Research On Construction Of Artificial Soil Based On Fine-grained Tailings

At present,the stockpiles of tailings are large in our country,which not only harms the surrounding ecological environment,and poses potential safety hazards,but also affects the sustainable development of enterprises.Hence,the resource utilization of tailings is imminent.The preparation of artificial soil from tailings is an effective solution,but the characteristics of tailings,such as fine particle size,large bulk volume,and infertility of nutrients,have become important constraints for the construction of artificial soil.Therefore,this study intends to select bentonite and microalgae as modifiers to promote the agglomeration of fine tailings particles and restore the physicochemical properties of soil,thereby constructing artificial soil.Firstly,in the pot experiment,the improvement effect was measured in terms of plant growth status,soil physicochemical properties,and soil aggregate fractal,so as to select the best concentration of bentonite and microalgae;then they are applied to the dry heap tailings site to comprehensively evaluate the improvement effect.The research results are as follows:（1）The research on the characteristics of fine-grained copper tailings shows that:the tailings have a median particle size of 27.94μm,relatively poor physicochemical property,such as a bulk density of up to 1.68 g/cm³and sterile fertility.It is alkaline soil dominated by carbonate minerals.The content of copper in the tailings is relatively high,at 489 mg/kg,but the content of other harmful metal elements is relatively low.The analysis shows that:the bentonite has fine particle size,the median particle size is 11μm,the expansion capacity is as high as 30 ml/g,the electronegativity is strong,and it shows strong water storage and fertilizer retention ability;The equilibrium concentration of microalgae is as high as 800 mg/L,and the algal filaments are entangled in clusters,showing strong cementing ability.So bentonite and microalgae can be used as tailings substrate improvement.（2）The screening study of the addition amount of bentonite and microalgae showed that the addition of the two modifiers could improve the growth height,fresh weight,and soil moisture content of plants.Cation exchange capacity（CEC）and organic matter increased significantly when the bentonite content was greater than8%and greater than 4%,respectively;when the microalgae-soil mass ratio was greater than 1:15000,CEC and organic carbon increased significantly.With the increase of bentonite content,soil aggregate stability index R_0.25,mean weight diameter（MWD）and geometric mean diameter（GMD）increased significantly,and tended to be stable after the content was more than 8%.With the increase of microalgae content,soil aggregate stability indicators R_0.25,MWD and GMD also increased significantly,and tended to be stable after the ratio more than 1:15000.During the improvement process,the addition of bentonite was beneficial to the transformation of copper from weak acid state to residue state,while the addition of microalgae was beneficial to the transformation of copper from oxidation state to residue state.The correlation results showed that under the improvement of bentonite and microalgae,the stability of soil aggregates was significantly positively correlated with plant height,fresh weight,water content,CEC and organic matter.Based on the above,the addition amount of bentonite was selected as 8%,and the microalgae-soil mass ratio was 1:15000.（3）The addition of bentonite and microalgae in the site remediation study showed that the bentonite group,microalgae group and composite group could increase plant fresh weight and soil moisture content,and reduce soil bulk density.The improvement in the bentonite group was more conducive to increasing plant height and fresh weight,and the compound group was beneficial for the accumulation of plant chlorophyll content and soil moisture content.The improvement in the bentonite group and the compound group significantly increased the soil CEC content,and the compound group had the largest CEC content at 86 days of improvement.The microalgae group and the composite group were beneficial to increase the content of soil organic carbon in the early stage of improvement,while the bentonite group had better improvement effect in the later stage.Bentonite group and composite group were more favorable for increasing soil aggregates,and R_0.25,MWD and GMD were significantly larger.Further microscopic scanning with three-dimensional showed that the composite group had the largest porosity and better pore structure.Through high-throughput sequencing,it was found that the bacterial communities of the control group and the experimental group were significantly different,among which the bentonite group had the greatest microbial diversity and abundance,while the microalgae and composite groups significantly increased the content of Thiobacillus and decreased the content of the pathogen Nocardia,and the results of redundancy analysis indicated that MWD,bulk density and GMD were the key driving forces for the formation of bacterial communities.Combining the results of plant growth traits,soil physicochemical properties,aggregate stability,bacterial community diversity,and soil pore structure reflected by three-dimensional CT microscopic images,the composite group had the best improvement effect on the tailings matrix.