Patent Application
20240375084
Gold, as a precious metal, is used,1,2 not only in jewelry and currency, but also as an increasingly indispensable element in chemical synthesis,3-10 nanotechnology,11-14 modern electronics,15,16 and medicine.17-19 One of the most commercially successful processes1 for gold mining from ores is heap leaching, where alkaline cyanide lixiviants are used to solubilize gold as its dicyanoaurate, Au(CN)2−. Activated carbon is introduced in order to separate the dissolved Au(CN)2− from the leached pulps, a technology known25,26 as carbon-in-pulp. The Au(CN)2− is stripped subsequently from the activated carbon, producing a concentrated solution for the final gold recovery by so-called electrowinning1. In order to strip the Au(CN)2− from the activated carbon, harsh conditions,27-30 including high temperatures (95-140° C.), high pressures (70-400 kPar), and concentrated cyanide and hydroxide solution are required. As a result, there exists a need for improved gold stripping processes that can be performed under mild conditions using nontoxic reagents.
Disclosed herein are compositions, methods, and systems for supramolecular gold stripping. One aspect of the technology is a composition comprising a surface-bound, linear gold anion and a solution, the solution comprising a molecular receptor.
Another aspect of the technology provides for methods for gold stripping. The method may comprise contacting a surface-bound, linear gold anion with a solution comprising a molecular receptor under conditions sufficient for transferring the linear gold anion from the surface into the solution. In some embodiments, the surface-bound linear gold anion is contacted with the solution in the presence of a contaminant and the linear gold-anion is selectively transferred into solution. The method may further comprise recovering the gold from the solution. In some embodiments, the linear gold anion is transferred from the surface into the solution at a temperature between about 10° C. and about 40° C.
Another aspect of the technology provides for an electrolytic system for recovering gold from solution. The system may comprise an electrode and an electrolyte comprising the molecular receptor and a linear gold anion.
In some embodiments of the compositions, methods, and systems described herein, the molecular receptor is α-cyclodextrin (α-CD). In some embodiments of the compositions, methods, and systems described herein, the linear gold anion is Au(CN)2−. In some embodiments of the compositions, methods, and systems described herein, the surface is the surface of activated carbon. In some embodiments of the compositions, methods, and systems described herein, the contaminant anion is Ag(CN)2−.
Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.
Disclosed herein are gold stripping methods and compositions produced therefrom. The present technology provides for a cost-effective and energy-saving method of removing linear gold anion, such as Au(CN)2−, bound to the surface of activated carbon, with an aqueous solution of environmentally benign cyclodextrin. The high binding affinity between the linear gold anion and cyclodextrin in solution enables effective molecular recognition of linear gold anion at room temperature. The gold anion containing composition obtained from performing the method can be processed subsequently to enable gold recovery by using common technologies in industry, such as electrolysis.
As demonstrated in the Examples, the binding affinity between the linear gold anion Au(CN)2− and α-cyclodextrin in aqueous solutions at room temperature can be as high as 8.1×104 M−1. These results demonstrate that this molecular recognition process between α-cyclodextrin and Au(CN)2− can be applied to the stripping of gold from the surface of activated carbon under mild conditions using readily available α-cyclodextrins, avoiding the traditional methods used in gold-mining protocol that employ harsh conditions and toxic chemicals. Furthermore, the Examples also demonstrate that the higher binding affinity of Au(CN)2− than Ag(CN)2− towards α-cyclodextrin can be utilized to realize selective stripping for Au(CN)2− in the presence of Ag(CN)2−.
One aspect of the technology is a composition comprising a surface-bound, linear gold anion and a solution. The term “surface-bound” refers to molecules that are capable of being attached non-covalently to the surface of various materials. In some embodiments, the surface is the surface of activated carbon. The term “activated carbon” refers to an adsorbent derived from carbonaceous raw material, in which thermal or chemical means have been used to remove most of the volatile non-carbon constituents and a portion of the original carbon content, yielding a structure with high surface area. Activated carbon is a porous material exhibiting amphoteric characteristics and is usually used for adsorption of organic and inorganic compounds.
