A rock softening agent and a method for determining its appropriate proportion

Abstract

The present invention discloses a rock softening agent and a method for determining its appropriate proportion. The rock softening agent includes sodium bisulfate, hydrochloric acid, a surfactant and water; the concentration ratio of sodium bisulfate to hydrochloric acid is 3:1.5 - 2.5; the concentration of the surfactant is 0.1 - 1%. The method for determining the appropriate proportion of the rock softening agent includes: measuring the initial rock sample parameters, determining the initial concentrations of sodium bisulfate and hydrochloric acid, preparing a mixed aqueous solution of sodium bisulfate, hydrochloric acid and the surfactant according to the concentration ratio, soaking the initial rock sample, measuring the softening degree after drying, and adjusting the concentrations of sodium bisulfate and hydrochloric acid until the target softening degree is achieved. The rock softening agent of the present invention neither produces a large amount of acidic waste liquid, reducing the adverse impact on the environment; nor can it avoid the problem that some mineral components are insensitive to a single chemical substance, and can achieve the softening of rocks in a shorter time, thereby improving work efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering, and particularly relates to a rock softening agent and a method for determining its suitable proportion. Background Art

[0002] The information disclosed in the background art of the present invention is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Rock softening is a method that makes rocks lose their original hardness and compressive strength to a certain extent through a series of physical or chemical processes. In the field of geotechnical engineering, softening rocks for drilling, mining, tunnel excavation, and underground construction is a common and challenging task.

[0004] The existing rock softening methods include blasting, heat treatment, high-pressure water jetting, and chemical softening, etc. Among them, chemical softening uses an acidic solution as a chemical softening agent to erode the mineral components in the rock, thereby reducing the hardness and strength of the rock. Its operation is simple and the energy consumption is low, so this method is widely used in softening rocks.

[0005] However, the currently used chemical softening agents are mostly single acid solutions, such as HCl solution, H2SO4 solution, etc. Due to the single substance and strong acid, acidic waste liquid is easily generated, thus polluting the environment; moreover, some rock minerals may be insensitive to this solution, resulting in unsatisfactory softening effects. In addition, the existing rock softening uses empirical values to determine the concentration of a single acid solution, which has blindness in operation and it is difficult to adjust the appropriate softening agent concentration according to different rock types. Therefore, a more effective and sustainable rock softening agent and a more targeted method for determining the suitable proportion of the rock softening agent are needed to meet the requirements of the geotechnical engineering field. Summary of the Invention

[0006] In view of this, the present invention provides a rock softening agent and a method for determining its suitable proportion, which solve the problems of serious pollution and low softening efficiency of the current chemical softening agent.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a rock softening agent, which includes sodium bisulfate, hydrochloric acid, a surfactant, and water; the concentration ratio of sodium bisulfate to hydrochloric acid is 3:1.5 - 2.5; the concentration of sodium bisulfate is 10 - 20%, the concentration of hydrochloric acid is 5 - 15%; the concentration of the surfactant is 0.1 - 1%.

[0009] Preferably, the surfactant is a cationic surfactant. More preferably, the cationic surfactant is an alkyl quaternary ammonium salt cationic surfactant, and further preferably cetyltrimethylammonium bromide.

[0010] In a second aspect, the present invention provides a method for determining the appropriate ratio of the above rock softening agent, comprising the following steps:

[0011] Measure the initial rock sample parameters, determine the initial concentrations of sodium bisulfate and hydrochloric acid, prepare a mixed aqueous solution of sodium bisulfate, hydrochloric acid and surfactant according to the concentration ratio, soak the initial rock sample, and measure the softening degree after drying. Adjust the concentrations of sodium bisulfate and hydrochloric acid until the target softening degree is achieved.

