Pearl bleaching process based on phase transfer catalyzed oxidation

Abstract

The present application belongs to the field of pearl processing, and relates to a pearl bleaching method based on phase transfer catalytic oxidation. Pearl grains are soaked in a potassium chlorate aqueous solution, cleaned, air-dried, and oven-dried. The oven-dried pearl grains are soaked in an 18-crown-6 alcohol organic solution, bleached until decolorization is complete, the pearl grains are removed, cleaned after being soaked in clean water, and dried to obtain finished products. The present application pre-permeates the oxidant potassium chlorate without oxidation capacity into the pearl layer and deposits it between the pearl layers, and then uses an organic phase containing crown ether (18-crown-6) to dissolve the potassium chlorate into the organic phase through complexation, so that the chlorate ion produces oxidation, and the pigment is oxidized. The present application can keep the bleaching oxidation degree of the pearl surface layer and the pearl deep layer from being greatly different, avoids the problem that the pearl layer surface is excessively oxidized and the pearl deep layer has insufficient oxidation capacity during the bleaching process, and has the advantages of simple process, simple operation, and good bleaching oxidation effect.

Description

Technical Field

[0001] This invention belongs to the field of pearl processing and relates to a pearl bleaching method, specifically a method for bleaching pearl particles using crown ether-regulated phase transfer catalysis with solid potassium chlorate. Background Technology

[0002] Pearls are beloved ornaments for their pure white color, iridescent sheen, warm and delicate luster, and beautiful natural shape. However, most pearls (including natural and cultured pearls) cannot be used directly in jewelry because they have defects such as variations in luster and color, as well as dullness, color differences, black spots, and blemishes. They must undergo bleaching treatment to make the pearls whiter and more translucent, increasing their luster to meet the requirements of jewelry.

[0003] Currently, common methods for pearl decolorization include boiling in water, hydrogen peroxide bleaching, or a combination of both. Hydrogen peroxide bleaching involves diluting hydrogen peroxide in water or an organic solvent, then allowing the solution to slowly penetrate the pearl layer from the surface inwards. The hydrogen peroxide in the solution gradually oxidizes the pigments and other organic matter in the pearl, causing it to whiten. However, during the penetration of the bleaching solution (hydrogen peroxide) from the surface inwards, the surface pearl layer begins to oxidize first. The oxidizing agent in the bleaching solution that penetrates first is consumed, reducing its concentration. This results in the bleaching solution having lower oxidizing power as it penetrates deeper into the pearl layer, while the oxidizing power of the bleaching solution closer to the pearl surface is higher. This can easily lead to over-oxidation of the pearl layer on the surface, causing the pearl to become brittle and easily peel off, while the deeper layers of the pearl lack sufficient oxidation power, leaving more pigment residue and affecting the bleaching effect. Furthermore, hydrogen peroxide can oxidize not only pigments but also many organic substances, including pearl protein, causing excessive oxidation of the pearl protein, which can also lead to a brittle pearl layer that is easily peeled off, thus affecting the quality of the pearl. Summary of the Invention

[0004] The purpose of this invention is to provide a pearl bleaching method based on phase transfer catalytic oxidation. First, potassium chlorate, which does not have oxidative bleaching ability, is adhered in solid form between the pearl layers. Then, it is complexed with 18-crown(ether)-6 to produce an oxidative reaction, which oxidizes the pigment and improves the oxidative bleaching ability. This method can maintain a small difference in the degree of bleaching oxidation between the pearl surface and the deep pearl layers, avoiding the problem of excessive oxidation of the pearl surface and insufficient oxidation ability of the deep pearl layers during conventional hydrogen peroxide bleaching.

[0005] The technical principle employed in this invention is as follows: Potassium chlorate, an oxidant with no oxidizing ability, is pre-permeated into the pearl layer and deposited between the pearl layers. Then, it permeates into an organic phase containing crown ether (18-crown(ether)-6) (using alcohols as solvents). Utilizing the cavitation effect of 18-crown(ether)-6, potassium chlorate is dissolved into the organic phase through the complexation of potassium ions (crown ether has a strong complexing and dragging effect on potassium ions). This results in a strong oxidizing effect from the negative ions (chlorate ions), oxidizing the pigment. At the same time, to reduce the corrosive effect of acidic substances on the pearl layer during the oxidation process, the pH of the 18-crown(ether)-6 solution is adjusted to weakly alkaline, and the concentration of 18-crown(ether)-6 in the solution is controlled to avoid excessive oxidative bleaching ability that could damage the pearl layer.

