Method for preparing high-purity snowflake salt by using well and rock salt brine

Abstract

The invention relates to the technical field of preparation of snowflake salt, in particular to a method for preparing high-purity snowflake salt by using well and rock salt brine, which comprises the following steps: performing multistage purification and impurity removal, and dynamically adding magnesium in a gradient manner; performing variable-temperature evaporative crystallization; performing ultrasonic centrifugal drying; according to the method for preparing the high-purity snowflake salt by using the well and rock salt brine, provided by the invention, the purity and the quality of the snowflake salt are remarkably improved by precisely controlling brine purification, crystallization conditions and subsequent treatment; through cooperation of four steps of purification, magnesium addition, variable-temperature evaporation and ultrasonic drying, directional removal of impurities in the well and rock salt brine and accurate regulation and control of snowflake salt crystals are realized. Wherein multi-stage purification ensures that impurity residues are lower than the food safety standard, dynamic gradient magnesium adding and variable-temperature evaporation inhibit generation of carnallite from the crystallization mechanism level, and ultrasonic centrifugal drying optimizes the physical performance of a finished product through a physical means.

Description

Technical Field

[0001] The invention relates to the technical field of snowflake salt preparation, and in particular to a method for preparing high-purity snowflake salt by using well salt brine. Background Art

[0002] Snowflake salt, a type of edible salt crafted from seawater or underground brine using a specialized production process, possesses unique properties. Its granules are relatively large and loose, resembling snowflakes. Under a microscope, the crystals appear flake-shaped or funnel-shaped, and their pure white color creates a visually appealing aesthetic. Furthermore, snowflake salt dissolves quickly, offers a delicious flavor, and contains a variety of beneficial trace elements, replenishing essential nutrients.

[0003] With the improvement of people's living standards, the market demand for high-quality table salt is also increasing. Snowflake salt is favored by consumers for its unique crystal structure and pure quality. Currently, most of the snowflake salt available on the market uses seawater and sea salt as raw materials. Actively studying how to convert well brine into high-quality snowflake salt not only has important economic value but also provides new directions for comprehensive resource utilization. Exploring its preparation process is of great significance for effectively increasing the added value of salt products and fully meeting market demand.

[0004] Salt substances such as sodium chloride in brine exist in the form of ions. When the water begins to evaporate, the ion concentration in the solution will continue to rise. After reaching saturation, the electrostatic force between the ions will cause them to combine to form sodium chloride crystals. In this process, no new substances are born, but the salt substances are simply crystallized from the solution. As the water evaporates further, the solubility of the salt continues to decrease, and the salt molecules will arrange and aggregate in a certain lattice structure, eventually condensing into crystals. Magnesium ions are common impurities in brine, and their content also has an important influence on the brine crystallization process. The present invention uses precise temperature control and the addition of different amounts of magnesium-containing reagents to cause the salt molecules to arrange and combine into larger and loosely structured funnel-shaped crystals. Summary of the Invention

[0005] The present invention provides the following technical solutions:

[0006] A method for preparing high-purity snowflake salt using well salt brine comprises the following steps:

[0007] Multi-stage purification and impurity removal: Brine is purified using a combined process of lime-carbon dioxide pre-precipitation, ceramic membrane filtration, and chelate resin adsorption. First, calcium and magnesium ions are removed through an intermittent lime-carbon dioxide process, reducing the magnesium ion content of the purified brine to ≤0.05%. The brine is then filtered through a ceramic membrane with a pore size of 0.3-0.5μm to intercept micron-sized impurities. Finally, the filtered brine is passed through a chelate resin column filled with iminodiacetic acid resin to adsorb residual heavy metal ions, reducing the lead and arsenic content to ≤1ppm.

[0008] Dynamic gradient addition of magnesium: In the initial stage of constant temperature evaporation, specifically before the brine concentration reaches saturation, the magnesium-containing reagent is added dropwise in three pulses at a ratio of 18-25g / 1000g brine, with a single drop amount of 1 / 3 of the total mass, a drop rate of 2-3g / min, and an interval of 15-20min between each addition to form a magnesium ion concentration gradient;

[0009] Variable temperature evaporation crystallization: using a stepped temperature evaporation process, first evaporating at 60-70°C at a rate of 1-2g / min until the solution volume remains 70%, then heating to 80-90°C at a rate of ≥3g / min until the remaining 50%, inhibiting sodium sulfate co-crystallization;

[0010] Ultrasonic centrifugal drying: After evaporation, use 30-40kHz ultrasonic assisted centrifugation to break the liquid film on the crystal surface, and then dry it at a vacuum degree of ≤50kPa and a temperature of 60℃ for 8-10 minutes;

[0011] The centrifugal speed is 1500r / min and the centrifugal time is 1-3min.

