| 简介 |
The present invention relates to a process for obtaining synthetic rutile with low contents of rare earth and radioactive elements from anatase mechanical concentrates, comprising the following sequential operations : calcination (1) of the anatase concentrate in a fluidized bed or rotary kiln, at a temperature between 400° C. and 600° C., during a period of time from 15 to 60 minutes, wherein hydrated iron oxides are converted into hematite after hydration water is removed, providing a reduction in the time required for next step; reduction (2) of the calcined product, in a fluidized bed or rotary kiln, at a temperature between 400° C. and 600° C., during a period of time from 5 to 30 minutes, using hydrogen, natural gas or any carbon based reducing agent such as metallurgical coke, charcoal, petroleum coke, graphite, among others, the result of which is the trans-formation of hematite into magnetite; dry or wet low-intensity magnetic separation (3) of the reduced product, in permanent magnet and drum magnetic separators, the magnetic field ranging between 600 and 800 Gauss, in which the magnetic fraction generated in the reduction step is discarded; high-intensity, high-gradient magnetic separation (4) of the low-intensity non-magnetic fraction, in rare-earth permanent magnet, either roll or drum, separators with magnetic field intensity ranging from 10000 to 15000 Gauss, extracting silicates, secondary phosphates, monazite, calzirtite, zircolinite and uranium and thorium-containing minerals; leaching (5) of the magnetic fraction of the high-intensity, high-gradient separation in agitated tanks or fluidized bed columns, with a solution of 20-25% w/w HCl, a solid-liquid ratio of 1/2 w/w, a temperature between 90° C. and 107° C., for a residence time in the leaching from 2 (two) to 4 (four) hours, providing solubilization of impurities rich in iron, aluminium, phosphates, magnesium, barium, calcium, strontium, rare earths, uranium and thorium; filtering of the leached product in a belt filter; drying of the filtered product in a rotary or fluidized bed drier; oxidation (6) of the dried product in a rotary kiln or fluidized bed reactor, at a temperature ranging 900° C. and 1200° C., in the presence of a mixture of the following substances : alkali metal sulphates (mainly lithium, sodium and potassium), alkali metal carbonates (mainly lithium, sodium and potassium), phosphoric acid (H3PO4) and, eventually, sodium chloride; quenching of the oxidized product in water or compressed air; leaching (7) of the quenched product in agitated tanks or columns, in such a way that said leaching can be carried out by using either a 25.0% w/w hydrochloric acid (HCl) solution, at a solid-liquid ratio of 1 : 2 w/w, at a temperature ranging from 90° C. to 107° C., for 2 (two) to 4 (four) hours, or a 55.0% w/w sulphuric acid (H2SO4) solution, at a solid-liquid ratio of 1 : 2 w/w, for 2 (two) to 4 (four) hours, at a temperature of 135° C.; filtering of the product from the second leaching (7) in a belt filter; and drying of the filtered product in a rotary or fluidized bed drier; dry, high-intensity, high-gradient magnetic separation (8) of the product of the second leaching, in rare-earth permanent magnet, either roll or drum, separators (10000 to 15000 Gauss), discarding of the magnetic fraction and recovering the non-magnetic fraction as final product (P), that is, the synthetic rutile of interest. |
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