| With the rapid development of China's copper mining industry,high density sludge(HDS)acidic wastewater treatment technology has been widely used in major copper mines in China.Causing a dramatic increase in acidic wastewater bottom sludge discharge from copper sulphide minesbottom sludge,due to its large stockpile volume and low comprehensive utilisation rate,taking the Dexing copper mine as an example,the annual production of bottom sludge is about600,000 tonnes,resulting in the occupation of a large amount of valuable mine space and land destruction.This poses a serious threat to the ecological environment of the mine.Phytoremediation has the advantages of low soil disturbance,convenient operation,low restoration cost and green environmental protection,etc.It is widely used in mine soil remediation and has a broad development prospect.In this study,the bottom sludge from the acidic water treatment plant of the Jiangxi Copper Group's Dexing Copper Mine was used as the research object,and the physical and chemical properties of the bottom sludge were analyzed to identify the key factors that make it difficult to use the bottom sludge for ecological reclamation and to provide a basis for the improvement and restoration of acidic wastewater bottom sludge in copper sulphide mines.On the one hand,by comparing different plant growth indicators,we can screen out the superior plants suitable for growing on the bottom sludge,and on the other hand,we can improve the physical and chemical properties of the bottom sludge and solve the technical problems such as high salinity,easy caking and low content of organic matter and other conventional nutrients,to realize the engineering application.The main research results are as follows:(1)The indicators of the hazardous components in the bottom sludge are lower than the concentration limits stipulated in GB 5085.3-2007 and GB 5085.1-2007,and the p H of the bottom sludge leachate is between 6 and 9,which belongs to Class I industrial solid waste.The water content,total nitrogen,effective phosphorus,fast-acting potassium and organic matter in the bottom sludge were 55.01%,0.266 g/kg,1.690 mg/kg,17.1 mg/kg and 4.15 g/kg respectively,and the content of various nutrients required for plant growth in the bottom sludge was extremely low.The subsoil is weakly alkaline(p H=7.63)with an electrical conductivity of 245 ms/m.It is lightly saline soil,prone to slaking and cracking.(2)Nine kinds of plants were planted in a 4:1 ratio of acidic wastewater bottom sludge from copper sulphide mines and soil,and the results showed that the germination rate of D.moldavica and L.perenne was 88.67% and 98.33% respectively,and the survival rate was 90.1% and 97.9%respectively,and the plant height at 60 days was 83.53 cm and 21.7 cm respectively,which were more suitable for growing on the bottom sludge than flat carpenter and can be used as pioneering plants for the ecological reclamation of bottom sludge.Among the shrubs,P.fraseri has a high survival rate and a greater 60-day height increment,making it more suitable for substrate habitats.The survival rate of three kinds of trees is in the order of R.pseudoacacia > P.tomentosa > P.elliottii,and the 60-day plant height increment is in the order of R.pseudoacacia > P.tomentosa >P.elliottii,making R.pseudoacacia and P.tomentosa more suitable for substrate habitats.(3)According to the research results of the soil pile planting experiment,combined with other research results of the group,we chose to use D.moldavica and L.perenne as pioneer plants.P.fraseri? L.lucidum? L.quihoui? R.pseudoacacia and P.elliottii to carry out a three-year field engineering experiment to verify the feasibility of replacing complete guest soil with bottom sludge as a plant growth substrate for mine ecological reclamation.The results showed that the plants in the trial area grew well and the plant cover reached 100% after two years.Herbaceous plants such as maize grass and ryegrass were gradually replaced;shrubs were basically established,with plant height ranging from 181.4 cm to 213.8 cm and crown width from 92.2 cm to 109.5 cm;trees were basically established,with plant height ranging from 181.4 cm to 213.8 cm and crown width from157.3 cm to 237.0 cm.(4)The results of the determination of the physical and chemical properties of the bottom sludge 3 years after the establishment of the test area showed that the comprehensive physical and chemical properties of the bottom sludge were significantly improved.The conductivity of the bottom sludge decreased from 1.15% to 5.40%,the water content decreased from 16.90% to24.36%,and the p H of the bottom sludge changed to a lesser extent.The organic matter content was 1.17-1.57 times higher than the original bottom sludge in all areas except for the P.tomentosa planting area;the total nitrogen content increased only in the R.pseudoacacia planting area,by26.50% compared to the control group;the total phosphorus content increased by 11.89%?20.75%;the total potassium content increased by 31.54%?311.53%.The effect of P.fraseri,R.pseudoacaci and P.elliottii on the effective phosphorus content of the bottom sludge was more pronounced,with increases of 15.19%,14.99% and 4.91% compared to the control group. |
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