A worker with the Sonora Lithium Project takes lithium samples. Photo: Bacanora.

Mexico leads in lithium

The Sonora Lithium Project in Mexico encompasses ten open-pit mining concessions for hard-rock lithium, a resource increasingly in demand for use in electric vehicle batteries. Due to harsh operating conditions, the valves used to effectively process hard-rock lithium are classified as severe service equipment, necessitating careful consideration at the project planning phase.
 
^ A worker with the Sonora Lithium Project takes lithium samples. Photo: Bacanora.

Article by Daniel Sweet
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Located on 100,000 hectares in the Mexican state of Sonora, the Sonora Lithium Project (SLP) includes ten lithium mining concessions owned by London-based Bacanora, a lithium development and exploration company.

Ganfeng Lithium, a Chinese lithium-ion battery producer, purchased a 29% stake in Bacanora in 2019, with an eye toward their Sonora holdings. A feasibility study produced by Bacanora established a Proven Mineral Reserve of 1.67Mt and a Probable Mineral Reserve of 2.85Mt across seven of the ten concessions in the SLP. This capacity makes the SLP one of the world’s larger—and by some accounts, the largest—developed sources of lithium. The estimated resource life of the concessions is 200 years, with an output of 17,500-35,000tpa Li2 CO3 per year.

The SLP involves open-pit mining throughout the concessions, and the company recently completed construction on a processing and upgrade facility in Hermosillo. That facility produced “high quality battery-grade (>99.5%) lithium carbonate during ongoing test work conducted over the last four years,” according to the Bacanora website, in line with Ganfeng Lithium’s stated ambitions to tap the growing demand for electric vehicle batteries.

Battery demand

Though perhaps most associated with consumer electronics, lithium demand in recent years has been driven by the widespread adoption of electric vehicles and other energy storage methods. According to a report by McKinsey, “the electric vehicle revolution is ushering in a golden age for battery raw materials, best reflected by a dramatic increase in the price” of lithium, and further, “the growing need for energy storage, e-bikes, electrification of tools, and other battery-intense applications is increasing” interest in lithium.

Despite the widely-recognized demand for lithium now and in the future, there is some debate about the ideal form of lithium for battery production. Lithium extraction can take on one of two forms—hard-rock and brine-based extraction—with varying effects in end battery products.

Lithium production

In hard-rock extraction, lithium-containing minerals like spodumene are mined and processed to create either lithium carbonate or lithium hydroxide. Lithium can also be extracted from lithium-containing brine. In this process, underground lithium-containing brine is pumped into ponds on the surface and allowed to evaporate, leaving behind lithium carbonate.

While brine-based extraction was the primary technique for lithium production throughout the 1990s and 2000s, according to the same report by McKinsey, hard-rock lithium has become both economically feasible and technically desirable. The report concludes that hard-rock lithium has regained “its market share and will be a major source of growth moving forward.”

This is due in large part to the fact that lithium hydroxide—resulting from hard-rock extraction—is “better suited in the production of the batteries with NCM 811 cathodes.” NCM 811 cathode batteries outperform older battery designs, and consequently, “brines look less attractive to battery producers, leading to” a scale up in hard-rock mine assets (New Age Metals).

Some of the performance benefits related to lithium hydroxide, as reported by New Age Metals, include:
  • More flexibility: the lithium hosted in spodumene can be processed into either lithium hydroxide or lithium carbonate. Brines initially can only be processed into carbonate, and then can be further processed into hydroxide at an additional cost
  • Faster processing: brines can take a lot longer to process due to the evaporation required, making for an inconsistent process compared to spodumene
  • Higher quality: spodumene typically hosts higher lithium content in comparison to most brines
  • Geographic location: rock minerals are more homogeneously distributed on earth
  • Comparable costs: while each mining operation may have its own defining factors regarding profitability, the hard-rock operations utilize low-cost, traditional mining techniques

Severe service

As opposed to other lithium extraction projects in Latin America, which favor brine-extraction, the operations in the Sonora project are carried out through open-pit mining, or via hard-rock, spodumene extraction.

In terms of process, hard-rock production requires mineral separation (the isolation of lithium compounds in spodumene); flotation (to generate a high grade of spodumene concentrate); and roasting, in which the concentrate is heated, cooled, mixed with sulphuric acid, and reheated, producing lithium sulphate, which is soluble in water (SGS Minerals Services).

The direct mining of high grade lithium ores in this fashion involves extreme conditions for machinery and hardware. As a result, valves used in hard-rock lithium production are classified as severe service equipment. Neles (formerly Metso Flow Control) notes in an “Application Report” on lithium production via hard rock that factors such as “high temperatures, abrasive particles and significantly high acidity levels” can impact valve performance, requiring careful consideration during project planning.

The same report details the types of valves used at various stages of the lithium production process, and that chart is reproduced here. As evidenced by the chart, a wide range of valve products are on offer for lithium production from hard rock, and companies like Neles also supply actuators and valve controllers for lithium processing.

Application Typical Valve types
Spodumene flotation Knifegate and segment valves
Calcination Ball and butterfly valves
Cooler Ball and butterfly valves
Ball mill discharge
Knife gate, pinch and diaphragm valves
Sulphuric acid feed Butterfly and ball valves
Leaching Process Ball, sleeved plug and knife gate valves
Thickening underflow Pinch and knife gate valves 
Thickening overflow Rubber-lined butterfly valves and knife gate valves
Purification and filtering  High performance butterfly, process ball and pinch valves
Evaporation Butterfly, segment and ball valves
Precipitation Butterfly and ball valves

 

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