Method for determining free calcium oxide in domestic sludge

Abstract

The embodiment of the invention provides a method for determining free calcium oxide in domestic sludge, and the method comprises the following steps: obtaining domestic sludge and doping ethanol to obtain a to-be-determined domestic sludge sample; freezing a to-be-detected domestic sludge sample into a solid, carrying out suction filtration until the solid is dehydrated, and crushing to obtain a detection sample with a preset size; the method comprises the following steps: preparing cane sugar-ethanol extract liquor, mixing the cane sugar-ethanol extract liquor with a detection sample, heating and boiling the cane sugar-ethanol extract liquor and the detection sample in a first container, performing centrifugal motion in a centrifugal machine, and extracting supernatant liquor in the first container to a second container; continuously adding deionized water, an ammoniacal buffer solution, triethanolamine and a calcium carboxylic acid indicator into the second container; and titrating in the second container by using an EDTA standard solution until the liquid is changed from red to blue so as to obtain the content of free calcium oxide. The method for determining free calcium oxide in domestic sludge disclosed by the invention has the advantages of good extraction effect, no toxicity and harmlessness by using cane sugar, obvious end point determination and more accurate determination result.

Description

Technical Field

[0001] The embodiments of the present disclosure belong to the field of sludge detection technology, and specifically relate to a method for determining free calcium oxide in domestic sludge. Background Art

[0002] With the acceleration of urbanization, the output of domestic sludge has increased year by year, and its resource utilization (such as incineration power generation, building materials preparation, etc.) has become a research hotspot in the field of environmental protection. Free calcium oxide, as a key indicator in the sludge treatment process, directly affects the stability of incineration ash, the volume stability of building materials and the solidification effect of heavy metals. However, the existing free calcium oxide determination technology is mostly designed for homogeneous materials such as cement and limestone, and its application in complex systems with high organic matter and multiple impurities such as domestic sludge has significant limitations. The related technology uses traditional chemical titration method (ethylene glycol-anhydrous ethanol method) for determination, but

[0003] The following problems exist:

[0004] (1) Although it can selectively dissolve free calcium oxide, there are problems such as humic acid interfering with the complexation reaction and incomplete masking of heavy metals. In addition, ethylene glycol is a hazardous chemical and is very harmful to the human body. The free calcium oxide in the sludge extracted by ethylene glycol is incomplete and has great harm.

[0005] (2) The air drying method is used to dry the domestic sludge, but the moisture content of domestic sludge can reach 70% to 85% and the viscosity is extremely high. Direct drying can easily cause free calcium oxide to react with water vapor to form calcium hydroxide, which interferes with the measurement results.

[0006] (3) Domestic sludge needs to be filtered and the filtration time is long, usually 4 to 6 hours;

[0007] (4) When using calcein-thymolphthalein as an indicator for titration, the endpoint color is difficult to define and can be easily confused. Summary of the Invention

[0008] The embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art and provide a method for determining free calcium oxide in domestic sludge.

[0009] An embodiment of the present disclosure provides a method for determining free calcium oxide in domestic sludge, the method comprising:

[0010] Obtaining a first weight of domestic sludge and adding a first volume of ethanol to obtain a domestic sludge sample to be tested;

[0011] Freezing the domestic sludge sample to be tested into a solid at a first temperature and filtering it to dehydrate it, and then crushing it after dehydration to obtain a test sample of a preset size;

[0012] Prepare a sucrose-ethanol extract; extract a second weight of the test sample and add the second volume of the sucrose-ethanol extract, mix the two in the first container and heat to boil for a first preset time;

[0013] The first container is placed in a centrifuge for centrifugal movement, and then the supernatant in the first container is extracted into a second container of a third volume;

[0014] A fourth volume of deionized water, a fifth volume of ammoniacal buffer solution, a sixth volume of triethanolamine, and a third weight of a calcium carboxylate indicator are added to the second container; and the EDTA standard solution is titrated in the second container until the liquid changes from red to blue, thereby obtaining the free calcium oxide content.

[0015] Optionally, the first weight is 90g to 110g, the first volume is 25ml to 35ml, the first temperature is -35℃ to -45℃, the preset size is less than 0.2mm, the second weight is 0.6g to 1.5g, the second volume is 45ml to 55ml, and the first preset time is 8min to 12min.

[0016] Optionally, the first weight is 100 g, the first volume is 30 ml, the first temperature is -40°C, the second weight is 1 g, the second volume is 50 ml, and the first preset time is 10 min.

[0017] Optionally, the fourth volume is 45ml to 55ml, the fifth volume is 8ml to 12ml, the sixth volume is 4ml to 6ml, and the third weight is 0.006g to 0.014g.