[0006] The technical solution adopted in this invention:

[0007] A pearl bleaching method based on phase transfer catalytic oxidation includes the following steps:

[0008] Step S1: Prepare a potassium chlorate aqueous solution with a concentration of 1.0-3.0%. Soak the pretreated pearl grains in the potassium chlorate aqueous solution. After the solution has fully penetrated into the pearl layer to the deep layer of the pearl, take out the pearl grains, clean them, and dry them for later use.

[0009] Step S2: Dry the pearl grains to dehydrate the solution in the pearl layer, and the potassium chlorate will turn into a solid powder that adheres to the pearl layer for later use.

[0010] Step S3: Prepare an organic solution of 18-crown(ether)-6 alcohol with a mass-volume ratio of 50.0-60.0 mg / mL using alcohol as a solvent, and adjust the pH of the organic solution of alcohol to 7-8.

[0011] Step S4: Soak the dried pearls from step S2 in an 18-crown(ether)-6 alcohol organic solution and bleach until completely decolorized. Remove the pearls, soak them in clean water, rinse them clean, and dry them to obtain the finished product.

[0012] Preferably, in step S1, the pearl grains are pretreated by soaking in methanol and ammonia, respectively.

[0013] Preferably, in step S1, an appropriate amount of surfactant is added to the potassium chlorate aqueous solution to promote the penetration of the potassium chlorate aqueous solution into the pearl particles. The surfactant is polyethylene glycol, SDS, or Tween.

[0014] Preferably, in step S2, the drying method is vacuum drying. Further, the drying temperature is 40–80°C.

[0015] Preferably, in step S3, the alcohol is methanol or ethanol.

[0016] Preferably, in step S3, the pH value of the alcohol organic solution is adjusted by using ammonium chloride and ammonia.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) In this invention, potassium chlorate, an oxidant with no oxidizing ability, is first penetrated into the pearl layer and deposited between the pearl layers. Then, potassium chlorate is dissolved into the organic phase containing crown ether (18-crown(ether)-6) through complexation, so that the chlorate ions produce an oxidizing effect and oxidize the pigment. This can keep the difference in the degree of bleaching oxidation between the pearl surface and the pearl depth small, and avoid the problem of excessive oxidation of the pearl surface and insufficient oxidation ability of the pearl depth during the bleaching process. The process is simple, easy to operate, and has a good bleaching oxidation effect.

[0019] (2) Add appropriate amounts of ammonia and ammonium chloride to the organic solvent phase to control the pH of the solution, avoid the acidic substances generated during the oxidation reaction from corroding the pearl layer, and at the same time do not affect the bleaching effect of the bleaching solution.

[0020] (3) This method is suitable for long-term bleaching of pearls and has a significantly less damaging effect on the pearl layer than traditional hydrogen peroxide bleaching technology. It is beneficial for bleaching dark pearls that are difficult to bleach using traditional methods. However, long-term bleaching of pearls with hydrogen peroxide will cause serious damage to the pearls, and short bleaching time will lead to problems such as incomplete bleaching and decolorization. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described in detail below with reference to the examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, the experimental methods in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available, with analytical grade reagents being preferred.

[0022] In this application, the luster of the pearls is graded according to the national standard GB / T18781-2008 Pearl Grading. Color is classified into four levels: light (leaking to the naked eye), medium (clearly visible), dark (deep), and colorless (not visible to the naked eye).

[0023] In this application, the damage to the pearl surface is graded, and the pearl surface is observed using a magnifying glass with a display screen at 100-500x magnification, and the pearl surface is scratched with a fingernail:

[0024] Perfect Grade: The surface has no obvious cracks or flaky deposits. When the pearl is scratched vigorously with a fingernail, there is no peeling.

[0025] Grade 1 damage: There are no obvious cracks or flaky deposits on the surface. If you scratch the surface of the pearl with your fingernail, a little powder will come off. This phenomenon will not occur after polishing and will not affect the use.