The term “linear gold anion” refers to gold-containing anions with linear geometries. The term “linear” refers to the molecular geometry around the central gold atom that is bonded to two other atoms is placed at a bond angle of approximately 180°. In some embodiments, the linear gold anion is Au(CN)2−. The counter cations of the linear gold anions include alkaline cations such as Li+, Na+, K+, Rb+, and Cs+. In some embodiments, the counter cation is K+.
In some embodiments, the solution comprises a molecular receptor. The term “molecular receptor” refers to host molecules that contain a binding site or a cavity for a smaller guest molecule or an ion to bind covalently or non-covalently. In some embodiments, the molecular receptor is cyclodextrin. The term “cyclodextrin” refers to any of the known cyclodextrins such as unsubstituted cyclodextrins containing from six to twelve glucose units, especially, alphα-cyclodextrin, betα-cyclodextrin, gammα-cyclodextrin and/or their derivatives and/or mixtures thereof. The alphα-cyclodextrin consists of six glucose units, the betα-cyclodextrin consists of seven glucose units, and the gammα-cyclodextrin consists of eight glucose units arranged in donut-shaped rings. The specific coupling and conformation of the glucose units give the cyclodextrins rigid, conical molecular structures with hollow interiors of specific volumes. The “lining” of each internal cavity is formed by hydrogen atoms and glycosidic bridging oxygen atoms; therefore, this surface is fairly hydrophobic. The unique shape and physical chemical properties of the cavity enable the cyclodextrin molecules to absorb inorganic or organic molecules or parts of inorganic or organic molecules which can fit into the cavity.
In some embodiments, the molecular receptor is cyclodextrin derivatives or modified cyclodextrins. The derivatives of cyclodextrin consist mainly of molecules wherein some of the OH groups are converted to OR groups. The cyclodextrin derivatives can, for example, have one or more additional moieties that provide additional functionality, such as desirable solubility behavior and affinity characteristics. Examples of suitable cyclodextrin derivative materials include methylated cyclodextrins (e.g., RAMEB, randomly methylated betα-cyclodextrins), hydroxyalkylated cyclodextrins (e.g., hydroxypropyl-cyclodextrin and hydroxypropyl-gammα-cyclodextrin), acetylated cyclodextrins (e.g., acetyl-gammα-cyclodextrin), reactive cyclodextrins (e.g., chlorotriazinyl-CD), branched cyclodextrins (e.g., glucosyl-betα-cyclodextrin and maltosyl-cyclodextrin), sulfobutyl-cyclodextrin, and sulfated cyclodextrins.
Cyclodextrin derivatives are also disclosed in U.S. Pat. No. 6,881,712 and include, e.g., cyclodextrin derivatives with short chain alkyl groups, such as methylated cyclodextrins and ethylated cyclodextrins, wherein R is a methyl or an ethyl group; those with hydroxyalkyl substituted groups, such as hydroxypropyl cyclodextrins and/or hydroxyethyl cyclodextrins, wherein R is a —CH2—CH(OH)—CH3 or a XH2CH2—OH group; branched cyclodextrins such as maltose-bonded cyclodextrins; cationic cyclodextrins such as those containing 2-hydroxy-3-(dimethylamino)propyl ether, wherein R is CH2—CH(OH)—CH2—N(CH3)2 which is cationic at low pH; quaternary ammonium, e.g., 2-hydroxy-3-(trimethylammonio)propyl ether chloride groups, wherein R is CH2—CH(OH)CH2N+(CH3)3Cl−; anionic cyclodextrins such as carboxymethyl cyclodextrins, cyclodextrin sulfates, and cyclodextrin succinylates; amphoteric cyclodextrins such as carboxymethyl/quaternary ammonium cyclodextrins; cyclodextrins wherein at least one glucopyranose unit has a 3-6-anhydro-cyclomalto structure, e.g., the mono-3-6-anhydrocyclodextrins, as disclosed in “Optimal Performances with Minimal Chemical Modification of Cyclodextrins”, F. Diedaini-Pilard and B. Perly, The 7th International Cyclodextrin Symposium Abstracts, April 1994, p. 49 said references being incorporated herein by reference; and mixtures thereof. Other cyclodextrin derivatives are