Method for determining water-soluble calcium content in stone powder

Abstract

The application discloses a method for determining water-soluble calcium content in stone powder, and relates to the technical field of material detection. The method comprises the following steps: firstly, mixing a stone powder sample with water to extract a sample solution; then, adding an excess of sodium bicarbonate solution to part of the sample solution, heating at 70-80 DEG C, cooling and standing, and then treating the sample solution by filtration, washing and drying to obtain a precipitate; finally, calculating the water-soluble calcium content in the stone powder according to the mass of the precipitate. The method realizes accurate detection of the water-soluble calcium content through sodium bicarbonate precipitation and constant weight determination. The method can also realize batch detection of samples, improves work efficiency, and is safe and environmentally friendly in the experimental process.

Description

Technical Field

[0001] This invention relates to the field of materials testing technology, and more specifically, to a method for determining the water-soluble calcium content in stone powder. Background Technology

[0002] Stone powder, primarily composed of natural calcium carbonate, is commonly found as a grayish-white or white powder with a calcium content of approximately 36-39%. It is a relatively inexpensive and readily available mineral raw material in livestock and poultry farming. Stone powder is a crucial source of calcium in livestock and poultry diets and is also widely used in feed production to dilute micronutrient premixes. Water-soluble calcium content refers to calcium ions that can be directly dissolved in water. This usually indicates insufficient purity of the stone powder, a high calcium content added, or the presence of water-soluble inorganic calcium salts.

[0003] Currently, the industry lacks specific standards for stone powder. Existing methods for determining calcium content mainly involve the potassium permanganate method and the disodium ethylenediaminetetraacetate complexometric titration method. Both methods target the total calcium content of the sample and cannot accurately reflect the key indicator of water-soluble calcium. These traditional methods also have limitations such as cumbersome operation, long processing time, and high requirements for personnel and equipment, making them difficult to meet practical needs. Therefore, developing a method that can rapidly and accurately determine the water-soluble calcium content in stone powder is of urgent practical significance for scientifically assessing stone powder quality and guiding procurement and efficient utilization.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the water-soluble calcium content in stone powder. This method uses a gravimetric method and requires only water and a saturated sodium bicarbonate solution, which greatly improves detection efficiency, shortens experimental time, and reduces experimental costs.

[0006] This invention is implemented as follows: This invention provides a method for determining the water-soluble calcium content in stone powder, comprising the following steps: mixing the sample to be tested with water, extracting the sample, and obtaining a sample solution. Take a portion of the test sample solution, add excess sodium bicarbonate solution, heat to 70-80℃, then cool and let stand. Filter, wash and dry the mixed solution until the mass is constant. The content of water-soluble calcium in the test sample is calculated based on the mass of the precipitate.

[0007] In some preferred embodiments, the determination method further includes preparing a blank test solution without adding a sample.

[0008] In some preferred embodiments, the extraction is performed by ultrasonic extraction at a frequency of 30-40 kHz for 30-40 min at a temperature of 30-35 °C.

[0009] In some preferred embodiments, the test sample solution is filtered using slow quantitative filter paper before aliquoting.

[0010] In some preferred embodiments, an excess of sodium bicarbonate solution is added to the test sample solution, and the temperature is raised to 70-80°C and held for 30-40 seconds. During the heating and holding process, no stirring is performed to avoid the formation of lumps.

[0011] In some preferred embodiments, the cooling and settling process involves stirring 3-4 times during cooling and continuing to settle for 0.5-1.5 hours for aging.

[0012] In some preferred embodiments, the filtration is performed using a glass sand crucible that has been pre-dried to a constant mass at 105-110°C.

[0013] In some preferred embodiments, the washing process involves first washing the precipitate 5-6 times using a decantation method, and then transferring all the precipitate to a glass frit crucible for further washing 3-4 times.

[0014] In some preferred embodiments, the drying process is performed at 105-110°C for 50-70 minutes.

[0015] In some preferred embodiments, the formula for calculating the water-soluble calcium content is as follows:

[0016] Where m1 is the total mass of the glass sand crucible after adding the precipitate and bringing it to constant weight; m0 is the mass of the glass sand crucible after bringing it to constant weight; m 空白 V is the mass of calcium carbonate precipitate formed in the blank solution; V is the volume of the dissolved sample; m is the mass of the sample; V1 is the volume of the test liquid used for precipitation.

