CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of United States Provisional Application No. 63/122,783, filed December 8, 2020, which is incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates to concentration of lithium, optionally precious metals, such as gold tetrachloride, gold sulfate, silver tetrachloride, silver sulfate, and optionally rare earth elements (REE), and more particularly, concentration of such compounds with ultrafiltration, nanofiltration, modified reverse osmosis membranes and/or adsorption with colloidal carbon from unconventional feed-water sources.

BACKGROUND

[0003] Gold recovery is often performed using the so-called cyanidation or cyanide process or, alternatively, a thiosulphate leaching process. In these common processes, the gold is complexed with cyanide or thiosulphate permitting separation and recovery. However, when gold or other precious metals are already bound or complexed with an anion or other compound, such as gold or metal salts, the traditional processes are less effective and/or time consuming in recovery. Gold tetrachloride or gold sulfate, for instance, tends to have little or no affinity for the traditional cyanide or thiosulphate leaching mechanisms. Moreover, prior evaporation methods tend to be tedious and slow with minimal recovery of such metals.

BRIEF DESCRIPTION OF FIGURES

[0004] FIG. 1 is a flow diagram of an exemplary recovery process for lithium and/or precious metals and/or REE from unconventional feed-water sources (e.g., flue gas scrubber blowdown water, underground mines, high-salinity brines, or other unconventional feed water source as discussed herein);

[0005] FIG. 2 is a flow diagram of an exemplary recovery process using colloidal carbon adsorption for recovering lithium and/or precious metals and/or REE from high salinity brines or other unconventional feed water source as discussed herein; and [0006] FIG. 3 is a flow diagram of an exemplary post carbon flow scheme for lithium, gold, silver, lithium and/or REE recovery from unconventional feed water sources (e.g. high salinity source unconventional feed water source as discussed herein).

SUMMARY

[0007] In one embodiment or approach, a method of recovering lithium from unconventional feed-water sources is described herein. In one aspect, the method includes selecting and/or providing a feed-water source including low levels of lithium, brine, and optionally precious metals. In some aspects, the feed-water source may include a salt-lake brine, a coal-fired plant flue-gas scrubber blowdown water, a high-salinity brine source, a water-source from an underground mine, and/or combinations thereof. Next, lithium from the feed water source is concentrated using one or more of ultrafiltration, nanofiltration, and/or reverse osmosis membranes and optionally adsorption with particles of colloidal carbon, and then the lithium is recovered from the concentrate.

[0008] The method of the preceding paragraph may be combined with optional features, embodiments, and/or method steps in any order and/combination. These optional features, embodiments, steps may include one or more of the following: wherein the water source includes the precious metals and the precious metals are selected from gold tetrachloride, gold sulfate, silver tetrachloride, silver sulfate, rate earth elements, or mixtures thereof; and/or wherein the feed water source including the lithium is initially contacted with a colloidal carbon for a time effective to adsorb the lithium; and/or wherein the colloidal carbon has an average particle size ranging from 0.1 to about 10 microns, and preferably, about 0.5 to about 2 microns; and/or wherein the about 5 to about 25 weight percent of the colloidal carbon is mixed the feed water source; and/or wherein the colloidal carbon is mixed with the feed water source including the lithium for about 5 to about 60 minutes, preferably about 5 to about 30 minutes; and/or wherein the concentrating includes an ultrafiltration membrane to concentrate the lithium, and/or the colloidal carbon adsorbed with the lithium, and optionally recirculating a portion of the concentrate back to a feed tank or other source holding the feed water source; and/or wherein the lithium is recovered from the colloidal carbon and/or wherein filtrate from the ultrafiltration membrane is processed through one or more nanofiltration membranes to concentrate any precious metals and lithium therein and optionally to be recirculated back to the feed source; and/or wherein a portion of the ultrafiltration concentrate is processed through a filter press or equivalent to dewater the colloidal carbon adsorbed with the optional precious metals and lithium; and/or wherein the lithium is in the form of lithium chloride, lithium sulfate, or combinations thereof; and/or wherein the concentrating includes an ultrafiltration membrane to generate a concentrate and a permeate and wherein the permeate is processed through one or two nanofiltration membranes to recover the lithium; and/or wherein the lithium is recovered a concentrate from the one or two nanofiltration membranes; and/or wherein the feed-water source includes about 100 to about 5000 ppm lithium, preferably, about 200 to about 2500 ppm lithium, or more preferably, about 400 to about 1500 ppm lithium; and/or wherein the feed-water sources include up to about 250,000 ppm salts or chlorides, up to about 200,000 ppm salts or chlorides, up to about 150,000 ppm salts or chlorides, or up to about 100,000 ppm salts or chlorides.