[0012] Furthermore, the method for determining the appropriate ratio of the rock softening agent comprises the following steps:

[0013] S1. Measure the uniaxial compressive strength, mass and mineral composition of the initial rock sample;

[0014] S2. Determine the initial concentrations of sodium bisulfate and hydrochloric acid according to the mineral composition;

[0015] S3. Prepare a mixed aqueous solution of sodium bisulfate, hydrochloric acid and surfactant with the initial concentrations;

[0016] S4. Immerse the initial rock sample in the mixed aqueous solution, dry it after soaking for a set time to obtain a posterior rock sample;

[0017] S5. Measure the uniaxial compressive strength and mass of the posterior rock sample, calculate the softening degree, and compare it with the target softening degree;

[0018] S6. When the target softening degree is not reached, increase the concentrations of sodium bisulfate and hydrochloric acid proportionally, and repeat steps S3 - S5 until the target softening degree is achieved; when the softening degree is too large, decrease the concentrations of sodium bisulfate and hydrochloric acid proportionally, and repeat steps S3 - S5 until the target softening degree is achieved.

[0019] Preferably, in step S1, the mineral composition is measured by an X-ray diffractometer (XRD).

[0020] Preferably, in step S4, the set soaking time is 10 - 20 days; preferably, the drying method is natural air drying.

[0021] Preferably, in step S5, the softening degree is the degree of reduction in uniaxial compressive strength and the degree of reduction in mass.

[0022] More preferably, the target softening degree is: the degree of reduction in uniaxial compressive strength is 25 - 30%; the degree of reduction in mass is 0.5 - 1.0%.

[0023] Preferably, in step S6, the incremental or decremental value of the sodium bisulfate concentration is 1-4%, and steps S3-S5 are repeated once for each increment or decrement.

[0024] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0025] (1) The present invention selects a strong acid HCl and a medium-strength acid salt NaHSO4 to soften the rock, which will neither produce a large amount of acidic waste liquid, reducing the adverse impact on the environment, nor avoid the problem that some mineral components are insensitive to a single chemical substance. In addition, from a safety perspective, the rock softening agent of the present invention is milder than a strong acid solution and is easier to manage and operate.

[0026] (2) A surfactant is added to the rock softening agent of the present invention. The surfactant can reduce the surface tension between the aqueous solution and the rock surface, promote better penetration of the acidic mineral into the rock interior, accelerate the softening process, and thus improve the erosion efficiency of the aqueous solution. At a suitable concentration, the rock softening agent of the present invention can achieve rock softening in a shorter time, thereby improving work efficiency. Compared with the traditional single acidic solution, from the perspective of uniaxial compressive strength, its softening effect is improved by 7%.

[0027] (3) The method for determining the ratio of the rock softening agent of the present invention can quickly determine the appropriate ratio of the rock softening agent for different rock samples, avoid the blindness of actual rock softening work, and ensure the optimal softening effect for the softening of various rocks. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 It is the XRD pattern of the mineral composition of the initial sandstone rock sample in Example 1 of the present invention (N = 4, four samples). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs.

[0031] As pointed out in the background art, existing rock softeners cause relatively large environmental pollution and have low softening efficiency. At the same time, in the actual work of rock softening, the concentration of the softener is selected based on experience, resulting in blindness in operation. Therefore, the present invention provides a rock softener and a method for determining its appropriate ratio.

[0032] In a typical embodiment of the present invention, a rock softener is provided, which includes sodium bisulfate, hydrochloric acid, a surfactant, and water; the concentration ratio of sodium bisulfate to hydrochloric acid is 3:1.5 - 2.5; the concentration of the surfactant is 0.1 - 1%.

[0033] Preferably, the concentration of sodium bisulfate in the present invention is 10 - 20%, and the concentration of hydrochloric acid is preferably 5 - 15%. The above concentration ranges are applicable to the softening of various rocks.

