Effects Of External Factors On Aging Of Copper And Zinc In Contaminated Soils

Red soil from Qiyang county, Hunan province, and paddy soil from.Jiaxing city, Zhejiangprovince, were collected and cultured to the single and combined of Cu/Zn contaminated soils.Through culture experiment in laboratory and pot experiment in solarium, the dynamic aging ofCu/Zn in three soils, and the effects of different addition,water,pH,amendments and plants onavailability of Cu/Zn in red and paddy soils were studied. The results in this experiment showed asfollows:1. The available Cu/Zn contents in three soils decreased with time. Whether in single orcombined contamination soils, the available Cu/Zn contents decreased promptly in initial agingtime, and kept decreasing slowly 30 days later. For example, the available Zn contents of red soildecreased from 106.09mg·kg^-1 to 57.70mg·kg^-1 in 2 to 30 days, and the rate of decrease to additionwas 12.1%. The available Zn contents of red soil decreased from 57.70mg·kg^-1 to 54.19mg·kg^-1 in30 to 360 days, and the rate of decrease to addition was 0.9%. The available Zn contents of paddysoil decreased from 51.02mg·kg^-1 to 26.51mg·kg^-1 in 2 to 30 days, and the rate of decrease toaddition was 6.1%. The available Zn contents of paddy soil decreased from 26.51mg·kg^-1 to18.14mg·kg^-1 in 30 to 360 days, and the rate of decrease to addition was 2.1%. The available Zncontents of brown soil decreased from 36.69mg·kg^-1 to 22.57mg·kg^-1 in 2 to 30 days, and the rate ofdecrease to addition was 2.8%. The available Zn contents of brown soil decreased from22.57mg·kg^-1 to 20.31mg·kg^-1 in 30 to 360 days, and the rate of decrease to addition was 0.5%.Perhaps, the mechanism of aging was that the surface of soil particle could adsorb Cu/Zn ions,leading to immobilization and diffusion.2. The available Cu/Zn contents of two soils increased with addition. The available Cu/Zncontents in combined contamination soils were higher than that in single contamination soils. Andthe difference of available Cu/Zn in single and combined contamination soils was significant at 5%.3. With the hydrous rate of two soils decreasing, the pH value and available Cu/Zn contentsnearly unchanged, and the differences were insignificant at 5%. The results showed that in thisexperiment conditon, the effect of water on availability of Cu/Zn was insignificant.4. The available Cu/Zn contents in two soils decreased promptly with the pH of soilsincreasing. In the same pH condition, the available Cu/Zn contents in combined contamination soilswere higher than that in single contamination soils. The difference of available Cu contents in single and combined contamination red soils was significant at 5%, but the difference of availableZn contents was reverse. And in the same pH condition, the difference of available Cu/Zn contentsin two soils which was insignificant at 5% with the application of acid or alkali. So it wasconcluded that pH was one of the most crucial factors which effected the availability of heavy metalin soils.5. The pH value of soils increased promptly with the application of amendments(lime,superphosphate and zeolite), and the increasing extent of red soil pH was the first place. The redsoil could improve about 2.1 units with application of lime, and 1.7-1.8 units with application ofsuperphosphate and zeolite. The paddy soil could improve about 0.8, 0.5 and 0.6 units withapplication of lime, superphosphate and zeolite respectively. The effects of three amendments onpH value of soils decreased in an order: lime＞zeolite＞superphosphate. Compared with CK, theavailable Cu/Zn contents in two soils decreaed promptly with application of amendments. And theeffects of three amendments on available Cu/Zn contents in two soils decreased in an order:lime＞zeolite＞superphosphate. The results showed that availability of Cu/Zn decreased withapplication of amendments through improving pH of soils.The available Cu/Zn contents in combined contamination soils were higher than that in singlecontamination soils. The difference of available Cu contents in single and combined contaminationsoils was significant at 5%, but the difference of available Zn contents was reverse. It was apotential reason that compared with copper, zinc was more stable, easier adsorbed by soils andsmaller affected by competition.6. The contents and concentrating coefficients of Cu/Zn in four plants decreased in an orderrespectively: wheat＞cabbage,rape＞tomato and wheat＞cabbage＞rape＞tomato. But the order ofavailable Cu/Zn contents in soils was reverse absolutely. Whether in uncontaminated orcontaminated soils, the pH value of soils unchanged significantly with vegetables planted, and thedifference of them was insignificant at 5%. The results showed that absorptive accumulation wasthe more improtant mechanism, which affected availability of Cu/Zn in soils.7. So to sum up, through studying the effects of external factors on availability of Cu/Zn in redand paddy soils, it was concluded that pH was on of the most crucial factor which effected theaging of Cu/Zn in soils. The availability of Cu/Zn in soils decreased promptly with pH increasing,because of the co-precipitation. The aging velocity could be accelerated by adding a small quantityof amendments, which affected the pH value of soils. Furthermore, the results showed that theavailable Cu/Zn contents in combined contamination soils were higher than that in singlecontamination soils. So it was believed that the interaction of heavy metal ions was also one of themost crucial factors, which effected the aging of heavy metal in soils.