Chemical Stability of Manganese and Iron in Mine Drainage Treatment Sludge: Effects of Neutralization Chemical, Iron Concentration, and Sludge Age.
The objective of this U.S. Bureau of Mines research was to determine how various factors influence the solubility of iron and manganese in mine drainage treatment sludge. Sludge samples from the field and laboratory-generated sludge samples were used for this study. The sludge collected in the field was subjected to lower ph conditions by sulfuric acid titration within 1 h of precipitation and after 1, 2, 4, and 6 months of aging. Two conditions were used for sludge aging: under the treated supernatant to simulate aging in a settling pond, and in air to simulate aging in a drying pond or disposal on coal spoil. Additional tests were performed using untreated mine drainage collected in the field and treated in the laboratory with hydrated lime, sodium carbonate, or sodium hydroxide. Prior to alkaline treatment, iron in the form of ferric sulfate was added to portions of this water to represent various levels of iron. The results of these tests indicate (1) sodium carbonate produced a less stable sludge than either lime or sodium hydroxide, (2) iron and manganese were less stable when iron was precipitated as ferrous as opposed to ferric hydroxide, (3) aging increased sludge stability, particularly aging in air, and (4) manganese was slightly more stable in sludge precipitated with high iron concentrations.