| Three oil crops including cole, sesame and castor were selected to remediate heavy metals (Cu, zinc, Pb, Cd, As and Hg) in soils from Tailing area of Hunan Chenzhou, and the remediation potential of the rapeseed-sesame rotation mode for accumulating heavy metals from contaminated soil was calculated. An optimal oil extraction solvent by comparing five organic solvents (hexane, petroleum ether, acetone, isopropyl alcohol and chloroform) for oil extraction of castor bean was analysed and determined. The three kinds of organic salt solvents (potassium citrate, potassium tartrate, EDTA ammonium salt) were used to remove heavy metals from castor meal after oil extraction. The results of the study are as follows:(1) It was obvious differences for each heavy metal in accumulating in crops tissue. Cu, Zn, Cd and Hg were mainly accumulated in cole leaves, while Pb and As were mainly accumulated in the underground part of the root. For sesame, Zn, Pb and Cd were mainly concentrated in the root, followed by leaf; and Cu, As and Hg were different, they were mainly accumulated in the leaves, followed by the root. The distribution characteristics of these heavy metals and As were showed that underground part was far higher than above part. For cole, except the aerial parts of cole leaves, Hg enrichment capability was strongest, other heavy metals enrichment capability were weak. For sesame and castor, Cu and Cd were showed good enrichment capability. Especially for Cu and Cd, accumulation coefficient of aboveground leaf and underground root of sesame was greater than 1.(2) This research useed rapeseed-sesame rotation mode to remediate soil heavy metals. Although the concentration of heavy metals for two oil crops was not as high as hyperaccumulator, the overall quality of dry matter can reach 800-1000 kg/acre which was far greater than the hyperaccumulator biomass. So that they could have good effective extraction of heavy metals in the soils. The enrichment ability of cole and sesame were different for heavy metals, so they play complementary role in the farmland of heavy metals contamination.(3) For extracting castor oil by five different organic solvents, the highest oil extraction rate is chloroform, up 33.74%,31.05% followed by acetone. Considering of the security, chloroform extraction of castor oil was the best choice. Because heavy metals such as Cd and Hg were not detected in castor oil, and the heavy metal content was much less than the concentration of castor peel which can be detected, so that a large number of heavy metals still exist in castor meal.(4) Comparing three extraction agent for detoxification heavy metals in castor meal, the best detoxification was EDTA ammonium salt when extracted only once. And with the increase of concentration of extractants, detoxification effect was better.30 mmol/L of EDTA ammonium salt on the removal rate of Zn reached 77.48%, while the removal rate of Cu reached 76.212%, Pb 58.58%, Cd 60.217%, compared with potassium citrate and potassium tartrate, the detoxification effect of EDTA ammonium salt was better. But potassium tartrate detoxification effect for Cd was the highest among the three kind of extraction agents. Compared with these two extraction agents, potassium citrate was not particularly obvious advantages in all aspects.(5) In the three consecutive leaching using 30 mmol/L extractants, the most comprehensive detoxification effect on the castor meal was EDTA ammonium salt. Its removal rate for Zn reached 97.720%, while the removal rate for Cu was 90.206%, Pb 80.55%, Cd 85.48%, As 63.99%. Compared with potassium citrate and potassium tartrate, EDTA ammonium salt comprehensive detoxification effect was the best. The next was potassium tartrate on the detoxification effects of Cd reached a maximum of 94.282%. Give priority to potassium tartrate when only separate the detoxification of Cd. |
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