The Effect Of Calcium Carbonate And Soil Clay On The Accumulation Of Heavy Metals In Soil

In recent year,heavy metal pollution has became a hot issue.carbonate rocks are widely distributed in guizhou province,the soil heavy metal content were significantly higher than that of other domestic areas,is a high risk area exposed to heavy metals.Studies have found that calcium carbonate and clay may be the main factors influencing the high exposure risks of heavy metals in the region,one of so discussion of calcium carbonate and clay soil heavy metal accumulation ability has important significance to the region.Selected two typical soil,yellow soil and lime soil as the research object by adopting the combination of indoor simulation and field investigation method.choose the adsorption kinetics and isothermal adsorption model to explore its adsorption properties on the dynamics,and discussed the adsorption temperature,initial p H,concentration of electrolyte,and other factors to explore soil heavy metals(As,Cu,Hg,Pb,zinc,Cr,Cd)accumulation ability,so As to carbonate area compound heavy metal contaminated soil repair can provide a scientific reference and research.The results are as follows:(1)According to the soil environment quality standard(GB15618-1995),the heavy metal in yellow soil Cu,Zn,Cd,Cr,Pb content accord with national level ? standards,As was in national? level standard,Hg beyond national ? level standards;lime soil heavy metal Cu,Cr,Pb conform to the national ? level standard,conform to the national ? level standard Zn,Cd.Hg and As were beyond national ? level standard.(2)The accumulation capacity of heavy metals in contaminated soils is with the increase of calcium carbonate content.With the increase of clay content,yellow soil and lime soil adsorption capacity increased,but no obviously promote or reduce the desorption amount.(3)The adsorption kinetics experiment shows,the adsorption rate of yellow soil and lime soil within 5 min of 50%,about 15 minutes can reach 80%,more than 95% within 90 minutes,after720 min 99%,yellow soil and lime soil adsorption process of heavy metals mainly concentrated in the first 90 minutes,followed by adsorption are going very slow.(4)Pseudo two order kinetic equation is the best one to fit the adsorption kinetics process and the average adsorption capacity of heavy metals is lime soil >yellow soil and the average adsorption rate is yellow soil>lime soil.(5)As in the yellow soil and lime soil on the isothermal adsorption curve has both the "S" type and "L" type.Langmuir model was the best for As adsorption in yellow soil and the Freundlich model was the best for As adsorption in lime soil.(6)The influence of temperature on the adsorption mechanism is more complex,different heavy metals may have different physical adsorption and chemical adsorption temperature transformation.By experiment the conclusion can be deduced that may be in 45 ?,the adsorption process of Cu in calcareous soil,a shift,from chemical adsorption to physical adsorption.Zn may be in 35 ? and 45 ? are they in the change of adsorption temperature.(7)The rise of pH will be good for most of the adsorption of heavy metals,has inhibitory effect on Cr.The analysis shows that the adsorption process is slow in pH<7 stage,rapid adsorption phase are occurred in the region of the pH > 7.(8)Electrolyte effect on heavy metal adsorption process is complicated,some obvious influence,some is not obvious,some not,need particular case is particular analysis.