The invention generally relates to methods of removing potassium, rubidium, and/or cesium, selectively or in combination, from brines using tetrafluoroborates. Also disclosed are methods of producing potassium, rubidium, and/or cesium chlorides using ionic liquids and exchange media. This invention also generally relates to treated geothermal brine compositions containing reduced concentrations of silica, iron, and potassium compared to the untreated brines. Exemplary compositions of the treated brine contain a concentration of silica ranging from about 0 mg/kg to about 15 mg/kg, a concentration of iron ranging from about 0 mg/kg to about 10 mg/kg, and a concentration of potassium ranging from about 300 mg/kg to about 8500 mg/kg. Other exemplary compositions of the treated brines also contain reduced concentrations of elements like rubidium, cesium, and lithium.