| The mining wastelands destroy and take up a great deal of land resources. The mining wastes, such as tailings and acidic wastewater, etc., causing serious pollution to the surrounding air, soil and water environment. Especially for the restoration of wastelands polluted by heavy metals, confronting series of difficulties, such as destruction of soil properties, heavy metals pollution, extreme pH values, and high salts content, etc. Furthermore, with the continuous improvement of urban sewage treatment rate, the amount of sludge generated by the sewage treatment process is sharply dramatically increasing. Seeking a reasonable treatment and disposal pathway has become a hot issue to be solved.This study explored the feasibility and existed problem of the use of lime-stabilized sewage sludge and composted sewage sludge on the restoration and remediation of mining wasteland soils polluted by heavy metals, aiming at simulated heavy metals contaminated mining wasteland soils and actually heavy metals contaminated soils in Jiahe County, Hunan Province. The main conclusions obtained in the study are summarized as follows:1. For the simulated contaminated soil, only lime-stabilized sludge used as stabilizer, the concentrations of heavy metals in the TCLP leachate reduced significantly, with the increase of the mass percentage of the sludge. The maximum removal rates are99.54%for Zn,99.60%for Pb,99.85%for Cd, which means the stabilization effect is very effective. The pH values of the stabilized soils increased with the increase of the lime-stabilized sludge, and the maximum is11.56, which is not suitable for plant growth.2. For the simulated contaminated soil, only composted sludge used as stabilizer, the concentrations of heavy metals in the TCLP leachate reduced significantly, with the increase of the mass percentage of the sludge, which is below30%. The maximum removal rates are99.54%for Zn,99.60%for Pb,99.85%for Cd. However, when the mass percentage is greater than30%, the concentrations of the three metals in the leachates increased on the contrary. The maximum pH value of the stabilized soils is7.91, suitable for plant growth.3. For the simulated contaminated soil, after stabilized by30%of lime-stabilized sludge and Fe salt, the pH of the soil reduced to the suitable range for plant growth. The concentrations of Zn and Pb in the leachates decreased a bit while the concentration of Cd increased. After stabilized by30%of lime-stabilized sludge as well as phosphoric acid, the pH of the soil reduced and the concentrations of the three metals decreased significantly.4. For the actual contaminated soil, only lime-stabilized sludge used as stabilizer, the concentrations of Zn、Pb Cd in the TCLP leachate reduced significantly, with the increase of the mass percentage of the sludge. The maximum removal rates are98.92%for Zn,96.84%for Pb,99.26%for Cd. However, the leaching concentration of As increased with the dose of sludge increasing, even higher than that of actual contaminated soil, mainly because of the high pH.5. For the actual contaminated soil, after stabilized by30%of lime-stabilized sludge and Fe salt, the pH of the soil reduced to the suitable range for plant growth. At the same time, the concentrations of Zn, Pb and As in the leachates decreased while the concentration of Cd increased a bit. The concentration of As in the leachates of soil stabilized by40%lime stabilized sludge and11%Fe salt decreased significantly by74.72%.6. Water stable aggregates compositions and nutrients of the soils have a significant improvement after stabilized by lime-stabilized sludge/composted sludge and pH adjusted. In addition, the germination rates of spring wheat are close to that in the natural soil, much more higher than that before stabilized.7. The concentrations of DOC、NO3-、NO2-of the soils increased greatly after stabilized by sewage sludge, especially by the composted sludge. This may have negative impacts on groundwater quality of the restoration area. |
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