A novel scheme for flotation tailings pulp settlement and chemical oxygen demand reduction with polyferric sulfate. (20th December 2019) - Meng, Xiangsong
Abstract: In most of the mining industries, lime is widely used to settle flotation tailings pulp. However, this conventional method has some drawbacks, as it increases pH, organic matter content and chemical oxygen demand (COD) of tailings dam wastewater (TDW) and further treatment is required. Therefore, current research provides an innovative and environmentally friendly technology that uses polyferric sulfate (PFS) instead of lime for pulp settlement. A series of laboratory tests showed that the final settlement effects of PFS and lime for tailings pulp settlement were comparable. However, the COD of tailings water by PFS settlement was considerably reduced compared with that of lime settlement. Total organic carbon and fluorescence excitation–emission matrix analysis showed that organic matter content in tailings water by PFS settlement was also significantly lower than that of lime settlement. Lead nitrate and benzohydroxamic acid (Pb-BHA) synthetic solutions analysis showed that increasing or decreasing the pH dissolved Pb-BHA precipitates into water, leading to an increase in COD. Therefore, in lime settlement, the pH value significantly increased, which dissolved the remaining Pb-BHA precipitates in the pulp into water, resulting in an increase in COD. In PFS settlement, the pH change was small, and polynuclear hydroxyl complex generated by the hydrolysis of PFS adsorbed part of the organic matter to precipitate, resulting in COD reduction. Results of laboratory tests were further verified by an industrial test. The COD and pH of the TDW significantly decreased from 110 mg/L before the industrial test (lime settlement) to 68 mg/L and from 11.8 to 7.1, respectively, after the industrial test (PFS settlement). Graphical abstract: Image 1 Highlights: This study proposes a new technology to reduce COD in tailings water from the source. The new technology uses PFS instead of lime for flotation tailings pulp settlement. COD and pH of tailings wastewater by PFS settlement are much lower than that of lime. Increasing or decreasing pH results in dissolution of Pb-BHA precipitates into water. The new technology has been successfully applied in Shizhuyuan plants.