Long-term removal of manganese in geothermal water: column experiment and model simulation

The high concentration of manganese (Mn 2+ ) in geothermal water will seriously reduce its utilization rate. Manganese sand has been used to rapidly remove Mn 2+ from water. This study investigated the long-term removal of Mn 2+ from simulated geothermal water by manganese sand filtration column system. The average Mn 2+ removal rate from simulated water with the inlet water temperature of 25, 50, 70 °C were 87.4%, 96.2% and 99.0% during the operation of 90 days. The effluent pH did not change much compared with influent pH value (7.6–8.0). The Mn 2+ removal rates during the operation of 90 days with influent concentration of 1, 10, 20 and 50 mg/L were respectively 98.2%, 99.8%, 91.4% and 63.4%. The average removal rates of Mn 2+ were respectively 99.8% and 94.0% with the influent flow of 5.2 mL/min and 10.4 mL/min. The temperature change in the manganese sand filtration column was further explored in this paper. The experiment of filtration column heated/non-heated showed that the manganese sand filtration column heated had a better effect of removal which could run for 152 days. The dispersion coefficient ( D ) analysis derived from inverse modeling showed that a small temperature change in the filtration column system was conducive to the homogenization of manganese sand medium in the column. The Mn 2+ removal process of manganese sand filtration column heated was proposed. Surface characteristics analysis of manganese sand in the column after reaction showed that Mn 2+ removal mainly occurred in the upper part of the filter column. The surface material of manganese sand in the filtration column heated after operation was manganese oxide material mainly composed of Mn 2 O 3 and MnO 2 . These findings suggested the potential of manganese sand in the engineering application of removing Mn 2+ in geothermal water.