[0034] In addition to facilitating the penetration of the mixed aqueous solution into the interior of the rock, the surfactant also helps to reduce the viscosity of the mixed aqueous solution and improve the fluidity of the solution, so that the ions in the mixed aqueous solution are more likely to react with the mineral components. In addition, the surfactant can disperse the solid particles generated after erosion in the liquid, which is beneficial to preventing the formation of new sediments. The surfactant in the present invention is a cationic surfactant, and the cationic surfactant has a high adsorption capacity for negatively charged particles or surface layers such as carbonate minerals and silicate minerals, and can improve the interfacial affinity between the solid and the liquid. Further preferably, the cationic surfactant is an alkyl quaternary ammonium salt cationic surfactant, which has excellent wetting and emulsifying properties. In addition, the alkyl quaternary ammonium salt cationic surfactant is relatively easy to degrade in the environment and can reduce the pollution to the rock and the environment after the rock softening is completed. Further preferably, it is cetyltrimethylammonium bromide, which can form a colloid in the liquid, helping to disperse, emulsify and wet. In addition, it helps to improve the wetting performance of the liquid on the solid surface, which is beneficial to the cleaning and coating of the rock surface.

[0035] The present invention places no special restrictions on water, and the water commonly used in the art for preparing rock softeners can be used. Preferably, the present invention uses drinking tap water.

[0036] In another typical embodiment of the present invention, a method for determining the appropriate ratio of the above rock softener is provided, including the following steps:

[0037] Measure the initial rock sample parameters, determine the initial concentrations of sodium bisulfate and hydrochloric acid, prepare a mixed aqueous solution of sodium bisulfate, hydrochloric acid, and surfactant according to the concentration ratio, soak the initial rock sample, measure the softening degree after drying, and adjust the concentrations of sodium bisulfate and hydrochloric acid until the target softening degree is reached.

[0038] Specifically, the method for determining the appropriate ratio of the rock softener of the present invention includes the following steps:

[0039] S1. Measure the uniaxial compressive strength, mass and mineral composition of the initial rock sample;

[0040] S2. Determine the initial concentrations of sodium bisulfate and hydrochloric acid according to the mineral composition;

[0041] S3. Prepare a mixed aqueous solution of sodium bisulfate, hydrochloric acid and surfactant at the initial concentrations;

[0042] S4. Completely immerse the initial rock sample in the mixed aqueous solution, dry it after soaking for a set time to obtain a posterior rock sample;

[0043] S5. Measure the uniaxial compressive strength and mass of the posterior rock sample, calculate the softening effect, and compare it with the target softening effect;

[0044] S6. When the target softening degree is not reached, increase the concentrations of sodium bisulfate and hydrochloric acid proportionally, and repeat steps S3 - S5 until the target softening degree is reached; when the softening degree is too large, decrease the concentrations of sodium bisulfate and hydrochloric acid proportionally, and repeat steps S3 - S5 until the target softening degree is reached.

[0045] The present invention does not make special limitations on the specific rock source of the rock sample. The rock sample can be taken from the construction sites of geotechnical engineering such as tunnels, roadways or coal mines, etc. The present invention does not make special limitations on the specific rock type of the rock sample. Sandstone, granite, marble, limestone, etc. can all be used for the preparation of the initial rock sample. To ensure the accuracy of the experiment, after selecting the rock sample, n rock samples of the same specification are made and recorded as the initial rock sample, and the subsequent test results are the average values of n rock samples of the same specification.

[0046] In step S1 of the present invention, the mineral composition is preferably determined by an X-ray diffractometer. XRD is a non-destructive analysis technique that does not require changing the properties of the rock sample and can simultaneously analyze all the mineral components in the rock to determine their mineral types. By measuring the intensity of the XRD peaks, the relative content of various minerals can be determined, which has high accuracy and repeatability. The addition concentrations of sodium bisulfate and hydrochloric acid in the mixed aqueous solution are initially selected according to the mineral composition. The initial concentration of the surfactant is set to 0.1 - 1%, and its specific concentration is adjusted according to the actual effect, and then the concentration of the surfactant is kept unchanged to ensure that sodium bisulfate and hydrochloric acid react with the rock mineral components as fully as possible.

