 Ytterbium is separated from other rare earths either by ion exchange or by reduction with sodium amalgam . In the latter method , a buffered acidic solution of trivalent rare earths is treated with molten sodium @-@ mercury alloy , which reduces and dissolves <unk> + . The alloy is treated with hydrochloric acid . The metal is extracted from the solution as oxalate and converted to oxide by heating . The oxide is reduced to metal by heating with lanthanum , aluminium , cerium or zirconium in high vacuum . The metal is purified by sublimation and collected over a condensed plate . 
