Electrochemical mineralization of industrial waste to form carbonates

Abstract

Provided herein are methods for the electrochemical conversion of industrial waste and carbon dioxide to form valuable mineral carbonate products, such as limestone and dolomite. The provided methods are flexible and can be utilized with a range of industrial waste streams from mining to industrial metal processing slag. The provided methods allow for the analysis and tailoring of processes based on the input industrial waste and can be performed at near ambient temperatures and pressures and, in some cases, utilize very low concentrations of carbon dioxide including at atmospheric levels.

Description

ELECTROCHEMICAL MINERALIZATION OF INDUSTRIAL WASTE TO FORM CARBONATESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 356,296 filed on June 28, 2022, the contents of which are incorporated herein by reference in their entirety.CONTRACTUAL ORIGIN

[0002] This invention was made with government support under Contract No. DE-AC36- 08G028308 awarded by the Department of Energy. The government has certain rights in the invention.BACKGROUND

[0003] It is increasingly likely to achieve carbon neutrality and reduce the effects of climate change that some form of carbon capture will be required to offset the production of carbon dioxide and its release into the atmosphere. One proposed method is geologic sequestration; however, current methods of geologic sequestration are expensive, inefficient and provide no materials of added value. Additionally, sequestration has added risks associated with the storage of carbon dioxide, such as acidification of ground water. As a result, there has been a recent focus on capturing carbon dioxide via mineralization, where carbon dioxide is captured in the production of mineral products in carbon negative processes, which then can be used in other applications such as building materials. Unfortunately, current methods of carbon dioxide mineralization require high temperatures and pressures and long processing times making them cost prohibitive.

[0004] It can be seen from the foregoing that there remains a need in the art for carbon mineralization processes that can be performed at or near ambient temperatures and pressures to enable the economic recapture of carbon dioxide.SUMMARY

[0005] Provided herein are methods for the electrochemical conversion of industrial waste and carbon dioxide to form valuable mineral carbonate products, such as limestone and dolomite. The provided methods are flexible and can be utilized with a range of industrial waste streams from mining to industrial metal processing slag. The provided methods allow for the analysis and tailoring of processes based on the input industrial waste and can be performed at nearambient temperatures and pressures and, in some cases, utilize very low input concentrations of carbon dioxide including at atmospheric levels.

[0006] In an aspect, provided is a method comprising: a) providing an industrial waste; b) analyzing the industrial waste, thereby determining an industrial waste composition; and c) applying a voltage to the industrial waste in the presence of at least one reactant thereby generating a carbonate; wherein the step of applying a voltage is modified by a voltage, a reactant composition; a reactant concentration, or a combination thereof based on the industrial waste composition.

[0007] Analyzing the industrial waste may comprise coupled plasma-based stoichiometric characterization, X-ray diffraction, or a combination thereof. The reactant may comprise carbon dioxide and the reactant composition may be a partial pressure selected from the range of 0.0004 atm to 2 atm, 0.0004 atm to 1 atm, or 0.0004 atm to 0.5 atm. Alternatively the carbon dioxide may be present in a concentration selected from the range of 0.004% to 100%, 0.004% to 50%, or 0.004% to 25%. In some cases, the carbon dioxide may be directly captured from the atmosphere and reacted at the concentration of atmospheric abundance.

[0008] The industrial waste being processed can be from a variety of industrial sources, including for example, mine tailings, blast furnace slag, steel slag, red mud, cement kiln dust, cement waste, ultramafic waste rock, and / or ash. The industrial waste may include or be primarily composed of calcium or magnesium compounds, for example, magnesium oxide, calcium oxide, magnesium hydroxide, magnesium silicate hydrate, and / or calcium silicate hydrate.

[0009] The described method may be performed in solution, for example, in the presence of water and the step of applying a voltage also is modified by pH based on the previous analysis step. The analysis step may also identify impurities (e.g., non- calcium or magnesium compounds), and may allow for the recovery of these impurities.

[0010] The described methods may be performed at or near ambient temperatures and / or pressures. For example, the step of applying the voltage may be performed at a temperature selected from the range of 0 °C to 50 °C, 0 °C to 25°C, 10 °C to 40 °C, or at about 25 °C. The step of applying the voltage may be performed at a pressure selected from the range of 0.7 atm to 1.3 atm, 0.8 atm to 1.2 atm, 0.9 atm to 1.1 atm, or optionally, at about 1 atm.