[0012] As a further technical solution, the intermittent lime-carbon dioxide process is:

[0013] The well salt brine is heated to 40-55°C, and under stirring conditions at a rate of 200-300 r / min, lime milk is added in 2-3 portions, and the pH value of the brine is controlled to 10.5-11.5. After reacting for 30-45 minutes, CO2 gas is introduced until the pH value drops to 8.0-8.5, so that calcium and magnesium ions are precipitated as calcium carbonate and magnesium hydroxide, respectively; after solid-liquid separation, the calcium ion content in the supernatant is ≤50 ppm; the Ca(OH)2 concentration in the lime milk is 50-80 g / L.

[0014] As a further technical solution, the flow rate of the CO2 gas is 10-15 L / min.

[0015] As a further technical solution, the adsorption capacity of the chelating resin column is ≥50 mg / g resin, calculated as lead, and the adsorption selectivity coefficient for arsenic is ≥1000:1 relative to chloride ions.

[0016] As a further technical solution, the ceramic membrane is an α-alumina ceramic membrane, and the retention rate of particles with a particle size of ≥0.3μm during filtration is ≥99.9%; the operating pressure of the ceramic membrane filtration is 0.1-0.3MPa, and the membrane surface flow rate is 3-5m / s.

[0017] As a further technical solution, the chelate resin column adsorption is specifically as follows: the filtered brine is passed through a resin column filled with iminodiacetic acid type chelate resin at a flow rate of 2-3BV / h (bed volume / hour), and the brine temperature is controlled to be 29-35°C;

[0018] The resin bed in the chelate resin column has a height of 1.8-2.0 m and a diameter of 0.6-1.0 m.

[0019] As a further technical solution, the magnesium-containing reagent is stirred synchronously during the dropwise addition process, with a stirring rate of 100-150 r / min.

[0020] As a further technical solution, the magnesium-containing reagent is magnesium chloride or magnesium sulfate solution with a concentration of 120-160 g / L.

[0021] As a further technical solution, in the step-type temperature evaporation treatment, the evaporation time in the high temperature stage accounts for 40%-50% of the total evaporation time.

[0022] As a further technical solution, the high-purity snowflake salt prepared by the method is used in high-end food seasoning or precision chemical fields.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The method provided by the present invention for preparing high-purity snowflake salt using well salt brine significantly improves the purity and quality of the snowflake salt by precisely controlling brine purification, crystallization conditions and subsequent treatment.

[0025] First, the multi-stage purification and impurity removal improves the purity by systematically removing calcium, magnesium and heavy metal impurities from the brine through the synergistic effects of chemical precipitation, membrane filtration and resin adsorption; the dynamic gradient addition of magnesium regulates the crystal form and purity by forming a magnesium ion concentration gradient through the pulsed dropwise addition of magnesium-containing reagents, inducing the formation of loose funnel-shaped crystals and inhibiting the co-crystallization of impure salts; magnesium ions hinder the close accumulation of sodium chloride crystals through electrostatic action, prompting them to grow into a porous funnel-shaped structure, and at the same time combine with sulfate ions to form soluble magnesium sulfate, reducing the co-crystallization of sodium sulfate.

[0026] The effect of variable temperature evaporation crystallization on impurity suppression is as follows: through stepped temperature control, the evaporation rate and solubility are adjusted in stages, suppressing the precipitation of impurity salts such as sodium sulfate. The low-temperature stage (60-70°C, evaporation to 70% volume remaining): slowly concentrates the brine to reduce the supersaturation of sodium sulfate. The high-temperature stage (80-90°C, evaporation to 50% remaining, accounting for 40%-50% of the total time): accelerates the evaporation rate, causing sodium chloride to crystallize first, while the high temperature reduces the solubility of magnesium sulfate, preventing the co-precipitation of impurities.

[0027] Compared with constant temperature evaporation, the variable temperature process can reduce the sulfate content from 1.110% (dry basis) to 0.172% and increase the chloride ion content to 58.59% (dry basis).

