"method for co2 sequestration in soils"

Abstract

The present invention relates to a method for C02 sequestration in soils using biocementation and sealing the soil with bentonite slurry. The method comprises the steps of adding biological agents (A) to the soil, adding a feed solution (B) to the soil, sealing the soil by adding a bentonite slurry (0), which can be phased or simultaneous, followed by mechanical mixing (D) and injection of CO2 (E).

Description

[0001] DESCRIPTION

[0002] "METHOD FOR CO2SEQUESTRATION IN SOILS"

[0003] FIELD OF INVENTION

[0004] The present invention relates to a method for CO2 sequestration in soils .

[0005] BACKGROUND TO THE INVENTION

[0006] CO2 sequestration is a process whose main obj ective is to prevent circulating CO2 from being released into the atmosphere , by requiring CO2 to be isolated and then permanently stored . Soil sequestration of CO2 is a way of capturing excess CO2 in the atmosphere and storing it . This can happen naturally, for example through photosynthesis , or arti ficially, for example by using mechanical collectors to take it to reservoirs for storage .

[0007] CO2 sequestration can make use of reservoirs created in impermeable rocks (marls , claystone , natural salt , etc . ) , where the CO2 is inj ected under high pressure in a liquid phase . For example , CA2660225C describes rock reservoirs where the inj ection is carried out together with a fluid or polymer to seal any discontinuities that naturally exist in the rocks , which are naturally impermeable . The method of the present invention for sequestering CO2 is an alternative to the aforementioned use of reservoirs created in impermeable rock .

[0008] WQ2011050385 (Al ) relates to a method of sequestering CO2 in saline formations , which are very impermeable , and the CO2 dissolved in water will react with the constituent

[0009] 1

[0010] SUBSTITUTE SHEET (RULE 26) salt of the formations into which it is inj ected . In the method of the present invention, the CO2 does not react with any salt present in the soil ; only acid-base reactions are involved .

[0011] US2021187437 (Al ) describes a system and method for sequestering CO2 using hydraulic binders ( cement and lime ) . In the case of lime , the sequestration of CO2 is fundamental to its curing over time . The process described in this document is a chemical process and is therefore not related to the application of biological agents or the hydrolysis of urea using the urease enzyme .

[0012] Meanwhile , US2019187386 (Al ) refers to a system and method in which CO2 is sequestered through chemical reactions with the calcium cation found in l ime , for example , which is released during its hydration . These reactions are acid-base reactions and depend on the dissolution of CO2 , brought about by changes in the pH of the water . These reactions are what happens in the biocementation process , too , but in this case the pH changes are achieved at the expense of the hydration of the urea triggered by the bacteria, which create a favourable environment for the sequestration of CO2 from the atmosphere , and with the addition of calcium to the feed solution .

[0013] Biocementation is a biological process for the production of calcium carbonate ( CaCOs ) by micro-organisms present in the environment , with calcium carbonate being precipitated in the presence of urea and a calcium source . The most common is the use of ureolytic bacteria, which by hydrolysing urea are able to precipitate calcium carbonate in the presence of a calcium source .

[0014] Biocementation is known for its application in various situations , such as : repairing cracks in concrete structures ; preventing steel corrosion; consolidating porous

[0015] 2

[0016] SUBSTITUTE SHEET (RULE 26) stones ; repairing cracks in rock and natural stone ; repairing the surface of structural stones ; preserving monuments ; improving soils ; and others .

[0017] Bentonite slurry is a fluid composed basically of water and bentonite , which is a natural clay containing a high percentage of montmorillonite . It is a hydrated aluminium silicate and its crystalline structure can contain atoms of magnesium, calcium, iron, and sodium . The structure of bentonite allows it to absorb large quantities of water within its structure and on its external surface , which gives it great swelling capacity . It is used in the construction industry in the form of slurry, for example in foundations , due to its thixotropic characteristics .

[0018] In the speci fic case of biocementation treatment of coarse sands with uni form granulometry it is already known that adding small amounts of bentonite slurry is beneficial because it facilitates bacterial fixation . This results in some filling of the voids , which proves that bentonite does not prevent biocementation . However, the purposed of this treatment is not to prevent gas migration in the soil , nor is it intended to sequester CO2 , which is what the present invention proposes .

[0019] The treatment of soils with mixtures of cement and bentonite is also common practice in some applications , for example in the construction of underground waterproofing curtains ; in this case , however, the only aim is to have a material that has some plasticity and ensures sealing after the cement has hardened . No bacteria are used, nor is there any concern about sequestering CO2 .

