Patent Application
20190233959
This invention relates generally to the field of recovery of metals from process solutions. The invention has particular utility for use in connection with recovery of alkali and alkaline earth metals such as lithium from geothermal brines and will be described in connection with such utility, although other utilities are contemplated.
Geothermal brines normally contain various metal ions, particularly alkali and alkaline earth metals, in varying concentrations. Recovery of these metals is important to the chemical and pharmaceutical industry. Lithium, in particular, is an important high value alkali metal having an increasing demand for its utility in storage batteries.
Several processes currently exist for recovery of lithium from lithium-containing brines. However, current extraction methods are expensive and time consuming, and the resulting material produced by existing processes typically is not sufficiently pure for use in lithium ion batteries, or pharmaceutical grade lithium without costly additional purification steps.
The present invention provides a system, i.e., method and apparatus for extracting lithium from aqueous brine. More particularly, the invention involves a liquid-liquid extraction and apparatus method, which comprises mixing an aqueous immiscible liquid ion exchange reagent having a capacity to selectively extract lithium, with the aqueous brine, in a liquid-liquid solvent extraction scheme. Several liquid ion exchange reagents that are immiscible with water and capable of extracting lithium are known and advantageously may be employed in the present invention. The liquid ion exchange reagents include but are not limited to tert-butyl benzo-12-crown-4 ether in a short chain linear polymer (SCP), halogenated β-diketones, preferably a chlorinated β-diketone, or a Lewis-based ion exchange such as an amine or oxime such as described in U.S. Pat. Nos. 3,479,147, 3,793,433 and 3,307,922, which are given as exemplary. Particularly preferred are tert-butyl benzo-12-crown-4 ether in a short chain linear polymer (SCP) and the chlorinated β-diketone.
In terms of liquid-liquid extraction apparatus useful in the scheme, the apparatus preferably comprises a liquid-liquid extraction apparatus such as described in U.S. Pat. No. 5,466,375, incorporated herein by reference. A particularly preferred apparatus is described in our co-pending U.S. application Ser. No. 15/051,352, tiled Feb. 23, 2016, and will be described in connection with such embodiment, although the invention is not limited to the use of such apparatus.
In one aspect of the invention there is provided a method for extracting an alkali or alkaline earth metal or other metal from a source of an aqueous brine containing said alkali or alkaline earth metal or other metal comprising the steps of: feeding the aqueous brine and an immiscible liquid ion exchange reagent having a capacity to selectively extract said alkali or alkaline earth metal or other metal to a first mixing vessel, wherein the mixing vessel comprises a first elongate housing having an inlet adjacent one end and an outlet adjacent the other end, and a permeable body coaxially disposed within the housing; passing the mixture from the first mixing vessel to a first centrifuge wherein the mixture is separated into a light organic phase which is mixed in a second mixer with lean electrolyte from a downstream electrowinning stage, and a heavy aqueous raffinate phase which is returned to the source; and passing the mixture from the second mixer to a second centrifuge where the mixture is separated into an aqueous raffinate phase, which is passed to an electrowinning cell wherein the alkali or alkaline earth metal or other metal is removed from the aqueous raffinate by electrowinning, and a lean electrolyte which is passed to the second mixer.
In one aspect of the invention the first and the second mixers have mixing channels substantially in the shape of a helix.
In another aspect of the invention, the first and second mixers include internal baffles formed of a series of elongated segments formed end-to-end.
In yet another aspect of the invention, the permeable body has pores in the range of 0.2 to 400 microns, preferably 20 to 200 microns, more preferably 60 to 100 microns.
In still yet another aspect of the invention, the permeable body comprises an elongate cylinder, in shape.
In a further aspect of the invention, the first and second mixers are sized and shaped to provide a travel or residence time between the first and second mixing devices and the first and second centrifuges of 5-120 seconds, preferably 20-60 seconds, more preferably 35-45 seconds.
In a preferred aspect of the invention, the aqueous or process solution comprises lithium and the immiscible liquid ion exchange reagent comprises tert-butyl benzo-12-crown-4 ether in a short chain linear polymer (SCP), a halogenated β-diketone or an ion exchange, more preferably an amine or an oxime ion exchange, or a hydroxyl oxime ion exchange.
In another aspect of the invention the aqueous raffinate from the first centrifuge is returned to the source.
In one aspect of the invention, the source comprises a geothermal brine, a brine from a mining source, an oil field brine, a relict hydrothermal brine, or an intercontinental salt lake.