[0017] The present invention has the following beneficial effects: This method, by specifically detecting water-soluble calcium content, can effectively determine whether stone powder has been adulterated, making the test results more reliable and accurate. Employing a gravimetric method, it requires only small amounts of safe reagents such as water and saturated sodium bicarbonate, replacing the time-consuming, cumbersome, and hazardous process of traditional calcium content testing. This significantly improves testing efficiency, shortens experimental time, and reduces experimental costs and safety risks. Furthermore, this method supports batch sample testing, greatly improving work efficiency. The overall process is safe and environmentally friendly, with high accuracy and good repeatability, demonstrating significant practical advantages. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] The following is a detailed description of a method for determining the water-soluble calcium content in stone powder proposed in this invention.

[0020] Currently, the main methods for detecting water-soluble calcium content in stone powder are the potassium permanganate method and the disodium ethylenediaminetetraacetate (EDTA) complexometric titration method. However, these methods have significant limitations in detecting water-soluble calcium content. The fundamental reason is that both methods require strong acid digestion of the sample first. This process dissolves all the water-insoluble calcium carbonate and any other calcium salts that may be present in the stone powder. The final result measures the total calcium content of the sample, not the specific water-soluble calcium portion, thus failing to effectively identify whether the stone powder has been artificially adulterated with water-soluble calcium salts. Furthermore, the potassium permanganate method is cumbersome, requires highly experienced personnel to determine the titration endpoint, and uses hazardous reagents with strong oxidizing properties. While the EDTA complexometric titration method is widely used, it is easily affected by interference from other metal ions in the sample when the calcium content is high, affecting the accuracy of the results. Both methods are time-consuming and consume many types of reagents, making it difficult to achieve efficient and rapid detection of batch samples and failing to meet the specific requirement of detecting water-soluble calcium.

[0021] To address the shortcomings of existing technologies, this invention proposes a method for determining the water-soluble calcium content in stone powder. This gravimetric method requires only water and saturated sodium bicarbonate, significantly improving detection efficiency, shortening experimental time, and reducing experimental costs. The steps include: S1. Mix the sample to be tested with water and extract it to obtain the sample solution.

[0022] In some preferred embodiments, the extraction is performed by ultrasonic extraction at a frequency of 30-40 kHz for 30-40 min at a temperature of 30-35°C. Ultrasonic extraction ensures the full dissolution of water-soluble calcium. The cavitation effect generated during ultrasonic extraction creates strong mechanical disturbances and microjets, effectively disrupting the agglomeration of stone powder particles. This allows the water-soluble calcium salts to be fully exposed and rapidly dissolved in the aqueous phase, thereby ensuring the accuracy and reproducibility of the detection results.

[0023] In some preferred embodiments, a blank test solution also needs to be prepared, which is exactly the same as the test solution except that no sample is added, and is treated in the same way as the sample.

[0024] S2. Take a portion of the test sample solution, add excess sodium bicarbonate solution, heat to 70-80℃, keep warm for 30-40s, and do not use open flame during heating. Do not stir when adding reagents or heating to avoid forming lumps. Then cool and let stand. Filter, wash and dry the mixed solution until the mass is constant.

[0025] This invention uses sodium bicarbonate to precipitate calcium ions, but the precipitate particles are relatively small and easily form colloidal precipitates. Heating in a water bath accelerates the precipitation process, reduces the settling time, weakens the adsorption of colloids on particles, and disrupts the hydration film of the colloidal micelles. This accelerates the movement of colloidal particles, increases the chance of collisions between them, and causes the colloidal particles to aggregate. In other words, it disrupts the stability of the colloidal precipitate and accelerates the precipitation of calcium carbonate.

[0026] Furthermore, the magnesium content in Grade 1 stone powder is ≤0.5%, and in Grade 2 stone powder it is ≤1.0%, while the calcium content in Grade 1 stone powder is ≥37%, and in Grade 2 stone powder it is ≥35%, with the magnesium content being much lower than the calcium content. In aqueous solution, magnesium carbonate precipitate is more soluble than calcium carbonate precipitate. Therefore, upon adding saturated sodium bicarbonate, calcium carbonate will preferentially form a precipitate, while a small or very small amount of magnesium carbonate will dissolve in the water through repeated washing, thus eliminating the interference of magnesium ions.