[0020] W02009098070A1 describes a process for sequestering CO2 in geological reservoirs using carbogenic bacteria that consume CO2 . In the present invention, the bacteria to be used are ureolytic, i . e . they have an enzyme that promotes

[0021] 3

[0022] SUBSTITUTE SHEET (RULE 26) the hydrolysis of urea. These bacteria do not consume CO2, making them different from carbogenic bacteria that do consume it, the latter being rare and pathogenic.

[0023] Therefore, considering the above, there is a technical need for a method that optimises the sequestration of CO2 in soils and that allows the gas to remain in contact with the bacteria long enough for the reactions to take place, thus preventing the gas from migrating into the atmosphere.

[0024] BRIEF DESCRIPTION OF THE DESIGNS

[0025] The following is a detailed description of the invention with reference to the attached drawings:

[0026] Figure 1 shows how the method of the present invention is implemented, with the injection of CO2 (E) being carried out after the addition of biological agents (A) to the soil, the feed solution (B) and the bentonite slurry (0) , which can be phased or simultaneous, followed by mechanical mixing (D) . The injection of the CO2 (E) can be carried out after or at the same time as the mechanical mixing of the bentonite slurry (C) and feed solution (B) into the soil.

[0027] Figure 2 shows a way of implementing the method where CO2 is also injected into the soil, after the biological agents (A) have been added to the soil, followed by the addition of the feed solution (B) and bentonite slurry (C) . The CO2 (D) can be injected after or at the same time as the bentonite slurry (C) or the feed solution (B) is added to the soil.

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[0029] SUBSTITUTE SHEET (RULE 26) SUMMARY OF THE INVENTION

[0030] The present invention relates to a method for sequestering CO2 in soils that comprises the following steps :

[0031] - adding biological agents to the soil ;

[0032] - adding the feed solution to the soil ;

[0033] - adding bentonite slurry to the soil ;

[0034] - inj ecting CO2 into the soil .

[0035] In one form of implementation, these biological agents include or enzymes responsible for biocementation .

[0036] In another form of implementation, these bacteria comprise non-pathogenic ureolytic bacteria .

[0037] In one aspect of the present invention, this enzyme is urease .

[0038] In one form of implementation of the present invention, said food solution comprises urea and a source of calcium .

[0039] In one aspect of the present invention, the calcium source is CaC12 and similar sources .

[0040] In one form of implementation, the feed solution is added to the soil at the same time as or after the addition of the biological agents .

[0041] 5

[0042] SUBSTITUTE SHEET (RULE 26) In another form of implementation, the feed solution is added to the soil at the same time as or before the bentonite slurry is added .

[0043] In one form of implementation of the present invention, the inj ection of CO2 is carried out at the same time as or after the addition of the bentonite slurry .

[0044] In another form of implementation of the present invention, the CO2 is inj ected into the soil together with the feed solution and after the inj ection of the biological agents .

[0045] In one form of implementation, the biological agents , the feed solution, the bentonite slurry and the inj ection of CO2 are added using inj ectors installed in the soil .

[0046] In one form of implementation, the method of the present invention is carried out continuously with multiple inj ections of the biological agents and food solution and bentonite slurry .

[0047] DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention relates to a method for sequestering CO2 in soils using biocementation and sealing the soil with bentonite slurry, which comprises the following steps :

[0049] - adding biological agents to the soil ;

[0050] - adding the feed solution to the soil ;

[0051] - adding bentonite slurry to the soil ; and

[0052] 6

[0053] SUBSTITUTE SHEET (RULE 26) inj ecting CO2 into the soil .

[0054] For biocementation to take place , biological agents must be present in the soil , which will precipitate calcium carbonate in the presence of CO2 . Biological agents include the enzyme urease or non-pathogenic ureolytic bacteria, for example bacteria such as S . Pasteuriiror urease enzyme such as that extracted from Canavalia ensiformi s .

[0055] Non-pathogenic ureolytic bacteria may already be naturally present in the soil or they may be added, for example by inj ection or prior mechanical mixing, and before the steps of inj ecting the CO2 , adding the feed solution and adding the bentonite slurry . Furthermore , the enzymes must always be added to the soil , also before the inj ection of the CO2 , the addition of the feed solution, and the addition of the bentonite slurry .

[0056] During the biocementation process , calcium carbonate ( CaCOs ) is precipitated in the presence of urea and a calcium source by the aforementioned bacteria or enzymes . The carbonate ion ( CO32- ) derives from the hydrolysis of urea by bacteria or enzymes ( see eq . 1 below) . The hydrolysis process involves acid-base reactions that convert carbonic acid (H2CO3 ) into the carbonate ion ( see eq . 2 below) . CO2 dissolved in water will also contribute to the formation of the carbonate ion since it forms carbonic acid when dissolved in water ( see eqs . 2 and 3 below) . This process must be controlled by the pH of the medium, which should be between 7 and 14 (preferably equal to 9 ) .

