Lithium concentration process and lithium concentrator for extracting lithium from brines

Abstract

A method for extracting lithium from a brine by means of sorption on a solid sorbent, characterized in that the desorption is carried out by reducing the salt content of the brine using a rinse with fresh water or fresh water-based solutions and wherein the sorbent used consists of lime, dolomite, magnesium carbonate, loam, clay, or a mixture thereof.

Description

[0001] The demand for lithium as a raw material is growing rapidly due to new applications such as lithium-ion batteries. Lithium is generally marketed as lithium carbonate or its equivalents (LCE = Lithium Carbonate Equivalent). Currently, lithium is extracted from lithium-bearing ore or from brine. Extraction from brine offers a price advantage. Using state-of-the-art technology, the brine is concentrated, and then the lithium is precipitated to lithium carbonate by adding sodium bicarbonate. Concentration is usually achieved by evaporation using solar power in ponds. At existing sites in desert regions, this method is the most cost-effective.

[0002] However, high concentrations are now also being reported in brines that originate in non-desert regions, for example, as a byproduct of deep geothermal energy production or as a residue from natural gas fracking. More energy-intensive concentration methods have been used in these cases, such as separation using ion-selective membranes or sorption via cation exchangers and desorption using ionic solutions or acids. These methods have the disadvantages of high plant investments, high operating costs, and undesirable residues / regenerates.

[0003] Procedures for extracting lithium from brines are described in US 2020 / 0 316 557 A1 and CN 1 04 310 446 A.

[0004] The process according to the invention eliminates these disadvantages. It enables the production of a lithium concentrate in a very simple manner, without requiring significant intervention in the standard operation of the geothermal plant or natural gas production. Investment costs are very low, and operation is simple and cost-effective. No expensive input materials are required, and no waste streams are generated.

[0005] The inventive method utilizes the fact that lithium ions bind to surfaces far more effectively at extremely high salt concentrations in a brine solution than under freshwater conditions. This allows for a remarkably simple separation and concentration process for lithium.

[0006] The process according to the invention involves passing brine through a granular sorbent. The sorbent consists of lime, dolomite, magnesium carbonate, loam, clay, or a mixture thereof. A characteristic feature of the process according to the invention is the sequential alternation between passing brine with a high salt concentration through the sorbent and washing with fresh water with a very low salt concentration. According to the invention, this change in salt concentration enables the desorption of lithium.

[0007] Slow flow allows the lithium ions to bind to the sorbent. The brine leaves the area through which it flows depleted of lithium. After a relatively long flow period, the brine flow is briefly stopped or diverted through a bypass. The sorbent can then be briefly washed / flushed with an isotonic NaCl solution to remove interfering ions such as magnesium, strontium, or barium.

[0008] In the next step, the sorbent is washed / percolated with fresh water. This dissolves the weakly sorbed lithium ions. Since the fresh water wash solution requires only a fraction of the volume of the previously percolated brine, a significant increase in concentration is achieved in the fresh water wash solution compared to the brine. The wash solution can then be collected as lithium concentrate and further processed. This enables the subsequent cost-effective production of commercial products such as lithium carbonate (LCE) through simple precipitation with sodium carbonates.

[0009] The mechanism can be explained by the different behavior of the hydration shells of the ions in brine and fresh water ( Fig. 1 and Fig. 2) Under freshwater conditions, the lithium ion forms a large hydration shell due to its high ionic strength, while larger ions have smaller hydration shells. Typical brines with solids contents of approximately 250 g / L create competition among the individual ions for water molecules to form hydration shells. Therefore, lithium cannot maintain its very large hydration shell under brine conditions. With a reduced hydration shell, the Li ion in the brine now exerts a much stronger attractive force on negatively charged surfaces due to its very high ionic strength than under freshwater conditions (see Fig. 1) Thus, a weak, reversible bond of lithium to negatively charged surfaces is possible even at significantly higher concentrations of the other alkali and alkaline earth ions in the brine. Washing with fresh water abruptly restores the shielding hydration shell of the lithium ion, thereby breaking the bond and releasing the lithium ion into the solution ( Fig. 2).

[0010] According to the invention, the sorbent should have a binding strength that enables binding in brine but not under freshwater conditions. To ensure detachment, sorbents with comparatively low binding strength are used, e.g., CaCO3 or MgCO3 granules. These are inexpensively produced from limestone or dolomite. They are available in unlimited quantities and are environmentally friendly. Other readily available sorbents include clays or loams, soils, or organic materials such as compost.

[0011] Sorption can be carried out in small ponds using a fixed-bed reactor. Ponds already used for the intermediate storage of the extracted brine are particularly suitable for this purpose. Fig. 9) Alternatively, a sorption pond can be used upstream or downstream of the buffer pond ( Fig. 10) High-performance sorption materials with high cation exchange capacity can also be used in tubular reactors or closed fixed-bed reactors ( Fig. 11).

