Comprehensive Utilization Of Zhijin Phosphate

Certain deposits of phosphate ore, especially the fluorapatite ore, contain significant amounts of the rare earths in nature. Among those the Xinghua deposit of phosphate ore in Zhijin district, Guizhou province of China is a super-large comprehensive phosphate and rare-earths deposit, which has great industrial values. As rare earth ions with very similar properties to calcium ion are mainly disseminated in the crystal lattices of phosphate minerals, when phosphate minerals are enriched by separation, the rare earths are also enriched to phosphate concentrate, and have very great recovery values.Therefore, in this paper, according to the need for exploitation and utilization of Guizhou Zhijin phosphate concentrates bearing rare earths, we use Zhijin flotation phosphate concentrates as raw materials, simulate the traditional production process of dihydrate wet-process phosphoric acid, and study on the way to improve the solubility of rare earths, recycled rare earth elements and phosphorus. At the same time, we use the ammonium carbonate to decompose phosphogypsum, which is generated during the production process of wet-process phosphoric acid, and to produce ammonium sulfate, recycle rare earth elements and sulfur from phosphogypsum.The study show that when using the traditional dihydrate wet-process phosphoric acid, the proportion of rare earth dissolving into phosphoric acid is only 42.20%～52.26%, the rest precipitate into the phosphogypsum, it depends on the technological conditions when sulfuric acid decompose phosphate. When at the optimum conditions ,the excess coefficient of sulfuric acid is 1.25, the temperature is 75℃,liquid to solid ratio is 3:1, time consumption is 4 hours, the leaching rates of Re₂O₃ and P₂O₅ in phosphoric acid are relatively good, which are 52.26% and 96.85%, ,respectively. It was found that when sulfuric acid decompose Zhijin phosphate, the reason of the low leaching rates of Re2O3 is in addition to rare earth easily through eutectic adsorption or generating composite sulfate precipitation and other forms into phosphogypsum, about 30% rare earths wrapped in the insoluble silicate minerals is also a crucial factor. This part of the rare earths only through grinding to damage the crystal structure of insoluble mineral, increase the contacting chance of rare earths and leaching agent can improve its solubility.Without changing the process of wet-process phosphoric acid, we grind the phosphate concentrates,improve phosphoric acid concentration of acid solution system, and add a small amount of DHO reducing agent to leach rare earths, can increase the leaching rates of Re2O3 in phosphoric acid to 73.17%.According to the phosphogypsum generated during the the traditional process of dihydrate phosphoric acid,in this article,we test to use the ammonium carbonate to decompose phosphogypsum and then produce ammonium sulfate,and examine the influence of the process conditions of decomposing phosphogypsum to leaching rates of Re2O3. The results show that althought ammonium carbonate can make 98.28% SO₄^2- of phosphogypsum into ammonium sulfate solution, the leaching rates of Re2O3 in ammonium sulfate solution is only about 40% or so. It mainly depends on material ratio[n (CO₃^2- ) /n ( SO₄^2- )], the other technological conditions have less effect on the leaching rates of Re₂O₃. As well, rare earths wrapped in the insoluble silicate minerals in phosphogypsum, even if we use nitric acid and hydrochloric acid or such strong acid, also cannot make it dissolve, only after grinding to damage the crystal structure of insoluble mineral can increase the leaching rates of Re2O3 to 81.14%.