Application of magnesium hydroxide and barium hydroxide for the removal of metals and sulphate from mine water

The proposed magnesium-barium-oxide process consists of metal removal with Mg(OH)2, magnesium and sulphate removal with Ba(OH)2 and calcium removal with CO2. The raw materials, Mg(OH)2 and Ba(OH)2 are recovered from the BaSO4 and Mg(OH)2 sludges that are produced. Laboratory studies showed that metals are removed to low levels. This includes iron(II), the dominant metal ion in mine water, which is first oxidised to iron(III), whereafter it precipitates as Fe(OH)3 resulting in residual levels of Fe(II) in the mine water of less than 20 mg/ . Sulphate is also removed to less than 25 mg/ . The final sulphate concentration is a function of the amount of Ba(OH)2 dosed, as the amount of sulphate removed is stoichiometrically equivalent to the Ba(OH)2 dosage. During CO2-dosing, CaCO3 is precipitated to the saturation level of CaCO3.