The impact of seawater with calcium and magnesium removal for the flotation of copper-molybdenum sulphide ores

•The impact of pretreated seawater on the floatability of Cu-Mo sulphide ores was analyzed.•Ca and Mg ions removal from seawater was carried out by adding a Na2CO3-CaO mixture.•Molybdenum recovery increased when the seawater hardness was reduced.•A high pyrite depression was reached due to the oxidizing atmosphere at pH 11.5.

The use of seawater in the flotation of copper-molybdenum sulphide ores is becoming increasingly important. However, the complex chemistry by the presence of calcium and magnesium hydroxyl-complexes interferes with the recovery of molybdenite. This study analyzes the impact of pre-treated seawater with calcium and magnesium removal on the floatability of copper-molybdenum sulphide ores. The pretreatment was carried out by a mixture of Na2CO3 and CaO, which promotes the precipitation of calcium and magnesium ions. Three different conditions were compared, (i) flotation in seawater at pH 11.5; (ii) flotation in pretreated seawater with calcium and magnesium removal at pH 11.5; and (iii) flotation in seawater at natural pH, i.e. pH ≈ 7.6. While the copper recovery was similar in all cases, the recovery of molybdenum at high alkaline condition was notably increased when seawater harness was reduced. On the other hand, a high pyrite depression was reached because the oxidizing atmosphere at pH 11.5 allows Fe(OH)3 formation.