Fundamentals Of Reducing MgO Minerals From Copper-nickel Sulphide Ores By Selective Magnetic Coating Technology

For the challenging issue of high magnesia(MgO)content in the concentrate during the flotation of copper-nickel sulphide ores,the selective magnetic coating method was proposed,which was different from the flotation process.By adjusting and enlarging the difference in magnetic characteristics between magnesium silicate(MgO)minerals(e.g.serpentine)and sulfide minerals(i.e.pentlandite),removing serpentine from pentlandite by the magnetic separation was achieved,and the objective of reducing magnesium content in pentlandite concentrate was accomplished.Single minerals of pentlandite and serpentine were used in this paper to observe such behaviors such as mineral dispersion,selective magnetic coating of magnetic seed on pentlandite,and magnetic separation after magnetic coating using micro-fine magnetite as magnetic seed.The adsorption behaviors of dispersant and coagulant on the minerals and magnetic seeds were analyzed with Zeta potential,FTIR,and adsorption measurements etc.The interaction mechanism between magnetic seeds and minerals was revealed by the theory of solution chemistry and DLVO or EDLVO models in presence of different reagents(dispersants and coagulants).The change regularities of magnetic products including concentrate and tailing after magnetic coating were investigated with laser particle analyzer,XRD,SEM,and vibrating sample magnetometer(VSM).The technical and theoretical systems were preliminary established for reducing magnesium minerals using the magnetic coating technology in nickel sulfide processing.Behaviors of magnetite fines as magnetic seeds coating on the two minerals after magnetic coating have been studied without adding any reagents.Results showed that interactions of serpentine with the magnetic seed and its separation performance in water differed from that of pentlandite,which only changed with pH values.The interaction energies between the two minerals and magnetic seeds were both attractive at the neutral pH.Furthermore,the attractive interaction between magnetite and pentlandite was much stronger than that between magnetite and serpentine.Therefore,in natural pH value,the pentlandite surfaces were coated by the micro-fine magnetite and then pentlandite minerals were separated from serpentine with the magnetic separation after magnetic coating.For the dispersion between magnetic seeds and the above two minerals in the magnetic coating system,coating behaviors of magnetic seeds on the serpentine and pentlandite minerals and dispersion mechanisms have been both investigated with adding different dispersants.Results showed that with dispersants addition,the coating of magnetite on the serpentine surface was weakened and the selectivity of magnetite coating on the pentlandite particles was improved.Addition of sodium hexametaphosphate(SHMP)has been proven to show better dispersion effects and to prevent fine magnetite particles coating serpentine surfaces.The action of the SHMP adsorbing to surfaces of serpentine and magnetite was to increase the repulsion interactions of electrical double layer,decrease the Van der Waals attraction,and produce the steric interactions.Thus,it was very difficult for magnetite fractions to coat the surface of serpentine.Meanwhile,the attractive interaction energy between magnetite and pentlandite particles was decreased to some extent,resulting in lower recoveries of pentlandite minerals.Under this premise,in order to enhance the magnetite coating on the pentlandite surfaces,the addition of coagulants was necessary.Behaviors and mechanisms of magnetite fines as magnetic seeds coating on the two minerals after magnetic coating have been investigated in presence of sodium oleate as the coagulant.Results showed that the recovery of pentlandite ascended sharply,because sodium oleate significantly promoted the adherence of magnetite fractions on the surface of pentlandite.Moreover,addition of an assistant reagent,kerosene,was more favorable to enhance magnetite coatings on the pentlandite particles.The action mechanism of sodium oleate adsorbing on the surfaces of pentlandite and magnetite produced a strong hydrophobic effect,leading to more agglomerations between them.And hence the magnetism of pentlandite was sharply enhanced,realizing the magnetic separation of pentlandite from serpentine.Based on above fundamental researches of dispersion and aggregation,the selective magnetic coating and magnetic separation were carried out in the serpentine,pentlandite,and magnetite fines mixture system with SHMP as the dispersant,sodium oleate and kerosene under the natural pH value and the portion of pentlandite to serpentine was kept to a mass ratio of 1:2 with the Ni grade of 8.68%and the MgO content of 22.52%.Results showed that pentlandite was selectively magnetic-coated and separated from serpentine,obtaining concentrate with MgO remaining below 5.0%,which achieved the desired effects of reducing magnesia(MgO)content.Results obtained from XRD,SEM,and VSM also confirmed that magnetite adhered predominantly to the surface of pentlandite to increase its magnetism but only marginally to serpentine and the magnetic property kept unchanged.This research demonstrates a possible alternative separation technology for pentlandite and serpentine minerals using the magnetic coating method.Furthermore,the technical and theoretical system of nickel sulphide ores separating and magnetic coating processing were enriched.