Method for obtaining concentrated brine of minimum impurity content from brine found in natural salt flats and salt marshes, said method having minimum environmental impact and maximum lithium recovery

A procedure of minimum environmental impact and maximum lithium recovery to obtain concentrated brines with minimum impurity content from brines that embed natural salt flats and salt marshes, the procedure wherein the following stages are comprised:

• a) building fractional crystallization ponds by solar evaporation;
• b) filling ponds with natural brine;
• c) initially pre-concentrating natural brine to the maximum possible lithium concentration in the liquid phase without precipitating lithium-containing salts;
• d) cooling the pre-concentrated brine obtained in stage c) to a temperature of between approximately −8° C. and approximately −6° C. ensuring maximum precipitation of sulfate anion-containing salts in these conditions and separation of a liquid phase in which sulfate anions are minimized;
• e) chemically pre-treating the liquid phase of stage d) by adding stoichiometrically an aqueous calcium chloride solution and/or an aqueous barium chloride solution, and separating crystallized and precipitated calcium sulfate and/or barium sulfate as solid effluent;
• f) pre-concentrating the liquid phase obtained in stage e) to a possible maximum lithium concentration in the same without precipitating lithium-containing salts, so the mass ratio of the magnesium/lithium concentrations is reduced to values less than approximately 2 by crystallization and precipitation of magnesium and potassium salts;
• g) chemically treating the liquid phase of stage f) to minimize the concentration of magnesium, calcium, boron and sulfate in the liquid phase by adding a quantity of water to reduce the lithium concentration by approximately 50%, then adding calcium hydroxide with approximately 10% in excess of the stoichiometric value needed to precipitate all magnesium ions, then adding an aqueous solution containing a stoichiometrically calculated quantity of sulfate anions to precipitate the remaining calcium ions in the liquid phase, then adding an aqueous sodium hydroxide solution in order to increase pH at approximately 11.2, then adding aqueous sodium carbonate solution in order to minimize the calcium ion content in the liquid phase, and then adding an aqueous barium chloride solution containing the stoichiometric quantity needed to precipitate all the sulfate anions contained in the liquid phase;
• and
• h) concentrating the liquid phase obtained at the stage g), by crystallizing and precipitating by evaporation principally sodium chloride crystals.