disclosed in U.S. Pat. No. 3,426,011, Parmerter et al., issued Feb. 4, 1969; U.S. Pat. Nos. 3,453,257; 3,453,258; 3,453,259; and 3,453,260, all in the names of Parmerter et al., and all issued Jul. 1, 1969; U.S. Pat. No. 3,459,731, Gramera et al., issued Aug. 5, 1969; U.S. Pat. No. 3,553,191, Parmerter et al., issued Jan. 5, 1971; U.S. Pat. No. 3,565,887, Parmerter et al., issued Feb. 23, 1971; U.S. Pat. No. 4,535,152, Szejtli et al., issued Aug. 13, 1985; U.S. Pat. No. 4,616,008, Hirai et al., issued Oct. 7, 1986; U.S. Pat. No. 4,678,598, Ogino et al., issued Jul. 7, 1987; U.S. Pat. No. 4,638,058, Brandt et al., issued Jan. 20, 1987; and U.S. Pat. No. 4,746,734, Tsuchiyama et al., issued May 24, 1988; all of said patents being incorporated herein by reference.
In some embodiments, the molecular receptor is α-cyclodextrin. As used herein, the term “α-cyclodextrin” refers to a cyclic oligosaccharide consisting of six glucose subunits joined by α-(1,4) glycosidic bonds forming the shape of a tapered cylinder as shown in
In some embodiments, the composition comprises an adduct formed from the molecular receptor and the linear gold anion. As used herein, an “adduct” is a new chemical species AB, each molecular entity of which is formed by direct combination of two separate molecular entities A and B in such a way that there is change in connectivity, but no loss, of atoms within the moieties A and B. Stoichiometries other than 1:1 are also possible, such as 2:1, 3:1, 4:1 and so forth. In some embodiments, the adduct is formed from a linear gold anion non-covalently bound to the cavity of α-cyclodextrin.
The solution is selected to allow for the transfer of the linear gold anion from the surface into solution. In some embodiments, the solution is an aqueous solution.
The concentration of molecular receptor may be selected by those of skill in the art based on several different factors, such as the amount of surface-bound gold to be transferred into solution. Other factors may include, without limitation, the solvent present, the counterions present, the presence and/or amount of contaminants present, the temperature at which transferring step is performed, whether the transferring step is performed in a single or multiple stages, whether the transferring step is performed in a batch or continuous process, and the like. Generally, higher concentrations of the molecular receptor allow for more gold to be transferred into solution. In some embodiments, the solution comprises the molecular receptor at a concentration of 1-10 w/v %. In some embodiments, the solution comprises the molecular receptor at a concentration of at least greater than 1 w/v %, at least 1.5 w/v %, at least 2 w/v %, at least 2.5 w/v %, at least 3 w/v %, at least 3.5 w/v %, at least 4 w/v %, at least 4.5 w/v %, at least 5 w/v %, at least 5.5 w/v %, at least 6 w/v %, at least 6.5 w/v %, at least 7 w/v %, at least 7.5 w/v %, at least 8 w/v %, at least 8.5 w/v %, at least 9 w/v %, or at least 9.5 w/v %.
Another aspect of the technology is to provide a method for gold stripping. The method comprises contacting a surface-bound, linear gold anion as described herein with a solution comprising a molecular receptor as described herein under conditions sufficient for transferring the linear gold anion from the surface into the solution. The conditions may generally refer to the chemical environment or processing conditions.
Chemical environment may refer to the amount of surface-bound gold, the concentration of the molecular receptor, the amount and/or type of surface onto which the gold is bound, the solvent, the presence or amount of contaminants, and the like.
Processing conditions may refer to the temperature at which the temperature at which the transferring step is performed, the pressure at which the transferring is being performed, the volumes being processed, whether the transferring step is performed in a single or multiple stages, whether the transferring step is performed in a batch or continuous process, and the like.
