Study Of Gangue Leaching Characteristics And In-Situ Remediation By Electrokinetics Coupled With Permeable Reactive Barrier

Gangue is a kind of solid waste discharged through coal mining and coal washing process, which accounts for a large proportion in the whole solid wastes mass. To resolve the area covering problem, gangue can be recycled in paving. However, gangue, used as renewable sources, is possible to produce secondary pollution to the environment. Large amounts of toxic and harmful pollutants like heavy metals and acid radical ions would dissolve easily and permeate into soils and groundwater along the road after long-term rainfall washing and soaking. Therefore, it is necessary to investigate the leaching characteristics of pollutants in gangue, and find effective measures to reduce the effects on soils and groundwater further.Firstly, experiments were conducted simulating natural rainfall to find the leaching characteristics of heavy metal ions and acid radical ions pollutants in gangue. Soaking time, solid-liquid ratio and pH of soaking solution were changed in the soaking experiment, and gangue porosity (the mass ratio of gangue, clay and gravel) were changed in the dynamic leaching experiment. The soaking experiment results showed the soaking equilibration time of metal and acid radical ions pollutants was48h. When the solid-liquid ratio and pH decreased, more pollution in gangue leached out. The dynamic leaching experiment results showed that the lower the gangue porosity was, the higher dissolution rates of metal and acid radical ions were, which caused secondary pollution to environment more easily.Then combined electrokinetics (EK) and permeable reactive barrier (PRB) in-situ remediation technologies were used to reduce or remove the pollutants in soil. The main purpose is to improve the EK remediation efficiencies of metal and acid radical ions through changing the reactive media in PRB, and to verify the most feasibility and efficient remediation among PAN nanofiber, chitosan (CTS) and methanal-epoxy chloropropane modified chitosan (MCTS) PRB coupled with EK technology. EK coupled with PRB in-situ remediation system remediated the metal ions (Zn2+, Fe3+and Ca2+) and acid radical ions (SO42-and NO3-) in soil. The electro-spinning PAN nanofiber used as the reactive medium in PRB was developed through electro-spinning. The EK/PAN nanofiber PRB system processed remediating experiment by changing the initial conditions of applied voltage, initial pollution concentration and soil pH. With the applied voltage of25V, initial ions concentration (Zn2+, Fe3+, Ca2+, SO42-and NO3-) of10,25,250,4000,500mg·L-1and soil pH of1.2, the remediation efficiency of metal ions reached more than94%and was close to80%of the acid radical ions. As for the EK/PRB system with chitosan or methanal-epoxy chloropropane modified chitosan for the reactive medium. The remediation efficiency of acid radical ions was better than that of EK/PAN nanofiber PRB system. The mechanical strength of modified chitosan was strengthened and the adsorptive property of ions was also improved. The acid radical ions remediation efficiency in EK/MCTS PRB system reached90%.