Still yet another aspect of the invention includes the step of prefiltering the brine to remove silica.
In still yet another aspect of the invention, the source comprises a geothermal reservoir well and the aqueous raffinate is returned to the geothermal reservoir well by injection into the well
Further features and advantages of the present invention will be seen from the following detailed description, taken in conjunction with the accompanying drawings, wherein like numerals depict like parts, and wherein:
The invention will now be described in connection with the separation of lithium from a geothermal brine.
Referring to
The outer wall of permeable body 24 is spaced from the interior wall of housing 18. A helical baffle 30 is located within the annular space between the outer wall of permeable body 24 and the inner wall of housing 18. Baffle 30 may be a continuous elongated helical strip or formed as a series of segments. Mixing vessel 14A also has a lateral inlet 32 adjacent the inlet 20 end.
Permeable body 24 can be made of permeable or porous metal, and is filled with loosely packed finely divided media or fits such as powdered metal particles or ceramic particles. Various permeable and porous metals are available commercially from a variety of vendors including Mott Metallurgical Corporation of Farmington, Conn. The permeable or porous metal used in this invention preferably has substantially uniform pore sizes, or at least most of the pores are within an acceptable range for the intended purpose, and typically are in the range of 0.2 to 400 microns, preferably 20 to 200 microns, more particularly 60 to 100 microns. The porous media or fits should be inert to the liquids being handled. For example, the media or frits can be made of particles of ceramic, or stainless steel, Nickel 200, Monel® 400, Inconel® 600, Hastelloy® C276, Alloy 20, gold, platinum, silver, and titanium. As will be described below, the media or fits, by their nature, cause the droplets of the organic solvent to finally divide, dispersing fine droplets on the outer surface of the permeable body 24, where they are picked up by the aqueous brine solution. In other words, the solution (either the aqueous phase or the organic) which passes through the permeable body 24 is dispersed into the continuous phase liquid passing through the annular space.
In use, the organic liquid ion exchange reagent in a high flash point diluent is introduced through inlet 20 into the interior of permeable body 24. Aqueous brine solution is introduced into the interior of mixing vessel 14A through lateral inlet 32, into the space between the outer wall of permeable body 24 and the inner wall of mixing vessel 14A. The organic liquid ion exchange reagent is forced through the permeable body 24 and emerges from the permeable body in the form of a fine organic liquid extractant droplets where the droplets are picked up by the flowing aqueous brine solution, forming a dispersion of organic droplets in the aqueous brine solution. The aqueous brine solution preferably is flowed under turbulent conditions so that the droplets of the organic liquid ion exchange reagent are quickly dispersed before having an opportunity to coalesce. The liquid ion exchange reagent, which is substantially immiscible with the aqueous brine solution, extracts lithium from the aqueous brine solution, and emerges from the mixing vessel 14A via outlet 22.
Alternatively, the aqueous brine solution may be introduced into the interior of permeable body 24, and the organic liquid extractant introduced into the interior of the mixing vessel 14A through lateral inlet 32, into the space between the outer wall of permeable body 24 and the inner wall of mixing vessel 14A. In such case, the aqueous brine solution is forced through the permeable body 24, and emerges from the permeable body in the farm of fine droplets, which are picked up by the flowing organic liquid ion exchange reagent, forming a dispersion of aqueous droplets in the organic phase.
The solution emerging from outlet 22 is passed via conduit 34A to an extract stage centrifugal separator 100A as will be described in detail below. Conduit 34A includes inline baffles shown phantom as 98A for maintaining the fluid in a mixed condition. Conduit 34A is sized and shaped relative to the flow of fluid from mixing vessel 14A to provide a travel or residence time sufficient to permit substantial mass transfer of lithium in the aqueous solution to the liquid ion exchange reagent. Ordinarily, a residence time of 5-120 seconds, preferably 20-60 seconds, more preferably 35-45 seconds, is sufficient before the fluid is introduced into a centrifugal separator 100A. Alternatively, one or more loops may be included in the conduit 34A, or the cross sectional size of the conduit 34A increased so that the flow from mixing vessel 14A is controlled to within the target residence time of 5-120 seconds.