An advantage of the present technology is that the transferring step may be performed without the need for harsh conditions, high temperatures, high pressures, or concentrated cyanide or hydroxide solutions.
The transferring step may be performed at moderate temperatures. Moderate temperatures refers to temperatures between 0° C. and 50° C. In some embodiments, the transferring occurs at a temperature between about 10° C. and about 40° C. In some embodiments, the linear gold anion is transferred from the surface into the solution at a temperature between about 15° C. and about 35° C., between about 20° C. and about 30° C., or between about 23° C. and about 27° C.
Another aspect of the technology is to provide a method for selective gold stripping from a surface. The method comprises contacting a composition comprising a surface-bound, linear gold anion and an anionic contaminant with a solution comprising a molecular receptor under conditions sufficient for selectively transferring the linear gold anion from the surface into the solution. “Selectively transferring the linear gold anion” refers to a selectivity for the linear gold anion over the contaminant of 10:1 or more. In some embodiments, the selectivity for the linear gold anion is greater than 15:1, 20:1, 25:1, or 30:1. Thus the methods disclosed herein allow for the recovery of gold where contaminants may be present in the source of gold or that result in the course of the processing or recovery of gold.
The contaminant may be a linear metal anion. In some embodiments, the contaminant and the linear gold anion differ by the substitution of the gold atom with another metal. Accordingly, the linear gold anion and contaminant may comprise the same ligands surrounding a central metal atom with substantially the same orientation. In some embodiments, the linear gold anion is Au(CN)2− and the contaminant is Ag(CN)2−.
In some embodiments, the contaminant is bound to the surface of activated carbon. In some embodiments, the contaminant is bound to the same surface on which the linear gold anion is bound. In some embodiments, the contaminant is bound to a different surface than which the linear gold anion is bound.
In some embodiments, the method further comprises recovering gold from the solution. In some embodiments, the gold is recovered electrolytically. Electrolytic processes of recovering gold from solution have been described, e.g., in Nehl et al. “Selective electrowinning of silver and gold from cyanide process solutions.” United States: N. p., 1993.
Electrowinning, also called electroextraction, is the electrodeposition of metals that have been put in solution. Electrowinning uses electroplating purification of metals. In electrowinning, an electrical current is passed from an inert anode (oxidation) through a solution containing the dissolved metal ions so that the metal is recovered as it is deposited in an electroplating process onto the cathode (reduction). The metal ions migrate through the electrolyte towards the cathode where the pure metal is deposited.
Another aspect of the technology is to provide an electrolytic system. The electrolytic system comprises an electrode and an electrolyte comprising a molecular receptor and a linear gold anion. The electrode and potential applied to the electrode should be selected to allow for the deposition of the gold from solution. In some embodiment, the electrolyte comprises the compositions as described herein.
The above aspects of the technology are illustrated in detail in the following exemplary embodiments of the invention, which finds applications in gold stripping processes that can be conducted at room temperature and in the absence of harsh or toxic chemicals. In order to achieve room temperature stripping of gold, a molecular receptor is utilized for Au(CN)2− in aqueous solution to facilitate (
Single crystals of a 1:1 adduct were obtained by slow evaporation of an aqueous solution containing a mixture of α-CD and KAu(CN)2. We note that α-CD (100 mM) requires heat for it to dissolve in H2O. In the presence of KAu(CN)2, α-CD dissolves instantly, suggesting that complexation is occuring. The solid-state superstructure of the 1:1 adduct between α-CD and Au(CN)2− is illustrated in
aThese short distances suggest that the supramolecular complexes are sustained by multiple [CH•••π] and [CH•••Anion] interactions.
