Phytoremediation is considered to be the most environmentally friendly green restoration technology for dealing with mine waste. Adding amendments can improve the substrate environment for plant growth and enhance remediation e ciency. Herbaceous plants have become the preferred species for vegetation restoration in abandoned mines because of their fast greening and simple management. Considering that, in this paper, to explore the effect of composite amendments on physicochemical properties of copper tailings repaired by herbaceous plants, the untreated copper tailings were employed as the control group, whereas copper tailings repaired by ryegrass (Lolium perenne L.), vetiver grass (Vetiveria zizanioides L.) and tall fescue (Festuca arundinacea Schreb) with or without conditioners and straw combination into the compound amendments, were taken separately as the test group. After 6 months of planting, the pH, electrical conductivity, water content, available potassium, organic matter, total nitrogen and available phosphorus in the main physical and chemical properties of copper tailings in each experimental area were analyzed. The results showed that the electrical conductivity, organic matter and total nitrogen content of copper tailings were improved to a certain extent by planting herbs without treatment. Meanwhile, compared with the control group, all indexes of planting herbs showed an upward trend after adding composite amendments. Among them, pH, water content and available potassium content of copper tailings were enhanced more obviously. Furthermore, as discovered from the grey correlation analysis results, vetiver grass planted with composite amendments has the best comprehensive effect of improving the physicochemical properties of copper tailings, followed by tall fescue and ryegrass.
Both chemical corrosion and axial compression impose critical influences on the internal microstructure of rock. Meanwhile, chemical corrosion can change a rock’s mineral composition, which in turn affects the physical and mechanical properties of the rock. To investigate the dynamic strength characteristics of white sandstone under the coupling effect of axial load and chemical corrosion, a dynamic and static combined loading test device was adopted for performing cyclic impact tests on white sandstone immersed in chemical solution. The results show that with the increasing number of cycles under the same load, the peak strength of the rock presented a trend of ‘strengthening first and then weakening’. The strength of rock resistance to impact failure reached its maximum when the solution of pH was 7 and axial pressure was 12.6 MPa. Under the same axial pressure, the effect of solution pH on the initial dynamic strength of white sandstone is a normal distribution. Acidic and alkaline environments are harmful to rocks during the initial impact, while neutral environments exert little effect and the pH of the solution influences the particle size of impact crushing particles. In addition, the chemical solution has a significant effect on the deterioration of rock strength during the process of initial impact, and the effect is inconspicuous in the later period.
To explore the influence of cyclic impact and axial pressure on the damage of chemically corroded sandstone, a series of cyclic impact tests were carried out on white sandstone by using Split Hopkinson Pressure Bar. The longitudinal sections and fractures of samples were observed with the scanning electron microscope. The aim was to investigate the damage characteristics and structural changes of sandstone, that subjected to the coupling of force and chemistry. The results show that: (1) When pH of solution is 7, the total cyclic impact number and stress peak of specimens both became larger, and the rock samples responded with a significantly high resistant strength. (2) The stress wave transmission coefficient of sandstone decreases gradually with the increase of the number of cyclic impacts, while the reflection coefficient shows a tendency of" decreasing first and then increasing". (3) Cylindrical specimens with a certain axial pressure present an "X" shaped conjugate failure under cyclic impact. When axial pressure is too large or excessive impact, the "X" shaped conjugate undergoes shear to a state of broken cone. (4) The vertical section and fracture surface damage degree of white sandstone soaked in Na2SO4 solution is more serious than that in NaCl solution.
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