DETAILED DESCRIPTION

[0009] A membrane filtration process using, for instance, ultrafiltration, nanofiltration, and/or modified reverse osmosis membranes is described herein to recover and concentrate precious metal salts and/or lithium salts, in particular, gold tetrachloride gold sulfate, and/or lithium chloride or sulfate from unconventional feed-water sources. For instance, certain unconventional feed water sources, such as those including brines, have been discovered to include precious metals, lithium, or salts thereof in small concentrations. These feed water sources include salt lake brines, coal-fired plant flue gas scrubber blowdown water, concentrated brine from desalination of seawater, high salinity brines, water sources from underground mines, and/or any other aqueous source where lithium, gold or other precious metals may have leached or been produced as a byproduct of a process. Such unconventional feed water sources often include lithium. In other approaches, the recovery and concentration processes herein may also apply to the recovery of silver tetrachloride, silver sulfate and rare earth elements (REE), which have been discovered in recoverable amounts in the various unconventional feed sources listed above. The rare earth elements may include, for instance, lanthanides, scandium, yttrium, cerium, and other known rare earth elements. Prior methods to recovery such metals used evaporation, which was tedious, time consuming, and necessitated significant surface area for the recovery. [00010] The amounts of gold, silver, lithium, and REEs (and/or salts thereof) in these unconventional water sources tend to be low. For instance, brine-water sources, such as those from underground mines (lithium mines and the like), may include lithium and exemplary underground mine water sources may preferably include from about 100 ppm to about 5000 ppm lithium, about 200 ppm to about 2500 ppm lithium, or even about 400 ppm to about 1500 ppm of lithium (as measured by AAS - the lithium may be as lithium salts such as lithium chloride, lithium sulfate, and/or the like). However, the unique processes herein utilize membrane technology optionally coupled with the unique application of colloidal carbon (carbon adsorption) in a specific manner to concentrate these low levels of precious metals, precious metal salts, and/or lithium to recoverable concentrations. In the process or through the process, the target metals (including lithium) may be extracted via gravity separation, carbon recovery (CIP, CIL, or CIC), packed carbon, merrill-crowe processing, solvent extraction, liquid-liquid extraction, electro-winning, combinations thereof, or the like, or even through use of finely milled micron-sized colloidal carbon to recover the lithium. In some approaches, initial extraction/adsorption (before membrane processing) of the gold salts and/or lithium salts with colloidal carbon particles of about 2 microns or less (in some approaches, about 1 micron or less) has been found effective to bind with/adsorb the gold and/or lithium specifically when it is in the form of a gold-chloride complex and/or a lithium-chloride complex. As mentioned above, traditional methods of gold leaching and recovery, such as gold cyanidation or thiosulfate leaching, are unable to effectively recover gold salts from such unconventional sources. Without wishing to be limited by theory, it is believed the prior processes using cyanide or thiosulfate are unable to complex with the gold or other precious metal when the gold or other metal is already bound with chloride or sulfate when such metals are found in these unconventional feed water sources.

[00011] In one approach of the recovery methods herein, the processes herein take low levels of precious metal salts, for instance gold tetrachloride, and/or lithium salts (such as lithium chloride) from these unconventional sources (in amounts ranging from about 0.01 ppm to about 5 ppm or even to about 10,000 ppm in some instances in the feed) and concentrate the gold and/or lithium as far as the chemistry of the process will allow using the optional colloidal carbon and/or the membrane filtration, such as nanofiltration. The concentration factor can be 2x concentration and up to as high as about 5x to about 20x concentration of the feed amounts of such metals/salts to insure the most efficient and smallest volumes with the highest metals concentrations possible as feed to the extraction of metals processes following the membrane systems.

[00012] For concentration using any embodiment herein, a variety of polymeric type membranes may be used. Examples include nanofiltration membranes such as modified (oxidized) polyamide polymers, carbon nanotube (CNT) backbone membranes, phenolformaldehyde polymers, polysulfonamide and/or cellulose acetate membranes. The membranes may have up to a nominal 300 molecular weight cut off. Any of the membranes are functional, but the modified nanofiltration membranes from oxidized polyamide and CNT membranes have demonstrated efficient membrane flux and separation factors for use with the unconventional feed water sources and unique form of the precious metals in salt forms (chlorides and sulfates, etc.).