[0027] In some preferred embodiments, the cooling and settling process involves stirring 3-4 times during cooling. Stirring 3-4 times in the initial cooling stage effectively breaks the temperature gradient of the solution, ensuring uniform heat dissipation and allowing the fine calcium carbonate crystal nuclei to fully contact and distribute evenly in the solution, creating favorable conditions for subsequent regular crystal growth. Then, the solution is allowed to stand for another 0.5-1.5 hours for aging. Utilizing the Ostwald ripening principle, unstable microcrystals in the solution gradually dissolve, while relatively stable larger crystals continue to grow. The key benefit of this process is that it significantly increases the average particle size of the calcium carbonate precipitate, improving its physical morphology and resulting in denser, coarser crystals. This precipitate exhibits excellent performance in subsequent filtration operations—it is less prone to membrane penetration, has high washing efficiency, and is easier to transfer and dry to constant weight. Ultimately, this provides a solid guarantee for obtaining accurate, stable, and reproducible weighing results, effectively avoiding measurement errors caused by precipitate penetration or loss.

[0028] In some preferred embodiments, the filtration is performed using a glass sand crucible that has been pre-dried to a constant mass at 105-110°C; the washing is performed by decantation, first washing the precipitate 5-6 times, then transferring all the precipitate to the aforementioned glass sand crucible for further washing 3-4 times; the drying process is performed at 105-110°C for 50-70 minutes.

[0029] In some preferred embodiments, the formula for calculating the water-soluble calcium content is as follows:

[0030] m1 is the total mass of the glass sand crucible after adding the precipitate to constant weight, in grams (g). m0 is the mass of the glass sand crucible after constant weight, in grams (g). m1-m0 represents the mass of calcium carbonate precipitate formed in the test solution, expressed in grams (g). m 空白 The mass of calcium carbonate precipitate formed in the blank solution is expressed in grams (g). V is the volume of the dissolved sample, in milliliters (mL). m is the mass of the sample, in grams (g). V1 is the volume of the test liquid used for precipitation, in milliliters (mL). 0.4004 — The coefficient for converting calcium carbonate to calcium. The gravimetric method for detecting water-soluble calcium proposed in this invention is based on the reaction between sodium bicarbonate and free calcium ions, and the reaction equation is as follows:

[0031] Therefore, the total mass of the precipitate must first be obtained by weighing, and the blank value introduced by reagents and the environment must be subtracted to correct for systematic errors, thus obtaining the true net mass of calcium carbonate derived from the sample. Subsequently, by multiplying by the ratio of the total sample volume to the fractionated volume, the fractionated measurement result is accurately converted into the total amount of the entire sample. The most crucial step is applying the conversion factor 0.4004—derived from the molar mass ratio of calcium to calcium carbonate—which precisely converts the mass of calcium carbonate into the actual mass of calcium element within it.

[0032] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0033] Example 1 This embodiment provides a method for determining the water-soluble calcium content in stone powder, including the following steps: S1. Extraction of water-soluble calcium: Weigh 10g of sample 1 into a 100mL volumetric flask, add about 80mL of water, sonicate at 30~35℃ for 30min, let stand for 30min, cool to room temperature, and dilute to volume with water.

[0034] S2. Preparation of blank test solution: Except for the absence of sample, the preparation is exactly the same as that of test solution, and the blank test solution is treated in the same way as the sample.

[0035] S3. After filtering with slow-speed filter paper, take 20 mL of the supernatant into a beaker, add excess saturated sodium bicarbonate solution, cover with a watch glass, and heat in a water bath until the temperature of the contents of the beaker reaches 75℃±5℃, maintain for 30 s (do not use open flame during heating, and do not stir when adding reagents or heating to avoid clumping). Allow to cool naturally to room temperature, stirring 3-4 times during the cooling process, and continue to stand for about 1 hour. Filter the supernatant using a glass frit crucible pre-prepared at 110±5℃ with constant mass. Wash the precipitate 5-6 times by decantation, using 15-20 mL of water each time, completely transferring the precipitate to the glass frit crucible. Continue washing with water 3-4 times, place the glass frit crucible in an electric drying oven at 110℃±5℃ for 1 hour, remove, cool to room temperature in a desiccator, and weigh.