[0018] Optionally, the fourth volume is 50 ml, the fifth volume is 10 ml, the sixth volume is 5 ml, the third weight is 0.01 g, and the third volume is greater than 250 ml.

[0019] Optionally, the filtering of the solid to dehydration and crushing it after dehydration to obtain a test sample of a preset size includes filtering to dehydration under a vacuum environment, crushing it with a powder making machine after dehydration and passing it through a standard sieve of the preset size to obtain the test sample smaller than the preset size.

[0020] Optionally, the preparation of the sucrose-ethanol extract includes placing a seventh volume of distilled water into a third container and adding an excess of sucrose until the sucrose is no longer soluble in the distilled water, filtering the filtrate and adding an eighth volume of anhydrous ethanol to the filtrate and mixing.

[0021] Optionally, the seventh volume is 100 ml and the eighth volume is 10 ml.

[0022] Optionally, mixing the test sample and the sucrose-ethanol extract in the first container and heating and boiling includes, after mixing the test sample and the sucrose-ethanol extract in the first container, adding at least one glass bead into the first container to prevent overheating or overboiling during the heating and boiling process.

[0023] Optionally, placing the first container in a centrifuge for centrifugal motion includes subjecting the first container to centrifugal motion in the centrifuge at a rotation speed of 3000 rpm to 5000 rpm, and the time of the centrifugal motion is 8 min to 15 min.

[0024] The presently disclosed embodiment discloses a method for determining free calcium oxide in domestic sludge, which uses freeze-drying and the addition of ethanol, followed by vacuum filtration to remove moisture from the domestic sludge to be tested. This method is highly efficient and does not affect the determination results of free calcium oxide. The sucrose-ethanol extraction system is less susceptible to interference from organic matter in domestic sludge, resulting in better extraction effects. Moreover, sucrose is not a hazardous chemical and is non-toxic and harmless. By using a centrifuge for filtration, the filtration time can be shortened from 4 to 6 hours to 10 to 20 minutes, which is more efficient. By using a calcium carboxylic acid indicator, the endpoint determination is more obvious and the results are more accurate compared to protocalcein-thymolphthalein. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic flow chart of a method for determining free calcium oxide in domestic sludge according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0027] like Figure 1 As shown, a method for determining free calcium oxide in domestic sludge includes S110 , obtaining a first weight of domestic sludge and adding a first volume of ethanol to obtain a domestic sludge sample to be measured.

[0028] Specifically, in this step, the domestic sludge is pretreated, such as by taking a first weight of domestic sludge and adding a first volume of ethanol to obtain a domestic sludge sample to be tested. For example, the first weight can be set to 90g to 110g, and the first volume can be set to 25ml to 35ml. As a specific example, 100g of domestic sludge is taken and 30ml of ethanol is added. The two are mixed to obtain the desired domestic sludge sample to be tested. The addition of ethanol lowers the freezing point of water, promoting rapid freezing, and partially replaces the water content.

[0029] S120, freezing the domestic sludge sample to be tested into a solid at a first temperature and filtering it to dehydrate it, and then crushing it after dehydration to obtain a test sample of a preset size.

[0030] Specifically, in this step, the domestic sludge sample to be tested is frozen at a low temperature of -35°C to -45°C, such as freezing the domestic sludge sample to be tested into a solid at a first temperature of -40°C, and then the solid is filtered under a vacuum environment to dehydrate. After dehydration, it is crushed by a pulverizer and passed through a standard sieve of a preset size to obtain a test sample smaller than the preset size. As an example, the preset size can be set to less than 0.2mm, that is, the dehydrated solid is crushed by a pulverizer and passed through a standard sieve of less than 0.2mm to obtain a test sample. Vacuum filtration accelerates the sublimation of water through negative pressure, avoiding the hydrothermal reaction caused by traditional heating. And a particle size of less than 0.2mm can ensure sufficient subsequent extraction reaction.

[0031] S130, preparing a sucrose-ethanol extract: extracting a second weight of the test sample and adding the second volume of the sucrose-ethanol extract, mixing the two in a first container and heating and boiling for a first preset time.

[0032] Specifically, in this step, a sucrose-ethanol extract is first prepared, and the specific preparation steps are as follows: seventh volume of distilled water is placed in a third container and an excess of sucrose is added until the sucrose is no longer soluble in the distilled water, the filtrate is filtered and the eighth volume of anhydrous ethanol is added to the filtrate and mixed. For example, 100 ml of distilled water is placed in a third container and an excess of sucrose is added until the sucrose is no longer soluble in water, the filtrate is filtered and 10 ml of anhydrous ethanol is added and mixed to obtain a sucrose-ethanol extract. Sucrose can selectively dissolve calcium ions and is non-toxic and harmless. The addition of ethanol can reduce the dielectric constant of the solution and reduce the dissolution of other calcium salts. Sucrose provides selective complexing ability, and ethanol adjusts the solubility selectivity, which is more environmentally friendly and less interfering than a pure ethylene glycol system.