[0057] 7

[0058] SUBSTITUTE SHEET (RULE 26) In the method of the present invention, the urea and the calcium source are supplied to the soil in the form of a feed solution for the bacteria or enzymes , which contains at least urea and a calcium source with concentrations of about 0 . 5M each . This feed solution is added to the soil after the bacteria or enzymes have been added to the soil , and can also be added together with the inj ection of CO2 . The calcium source is preferably CaC12 , but it can be any other similar calcium source .

[0059] As mentioned above , the bentonite slurry consists o f a fluid made up essentially of water and bentonite , which is a natural clay . In this invention, the low air permeability characteristic of bentonite will allow CO2 to be trapped in the soil more ef fectively, since clay soils are not very permeable to air, and so with the method of the present invention it is possible to keep the gas in contact with the bacteria long enough for the reactions to take place , and therefore prevent the CO2 migrating back into the atmosphere .

[0060] Thus , the bentonite slurry is added to seal the soil , i . e . to reduce air permeability and thus retain the sequestered CO2 until it dissolves .

[0061] An important aspect of the method of the present invention is the composition of the bentonite slurry, since it will have to be adj usted to the soil in order to prevent gas migration and continue to allow biocementation to take place . Thus , the composition of the bentonite , which makes up the bentonite slurry, is defined according to the type of soil . For example , for sands with uni form granulometry, the percentage of bentonite ( in relation to the weight of dry soil ) will be higher than when the soil has some percentage of clay . The percentage of bentonite to be adopted must also be limited to ensure that it does not interfere with biological activity . Based on these two constraints , bentonite percentages by weight will be between 1 and 5% , but higher percentages are possible i f the soils are very coarse ( e . g . gravels ) . The bentonite is added to the soil in

[0062] 8

[0063] SUBSTITUTE SHEET (RULE 26) a mixture with plenty of water (water : bentonite ratio ranges, by weight, between 1:2 and 1:20) to form a fluid slurry, the bentonite slurry, to mix more easily with the soil. The bentonite slurry thus obtained can be added at the same time as the bacteria or enzyme feed solution, or it can be added together with the injection of CO2.

[0064] Thus, the method of the present invention relates to CO2 sequestration in soils mixed with bentonite slurry and a biological agent (ureolytic bacteria or urease enzyme) , during the biocementation process. This requires exposing the soil to CO2, which can be done by injecting CO2 as a gas.

[0065] The method of the present invention begins with the addition of the biological agents to the soil (the urease enzyme or non-pathogenic ureolytic bacteria) , which is carried out before the addition of the feed solution in order to maximise its fixation. The feed solution and bentonite slurry are then added in no particular order, or the feed solution and bentonite slurry are added simultaneously. Finally, the soil is exposed to CO2, using the injection of CO2 in gas form.

[0066] In one form of implementation, the CO2 is injected along with the addition of the bentonite slurry and after the soil has been previously treated by biocementation, i.e. after the biological agents and the feed solution have been added (FIG. 2) .

[0067] In another form of implementation, CO2 is injected together with the feed solution, but after the biological agents and bentonite slurry have been injected (FIG. 2) .

[0068] In yet another way of implementing the method of the present invention, the CO2 is injected after the biological agents have been added to the soil and after the feed

[0069] 9

[0070] SUBSTITUTE SHEET (RULE 26) solution and bentonite slurry have been added, which can be done in stages or simultaneously, followed by mechanical mixing (FIG. 1) . The injection of CO2 can be carried out after or at the same time as the bentonite slurry and feed solution are mechanically mixed into the soil (FIG. 1) .

[0071] The biological agents, feed solution, bentonite slurry and CO2 can be added using injectors installed in the soil. The same injectors can be used for the bacteria, feed solution, bentonite slurry and CO2, as long as it is easy to change the reservoirs that feed them. These injectors can be permanently installed in the ground at the desired depth. Ideally, the injection will be carried out up to a depth of 5 metres to ensure that there is some trapped air for the bacteria to survive.