[0011] Examples of carbonates include limestone and dolomite.BRIEF DESCRIPTION OF DRAWINGS

[0012] Some embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting.

[0013] Figure 1 provides an exemplary flow chart of the methods described herein.DETAILED DESCRIPTION

[0014] The embodiments described herein should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein. References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, “some embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0015] As used herein the term “substantially” is used to indicate that exact values are not necessarily attainable. By way of example, one of ordinary skill in the art will understand that in some chemical reactions 100% conversion of a reactant is possible, yet unlikely. Most of a reactant may be converted to a product and conversion of the reactant may asymptotically approach 100% conversion. So, although from a practical perspective 100% of the reactant is converted, from a technical perspective, a small and sometimes difficult to define amount remains. For this example of a chemical reactant, that amount may be relatively easily defined by the detection limits of the instrument used to test for it. However, in many cases, this amount may not be easily defined, hence the use of the term “substantially”. In some embodiments of the present invention, the term “substantially” is defined as approaching a specific numeric value or target to within 20%, 15%, 10%, 5%, or within 1% of the value or target. In further embodiments of the present invention, the term “substantially” is defined as approaching a specific numeric value or target to within 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1% of the value or target.

[0016] As used herein, the term “about” is used to indicate that exact values are not necessarily attainable. Therefore, the term “about” is used to indicate this uncertainty limit. In someembodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±20%, ±15%, ±10%, ±5%, or ±1% of a specific numeric value or target. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±1%, ±0.9%, ±0.8%, ±0.7%, ±0.6%, ±0.5%, ±0.4%, ±0.3%, ±0.2%, or ±0.1% of a specific numeric value or target.

[0017] As used herein, the term “about” is used to indicate that exact values are not necessarily attainable. Therefore, the term “about” is used to indicate this uncertainty limit. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±20%, ±15%, ±10%, ±5%, or ±1% of a specific numeric value or target. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±1%, ±0.9%, ±0.8%, ±0.7%, ±0.6%, ±0.5%, ±0.4%, ±0.3%, ±0.2%, or ±0.1% of a specific numeric value or target.

[0018] As used herein, the term “electrochemical” refers to applying a voltage to at least one chemical compound to trigger a chemical reaction and / or decomposition. The voltage may be applied using a battery or other electrical device.

[0019] Among other things, the present disclosure relates to an adaptive electrochemical approach to rapidly convert alkaline industrial waste into carbonates, such as dolomite. These carbonates may have various uses, including in materials such as concrete. Accelerated carbonation from aqueous solutions of alkaline precursors, in excess of equilibrium precipitation, may be achieved by utilizing an electrochemical bias. In some embodiments, the process as described herein may be adapted to a wide range of alkaline industrial waste, able to still provide the optimal pH and electrical potential for target product carbonates. In some embodiments, the processes described herein utilizing low electrochemical potentials to drive rapid precipitation of carbonates and targets evaluating the relationship between electrochemical driving force and lower necessary chemical potential of carbon dioxide such that results may be achieved with lower pressure carbon dioxide, enabling use of a broad range of direct air capture technologies.

[0020] Using traditional methods, thermal precipitation of carbonates is prohibitively slow. Precipitation of carbonates from alkaline solutions of magnesium oxide and calcium oxide at saturation levels of carbon dioxide may take long period of time at high temperatures (for example, about 100 days or more at about 100 °C or about 10 days or more at about 200 °C).

[0021] In some embodiments, the present disclosure, using electrochemical processes, may beable to increase the rate of approximately room temperature carbonate precipitation by multiple orders of magnitude compared to traditional elevated temperature thermal processes. The increased rate and absence of heating costs may at least offset the energy used by low-voltage electrical energy (for example, less than about 2 V) used in the electrochemical process.

[0022] Using traditional methods, the variability of feedstocks poses technological challenges and increases risks associated with adoption of carbonation technologies. This variability may also increase the risk facing industrial waste stewards looking to carbonate their industrial wastes, as each supply of industrial wastes may have its own unique distribution of constituents and impurities with little forewarning about whether the eccentricities capable of application to a large fraction of alkaline industrial wastes, the present disclosure may be capable of processing feedstocks with different ratios of magnesium oxide, calcium oxide, magnesium hydroxide, magnesium silicate hydrate, calcium silicate hydrate, and / or sodium oxide in addition to other impurities.

