Experimental Study On Enhanced Regrass Absorption Of Heavy Metals From Copper Tailings By Activator

Heavy metal pollution is an urgent ecological control problem in a mining area.Currently,the method of adding activators to strengthen plant remediation of heavy metal-contaminated soil is the current research hotspot;However,the direct remediation of heavy metal-rich copper tailings using activators-assisted plants has not been reported.Therefore,in this paper,the copper tailings of the 4#tailing pond of Dexing Copper Mine were selected as the research object;three biodegradable activators poly aspartic acid(PASP),citric acid(CA)and fulvic acid(FA),were selected,and ryegrass(Lolium perenne L.)was used as the test plant.A pot experiment explored the effect of different PASP,CA and FA concentrations on enhancing the absorption and extraction of heavy metals from ryegrass.The physicochemical properties,heavy metal content and morphological changes of copper tailings in each treatment group under the application of three kinds of activators were analyzed,as well as the absorption,accumulation and transfer ability of Cu and Cd in ryegrass,and the comprehensive effect of the ability of ryegrass to extract and repair Cu and Cd in copper tailings under the treatment of activators was evaluated.The main research results are as follows:(1)The effects of PASP,CA and FA at different concentrations on physicochemical properties of copper tailings were studied.The results showed that the p H of copper tailings was increased by applying an activator.The conductivity of copper tailings changed significantly with different types and concentrations of activators.When PASP concentration was 1 g/L,the conductivity of copper tailings was 482.67 μS/cm,significantly higher than that of other treatments.Except for FA-10 treatment,the organic matter content of copper tailings in other treatment groups increased to varying degrees,and CA-10 treatment had the best improvement effect,which increased by 42.88%compared with the control.Compared with the control group,the cation exchange capacity of copper tailings was decreased by activating agents,and the content of copper tailings was decreased by 47.87% under FA-10 treatment,which showed the most significant effect.However,the redox potential of copper tailings did not change significantly with different concentrations of three activators.(2)The effects of PASP,CA and FA at different concentrations on the total and available content of Cu and Cd in copper tailings and the content changes of various forms were studied.The results showed that,except adding 10 mmol/L CA increased the content of Cd in copper tailings compared with the control group,the other treatments could effectively reduce the total content of Cu and Cd in copper tailings.Three kinds of activators can increase the content of Cu and Cd in copper tailings,and CA-10 and PASP-4 treatments have the best effect on the content of Cu and Cd,respectively,increasing by 29.27% and 18.03% compared with the control group.The activated agent can change the form of heavy metals in copper tailings,promote the transformation of Cu and Cd from residual state to a soluble state of the weak acid,improve the bioavailability of heavy metals Cu and Cd in copper tailings,and make them easier to be absorbed by plants.(3)The effects of PASP,CA and FA at different concentrations on the growth,absorption and transport of Cu and Cd in ryegrass were studied.The results showed that activator CA inhibited the growth of ryegrass,and the other two activators increased the biomass of ryegrass.The biomass of ryegrass was increased by the largest amount under PASP-7 treatment,and the total dry weight was increased by 151.01% compared with the control.The three activators all promoted the absorption of Cu and Cd in ryegrass,and the absorption content was higher than that in a stem;The enrichment coefficient of Cu and Cd in ryegrass was increased in different degrees.Compared with the control group,the transport coefficients of Cu in ryegrass under CA-1,FA-4 and PASP-1 increased by29.41%,23.06% and 17.65%,respectively.Except for CA-1,CA-10 and FA-10,the transport coefficients of Cd in ryegrass under other treatments significantly increased.Under FA-7 and PASP-7 treatments,the removal rates of Cu and Cd from ryegrass were the highest,which were0.23% and 0.44%,respectively.Through principal component analysis,it was found that the composite score of PASP-7 treatment was the highest,which was 2.708,indicating that 7 g/L PASP had the best effect on the overall migration of Cu and Cd in copper tailings.To sum up,among the three activators,PASP,CA and FA,the comprehensive effect of PASP enhancing ryegrass’ s absorption of heavy metals Cu and Cd in copper tailings is the best,and the optimal application concentration of PASP is 7 g/L.