Research On Reaction Mechanism Of Rare Earth In Phosphate Rock Under The System Of Mixture Of Sulfur And Phosphorous Acid

China is rich in rare earth and phosphorus resource, but the rare earth and phosphorus ore resources are disposable, never recycled again. Rare earth and phosphorus are essential to economic and technological development, especially comprehensive recovery of phosphorus ore associated with rare earth. Therefore,mineralogical characteristics of typical phosphate ore containing rare earth,distribution law and leaching mechanism of leaching rare earth through mixtures of sulfuric and phosphoric acids in China were studied in this paper, basic theory of comprehensive development and utilization of phosphate ore containing rare earth were provided for the study in future.Mineralogical properties of phosphorite containing rare earth were studied.The results showed that the mineral composition and rare earth content among Chinese typical phosphate ores containing rare earth were different, like Guizhou Zhijin, Hebei Fanshan and Yunnan phosphate minerals.Zhijin phosphate mainly contained collophanite and dolomite, the total amount of rare earth was the highest, reaching0.118%; Fanshan Phosphate mainly contained apatite and diopside, total content of rare earth 0.093%, while phosphate ore in Yunnan Province mainly contained apatite and silicate with the least rare earth content, less than 0.03%. Rare earth of the phosphorite ore was mainly Ce(CeO2), La(La2O3), Nd(Nd2O3) and Y(Y2O3),accounting for over 85%, mainly light rare earth and its content reached more than60%. The content of light rare earths in Fanshan phosphate ore reached up to 81.56%.Rare earth in Guizhou Zhijin and Yunnan phosphate ore mainly hosted in phosphorus mineral, while rare earth in Hebei Fanshan Phosphate Mine not only hosted in apatite,but also diopside, hematite and other gangue minerals. Independent minerals of rare earth may exist in Guizhou Zhijin and Hebei Fanshan phosphorus ore, but smallquantity.Leaching experiment on phosphorus ore containing rare earth under the mixture of sulfur and phosphoric acid was studied. The results showed that the way of adding sulfuric and phosphoric acid affected the leaching rate, fully leaching phosphate ore with firstly phosphoric acid and secondly sulfuric acid to produce phosphoric gypsum leaching, which was beneficial to improve the leaching rate of rare earth in solution;high initial phosphate concentration, high leaching liquid solid ratio, increasing the leaching temperature and prolonging leaching time, were profitable to improve rare earth leaching rate during the leaching process. Optimum leaching conditions were obtained in the experiment, initial phosphate concentration of solution was 50%,sulfate excess coefficient of sulfate was 1, liquid-solid ratio was 6:1, leaching temperature was 80℃, reaction time was 180min; under these conditions, the leaching rate of P2O5 reached above 90%, the leaching rate of ∑REO reached 63.402%.The reaction mechanism of phosphate ore containing rare earth under the mixture of sulfuric and phosphoric acid was analyzed. The results showed that phosphorus mineral firstly reacted with phosphate acid to produce Ca(H2PO4)2, and then Ca(H2PO4)2 reacted with sulfuric to generated CaSO4·nH2O. Adding phosphate acid to fully reacted with phosphate particles and formed permeable Ca(H2PO4)2 on the reaction interface of particles. Soluble rare earth phosphate, which formed by rare earth exist as isomorphism in phosphoric ore reacted with phosphate acid, can penetrate the film fully and diffused to the bulk solution, then adding sulfuric. Though Ca2+ and SO42–in solution generated CaSO4· nH2 O very quickly, the affection of calcium sulfate crystal wrap rare earth was reduced, and the yield of rare earth in solution increased. At the same time, after leaching phosphate ore containing rare earth under the mixture of sulfur and phosphoric acid, the size of phosphorus gypsum crystal was small, mostly less than 10 μ m, mainly needle and flake, and as leaching time was prolonged, phase of phosphorus gypsum tended to transform from dehydrate to semi water, the rare earth wrapped possibly to be released, which was favorable for improving the leaching rate of rare earth.Finally,the occurrence status of rare earth in phosphate rock resulted in thedifferences of leaching rate of rare earth,but the chemical reaction mechanism for rare earth is rational.