bThe number of protons from the glucose subunits involve in short contacts with Au(CN)2
Single crystals of a 2:1 adduct were also obtained (
The association between α-CD and KAu(CN)2 in D2O was investigated by 1H NMR titrations. Inner protons H-3 and H-5 (
In order to shed more light on the driving force for the 1:1 adduct formation between Au(CN)2− and α-CD in water, isothermal titration calorimetry (ITC) was performed at 25° C. A stock aqueous solution of α-CD in a syringe was titrated into an aqueous solution of KAu(CN)2 (0.5 mM) placed in a titration cell. The molecular recognition between α-CD and Au(CN)2− is accompanied (
The binding affinity (Ka=1.4×103 M−1) between Ag(CN)2− (
The decrease in binding affinity of α-CD for Ag(CN)2− in H2O is the result of a larger entropic penalty associated with a TΔS value of −3.7 kcal mol−1, which can be attributable to the difference in hydration states of the Au(CN)2− and Ag(CN)2− ions in water. This result suggests that the binding of Au(CN)2− in water is most likely aided and abetted by hydrophobic effects97-99 that provide a favorable binding enthalpy by (i) releasing high-energy water from inside the α-CDs (ii) while reducing the entropic penalty resulting from the transfer of surface-bound water from the CDs and Au(CN)2− anions into the bulk solution.
The high affinity of α-CD for Au(CN)2− anions in H2O can be applied as a stripping agent to remove Au from the surface of activated carbon at room temperature. The Au-stripping experiments were performed at room temperature. An aqueous solution (5 mL) of α-CD at a range of concentrations (1-10% w/v) was mixed with Au-loaded carbon (50 mg, containing 0.6 mg Au) and the suspension was stirred for 30 min, after which time the carbon was isolated by filtration. The concentration of Au in the filtrate was determined by inductively coupled plasma mass spectrometry. The concentration of the stripped Au increases (
Ag stripping using the same protocol was also tested. Compared with Au, the recovery (
The Examples demonstrate that molecular recognition of Au(CN)2− by α-cyclodextrin in aqueous solution with a binding affinity in the order of 104 M−1. The binding is driven by a favorable enthalpy against a small entropic penalty. The 1:1 and 2:1 adducts, respectively, between α-cyclodextrin and KAu(CN)2 are sustained by multiple [C—H . . . π] and [C—H . . . Anion] interactions in addition to hydrophobic effects. The Examples also demonstrate that the molecular recognition between α-cyclodextrin and Au(CN)2− can be applied to strip gold from the surface of activated carbon at room temperature. We also show that α-cyclodextrin can strip selectively Au(CN)2− in the presence of Ag(CN)2−, a process that is difficult to achieve using the current carbon-in-pulp process. These findings allow for integration into commercial gold-mining protocols and lead to significantly reduced costs, energy consumption, and environmental impact.
Unless otherwise specified or indicated by context, the terms “a”, “an”, and “the” mean “one or more.” For example, “a molecule” should be interpreted to mean “one or more molecules.”
As used herein, “about”, “approximately,” “substantially,” and “significantly” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, “about” and “approximately” will mean plus or minus ≤10% of the particular term and “substantially” and “significantly” will mean plus or minus >10% of the particular term.
As used herein, the terms “include” and “including” have the same meaning as the terms “comprise” and “comprising.” The terms “comprise” and “comprising” should be interpreted as being “open” transitional terms that permit the inclusion of additional components further to those components recited in the claims. The terms “consist” and “consisting of” should be interpreted as being “closed” transitional terms that do not permit the inclusion additional components other than the components recited in the claims. The term “consisting essentially of” should be interpreted to be partially closed and allowing the inclusion only of additional components that do not fundamentally alter the nature of the claimed subject matter.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
Preferred aspects of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred aspects may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect a person having ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
The invention solves the commercial problems faced by today's gold-mining protocol, which requires the use of harsh conditions, including high temperature, high-pressure operation, and the use of toxic, corrosive and environmentally objectable chemicals, namely, NaCN and NaOH.
