| Acid mine drainage has the characteristics of low pH, large quantity and high content of metal ions. If it is discharged into natural environment without being treated, it will make the water body polluted badly, the ecological environment damaged, even it will endanger human health.Two methods were used to treat acid mine drainage, in which the concentrations of Fe2+, Fe3+, Mn2+ and Zn2+ are 2742 mg·L-1,158 mg·L-1, 315 mg·L-1 and 150 mg·L-1 respectively. The results show that the treated wasterwater can reach the Chinese standards of wastewater discharge (GB8978—1996) and realize the reclamation.The treatment of acid mine drainage by two-steps neutralization method of lime and sodium hydroxide was studied. After the pH of the wastewater is adjusted to about 5 with lime, the removal rates of total iron(TFe), Mn and Zn are 14.14%,5.94% and 13.91% respectively. The first-step sediment is gypsum(CaSO4·2H2O). In the second-step, sodium hydroxide was used as neutralizing agent. Under the conditions that pH is 10.20, airflow is 50mL·min-1, reaction time is 20 min,reaction temperature is 12℃, the removal rates of TFe, Mn and Zn are all up to 99.7%, and the concentrations of TFe, Mn and Zn are 0.08 mg·L-1,0.81 mg·L-1 and 0.03 mg·L-1 respectively. XRD shows that the second-step sediment are Fe2Mn0.5Zn0.504·nH20 and Fe3O4. Comparing two-steps neutralization method with lime neutralization method, the two-steps neutralization method produces less slag which has comprehensive utilization value.Separation and recovery of Zn, Fe and Mn from acid mine drainage were researched by applying absorption with mechanically activated pyrite, oxidation-precipitation and sodium hydroxide neutralization. The results show that the optimum conditions of mechanically activated pyrite are as follows:ball-to-pyrite weight ratio is 8:1, grinding time is 4h, liquid-solid ratio is 2:1. The concentrations of TFe, Mn and Zn are 5466.84 mg·L-1, 353.04 mg·L-1 and 1.33 mg·L-1 respectively when the pH of the acid mine drainage is 1.83, the dosage of activated pyrite is 975g in 10L wastewater, reaction time is 20 min. In 10 L wastewater after removing Zn, the residual Fe and Mn are 97.96 mg·L-1 and 290.55 mg·L-1 respectively when the pH of the wastewater is 6.92, airflow is 500mL·min-1, reaction time is 2.5h, stirring speed is 300r·min-1. XRD shows that the product of oxidation-precipitation is Fe3O4, in which the content of Fe is 52.73%. The residual Mn is 1.15 mg·L-1, and the Mn content in the sediment is 34.47% when the pH of the wastewater is adjusted to about 11.01 with sodium hydroxide solution, reaction time is 30min. The effluent quality can meet the Chinese standards of wastewater discharge (GB8978—1996) after the pH of the Mn removing wastewater is adjusted to 7 with sulfuric acid.After griding, pyrite particle size became smaller, specific surface area increased, reaction activity increased, SO42- and OH which can improve its hydrophilicity were produced, and the solubility of pyrite increased. Research shows that under the acidic conditions, activated pyrite dissolves and produces S2-,S2- reacts with Zn2+ and produces ZnS, which is adsorbed and co-precipitates with activated pyrite. The main mechanism of removing Zn by activated pyrite is chemic precipitation reaction and absorption co-precipitation. |
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