[0012] The fresh water used for desorption and concentration can have a neutral pH or be acidified using acid or an acidic buffer system. Purification and conditioning agents can also be added.

[0013] Preferably, several differently enriched fractions generated in previous rinsing cycles, preferably three fractions, can be used for rinsing. According to the invention, rinsing is performed first with the highest concentration Li solution, then with the lower concentration, and finally with fresh water. The highest concentration solution is then used as a concentrate for further treatment, preferably for precipitation by means of NaHCO3 precipitation; the two lower concentrations are available for the next rinsing cycle. Detailed description of the invention and drawings

[0014] The invention is illustrated in 11 figures and is explained in more detail using exemplary embodiments. Fig. 1 and Fig. Figure 2 shows the hydration behavior of lithium ions (1) to be separated and the numerous sodium ions (2) present in brine (1, 2) and fresh water (9, 10), which could explain the process according to the invention. Due to competition among the ions for the water molecules in the brine, the lithium ion loses part of its hydration shell. This brings the high ionic strength of the lithium ion into play. It binds reversibly (7) in brine to sorbents with a negatively charged surface (5). If the brine is drained and the sorbent is rinsed with fresh water, sufficient water molecules are again available to rebuild the normal hydration shell. This causes the lithium ions to detach from the surface (13). This effect is used in the process according to the invention. Fig. Figure 3 shows the brine management system at the site of a geothermal or fracking plant. Brine is extracted from a production well (15) and fed into the plant (14). After heat has been extracted in the geothermal plants, the brine is temporarily stored in a pond (16) until it is reinjected via another well (19).

[0015] The lithium extraction process according to the invention removes the lithium from this brine stream and concentrates it into a lithium concentrate. The concentrate can then be processed on-site or, preferably, at a central plant into marketable products such as lithium carbonate.

[0016] Preferably, the extraction according to the invention is carried out in an integrated manner using the buffer pond for sorption / desorption ( Fig. 9) For this purpose, it is partially or completely covered with a layer of granulated sorbent. Inexpensive, environmentally friendly, and readily available materials such as lime, dolomite, clay granules, loam granules, or many others with reversible cation exchange can be used as sorbents.

[0017] Fig. 4 to Fig. Figure 8 shows the integrated lithium extraction process. Fig. 9 in the individual process steps. In the first step ( Fig. 5) After a long sorption period (weeks - months), the brine supply is stopped for a while or diverted via a bypass (not shown). Now the brine (23) in the pond is drained or pumped out and injected via the borehole (19). In the next step ( Fig. 6) Interfering ions such as magnesium, barium, strontium, etc., which are present in the remaining brine film on the sorbent surfaces, can be washed out. A sprinkler system, which can be stationary or mobile, can preferably be used for this purpose (26). An NaCl solution, isotonic to the brine flow, is used as the flushing solution. This flushing solution is preferably injected via the outlet (28) and the borehole (19). The flushing step It. Fig. Step 6 can be omitted if the concentration of accompanying ions is not considered disruptive. In the next step ( Fig. 7) Freshwater or lithium concentrate from previous rinses is used as a rinsing solution. This causes the lithium ions adhering to the sorbent to desorb, and the rinsing solution is concentrated accordingly. This is fed via a drain (33) to a lithium concentrate tank (34). The concentrate tanks can be stored on site or transported by tanker truck to the central processing plant. In the next step, the usual brine management is restarted ( Fig. 8) by switching on the brine supply. This refills the pond, the sorbent is permeated, and finally the injection (19) can also be switched on again. Due to the alternation of very long sorption phases and short desorption phases, only a very small intervention occurs in the processes at the site.

[0018] If this integrated process utilizes the buffer pond ( Fig. 9) is not desired, alternative interpretations may be chosen. Fig. 10 and Fig. 11. show these alternative technical interpretations. Fig. Figure 10 shows the upstream placement of a sorption pond (41) before the buffer pond (16). Alternatively, the pond can be placed downstream of the buffer pond. In these cases, the sorption and desorption steps described above are carried out similarly, without affecting the buffer pond (16). Sorption occurs with the flow passing through both ponds, while the sorption pond is bypassed for desorption. In these cases, washing is also preferably carried out via a sprinkler system (39). Concentrate production is also carried out similarly to the integrated process by collecting the concentrate in a concentrate tank (44).