[0028] Ultrasonic centrifugal drying optimizes the quality of the finished product, effectively removes the liquid film and moisture on the crystal surface, improves particle dispersion, and avoids impurity residue. 30-40kHz ultrasonic assisted centrifugation uses the cavitation effect to break the surface tension of the liquid film, and combined with vacuum drying, quickly reduces the moisture content to 1.27% (10.26% for natural air drying), reducing the adsorption of impurity ions in the mother liquor. After centrifugation, the crystal structure is loose (no adhesion), the funnel-shaped shape is highly retained, and the bulk density is as low as 547kg / m 3 , meeting the dispersion requirements of high-end food and chemical industries.

[0029] This invention achieves targeted impurity removal from well salt brine and precise control of snowflake salt crystals through a four-step process: purification, magnesium addition, variable temperature evaporation, and ultrasonic drying. Multi-stage purification ensures that residual impurities remain below food safety standards, dynamic gradient magnesium addition and variable temperature evaporation inhibit the formation of impurities through crystallization mechanisms, and ultrasonic centrifugal drying optimizes the physical properties of the finished product. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a microscope observation picture of the finished product of Example 1;

[0031] Figure 2 This is a microscope observation picture of commercially available snowflake salt;

[0032] Figure 3 This is a microscope observation picture of the finished product of Comparative Example 1;

[0033] Figure 4 This is a microscope observation picture of the finished product of Comparative Example 2. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0035] The present invention provides a method for preparing high-purity snowflake salt using well salt brine, comprising the following steps:

[0036] Multi-stage purification and impurity removal: Brine is purified using a combined process of lime-carbon dioxide pre-precipitation, ceramic membrane filtration, and chelate resin adsorption. First, calcium and magnesium ions are removed through an intermittent lime-carbon dioxide process, reducing the magnesium ion content of the purified brine to ≤0.05%. The brine is then filtered through a ceramic membrane with a pore size of 0.3-0.5μm to intercept micron-sized impurities. Finally, the filtered brine is passed through a chelate resin column filled with iminodiacetic acid resin to adsorb residual heavy metal ions, reducing the lead and arsenic content to ≤1ppm.

[0037] Dynamic gradient addition of magnesium: In the initial stage of constant temperature evaporation, specifically before the brine concentration reaches saturation, the magnesium-containing reagent is added dropwise in three pulses at a ratio of 18-25g / 1000g brine, with a single drop amount of 1 / 3 of the total mass, a drop rate of 2-3g / min, and an interval of 15-20min between each addition to form a magnesium ion concentration gradient;

[0038] Variable temperature evaporation crystallization: using a stepped temperature evaporation process, first evaporating at 60-70°C at a rate of 1-2g / min until the solution volume remains 70%, then heating to 80-90°C at a rate of ≥3g / min until the remaining 50%, inhibiting sodium sulfate co-crystallization;

[0039] Ultrasonic centrifugal drying: After evaporation, use 30-40kHz ultrasonic assisted centrifugation to break the liquid film on the crystal surface, and then dry it at a vacuum degree of ≤50kPa and a temperature of 60℃ for 8-10 minutes;

[0040] The centrifugal speed is 1500r / min and the centrifugal time is 1-3min.

[0041] The present invention first performs multi-stage purification and impurity removal. In this intermittent lime-carbon dioxide process, the following steps are used: well brine is heated to 40-55°C. Lime milk is added in two or three portions while stirring at a rate of 200-300 rpm. The pH of the brine is controlled to 10.5-11.5. After reacting for 30-45 minutes, CO₂ gas is introduced until the pH drops to 8.0-8.5, causing calcium and magnesium ions to precipitate as calcium carbonate and magnesium hydroxide, respectively. After solid-liquid separation, the calcium ion content in the supernatant is ≤50 ppm. The Ca(OH)₂ concentration in the lime milk is 50-80 g / L, and the CO₂ gas flow rate is 10-15 L / min.

[0042] In the present invention, the adsorption capacity of the chelate resin column is ≥50mg / g resin (in terms of lead), and the adsorption selectivity coefficient for arsenic is ≥1000:1 (relative to chloride ion). The chelate resin column adsorption specifically comprises the following steps: filtering brine at a flow rate of 2-3BV / h (bed volume / hour) through a resin column filled with iminodiacetic acid type chelate resin, and controlling the brine temperature to be 29-35°C; and the resin bed in the chelate resin column has a height of 1.8-2.0m and a diameter of 0.6-1.0m.