[0033] Extract 0.6g to 1.5g of the test sample and add 45ml to 55ml of sucrose-ethanol extract to extract the free calcium oxide. As a specific embodiment, extract 1g of the test sample and add 50ml of sucrose-ethanol extract thereto. After mixing the two in a first container, add at least one glass bead to the first container. The specific amount of addition can be selected according to actual needs. The embodiments of the present disclosure do not impose specific restrictions on this. Subsequently, continue to heat and boil the two, such as heating to boiling for a first preset time. The first preset time can be set to 8min to 12min, for example, set to 10min. The addition of glass beads can prevent overheating or overboiling during the heating and boiling process. Boiling can increase the speed of molecular movement and accelerate the dissolution of free calcium oxide and the kinetics of complexation reactions.

[0034] S140, placing the first container in a centrifuge for centrifugal motion, and extracting the supernatant in the first container into a second container of a third volume.

[0035] Specifically, in this step, after heating and boiling, the first container is placed in a high-speed centrifuge and centrifuged at 3000-5000 rpm for 8-15 minutes, with 10 minutes being an example. High-speed centrifugation can rapidly separate the solid and liquid phases by utilizing density differences, replacing traditional filtration. The supernatant in the first container is then transferred to a second container for further analysis. The second container can be a conical flask, and the third container can be larger than 250 ml.

[0036] S150: Add a fourth volume of deionized water, a fifth volume of ammoniacal buffer solution, a sixth volume of triethanolamine, and a third weight of calcium carboxylate indicator to the second container. Titrate the solution in the second container with the EDTA standard solution until the liquid changes from red to blue, thereby determining the free calcium oxide content.

[0037] Specifically, in this step, the supernatant is added to a 250ml conical flask, and then 45ml to 55ml of deionized water, 8ml to 12ml of ammonia buffer solution, 4ml to 6ml of triethanolamine, and 0.006g to 0.014g of calcium carboxylate indicator are added to the conical flask. As a specific example, 50ml of deionized water, 10ml of ammonia buffer solution, and 5ml of triethanolamine are added to the conical flask, followed by 0.01g of calcium carboxylate indicator. Thereafter, the EDTA standard solution is titrated in the second container until the liquid changes from red to blue, and the color of the liquid in the second container specifically changes from light wine red to pure blue.

[0038] Deionized water plays a diluting role, and the ammonia buffer solution can control the pH value to be maintained at about 10, ensuring that EDTA and calcium ions are quantitatively complexed. Triethanolamine masks interfering ions such as iron ions and aluminum ions, and the calcium carboxylate indicator has a more sensitive endpoint color change than traditional indicators. Before titrating the EDTA standard solution, the liquid in the second container is wine red. As the EDTA standard solution is titrated, when the liquid in the second container is pure blue, it indicates that the calcium ions are completely complexed. At this time, the corresponding free calcium oxide content can be obtained by the consumption of the EDTA standard solution. The relevant calculation steps can be obtained using some calculation methods in the prior art, so I will not repeat them here.

[0039] The presently disclosed embodiment discloses a method for determining free calcium oxide in domestic sludge, which uses freeze-drying and the addition of ethanol, followed by vacuum filtration to remove moisture from the domestic sludge to be tested. This method is highly efficient and does not affect the determination results of free calcium oxide. The sucrose-ethanol extraction system is less susceptible to interference from organic matter in domestic sludge, resulting in better extraction effects. Moreover, sucrose is not a hazardous chemical and is non-toxic and harmless. By using a centrifuge for filtration, the filtration time can be shortened from 4 to 6 hours to 10 to 20 minutes, which is more efficient. By using a calcium carboxylic acid indicator, the endpoint determination is more obvious and the results are more accurate compared to protocalcein-thymolphthalein.

[0040] As a specific example, a domestic sludge was selected and measured using the above-mentioned measurement method as follows:

[0041] Take 100g of domestic sludge, add 30ml of ethanol, freeze it into a solid at -40℃, and then filter it under vacuum to dehydrate it. The dehydrated sample is crushed in a pulverizer and passed through a standard sieve of less than 0.2mm to obtain the test sample.

