Effective Extraction Of Valuable Metal From Saprolitic Laterites And Preparation Of Magnesium Hydroxide Flame Retardant

With the continuous depletion of high grade nickel sulphide ores, discovery of huge and extremely huge laterites mines which are large scale, not imbedded deep, easy to exploration and always intergrowth with cobalt and also advance in beneficiation and hydrometallurgy, nickeliferous laterites have become the major source for the production of nickel and cobalt. The saprolitic laterites collected from the second largest nickel mine of China-Yuanjiang laterites were used in this dissertation. Firstly, the fast extraction of nickel from saprolitic laterites by sulphuric acid was investigated under mechanically agitation at atmospheric pressure based on the results of applied mineralogy and thermodynamic analysis. Secondly, the mixed nickel and cobalt hydroxide was synthesized from the leachate by hydrolysis purification. Thirdly, magnesium hydroxide was prepared from the purified magnesium rich solution by a surfactant templating route. At last, the surface modification of magnesium hydroxide was studied in detail. Main conclusions and innovations are obtained as follows:1. Applied mineralogy of nickeliferous lateritesThe grade of nickel in the laterites is of industrial grade and the nickel is mainly embedded in nickel-substituted lizardite. The grade of cobalt is low and the cobalt is mainly embedded in cobalt-substituted hematite. Applied mineralogy of nickeliferous laterites was analyzed detailedly, which provides novel thought and method for the determination of proper extraction technology.Mineralogical analyses showed that the laterites consist mainly of siliceous and ferruginous rock. Main mineral is nickel-substituted lizardite and the minor phases are quartz, maghemite, phlogopite, chlorite and carbonate. The content of nickel is 1.38% and phase analysis of nickel in saprolitic laterites illustrates that 72.46% of the nickel is embedded in nickel-substituted lizardite while the others are present as adsorptive nickel, nickel sulphide, nickel oxide and nickel-substituted iron oxide. The content of cobalt is 0.023% and phase analysis of cobalt in saprolitic laterites illustrates that 68.38% of the cobalt is embedded in cobalt-substituted iron oxide while the others are present as cobalt oxide, cobalt sulphide and cobalt-substituted silicate. The content of magnesium, silicon and iron are 19.51%,18.93% and 7.48%, respectively. The saprolitic laterites are distinguished by its rich magnesium silicate content.2. Thermodynamics of nickel extraction from saprolitic laterites by sulphuric acid under mechanically agitation at atmospheric pressureThermodynamical analysis show that nickel in lizardite is fit to extract by atmospheric leaching. But cobalt in iron oxide is unable to leach at atmospheric pressure. The introduction of thermodynamics to the leaching system provides theoretical foundation and direction for the experimental study, and supports the experiment design and result analysis with helpful information and assistance.According to the results of applied mineralogy, the main experimental process and the calculation principle, potential-pH equilibrium diagrams of Ni-H2O and also the Ni-H2O system concluding lizardite acidic dissolution at 298.15K and 363.15K, ionic partition diagrams of Na2Si03 solution and phase diagram of MgSO4-H2O have been plotted in detail. From the analytical results of solution chemistry diagrams, basic experimental conditions of nickel extraction from saprolitic laterites have been determined which validly supports the subsequent experiment study and result analysis.3. Effective extraction of nickel from saprolitic laterites by sulphuric acid under mechanically agitation at atmospheric pressureBy the methods of sulphuric acid leaching under mechanically agitation at atmospheric pressure, valuable metal have been extracted in short time, which introduces novel route for the effective extraction of valuable metals, and supports the extraction of other type of nickeliferous laterites with useful reference and consultation.Using the results of applied mineralogy and basing on the calculation of thermodynamics, fast extraction of nickel have been realized and investigated different experimental variables on the effect of the percentage of nickel leached. As much as 91.3% nickel could be extracted after 12min under the most optimal experimental conditions of particle size d5o=25μm,10%(v/v) H2SO4, reaction temperature 90℃, liquid to solid 3 and stirring at 500rpm. Kinetics of nickel and magnesium leaching from saprolitic laterite have been investigated and the activation energies were determined to be 53.9kJ mol-1 for nickel and 59.4kJ mol-1 for magnesium respectively, which are characteristic for a chemical reaction controlled process.4. Preparation and characterization of magnesium hydroxideThrough the methods of hydrolysis purification and surfactant templating, the mixed nickel and cobalt hydroxide and magnesium hydroxide have been synthesized from the purified solution, which introduces revolutionary route for the fabrication of hybrid nickel and cobalt hydroxide, and supports the synthesis of magnesium hydroxide flame retardant with useful reference and consultation.Using magnesium hydroxide as neutralization reagent, acidic leachate has been purified. Hybrid nickel and cobalt hydroxide have been prepared from this purified solution, which results in magnesium rich solution. The precipitation rate of nickel and cobalt from the purified solution is 99.9% and 98.7%, respectively. Using ammonia as precipitating agent and basing on the method of surfactant templating, lamellar mesostructured magnesium hydroxide particles with 98.3% purity, mean particle size d5o=27μm and even lamellar morphology have been synthesized through surfactant templating under mild experimental conditions.5. Preparation and characterization of magnesium hydroxide flame retardantMagnesium hydroxide prepared from purified magnesium rich solution has been modified by fatty acid and organosilane and the surface properties have been studied in detail by indirect characterization, which has important significance for the study of the rheological, mechanical and flame resistant properties and applications of this kind of mineral reinforcement as well as halogen-free flame retardant.Magnesium hydroxide flame retardant with excellent modification effect as well as 99.8% activation index was synthesized by stearic acid under optimal experimental conditions. The additive amount of stearic acid, reaction time and temperature have much influence on the modification. The type of orientation of y-aminopropyltriethoxysilane (y-APS) on magnesium hydroxide surface was depended on the solution alkalescence as well as the chemical nature of its functional groups at 25℃. Results implied that y-APS molecule preferentially adsorbs to the surface with the silicon moiety towards the surface at pH 8.0, but increasing solution pH to 10.9 which is close to the IEP of magnesium hydroxide leads to parallel orientation, while at pH 12.0, y-APS molecule bonds to the surface with the amino moiety towards the surface.