Evaluation of water quality change and sludge generation according to hydrogen peroxide treatment during lime neutralization

This study investigated the effect of hydrogen peroxide treatment on the removal pH for Fe, Al, and Mn and sludge production in the lime neutralization process. In the laboratory, the AMD collected from the coal mine was oxidized with 5% H₂O₂, and then neutralized to pH 3, 5, 7 and 9, respectively, with 20% lime slurry. In the control experiment, the same neutralization experiment was performed without H₂O₂ treatment. During the experiment, the supernatant was measured for pH and Eh and analyzed for Fe, Al, Mn, Ca and SO₄^2- ions. Simple neutralization without H₂O₂ treatment up to pH 8 resulted in almost 100% Fe (<0.3 mg/L), Al (<0.3 mg/L), and Mn (2 mg/L) removal. Neutralization with pre H₂O₂ treatment also eliminated Fe and Al at pH 6 to the same removal efficiencies and Mn remained at 15 mg/L. The use of lime was 17% less and the weight of sludge was 35% less, and the volume of sludge decreased by 47%. As a result of evaluating the pH-Eh-Fe diagram for hydrogen peroxide/lime neutralization facilities, it was evaluated that Fe could be removed at pH 5-6. It can be concluded that neutralizing up to pH 6 after oxidation effectively minimizes the amount of sludge generated by removing Fe and Al and suppressing gypsum production.