Less is More: Efficient Removal of Calcium from Lithium Brines

Speciality chemicals company LANXESS is adding Lewatit TP 308 to its portfolio of selective ion exchange resins, which are ideally suited for the purification of lithium salt solutions. ‘This type of purification process plays a very important role in helping to create ultra-pure lithium salts for the production of lithium and rechargeable lithium-ion batteries.’ said Dirk Steinhilber, Technical Marketing Manager of the Liquid Purification Technologies business unit at LANXESS Deutschland GmbH.

Ion analysis at LANXESS' analytical laboratory in Leverkusen.

Photo: LANXESS Chemie

Cost-effective softening of diluted lithium-containing brines

The use of ion exchange resins offers numerous advantages over conventional methods of final fine treatment of lithium-containing brines, which are mainly based on precipitation operations. steinhilber describes: ‘The removal of calcium using an ion exchange process significantly reduces time and costs.’

The macroporous Lewatit TP 308 has been developed specifically for the treatment of low-concentration lithium salt solutions (cLi < 2 g/l, with high concentrations of alkalis, alkaline earths and heavy metals reaching 100 mg to several grams per litre). Such solutions are derived from the treatment of geothermal brines produced after desorption of the main adsorbent materials.

The removal of multivalent ions - mainly calcium - from these solutions can be carried out very efficiently, with low leakage and high flow rates, advantages that are due to the excellent exchange kinetics. At the same time, the pressure drop across the resin bed is low. Laboratory tests have demonstrated the superior performance of Lewatit TP 308 when compared to a wide range of competitors' products.

A compelling feature of this resin is the total capacity of more than 4.3 eq/l (equivalents per litre). This means that the resin has a longer service life and longer regeneration intervals than standard resins. As a result, there is a lower demand for regeneration chemicals and water. This results in an overall increase in system availability and lower operating costs. ‘The polymer structure of this resin has been specially modified to ensure a longer service life even with frequent regeneration and to significantly reduce process costs.’ Steinhilber said.

Laboratory tests have demonstrated the superior performance of Lewatit TP 308 compared to a wide range of competitors' products. Multivalent ions - mainly calcium - can be removed from these solutions very efficiently, with low leakage and high flow rates, all thanks to excellent exchange kinetics. At the same time, the pressure drop across the resin bed is low. The graph shows the calcium concentration (ppm) in the effluent from the ion exchange process, a measure of the purity of the lithium brine produced, on the y-axis. the flow rate (BV/h) per hour of bed volume is shown on the x-axis.

Image: LANXESS Chemical

Customised resins for different lithium concentrations

LANXESS also offers customised ion exchange resins for the purification of concentrated lithium salt solutions, thus extending the application range of Lewatit TP 308.

In this way, the monodisperse resins Lewatit MonoPlus TP 208 and Lewatit MonoPlus TP 260 can be used to remove divalent ions (i.e., calcium, magnesium, strontium and/or barium) at concentrations ranging from 1 to 100 mg/l in brines with a typical lithium content of 10 g/l, Lewatit MonoPlus TP 208 is a resin containing chelated iminodiacetic acid (IDA) groups and is best suited for lithium chloride, lithium hydroxide and lithium sulphate solutions.

In addition to the monodisperse resin types in the MonoPlus range, LANXESS also offers these two resins in the MDS type, which have polymer beads with a diameter of approximately 0.4 mm, which is smaller than the diameter of the standard type (0.6-0.7 mm). Due to the much larger specific surface area, MDS resins have enhanced exchange kinetics and significantly higher effective capacity. In addition, they have higher permeation stability and mechanical stability.

These resins remove virtually all impurities. For example, after treatment of lithium chloride and sodium chloride concentrates containing 10 ppm calcium using Lewatit MDS TP 208. only trace amounts of calcium on the order of ppb remain.

Ultrapure lithium salt solutions obtained in this way are mainly used for the direct production of LiOH by chlor-alkali electrolysis. in this process, the expensive films need to be protected from deposition and blockage.