Lithium Harvesting from the Most Abundant Primary and Secondary Sources: a comparative Study on Conventional and Membrane Technologies

Figure 1. 
Annual use of lithium in tonnes in each of the primary lithium usage industries from 2003–
2010 [9]. 
In terms of abundance, seawater brines (59%) and mineral clays (25%) are the most 
profound naturally occurring primary sources of lithium, with seawater brines dominat-
ing the natural supply (Figure 2a) [21]. However, Li does not occur naturally in its free 
state due to its highly reactive nature, hence more stable compounds such as Li
2
CO
3
, LiOH 
or LiCl are generally formed. More importantly, in different resources, they normally co-
exist with abundant other ions including, but not limited to, magnesium, calcium, iron, 
sodium, potassium, borates, sulphate, and bicarbonates, which makes lithium harvesting 
much more challenging [22–25]. Among these resources, lithium recovery from lithium-
bearing minerals and clays (spodumene, lepidolite, zinnwalidite, ambloygonite and pet-
alite) has been well studied. Some commonly used methods developed to date include 
chemical leaching [26], bioleaching [27], and pressure leaching [28]. Whilst harvesting a 
high purity Li
2
CO
3
at 99%, these conventional processes are generally energy-intensive 
and cause environmental concerns [29,30]. For example, lithium derived from Portuguese 
granite rock is around 2.5 times more costly than lithium collected from Chilean brine 
reserves. Hence, owing to the high availability of the aqueous reservoirs, such sources can 
serve as a major supply for effective lithium recovery in comparison to their hard rock 
equivalents (Figure 2a). 
Furthermore, lithium recovery and recycling from secondary resources has quickly 
grown in importance to accommodate the ever-rising demand for lithium consumption 
through sustainable lithium harvesting. Over the past few years, out of all the available 
secondary resources, lithium-ion batteries have emerged as the most prominent source 
for lithium recycling, accounting for 35% of total lithium consumption which is expected