[0019] In the event that an integrated process is not to be used and an even smaller "footprint" of the system is desired, It. Fig. 11. Performance sorbents are used in a fixed-bed reactor or a fluidized bed reactor (48). The supply of the rinsing solutions and the collection of the concentrate are carried out similarly to the other two designs. Reference symbol list 1 Lithium ion in brine. The hydration shell (dotted line) is thin due to competition for water molecules. 2 Sodium ions in brine 3 Free sodium ions in the brine 4 Sodium ions bound to the sorbent 5 sorbent particles 6 brine 7. Sorption direction: Binding at the sorbent 8 Lithium ion bound to the sorbent 9. Lithium ions in freshwater. The hydration shell (dotted line) is thick due to the high ionic strength of the lithium ion. 10 Sodium ions in freshwater 11 Free lithium ion with thick hydration shell in solution 12. Sorption direction: Dissolution from the sorbent 13 Sodium ions bound to the sorbent 14. Supply of brine from the borehole to the system / buffer pond 15 boreholes for extracting the brine 16 Buffer ponds for the temporary storage of the brine 17 Intermediate storage brine 18. Discharge of the brine to the injection borehole 19 boreholes for injecting the brine 20 ponds for integrated use for brine buffering and lithium extraction 21 Pond partially or completely filled with sorbent granules 22 Stop the brine supply or line via bypass (not shown) 23 Wet sorbent granules 24 Draining the brine from the pond 25 Sorbent granules rinsed with NaCl 26 Irrigation system 27 Supply of the (isotonic to the brine) NaCl solution 28. Removal of the isotonic NaCl solution 29 Freshwater supply, freshwater concentrates 30 Stop the injection 31. Grouting stopped 32. Sorben rinsed with fresh water, release of Li ions and enrichment in the rinsing solution, thereby increasing the Li concentration / concentrate production 33 Supply to the concentrate tank 34 Li concentrate tank, optional for off-site transport 35 Refilling the pond 36. Closing the concentrate line 37 Feed to the upstream sorption pond 38 Bypass of the sorption pond 39 Irrigation system for pre-pond 40 Inflow of washing solutions (isotonic NaCl, fresh water) 41 Sorption pond 42 Outflow of the sorption pond 43 Concentrate line 44 Concentrate tank 45 Bypass fixed-bed reactor 46 Fixed-bed reactor inlet 47 Inflow of washing solutions (isotonic NaCl, fresh water) 48 fixed-bed reactor 49 Fixed-bed reactor outlet

Claims

[1] Method for extracting lithium from a brine by sorption on a solid sorbent, characterized by , that desorption is carried out by reducing the salt content of the brine using a rinse with fresh water or fresh water-based solutions and wherein the sorbent used consists of lime, dolomite, magnesium carbonate, loam, clay, or a mixture thereof. [2] Method according to claim 1, characterized by , that the sorption time and flow rate are much greater compared to the desorption time during rinsing and the rinsing volume, resulting in a concentration of lithium ions in the rinsing solution. [3] Method according to claim 1, characterized by that the pH value of the freshwater rinsing solution is adjusted to a value below 7 using acid or buffer systems. [4] Method according to claim 1, characterized bythat substances for cleaning or regenerating the granular sorbent are added to the freshwater rinsing solution. [5] Method according to claim 1, characterized by that a rinse with a NaCl solution takes place before the freshwater rinse and that this NaCl solution is largely isotonic to the salt content of the brine. [6] Method according to claim 1, characterized by that the sorbent is located in a fixed-bed or fluidized bed reactor and that this is located upstream or downstream of a buffer pond of a brine treatment plant. [7] Apparatus for extracting lithium from a brine according to the method of claim 1, comprising: - a pond-like area with an inflow and an outflow, - a sorbent introduced into the pond-like area for the sorption of lithium, consisting of lime, dolomite, magnesium carbonate, loam, clay, or a mixture thereof, and - an irrigation system for irrigating the sorbent in the pond-like area, wherein the brine can flow into the pond-like area via the inflow and can flow out of the pond-like area via the outflow, wherein the system is arranged so that the brine flows through the sorbent in the pond-like area and that desorption in the drained state takes place by irrigation with fresh water. [8] Plant according to claim 7, characterized by , that the pond-like area is a buffer pond of a brine treatment plant, a natural gas production plant or a geothermal plant, wherein the inflow is connected via a supply line to a borehole for extracting the brine and wherein the outflow is connected via a discharge line to a borehole for injecting the brine. [9] Plant according to claim 7, characterized by that the pond-like area is a sorption pond, - which is located upstream of a buffer pond of a brine treatment plant, wherein the inflow is connected via a supply line to a borehole for extracting the brine and the outflow is connected via a discharge line to the buffer pond, or - which is downstream of a buffer pond of a brine treatment plant, wherein the inflow is connected to the buffer pond via a supply line and the outflow is connected to a borehole for injecting the brine via a discharge line, and wherein, preferably, a bypass line is arranged between the supply line and the discharge line. [10] Plant according to claim 9, characterized by that the sorbent is located in a fixed-bed or fluidized bed reactor and that this is located upstream or downstream of the buffer pond of the brine treatment plant.

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