[0047] The method for determining the initial concentrations of sodium bisulfate and hydrochloric acid is as follows:

[0048] Summarize the components such as carbonate minerals and silicate minerals that can react with acid solutions, and determine the content of each component. The principle of rock softening lies in the chemical reaction between the anions in the mineral components and the hydrogen ions in the acidic solution, thereby forming erosion of the rock. Therefore, by determining the content of anions in various mineral components, the content of hydrogen ions in the required acidic solution is further determined, so as to obtain the initial concentrations of sodium bisulfate and hydrochloric acid in the mixed aqueous solution. Taking the mineral component calcite as an example, the equations are as follows:

[0049] 2HCl + CaCO3 → CaCl2 + CO2↑ + H2O

[0050] 2NaHSO4 + CaCO3 → CaSO4 + Na2SO4 + H2O + CO2↑

[0051] In the above equations, two HCl react with one CaCO3, and two NaHSO4 react with one CaCO3. After the mineral component analysis, if the content of CaCO3 is x, the total content of hydrochloric acid and sodium bisulfate required for the acidic solution is 2x. According to the ratio of sodium bisulfate to hydrochloric acid being 3:1.5 - 2.5, the respective required contents of sodium bisulfate and hydrochloric acid are determined. The same applies to other mineral components as the above calcite. Finally, the contents of sodium bisulfate and hydrochloric acid are added together respectively to further obtain the initial concentrations of sodium bisulfate and hydrochloric acid in the mixed aqueous solution.

[0052] The present invention mixes and adds the weighed components in sequence according to the order of water, hydrochloric acid, sodium bisulfate, and surfactant, and the mixing and adding process is strictly carried out in accordance with the relevant laboratory test operation procedures.

[0053] The present invention sets the soaking time of the initial rock sample in the mixed aqueous solution to 10 - 20 days, and there is no specific rigid requirement for the environmental temperature, and it is advisable to use the indoor temperature. Observe the chemical and physical changes of the rock sample and make records. After soaking, move it to the sun to dry naturally to obtain the post - test rock sample.

[0054] After obtaining the post - test rock sample, the present invention measures the uniaxial compressive strength and mass of the post - test rock sample, calculates the softening effect, and compares it with the target softening effect. The softening effect is the degree of reduction in uniaxial compressive strength UCS 变 and the degree of reduction in mass M 变 , and the calculation formulas are as follows:

[0055]

[0056]

[0057] Among them, UCS represents the uniaxial compressive strength, M represents the mass of the rock sample in the dry state, the subscript 1 represents the data of the rock sample after soaking, and the subscript 0 represents the data of the rock sample before soaking.

[0058] The judgment of the quality of the softening effect of the present invention depends on specific engineering applications and actual rock types. The degree of rock softening aims at a 25-30% reduction in uniaxial compressive strength and a 0.5-1.0% reduction in mass.

[0059] Observe the surface of the rock sample after soaking. If there is no obvious change on the surface of the rock sample, or the uniaxial compressive strength (bearing capacity) of the rock sample does not decrease significantly, then the degree of softening of the rock sample is too small. At this time, increase the concentrations of sodium bisulfate and hydrochloric acid proportionally, and keep the concentration of the surfactant unchanged. Repeat steps S3-S5 until the target softening degree is reached. The incremental value of the sodium bisulfate concentration is 1-4%, which is appropriately selected according to the actual adjustment situation. Repeat steps S3-S5 once for each increment.

[0060] If the pore diameter on the surface of the rock sample is large and clearly visible, or the degree of decrease in the uniaxial compressive strength of the rock sample is too large and it almost no longer has bearing capacity, affecting the stability of the rock sample itself, then the degree of softening of the rock sample is too large. At this time, decrease the concentrations of sodium bisulfate and hydrochloric acid proportionally, and keep the concentration of the surfactant unchanged. Repeat steps S3-S5 until the target softening degree is reached. The decremental value of the sodium bisulfate concentration is 1-4%, which is appropriately selected according to the actual adjustment situation. Repeat steps S3-S5 once for each decrement.

