The results of geophysical survey suggest that the deepest part of the basin is in the center, where salar deposits may reach up to 300 m thick.

The results indicate that the eastern and northern basins of the Salar de Hombre Muerto are floored largely by clastic material with thin horizons of precipitated borax, halite, gypsum, and calcite.

Field observations indicated groundwater associated with each of the sand units, so that they may be termed aquifers. The clay units did not produce water and in each case they created a confining bed to the underlying sand unit, so that they may be termed aquicludes, or possibly aquitards (the latter implies the possibility of slow leakage across the bed). Unconfined groundwater in sand unit 1 occurs between 0.7- 0.9 m depth. Sand unit 2 averages 1.8-2.3 m depth. Both these units produced relatively small quantities of fluid. Sand unit 3 produced greater quantities of fluid between 4.1 to >4.7 m depth, and is thus likely to have higher permeability. Sand unit 4 occurred at only a few locations towards the south of the area investigated.

The base of the second clay unit has a distinctive black, organic horizon that can be correlated across the salar. Two depocenters can be identified in the central southern part of the eastern basin, and towards the north, with the source of the sediment infill, looking to be sourced from the Rio Los Patos delta region.

The total sand thickness of all Sand Units in the pits is greatest along the toe of the Rio Los Patos delta, where it reaches >4 m in total. Towards the northern depocenter, the Sand Units reach 3 m thickness. The sand fraction again emphasizes the importance of the input of sediment from the Rio Los Patos and the northern depocenter, both of which show >80% sand content in the pit sections.

Mineralization.
Brine prospects differ from solid phase industrial mineral prospects by virtue of their fluid nature. Therefore, the term ‘mineralization’ is not strictly relevant to a brine play, so that here the brine is considered; its flow regime, and its physical and chemical properties.

The distribution of density in the eastern part of the salar shows a general increase away from the Rio Los Patos delta, where relatively fresh water (density ~1.0 gram per centimeter cubic to minus the third degree) enters. As the fluid moves through the more permeable units away from the delta, concentrations, and hence density, rapidly increase to >1.1 grams per centimeter cubic to minus the third degree. This increase is the result of evaporation around the toe of the delta where groundwater is relatively close to the surface. Over much of the eastern basin the density is greater than 1.15 grams per centimeter cubic to minus the third degree, although a tongue of slightly lower density extends from the delta north of the Farralon Catal.

Groundwater enters the salar from the Rio Los Patos delta, from where flow bifurcates with a significant flow extending towards the northwest. Low fluid elevations, or sinks, are seen towards the north and towards the southwest.

The chemistry of the fluids confirms that there is only one brine type within the salar, originating from the evaporation of influent waters.

As calcium reaches a concentration of approximately 40 mmol/l in minus first degree gypsum starts to precipitate and the fluid becomes enriched in sulphate. Throughout the brine evolution sodium and chloride react conservatively, gradually increasing in concentration, and halite saturation which by analogy with other salars in the region occurs at approximately 280 gm/l in minus first degree NaCl.

The distribution of lithium and potassium in the eastern basin at Hombre Muerto are shown that maximum concentrations are associated with the areas of higher density, > 1000 mg/l minus first degree Li, and >10,000 mg/l minus first degree K in the central south, with subsidiary peaks of >800 mg/l minus first degree Li and >8,000 mg/l minus first degree K towards the north.

The area is underlain by the extensive APVC (the Altiplano-Puna Volcanic Complex magma) chamber at depths of only 4 km and it seems likely that this could be the ultimate source, being transferred to the surface via volcanic activity, especially hydrothermal vents. However it is not known whether such transference was direct, or indirect as a result of the leaching of lithium-bearing volcano-clastic sediments, or by the recycling of trapped lithium-bearing solutions. It is known that several hot springs bordering the salar drain directly into the basin. Another possible source of lithium may be related to the borate deposits in the area.

Well fields.
The approach to recovery of brine has focused on the use of two well fields (Southwest and East). The two locations for the proposed well fields were determined based on brine quality, extent of the brine aquifer, and the ability to pump the brine aquifer at sufficient quantity and rate to support filling and maintaining levels of the evaporation ponds. Pump tests and daily samples collected showed little variation in lithium and potassium concentrations, indicating dilution of produced brine was not evident during the 30-day pumping periods. A total of 24 well field pumps will provide a continuous flow of brine to the liming and evaporation ponds.

The ultimate production level for the plant is determined by evaporation rate, which varies depending on season. In summer months when temperatures are highest and rainfall low, evaporation rates can double. In these periods additional wells will be brought online to increase the flow of brine to the evaporation ponds.

Well pumping rate and lime plant throughput can be operated at 40% above the average to take advantage of high evaporation rates.

Ponds and Evaporation.
Extracted brine from the well fields is pumped to the liming ponds for magnesium removal as the first step of the brine purification process. Magnesium is precipitated as magnesium hydroxide Mg(OH)2 after reacting it with a milk of lime solution. Following reaction, brine is pumped into the active lime settling pond where magnesium hydroxide solids settle to the pond floor and clarified brine overflows into a pumping well.

