A Study On Arsenic Adsorption Mechanism By Iron Sulfide Minerals

With the rapid development of the social economy and technology, thepollution of arsenic is increasingly serious. Recently, because the arseniccompounds are lethal toxicants and widely used in the agriculture and industry,environmental scientists around the world have paid attention to the problemsbrought out by arsenic compounds that contaminat the environmeng, espcially thewater sources. In China, the high-arsenic groundwater are widely distributed, theeconomic and efficient arsenic removal technology of drinking water arewidespread concern. Therefore, choose an inexpensive and effective adsorbent is animportant direction of the adsorption studies. Pyrite and pyrrhotite, which arewidely distributed and low prices, can adsorb a variety of heavy metals. Arsenicwhose mobility and availability are largely controlled by sorption on sulfideminerals in nature environments.Natural pyrite and pyrrhotite have been used as adsorbents for As removal inthis study, Which are investigated by the static experiment and dynamic experiment.Effects of reaction time, pH value, initial concentration,temperature on Asadsorption were intensively investigated.And combined with the XPS technique toinvestigate the adsorption mechanism.Static experiments results show that it takes6h to reach equilibrium of Asadsorption, and the removal efficiency of arsenic greater than95%in balance. Theadsorption kinetics data of both sample agrees with Lagergren pseudo-second ordermodel equation. Langmuir isotherm gives a better description of adsorption data ofAs(III) and As(V) on natural pyrite and pyrrhotite, indicating that the physicsadsorption controls the whole process. The optimum pH for As(III) and As(V)removal by pyrite and pyrrhotite is broad, ranging from4.0to9.0.Dynamic experiments results show that two dynamic column of the pyrite havebeen ran for70days, and the column of pyrrhotite has been ran for180days.Influent concentration of1mg/L and influent flow of10mL/h, The1mg/L ofAs5+concentration can be reduced to below10μg/L at beginning, which passthrough pyrite sample column.And reach saturation in the70days. Different,the1mg/L of As3+concentration is slowly reduce and reached to below10μg/L at15days. The1mg/L of As3+concentration can be reduced to below10μg/L atbeginning and reached saturation in110days. By regeneration, the Asconcentration is still less than10μg/L. The adsorption experiments in aerobic and anaerobic conditions results showthat, in addition to two system did not appear to release phenomenon, FeS2+As(V)in aerobic conditions and Fe1-XS+As(III) in anoxic conditions, the other reactionsystem began to release after1.5days. Scan the samples before and after reactionby XPS and found that the sample surface oxidation has a clear link with adsorptioneffect.In general, the oxidation can promote adsorption, also inhibit the retention ofarsenic in the sample. The adsorption mechanism of arsenic including the thephysical adsorption of the sample, as well as the adsorption by oxidation productand precipitation of FeAsS and As2S3.