[0043] In the present invention, the ceramic membrane is an α-alumina ceramic membrane, and the retention rate of particles with a diameter of ≥0.3 μm during filtration is ≥99.9%. The operating pressure of the ceramic membrane filtration is 0.1-0.3 MPa, and the membrane surface flow rate is 3-5 m / s.

[0044] After completing the multi-stage purification and impurity removal, dynamic gradient magnesium addition is performed. In the present invention, the magnesium-containing reagent is stirred during the dropwise addition process at a stirring rate of 100-150 r / min. The magnesium-containing reagent is a magnesium chloride or magnesium sulfate solution with a concentration of 120-160 g / L.

[0045] Then, variable temperature evaporation crystallization is performed. In the present invention, in the step-by-step temperature evaporation process, the evaporation time in the high temperature stage accounts for 40%-50% of the total evaporation time.

[0046] Finally, ultrasonic centrifugal drying is performed to obtain high-purity snowflake salt. The high-purity snowflake salt prepared by the method can be used in high-end food seasoning or precision chemical fields.

[0047] The method provided by the present invention for preparing high-purity snowflake salt using well salt brine can effectively remove impurities in the brine through multi-stage purification and impurity removal, dynamic gradient magnesium addition, temperature-variable evaporation crystallization, ultrasonic centrifugal drying and other steps, and prepare high-purity snowflake salt. The method has the advantages of reasonable process, simple operation and high product purity.

[0048] To further illustrate the present invention, the following examples are provided for detailed description. The well salt brine used in the following examples of the present invention is conventional commercial brine, the lime milk, CO2 gas, magnesium-containing reagent (magnesium chloride solution, concentration 140 g / L), iminodiacetic acid type chelating resin, etc. used are all conventional commercial products, and the ceramic membrane used is an α-alumina ceramic membrane with a pore size of 0.4 μm.

[0049] Example 1

[0050] Multi-stage purification impurity removal: well salt brine is heated to 45 ℃, under the stir speed (S.S.) 250r / min condition, divide 2 times and add milk of lime (Ca (OH) Concentration 60g / L), control brine pH value to 11.0, after reaction 40min, feed CO Gas (flow 12L / min) is reduced to 8.3 to pH value, after solid-liquid separation, calcium ion content is 45ppm, magnesium ion content 0.04% in the supernatant; Then through ceramic membrane filtration (operating pressure 0.2MPa, membrane surface flow rate 4m / s); The brine after the last filtration is passed through the resin column (resin bed height 1.9m, diameter 0.8m, brine temperature 32 ℃) of filling iminodiacetic acid type chelating resin with the flow velocity of 2.5BV / h, and handles the back lead, arsenic content and are 0.8ppm.

[0051] Dynamic gradient addition of magnesium: In the initial stage of constant temperature evaporation (before the brine concentration reaches saturation), magnesium chloride solution is added dropwise in three pulses at a ratio of 20 g / 1000 g brine. The single drop amount is 1 / 3 of the total mass, the drop rate is 2.5 g / min, and the interval between each addition is 18 min. The stirring rate during the drop addition is 120 r / min.

[0052] Variable temperature evaporation crystallization: using a stepped temperature evaporation process, first evaporating at 65 ° C at a rate of 1.5 g / min until the solution volume remains 70%, then heating to 85 ° C and evaporating at a rate of 3.5 g / min until the remaining 50%. The evaporation time in the high temperature stage accounts for 45% of the total evaporation time.

[0053] Ultrasonic centrifugal drying: After evaporation, the liquid film on the crystal surface is broken by 35kHz ultrasonic-assisted centrifugation (centrifugal speed 1500r / min, centrifugal time 2min), and then dried at a vacuum degree of 40kPa and a temperature of 60°C for 9min to obtain high-purity snowflake salt.

[0054] Example 2

[0055] Multi-stage purification impurity removal: well salt brine is heated to 50 ℃, under the stir speed (S.S.) 280r / min condition, divide 3 times and add milk of lime (Ca (OH) Concentration 70g / L), control brine pH value to 11.2, after reaction 35min, feed CO Gas (flow 13L / min) is reduced to 8.2 to pH value, after solid-liquid separation, calcium ion content is 40ppm, magnesium ion content 0.03% in the supernatant; Then through ceramic membrane filtration (operating pressure 0.25MPa, membrane surface flow rate 4.5m / s); The brine after the filtration is with the flow velocity of 2BV / h by the resin column (resin bed height 1.85m, diameter 0.7m, brine temperature 30 ℃), and the back lead and arsenic content of the processing are 0.7ppm.

