| Acid mine drainage (AMD) forms when sulfide minerals in coal seam and surrounding rocks are exposed to chemical oxidants (such as Fe3+and O2) and thiobacillus ferrooxidans. AMD usually has a low pH value, in addition to rich in Fe3+and SO42-, and leaches heavy-metals in the associated minerals, such as lead, copper, cadmium, zinc, chromium, etc. It causes serious harm for mining production, groundwater resources and ecological environment. In this study, in combination with the structure design of permeable reaction barrier (PRB), activated carbon, bamboo charcoal, ceramsite, fly ash, coal cinder were employed as the reaction medium of permeable reaction barrier (PRB) to remediated heavy metal ions and other pollutants in AMD, and the study of coal ash modification and activated carbon regeneration were made. It provides a new way of for the treatment of underground AMD, and have important significance on the green production of high sulfur coal, what’s more, it is conducive to the protection of groundwater resources and ecological environment of the mining area.First, based on the characteristics of permeable bed reaction, a PRB reactor suitable for laboratory operation was designed, and the laboratory system was established.Second, ceramsite (two particle size), coal cinder, charcoal (two size) and fly ash were compared on COD, SO42-and heavy metal removal and pH adjustment. The results showed that:(1) the six reaction fillers displayed certain removal for COD and SO42-in eight hours, and pH can be adjusted from4to7(fly ash can adjust pH to8);(2) the removal efficiencies of COD and SO42-were between10%and50%(coal cinder presents the lowest removal effect, and the removal rate was only about10%in8h);(3) when the reaction time was2days, fly ash (small size), ceramsite and bamboo charcoal (small size) still maintained a high removal rate of COD, and bamboo charcoal (large size) presented a high removal rate of SO42-.Third, the reaction materials mentioned above were tested for remediation of simulative AMD. The results showed that:(1) fly ash had a good adjustment for pH and the removal efficiency of COD and SO42-can achieve50%;(2) a high removal efficiency of SO42-can be maintained for6days when bamboo charcoal was used as the reaction material;(3) coal cinder can only display a good treatment effect for12hours;(4) ceramsite presents a good removal for SO42-and stable in performance.And then, in order to prepare simulative wastewater of which the water quality is similar to practical AMD, the heavy metal ions including Cd2+, Cu2+, Zn2+were added. The feasibility of using different filling materials to treat the three metal ions was studied, and the effect of the mixture ratio of several filling materials was investigated, and the treatment effect of simulative wastewater using PRB. The results indicated that good treatment efficiencies were obtained using several filling materials separately, and that when they are mixed according to a certain ratio, the treatment efficiencies were increased. Fly ash was proved to be a good filling material with Cd2+removal of35%and with Cu2+removal of50%in24h, and thereafter, the removal rate decreased with no obvious treatment being observed. The mixture of ceramsite and fly ash had a better removal of three heavy metals used than separate filling material, and good removal efficiencies could be maintained for a long time, and the removal rates of Cd2+, Cu2+, Zn2+were91%,98%,92%, respectively. Activated carbon, as a filling material, had a good treatment for the removal of heavy metals, especially Cu2+, of which the removal could reach over99%, even when the reaction time was66h.To further enhance the durability of the filler, various modifications of fly ash were made. Results showed that the treatment efficiency using acid-modified fly ash was the best. Acid chemically modified fly ash improved treatment of various pollutants with the Cd2+removal increased from42.9%to82.4%, the Zn2+removal from26.7%to57.2%, and especially the Cu2+removal from74.8%to91.85%.Finally, to compare other viable materials, activated carbon was chosen as the reaction medium, and the treatment of AMD water was studied. Results showed that activated carbon had a good treatment effect for AMD, and the highest removal of COD and SO42-was achieved in8h up to46.7%,70%, respectively; the highest removal of Cd2+, Cu2+, Zn2+can be up to90%,98.8%,90%, respectively, the removal of Cu2+was still80%when the reaction time was200h. Therefore, activated carbon is an ideal reaction medium. Due to the high costs of activated carbon and secondary pollution problems, the regeneration of activated carbon were studied in this work, and the results indicated that acid regenerate of activated carbon shows good treatment effect on acid mine water. |
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