[0023] In some embodiments, the present disclosure may use chemical assays of industrial wastes to predict achievable carbonation products. The target carbonation product or products may including using electrochemical processes and / or conditions aimed at achieving that target carbonation product (based on lab-scale testing). This may allow the processes as described herein to be used for a variety of alkaline industrial wastes and / or target carbonation products.

[0024] Using traditional methods, direct air capture is relatively early stage and may constitute a high economic risk for adoption. Thermochemical precipitation of carbonates from solution may depend on driving solubility of carbonate phase downwards by increasing the dissolved carbon content. This dissolved carbon content is proportional to the partial pressure of carbon dioxide at the solution / gas interface, and capable of reaching to saturation of the carbon in the solution at an elevated pressure of carbon dioxide. Depending on the direct air capture technology, the separated carbon dioxide may often require some degree of mechanical or chemical compression to reach a pressure of approximately 1 bar.

[0025] In some embodiments, the present disclosure use electrochemistry to drive precipitation at carbon dioxide pressures of approximately atmospheric levels, allowing the present disclosure to operate without traditional direct air capture and with increased performance at varying degrees of carbon dioxide compression. Carbon dioxide may be introduced into solution by bubbling a carbon dioxide containing gas flow through the water. A concentration of dissolved carbon of approximately 0.002 molc / khmo may be achieved by bubblingapproximately 1 atm of air (approximate 400 ppm carbon dioxide) through 25 °C water, with this carbon concentration manifesting as the sum of approximately aqueous carbon dioxide, carbonic acid, bicarbonate, and carbonate. At approximately 25 °C, this dissolved carbon concentration is directly proportional to the partial pressure of carbon dioxide used. Even at approximately 400 ppm carbon dioxide metal carbonates may be capable of being precipitated. For example, calcium carbonate may be formed from shells from sea creatures. While the driving force for carbonate precipitation at these low temperatures and pressures is relatively small, leading to the approximately 10s to approximately 100s of day kinetics of purely thermochemical precipitation.

[0026] In some embodiments, there may be tradeoff or balancing between the electrical energy used to electrochemically drive precipitation and the pressure of carbon dioxide used. The solubility limits of carbonates may change as functions of carbon dioxide pressures. As the solubility limit decreases, the electrochemical driving force necessary to reach the same precipitation rate may decrease. For relatively simple carbonates, such as magnesium calcium carbonate, the solubility limit scales with approximately l / (pco22). This means that direct air capture and compression of carbon dioxide may be utilized to substantially decrease the solubility limit of carbonate phases, speeding up precipitation. This is where the tradeoff or balancing of electrochemical costs and direct air capture costs may be considered.

[0027] In some embodiments, the chemical makeup of mines tailings may be characterized and / or analyzed using inductively coupled plasma-based stoichiometric characterization and / or X-ray diffraction. These results may be used to determine the fractional content and makeup of amorphous phases in mines tailings. These results may be used to identify representative alkaline materials and ratios for electrochemical testing, and key impurities, which may be uses to test the impact of impurities on electrochemical carbonation.

[0028] In some embodiments, an electrochemical synthesis of carbonated species from alkaline feedstocks may be performed. Multiple reactors may be used to decouple bulk testing from smaller scale and more agile investigations of the impurity chemistries. A large electrochemical reactor may be utilized for producing approximately kg-scale product quantities for use in subsequent aggregate testing. Smaller reactors may be utilized to investigate the nuances of electrochemistry on solutions containing a wide range of impurities. In some embodiments, two separate reactors may be used for parallel screening of different impurities. These smaller reactors may be designed for approximately room temperature operation, may utilized low-cost carbon and metallic electrodes, and may utilize pH meters toconstantly monitor the alkalinity of the solution (which acts as the electrolyte).

[0029] In some embodiments, both magnesium and calcium feedstocks may be utilized, either alone or in combination, at ratios and phases determined by the characterization and analysis previously performed. For example, magnesium oxide, calcium oxide, magnesium hydroxide, magnesium silicate hydrate, and / or calcium silicate hydrate may be used, among other feedstocks. These feedstocks may be dissolved in water to form the solutions being tested. pH measures may be used to determine the alkalinity of the feedstock solutions, and when necessary the alkalinity will be adjusted using sodium hydroxide, which has been previously shown to be compatible with formation of magnesium calcium carbonate. Carbon may be introduced into the solution by bubbling a gas with a controlled pCCh through the solution. By modifying the pCCh between approximately 1 atm and approximately 0.0004 atm (i.e., atmospheric abundance), with testing at every order of magnitude in between, the necessity of varying degrees of carbon dioxide separation necessary for this process may be determined.