[0056] Dynamic gradient addition of magnesium: In the initial stage of constant temperature evaporation (before the brine concentration reaches saturation), magnesium chloride solution is added dropwise in three pulses at a ratio of 22 g / 1000 g brine. The single drop amount is 1 / 3 of the total mass, the drop rate is 2.8 g / min, and the interval between each addition is 16 min. The stirring rate during the drop addition is 130 r / min.

[0057] Variable temperature evaporation crystallization: using a stepped temperature evaporation process, first evaporating at 68 ° C at a rate of 1.2 g / min until the solution volume remains 70%, then heating to 88 ° C and evaporating at a rate of 3.2 g / min until the remaining 50%. The evaporation time in the high temperature stage accounts for 48% of the total evaporation time.

[0058] Ultrasonic centrifugal drying: After evaporation, the liquid film on the crystal surface is broken by 38kHz ultrasonic-assisted centrifugation (centrifugal speed 1500r / min, centrifugal time 1.5min), and then dried for 8.5min under vacuum degree 35kPa and temperature 60℃ to obtain high-purity snowflake salt.

[0059] Example 3

[0060] Multi-stage purification and impurity removal: well salt brine is heated to 40 ℃, under the stirring speed (S.S.) 200r / min condition, divide 2 times and add lime milk (Ca (OH) Concentration 50g / L), control brine pH value to 10.5, after reaction 45min, feed CO Gas (flow 10L / min) is reduced to 8.0 to pH value, after solid-liquid separation, calcium ion content is 50ppm, magnesium ion content 0.05% in the supernatant; Then through ceramic membrane filtration (operating pressure 0.1MPa, membrane surface flow rate 3m / s); The brine after the filter at last is passed through the resin column (resin bed height 1.8m, diameter 0.6m, brine temperature 29 ℃) of filling iminodiacetic acid type chelating resin with the flow velocity of 3BV / h, and handles the back lead, arsenic content and are 1ppm.

[0061] Dynamic gradient addition of magnesium: In the initial stage of constant temperature evaporation (before the brine concentration reaches saturation), magnesium chloride solution is added dropwise in three pulses at a ratio of 18 g / 1000 g brine. The single drop amount is 1 / 3 of the total mass, the drop rate is 2 g / min, and the interval between each addition is 20 min. The stirring rate during the drop addition is 100 r / min.

[0062] Variable temperature evaporation crystallization: using a stepped temperature evaporation process, first evaporating at 60 ° C at a rate of 1g / min until the solution volume remains 70%, then heating to 80 ° C and evaporating at a rate of 3g / min until the remaining 50%. The evaporation time in the high temperature stage accounts for 40% of the total evaporation time.

[0063] Ultrasonic centrifugal drying: After evaporation, the liquid film on the crystal surface is broken by 30kHz ultrasonic-assisted centrifugation (centrifugal speed 1500r / min, centrifugal time 3min), and then dried for 8min under vacuum degree 50kPa and temperature 60℃ to obtain high-purity snowflake salt.

[0064] Example 4

[0065] Multi-stage purification impurity removal: well salt brine is heated to 55 ℃, under the stir speed (S.S.) 300r / min condition, divide and add lime milk (Ca (OH) 2 concentration 80g / L) for 3 times, control brine pH value to 11.5, after reaction 30min, feed CO 2 gas (flow 15L / min) is reduced to 8.5 to the pH value, after solid-liquid separation, calcium ion content is 35ppm, magnesium ion content 0.02% in the supernatant; Then through ceramic membrane filtration (operating pressure 0.3MPa, membrane surface flow rate 5m / s); The brine after the last filtration is passed through the resin column (resin bed height 2.0m, diameter 1.0m, brine temperature 35 ℃) of filling iminodiacetic acid type chelating resin with the flow velocity of 2.8BV / h, and the back lead and arsenic content of handling are 0.6ppm.

[0066] Dynamic gradient addition of magnesium: In the initial stage of constant temperature evaporation (before the brine concentration reaches saturation), magnesium chloride solution is added dropwise in three pulses at a ratio of 25g / 1000g brine. The single drop amount is 1 / 3 of the total mass, the drop rate is 3g / min, and the interval between each addition is 15min. The stirring rate during the drop addition is 150r / min.

