| Arsenic and antimony are thiophile elements widely found in the environment,with similar chemical,toxicological and geochemical properties.The co-contamination of arsenic and antimony is very common in the vicinity of mines.In recent years,the co-contamination of arsenic and antimony in the environment has received extensive attention from many scholars and become a research hotspot in the field of environmental science.Northwest guizhou province is a typical indigenous zinc smelting area in China.Many years of metal mining activities have resulted in a large number of waste dumps around the mine,artificially speeding up the entry of arsenic and antimony into the surrounding environment,and the health and ecological environment of the surrounding residents have a bad effect.Phytoremediation is generally regarded as an effective and low-consumption method to clean the soil.The use of plants to repair slag yard and abandoned land is of great significance to effectively control the diffusion of heavy metals to surrounding environmental media,and realize the restoration of polluted environment and damaged ecosystem.In this study,a indigenous smelting slag yard in Houchang town,Weining County,Guizhou Province,which has been under phytoremediation for 7 years was selected as the research area.Six dominant plants,namely Broussonetia papyrifera,Cryptomeria fortunei,Arundo donax,Robinia pseudoacacia,Photinia serrulata and Lolium perenne,were selected as the research objects.Systematically studied different plant root layer of slag and vertical space in different depth gradient profile of the slag of arsenic,antimony and plant tissue migration characteristics of arsenic,antimony.The aim of this study was to reveal the effect of dominant phytoremediation on the transfer and transformation of arsenic and antimony in the slag of indigenous zinc smelting.In order to provide scientific basis for ecological restoration or vegetation reconstruction on the slag of indigenous zinc smelting.The results are as follows:1.Phytoremediation can obviously change the physical and chemical properties of zinc smelting slag.The control slag had the characteristics of neutral alkaline p H,poor physical structure,poor water and fertilizer holding capacity,etc.After phytoremediation,the p H and Eh of the six plant rhizosphere and slag with different gradients were more significant than that of the control slag decreased,the control slag Eh decreased with the increase of slag depth,the slag Eh increased with the increase of slag depth with the participation of different plants,and the slag Eh reached the maximum value of 40?50 cm.The EC of plants participating in the lower rhizosphere and slag at various depths was significant was lower than the control residue,the control residue EC had no significant change trend with the depth,and the slag EC with the participation of different plants increased significantly with the slag depth increased.The water content of slag in different rhizosphere was significant was higher than that of non-rhizosphere slag,and the change was different compared with that of control slag.The water content of slag at different depths under the action of different plants all decreased compared with that of control slag,but there was no obvious change rule in the water content of slag at different depths under the action of control and plants.The content of free iron oxide in rhizosphere residue was higher than that in control residue,the content of free alumina was lower than that in control residue,and the content of free iron oxide in rhizosphere residue was lower than that in non-rhizosphere residue.2.Phytoremediation significantly promoted the accumulation of nutrients in slag.The effect of phytoremediation on the nutrients in slag was that the contents of organic matter,DOC,total nitrogen,alkali-hydrolyzed nitrogen,total phosphorus and available phosphorus in 6 plant rhizosphere and slag with different gradient were more significant than those in control residue increase,but the increase range is different,specifically manifested as the increase range of nitrogen element is greater than that of phosphorus element,and the increase range of DOC is greater than that of organic matter.The contents of alkali-hydrolyzed nitrogen and DOC increased significantly with the increase of slag depth(p<0.05;The total nitrogen content was significantly higher in the upper layer?0?20 cm?than in the lower layer?20?50 cm?.The changes of total phosphorus and available phosphorus were independent of depth.3.Phytoremediation can obviously change the physical structure and chemical composition of zinc residue.The effect of phytoremediation on the morphology of slag showed that the surface of the control slag was relatively flat,while the surface of the rhizosphere slag was loose and porous due to the interpenetration of plant roots and the possible dissolution of root exudates.The influence of phytoremediation on the particle size composition of slag is generally shown as follows:the proportion of clayey slag in plant rhizosphere slag is higher than that of control slag,and the proportion of powdery and fine sand slag is lower than that of control slag.The elements with the highest relative contents in the slag are C,O and Si.The proportion of element C in the plant rhizosphere slag increases to different degrees compared with the control slag,while the proportion of element Si,Fe,S and O decreases to different degrees.The influence of phytoremediation on the mineral composition of slag is shown as decreasing the relative content of calcite and hematite in rhizosphere slag and increasing the relative content of gypsum and cristobalite slag.The results of functional group characterization showed that the peak strength of hydroxyl group,aliphatic group,aromatic group,calcite and quartz in the four kinds of plant rhizosphere slags decreased to different degrees,and the peak strength of carbohydrate/organosilicide and c-n triple bond increased.4.Phytoremediation has a significant effect on the migration and transformation of arsenic and antimony in slag.After phytoremediation,the contents of arsenic,antimony,inorganic arsenic and antimony in rhizosphere slag of 6 plants were generally lower than that of control slag,and the contents of arsenic?III?and antimony?III?were significant was higher than arsenic?V?and antimony?V?,and the proportion of arsenic?III?and antimony?III?in rhizosphere residue increased compared with that of slag.The arsenic content in the control residue and the plant residue increased with the increase of the residue depth.The proportion of residual arsenic and antimony in the plant rhizosphere slag was the highest,and the proportion of arsenic and antimony in the exchangeable state,aluminum binding state and calcium binding state was lower than that in the control slag,and the bioavailability of arsenic and antimony in the slag was significantly reduced.The proportion of exchangeable arsenic increased with the increase of slag depth,but there was no significant correlation between the proportion of different forms of antimony and slag depth.The content of arsenic and antimony in each tissue of 6 plants varied from 0.076 to 1.564 mg·kg-1,0.022 to 0.488 mg·kg-1,respectively.Leaf>Stems.The enrichment coefficients of arsenic and antimony in different plants were all less than 0.001 and the transfer coefficients were all less than1,indicating that the enrichment and transport capacities of arsenic and antimony in 6self-plants were all low,and the correlation analysis also showed that there was no significant positive correlation between arsenic and antimony in plants and arsenic and antimony in slag.In summary,7 years of phytoremediation can significantly improve the rhizosphere microenvironment?increasing the accumulation of nutrients in slag and the process of mineral weathering into soil?by repairing the rhizosphere activities of plants?root exudates and rhizosphere microbial activities?and the return of plant litters.On the other hand,after phytoremediation,the content and bioavailability of arsenic and antimony in slag are significantly reduced,and the enrichment degree of arsenic and antimony in plant tissues is also low.Therefore,it is speculated that the early stage of phytoremediation may increase the migration of arsenic and antimony in slag,but later stage can inhibit the bioavailability of arsenic and antimony. |
PDF Full Text Request