Halite Ponds.
The function of the halite ponds (rock salt, NaCI) is to concentrate limed brine to its potassium chloride saturation limit and remove the sodium chloride (NaCl). This is accomplished through evaporation as a result of solar radiation, wind, and temperature. The halite ponds (lined) consist of five strings (4 operating, 1 in harvest) with a total surface area of 7.7 square kilometres and designed to minimise entrainment of concentrated brine in the halite. The crystallised salts rich in sodium chloride accumulate at the bottom of the ponds and are recovered by harvesting. An additional string has been included for harvesting to allow continuous operation of four strings, while one string is being harvested.

Muriate (KCI) Ponds.
From the last halite pond the brine is transferred into the muriate (KCI) ponds where it is concentrated to 2% lithium while at the same time potassium chloride (KCl) crystallizes along with the halite, gypsum and borate. The muriate ponds consist of five strings (4 operating, 1 in harvest) with a total surface area of 1.5 square kilometres, which are each connected to one of the halite pond strings. Muriate salts, rich in potassium chloride and sodium chloride, accumulate at the bottom of the ponds as they crystallise and are to be harvested as the raw material feed for the potassium chloride process plant. Ponds will be harvested sequentially in 18 month cycles using specialised salt harvesting machinery.

Concentrated brine from the final muriate pond in each of the operating strings is pumped into a surge pond, and then to the lithium carbonate plant. This feed rate will be maintained throughout the year, regardless of the seasonal flow variation experienced in the solar evaporation ponds.

Potash (KCl) Plant.
When operating at design capacity, 95,000 tpa of agricultural grade potash is expected to be produced annually. 0.5 million tonnes per year of muriate will be harvested from the muriate ponds and transferred to the potash plant feed stockpile. The harvested muriate contains approximately 71% NaCl and 25% KCl. The potash plant is designed to extract and purify the potash (KCl) to 97% grade which is suitable as a fertiliser for the agricultural industry. The process involves the crushing and milling circuit from the stockpile feed system, conditioning and flotation, centrifugation, drying and packaging.

Lithium Carbonate Plant.
The lithium carbonate plant is designed to produce 25,000 tonnes per annum of battery grade (99.5%) lithium carbonate (Li2CO3). Brine is supplied from the muriate ponds at 33 m3/h with a minimum 2%(w/w) lithium content. The plant consists of several process stages:
- Boron Removal (solvent extraction),
- Calcium and Magnesium Removal,
- Lithium Carbonate Precipitation,
- Purification,
- Dewatering and Drying,
- Micronizing, and
- Bagging.

Boron Removal.
Brine is pumped into the lithium carbonate plant, heated and pH adjusted before the solvent extraction (boron removal) process. The solvent extraction circuit consists of three extraction stages, where the process brine is mixed with organic extractant and five stripping stages where the organic extractant, loaded with boron, is exposed to an aqueous stripping solution, which then releases boron. Solvent extraction reduces the boron concentration in the process brine to 50ppm. The low boron-calcium-magnesium brine concentrate is pumped to the primary ion exchange feed tank where further calcium, magnesium and boron contaminants are removed using ion exchange technology.

Calcium and Magnesium Removal.
Brine is pumped into the lithium carbonate plant, and reacted with soda ash (sodium carbonate) to precipitate calcium and magnesium as carbonates. The brine is pumped through a press filter and a polish filter to remove the precipitated solids.

Lithium Carbonate Precipitation.
Once the brine has been purified by precipitation, solvent extraction and ion exchange it passes through a series of heat exchangers to raise its temperature. The brine is then reacted with soda ash (Na2CO3) solution in draft tube crystallisers, precipitating lithium carbonate (Li2CO3). The reactor product is pumped to the crystalliser thickener following which the final lithium carbonate is extracted via a bank of centrifuges.

Purification.
Galaxy developed and patented its purification technology in 2010 and has successfully proven the technology at its Jiangsu Plant in China. Galaxy’s purification technology is designed to be applied to either hard rock or brine based lithium carbonate production processes. The function of the purification circuit is to remove impurities entrained in the lithium carbonate crystal structure, which cannot be removed by washing. This is achieved using digestion, ion exchange and recrystallisation. During digestion the solid lithium carbonate crystals are digested in cold process liquor in the presence of carbon dioxide. Carbon dioxide reacts to form lithium bicarbonate (LiHCO3), which has a much greater solubility than lithium carbonate. The resulting liquor is filtered and passed through an ion exchange unit to remove excess entrained contaminants. The final pure liquor is steam-heated and the final pure lithium carbonate crystals precipitate out of solution. The product is pumped to the crystalliser thickener where the lithium carbonate is extracted via a bank of centrifuges and dried.

Micronisation and Bagging.
The dried lithium carbonate is jet milled using three micronizers operating in parallel. This process reduces the product particle size to around 5 micron. The micronized product is pneumatically conveyed to the bagging units, storage silos and packaged in either 25kg bags or bulk bags.