[0067] Variable temperature evaporation crystallization: using a stepped temperature evaporation process, first evaporating at 70 ° C at a rate of 2g / min until the solution volume remains 70%, then heating to 90 ° C and evaporating at a rate of 4g / min until the remaining 50%. The evaporation time in the high temperature stage accounts for 50% of the total evaporation time.

[0068] Ultrasonic centrifugal drying: After evaporation, the liquid film on the crystal surface is broken by 40kHz ultrasonic-assisted centrifugation (centrifugal speed 1500r / min, centrifugal time 1min), and then dried for 10min under vacuum degree 20kPa and temperature 60℃ to obtain high-purity snowflake salt.

[0069] Example 5

[0070] The multi-stage purification and impurity removal steps are the same as those in Example 1;

[0071] Dynamic gradient addition of magnesium: at the initial stage of constant temperature evaporation (before the brine concentration reaches saturation), the magnesium-containing reagent is replaced with magnesium sulfate solution (concentration 160 g / L), which is added dropwise in three pulses at a ratio of 21 g / 1000 g brine. The single drop amount is 1 / 3 of the total mass, the drop rate is 2.5 g / min, and the interval between each addition is 18 min. The stirring rate during the dropwise addition is 120 r / min.

[0072] The steps of temperature-variable evaporation crystallization and ultrasonic centrifugal drying are the same as those in Example 1 to obtain high-purity snowflake salt.

[0073] Comparative Example 1

[0074] The treatment method provided in Example 1 was adopted, except that the dynamic gradient magnesium addition step was omitted, and the other steps were the same as in Example 1.

[0075] Comparative Example 2

[0076] The treatment method provided in Example 1 was adopted, except that in the variable temperature evaporation crystallization step, evaporation was performed at 65° C. at a rate of 1.5 g / min until the solution volume remained at 50%, and no step-by-step temperature evaporation treatment was performed. The other steps were the same as in Example 1.

[0077] test

[0078] This experiment is based on the process parameters in the specific implementation method. By exploring the impact of various process conditions on the quality of snowflake salt, the feasibility and optimization effect of the process are verified.

[0079] Raw materials and instruments

[0080] Raw materials: Glauber's salt type well salt brine (purified by intermittent lime-carbon dioxide process, the main components are NaCl, Na2SO4, and a small amount of Ca 2+ Mg 2+ , magnesium chloride solution (concentration 140g / L), α-alumina ceramic membrane (pore size 0.4μm), iminodiacetic acid type chelating resin.

[0081] Experimental plan and results

[0082] Verification of multi-stage purification and impurity removal effect

[0083] Adopt the purification parameters of Example 1 (lime milk concentration 60g / L, CO2 flow 12L / min, ceramic membrane pressure 0.2MPa, chelating resin column flow velocity 2.5BV / h), measure the ion content of brine before and after purification.

[0084] result:

[0085] Brine before purification: Mg 2+ Content 0.3%, Ca 2+ Content 200ppm, Pb 2+ 2ppm, As 2+ 1.5ppm.

[0086] Purified brine: Mg 2+ Content 0.04% (≤0.05%), Ca 2+ Content 45ppm (≤50ppm), Pb 2+ 、As 3+ All dropped to 0.8ppm (≤1ppm).

[0087] Conclusion: The multi-stage purification process effectively removes calcium, magnesium and heavy metal ions from brine and meets the requirements of subsequent crystallization process.

[0088] Effect of dynamic gradient magnesium addition on crystal form

[0089] With reference to the magnesium addition parameters of Examples 1-5 (18-25 g / 1000 g brine, added dropwise in three pulses), the effects of different magnesium-containing reagent addition amounts on the crystal morphology were compared, with the blank group (no magnesium added) as the control.

[0090] result:

[0091] Blank group (Comparative Example 1): The crystals were in the form of fine particles without a funnel-shaped structure, with a bulk density of 722 kg / m3 and a magnesium content of 0.207% (dry basis).

[0092] Example 1 (20 g / 1000 g magnesium added): 73.8% of the crystals were regular funnel-shaped with a loose structure and a bulk density of 547 kg / m 3 , magnesium content 0.059% (dry basis).

[0093] Example 2 (22 g / 1000 g magnesium): 75.0% of the crystals were regular funnel-shaped with a loose structure and a bulk density of 543 kg / m 3 , magnesium content 0.051% (dry basis).

