Method for producing high purity lithium hydroxide monohydrate

A method for producing high purity lithium hydroxide monohydrate from materials containing a lithium salt selected from lithium sulfate, lithium chloride, lithium chloride monohydrate, lithium carbonate, or mixtures thereof, the method comprising:

• performing membrane electrolysis of an aqueous solution of the lithium salt using a cation-exchange membrane as the membrane separating cathode and anode circuits of electromagnetic cells in the mode of circulation of the catholyte in the form of a solution of lithium hydroxide and anolyte in the form of a lithium salt solution, wherein a cathode for the membrane electrolysis is made of nickel-plated stainless steel and the cation-exchange membrane is selected from a membrane resistant to alkalis and acids;
• withdrawing a volume of the catholyte from a circulating catholyte stream and evaporating the withdrawn volume of the catholyte to obtain crystals of lithium hydroxide monohydrate in a mother liquor;
• separating the crystals from the mother liquor, washing the crystals with water and drying the washed crystals to obtain final high purity lithium hydroxide monohydrate;
• wherein the method is further characterized by the following steps:
• removing cathodic and anodic gases formed during the electrolysis;
• feeding a part of a resulting stream of spent washing solution to a catholyte evaporation process and using part of the spent washing solution fed to the catholyte evaporation process in recycling of withdrawn spent anolyte stream;
• returning a part of the mother liquor formed after separation of the crystals of lithium hydroxide monohydrate to the catholyte evaporation process;
• recycling a part of the spent catholyte stream, which is withdrawn from the evaporation process and represents a concentrated solution of lithium hydroxide with an admixture of sodium and potassium hydroxides;
• replenishment of a circulating anolyte stream with a concentrated solution of a lithium salt prepared from an original source of lithium salt and a solution of a lithium salt obtained as a result of the recycling the withdrawn spent anolyte stream.