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.