Abstract

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 (q_m) 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