In recent years, with the development of lithium ion battery cathode materials from single lithium cobalate or lithium manganate to lithium nickel cobalt manganate ternary with precise coordination and strict impurity concentration control, the purity of manganese sulfate is required to be very high, especially the content of harmful impurities such as potassium, sodium, calcium and magnesium must be controlled.
High purity manganese sulfate is mainly used as the precursor of ternary or binary materials for lithium battery cathode and the production of high-purity manganese oxide. Therefore, the preparation of battery grade high-purity manganese sulfate is the key to the production of lithium ion battery cathode materials.
Potassium, sodium and heavy metals in industrial manganese sulfate can be reduced to a very low level by various methods, while the removal of calcium and magnesium is always a major problem in the production of high-purity manganese sulfate, especially battery grade high-purity manganese sulfate requires deep impurity removal.
The methods for removing calcium and magnesium from manganese sulfate mainly include crystallization, electrolysis, chemical precipitation and extraction.
The crystallization method is to inhibit the dissolution of Mgso4 and Caso4 in the solution by increasing the concentration of Mnso4 in the solution, so as to achieve the purpose of removing magnesium and calcium. However, for the leaching solution containing a large amount of magnesium and calcium, the impurity removal process needs to be repeated for many times, resulting in a reduction in the recovery rate of manganese and an increase in production costs. At the same time, mnso_4 and mgso_4 will form mixed crystals, which will affect the solubility, and then affect the magnesium removal effect.
The electrolytic method for removing calcium and magnesium impurities has many processes, long process, low efficiency and high energy consumption. If the calcium and magnesium impurities in the solution are high, the hydrogen potential will be reduced, thus affecting the production efficiency of the target product.
In order to overcome the shortcomings of the existing technology, Tiei Extraction recommended the centrifugal extraction system of manganese sulfate, which has the advantages of short process, high efficiency, low energy consumption, which can be prepared battery grade high-purity manganese sulfate.
The core of the system is the centrifugal extraction section, washing section and stripping section. The main equipment is CWL-M series centrifugal extractor, which has low energy consumption and high extraction efficiency. It is made of corrosion resistant PVDF, widely used in the extraction of rare earth, nickel, cobalt, manganese, lithium and copper in hydrometallurgy.
Manganese sulfate extraction process designed by Tiei Extraction for a factory in Shanghai: 4-stage extraction section+8-stage washing+6-stage stripping.
The solvent extractant is composed of cyanex 272 and sulfonated kerosene as diluent. Mg2+and ca2+in the manganese sulfate solution were reduced to 3.12mg/l and 1.18mg/l respectively after being treated by the centrifugal extraction device, after extraction, the final products can be reaching the battery grade high-purity manganese sulfate index.