Optimisation of boric acid production plant wastewater treatment by calcium hydroxide and advanced treatment by ion exchange

The Emet boric acid production plant in Türkiye produces boric acid from the reaction of colemanite (Ca₂B₆O₁₁·5H₂O) with sulphuric acid (H₂SO₄). Sulphate, arsenic (III + V) and boron are released with the plant wastewater to the wastewater dam. This study aims to treat this boric acid production plant wastewater using calcium hydroxide in a batch reactor. The concentrations of the contaminants were 3956 mg/L sulphate, 2541 mg/L boron and 36.4 mg/L total arsenic (III + V). The boron removal kinetic studies were conducted to obtain the optimum parameter intervals for the application of the central composite experimental design method to remove these contaminants. The optimum conditions in the kinetic studies for boron removal were obtained as natural wastewater pH (5.32-5.68), temperature (20 °C), stirring speed (300 rpm), calcium hydroxide dosage (15 g/L) and time (90 min). Maximum boron removal obtained from the kinetic studies was calculated as 90.7%. The kinetics of boron removal obeyed the second-order model. Sulphate, boron and arsenic removal in the optimisation studies were calculated as 23.94, 87.94 and 98.36% in optimum boron removal conditions, respectively. An ion exchange treatment was applied to the calcium hydroxide treated wastewater containing boron and sulphate residues for ~ 100% removal.