Highly efficient purification of the process solution when producing lithium hydroxide by caustification

Relevance. The need to develop highly effective methods for purifying the process solution from impurity calcium and aluminum ions for the industrial production of lithium hydroxide at the Chemical Metallurgical Plant JSC in Krasnoyarsk. Aim. Development of methods for reducing the content of impurity calcium and aluminum ions in the process solution of lithium hydroxide after caustification to a concentration of 5–10 mg/l. Methods. Evaporation and crystallization, precipitation of colloidal sediments of aluminum and calcium with an ammonia buffer solution, chemical precipitation with 8-hydroxyquinoline. Results and conclusions. The effectiveness of the applied methods for purifying a process solution of lithium hydroxide from calcium and aluminum ions was shown: evaporation followed by crystallization, precipitation with an ammonia buffer solution, precipitation in the form of hydroxyquinolates. It was experimentally established that when using the evaporation method followed by crystallization, the degree of extraction of impurity aluminum ions Al3+ is achieved 29%; and calcium ions Ca2+ – 56%. When cleaning the process solution by precipitation of aluminum hydroxide colloid with an ammonia buffer solution, the degree of extraction for aluminum ions Al3+ was 96%; for calcium ions Ca2+ – 67%. The use of the chemical precipitation method with 8-hydroxyquinoline in an alkaline solution showed the degree of extraction of aluminum ions Al3+ 20%; and calcium ions Ca2+ – 76%. It was established that the method of evaporation and crystallization of the process solution does not require the use of special reagents. A method using an ammonia buffer solution to remove impurity calcium and aluminum ions shown to be simple and effective. For the first time, a method was proposed for cleaning the process solution after caustification using an aqueous-alkaline solution of 8-hydroxyquinoline, excluding the use of organic, flammable and toxic solvents.