Molecular recognition of the Au(CN)2− anion, a crucial intermediate in today's gold mining industry, by α-cyclodextrin is demonstrated. Three X-ray single-crystal superstructures, KAu(CN)2⊂α-cyclodextrin, KAu(CN)2⊂(α-cyclodextrin)2 and KAg(CN)2⊂(α-cyclodextrin)2, demonstrate that the binding cavity of α-cyclodextrin is a good fit for metal-coordination complexes, such as Au(CN)2− and Ag(CN)2− with linear geometries, while the K+ ions fulfil the role of linking α-cyclodextrin tori together as a result of [K+ . . . O] ion-dipole interactions. A 1:1 binding stoichiometry between Au(CN)2− and α-cyclodextrin in aqueous solution, revealed by 1H NMR titrations, has produced binding constants in the order of 104 M−1. Isothermal calorimetry titrations indicate that this molecular recognition is driven by a favorable enthalpy change overcoming a small entropic penalty. The adduct formation of KAu(CN)2⊂α-cyclodextrin in aqueous solution is sustained by multiple [C—H . . . π] and [C—H . . . Anion] interactions in addition to hydrophobic effects. The molecular recognition has also been investigated by DFT calculations, which suggest that the 2:1 binding stoichiometry between α-cyclodextrin and Au(CN)2− is favored in the presence of ethanol. This molecular recognition process between α-cyclodextrin and KAu(CN)2 can be applied to the stripping of gold from the surface of activated carbon at room temperature. Moreover, this stripping process is selective for Au(CN)2− in the presence of Ag(CN)2−, which has a lower binding affinity toward α-cyclodextrin. This molecular recognition process allows for integration into commercial gold-mining protocols and lead to significantly reduced costs, energy consumption, and environmental impact.
(d) Solvent Treatment Details: The solvent masking procedure implemented in Olex2 was used to remove the electronic contribution of solvent molecules from the refinement. As the exact solvent content is unknown, only the atoms used in the refinement model are reported in the formula here. Total solvent-accessible volume/cell=889.1 Å3 [5.3%] Total electron count/cell=175.9.
Under the same conditions, we obtained the X-ray crystal superstructure of a 2:1 adduct between α-CD and KAg(CN)2. It is worth noting that KAg(CN)2 is a byproduct in the cyanide-based, gold-mining process. The adduct has an identical superstructure with the 2:1 adduct between α-CD and KAu(CN)2. The two crystal superstructures are isostructural, suggesting the high similarity in superstructures and properties between these two 2:1 adducts.
Independent Gradient Model (IGM) analysis is an approachS5 based on promolecular density (an electron density model prior to molecule formation) to identify and isolate intermolecular interactions. Strong polar attractions and van der Waals contacts are visualized as an iso-surface with blue and green color, respectively. Single crystal superstructures were used as input files. The binding surface was calculated by Multiwfn 3.6 programS6 through function 20 (visual study of weak interaction) and visualized by Chimera software.S7
The xyz coordinates for the single-point calculations were extracted from the X-ray single crystal data. All optimizations and single-point calculations were performed with density functional theory (DFT) in the Orca programS8 (version 4.1.2) using the Coulomb attenuated method (range-corrected) and hybrid Becke three-parameter Lee-Yang-ParrS9 (CAM-B3LYP) functional, the Ahlrich's double zeta basis set with a polarization functionS10 Def2-SVP, and Grimme's third-generation dispersion with Beck Johnson damping (D3BJ). In order to speed up the DFT optimizations, the Coulomb integral and numerical chain-of-sphere integration for the HF exchangesS11,S12 (RIJCOSX) method was applied with the Def2/J auxiliary basissS13 (AuxJ). The optimizations in a water continuum were performed with the Conductor like Polarizable Continuum ModelS14 (CPCM) in Orca.
The binding analysis of [α-CD . . . α-CD] interaction is illustrated below. The excess of free water molecules around the cyclodextrins and not bound to K+ ions were removed. Only one potassium ion (labeled K1+) was selected to reduce computational cost.
1H NMR Titration experiments in D2O were performed at 25° C. Aliquots from a stock solution containing the appropriate KAu(CN)2 were added sequentially to an NMR tube containing the cyclodextrins, and a 1H NMR spectrum was acquired after each addition. The titration isotherms were fitted to either 1:1 or 1:2 receptor-substrate binding model using Thordarson's equationsS15 at http://app.supramolecular.org/bindfit/. All the titrations were independently duplicated (shown below is one set of titration isotherms) and all isotherm fittings were used to calculate the average Ka with standard errors.