[0042] Take 100 ml of distilled water, add excess sucrose until the sucrose is no longer soluble in water, filter the filtrate, add 10 ml of anhydrous ethanol, and mix well to obtain a sucrose-ethanol extract.

[0043] Weigh 1g of test sample, add 50ml of sucrose-ethanol extract, shake well, then add 2-3 glass beads, heat to boiling for 10 minutes, remove and place in a high-speed centrifuge, centrifuge for 10 minutes, and take the supernatant.

[0044] Pour the supernatant into a 250ml conical flask, add 50ml deionized water, 10ml ammonia buffer solution and 5ml triethanolamine, then add 0.01g calcium carboxylate indicator, and titrate with EDTA standard solution until the liquid changes from light wine red to pure blue. The free calcium oxide content is calculated to be 0.15%.

[0045] It is understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present disclosure, and the present disclosure is not limited thereto. Those skilled in the art may make various modifications and improvements without departing from the spirit and substance of the present disclosure, and such modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A method for determining free calcium oxide in domestic sludge, characterized in that: The determination method comprises: Obtaining a first weight of domestic sludge and adding a first volume of ethanol to obtain a domestic sludge sample to be tested; Freezing the domestic sludge sample to be tested into a solid at a first temperature and filtering it to dehydrate it, and then crushing it after dehydration to obtain a test sample of a preset size; Prepare a sucrose-ethanol extract; extract a second weight of the test sample and add the second volume of the sucrose-ethanol extract, mix the two in the first container and heat to boil for a first preset time; The first container is placed in a centrifuge for centrifugal movement, and then the supernatant in the first container is extracted into a second container of a third volume; A fourth volume of deionized water, a fifth volume of ammoniacal buffer solution, a sixth volume of triethanolamine, and a third weight of a calcium carboxylate indicator are added to the second container; and the EDTA standard solution is titrated in the second container until the liquid changes from red to blue, thereby obtaining the free calcium oxide content.

2. The method for determining free calcium oxide in domestic sludge according to claim 1, wherein: The first weight is 90g to 110g, the first volume is 25ml to 35ml, the first temperature is -35℃ to -45℃, the preset size is less than 0.2mm, the second weight is 0.6g to 1.5g, the second volume is 45ml to 55ml, and the first preset time is 8min to 12min.

3. The method for determining free calcium oxide in domestic sludge according to claim 2, wherein: The first weight is 100 g, the first volume is 30 ml, the first temperature is -40°C, the second weight is 1 g, the second volume is 50 ml, and the first preset time is 10 min.

4. The method for determining free calcium oxide in domestic sludge according to claim 1, wherein: The fourth volume is 45ml-55ml, the fifth volume is 8ml-12ml, the sixth volume is 4ml-6ml, and the third weight is 0.006g-0.014g.

5. The method for determining free calcium oxide in domestic sludge according to claim 4, wherein: The fourth volume is 50 ml, the fifth volume is 10 ml, the sixth volume is 5 ml, the third weight is 0.01 g, and the third volume is greater than 250 ml.

6. The method for determining free calcium oxide in domestic sewage sludge according to any one of claims 1 to 5, characterized in that: The solid is filtered to be dehydrated, and then crushed after dehydration to obtain a test sample of a preset size, including filtering to be dehydrated under a vacuum environment, crushing it with a powder making machine after dehydration, and passing it through a standard sieve of the preset size to obtain the test sample smaller than the preset size.

7. The method for determining free calcium oxide in domestic sewage sludge according to any one of claims 1 to 5, characterized in that: The preparation of the sucrose-ethanol extract includes: placing a seventh volume of distilled water into a third container and adding an excess amount of sucrose until the sucrose is no longer soluble in the distilled water; filtering the filtrate; and adding an eighth volume of anhydrous ethanol to the filtrate and mixing.

8. The method for determining free calcium oxide in domestic sludge according to claim 7, wherein: The seventh volume is 100 ml, and the eighth volume is 10 ml.

9. The method for determining free calcium oxide in domestic sludge according to any one of claims 1 to 5, characterized in that: The mixing of the test sample and the sucrose-ethanol extract in the first container and heating and boiling the mixture includes: after the test sample and the sucrose-ethanol extract are mixed in the first container, at least one glass bead is added into the first container to prevent overheating or overboiling during the heating and boiling process.

10. The method for determining free calcium oxide in domestic sewage sludge according to any one of claims 1 to 5, characterized in that: Placing the first container in a centrifuge for centrifugal motion includes subjecting the first container to centrifugal motion in the centrifuge at a rotation speed of 3000 rpm to 5000 rpm, and the time of the centrifugal motion is 8 minutes to 15 minutes.

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