Access to this article is restricted until 12 months after publication by request of the publisher. Restriction lift date: 2022-04-15
Mineral precipitations and hydrochemical evolution of brines in graduation towers
The purpose of this study is to examine hydrochemical changes of saline groundwater and precipitation of mineral phases during evaporative graduation processes. Therefore, concentrated brines and mineral precipitates were sampled at four graduation towers with differing evaporation approaches. Solid phase compositions were qualitatively and quantitatively analysed. Hydrochemistry changes of dissolved ion concentrations during successive evaporation was assessed by comparing natural with concentrated brines. PHREEQC was used to simulate sequence and quantity of mineral precipitates. Finally, a prognosis for expected precipitations of a newly built graduation tower was made using PHREEQC modelling. The identified mineral phases included calcite, aragonite, gypsum and halite in varying proportions. Concentrations of all investigated ions (except bicarbonate) increase, eventually leading to supersaturation and sequential precipitation of evaporite minerals. Modelled saturation indices show that calcite is the first and halite is one of the last precipitating phases at all sites. Further calculated precipitates include the carbonates dolomite, siderite and strontianite; manganese oxide and hematite; and the sulphates baryte, celestine and gypsum which precipitate depending on local hydrogeochemistry and graduation conditions. Calculated precipitation quantities reach a maximum of 48.6 g/L of applied natural brine at an evaporation grade of 90%. After 25 years, the total expected mass of precipitates at the new graduation tower is about 34.4 t for a graduation process up to a salt content of 19%, and about 356 t for a permanent evaporation grade of 90%.
Concentrated brine , Evaporite mineralogy , Germany , Graduation tower , Saline groundwater , Münsterland Cretaceous Basin
Ostwald, L. J. and Banning, A. (2021) ‘Mineral Precipitations and Hydrochemical Evolution of Brines in Graduation Towers’, Environmental Processes, 8 (2), pp. 729–746. doi: 10.1007/s40710-021-00511-5