Kinetic Modeling and Mechanisms of Manganese Removal from Alkaline Mine Water Using a Pilot Scale Column Reactor

Manganese (Mn) is a major element in various aqueous and soil environments that is sometimes highly concentrated in mine water and other mineral processing wastewater. In this study, we investigated Mn removal from alkaline mine water (pH > 9) with an Mn-coated silica sand packed into a pilot-scale column reactor and examined the specific reaction mechanism using X-ray absorption near-edge structure (XANES) analysis and geochemical kinetic modeling. The kinetic effect of dissolved Mn(II) removal by birnessite (δ-Mn(IV)O2) at pH 6 and 8 was evaluated at different Mn(II)/Mn(IV) molar ratios of 0.1–10. Our results confirmed the positive effect of the presence of δ-MnO2 on the short-term removal (60 min) of dissolved Mn. XANES analysis results revealed that δ-MnO2 was more abundant than Mn(III)OOH in the reactor, which may have accumulated during a long-term reaction (4 months) after the reactor was turned on. A gradual decrease in dissolved Mn(II) concentration with depth was observed in the reactor, and comparison with the kinetic modeling result confirmed that δ-MnO2 interaction was the dominant Mn removal mechanism. Our results show that δ-MnO2 contents could play a significant role in controlling Mn removability from mine water in the reactor.

Effect of Cone-Plate Clarifier Structure Parameters on Flocculation Efficiency

In this study, a coal mine water flocculation system was established. A series of flocculation tests were carried out at different structural parameters (cylinder height, cone-plate insertion depth and cone-plate spacing) to better investigate the effect of the cone-plate clarifier on coal mine water treatment performance. Sixteen sampling points were set up in the system for data monitoring to generate the required data. The cone-plate clarifier was divided into five zones for flocculation analysis. The increased cylinder height facilitated the flocculation of particles in the micro flocculation zone and the settling of particles in the settlement zone. The chemicals used are polyaluminum chloride (PACl), Fe3O4 and polyacrylamide (PAM), corresponding to doses of 60 mg/L, 40 mg/L and 6 mg/L, respectively. Insufficient insertion depth of the cone-plate will cause the small flocs that have not been fully flocculated to enter the exit pipe zone directly through the cone-plate, while too much insertion depth will cause the large floc in the settlement zone to re-enter the exit pipe zone. The flocculation effect of small flocs increased as the cone-plate spacing decreased, which is consistent with the shallow pool theory. When the cone plate spacing was too narrow, the amount of fluid was reduced and the increase in fluid velocity reduced the flocculation effect. Curve fitting was conducted for Suspended solids(SS) and turbidity removal efficiency under each structural parameter to derive the variation of SS and turbidity removal efficiency under different structural parameters. The regression models of SS and turbidity removal efficiency on the cylinder height, cone-plate insertion depth and cone-plate spacing were established based on the curve fitting results, and the regression models were verified to be well fitted based on the comparison of experimental results. Finally, the optimal values of SS and turbidity removal efficiency were found based on the regression model. The flow rate of the cone-plate clarifier is 0.6 m3/h. The SS removal efficiency reached 96.82% when the cylinder height was 708 mm, the cone-plate insertion depth was 367 mm and the cone-plate spacing was 26 mm. The turbidity removal efficiency reached 86.75% when the cylinder height was 709 mm, the cone-plate insertion depth was 369 mm and the cone-plate spacing was 26 mm.

Closure of German Hard Coal Mines: Effects and Legal Aspects of Mine Flooding

Following the closure of the last hard coal mines in Germany, pumping is no longer necessary. However, the resulting rise of mine water can affect the environment. Laws have been enacted at the European and national level to protect properties. Within the framework of the approval procedure, it must be determined whether the cessation of pumping may cause unacceptable effects, including water pollution. With regard to water protection, the European Union has issued the Water Framework and Groundwater Directives, which have been implemented into German national law. These contain the prohibition of deterioration and the requirement for improvement, with the aim of maintaining or achieving good ecological and chemical status. However, before the target mine water level is reached, the water does not need to comply, since although the pumps are switched off, no mine water is being discharged. This also rules out permit requirements, which only go into effect when the target mine water level has been reached and mine water is discharging. Obviously, however, detailed planning before then is necessary.

Economic Analysis of the Application of the Technological System for Removing Suspended Solids from Mine Drainage Waters

This paper presents the results of the technological and economic analysis of mine water treatment systems before their discharge into the environment. The following analysis enabled us to determine the profitability of the investment, taking into account the TSS (total suspended solids) concentration in mine water. The simulation results showed that it is economically profitable to apply a water treatment system if natural sedimentation carried out in underground mine water passages, or in sedimentation tanks located on the ground, is ineffective for TSS removal. Economic and financial parameters allow us to conclude that all analyzed variants of the application of a pre-treatment system are characterized by high economic effectiveness. This mainly results from the high profitability of an analyzed investment, comparatively low capital expenditure, and present low market percentage rates. The most profitable variant (TSS concentration is 1000 mg/dm3) brings significant economic indicators, i.e., high NPV–Net Present Value (100 319 270.28 PLN), a high NPVR–Net Present Value Ratio (8.96 PLN/PLN), and a short discount payback period (1 year 236.6 days). A high internal rate of return (157.8%) for this variant reduces the risk of losing profitability in a situation of growing capital costs in the monetary market.