As will be described below, centrifuge separator 100A creates two exit streams-a light phase (organic) and a heavy phase (aqueous raffinate). The aqueous raffinate is recycled to the brine feed to dissolve more lithium. The organic phase liquid ion exchange reagent exiting the centrifuge 100A is transferred to another mixing vessel 14B, similar to mixing vessel 14A, where it is mixed with lean electrolyte from the electrowinning stage 60 as will be discussed below. As before, the organic liquid ion exchange reagent is forced through the permeable body 24 contained in mixing vessel 14B, and emerges from the permeable body in the form of a fine organic liquid ion exchange reagent droplets where the droplets are picked up by the flowing electrolyte, forming a dispersion of liquid ion exchange reagent droplets in the electrolyte. As before, the electrolyte preferably is flowed under turbulent conditions so that the droplets of the organic liquid ion exchange reagent are quickly dispersed before having an opportunity to coalesce. The electrolyte or stripping solution, which is substantially immiscible with the organic liquid ion exchange reagent removes (strips) lithium from the organic liquid ion exchange reagent and emerges from the mixing vessel 14B, where it is passed via conduit 34B which also contains inline baffles shown in phantom as 98B, similar to conduit 34A, for maintaining the fluid in a mixed condition. As before, conduit 34B is sized and shaped relative to the flow of the fluid from mixing vessel 14A to provide a travel or residence time sufficient to permit substantial mass transfer of lithium in the aqueous solution to the organic liquid ion exchange reagent. As with mixer 14A, mixer 14B can be operated where the aqueous stripping solution passes through the permeable body 24 and is dispersed into the organic phase passing through the annular space. The fluid then passed to a second strip stage, centrifuge 100B which is similar in construction to centrifuge 100A as will be described in detail below, and in which a light organic liquid ion exchange reagent phase is partially stripped of lithium and returned to tank 16, and a rich lithium electrolyte phase is passed to an electrowinning cell 60 where 99.99+ pure lithium may be collected at the cathode.
Referring in particular to
After being stripped of lithium, the brine may be returned to the geothermal reservoir via reinjection wells.
The present invention provides various advantages over prior art processes. For one, the system is closed. Thus, loss of the liquid ion exchange reagent and other organic solvents, i.e. due to evaporation is avoided. Also, by passing the organic phase through finely divided media or frits, and a permeable body before the organic phase is mixed with the aqueous brine solution, a micro dispersion of the organic phase is formed in the aqueous brine solution. Thus, less organic liquid ion exchange reagent solvent is needed in the overall process. Also, higher throughput may be achieved with smaller equipment overall, thus adding to equipment savings, as well as operational savings.
Also, from studies and tests we found that entrainment of the organic phase in the aqueous is generated in mixing step and not influenced by the separator. The quantity of entrainment is substantially affected by air ingestion. Using the hollow permeable body mixing apparatus as above described greatly reduces the possibility of air entrainment in the liquid and thus improves separation in the downstream separator (any separator for that matter).
Also, if air is excluded from the dispersion in the mixer, then organic-in-aqueous entrainment is minimized and aqueous-in-organic entrainment essentially reduced essentially to undetectable levels. Thus, our mixing apparatus as above described allows for a reduction, if not essentially elimination of air entrainment in the liquid thus reducing entrainment of one phase in the other phase. Conventional prior art mixing devices cannot achieve this since by design conventional mixing systems are exposed to the atmosphere and draw air into the liquid.
Various changes may be made in the above invention without the departing from the spirit and scope thereof For example, the lithium-containing brines may be concentrated for example, by evaporating some of the water, before mixing with the organic liquid extractant. Also, while a kerosene having a flash point above 67° C. is the preferred diluent, other liquid hydrocarbon mixtures and other organic compound mixtures having a flash point above about 67° C., advantageously may be used. And, while geothermal brine sources have been described, other brine sources such as from mining sources, oil field and relict hydrothermal brines, and brines from intercontinental salt lakes also advantageously may be used as a feed brine. And, other metals including, but not limited to zinc, nickel, cobalt, uranium, lead, silver and manganese, rare earth elements such as Neodymium (Nd), Yttrium (Y), Cerium (Ce), Praseodymium (Pr), Terbrium (Tb), Europium (Eu), Scandium (Sc), Ytterbium (Yb) and Lanthanum (La), and various alkali and alkaline earth metals which also are known to be present in geothermal brines also may be recovered using appropriate extractants, e.g. as above described, and electrowinning at appropriate potentials. Additionally, metals of interest may be collected using spray-drying techniques. Still other changes are possible without departing from the scope and spirit of the invention.