[0026] Level 2 damage: The surface has slight cracks and flaky deposits. Scratching the pearl surface with a fingernail will cause slight powder to fall off. This phenomenon does not occur after polishing and does not affect the use.

[0027] Level 3 damage: The surface has obvious cracks and flaky deposits. When the pearl surface is scratched with a fingernail, obvious powder comes off. This phenomenon does not occur after polishing. It needs to be downgraded or even scrapped.

[0028] Example 1 (Pearl diameter 6-7mm)

[0029] Freshwater beads (6-7mm in diameter) were soaked in methanol and 0.1% ammonia for 48 hours respectively, and then sorted by color, with 200 beads of each color taken.

[0030] Preparation of bleach solution:

[0031] Solution A: Add 214g potassium chlorate and 260g polyethylene glycol (200) to every 10 liters of water, and stir until completely dissolved.

[0032] Solution B: Add 510g of 18-crown(ether)-6 per 10 liters of methanol, and stir until completely dissolved. Adjust the pH to 7.0 with ammonium chloride and ammonia (reagent grade).

[0033] The pearl grains were immersed in solution A at 50°C for 48 hours, then cleaned and dried in a vacuum drying oven at 50°C and 0.08 MPa for 4 hours. The resulting pearl grains were then bleached by immersion in solution B.

[0034] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 1.1 to 1.3.

[0035] Table 1.1 Color grading of pearl grains before and after bleaching and decolorization

[0036]

[0037] Table 1.2 Grading of the luster of pearls before and after bleaching

[0038]

[0039]

[0040] Table 1.3 Grading of Pearl Surface Damage Before and After Discoloration

[0041]

[0042] Example 2 (Pearl diameter 10-11mm)

[0043] Freshwater beads (10-11 mm in diameter) were soaked in methanol and 0.1% ammonia for 48 hours respectively, and then sorted by color, with 200 beads of each color taken.

[0044] Preparation of bleach solution:

[0045] Solution A: Add 120g potassium chlorate and 220g Tween 40 to every 10 liters of water, and stir until completely dissolved.

[0046] Solution B: Add 575g of 18-crown(ether)-6 per 10 liters of ethanol, and stir until completely dissolved. Adjust the pH to 8.0 with ammonium chloride and ammonia (reagent grade).

[0047] The pearl grains were immersed in solution A at 50°C for 48 hours, then cleaned and dried in a vacuum drying oven at 60°C and 0.08 MPa for 4 hours. The resulting pearl grains were then bleached by immersion in solution B.

[0048] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 2.1 to 2.3.

[0049] Table 2.1 Color grading of pearls before and after bleaching

[0050]

[0051]

[0052] Table 2.2 Grading of the luster of pearls before and after bleaching

[0053]

[0054] Table 2.3 Grading of Pearl Surface Damage Before and After Discoloration

[0055]

[0056] Example 3 (Seawater pearls, 6-7mm in diameter)

[0057] Seawater pearls (6-7mm in diameter) were soaked in methanol and 0.1% ammonia for 48 hours respectively, and then sorted by color, with 200 pearls of each color taken.

[0058] Preparation of bleach solution:

[0059] Solution A: Add 244g potassium chlorate and 300g polyethylene glycol (100) to every 10 liters of water, and stir until completely dissolved.

[0060] Solution B: Add 528g of 18-crown(ether)-6 per 10 liters of methanol, and stir until completely dissolved. Adjust the pH to 7.5 with ammonium chloride and ammonia (reagent grade).

[0061] The pearl grains were immersed in solution A at 50°C for 48 hours, then cleaned and dried in a vacuum drying oven at 60°C and 0.08 MPa for 4 hours. The resulting pearl grains were then bleached by immersion in solution B.

[0062] The damage to the color and luster of the pearl grains before and after bleaching was classified and statistically analyzed. The results are shown in Tables 3.1 to 3.3.

[0063] Table 3.1 Color grading of pearls before and after bleaching

[0064]

[0065] Table 3.2 Grading of the luster of pearls before and after bleaching

[0066]

[0067] Table 3.3 Grading of Pearl Surface Damage Before and After Discoloration

[0068]

[0069] Example 4 (pearl diameter 6-7mm)

[0070] Freshwater beads (6-7mm in diameter) were soaked in methanol and 0.1% ammonia for 48 hours respectively, and then sorted by color, with 200 beads of each color taken.

