The invention provides a method for separating
magnesium from
lithium and extracting the
lithium from
high magnesium-
lithium ratio brine (brine from a
saline lake, from underground and from an oil-gas field). The method comprises:
sodium salt and
potassium and
magnesium mixed salt are separated from the brine by
evaporation of a saltpan; after
boron extraction,
sodium hydroxide is used for precipitating Mg<2+> from obtained old brine, and crystallized Mg(OH)2 is obtained by modification and
precipitation condition control;
filtration and separation are carried out to remove the Mg(OH)2 to realize separation of
magnesium and lithium; after filtered mother solution is vaporized and concentrated for 2-4 times, Na2SO4 and NaCl are separated by
crystallization, and pure caustic soda can be added to form
lithium carbonate from lithium; or the operation of further
evaporation is carried out until Na2SO4 and NaCl are separated by multiple times of natural
evaporation or forced evaporation concentration and multiple times of cooling
crystallization; the operations of evaporation and concentration are carried out until LiCl saturation, and LiCl products can be prepared after the operation of cooling
crystallization is carried out. Compared with the prior art for separating the magnesium from the lithium and extracting the lithium from the brine, the method obtains the crystallized Mg(OH)2 by modification and
precipitation condition control, solves the existing technical problem of hard
filtration of Mg(OH)2, solves the defects of
high energy consumption, complex process and high cost of the existing
calcination method, and solves the fundamental defects of low Li<2+>
recovery ratio and complex technical process of the traditional
precipitation method. The Li<2+>
recovery ratio ranges from 85-93%, Mg<2+> removal ratio is more than 99.5%, and the method solves the problem of extracting Li<+> and Mg<2+> from high-magnesium and low-lithium brine with Mg<2+> / Li<+>>=20
mass ratio.