration of SeO2 remains unchanged and the concentration of As2O3 is gradually increased,the adsorption amount of As2O3 will increase rapidly,and then the increase rate will slow down,while the adsorption amount of SeO2 will gradually decrease and stabilize at a lower value;When the concentration of As2O3 does not change and the concentration of SeO2 is gradually increased,the adsorption amount of As2O3 is initially high and relatively stable,and will slowly decrease in the future,while the adsorption amount of SeO2 is initially low,and then will slowly increase.