| There are hundreds of years of indigenous zinc smelting history in the northwest of Guizhou Province.The process is simple,the energy consumption is large,the technology is backward,the zinc recovery rate is low,most of the associated metals remain in the smelting waste and are not recovered.In 2004,although the indigenous zinc smelting process was stopped,a large number of zinc smelting waste residues were exposed to the surface after years of accumulation.Under the action of wind,leaching and surface water erosion,a large number of harmful elements entered the surrounding water,soil and other environmental media in granular or ionic state.Because the area belongs to typical karst landform and carbonate rock is widely distributed,calcium and magnesium ions will be produced after weathering,and they will enter the soil and sediment as the main components,which will have different degrees of impact on the migration and transformation of heavy metals in the environment and the biological toxicity effect.However,there are few data about the change of bioavailability of heavy metals in the lead-zinc smelting waste plant system under the restriction of karst environment,so it is very important to study the release characteristics and environmental effects of heavy metals in the unique karst landform of Guizhou Province.In this paper,the lead-zinc smelting waste plant system in the ecological restoration demonstration base of lead-zinc smelting waste in the northwest of Guizhou Province in karst area is taken as a reference.By adding different carbonate rocks to the lead-zinc smelting waste plant system,and simulating the leaching of carbonate rocks in the action state with different calcium salt and magnesium salt?once every two weeks,four times for eight weeks,respectively recorded as T1,T2,T3,T4?,and The physical and chemical characteristics and biological toxicity of the leachates were studied.The effects of different types of calcium salt,magnesium salt and carbonate rock widely existing in karst environment on the leaching of heavy metals from lead-zinc smelting residue plant system,the toxic effect of leachates on luminescent bacteria,the transformation of heavy metal forms and the effect of ryegrass on heavy metal accumulation were analyzed.The results are as follows:?1?The physical and chemical characteristics of leaching solution of lead-zinc smelting slag plant system will be significantly affected by the presence of different exogenous carbonate rocks.In the 8-week leaching time after adding different external carbonate rocks to the system,the p H value of the leaching solution of the system gradually increased and the soluble salt concentration?EC?gradually decreased with the extension of the leaching time.The redox potential?Eh?of the leaching solution of the calcium salt treatment group increased first and then decreased,while that of the magnesium salt,mixed,dolomite and limestone treatment group increased gradually.Compared with the blank group,the p H value of leachate in the treatment group added calcium chloride decreased,while the p H value of leachate increased with the addition of magnesium carbonate and magnesium chloride,and the greater the addition,the more obvious the effect;the EC of leachate increased significantly with the addition of calcium chloride and limestone in T1-T2?p<0.05?,and the Eh of leachate decreased significantly in the treatment group of magnesium salt,mixed,dolomite and limestone in T1-T3 period?p<0.05?,among which magnesium chloride had the most significant effect on the decrease of Eh.?2?Different carbonate rocks affect the leaching of heavy metals from lead-zinc smelting slag plant system and the biological activity of leaching solution to luminescent bacteria.The concentration of Ca,Mg and heavy metals in the leachate of the same treatment group decreased with the increase of time in the 8-week leaching time after adding different exogenous carbonate rocks to the lead-zinc smelting residue plant system.The concentration of Ca and Mg in the leachate is mainly affected by the exogenous Ca and Mg salts.The soluble calcium chloride and magnesium chloride can increase the concentration of Ca and Mg in the leachate,and the larger the ratio is,the more significant the effect is.For the leaching of heavy metals in the system,the correlation analysis shows that exogenous addition of different carbonate rocks in T1-T2 will increase the leaching of heavy metals in the system,showing that in the karst environment,the lead-zinc smelting slag plant system in the presence of different exogenous carbonate rocks will promote the release of heavy metals in the smelting slag.The results show that the leachates and the leachates of waste residue can produce toxic effects on the photobacteria,reduce the biological activity of the photobacteria and inhibit the photoluminescence,while the presence of carbonate rock with appropriate concentration can reduce the biological toxicity of the leachates and leachates to the photobacteria,but the presence of carbonate rock with excessive concentration will increase Biotoxicity of eluate to Photobacteria,Among them,exogenous magnesium salt is better to alleviate the toxicity of heavy metals.?3?Different carbonate rocks have different effects on the physical and chemical properties of lead-zinc smelting slag plant system.The addition of calcium salt and magnesium salt has little effect on the p H value of waste residue system,and can reduce the EH of waste residue.The total nitrogen content of waste residue in different treatment groups decreased first and then increased with the increase of carbonate concentration.Compared with the blank group,the addition of different carbonate rocks increased the effective nitrogen content in the waste residue system,and the effective nitrogen content in the waste residue of each treatment group increased by 0.67-35.10 mg·kg-1.The single addition of calcium salt and magnesium salt can reduce the content of total phosphorus,available phosphorus,available potassium and organic matter in the waste residue,while the mixed carbonate rock treatment group can reduce the total phosphorus in the waste residue by low concentration and increase the concentration by high concentration,which has little effect on the organic matter,while the dolomite and limestone can increase the content of effective phosphorus in the waste residue with the increase of the addition amount.For the content of exchangeable calcium and magnesium in the waste residue,dolomite and limestone have little influence,but different calcium salt and magnesium salt treatments increase the content of exchangeable calcium in the waste residue,and increase with the increase of the concentration.The larger the proportion of single calcium salt is,the lower the exchangeable magnesium content in the waste residue is,and the magnesium salt and mixed treatment can increase the exchangeable magnesium content in the waste residue as a whole,which is linear with the added concentration The results show that the content of exchangeable calcium and magnesium is mainly affected by the concentration of exogenous calcium salt and magnesium salt,and a single calcium salt can promote the loss of exchangeable magnesium in the waste residue.?4?The effects of different carbonate rocks on the bioavailability and occurrence of heavy metals in waste residue vary with the types of heavy metals.On the whole,the acid soluble proportion of Cu,Pb,Zn and Cd in the waste residue of different exogenous calcium salt and magnesium salt treatment groups decreased,while the residual proportion of Zn and Cd increased.The single addition of magnesium carbonate and magnesium chloride can reduce the content of Cu,Zn and Cd in the waste residue,which shows that the existence of magnesium carbonate and magnesium chloride can reduce the bioavailability of Cu,Zn and Cd in the waste residue.The effect of each treatment on acid soluble heavy metals in waste residue is:magnesium carbonate>mixed>calcium chloride>calcium carbonate>magnesium chloride>dolomite and limestone,which shows that single magnesium carbonate treatment has a better effect on reducing acid soluble heavy metals in waste residue.?5?The addition of different carbonate rocks affected the absorption and transportation of calcium,magnesium and heavy metals by ryegrass.The addition of exogenous calcium salt can increase the content of calcium in Ryegrass and reduce the accumulation of magnesium in ryegrass leaves,while the addition of magnesium salt can increase the content of magnesium in Ryegrass and reduce the content of calcium in ryegrass leaves.The accumulation of heavy metals in ryegrass was Zn>Cd>Cu>Pb.Ryegrass had a large accumulation of Zn.The accumulation of Cu,Pb,Cd in ryegrass was reduced by adding different carbonate rocks,and the effect on Zn was less.The content of Cu,Pb,Cd in ryegrass was increased with the addition of calcium carbonate,magnesium carbonate,mixed,dolomite and limestone The transport and enrichment coefficients of heavy metals Cu,Pb,Cd in ryegrass were lower than those in the blank group,and the absorption of ryegrass could be inhibited by the antagonistic effect of different carbonate rock addition and Cu,Pb,Cd. |
PDF Full Text Request