A comparative study for removal of boron by chelating adsorbents containing N-methyl-D-glucamine group and separation of lithium by λ-MnO2 from geothermal waters

Direct release of geothermal waters to the environment may cause some adverse effects to plants because they contain some toxic species such as boron, arsenic, fluoride etc. despite valuable minerals including lithium. Although boron is essential element for some metabolic activities in plants, there is a small range between boron deficiency and boron toxicity for plants.In this study, batch and column mode tests were performed to evaluate the abilities of boron selective ion exchange resins, Diaion CRB 02 and Diaion CRB 05, as well as a novel chelating fiber Chelest Fiber GRY-HW for boron removal from geothermal water. On the other hand, geothermal water with higher lithium concentration (1-10 mg/L) due to the thermal interactions with rocks and sand in the aquifer can be considered as an alternative resource for lithium which has a very important place in many applications such as ion batteries, thermonuclear fusion, medicines, ceramic glasses, adhesives and electrode welding, when compared to the lithium concentration of seawater (~0.17 mg/L), which is widely used for lithium recovery.For the separation of lithium from geothermal water batch and column adsorption studies were performed by using both powdery and granulated forms of λ-MnO2 derived from spinel-type lithium manganese dioxide. In addition, a hybrid process coupling adsorption and membrane filtration was used to separate lithium from geothermal water. In these studies, the effect of process parameters on the separation of lithium such as adsorbent type, adsorbent concentration, the replacement speed of fresh and saturated adsorbents and flow rate of permeate stream were investigated. Besides, by utilization of a boron selective resin, Dowex XUS-43594.00, together with λ-MnO2 in the hybrid studies, simultaneous separation of boron and lithium from geothermal water was also conducted. All data obtained from batch adsorption studies were interpreted by using adsorption isotherm models. Moreover, mathematical models related with adsorption kinetics were used to figure out the rate order and rate determining step of boron and lithium sorption for both boron and lithium selective materials.The results showed that boron selective chelating resins along with novel chelating fiber could be employed as efficient adsorbents to decrease boron concentration in geothermal water below the permissible level for irrigation water (<1.0 mg/L). The lithium separation and recovery from geothermal water is possible by using λ-MnO2 adsorbent derived from spinel-type manganese dioxide. The adsorption-membrane filtration hybrid system providing an advantage to work with very fine particles easily can be considered as a favorable process for the separation of lithium from geothermal water. Also, combination of boron selective ion exchange resin Dowex XUS-43594.00 with lithium selective adsorbent λ-MnO2 can be successfully applied for the simultaneous separation of boron and lithium from geothermal water.