| To deal with crisis that high-quality phosphate rocks of the whole world are depleted, the plans to employ low-grade phosphate ores are already in full swing in some of countries presently. Though plenty of phosphate reserve exsist in our country, mainly are middle and low grade and high content impurities and difficult to beneficiat, which need to be beneficiated economically and efficiently to meet demand of phosphorous produces. Result of that, there are large quanlity of tailings to be discarded and not to be recoveried. The tailings belong to phosphorite tailings with high magnesium content and should become available secondary resource. Therefore, it is urgently important to engage in researching and developing to comprehensively utilize tailings in order to satisfy with chemical industry as well as fertilizers. Facing this chanllenge, we chose the floated tailings from Wengfu phosphate ores and made extensive study about some important theories involving in their recovery such as mineralogical structure and physical and chemical characteristics of the tailings, aqueous thermodynamic, effects of impurities in digesting process, complicated reactive mechanism and reaction kinetics, and then obtained significant results, which can provide some theretical basis and reference for cellophane and dolomite separation, comprehensive recovery on phosphorite tailing with high magnesium content, even on low grade phosphorite and high magnesium content ores.The important characteristics such as mineralogical structure, appearance, exsist state of Mg and P of the phosphate tailings were detected by using X ray diffraction (XRD), electron probe, transmission electron micrograph (TEM), spectrometer, scanning electron microscope (SEM), electron microscope (EMS), analytical electron microscope (AEM) and chemical analysis. It is obtained that the key physical and chemical behavior parameters including reactive activity, resistance to retardancy, foaming characteristic and it is discovered that the relation between tailings and their originals. The results indicate that tailings are mainly made of dolomite and phosphorite, accounting for 87.14%and 8.56% respectively, which belong to low grade phosphorite rock with high magnesium content. P2O5 and MgO comparably enriched in fine particle size, accounting for 65.66% and 66.96% respectively, and MgO mainly concentrated to the internal tailing's particle. On the basis of mineralogical components and internal structure of phosphorite tailing, its brand of tailing is successively divided into dolomite based tailings, dolomite and phosphorite based tailings, dolomite and phosphorite and quartz based tailings, quartz based tailings, phosphorite based tailings and brown iron ore based according to their content's amount. The existing state of Mg and P is respectively independent dolomite particle and intergrowth of phosphorite and dolomite, and amount of independent phosphorite is very low. Compared with the original phosphate ores, the phosphate tailings'reactivity is higher, resistance to retardancy is lower and the foaming ability is stronger. When calcination temperature is up to 900℃, dolomite decomposed completely.The phenomena of solution-mineral dissolution and precipitatation are discussed through the analyses on thermodynamic equilibriums of Mg2+-Ca2+-H2CO3-H2O, CaCO3·MgCO3-SO42--H2O, Ca2+-F--H3PO4-H2O, Ca5(PO4)3F-SO42--H2O and Mg2+-H3PO4-H2O systems at normal temperature. It is dicovered that the pH0 values of digestion reactions of Mg and P decrease with increasing temperature, and they exsist in the forms of Mg2+,H3PO4 in strong-acid solution respectively. While H2SO4 is as acid solvent, the digestion of Ca, Mg and P will accelerate, exsisting in the forms of CaSO4 crystallines, Mg2+ and H3PO4 in solution, respectively.Based on the above work, the reacting kinetic processes are investigated in a specially designed reactor system by using SEM, plasma emission spectroscopy (PES) analysis. As important results, the digesting behavior of Mg is similar to P's, not selective dissolution and the negative temperature effect of the digestion of Fe and Al are revealed in the reaction system, which will be of benefit to restrain impurities dissolution from ore particles to acid solution. The strong effects of solid film forming on the surface of tailing particle on acidolysis reaction show stronger retardancy property. It is also noticed that the Drozdov equation (1/tln1/(1-x)-βx/t=k), which took into account the self-impeding effect, can describe the dissolution process of P2O5 and MgO quite well. The result of apparent reaction activation energy of P2O5 and MgO is 14.881 and 11.908 kJ·mol-1 respectively indicates that the main reactions of tailing dissolution are solid film diffusion control process. The detailed investigations on solid film are found that the particle surface turns densy and smoothy into loosy and porus, get thick and bulky, turns finely, and the appearant form turn short, small and needle shapes into big, rough and short column shapes, and the surface materials successively form assanite, plaster and anhydrite.From above results, the reacting mechanism is explored that the reactive components can diffuse in the tailing particle through a large amount of mico pores. With the reaction proceeding, the penetration and the reaction region will move towards the center of the particle, finally remain siliceous survival and calcareous coating. There are three regions in the system, which include penetration region where liquid diffuse in the surface of paticle, reaction region where reaction and diffusion phenomena exist at the same time, and unreacted region.Besides these, cyclic leaching-extraction-stripping method recovering P2O5 in form of high quality phosphoric acid from phosphorite tailing with high magnesium content is already proved to be available.
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