Removal of Mn ²⁺ in geothermal water by manganese sand: process and mechanisms

Abstract

Geothermal water resources are being exploited widely in many areas to relieve pressure on water resources. 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 the concentration of 10 mg/L by 2 g manganese sand at 298, 323, 343, 363 K was more than 90%. The removal efficiency of Mn2+ could be influenced by the adsorbent dosage, adsorbent particle size, initial Mn2+ concentration and ions and could be influenced less by pH of 5-9. A pseudo-first-order kinetic model fit 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 K to 363 K. The Langmuir isotherm model could fit 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 0.91/1.01/1.22/1.23 mg/g 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 great.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