The use of Sodium Citrate as a Reagent for Improved Process Performance of Ultramafic Nickel Ores

Wani, Omar

Abstract

The processing of ultramafic ores requires fine grinding, which results in slime-coating of the nickel-bearing mineral, pentlandite, by the phyllosilicate (clay) gangue mineral, serpentine. This lowers nickel recovery and concentrate grade during the froth flotation unit operation. The presence of divalent cations in process water exacerbates detrimental effects on nickel recovery by enhancing the positive surface charge of serpentine and causing charge reversal of pentlandite. The reagents currently used are either non-renewable, non-selective and toxic to the biodiversity around the processing plant. To explore environmentally benign reagents, the performance of sodium citrate as a reagent during the processing of ultramafic nickel ores was evaluated. Strong adsorption of the citrate molecule onto the serpentine surface was observed, whereas the interaction with pentlandite was inconsequential. In the presence of divalent cations, pentlandite becomes hydrophilic whereas its surface charge is reversed, thereby, reducing its recovery during froth flotation. The addition of citrate results in the formation of metal-citrate chelates which are negatively charged and are therefore desorbed from the pentlandite surface, thereby, restoring its charge and hydrophobicity as observed by zeta potential and contact angle measurements. Micro-flotation studies showed that using citrate as a reagent, nickel recovery and grade increased by 21% and 4% respectively, which demonstrated the binary depressive and dispersive effects of sodium citrate. The results have proven that sodium citrate, a bio-degradable and inexpensive reagent, can be not only be used as a pentlandite surface regenerator, but also a dispersant and depressant for the serpentine. The use of this reagent is anticipated to make the processing of low-grade ultramafic nickel ores economically feasible.

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The use of Sodium Citrate as a Reagent for Improved Process Performance of Ultramafic Nickel Ores

Abstract