The titrations for β- and γ-CD using Au(CN)2− reveal (
2:1 Binding models were used for the data fitting, resulting in Ka values in the order of 102 and 101 M−1 for β- and γ-CD, respectively, matching the results obtained from 1H NMR titration experiments. The binding affinities of KAu(CN)2 with β- and γ-CD are much weaker and fit poorly to isotherms employing (
Isothermal titration calorimetry (ITC) was performed by TA Nano Isothermal Titration calorimeter at 25° C. A Hastelloy cell was used with an active cell volume of 190 μL. The stirring speed was set at 75 rpm. Receptor and substrate solutions were prepared in Milli-Q water and allowed to equilibrate overnight if necessary. In each titration experiment, 20-25 injections were performed with gradually decreased titration peaks until saturation is reached, at which point only heat of dilution was measured. The heat of dilution, when using γ-CD, was directly measured by titrating KAu(CN)2 into a blank solution. After subtracting the heat of dilution, the resulting data were analyzed with NanoAnalyze software using either a 1:1 or a 1:2 receptor-substrate binding model and plotted by Origin Lab 8.6 software. All the titrations were independently duplicated. Shown below is one set of titration isotherms. All isotherm fittings were used to calculate the average Ka and ΔH with relevant standard errors.
Activated carbon (10 g) was added to an aqueous solution (50 mL) of KAu(CN)2 (150 mg, Au concentration: 2041 ppm), and the suspension was stirred at room temperature for 3 days. The activated carbon was filtrated and dried over the oven at 110° C. overnight. The remaining gold in the filtrate was analyzed by ICP, which revealed that the concentration of gold is less than 3 ppm, suggesting quantitative adsorption of Au on activated carbon. The activated carbon had a weight loss of 15% after drying under the same conditions, indicating 102 mg Au was adsorbed on 8.5 g activated carbon. The gold loading on activated carbon was thus calculated to be 12 mg/g.
Activated carbon (10 g) was added to an aqueous solution (50 mL) of KAg(CN)2 (150 mg, Ag concentration: 1613 ppm), and the suspension was stirred at room temperature for 3 days. The activated carbon was filtrated and dried in an oven at 110° C. overnight. The remaining gold in the filtrate was analyzed by ICP, which revealed that the concentration of gold is less than 3 ppm, suggesting quantitative adsorption of Ag on activated carbon. The activated carbon had a weight loss of 15% after drying under the same conditions, indicating 88 mg Ag was adsorbed on 8.5 g activated carbon. The silver loading on activated carbon was estimated to be 10 mg/g.
Activated carbon (10 g) was added to an aqueous solution (50 mL) of KAu(CN)2 (150 mg, Au concentration: 2041 ppm) and KAg(CN)2 (150 mg, Ag concentration: 1613 ppm), and the suspension was stirred at room temperature for three days. The activated carbon was filtrated and dried in an oven at 110° C. overnight. The remaining gold and silver in the filtrate were analyzed by ICP, which revealed that the concentrations of gold and silver are less than 3 ppm, suggesting quantitative adsorption of Au and Ag on activated carbon. The activated carbon had a weight loss of 15% after drying under the same conditions, indicating 102 mg Au and 88 mg Ag were adsorbed on 8.5 g activated carbon. The gold and silver loading on activated carbon was estimated to be 12 and 10 mg/g, respectively.
Metal loaded activated carbon (50 mg, containing either 0.6 mg Au or 0.5 mg Ag) was added to an aqueous solution (5 mL) of α-CD (0-10 w/v %, heat is applied to dissolve α-CD when its concentration is >2% w/v %). The suspension was stirred for 30 min at room temperature, after which the activated carbon was separated by centrifuge. The supernatant was filtrated by a 0.45 μm syringe filter, and the concentration of Au and Ag was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Each experiment was duplicated independently, and the average concentrations were presented with standard deviations. The same protocols were performed for gold stripping using γ-CD and selective gold string from the activated carbon loaded with both gold and silver.
