Potential Use of Oxygen Depleted Air In Nickel Sulphide Flotation

Abstract: Copper-nickel low grade ore deposits normally have complex mineralogy and process behaviour. Implementing an optimum process that is able to recover all the valuable minerals efficiently is challenging. One concentration strategy in mineral processing of copper-nickel sulphide ores is stage-wise flotation. The first flotation stage concentrates mainly copper minerals. The copper middling is re-floated to obtain nickel concentrate.During the industrial process of copper-nickel ore, it was observed that significant amount of nickel sulphides was lost to the tailings during the nickel flotation. When the nickel flotation feed was sampled and tested in laboratory scale, most of the liberated nickel sulphides were recovered. On the contrary, when the industrial nickel tailing was re-floated in laboratory, most of these nickel sulphides were not recovered. In this work, laboratory tests were performed on the ore to investigate the effect of oxygen depleted gas in nickel circuit recovery. Mechanical surface cleaning and slimes dispersion with dispersant addition before the nickel stage were also tested.Pure nitrogen gas flotation results proved that zero oxygen activity is detrimental for sulphides recovery during the nickel stage. The 5% oxygen gas achieved higher nickel recovery and selectivity than air flotation. Most of the pentlandite lost in the tailings of air and depleted oxygen gas were locked. In the fractions finer than 45 μm, the tailing of air flotation contained more liberated pentlandite than the 5% oxygen gas.Mechanical surface cleaning by short stirred mill applied before the nickel stage improved significantly the nickel recovery of every gas flotation, except for the 5% oxygen gas. When dispersant was added to the standard laboratory flotation, iron slimes were observed in the tailing filtrate.Due to the long residence time and high reactivity of sulphides, excessive surface oxidation is believed to be the major reason of the nickel flotation impairing. Colloidal hydroxide slimes formed during sulphides oxidation may smear on mineral surfaces making them hydrophilic. Consequently, the flotation kinetics are slowed down. Short attrition grinding to clean mineral surfaces, along with dispersant addition to keep dislodge slimes in solution is one remedy. Another solution is applying lower oxygen activity of the flotation gas to decelerate the sulphides oxidation and therefore diminish the colloidal hydroxide slimes presence. The flotation residence time can be dramatically shortened in both cases. Further tests are recommended.