[0030] In some embodiments, an analysis on the impact of impurities may be performed, including, for example, sodium oxide and sulfurous phases on electrochemical carbonation. The smaller reactors may be used to screen whether these impurities may have a substantial impact on the electrochemical conditions for precipitation of dolomite and / or other magnesium and / or calcium carbonate phases, as well as the impact on the phases formed. The larger reactor may be used to generate bulk samples of carbonated phases for aggregate testing, initially using magnesium and / or calcium containing feedstocks, and at later stages of the product using less purse (and thus bearing a closer resemblance to application) feedstocks. Such testing may also be performed in bulk and / or on actual industrial wastes.

[0031] In some embodiments, electrochemical reactor experiments may be performed, including, for example, cyclic voltammetry. During cyclic voltammetry testing, the applied voltage (relative to a reference electrode) may be swept across a range of voltages while reading the current. Depending on the electrochemical reactions available between the solution and the electrodes, at specific voltages the electrochemical driving force may initiate a reaction, resulting in a large current spike. With this technique, the tradeoff between voltage and carbonate precipitation reaction may be investigated and the impact of increased voltages to drive secondary reactions involving impurities or alternate magnesium or calcium carbonate formation may be done. These results may inform whether impurities can be separated out of solution readily through an initial voltage spike, or whether impurities can be kept in solution while magnesium and calcium carbonates are formed.

[0032] In some embodiments, the rates and / or kinetics of precipitation and / or formation of carbonates may be investigated using fixed-voltage testing, pulsed voltage, and / or pulsed- reversed voltage testing. In fixed voltage testing the voltage is kept substantially constant, which may initially grow carbonate but may slow down over time. In pulsed voltage, a top-hat shaped voltage-over-time profile is used, cycling back to about 0 volts periodically, which may allow precipitates to fall off electrodes. In pulsed-reversed voltage testing the voltage is periodically reversed for short periods, which has the potential effect of dissolving the interface of the precipitate and electrode to cause the bulk of the precipitate to fall off the electrode.

[0033] In some embodiments, modeling may be used to predict the different carbonate products available from given feedstock compositions and carbon dioxide pressures. This may be done by generating Pourbaix diagrams tailored to the feedstock compositions of interest. These models may be used to predict the dependence of product carbonates on a variety of parameters including CO2 pressure and impurity compositions. The voltage and pH dependent phase formations predicted by these models identify trends with a high degree of confidence, but absolute voltage and pH thresholds at which the product change as well as the kinetics of these reaction will require experimental determination. These models may be verified using a set of representative set of conditions. Current modeling of a Pourbaix diagram at a fixed ratio of magnesium and calcium to carbon dioxide takes on the scale of tens of seconds, and can run for approximately 24 hours a day, meaning that the multi-variable space of feedstock compositions and operating conditions may be utilized. Solutions containing magnesium, calcium, and carbon dioxide may be analyzed. Confirmation of the results on this simple system may enable confidence in more complex systems involving the same impurities investigated experimentally. These models may be used investigate a range of impurities that approach or exceed the impurities identified in the tailings.

[0034] In some embodiments, the precipitated carbonate species may be characterized using inductively coupled plasma-based stoichiometric characterization and / or X-ray diffraction. Additional electron and / or optical microscopy may be used to determine details about particle size distributions and other morphological details.

[0035] In some embodiments, the use of carbonate as a constituent in concrete aggregates may be investigated. For example, testing may be performed on the impact of the concentration of dolomite on aggregate’s mechanical properties.

[0036] The provided discussion and examples have been presented for purposes of illustration and description. The foregoing is not intended to limit the aspects, embodiments, or configurations to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the aspects, embodiments, or configurations are grouped together in one or more embodiments, configurations, or aspects for the purpose of streamlining the disclosure. The features of the aspects, embodiments, or configurations, may be combined in alternate aspects, embodiments, or configurations other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the aspects, embodiments, or configurations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment, configuration, or aspect. While certain aspects of conventional technology have been discussed to facilitate disclosure of some embodiments of the present invention, the Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate aspect, embodiment, or configuration.

