Fundamental And Technological Study On The Comprehensive Utilization Of Nickel Laterite Ore For Synthesis Of Spinel Ferrites

With the depletion of the world’s nickel sulfide ore and the rising demand for nickel, laterite ore which occupies 72% world nickel reserves is becoming the primary resource for extraction of nickel. In this thesis, novel processes for direct fabrication of spinel ferrites from nickel laterite ore were proposed by using acid leaching-coprecipiation-calcination and alkali fusion-water leaching-calcaination methods. The element distribution and migration in each process stage were fully revealed. The micro-mechanisms of the effects of selective leaching, selective enrichment and separation processes on the chemical composition, structure and magnetic properties of as-prepared spinel ferrites were intensively elucidated. These innovative processes colud not only recover valuable metals (Ni. Co, Mn, Mg, Fe, etc.), but synthesize high value-added spinel ferrite materials, leading to effective and comprehensive utilization of laterite ore.By using a hydrothermal pressure acid leaching-hydrothermal coprecipitation-calcination method. Co-Mn-Al co-doped nickel ferrite (NiFe2O4) was synthesized from only saprolite laterite ore. The effects of critical factors, including the leaching temperature and HCl solution concentration, on the metal leaching efficiency and the mole ratio of Fe to Ni in the leaching solution (RFe/Ni) were systematically investigated. Then the separation mechanisms of Ni. Co. Fe. Mn and Al from Mg ions in the leaching solution by the hydrothermal coprecipitation method were elucidated. Finally, the influence rules of selective leaching and separation processes on the structure and magnetic properties of as-synthesized ferrites were fully revealed. The results showed that the leaching efficiencies of Ni and Fe were approximately 85.0% and 17.0% with an R.Fe/(Ni.co, Mn) of 2.0 after hydrothermal leaching at 200℃with a liquid-to-solid ratio of 6:1 mL·g-"1 and HCl solution concentration of 2 mol·L-1. After the leaching process, the hydrothermal coprecipitation method (200℃.2 h) was adopted to separate Ni, Co. Fe, Mn and Al from Mg ions in the leaching solution by controlling the initial pH value of 7.0. Finally, the Co-Mn-Al co-doped NiFe2O4 with high purity, crystllinity and great magnetic properties was synthesized by calcinating the precipitates at 1000℃for 2 h.By using an atmospheric pressure acid leaching-coprecipitation-calcination method, metal-doped magnesium ferrites (MgFe2O4) were synthesized from saprolite and limonite laterite ore blends. The effect rules of initial acid concentration, liquid to solid ratio and leaching time on the metal leaching were systematically investigated. The influence mechanisms of precipitant reagent, equilibrium pH value, precipitation method and initial metal ion concentration on the metal ion precipitation, enrichment and separation were illustrated. The influence rules of precipitant reagent and initial acid concentration on the structure and magnetic properties of as-prepared metal-doped MgFe2O4 were investigated and revealed. The results showed that the leaching efficiencies of Fe, Ni, Mn, Co and Mg could reach 94.6%.96.9%.86.0%,84.8% and 72.6%, respectively, after leaching for 60 min at 100℃with the liquid (2.75 mol·L-1 HCl solution) to solid (saprolite and limonite laterite blends) ratio of 10:1 mL·g=1. During the coprecipitation process, about 93.0% Ni and 92.0% Co could be enriched in the filtrate by using ammonia solution (NH3H2O) as precipitant reagent, while the recovery of Al and Cr were 92.0% and 90.0% by using sodium hydroxide solution (NaOH), and simutanously. the precipitates were used to preparation of spinel ferrites. Single-phase Mn-Al-Cr doped and Ni-Co-Mn doped MgFe2O4 with high purity could be synthesized when the precipitates were obtained with the Ms/L of 9:1 and 7:3 by using NH3 H2O and NaOH solutions as precipitant reagents, and then calcinated at 1000℃ for 2 h. respectively.A series of Zn substituted Ni-Co-Mn-Mg ferrites and Ni substituted spinel ferrites were synthesized from laterite ore blends leaching solutions by using a coprecipitation-calcination method. The effects of Zn substitution and Ni substitution on the structure and magnetic properties of as-prepared samples were investigated. The results showed that with the Zn substitution content increasing, the lattice constant, average grain size and X-ray density increased accordingly. However, as the Ni substitution content increased, the lattice constant decreased. The magnetic property teste indicated that when the Zn substitution content was 0.4, the saturation magnetization Ms value was the highest (55.6 emu·g-1). Whereas as the Ni substitution content increased to 0.9, the highest Ms value was 41.0 emu·g-1 By comparision. it could be found that the appropriate amount of Zn substitution is more benefit for the improvement of magnetic properties for spinel ferrites.By using an alkali fusion-water leaching-solid state reaction method, Ni-Co-Mn co-doped MgFe2O4 were directly fabricated from saprolite and limonite laterite ores. The effects of alkali fusion temperature, time and ore-to-alkali mass ratio on the impurities removal rate were studied. The influence rules of treated saprolite to limonite laterite mass ratio (MTSI/TLL). calcination temperature and impurity SiO2 on the structure and magnetic properties of as-prepared ferrites were studied and elucidated. The results showed that when the alkali fusion temperature and time were 550℃and 30 min. the treated laterite ore blends containing 5%,3% and 2% of SiO2 were formed with the ore-to-alkali mass ratio of 1:1,1:1.25 and 1:1.5. respectively, meanwhile, the mass fractions of Al and Cr decreased from 0.65% to 0.18% and from 0.43% to 0.12%. respectively. When the MTSL/TLL and calcination temperature were controlled at 6:4 and 1000 ℃. metal-doped magnesium ferrite with high crystallinity and purity could be obtained. With the SiO2 content increasing from 2% to 5%, the Ms value decreased from 45.4 emu·g-1 to 31.5 emu·g-1. The reduction of He value from 120 Oe to 75 Oe with the increasing of SiO2 contents may be ascribed to that the anisotropy energy of magnetic nanoparticles decreased because of the presence of SiO2 shell on the surfaces of magnetic particles.Based on the above three new technological processes, the element migration behavior and value metal recovery from the saprolite and limonite laterite ores were quantitatively summarized. It is shown that the overall metal recoveries could reach 89.2%.85.4% and 99.5% from the laterite blends, respectively.