Salars occur in closed (endorheic) basins without external drainage, in dry desert regions where evaporation rates exceed stream and groundwater recharge rates, preventing lakes from reaching the size necessary to form outlet streams or rivers. Evaporative concentration of surface water over time in these basins leads to residual concentration of dissolved salts (Bradley et al., 2013) to develop saline brines enriched in one or more of the following constituents: sodium, potassium, chloride, sulfate, carbonate species, and, in some basins, metals elements such as boron and lithium.

Salar de Maricunga is a mixed style salar, with a halite nucleus of up to 34 m in thickness in the central northern part. The halite unit is underlain by a clay core on the eastern and central part of the Salar. The clay is locally interbedded with silt and silty sands. The Salar is surrounded by relative coarse grained alluvial and fluvial sediments. These fans demark the perimeter of the actual salar and at depth grade towards the center of the Salar where they form the distal facies with an increase in sand and silt. At depth two unconsolidated volcaniclastic units have been identified that appear quite similar. These two volcaniclastic are separated by a relatively thin and continuous sand unit which may be reworked material of the lower volcaniclastic unit.

The brines from Maricunga are solutions saturated or close to saturation in sodium chloride with an average concentration of total dissolved solids (TDS) of 311 g/l. The average brine density is 1.20 g/cm3. Other components present in the Maricunga brine are: K, Li, Mg, Ca, SO4, HCO3 and B. Elevated values of strontium (mean of 359 mg/l) also have been detected.

The production process starts with the brine extraction wells in the Salar.

Results of the pumping tests on the Blanco Project indicate that brine abstraction from the Salar will take place by installing and operating a conventional brine production wellfield. Brine from the individual production wells will be fed into two collection/transfer ponds in the northwest of the Salar from where it will be boosted through the main trunk pipeline up to the evaporation ponds some 12 km to the north in the general plant area.

The brine composition and lithium concentrations of the Blanco Project indicate that a 20,000 TPY lithium carbonate production will require an average annual brine feed rate of 16,4120 m3/d. Seasonal fluctuations in the evaporation rate dictate that the required brine feed rate may be as low as 5,110 m3/d (59 l/s) during the winter months and will reach a maximum of 21,560 m3/d (250 l/s) during the summer months.

Results of the Blanco Project pumping tests and the reserve model simulations indicate that pumping rates of individual brine production wells will range between 14 l/s and 25 l/s. Well completion depths will vary between 40 m (upper brine aquifer) and 200 m (lower brine aquifer). The brine production wells will be completed with 12-inch diameter stainless steel production casing and equipped with 380 V submersible pumping equipment. It is projected that a total of 44 wells will be required over the life of the Project. However, no more than 15 wells will be operating at a single time. Permanent power will be delivered to the wellfield area through a mid- range power line.

Brine discharge from each wellhead will be piped through 8-inch diameter HDPE feeder pipelines to two central collection/transfer ponds in the northwest of the Salar. A 12 km length, 20-inch diameter steel / HDPE main trunk pipeline will be installed between the collection/transfer ponds and the evaporation ponds area. A booster pumping station will be installed at the bottom of the main trunk line adjacent to the collection ponds to pump the brine up to the evaporation ponds (130 m lift).

The objective of the Project is to produce 20,000 TPY of battery grade lithium carbonate (Li2CO3).

The raw material for both processes is the brine extracted from MSB’s mineral properties in the salar. This brine is fed to evaporation ponds where various salts precipitate. Enriched Li+ ion brine is obtained as a result of the evaporation stage.

This lithium-rich brine is fed to the Salt Removal Plant to remove most of the calcium and magnesium and further concentrate lithium in the brine. This brine is then pumped to the lithium carbonate production process, which consists of purification steps for boron, calcium and magnesium removal, a precipitation step for lithium carbonate, and steps for solid and liquid separation. Finally, there is a phase for drying, micronizing and packaging.

SOLAR EVAPORATION PONDS
The solar evaporation ponds are a group of concentration facilities that take advantage of the natural water evaporation effect to concentrate the brine. The evaporation rate depends on four main factors: solar radiation, the air’s relative humidity, wind speed and temperature changes. These four factors are favorably present in the Salar de Maricunga area.

The system behaves like a crystallization or salt separation mechanism through precipitation, using the brine’s natural saturation property. In this way, salts precipitate when the brine reaches its saturation point and the resulting brine, with a higher lithium concentration is transported to the next pond, as indicated previously. Precipitated salt must be harvested (extracted) from the ponds when it reaches pre-defined levels. Approximately 8,300,000 tonnes per year of brine are treated in the evaporation ponds annually.

Harvested salts are deposited in authorized stocking areas and separated by the type of salt, depositing them directly on the stocking ground using the same backhoes that are used for harvesting. The floor of each stocking area will have a drainage system to recover the brine impregnated in the salts and other solutions that could be generated by rain or snow falls. This brine recovered will be sent back to the evaporation ponds.

SALT REMOVAL PLANT
The brine that comes from the ponds is in the first instance fed to the Salt Removal Plant, which, through the processes of evaporation and crystallization, allows increased concentration of the lithium contained in the brine. At the same time this plant enables the elimination of excess calcium and other impurities from the brine in the form of tachyhydrite and calcium chloride salts. This stage allows the of a more concentrated brine feed to the lithium carbonate plant, thus improving the plant’s efficiency and producing a final product that will have improved market potential. It additionally generates water that is used in the process, thus reducing water consumption.

LITHIUM CARBONATE PLANT
The Lithium Carbonate Plant is a chemical plant that receives concentrated brine from the Salt Removal Plant. This lithium rich brine also contains concentrations of impurity elements. These impurity elements must be removed from the brine to generate a lithium carbonate product of high purity, in accordance with the international standards of the industry.

Boron extraction is carried out using a solvent extraction process. The boron extraction phase is carried out with an acidic pH and using a mixture of reagents (including diluent and extractant) to transfer the boron from the aqueous phase (boron free brine) to the organic phase. The phase of re- extraction (or stripping) to recover the organic phase is carried out in a basic pH, obtaining a boron rich solution to be sent to the discard pond, while the boron free brine is sent to the next stage.

For the elimination of other contaminants present in the brine, a primary reduction of calcium is carried out, using a recirculation of the mother liquor and a soda ash solution in a process at 40 °C to promote the formation and precipitation of calcium carbonate.

To assure the elimination of all contaminants, a second reduction stage for magnesium and calcium is carried out by mixture of soda ash solution with a slaked lime slurry, which allows the formation of calcium carbonate and magnesium hydroxide. The magnesium and calcium solids precipitated are filtered and later sent to the discard pond. The magnesium and calcium free brine is sent to an ionic exchange stage, to ensure that no contaminants are left in the brine.

The contaminant free brine enters the carbonation stage, where it is placed in contact with a soda ash solution. The formation of lithium carbonate using soda ash is optimum at temperatures close to 80 °C, allowing the precipitation of the lithium carbonate in a solid state.

The pulp obtained from the carbonation stage is processed in solid/liquid separation centrifuges, and the product is also washed. Lithium carbonate obtained in the carbonation stage is transported to a dryer. After drying, some goes through size reduction in a micronizer. Finally, the dry, unmicronized and micronized lithium carbonate is packed into separate maxi bags and stored in a final product warehouse and is later delivered to clients as required.