[0037] The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments, exemplary embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims. The specific embodiments provided herein are examples of useful embodiments of the present invention and it will be apparent to one skilled in the art that the present invention may be carried out using a large number of variations of the devices, device components, methods steps set forth in the present description. As will be obvious to one of skill in the art, methods and devices useful for the present methods can include a large number of optional composition and processing elements and steps.

[0038] As used herein and in the appended claims, the singular forms "a", "an", and "the" include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to "a cell" includes a plurality of such cells and equivalents thereof known to those skilled in the art. As well, the terms "a" (or "an"), "one or more" and "at least one" can be used interchangeably herein. It is also to be noted that the terms "comprising", "including", and "having" can be used interchangeably. The expression “of any of claims XX- YY” (wherein XX and YY refer to claim numbers) is intended to provide a multiple dependent claim in the alternative form, and in some embodiments is interchangeable with the expression “as in any one of claims XX- YY.”

[0039] When a group of substituents is disclosed herein, it is understood that all individual members of that group and all subgroups, are disclosed separately. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure. For example, when a device is set forth disclosing a range of materials, device components, and / or device configurations, the description is intended to include specific reference of each combination and / or variation corresponding to the disclosed range.

[0040] Every formulation or combination of components described or exemplified herein can be used to practice the invention, unless otherwise stated.

[0041] Whenever a range is given in the specification, for example, a density range, a number range, a temperature range, a time range, or a composition or concentration range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. It will be understood that any subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein.

[0042] All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art as of their publication or filing date and it is intended that this information can be employed herein, if needed, to exclude specific embodiments that are in the prior art. For example, when composition of matter is claimed, it should be understood that compounds known and available in the art prior to Applicant's invention, including compounds for which an enabling disclosureis provided in the references cited herein, are not intended to be included in the composition of matter claims herein.

[0043] As used herein, “comprising” is synonymous with "including," "containing," or "characterized by," and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, "consisting of' excludes any element, step, or ingredient not specified in the claim element. As used herein, "consisting essentially of' does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In each instance herein any of the terms "comprising", "consisting essentially of and "consisting of may be replaced with either of the other two terms. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.

[0044] All art-known functional equivalents, of any such materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A method compri sing : providing an industrial waste; analyzing the industrial waste, thereby determining an industrial waste composition; applying a voltage to the industrial waste in the presence of at least one reactant thereby generating a carbonate; and wherein the step of applying a voltage is modified by a voltage, a reactant composition; a reactant concentration, or a combination thereof based on the industrial waste composition.

2. The method of claim 1, wherein the step of analyzing the industrial waste comprises coupled plasma-based stoichiometric characterization, X-ray diffraction, or a combination thereof.

3. The method of claim 1 or 2, wherein the reactant comprises carbon dioxide.

4. The method of claim 3, wherein the reactant composition of carbon dioxide is a partial pressure selected from the range of 0.0004 atm to 2 atm.

5. The method of any of claims 2-4, wherein the carbon dioxide is captured from the atmosphere.

6. The method of any of claims 1-5, wherein the industrial waste comprises calcium or magnesium.

7. The method of claim 6, wherein the industrial waste comprises magnesium oxide, calcium oxide, magnesium hydroxide, magnesium silicate hydrate, calcium silicate hydrate or a combination thereof.

8. The method of any of claims 1-7, wherein the industrial waste comprises mine tailings, blast furnace slag, steel slag, red mud, cement kiln dust, cement waste, ultramafic waste rock, ash or a combination thereof.

9. The method of any of claims 1-8, wherein the step of applying a voltage is performed in solution.

10. The method of claim 9, wherein the solution comprises water.

11. The method of claim 10, wherein the pH of the solution is modified based on the industrial waste composition.

12. The method of any of claims 1-11, wherein the step of analyzing the industrial waste further comprises identifying impurities.

13. The method of any of claims 1-12, wherein the step of applying a voltage is performed at a temperature selected from the range of 0 °C to 50 °C.

14. The method of any of claims 1-13, wherein the step of applying a voltage is performed at a pressure of 0.8 atm to 1.2 atm.

15. The method of any of claims 1-14, wherein the carbonate is limestone.

16. The method of any of claims 1-15, wherein the carbonate is dolomite.

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