The way from monazite sand to lanthanum: The monazite sand does not contain enough monazite, so initially it should be concentrated. The first step is completed on the drag. Density of monazite is 4.9...5.3 and that of the regular sand is 2.7 g/sm3; with such difference the gravitational separation should not be a big deal. However other minerals have to be separated too, so for achieving 92...96% purity a complex of gravitational, magnetic ad electrostatic methods is applied.
Monazite concentrate is treated by H2SO4, the rare earth elements and thorium sulphates are leached by water.
After cerium separation the solution contains a big quantity of lanthanum, which is extracted from this solution adding hydrogen nitride (ammonia) as well as ammonia and cadmium nitrates. Cadmium is precipitated by hydrogen sulphide; meanwhile the solution of lanthanum nitrate is refined from lanthanides via series of fractional crystallization.
Lanthanum chloride LaCl3 is the final product which is electrolyzed which final of lanthanum with 99.5% purity. More pure 99.79% lanthanum may be obtained using the calcium-thermal reduction. |