[0094] Example 3 (18 g / 1000 g magnesium): 72.2% of the crystals were regular funnel-shaped with a loose structure and a bulk density of 551 kg / m 3 , magnesium content 0.055% (dry basis).

[0095] Example 4 (25 g / 1000 g magnesium added): 74.3% of the crystals were regular funnel-shaped with a loose structure and a bulk density of 550 kg / m 3 , magnesium content 0.056% (dry basis).

[0096] Example 5 (21 g / 1000 g magnesium added): 74.7% of the crystals were regular funnel-shaped with a loose structure and a bulk density of 549 kg / m 3 , magnesium content 0.053% (dry basis).

[0097] Conclusion: Dynamic gradient addition of magnesium can promote the formation of funnel-shaped crystals, reduce bulk density, and improve the quality of snowflake salt.

[0098] Verification of variable temperature evaporation crystallization effect

[0099] The step-by-step temperature evaporation (65°C → 85°C) of Example 1 was compared with the constant temperature evaporation (65°C throughout) of Comparative Example 2 to observe the crystal morphology and sodium sulfate co-crystallization.

[0100] result:

[0101] Step evaporation (Example 1): The evaporation rate is slow at first and then fast, with the high temperature stage (85° C.) accounting for 45%. The crystals are mainly thin funnel-shaped, with a sulfate content of 0.172% (dry basis), and no obvious sodium sulfate crystals.

[0102] Constant temperature evaporation (Comparative Example 2): The evaporation rate is uniform, the crystals are thick and compact, the sulfate content is 1.110% (dry basis), and sodium sulfate co-crystallization is present.

[0103] Conclusion: Temperature-variable evaporation can inhibit sodium sulfate co-crystallization and improve the purity of snowflake salt.

[0104] Verification of ultrasonic centrifugal drying effect

[0105] The ultrasonic centrifugal drying (35 kHz, 1500 r / min, 2 min) of Example 1 was compared with natural air drying (the centrifugal drying step was omitted in Example 1), and the moisture content and dispersibility of the finished products were measured.

[0106] result:

[0107] Ultrasonic centrifugal drying: moisture content 1.27%, loose crystals without adhesion, high proportion of funnel-shaped structure.

[0108] Natural drying in the shade: moisture content 10.26%, severe crystal adhesion, high bulk density.

[0109] Conclusion: Ultrasonic centrifugal drying can effectively break the liquid film on the crystal surface, reduce the moisture content and improve the dispersion of particles.

[0110] Comparison of physical and chemical indicators of finished products

[0111] Table 1

[0112]

[0113] It can be seen from Table 1 that all indicators of the finished product of Example 1 meet the industry standards, and the bulk density, magnesium content, and sulfate content are better than those of commercially available products, indicating that the snowflake salt prepared by this process is of high purity and excellent quality.

[0114] Through experiments, it is verified that the method for preparing high-purity snowflake salt from well salt brine provided by the present invention can effectively control the crystal morphology and improve the purity and looseness of the product through the synergistic effect of multi-stage purification and impurity removal, dynamic gradient magnesium addition, variable temperature evaporation crystallization and ultrasonic centrifugal drying. The process parameters are scientific and feasible, and it has the potential for industrial production. Further large-scale experiments can be carried out in the future to optimize the process stability.

[0115] Figure 1 This is a microscope observation picture of the finished product of Example 1; Figure 2 This is a microscope observation picture of commercially available snowflake salt; Figure 3 This is a microscope observation picture of the finished product of Comparative Example 1; Figure 4 This is a microscope observation picture of the finished product of Comparative Example 2; it can be seen that the finished product of Example 1 is white and translucent in appearance, the crystals are relatively regular, the funnel-shaped and flaky crystals are intertwined, and most of the crystals are funnel-shaped, the finished product has a low bulk density and is relatively loose; the commercially available snowflake salt has relatively few funnel-shaped crystals, the finished product has a high bulk density, and the looseness is relatively low; the finished product of Comparative Example 1 is white fine particles, and no funnel-shaped crystals are observed; the crystals of the finished product of Comparative Example 2 are white, most of them are slightly thick funnel-shaped, and some are slightly thick flakes, and the crystals are slightly compact.

[0116] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. The preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification.