[0061] Through the above steps, the appropriate ratio of the rock softener for different rock samples can be quickly determined, so as to obtain a rock softener suitable for a specific rock sample, avoid the blindness of actual rock softening work, and ensure the optimal softening effect for the softening of various rocks.

[0062] The technical solution of the present invention will be further elaborated below with specific embodiments.

[0063] Example 1

[0064] The rock sample provided in this example is a sandstone rock sample. The uniaxial compressive strength of the initial sandstone rock sample is measured to be 85.61 MPa and the mass is 531.41 g. Use XRD to measure its mineral composition, and its spectrum is as Figure 1As shown in the figure, the average value of the test results at four different positions of the sandstone is taken as the final result of the mineral composition content in the rock sample, and its contents are as follows: quartz 58%, feldspar 10%, calcite 6%, mica 3%, chlorite 1%, siliceous rock cuttings 6%, limestone cuttings 2%, clay 3%, cement 7%, and others 4%. The concentration ratio of sodium bisulfate to hydrochloric acid is 3:2. A mixed aqueous solution is prepared with an initial concentration of 12.4% sodium bisulfate, 8.3% hydrochloric acid, and 0.4% cetyltrimethylammonium bromide. After soaking for 15 days, the uniaxial compressive strength is measured to be 67.52 MPa, the mass is 529.14 g, and the degree of decrease in uniaxial compressive strength is 21.13%, which does not reach the target degree of decrease. Keeping the concentration of the surfactant unchanged, the concentration of sodium bisulfate is increased by 1.5% and the hydrochloric acid is increased proportionally. After soaking, the measurement is carried out; after 2 increments, the target degree of decrease is reached. At this time, the concentration of sodium bisulfate is 15.4% and the concentration of hydrochloric acid is 10.3%.

[0065] Example 2

[0066] The rock sample provided in this example is a granite rock sample. The uniaxial compressive strength of the initial granite rock sample is measured to be 132.26 MPa and the mass is 562.12 g. Its mineral composition is determined by XRD. The concentration ratio of sodium bisulfate to hydrochloric acid is 3:2.2, and the concentration of cetyltrimethylammonium bromide is 0.8%. The appropriate ratio is determined in the same way as in Example 1. In the obtained rock softener, the concentration of sodium bisulfate is 19.3% and the concentration of hydrochloric acid is 14.2%.

[0067] Example 3

[0068] The rock sample provided in this example is a marble rock sample. The uniaxial compressive strength of the initial marble rock sample is measured to be 68.53 MPa and the mass is 542.76 g. Its mineral composition is determined by XRD. The concentration ratio of sodium bisulfate to hydrochloric acid is 3:1.6, and the concentration of cetyltrimethylammonium bromide is 0.32%. The appropriate ratio is determined in the same way as in Example 1. In the obtained rock softener, the concentration of sodium bisulfate is 17.6% and the concentration of hydrochloric acid is 9.4%.

[0069] Application Example

[0070] The rock softener obtained in Example 1 was used to soften three sandstone rock samples N1 - N3, namely, the concentration of sodium bisulfate was 15.4%, the concentration of hydrochloric acid was 10.3%, and the concentration of cetyltrimethylammonium bromide was 0.4%. The unsoftened sandstone was used as a control. According to the concentrations of single - substance softening solutions commonly used in the prior art and in combination with the total concentration of acidic solutions in this mixed aqueous solution, 22.5% sulfuric acid, 21.5% hydrochloric acid, and 25.5% sodium bisulfate were selected as three comparative softening agents respectively to improve the scientificity and rationality of the softening effect of this mixed aqueous solution. After softening the rock samples for 15 days respectively, a comparative analysis of the softening effect after 15 days was carried out, as shown in Table 1.

