The Synchronous Hydrophobic Theory And Technology Of Nickel-bearing Sulfide Minerals In Low-grade Nickel Sulfide Ore

With the continues decline of high-grade nickel sulphide ore reserves, the development of low-grade nickel sulfide ore becomes increasingly important. In low-grade nickel sulfide ore, nickel is mainly in the form of pentlandite, but the particle size distribution of pentlandite, pyrrhotite and pyrite embedded in close symbiosis and uneven, it is difficult to liberation. To solve the problem in the flotation of low-grade nickel sulfide ore and improve the nickel resource utilization, the synchronous hydrophobic thought was proposed. To achieve this thought, the properties of mainly nickel bearing sulfides pentlandite, pyrrhotite and pyrite were investigated using thermodynamics, electrochemistry, and first-principles calculation, then the influence of collector, inevitable metal ions and pulp regulator on the flotation behavior and surface products was identified. By the above systematic study, the synchronous hydrophobic mechanism was formed, and combined it with the synchronous dispersion/inhibition theory of magnesium silicate minerals, an enhanced low-grade nickel sulfide ore flotation technology was developed. The main contents of this paper and conclusions are as follows:(1) Flotation behavior and hydrophobic products of sulfide mineralsThe surface products and electrochemical reactions on nickel bearing sulfide minerals were studied by thermodynamics, flotation tests, electrochemical and surface analytics, the synchronous hydrophobic pH range was determined.According to solution chemistry, the FeS2-H2O system, FeS-H2O system,(Ni,Fe)9S8-H2system and NiS-H2O system of Eh-pH diagram were drawn, these diagrams show all investigated sulfide minerals might be hydrophobic at appropriate Eh, pH range by forming elemental sulfur; the mainly hydrophobic products in self-induced flotation are formed by the dissolution of metal ions from the surface, forming a metal-deficient sulfides and elemental sulfur S0; the main hydrophobic surface products in Na2S-induced flotation is S0which is the oxidized product of HS-,the formed S0adsorbed on the mineral surface causes the hydrophobic of sulfide minerals; in xanthate collector-induced flotation, the main hydrophobic product is dixanthogen; at different flotation system, these three sulfide minerals’synchronous hydrophobic range are different, in self-induced flotation, the pH range is4<pH<7, in sulfur-induced flotation, the range is:2.6<pH<11, and in collector-induced flotation, the range is:2<pH<11, by adding collector to the flotation system, the synchronous hydrophobic range is expanded, and it is benefit for the synchronous hydrophobic of nickel bearing sulfides.(2) Electronic structure of nickel-iron sulfide minerals and the effect on the flotation behaviorUsing First-principles calculation to investigate the electronic structure of nickel-iron sulfide minerals, the conductivity type of sulfide minerals and surface activity particles of mineral was determined, and the implication on the flotation behavior was discussed.Pyrite and millerite are direct band gap p-type semiconductor, pentlandite and pyrrhotite is metal conductor. The quantity of electrons in conduction band determines the tendency of collector’s adsorption, hence, the collector is likely to adsorb on pyrite, less likely to adsorb on pentlandite and pyrrhotite; density of states and partial density of states analysis showed that Fe atoms is the most active particle in nickel-iron sulfide minerals, followed by Ni atoms, this is the reason why Fe atoms dissolved preferentially from nickel-iron sulphide minerals, and the difference of surface active particle leads to the difference of flotation behavior.(3) Inevitable metal ions in nickel sulfide pulp and the influence on the corrosion electrochemistry of sulfide mineralsThrough the pulp solution analysis, the species of inevitable metal ions were identified, open circuit potential tests, Tafel polarization curves, cyclic voltammetry and AC impedance were used to study their influence on the corrosion behavior of sulfide minerals.In nickel sulfide flotation pulp, Ni2+, Fe3+, Cu2+, and Mg2+are the main inevitable metal ions, all of them will increase the difference between pyrrhotite and pyrite, pentlandite in electrostatic potential, enhancing galvanic corrosion. Mg2+will increase the corrosion rate of pentlandite, while decrease the corrosion rate of pyrrhotite and pyrite; Ni2+would inhibit the oxidation of sulfide minerals at low concentrations (<5×10-4mol·L-1), increase the Ni2+concentration, the inhibit effect reduced; Fe3+can accelerate the oxidation of sulfide mineral surfaces, mineral surface would generation of large amount of hydrophobic product (S0) in shorter time, extend the duration, the surface hydrophobic substances are further oxidized to hydrophilic products, reduce the hydrophobic of sulfide minerals; Cu2+would be in the form of CuS through displacement reaction at pentlandite surface, increase the hydrophobicity of nickel bearing sulfide mineral.(4) Effect of pulp regulator on the hydrophobic of sulfide minerals and the synchronous hydrophobic mechanism of sulphide mineralsBy investigating the surface wettability, surface potential, collector adsorption amount, flotation behavior and corrosion behavior of sulfide minerals in the presence of pulp regulator, the key factor of synchronous hydrophobic was determined.Pulp regulator(CMC, gur gum) will reduce the hydrophobicity and flotation recovery of sulfide minerals; the adsorb mechanism of collector(PAX) and pulp regulator(CMC, gur gum) on sulfide mineral surface is competitive adsorption, preferentially adding collector can reduced the inhibition of sulfide minerals by regulators, increasing the adsorption of collector and improve the hydrophobic of sulfide minerals.(5) Enhanced flotation technology of low-grade nickel sulfide oreCombining the synchronous hydrophobic mechanism of sulfide minerals and synchronous dispersion/inhabitation mechanism of gangue minerals, the enhanced flotation technology of low-grade nickel sulphide ore was proposed, for the low-grade nickel sulfide ore containing0.68%of Ni, using this new technology, the Ni and Cu grade were6.84%and0.91%in the obtained concentrate, Ni, Cu recovery were81.3%and81.4%. on the basis of ensure the quality of concentrate, largely increase the metal recovery.