Lithium brines in the USA
Clayton Valley is host to the only commercially producing lithium project in North America, Albemarle’s Silver Peak brine evaporation pond project (Figure 7). Historically, the Clayton Valley playa produced about one-third of the US lithium requirements, but its economic viability suffered from fierce market competition, especially from South America, and a largely depleted brine supply. Originally, the central valley area contained 100–800 ppm Li, and the discovery well at 229 m depth contained 678 ppm when pumped at 450 gpm (Garrett, 2004). The average brine analysis when commercial production of lithium carbonate began in 1966 was about 400 ppm (Figure 7). Since that time the feed concentration of lithium has been slowly declining, and in 1998 the concentration was about 100–300 ppm Li (averaging 160 ppm, Harben and Edwards, 1998).
The Silver Peak Playa has an area of 50 km2 and an elevation of 1300- 1400 m (Figure 7). It lies in the rain-shadow of the Sierra Nevada, with an annual rainfall ≈130 mm and an evaporation rate of ≈1380 mm. Near-surface sediments consist of a mixture of clays (smectite, illite, chlorite, kaolin) and salts (halite and gypsum) and widespread pedogenic calcite. Lithium in the brines is derived from weathering and leaching of volcaniclastics in the Tertiary Esmeralda Formation and Quaternary ash-fall tuffs (Davis et al., 1986). Lithium content is highest on the eastern side of the playa adjacent to the outcropping marls of the Esmeralda Fm. Before it is leached, lithium is held in the clay fraction of the playa sediments and is probably part of the clay structure (hectorite is a widespread but minor component in the Clayton Valley clays - see later)). Lithium-rich brine feed to the plant averages 0.023% (230 ppm) lithium in a background NaCl concentration of 200,000 ppm, is pumped from depths of 100-300m in the Clayton Valley (Silver Peak) playa via a number of gravel-packed wells. The lithium (and potassium) in the deposit probably originated from hot springs along the Silver Peak Fault, with the current brine composition being a blend of evaporated water from these springs and surface and ground water that drains into the basin (Garrett, 2004). Modern saline spring outflows contain 9280–10,000 ppm Na, 786–826 ppm K and 24–43 ppm Li. Unusually high brine temperatures in some areas of the deposit (up to 44°C at fairly shallow depths ≈ 25m) tend to support a volcanic/geothermal origin for the lithium. Some of the brine feeder wells show elevated levels of radon gas. Pumped brine progresses through a series of fractionating evaporation ponds (Figure 7; Zampirro, 2004). Lithium concentration in the liquor increases to 6,000 ppm over the course of 12 to 18 months in the solar evaporation pans. When the lithium chloride level reaches optimum concentration, the liquor is pumped to a recovery plant and treated with soda ash to precipitate lithium carbonate, which is then removed by filtration, dried, and shipped.
Lithium from brine, when the Clayton Valley first produced product in the 1970s, was considered a unique deposit. Its operations established the technology and economic viability of lithium recovery from saline brine, which led to the development of brine production from the salars of South America that now dominate world production of lithium from brine.
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