Influence Of Humic Acid On Adsorption And Speciation Distribution Of La,Nd In Soil

China is a major country of rare earth (RE) consumption. It's RE application in agriculture ranks the third of the total RE consumption in the whole country. With the application of RE in agriculture, it has great economic benefits. Meanwhile it also quicken the accumulation of RE in the environment. Excessive amount of RE might bring about several eco-toxic effects. The application of Humic acid decreases the water-soluble, exchangeable and carbonate-bound forms of RE and increases the residual and organic-bound forms of RE. So it can be used to control the transition, transformation and bio-availability of RE in the environment.This essay focused on the adsorption of several heavy metals and La,Nd by Humic acid and influence of Humic acid on speciation distribution of endogenous and exogenous La,Nd in red soil(pH<7), yellow cinnamon soil (pH≈7)and lime concretion black soil(pH>7).The results indicated that:1. By making an adsorption test in a multi-metal-ion system, the optimum conditions on adsorption of La³⁺,Nd³⁺ by Humic acid which concentration is 1.2g/L are selected as follows: pH5.4, temperature 313K, oscillation time 8h, heavy metal ions'initial concentration 0.15mmol/L. The result also indicated that under those circumstances, the selectivity sequence of Humic acid to heavy metal ions is La³⁺>Pb²⁺>Cu²⁺>Nd³⁺>Cd²⁺> Zn²⁺>Co²⁺>Cr³⁺. Total adsorption by Humic acid fits the best with second-order Kinetic equation in 298k; process of adsorption by Humic acid in isothermal conditions can be well described by the Langmuir isothermal equation; and the largest adsorption by Humic acid increased as the temperature rose; the selectivity sequence of La³⁺,Nd³⁺ and other heavy metal ions were collectively determined by pH, temperature, oscillation time, heavy metal ionic initial concentration and nature. In addition, each heavy metal's geochemical nature was the dominant factor.2. There is little effect of cultivation methods (dry or submergic condition) on speciation distribution of endogenous and exogenous La,Nd in soils. In three kinds of soils, speciation distribution of endogenous La,Nd is form B4>form B3>form B2>form B1,speciation distribution of exogenous La,Nd is form B3>form B2>form B1, and the content of form B1 is extremely low in lime concretion black soil and yellow cinnamon soil.3. Form B1 and form B3 of endogenous and exogenous La,Nd in red soil is the highest and the lowest in those kinds of soil; form B2 of endogenous and exogenous La,Nd in lime concretion black soil is the lowest in those kinds of soil; the concentration sequence of form B3 of endogenous and exogenous La,Nd in those kinds of soil is yellow cinnamon soil> lime concretion black soil> red soil.4. There is little effect of Humic acid on form B4 of endogenous La,Nd in three kinds of soil, form B1 and B2 of endogenous and exogenous La,Nd decreased slightly with the increase of Humic acid, form B3 of endogenous and exogenous La,Nd increased slightly with the increase of Humic acid, with the addition of Humic acid increased, the speciation distribution of endogenous and lower concentration disposal of exogenous Nd fluctuate greatly, the speciation distribution of higher concentration disposal of exogenous Nd fluctuate slightly.5. Except for the type of RE, soil types,cultivation methods,concentration of RE and addition of Humic acid had a very significant association with soil pH, soil pH showed a very significant negative correlation with the form B1,B2 of endogenous and exogenous La,Nd, and expressed a very marked positive correlation with the form B1,B2 of endogenous and exogenous La,Nd, had no significant correlation with the form B4 of endogenous La,Nd, soil types showed a very significant correlation with all forms of endogenous La,Nd and form B1,B2,B3 of exogenous La,Nd, concentration of RE had a significant correlation with form B1,B2,B3 of exogenous La,Nd, cultivation methods had no significant correlation with any forms of endogenous and exogenous La,Nd, the type of RE expressed a very marked correlation with the form all forms of endogenous La,Nd and form B2,B3 of exogenous La,Nd, addition of Humic acid had a very significant association with form B1,B2,B3 of endogenous La,Nd and form B1,B3 of exogenous La,Nd, the addition of Humic acid had the greatest effect on the speciation distribution of endogenous and exogenous La,Nd in red soil, addition of Humic acid had a significant correlation with the form B3 of endogenous La,Nd and form B1,B2,B3 of exogenous La,Nd.