Quantification of gold (Au) and silver (Ag) was accomplished using ICP-MS of acidified samples. Specifically, samples (100 μL) designated for Au analysis were digested in concentrated HNO3 (200 uL, 69%, Thermo Fisher Scientific, Waltham, MA, USA) and concentrated HCl (200 uL, 34%, Thermo Fisher Scientific, Waltham, MA, USA) at room temperature for 10 min in a ventilated hood. Cyanide test strips were used to ensure that no cyanide gas was evolving after this time, and ultra-pure H2O (18.2 MΩ·cm) was added to produce a final solution of 2.0% HNO3 and 2.0% HCl (v/v) in a total sample volume of 10 mL. A quantitative standard was made using a 100 μg/mL Au elemental standard (Inorganic Ventures, Christiansburg, VA, USA), which was used to create a 100 ng/g Au standard in 2.0% HNO3 and 2.0% HCl (v/v) in a total sample volume of 50 mL. A solution of 2.0% HNO3 and 2.0% HCl (v/v) was used as the calibration blank.
Samples designated for Ag analysis were digested in 200 uL concentrated trace nitric acid (>69%, Thermo Fisher Scientific, Waltham, MA, USA) at room temperature for 10 min in a ventilated hood. Cyanide test strips were used to ensure that no cyanide gas was evolving after this time, and ultra-pure H2O (18.2 MΩ·cm) was added to produce a final solution of 2.0% HNO3 in a total sample volume of 10 mL. A quantitative standard was made using a 100 μg/mL Ag elemental standard (Inorganic Ventures, Christiansburg, VA, USA), which was used to create a 100 ng/g Ag standard in 2.0% nitric acid in a total sample volume of 50 mL. A solution of 2.0% nitric acid was used as the calibration blank.
ICP-MS was performed on a computer-controlled (QTEGRA software) Thermo iCapQ ICP-MS (Thermo Fisher Scientific, Waltham, MA, USA) operating in STD mode and equipped with an ESI SC-2DX PrepFAST autosampler (Omaha, NE, USA). The internal standard was added inline using the prepFAST system and consisted of 1 ng/ml of a mixed element solution containing Bi, In, 6Li, Sc, Tb, Y (IV-ICPMS-71D from Inorganic Ventures). Online dilution was also carried out by the prepFAST system and used to generate a calibration curve consisting of 100, 50, 10, 2 and 1 ppb Au or Ag. Each sample was acquired using 1 survey run (10 sweeps) and 3 main (peak jumping) runs (40 sweeps). The isotopes selected for analysis were 107,109Ag or 197Au and 89Y, 115In, 159Tb, 209Bi (chosen as internal standards for data interpolation and machine stability). Instrument performance is optimized daily through autotuning, followed by verification via a performance report (passing manufacturer specifications).
Commercially available solvents and chemicals were purchased from Sigma-Aldrich and Fisher Scientific and used without further purification unless otherwise stated. Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AVANCE III 600 MHz spectrometer. Chemical shifts are reported in ppm relative to the signals corresponding to the residual non-deuterated solvents. Single crystal data were obtained on a XtaLAB Synergy, Single source at offset/far, HyPix diffractometer. ICP-MS was performed on a computer-controlled (QTEGRA software) Thermo iCapQ ICP-MS (Thermo Fisher Scientific, Waltham, MA, USA) operating in STD mode and equipped with an ESI SC-2DX PrepFAST autosampler (Omaha, NE, USA). Detailed experimental procedures are provided in the appropriate sections that follow this one. Activated carbon (Part number: 05105, Lot code: 1136095) were purchased from Fluka with the following specifications (Table 11):
<1%
This application represents the National Stage entry of PCT/US2021/073050 filed on Dec. 21, 2021, which claims benefit of priority to U.S. Provisional Application Ser. No. 63/128,459, filed Dec. 21, 2020, the contents of each are incorporated by reference in their entireties.
This invention was made with government support under Grant No. ER18-1026 awarded by the Department of Defense. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/073050 | 12/21/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63128459 | Dec 2020 | US |
