The April 2024 preliminary economic assessment for the Hombre Muerto North lithium project in Salta, Argentina describes 14 production wells, ponds concentrating brine to 0.75% lithium, and a carbonate plant with soda ash precipitation and centrifuging.
Hombre Muerto North is a lithium brine project in Salta, Argentina. The NI 43-101 Preliminary Economic Assessment (PEA), with a report date of April 24, 2024, was prepared for Lithium South Development Corporation. The brines from the Salar de Hombre Muerto Norte are solutions nearly saturated in sodium chloride. The brine chemistry is similar to other brines at Hombre Muerto, since they come from the same basin, and the Mg/Li and Li/SO4 ratios of the brine are close enough to those of the Cauchari and Olaroz brines that the report states the brine could be processed with technology like that used at the Olaroz production facility. The process covers a well field, solar evaporation ponds, a liming plant, a lithium carbonate plant, a soda ash plant and utilities.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Brine lithium | 684 | mg/L | Hombre Muerto Norte |
| Brine Mg/Li ratio | 3.5 | Not applicable | Compared with 1.4 at Olaroz |
| Brine SO4/Li ratio | 17.9 | Not applicable | Table of similar deposits |
| Realistic pumping | 253 | L/s | 14 wells |
| Nominal extraction | 176 | L/s | Summer peaks about 250 L/s |
| Lithium in brine | 22,086 | LCE tpy | Block diagram basis |
| Lithium carbonate output | 15,639 | LCE tpy | 70.8% of lithium; quality above 99.2% |
| Overall lithium recovery | 74.78 | % | Process block diagram |
| Pond concentration | 0.75 | % lithium | Design; suitable from about 0.7% |
| Liming preconcentration | About 0.15 | % lithium | Lime added to remove Mg and sulphate |
| Lime consumption | 2.6 | tonne per tonne LC | Soda ash 2.45 and water 29.0 |
| Hydrochloric acid | About 800 | t (33%) | Ion exchange and acid washing |
| Sodium hydroxide | About 800 | t (50%) | Ion exchange |
| Soda ash solution | 27 | % w/w | Ca/Mg removal and carbonation |
| Water for ion exchange | About 14 | L/s | Process |
Overview
The brine is pumped from a well field to evaporation ponds designed to crystallize mainly halite, some Glauber salt, glaserite, sylvite and borate salts. After preconcentration to about 0.15% lithium, lime is added to remove much of the magnesium as magnesium hydroxide and the sulphate as gypsum. Brine is concentrated further in a second set of ponds, then treated in the lithium carbonate plant, where remaining impurities are removed and technical grade lithium carbonate is made.
Key Process Stages
Well field
A first approach by Mark King and others finds that 253 L/s of brine can be pumped from 14 wells in a realistic scenario. The well schedule gives four wells at 25 L/s for one property, six at 22.5 L/s for another, and four at 4.5 L/s for a third, with average lithium concentrations of 680 to 1,100 mg/L. The nominal extraction rate is 176 L/s, and summer peaks of about 250 L/s can be reduced by building higher brine inventories in the ponds during winter.
Evaporation ponds
The evaporation path follows seasonal temperature. Glauber salt precipitates in cold weather, and glaserite along with gypsum precipitates in hot months. At about 0.3% to 0.4% lithium the brine saturates in sylvite. When concentrated to about 0.7% lithium, it is suitable for the lithium carbonate plant, and 0.75% is the design figure. Higher concentration could crystallize lithium schoenite and cause lithium losses in the ponds, depending on sulphate. Ponds are shallow and large, absorbing solar energy for natural evaporation, with floors and dykes covered in geomembrane to avoid leakage. Salts are harvested at a defined height and stockpiled outside the ponds, and pumps transfer brine between ponds. Pond area is calculated from the evaporation rate and rainfall for the site.
Liming plant
The mother liquor from the carbonate plant is treated with lime so the carbonate forms calcium carbonate solids and a lithium hydroxide solution, and the sludge returns to the liming reactor of the brine. The liming plant, near the ponds, slakes lime with water.
Lithium carbonate plant
Calcium and magnesium are removed first, by adding soda ash and slaked lime to the concentrated brine in an agitated reactor to precipitate magnesium hydroxide and calcium carbonate. Batch reactors avoid lithium carbonate co-precipitation. After filtering, solids are repulped and returned to the liming reactor to recover entrained lithium. The brine goes through ion exchange to remove calcium, magnesium and other di- and trivalent metals, then to carbonation reactors where hot soda ash solution precipitates technical grade lithium carbonate. The solid is centrifuged, washed, repulped, centrifuged again and washed, dried in an indirect dryer and packaged in maxi bags.
Additional Interesting Data and Summary
The report compares the brine with other deposits, listing lithium at 841 mg/L for Sal de Vida, 744 at Olaroz, 796 at Silver Peak and 245 at Cauchari. Magnesium to lithium ratios range from 1.4 at Olaroz and Cauchari to 8.6 for another historic salar.
The process mass balance shows 675 LCE tpy lost in the first pond stage, 352 LCE tpy to leakage, and a final recovery to lithium carbonate of 15,639 LCE tpy. The soda ash plant dissolves solid soda ash for both the removal and carbonation stages.
The report's reagent summary says the main reagent is lime, slaked with water in the liming plant, which is conventional equipment in the industry, and the second is soda ash, which is dissolved from solid to a 27% w/w solution for the precipitation. Slaked lime for the lithium carbonate plant is taken from the liming plant, and hydrated lime received from vendors is dissolved in agitated tanks. The outcome of the mass balance is a production of about 15,600 tonnes of product above 99.2% quality.
Key Processes
- Brine pumping from a 14-well field
- Solar evaporation in lined ponds
- Lime removal of magnesium and sulphate
- Ion exchange polishing of the brine
- Soda ash precipitation of lithium carbonate
- Centrifuging, washing, drying and bagging
Source: NI 43-101 Preliminary Economic Assessment, Hombre Muerto North Lithium Project, Salta, Argentina, April 24, 2024.
