Study On The Occurrence Of Dust Minreals And Heavy Metals In The Surface Soil Of The Western Plain Of Sichuan Basin

Fog and haze have become one of the most important issue in China,especially in the past two years,fog and haze was often occrrued in China.The Sichuan basin is a typical middle low plain area,surrounded by hills and mountains with high topography.The humid climate and low wind speed cause Sichuan's unique air pollution pattern.This thesis takes the western plain region in Sichuan basin as the geological background of the typical enviornment,Pb(?),Cd(?)and As(?)as the main representative of variable and non valence ions of haze pollutants in Sichuan basin.Taking the soil dusting and minreal dust particles as the research object,simulation analysis is carried out in the system of “the cationic pollutants in soil surface transport behavior”.Discussed and analyzed the relationship between the law of surface dusting,heavy metal ions in suspended particulate matter,mineral content and particle size.The conclusion is as follows.After simulated the wind speeds up the dust,with the increase of dust time,the mass concentration of particulate matter at all levels is decreasing.The average concentration of particulate matter(0.41-0.73?m ? 0.73-1.4?m ?1.4-2.1?m?2.1-4.2?m?4.2-10.2?m?>10.2?m)is the lagest in the ealy stage of dust emission(0-1h),and then gradually decline,after 24 h,it tends to be stable.With the increase of dusting distance,the weight of dustfall in different time show a tend of inceasing first and then decreasing.The dustfall weight is the most in the 1-2m area,which accounts for about 30% of the total surface dust.The disturbing effect makes the fine particles in the soil moe into the air,and the disturbance increases air pollution.After the wind blows the dust,the content of lead,cadmium and arsenic in dust is about 2-3 times that of soil before dust.It is known that the process of soil dusting is a migration process of heavy metals with the concentration high than the background.The distribution of lead,cadmium and arsenic on different particle size particles is different after dusting.The content of lead,cadmium and arsenic decreased with the increase of particle size of suspended particles,which had a negative correlation with the particle size.The clay mineral content of different particle size suspended particles decreases with the increase of particlesize,and the content of clay minerals on the suspended particles is positively correlated with the content of lead,cadmium and arsenic,which has a negative coelation with the particle size.Cadmium mainly exists in the from of exchangeable states,lead mainly exists in the from of carbonate bound.Both lead and cadmium are bioavailability elements,thee bioavailability coefficients are all over 0.6.Scanning electron microscopy(SEM)analysis showed that the distribution of Pb,Cd elements and O,Al and Si elements have a certain correlation,they are mainly concentrated on minerals composed of O,Al and Si elements.The sum of relative mass percentage and relative atomic number percentage of the three elements are all above 90%.It further indicates that lead and cadmium mainly exist on clay minerals.The X ray photoelectron spectroscopy analysis shows that arsenic can be combined with oxygen in the O-C/O=C group on the surface of the particles to be O-As,and the small the particle size,the high the relative atomic percentage of the combined O-As functional group.The Zeta potential analysis showed that the larger the particle size of the dust particles,the greater the potential difference,indicating that the particles with smaller particle size adsorbed more heavy metal ions.This thesis reveals the mineral properties of particulate matter in the atmosphere and coupling mechanism of heavy metal pollution.Providing theoretical support for atmospheric physical process in typical polluted regions of China and interaction mechanism between air pollutant transport and clearance.