| High content of magnesium-silicate minerals like serpentine and talc not only obstructs the flotation separation of copper-nickel sulfide ores but also makes a undesirable high content of MgO in concentrate to impede the subsequent smelting process, which restricts the efficient utilization of copper and nickel resources in China. Basing on the layered magnesium-silicate minerals, this thesis firstly investigated the enhanced dispersion and selective depression of magnesium-silicate minerals by various experimental methods and analysis technologies. Then, the regulation principle of "selective migration of ion in solid/liquid interface-molecular assembly of flotation agent" in the floatation system of copper-nickel sulphide ores was established. Last but not least, the technical prototype of strengthening flotation of copper-nickel sulphide ores was proposed. Main conclusions and innovations of this thesis are listed as follows:1. Relevance among crystal structure, surface property and floatability of layered magnesium-silicate mineralsLayered magnesium-silicate minerals associated with copper-nickel sulfide ores include serpentine, talc and chlorite. All of them are characterized with uniform crystal structures consisting of silicon-oxygen tetrahedron and magnesium-oxygen octahedron. The magnesium-oxygen octahedron layers are broken during the liberation of serpentine to expose the magnesium-oxygen bonds with strong ionicity and hydration, which results in natural hydrophilicity of serpentine. For talc, characterized as good natural hydrophobicity, the liberation comes from the interlaminar fracture to remain molecular bonds on surface with weak hydration. Meanwhile, both molecular bonds and magnesium-oxygen bonds are exposed on chlorite surface when liberation occurs, resulting in moderate natural hydrophobicity between serpentine and talc.In water, the hydroxyl on serpentine surface ruptures and dissolves into the aqueous phase while the Mg2+remains, resulting in surface positive charge with pHPZC of10.0. On the other hand, the preferential adsorption of OH-on liberated talc and chlorite make surface negatively charges the minerals’ surfaces with pHPZC of3.0and4.4, respectively. Hetercoagulation is easy to occur between serpentine and negatively charged sulfide ores due to the electrostatic interaction when pH<10, which hinders the flotation of copper-nickel sulfide ores.2. Influence of hetercoagulation among mineral particles on mineral flotation separationFirstly hetercoagulation between serpentine and sulfide ore particles reduces the adsorption capacity of collector on sulfides surface and leads to lower floatability of sulfide ores. Secondly hetercoagluation between serpentine and talc not only decreases the floatability of talc, but also weakens the adsorption capacity of talc to depressant, which hinders talc to be totally depressed. Polyphosphate and sodium silicate can effectively disperse serpentine and sulfide, as well as talc, and can weaken, even eliminate the hetercoagulation among mineral particles.3. Strengthening regulation mechanism of serpentine surface electrical propertyKey to eliminate hetercoagulation among minerals is to reduce the surface electrical potential of serpentine, and key to regulate surface electrical potential of serpentine is to control the migration behaviour of Mg2+on serpentine surface from solid particles to aqueous solution. Namely, increase of migration of Mg2+from particles to solution will decrease the positive charge density of positioning ion Mg2+in electric double layer and then reduce the surface potential of serpentine.The reduction of surface potential of serpentine by chained polyphosphate is determined by three factors. First, chained polyphosphate can promote the migration of Mg2+from particles to solution to lower the surface potential of serpentine. Second, stable soluble complex can be formed by combining Mg2+with chained polyphosphate, which hinders the readsorption of Mg2+onto serpentine surface and maintains the negative potential of serpentine surface. Third, the surface potential of serpentine can be further reduced by the specific adsorption of chained polyphosphate onto the serpentine surface.Through the strengthening regulation of serpentine surface electrical property, the influence of hetercoagulation on floatability of sulfide ores has been edulcorated, and the talc has been totally depressed.4. Molecular assembly of flotation agents on solid-liquid interfaceOrganic polymer guar gum and CMC are efficient depressant for talc and also have certain depression for sulfide floatability. Meanwhile the thiol collector xanthate only reacts with sulfide ores and has nothing to do with talc. Preferential addition of collector can prevent the adsorption of depressant onto sulfide surface. Therefore the selective interaction between flotation agents and different minerals is achieved. Thus, through changing the addition sequence of flotation agents and adjusting the assembly process of collectors and depressants onto mineral surface, the surface wettability difference between sulfide and talc can be enlarged enough to benefit the flotation separation.5. Strengthening flotation technique for copper-nickel sulfide oreBasing on the control principle of strengthening dispersion synchronous depression for kinds of magnesium-silicate minerals, the strengthening flotation technique has been proposed and experimented industrially by using Kami low grade copper-nickel sulfide ore (Ni of0.53%and Cu of0.27%) as raw material. The high grade mixed concentrate of copper-nickel (Ni of5.68%and Cu of3.14%) have been obtained with the nickel and copper recovery of80.23%and88.05%, respectively. In the case of similar concentrate grade, the recovery of nickel and copper has been increased by3.04%and9.92%, respectively, though applying the strengthening flotation technique. |
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