| With the development of our society,more and more electronic and electrical products are applied in our real life,which results in the the disposal of electronic waste.Some areas in China rely on dismantling electronic waste to recover value metals as economic income.However,the dismantling of such irregular small workshops will cause heavy metal pollution at the dismantling site.Pb,Cd,Cu are the most severely polluted heavy metals in the soil of contaminated sites.If these heavy metals accumulate in the human body through the food chain,they will harm human health.These heavy metal hazard incidents have aroused the attention of the government and society,and find ways to reduce or even eliminate these hazards.This research is aimed at contaminated soil with composite heavy metals（Pb,Cd,Cu）.The mechanochemical method is used to solidify the heavy metals in the contaminated soil to reduce the leaching and transfer of heavy metals in the soil.The main research conclusion include:（1）Pure ball milling and TCLP procedure were applied to remediate lead-contaminated soil and evaluate its solidification efficiency.Taking the soil lead concentration of 10439.35mg·kg-1 as an example,the toxic leaching concentration of the original contaminated soil was214.13 mg·L-1.When a ball milling speed 550 r·min-1,the ball-to-material mass ratio 14,and the pure ball milling time 4 h,the leaching concentration of Pb in the soil was 26.85 mg·L-1.The above result showed that mechanical ball milling could reduce the leaching concentration of lead to a certain extent,but it cannot reach the standard value of 5 mg·L-1.It shows that pure mechanical force has limited ability to solidify heavy metals in contaminated soil.（2）In order to further improve the solidification effect of heavy metal lead in soil,the effects of Ca（H2PO4）2dosage,ball milling time and rotational speed on the solidification effect of lead were experimentally studied.The experimental result showed that when the additive ratio 10%,the ball milling time 2 h,and the ball milling speed 550 r·min-1,the lead leaching concentration was reduced from the original 214.13 mg·L-1to 4.36 mg·L-1,which was lower than the standard lead value of 5 mg·L-1in GB 5085.3-2007.From the analysis of BCR morphology,it can be observed that with the increase of ball milling conditions,the acid-extractable fraction of lead in soil decreased significantly,and the content of residual fraction and oxidizable fraction increases,which indicated that enhanced ball milling conditions were beneficial to the stabilization of Pb in contaminated soil.（3）In order to explore the effect of mechanochemical method on the remediation of soil contaminated by composite heavy metals（Pb,Cd,Cu）,four stabilizing agents,nano-hydroxyapatite,dipotassium hydrogen phosphate（K2HPO4）,calcium dihydrogen phosphate（Ca（H2PO4）2）and palygorskite powder were chosen to select the suitable stabilizing agent.The results showed that the best stabilizing effect was Ca（H2PO4）2,which could reduce the leaching concentration of Pb from 154.29 mg·L-1to 0.82 mg·L-1,and the leaching concentration of Cd from 4.90 mg·L-1to 0.32 mg·L-1,Cu leaching concentration decreased from 177.64 mg·L-1to 17.92 mg·L-1.（4）In order to improve the solidification effect of composite heavy metals（Pb,Cd,Cu）contaminated soil,this experiment investigated the leaching effect of different ball milling conditions（Ca（H2PO4）2dosage,ball milling time,ball milling speed and ball-to-material mass ratio）.The results showed that under the conditions of additive ratio of 20%,ball milling time of 4 h,ball milling speed of 550 r·min-1,and a ball-to-material ratio of 14,the leaching concentrations of Pb,Cd and Cu were reduced,respectively from 154.29 mg·L-1to 0.083mg·L-1,177.64 mg·L-1to 0.008 mg·L-1,and from 4.90 mg·L-1to 1.052 mg·L-1,all of which reached the standard value.From the analysis of BCR morphology,it can be seen that with the increase in ball milling time,speed and ball-to-material ratio,the acid-extractable fraction of heavy metals in the soil significantly decreases,and the residual fraction increases,indicating that enhanced ball milling conditions are conducive to the solidification and stabilization of compound heavy metals in contaminated soil.（5）In order to explore the mechanism of the solidification of heavy metals in soil by mechanochemical remediation,scanning electron microscope（SEM）,particle size analysis and XRD analysis methods were used to analyze the soil samples before and after ball milling.The results show that mechanochemical ball milling causes agglomeration of soil particles,and stabilizing agents and heavy metals in the soil form a precipitate during the ball milling process.This precipitate has low solubility and bioavailability,and can be stable in the environment.This reduces the leaching concentration of heavy metals. |
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