Removal of Mn2+ in geothermal water by manganese sand: process and mechanisms

Geothermal water resources are being exploited widely in many areas to relieve pressure on water resources generally. Excessive Mn2+ concentration in geothermal water will seriously reduce its utilization rate. Therefore, this study investigated the removal of Mn2+ from simulated geothermal water by manganese sand. The Mn2+ removal rate from simulated water with a concentration of 10 mg l−1 by 2 g manganese sand at 298, 323, 343 and 363 K was more than 90%. The removal efficiency of Mn2+ is influenced by adsorbent dosage, adsorbent particle size, initial Mn2+ concentration and competing ions, and less so by a pH of 5–9. A pseudo-first-order kinetic model fits the adsorption data better than a pseudo-second-order model. The pseudo-first-order adsorption rate constants (K1) ranged from 0.14 to 0.5 h−1 as the temperature increased from 298 to 363 K. The Langmuir isotherm model fits the adsorption data better than the Freundlich and Temkin isotherm models. The maximum monolayer adsorption capacities (qm) obtained by the Langmuir isotherm model fitting were 0.91/1.02/1.22/1.23 mg g–1 at 298/323/343/363 K. Thermodynamic studies revealed that the adsorption was endothermic and physical in nature. These findings suggest that the potential of manganese sand for removing Mn2+ in geothermal water is considerable. Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues