Research article · Science of the Total Environment 791 (2021), article 148192 · DOI: 10.1016/j.scitotenv.2021.148192

Performance of a double-slope solar still for the concentration of lithium rich brines with concomitant fresh water recovery

Celso F. Baspineiroa, Judith Francob, Victoria Flexera

aCentro de Investigación y Desarrollo en Materiales Avanzados y Almacenamiento de Energía de Jujuy-CIDMEJu, CONICET, Universidad Nacional de Jujuy, Av. Martijena S/N, Palpalá 4612, Argentina.
bInstituto de Investigaciones en Energía No Convencional (INENCO), 5150 Bolivia Av, 4400 Salta, Argentina.

Received 21 April 2021; revised 28 May 2021; accepted 29 May 2021; available online 1 June 2021; version of record 10 June 2021. Editor: Huu Hao Ngo.

Highlights

Abstract

Lithium recovery from brines has become a hot topic. The current evaporitic technology is slow, and serious environmental concern has been raised regarding the large volumes of water used, relating both to brine concentration through evaporation, and intensive pumping of fresh water needed in the fine chemical processing to produce high purity lithium carbonate.

In this work, an experimental and theoretical analysis of brine desalination using a double-slope Solar Still was carried out. The Solar Still was installed right next to an existing lithium mining facility in northwest Argentina, and was tested with native high salinity lithium rich brine for a continuous year under the typical weather conditions of lithium deposits: high altitude, large thermal amplitude between day and night, strong winds, and high solar radiation. The performance of the solar still as an evaporator was compared with that of a PAN evaporimeter class A, and correlated to experimentally determined weather parameters. While the performance of the Solar Still for brine concentration was below that of open air evaporation, the Solar Still allowed for the production of an average of 2 L day−1 m−2 of distilled water, in marked contrast with current practice. Numerical simulations allowed us to quantify heat exchanges in both the Solar Still and the open air system.

Keywords: Hydrometallurgy; Sustainable mining; PAN-evaporimeter; Direct solar desalination.

Introduction

Lithium has become an essential raw material for electric mobility, storage of renewable energy, and cordless devices, while lithium compounds are still also used in far wider applications such as specialty glasses and ceramics, and aluminium production, amongst others (Evans, 2014). A steady increase of 15% in annual demand for lithium is anticipated in coming years, since different types of lithium batteries are very promising candidates for those applications (Brouwer et al., 2016; Opitz et al., 2017; Pellow et al., 2015; Sternberg and Bardow, 2015). Lithium can be extracted from both hard rock ores and concentrated lithium-rich brines. Lithium reserves in brines are considerably more abundant than those in hard rock ores, extraction from brines is cheaper than from hard rock (Grosjean et al., 2012). It is speculated that in the long run, the largest proportion of the worldwide lithium production will come from brines, rather than ores. The largest lithium resources in brines are concentrated in a rather small region, referred to as the Lithium Triangle, extending between northwest Argentina, southwest Bolivia and northern Chile (Flexer et al., 2018; Kesler et al., 2012).

The evaporitic technology currently in use for lithium recovery from brines consists in pumping up brines from the underground deposits, and pouring them into a series of large open air shallow evaporation ponds, where brines are concentrated by solar/wind evaporation. While brines get concentrated, a fractional crystallization of salts of the other ions (Na+, K+, Mg2+) takes place (Border and Sawyer, 2014; Choubey et al., 2016; Swain, 2017), i.e. lithium carbonate is obtained by precipitation with soda ash (Flexer et al., 2018), a process that can only be attempted after important brine concentration, since lithium carbonate has a relatively high solubility, and is a minor component in the complex brine mixture. The evaporitic technology is a relative low cost/high margin process. It suffers, however, from both economic and sustainability shortcomings (Flexer et al., 2018). It takes between 10 and 24 months, from pumping to reaching the necessary lithium concentration. The inherent slowness of the process carries out economic implications. Firstly, it takes several years since investment decisions to achieve planned total production levels, since large stocks of concentrated brine are needed. Also, the technology is maladapted to sudden changes in demand. Production levels depend on the stock of highly concentrated brine, which in turn are a function on brine volumes pumped, on average, a year in advanced (Garrett, 2004). This is a problem both for demand surges, and also for temporary recessions, as was the case with the recent COVID pandemic.

Regarding the overall sustainability of the process, water usage is the big question. Lithium mining makes intensive use of both brine, i.e. extremely high salinity water, and low salinity water, found in the border of the salt lake basin (Flexer et al., 2018). Fresh water, used in the fine chemical processing, is estimated at 5–50 m3 per final ton of lithium carbonate produced (Flexer et al., 2018). Brine water as such is very far from being apt for either human or animal consumption. The volume of evaporated water (brine) averages about half a million liters per ton of lithium carbonate (Flexer et al., 2018). Both types of water have been the source of environmental concerns. Freshwater, due to the water demand of local communities located in an arid land with fresh water scarcity, where limited water resources for food production and industrial and domestic use present a critical factor that affects development. Most importantly, there is also concern about the possible interaction of the saline and freshwater aquifers, with some evidence of this process recently published (Liu and Agusdinata, 2020; Liu et al., 2019; Marazuela et al., 2020; Marazuela et al., 2019a; Marazuela et al., 2019b). The potential freshwater volumes that could be infiltrated to at least partially replenish the evaporated brine are even larger than the volumes of freshwater pumped for the fine chemical processing. Geographically, the areas where lithium brine deposits are located are especially vulnerable to slight changes in the environment too (Goosen and Walid, 1999). Moreover, remote areas face particular infrastructure challenges relating to the provision of clean drinking water and electricity (Kharraz et al., 2017). In these areas, it is more cost-effective to build small-scale water supply systems than to transport water (Glueckstern, 1999; Peter-Varbanets et al., 2009).

In this context, we recently proposed the use of advanced desalination technologies as a complement to the evaporitic technology. Our ultimate idea is to think of brines not just a source of valuable raw materials, but also as a possibility for water supply (Baspineiro et al., 2020; Flexer et al., 2018). Advanced desalination technologies and the current evaporitic technology indeed share the purpose of separating water from salts. Because of the extremely high salinity of lithium-rich brines, with much higher total dissolved solids values than sea water, the main challenge is to achieve this purpose efficiently, and at a reasonable cost. Desalination processes in general are energy-intensive. We have recently calculated that the least work of separation for water recovery from brines ranges from 18 to 42 kJ kg−1 depending on the total salinity of the feed (Baspineiro et al., 2020). However, in remote areas, desalination technologies could be the best solution to provide safe drinking water (Kharraz et al., 2017).

Coupling desalination systems with renewable energy sources represents an attractive solution for remote areas. Solar-powered desalination systems are considered the most promising. Around 70% of renewable energy desalination systems worldwide are solar-driven (Pugsley et al., 2016). Those systems are autonomous and independent of the electricity grid (Kharraz et al., 2017; Zheng, 2017). Direct desalination systems are those that use solar energy directly without needing energy conversion, such as solar stills and solar humidification-dehumidification systems. Indirect desalination systems are fed with electricity, such as electrodialysis, and thus they need an energy capture and conversion system, e.g. photovoltaic panels, with consequent energy capture inefficiencies. Considering the high salinity of the brines, direct desalination systems are much more likely to tolerate feeds of any quality, using low-grade energy with low operation and maintenance costs, and are suitable for decentralized systems. Finally, we should notice that the Lithium Triangle area is one of the regions with the highest annual average global insolation levels worldwide, making it an ideal location for solar systems in general (Piacentini et al., 2003).

A solar still is one of the simplest solar desalination systems developed to convert wastewater or brackish water into freshwater (El-Gazar et al., 2021; Elmaadawy et al., 2021; Nadal-Bach et al., 2021; Rahmani et al., 2021). Its maintenance is inexpensive and simple, requiring no proficient labour (Sharshir et al., 2017). Its main disadvantage, however, is the relatively low output of distilled water in comparison with other desalination systems. The production capacity of a simple type still is in the range of 2–5 L m−2 day−1 only (Velmurugan and Srithar, 2011). Interestingly, the concept of a solar still would be relatively easy to adapt to currently existing evaporation ponds, which could already act as the basins, requiring addition of cover, distillation collection trays, and containers for the recovered freshwater.

Here we report on the performance of a double-slope solar still, simply abbreviated solar still in the following text, installed next to an operational lithium mining facility, i.e. at 3940 m above sea level, and exposed to the abruptly changing temperature and wind conditions which are inheriting to these mining facilities. The solar still was fed with high salinity native brine, and was tested for a period of 12 months, during which its efficiency was compared with that of open air evaporation. An energy analysis was made, a model was established and numerical simulations of both the solar still and the natural evaporation process were carried out under the climatic conditions characteristic of the region. The model was adjusted until good correlation was observed between the simulations and the experimental results. A faster evaporation, and consequent brine concentration was observed for the open evaporation system as compared to the solar still. Conversely, the solar still allowed for the recovery of large freshwater volumes that are otherwise lost in the evaporation ponds.

Section snippets

Solar still and PAN evaporimeter

The experimental work was carried out in Olaroz salt lake located in the Lithium Triangle, in the high Andean plateau in Argentina, coordinates −23.554854°, −66.759093°, at 3940 m above sea level (masl). A conventional double slope solar still, schematically shown in Fig. 1a was tested using pure brine pumped from the salt lake. The solar still was made mostly of wood at our mechanical workshop. It stands on four 1 m high legs, which were in turn inserted in a concrete base to make the solar …

Results and discussion

Our simulated results for the vapour pressure and the specific heat capacity as a function of brine temperature are shown in Fig. 2, where they are compared to those of pure water. Data for the simulated brine density (ρ) are shown in Fig. S2. Evidently, the large values of vapour pressure lowering at the extreme salinity values of the brine lead to a considerably lower evaporation rate for the same temperature compared to pure water (Biazar et al., 2020). Thus, while the simple solar still is …

Conclusions

We have built a double slope solar still and tested its performance under the typical operating conditions of a lithium brine mining facility: high altitude, large thermal amplitude between day and night, strong winds and extremely high solar irradiation. The performance of the solar still was compared to open air evaporation. The performance of our device indicated a potential production of an average 2 L day−1 m−2 of fresh water in the summer, and 1 L day−1 m−2 in the winter. Actually, the …

CRediT authorship contribution statement

Celso F. Baspineiro: Conceptualization, Formal analysis, Investigation, Methodology, Writing – original draft. Judith Franco: Conceptualization, Supervision, Writing – review & editing. Victoria Flexer: Conceptualization, Formal analysis, Methodology, Writing – original draft, Writing – review & editing, Supervision, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

CFB acknowledges a doctoral fellowship from CONICET. VF and JF are permanent research fellows from CONICET. Financial support given to the project “A highly versatile selective approach for lithium production” by the Royal Society (IC170232) is acknowledged. Funding from CONICET for relocation expenses for VF is also acknowledged. Sales de Jujuy mining company is gratefully acknowledged for providing the location for solar still in their premises and technical personnel who performed the daily …

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