Adsorption Of Arsenic From Soil Colloids In Contaminated Rice Fields

The village of Jiaole in southwest Guizhou Province is a typical area of endemic arsenic poisoning in the country,The arsenic pollution in the soil and irrigation water left by coal mining has had a lasting impact on the arsenic exposure of local residents.In this article,through field observation and simulation studies,the adsorption characteristics of arsenic in soil colloids from contaminated rice fields were discussed.The following conclusions were drawn:(1)The pH of the soil colloids in the study area was neutral(pH was maintained at 7.4 during the extraction process),and there were obvious enrichment characteristics for As and Fe.Soil colloids in contaminated areas contained higher iron oxides.The SEM results show that the microstructures of soil colloids in contaminated areas and mixed areas are not distinct,and the structure of the soil colloids in clean areas is obviously loose.XRD results show that the main components of the three colloids are quartz,lepidocrocite,goethite and some amorphous materials,and no crystalline iron.(2)Soil colloids in contaminated areas,mixed areas and clean areas adsorption of As(V)that reached adsorption equilibrium at 13 h.When adsorption equilibrium was reached,the amount of soil colloids in contaminated areas that adsorbed was greater than that of soil colloids in mixed areas and clean areas.The total adsorption trend is divided into three stages:fast,slow,and steady.The description of colloidal adsorption of arsenic by the pseudo-second-order kinetic model is more accurate than the first-order kinetic model,and it can truly reflect the adsorption mechanism of As(V)by the colloid.(3)Choosing Freundlich model for isothermal adsorption can better describe the process of isothermal adsorption of As(V)in soil colloids.Soil colloids in contaminated areas,mixed areas and clean areas adsorption process of As(V)both single-layer adsorption and multi-layer adsorption occur simultaneously and multi-layer adsorption mainly.(4)The pH value of the system has a great influence on the adsorption of As(V),and the adsorption of As(V)decreases with the increase of the pH value of the system.With the increase of pH value,the adsorption amount of As(V)in the soil colloids(pH=2.0~9.0)in the contaminated zone,mixed zone,and clean zone decreased by1.28mg/g,0.68mg/g,and 1.25mg/g,respectively.(5)When the ionic strength is less than 0.1 mol/L,the adsorption of As(V)with soil colloids in contaminated areas,mixed areas and clean areas increases with increasing ionic strength as the ionic strength in the solution increases.This effect is the performance of the specific adsorption and the coordination of the inner layer.(6)After anaerobic flooding for 20 days,the pH of the colloids tends to be neutral and Eh decreases.Compared with the fitting parameters of aerobic and anaerobic flooding on the 20th-day Freundlich model,the overall K_F decreased slightly,and the total value of 1/n also decreased.This indicates that the adsorption capacity of arsenic decreased and the adsorption affinity of the colloid decreased after flooding.And intensity weakens.After 20 days of anaerobic flooding treatment,the overall trend is that as the amount of As in the soil colloid increases,the desorption amount also increases,but when the amount of adsorption is low,the amount of desorption with the flooding time no significant change in the extension.The desorption amount of arsenic after 20 days of anaerobic flooding was greater than that of aerobic.