Claims

1. A method for preparing high-purity snowflake salt using well salt brine, characterized in that: The following steps are involved: Multi-stage purification and impurity removal: Brine is purified using a combined process of lime-carbon dioxide pre-precipitation, ceramic membrane filtration, and chelate resin adsorption. First, calcium and magnesium ions are removed through an intermittent lime-carbon dioxide process, reducing the magnesium ion content of the purified brine to ≤0.05%. The brine is then filtered through a ceramic membrane with a pore size of 0.3-0.5μm to intercept micron-sized impurities. Finally, the filtered brine is passed through a chelate resin column filled with iminodiacetic acid resin to adsorb residual heavy metal ions, reducing the lead and arsenic content to ≤1ppm. Dynamic gradient addition of magnesium: In the initial stage of constant temperature evaporation, specifically before the brine concentration reaches saturation, the magnesium-containing reagent is added dropwise in three pulses at a ratio of 18-25g / 1000g brine, with a single drop amount of 1 / 3 of the total mass, a drop rate of 2-3g / min, and an interval of 15-20min between each addition to form a magnesium ion concentration gradient; Variable temperature evaporation crystallization: using a stepped temperature evaporation process, first evaporating at 60-70°C at a rate of 1-2g / min until the solution volume remains 70%, then heating to 80-90°C at a rate of ≥3g / min until the remaining 50%, inhibiting sodium sulfate co-crystallization; Ultrasonic centrifugal drying: After evaporation, use 30-40kHz ultrasonic assisted centrifugation to break the liquid film on the crystal surface, and then dry it at a vacuum degree of ≤50kPa and a temperature of 60℃ for 8-10 minutes; The centrifugal speed is 1500r / min and the centrifugal time is 1-3min.

2. The method for preparing high-purity snowflake salt using well salt brine according to claim 1, characterized in that: The intermittent lime-carbon dioxide process is: The well salt brine is heated to 40-55°C, and under stirring conditions at a rate of 200-300 r / min, lime milk is added in 2-3 portions, and the pH value of the brine is controlled to 10.5-11.

5. After reacting for 30-45 minutes, CO2 gas is introduced until the pH value drops to 8.0-8.5, so that calcium and magnesium ions are precipitated as calcium carbonate and magnesium hydroxide, respectively; after solid-liquid separation, the calcium ion content in the supernatant is ≤50 ppm; the Ca(OH)2 concentration in the lime milk is 50-80 g / L.

3. The method for preparing high-purity snowflake salt using well salt brine according to claim 2, characterized in that: The flow rate of the CO2 gas is 10-15 L / min.

4. The method for preparing high-purity snowflake salt using well salt brine according to claim 1, characterized in that: The adsorption capacity of the chelating resin column is ≥50 mg / g resin, calculated as lead, and the adsorption selectivity coefficient for arsenic is ≥1000:1 relative to chloride ions.

5. The method for preparing high-purity snowflake salt using well salt brine according to claim 1, characterized in that: The ceramic membrane is an α-alumina ceramic membrane, and the retention rate of particles with a particle size of ≥0.3 μm during the filtration process is ≥99.9%; the operating pressure of the ceramic membrane filtration is 0.1-0.3 MPa, and the membrane surface flow rate is 3-5 m / s.

6. The method for preparing high-purity snowflake salt using well salt brine according to claim 1, characterized in that: The chelate resin column adsorption is specifically as follows: the filtered brine is passed through a resin column filled with iminodiacetic acid type chelate resin at a flow rate of 2-3 bed volumes / hour, and the brine temperature is controlled at 29-35°C; The resin bed in the chelate resin column has a height of 1.8-2.0 m and a diameter of 0.6-1.0 m.

7. The method for preparing high-purity snowflake salt using well salt brine according to claim 1, characterized in that: The magnesium-containing reagent is added dropwise with simultaneous stirring at a stirring rate of 100-150 r / min.

8. The method for preparing high-purity snowflake salt using well salt brine according to claim 1, characterized in that: The magnesium-containing reagent is magnesium chloride or magnesium sulfate solution with a concentration of 120-160 g / L.

9. The method for preparing high-purity snowflake salt using well salt brine according to claim 1, characterized in that: In the step-by-step temperature evaporation process, the evaporation time in the high-temperature stage accounts for 40%-50% of the total evaporation time.

10. The method for preparing high-purity snowflake salt using well salt brine according to claim 1, characterized in that: The high-purity snowflake salt prepared by the method is used in high-end food seasoning or precision chemical fields.

Images