| Xinhua phosphorite in Zhijin County of Guizhou is one of the super large-scale REE-bearing medium-low grade phosphorite deposits in Southwest of China. The proved up reserve of phosphorite ores was 13.34×108t, which accounts for about 50% of total phosphorite reserve of Guizhou Province. Previous investigations have revealed that the total reserve of REE oxide comes up to 140×104t, among which yttrium oxide accounts for 32.18% of the total REE oxide. The average contents of P2O5 in phosphorite was 17.51%, and the contents of EREO (which stands for the total REE oxides) ranges from 0.05% to 0.13%. This phosphorite is noted for its greatly abundant reserve of REE but considerably low contents of REE. Moreover, it is very difficult to recovery REE from ores due to the isomorphous substitution of REE for the lattices of calcium ion in collophanite. Nevertherless, the studying on recovering REE is still necessary at present. In this paper, the samples derived from mined ores in the big scale of industrial explotation. Hence, the samples were better representative for the studing on Zhijin Xinhua phosphorite ores. Based on the samples, the existing state of REE in ores, the enrichment rule of REE by flotation, the behavior and reacting mechaniism of REE disoluted by acid were systematiclly and deeply investigated in this paper. This research will provide the valuable reference for the development and utilization of Zhijin REE-bearing phosphorite deposits.The exiting state of REE in Zhijin Xinhua phosphorite ores were investigated systematically. The results showed that Y2O3, La2O3, Nd2O3 and CeO2 were main four rare earth elements in ore, which accounted for 81.20%of∑REO. The contents of∑LREO (which stands for the total light rare earth oxides) were slishtly higher than those of∑HREO (which stands for the total heavy rare earth oxides), accounting for 55.90%and 42.15%of∑REO, respectively. Among∑REO, Y2O3 was most abundant, accounting for 32.18%of∑REO and 76.29%of∑HREO. Remarkably, there existed good positive correlationship between REE and phosphorus, and the correlation coefficient was 0.98191. There existed independent minerals of REE in single collophanite mineral, such as cerianite and monazite, moreove, cerianite was found first time, but the amount of them was extremely little. No independent mineral of yttrium has been found in this investigation. Therefore, REE were mainly present in the form of ions in the lattices of collophanite, which leaded to it extremely difficult to extract REE from phosphorites.The enrichment rule of REE by flotation was investigated for Zhijin Xinhua phosphorite ores. The results indicated that REE can be.mainly enriched in concentrate by reverse flotation technology. Moreover, it has been found that a high flotation efficiency and excellent selectivity could be achieved when collector WF-01 was used to effectively collect dolomite minerals and other gangue minerals and phosphoric acid was used as phosphate minerals depressant and pH adjustment of pulp. The∑REO recovery rate of flotation concentrates came up to 90% and the enrichment ratio of∑REO in concentrates was up to 1.50. In addition, based on the classical first-order rate model ofε=ε∞(1-e-kt), the reverse flotation rate model ofε=ε∞+(100-ε∞)e-k(t+θ) was obtained, which could fit the data very well to describe the effect of flotation time on recovery rate of EREO and MgO in concentrate. Furthermore, a modified flotation rate constant kmod defined as theproduct ofε∞and k, i.e., kmod=ε∞·k and selectivity index SI defined as the ratio of the modifiedrate constant of valuables to the modified rate constant of gangue, i.e., SI=kmod1/kmod2, were also used to better measure the separability between bearing-REE phosphoric mineral and gangue mineral. The kinetics based on flotation Orthogonal experiment showed that the collector WF-01 dose was the most significant variable affecting kmod for∑REO, while depressant H3PO4 dosage affected the SI significantly. In order to further analyzed the effect of compounding reagents with WF-01 and H3PO4 on parameters kmod and SI, the response surface graphs and the contour graphs were drawn for kmod of∑REO, kmod of MgO and SI. The result indicated that the excellent separation between∑REO and MgO could be obtained by increasing depressant H3PO4 dosage in the condition of collector WF-01 dosage of 0.8 kg/t when reverse flotation were carried out for Zhijin Xinhua phosphorite ores.The behaviors and reacting mechanisms of REE dissoluted by acid were studied deeply for Zhijin Xinhua phosphorite ores. It was found that the acidic value of solution was the main effect factor on the distribution of REE in products. The distribution proportions of∑REO in phosphoric acid solution could be decreased to lower than 5% by increasing sulphuric acid or phosphoric acid concentration in reacting solution. The kinetics of ores dissoluted by acid showed that the Drozdov equation , which taked into account the self-impeding effect, could describe the dissolution progress of∑REO of ore quite well. The correlation coefficient fitting experimental data was more than 0.99.The reaction apparent activation energy of P2O5 calculated by Arrenius equation indicated that the main reaction of Zhijin Xinhua phosphorite ores dissoluted by sulphuric acid was a diffusion control process, as well as for REE. In addition, the studing on the reacting mechanisms of REE dissoluted by acid showed that the reactions included four main processes. One was the reactants, such as ions of H+,SO42-,PO43- or H2PO4-, and molecule of H2SO4 or H3PO4, diffusing toward the particle interface of ore. Another was REE reacting with reactants in particle interface. RE2(SO4)3 would be obtained when there were high SO42- ion or H2SO4 molecule concentration, while REPO4 or REH2PO42+ would be obtained when there were high PO43-, H2PO4- or H3PO4 concentration. The third was the resultants diffusing toward the solution main system, in which the insoluble REPO4 or part of RE2(SO4)3 would be precipitated in the solid film formed by calcium sulphate crystal, while the soluble RE2(SO4)3 or REH2PO42+ diffusing toward the solution main system through diffusion layer. In addition, the phenomenon of REE being enwraped by calcium sulphate crystal was happened due to the fact that the speed of calcium sulphate crystalizing was faster than that of REE diffusing through solid film, which was the main reason that the distribution proportions of∑REO in phosphogypsum was more than that in phosphoric acid.Based on the studying in this paper, The distribution proportions of IREO in phosphogypsum could come up to 90% by increasing solution acidic value in wet-phosphoric acid process. Then, economical and reasonable method will be seeked to recovery REE from phosphogypsum. |