[00013] In other approaches and in some instances for high salinity brine feed sources may include brine, such as about 50 to about 200 mg/1 salts and/or chlorides (or in some instances even up to about 200,000 ppm or to 250,000 ppm of salts or chlorides or any other range therewithin), any process herein may use colloidal carbon or activated colloidal carbon (such as colloidal carbon with an average particle size of about 10 microns or less, preferably 2 microns or less, and even 1 micron or less) to initially adsorb the gold salts and/or lithium salts from these types of unconventional feed sources (See, e.g., FIG. 2). In some approaches, the activated colloidal carbon may be, for instance, activated carbon as described in US Patent No. 9,770,743, which is incorporated herein by reference. The activated colloidal carbon may be provided with stabilizers and other additives as further described in US 9,770,743. Surprisingly, conventional activated and packed activated carbon do not adsorb gold chloride and/or lithium chloride from high salinity brines (that is, traditional carbon may only absorb less than 10% gold and/or lithium). Unexpectedly, colloidal carbon with an average particle size of about 0.1 to about 10 microns, and preferably about 0.5 to about 2 microns, and in other approaches, about 0.5 to about 1 microns, efficiently adsorbed gold chloride and/or lithium chloride (or other salts thereof) from the above noted unconventional feed-water sources at factors greater than about 60%. Without wishing to be bound by theory, the increased surface area in colloidal carbon may aid in the increased gold and/or lithium adsorption. In some approaches, both gold and lithium may be adsorbed with the colloidal carbon at similar amounts of 2x to 5x adsorption of the gold and/or lithium onto the colloidal carbon.

[00014] In one exemplary process (such as shown in FIG. 2), the colloidal carbon may be provided as a 5 to 25 with percent solution and using about 5 to about 60 minutes (and preferably about 5 to about 30 minutes) retention time in a tank or other holding vessel, such as a pond, to adsorb the gold chloride/sulfate and/or lithium chloride/sulfate to the colloidal carbon. Then, an ultrafiltration membrane may be used to remove the adsorbed colloidal carbon and recirculate it back to the feed source (such as, a tank or pond) and continue in this concentration mode until the UF filtrate increases in gold and/or lithium content (whereby the colloidal carbon is being loaded with the gold and/or lithium). Thereafter or simultaneously as shown in FIG. 2, and once sufficient metal and/or lithium is adsorbed on the colloidal carbon, the UF filtrate can be sent to a post recovery process or a nanofiltration unit (FIG. 1 and/or 3) using either one or two stages to concentrate the gold and/or lithium (FIG. 3) and return it to the feed source for further recovery of gold and/or lithium in the NF concentrate. In some instances, a portion of the UF concentrate may also sent to a filter press (or equivalent unit operation) to dewater the colloidal carbon adsorbed with the gold and/or lithium. The filtrate from the filter press then can be sent to extraction, post processing, or a further nanofiltration process, again using either one or two stages of filtration, with the final concentrate being returned to the feed for further adsorption by colloidal carbon. Centrifugal processing may further be used to remove the adsorbed metals.

[00015] FIGS. 1 to 3 provide further details of exemplary methods of precious metal and/or lithium (or salts thereof) recovery from unconventional feed sources when the metals and/or lithium may be complexed or bound to chlorides, sulfates, and the like and/or may be rare earth elements. Each may use a combination of ultrafiltration (UF), nanofiltration (NF), and/or reverse osmosis (RO) membranes as described above or further described below in the configurations as shown in the figures to recover the target precious metals and/or lithium from the unconventional fed water sources. The methods of FIGS. 1-3 recover gold and/or lithium as concentrate from one or two stage nanofiltration systems with or without colloidal carbon adsorption.

[00016] In any approach or embodiment herein, exemplary ultrafiltration membranes may have a pore size of about 0.01 microns to about 0.5 microns and may be operated at about 10 to about 100 psi. In any approach or embodiment herein, nanofiltration membranes (as modified herein or above) may have a pore size of about 0.0007 microns to about 0.0012 microns and may be operated at about 200 to about 2000 psi and/or have up to about 300 molecular weight cut-off. In another approach or embodiment herein, exemplary reverse osmosis membranes may have a pore size of about 0.0005 microns to about 0.001 microns and may be operated at about 200 to about 2000 psi and/or have up to about 300 molecular weight cut-off. Membrane sizes and operating pressures may be varied as needed for particular applications. As used herein, the membrane processing may substantially retain or permeate various streams, and preferably, nanofiltration membranes unexpectedly retain the precious metals, lithium, and or salts thereof found in the unconventional feed water sources. In this context, substantially means at least a majority or at least about 50 percent, in other approaches, at least about 70 percent, and in other approaches, at least about 90 percent retention or permeation as the case may be.

[00017] It is to be understood that while the materials and methods of this disclosure have been described in conjunction with the detailed description thereof and summary herein, the foregoing description is intended to illustrate and not limit the scope of the disclosure, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the claims. As used herein, any percentages, amounts, or ratios are by weight unless the context of the discussion suggests otherwise.