[0036] S4. Calculate the water-soluble calcium content according to the formula for calculating water-soluble calcium content.

[0037] Example 2 This embodiment provides a method for determining the water-soluble calcium content in stone powder. The steps are the same as in Example 1, except that sample 2 is used for testing.

[0038] Example 3 This embodiment provides a method for determining the water-soluble calcium content in stone powder. The steps are the same as in Example 1, except that sample 3 is selected for testing.

[0039] Example 4 This embodiment provides a method for determining the water-soluble calcium content in stone powder. The steps are the same as in Example 1, except that sample 4 is selected for testing.

[0040] Example 5 This embodiment provides a method for determining the water-soluble calcium content in stone powder. The steps are the same as in Example 1, except that sample 5 is selected for testing.

[0041] The water-soluble calcium content of Examples 1-5 is statistically shown in Table 1.

[0042] Table 1. Water-soluble calcium content of each embodiment.

[0043]

[0044] In summary, this method establishes a specific procedure for determining the water-soluble calcium content in limestone powder. By combining water extraction with sodium bicarbonate heating precipitation, this gravimetric analysis effectively overcomes the limitations of traditional potassium permanganate and EDTA titration methods, which can only determine total calcium and cannot detect adulteration. This method ensures the full dissolution of water-soluble calcium through ultrasonic extraction and optimizes the precipitation characteristics through cooling, settling, and aging processes, thus significantly improving overall detection efficiency and accuracy. The procedure is simple and safe, with low reagent costs, greatly shortening the detection time, reducing operational risks for laboratory personnel, and enabling rapid and environmentally friendly analysis of batch samples. Verification shows that this method yields accurate and stable results, providing a reliable and practical technical means for the quality control and authenticity identification of limestone powder, and has significant practical guiding value for feed industry production and raw material procurement.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the water-soluble calcium content in stone powder, characterized in that, Includes the following steps: The sample to be tested is mixed with water and extracted to obtain the sample solution. Take a portion of the test sample solution, add excess sodium bicarbonate solution, heat to 70-80℃, then cool and let stand. Filter, wash and dry the mixed solution until the mass is constant. The content of water-soluble calcium in the test sample is calculated based on the mass of the precipitate.

2. The method for determining the water-soluble calcium content in stone powder according to claim 1, characterized in that, The determination method also includes preparing a blank test solution without adding any sample.

3. The method for determining the water-soluble calcium content in stone powder according to claim 1, characterized in that, The extraction was performed by ultrasonic extraction at a frequency of 30-40 kHz, a time of 30-40 min, and a temperature of 30-35 ℃.

4. The method for determining the water-soluble calcium content in stone powder according to claim 1, characterized in that, The test sample solution was filtered using slow quantitative filter paper before being separated.

5. The method for determining the water-soluble calcium content in stone powder according to claim 1, characterized in that, The test sample solution is added with an excess of sodium bicarbonate solution, heated to 70-80℃ and held at that temperature for 30-40 seconds, and no stirring is performed during the heating and holding process to avoid the formation of lumps.

6. The method for determining the water-soluble calcium content in stone powder according to claim 1, characterized in that, During the cooling and settling process, the mixture is stirred 3-4 times during cooling and then allowed to stand for another 0.5-1.5 hours for aging.

7. The method for determining the water-soluble calcium content in stone powder according to claim 1, characterized in that, The filtration is carried out using a glass sand crucible that has been pre-dried to a constant mass at 105-110°C.

8. The method for determining the water-soluble calcium content in stone powder according to claim 1, characterized in that, The washing process involves first washing the precipitate 5-6 times using decantation, and then transferring all the precipitate to a glass frit crucible for further washing 3-4 times.

9. The method for determining the water-soluble calcium content in stone powder according to claim 1, characterized in that, The drying process involves drying at 105-110℃ for 50-70 minutes.

10. The method for determining the water-soluble calcium content in stone powder according to claim 1, characterized in that, The formula for calculating the water-soluble calcium content is as follows: Where m1 is the total mass of the glass sand crucible after adding the precipitate to constant weight; m0 is the mass of the glass sand crucible after constant weight; m 空白 V is the mass of calcium carbonate precipitate formed in the blank solution; V is the volume of the dissolved sample; m is the mass of the sample; V1 is the volume of the test liquid used for precipitation.

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