Concentrating brine for lithium recovery using GO composite pervaporation membranes

Highlights

• GO pervaporation membranes with crystallizer postponed salt crystallization in lithium-containing brine.

• Water flux from submerged pervaporation membrane was 20 times higher than that of a solar evaporation pond.

• GO composite membrane increased lithium concentration from 0.3 to 1.27 g/L with 73% reduction of the feed volume.

• The scale-up simulations with a membrane area of 100 m² showed less than 10% flux decline relative to the lab-scale module.

• The pervaporation process becomes competitive with the solar pond when aiming at simultaneously producing water and lithium.

Abstract

The extraction process of highly demanded lithium from brine normally starts with a solar evaporation pond to increase the lithium concentration, which takes more than a year and is weather-dependent. This work evaluated the enrichment of lithium from salt lake brine using graphene oxide (GO) composite pervaporation membrane with the crystallizer unit. The deposition of stacked GO layer on the commercially available hydrophobic membranes can tackle the membrane wetting and salt crystallization issues. The initial water flux was 11 L/m² h at 70 °C, which was 20 times higher than that of solar evaporation pond (~0.5 L/m² h) and 10 times lower footprint. With high initial feed concentration (>200 g/L of salt) the GO composite pervaporation membrane increased lithium concentration from 0.3 to 1.27 g/L (73% feed volume reduction). Assuming 10 m³/day capacity of the proposed solar pervaporation system, an economic analysis showed that the technique is not economically sustainable when solely aiming at the lithium extraction, while it becomes competitive with the traditional method when aiming at simultaneously producing deionized water and lithium. A payback time of 3.6–27 years is achievable with the sale price of water and LiOH at US$ 0.3–1 per 20 L and US$ 20 per kg, respectively. A continuous process is also possible with backup gas heater and waste heat.

Introduction

Lithium is an important element that is used in ceramics, glass, lubricants, alloys, medicine, and batteries. The fast-growing lithium-ion (Li⁺) battery industries for electric devices and vehicles increase global lithium production by approximately 20% annually [1,2]. Also, wind and photovoltaic systems are estimated to become the largest source of electricity generation worldwide in 2025 [3], therefore the demand for lithium battery will increase significantly. Lithium is recovered from brine and ores from more than 17 million tons of estimated reserves [2]. However, the conventional production process is not efficient due to the high investment cost and is time-consuming [4]. The lithium extraction from ores is harmful to the environment due to the complex process and the use of an acid [5]. For the conventional lithium recovery process from brine deposits, the concentration of lithium has to increase from an average of ~0.4 g/L to ~60 g/L [6,7]. Typically, lithium brine is concentrated by solar evaporation ponds. This process takes more than 13 months to reach the desirable lithium concentration for lithium carbonate (Li₂CO₃) production [8,9]. Currently, LiOH is preferred over Li₂CO₃ for the preparation of nickel cobalt manganese with a molar ratio of 8:1:1 (NCM811) due to lower melting point and high reactivity, which reduces the calcination temperature [[10], [11], [12]]. The cathode materials prepared from LiOH showed more uniform morphology, stable layer structure and better electrochemical performance than that prepared by using Li₂CO₃ [13].

The conventional lithium production process can lead to difficulty in obtaining lithium due to long evaporation time, large footprint, the effect of weather and potential leakage to contaminate nearby potable water aquifers [14]. Furthermore, the distilled water evaporated from the pond is not recovered, which is a waste of a pure water resource. Other technologies that have been used instead of solar evaporation ponds include precipitation [7], electrochemical methods [[15], [16], [17]], ion-exchange resins [18], and liquid-liquid extraction [19,20]. However, all the mentioned technologies have drawbacks, while the electrochemical methods are currently at laboratory stage of development, the others require large amount of chemicals.