[0071] Table 1 Softening effects of different rock softeners

[0072]

[0073] As described in the above table, the hydrochloric acid solution softens by about 18% in terms of compressive strength, and the sulfuric acid solution softens by about 20%. Its relatively high softening property benefits from the fact that both solutions are strong - acid solutions. Due to the existence of the oleophobic layer on the rock surface, the hydrogen ions in the strong - acid solution cannot react quickly with the anions in the mineral components. Therefore, its effect is not as good as the mixed solution proposed in the present invention. The sodium bisulfate solution is an acid - salt solution, and its softening effect is limited. The compressive strength only decreases by about 12%. On the one hand, in terms of ionizing hydrogen ions, this solution is not as good as the strong - acid solution, and there is also the problem of the oleophobic layer on the rock surface. The mixed solution prepared with hydrochloric acid and sodium bisulfate has a good softening effect. The rock softener prepared with hydrochloric acid, sodium bisulfate, and cetyltrimethylammonium bromide, from the perspective of uniaxial compressive strength, its softening effect is improved by more than 7% compared with the prior art. From the perspective of quality, its softening effect is improved by more than 0.4% compared with the prior art. It shows that within the same soaking time, the rock softener of the present invention has more H + ions reacting with the mineral components, further proving that the surfactant cetyltrimethylammonium bromide in the mixed aqueous solution can promote the better penetration of acidic minerals into the rock interior and accelerate the softening process.

[0074] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A rock softening agent, characterized in that, It includes sodium bisulfate, hydrochloric acid, surfactant and water; the concentration ratio of sodium bisulfate to hydrochloric acid is 3:1.5 - 2.5; the concentration of sodium bisulfate is 10 - 20%, the concentration of hydrochloric acid is 5 - 15%, and the concentration of the surfactant is 0.1 - 1%; The appropriate proportion of the rock softening agent is determined by the following method steps: Measure the initial rock sample parameters, determine the initial concentrations of sodium bisulfate and hydrochloric acid, prepare a mixed aqueous solution of sodium bisulfate, hydrochloric acid and surfactant according to the concentration ratio, soak the initial rock sample, and measure the softening degree after drying, and adjust the concentrations of sodium bisulfate and hydrochloric acid until the target softening degree is reached; S1. Measure the uniaxial compressive strength, mass and mineral composition of the initial rock sample; S2. Determine the initial concentrations of sodium bisulfate and hydrochloric acid according to the mineral composition; S3. Prepare a mixed aqueous solution of sodium bisulfate, hydrochloric acid and surfactant according to the concentration ratio and with the initial concentrations; The surfactant is a cationic surfactant; The cationic surfactant is an alkyl quaternary ammonium salt cationic surfactant; S4. Immerse the initial rock sample in the mixed aqueous solution, dry it after soaking for a set time to obtain a posteriori rock sample; S5. Measure the uniaxial compressive strength and mass of the posteriori rock sample, calculate the softening degree, and compare it with the target softening degree; The target softening degree is: the reduction degree of uniaxial compressive strength is 25 - 30%; the reduction degree of mass is 0.5 - 1.0%; S6. When the target softening degree is not reached, increase the concentrations of sodium bisulfate and hydrochloric acid proportionally, and repeat steps S3 - S5 until the target softening degree is reached; when the softening degree is too large, decrease the concentrations of sodium bisulfate and hydrochloric acid proportionally, and repeat steps S3 - S5 until the target softening degree is reached; The increment or decrement value of the sodium bisulfate concentration is 1 - 4%; repeat steps S3 - S5 once for each increment or decrement.

2. The rock softening agent according to claim 1, wherein The alkyl quaternary ammonium salt cationic surfactant is cetyltrimethylammonium bromide.

3. The rock softening agent according to claim 1, characterized in that, In step S1, the mineral composition is measured by an X-ray diffractometer.

4. The rock softener according to claim 1, characterized in that, In step S4, the set soaking time is 10 - 20 days; the drying method is natural air drying.

5. The rock softening agent according to claim 1, characterized in that, In step S5, the softening degree is the reduction degree of the uniaxial compressive strength and the reduction degree of the mass.

Images