[0072] The liquids are injected at relatively low pressure (maximum 10-20 bar) to ensure the survival of the biological agents. If the soil has a significant percentage of silt or clay, there must be mechanical mixing. When the injection of CO2 is separate from the injection of the fluid with the biological agents, it must be carried out at low pressure so as not to break the soil structure that was achieved with the previous injection, with fluid with the biological agents, (maximum 5 bar) . The pressure must be reduced to below 1 bar if it is being done continuously in the soil. Whether through one-off or continuous injections, this pressure must be adjusted to prevent any leakage of this gas into the atmosphere.

[0073] The method of the present invention can be implemented for continuous operation in order to sequester the CO2 as it is produced. In this case, multiple injections of the biological agents and feed solution, as well as the bentonite slurry, are envisaged.

[0074] 10

[0075] SUBSTITUTE SHEET (RULE 26) I f the biological agent used is the urease enzyme , for example urease extracted from beans ( Canavalia ensiformi s) , this has to be inj ected according to the amount of feed solution, with the typical enzyme dosage being 15 mg / mL for equal concentrations of urea and calcium ion ( 0 . 5 M of each) .

[0076] On the other hand, i f bacteria are used as the biological agent instead of the urease enzyme , the frequency of biological agent inj ections decreases signi ficantly, since the bacteria are alive and are continuously producing enzymes . In this case , a one-of f inj ection of feed solution is required, for example about once a week . In the case of enzymes , the inj ection of feed solution is about once every three days .

[0077] In the case of multiple inj ections of bentonite slurry, these must be accompanied by monitoring of the biological activity to ensure that it is not excessive .

[0078] The method of the present invention can be implemented with producers of CO2 in non-industrial quantities , for example in urban areas . It can also be used in addition to biocementation as a soil treatment in surface layers , for example to prevent gully formation and surface erosion on slopes , by first sequestering CO2 .

[0079] In the version where CO2 is inj ected into the ground, the implementation of the method requires equipment to collect this gas . For example , near tunnels or underground car parks , or any other infrastructure where air pollution is controlled and where a gas collection system can be installed .

[0080] Another example of the application of the method of the present invention is to use it in addition to airtightness systems , to make a kind of stopper which in this case

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[0082] SUBSTITUTE SHEET (RULE 26) decarbonises the trapped air. This stopper can be materialised in the form of a tablet or plaster, and can be changed on a regular basis.

[0083] In the context of this description, the term "bentonite" should be understood as referring to sodium, calcium and / or magnesium bentonite.

[0084] The term "biological agent" should be understood as any urease enzyme or non-pathogenic ureolytic bacteria, which precipitate calcium carbonate in the presence of CO2.

[0085] For its part, the term "comprising" should be understood as "including, among others". As such, it should not be interpreted as "consisting only of".

[0086] It should be noted that any X value presented in the course of this description should be interpreted as an approximate value of the real X value, since such an approximation to the real value would reasonably be expected by the specialist in the technique due to experimental and / or measurement conditions that introduce deviations from the real value. So, for example, the reference to "80%" means a value of "around 80%".

[0087] Unless stated otherwise , the value ranges given in this description are intended to provide a simplified and technically acceptable way of indicating each individual value within its range. By way of example, the expression "15% to 25%" or "between 15% and 25%" means any value within this range, for example 15%; 16%; 17%; 18%; 19%; 20%; 21%; 22%; 23%; 24%; 25%; or others, for example including a decimal place.

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[0089] SUBSTITUTE SHEET (RULE 26) EXAMPLES

[0090] Example 1 - Effect of CO2 on biocementation

[0091] In this experiment, tests were carried out on sand specimens with an average particle diameter of 1.1 mm, prepared with the same void ratio of 0.78. Both were treated by biocementation, with the addition of 15 mg / mL of urease enzyme extracted from Canavalia ensiformis from Sigma- Aldrich, dissolved in distilled water, to which a feed solution containing 0.5 M urea and 0.5 M calcium chloride was added.

[0092] Two different cases were analysed, with three samples for each case:

[0093] (1) sand with bentonite (5% dry mass of sand) , with the addition of only urease enzyme and feed solution;

[0094] (2) sand with bentonite (5% dry mass of sand) , with added urease enzyme, feed solution, and carbonated water with 2.81 kg / m3of CO2.

[0095] The specimens without the carbonated water (1) served as a control for the experiment (without the injection of CO2) .

[0096] Bentonite was added to the dry sand to allow greater homogenisation, and the solution with the enzyme was added to fill half the volume of soil voids, followed by the addition of the feed solution to fill the rest of the volume of voids.

[0097] After mechanical mixing, in both cases water was added in the same quantity as the feed solution and mechanical

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[0099] SUBSTITUTE SHEET (RULE 26) mixing was carried out again, the amount of liquid in the soil being sufficient to create a slurry in the case bentonite was already present.