Thermal-driven membrane desalination combined with solar power can be used to concentrate brine instead of the solar evaporation ponds. This allows the production of freshwater, salts, and brine enrichment for lithium recovery at the same time. In terms of the environmental impacts, solar collector fields have some negative environmental impacts during the construction phase, which is similar to the conventional evaporation ponds such as noise pollution and human presence. The invasion of the lands for solar collector fields or solar evaporation pond can cause harm to the sensitive ecosystem. While the solar collector system may have thermal pollution during the operation, the rise in the brine salinity from the solar evaporation pond can also increase the growth of algae, affect fish and bird habitat. At the salinity higher than 200 g/L, the productivity of brine shrimp declines resulting in lower food supply for birds [21,22]. Both systems have some negative environmental impacts, however the solar collector fields require significantly smaller area compared to solar ponds resulting in lower environmental issues. Moreover, the integration of solar power with the membrane process is another step in moving toward lower carbon footprint and achieving a sustainable thermal-driven membrane process.

Park et al. [23] and Pramanik et al. [24] used membrane distillation and nanofiltration processes for lithium enrichment. However, their feed solution did not represent the commercial salt lake brine due to low concentrations or simple model solutions with only magnesium and lithium. Membrane distillation was also used to regenerate the liquid desiccant solution such as lithium chloride [25]. In membrane distillation, many researchers reported that a hydrophobic membrane is prone to pore wetting, which led to the loss of Li⁺ [[26], [27], [28]]. Moreover, the salt crystallization on the membrane surface creates a significant issue in thermal-driven membrane desalination due to severe flux decline and its direct link to pore wetting [29]. Scaling mitigation strategy such as agitation, crystallizer, and thermal water softening had been recorded to reduce salt crystal on the membrane surface in membrane distillation [30,31]. Cooling in the crystallizer is effective at precipitating NaCl by to reduce the solubility of NaCl in the solution [[32], [33], [34]].

From our previous study, the GO composite membranes in pervaporation are capable of rejecting salt ions in brine containing divalent cations due to cation-GO sheets cross-linking as well as minimizing salt crystallization on the membrane surface due to smooth and negatively charged GO layer [35,36]. The modification of commercially available membranes by the addition of GO-based layer on the surface for the purpose of anti-fouling properties, desalination and dye removal was also found in other literature [[37], [38], [39]]. In thermal-driven desalination process, a vacuum was applied resulting in higher permeate flux than counter-current flow membrane module [[40], [41], [42]]. Submerged membrane set up was chosen over the conventional cross-flow configuration due to limited number of studies [[29], [30], [31],43,44]. In crossflow system, the membrane unit is separated from the feed solution, therefore an external pump is required, which can increase the operational cost. Although shear forces in the cross-flow process helps limit salt crystallization on the membrane surface, the membranes in a submerged system is easier to be taken out for maintenance and cleaning than that in a conventional cross-flow configuration [29].

Even though GO-based membranes have been investigated as Li⁺ selective membranes using the electric-driven method, the transport mechanism of Li⁺ through the confined nanoscale environment is complicated and it is still difficult to scale-up the system [45,46]. Moreover, the use of GO composite pervaporation membrane to concentrate the lithium-containing brine has not been studied.

The GO composite pervaporation membranes help prevent membrane wetting and prolong sustainable membrane performance for lithium enrichment from highly concentrated brine. In addition, solar energy can be integrated with the pervaporation system, which is beneficial in remote areas. Cha-Umpong et al. [36] showed that the effect of intermittent operation from solar energy caused severe pore wetting in the hydrophobic membrane used in thermal-driven membrane desalination. However, the GO composite pervaporation membranes were not affected by oscillations in the feed temperature.

In this study, the recovery of lithium from simulated salt lake brine was investigated using the GO composite pervaporation membranes to improve salt rejection and reduce heterogeneous nucleation. The addition of thermal water softening and crystallizer unit were also evaluated to minimize salt crystallization on the membrane surface and prolong the membrane operation. At the end of the membrane process, LiOH crystals were obtained from chemical precipitation and evaporation. Furthermore, computational fluid dynamics (CFD), Matlab simulator and experiments were conducted to investigate the performance of thermal-driven membrane desalination process. In addition, the techno-economic analysis was performed to evaluate the feasibility of the solar thermal-driven membrane pervaporation system compared with solar evaporation pond.