[0100] About 15 minutes later, distilled water was added to the test specimens (1) and carbonated water to the test specimens (2) , both in the same amounts as the feed solution.

[0101] Three days later, the percentage of calcium carbonate precipitated in the soil was measured using a leaching test with 0.5 M hydrochloric acid.

[0102] Average calcium carbonate values of 2.9% and 3.5% were obtained for the samples without and with CO2, respectively, which shows that the presence of the dissolved CO2 bubbles favoured the precipitation of calcium carbonate in the soil (biocementation) .

[0103] Example 2 - Effect of bentonite on CO sequestration in the soil

[0104] Following the methodology of the tests described in Example 1 above, tests were also carried out on specimens with :

[0105] (1) sand only, and

[0106] (2) sand and bentonite (5% weight of bentonite in relation to the weight of dry sand) .

[0107] In both tests, the amount of calcium carbonate precipitated was quantified with and without mixing with bentonite, and with and without the addition of CO2.

[0108] 14

[0109] SUBSTITUTE SHEET (RULE 26) In these tests, the urease enzyme extracted from Canavalia Ensiformis or bacteria of the S. Pasteurii species was added and the tests were carried out following the methodology described in Example 1.

[0110] In one set of test specimens no CO2 was added, while in the other, CO2 was dissolved in the water used to prepare the food solution, as described in Example 1.

[0111] The following results were obtained from these tests:

[0112] - in the tests in which bentonite was added to the sand, without the addition of CO2 and with the addition of enzyme or bacteria, the amount of calcium carbonate precipitated decreased by around 0.7% for the test carried out with the addition of enzyme, and by around 0.8% for the test carried out with the addition of bacteria;

[0113] - using enzyme or bacteria as a biological agent, when CO2 was added to the samples prepared only with sand, there was no significant difference in the precipitation of calcium carbonate; this is explained by the absence of the addition of bentonite, which is needed to contain the gas in the soil;

[0114] - adding CO2 to the sand samples mixed with bentonite increased the amount of calcium carbonate precipitated by around 0.6% for the test carried out with the addition of the enzyme, and by 1.1% for the test carried out with the addition of bacteria.

[0115] These results show that adding CO2 favours biocementation, i.e., the precipitation of calcium carbonate, as long as the gas remains in the soil due to the addition of bentonite. It can therefore be seen that CO2 increases the effect of biocementation in the presence of bentonite, i.e., when the soil is sealed, and CO2 sequestration is consequently optimised.

[0116] 15

[0117] SUBSTITUTE SHEET (RULE 26) It should be noted that although the present invention has been described with reference to its preferred forms of implementation, many modi fications and alternatives can be made by a person skilled in the technique without leaving the field of the invention, which is defined by the claims .

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[0119] SUBSTITUTE SHEET (RULE 26)

Claims

CLAIMS1. A method for CO sequestration in soils characterised as comprising the following steps:- adding biological agents to the soil;- adding the feed solution to the soil;- adding bentonite slurry to the soil;- injecting CO2 into the soil.

2. The method according to claim 1, characterised in that said biological agents comprise bacteria or enzymes responsible for biocementation.

3. The method according to claims 1 and 2, characterised in that said bacteria comprise non-pathogenic ureolytic bacteria .

4. The method according to claims 1 and 2, characterised in that the said enzyme is urease.

5. The method according to claim 1, characterised in that the said feed solution comprises urea and a calcium source.

6. The method according to claim 5, characterised in that the calcium source is CaC12 and similar sources.

7. The method according to any one of claims 1 to 6, characterised in that the addition of the feed solution to the soil is carried out at the same time as or after the addition of the biological agents.

8. The method according to any one of claims 1 to 6, characterised in that the addition of the feed solution to17SUBSTITUTE SHEET (RULE 26)the soil is carried out at the same time as or before the addition of the bentonite slurry .9 . The method according to any one of claims 1 to 6 , characterised in that the inj ection of CO2 is carried out at the same time as or after the addition of the bentonite slurry .10 . The method according to any one of claims 1 to 6 , characterised in that the inj ection of CO2 into the soil is carried out together with the feed solution and after the inj ection of the biological agents .11 . The method according to any one of claims 1 to 10 , characterised in that the addition of the biological agents , the feed solution, the bentonite slurry and the inj ection of CO2 are carried out via inj ectors installed in the ground .12 . The method according to any one of claims 1 to 11 , characterised by being continuous with multiple inj ections of the biological agents and feed solution and the bentonite slurry .18SUBSTITUTE SHEET (RULE 26)

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