[0071] Preparation of bleach solution:

[0072] Solution A: Add 285g potassium chlorate and 320g polyethylene glycol (400) to every 10 liters of water, and stir until completely dissolved.

[0073] Solution B: Add 590g of 18-crown(ether)-6 per 10 liters of methanol, and stir until completely dissolved. Adjust the pH to 8.0 with ammonium chloride and ammonia (reagent grade).

[0074] The pearl grains were immersed in solution A at 50°C for 48 hours, then cleaned and dried in a vacuum drying oven at 70°C and 0.08 MPa for 4 hours. The resulting pearl grains were then bleached by immersion in solution B.

[0075] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 4.1 to 4.3.

[0076] Table 4.1 Color grading of pearl grains before and after bleaching and decolorization

[0077]

[0078] Table 4.2 Grading of the luster of pearls before and after bleaching

[0079]

[0080] Table 4.3 Grading of Pearl Surface Damage Before and After Discoloration

[0081]

[0082]

[0083] Control group 1 (without 18-crown(ether)-6)

[0084] Freshwater pearls (6-7mm in diameter) were bleached. The pretreatment, color classification, A solution, and subsequent soaking, drying, and bleaching methods were the same as in Example 3. The bleaching time was 32 days.

[0085] Solution B: Take methanol, without adding 18-crown(ether)-6, and adjust the pH to 7.5 with ammonium chloride and ammonia (reagent grade).

[0086] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 5.1 to 5.3.

[0087] Table 5.1 Color grading of pearls before and after bleaching

[0088]

[0089] Table 5.2 Grading of the luster of pearls before and after bleaching

[0090]

[0091]

[0092] Table 5.3 Grading of Pearl Surface Damage Before and After Discoloration

[0093]

[0094] Control group 2 (without potassium chlorate)

[0095] Freshwater pearls (6-7mm in diameter) were bleached. The pretreatment, color classification, B solution, and subsequent immersion soaking, drying, and immersion bleaching methods were the same as in Example 3. The bleaching time was 32 days.

[0096] Solution A: Add 300g of polyethylene glycol (100) to every 10 liters of water and stir until completely dissolved.

[0097] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 6.1 to 6.3.

[0098] Table 6.1 Color grading of pearls before and after bleaching

[0099]

[0100] Table 6.2 Grading of the luster of pearls before and after bleaching

[0101]

[0102]

[0103] Table 6.3 Grading of Pearl Surface Damage Before and After Discoloration

[0104]

[0105] Control group 3 (potassium chlorate was replaced with potassium nitrate)

[0106] Freshwater pearls (6-7mm in diameter) were bleached. The pretreatment, color classification, B solution, and subsequent soaking, drying, and bleaching methods were the same as in Example 3. The bleaching time was 16 days.

[0107] Solution A: Add 244g potassium nitrate and 300g polyethylene glycol (100) to every 10 liters of water, and stir until completely dissolved.

[0108] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 7.1 to 7.3.

[0109] Table 7.1 Color grading of pearls before and after bleaching

[0110]

[0111] Table 7.2 Grading of the luster of pearls before and after bleaching

[0112]

[0113] Table 7.3 Grading of Pearl Surface Damage Before and After Discoloration

[0114]

[0115] Control group 4 (without adding buffer, ammonia, or ammonium chloride to adjust pH)

[0116] Freshwater pearls (6-7mm in diameter) were bleached. The pretreatment, color classification, A solution, and subsequent soaking, drying, and bleaching methods were the same as in Example 3. The bleaching time was 16 days.

[0117] Solution B: Add 528g of 18-crown(ether)-6 to every 10 liters of methanol and stir until completely dissolved.

[0118] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 8.1 to 8.3.

[0119] Table 8.1 Color grading of pearls before and after bleaching

[0120]

[0121] Table 8.2 Grading of the luster of pearls before and after bleaching

[0122]

[0123] Table 8.3 Grading of Pearl Surface Damage Before and After Discoloration

[0124]

[0125] Control group 5 (pH of solution B adjusted to 9.0)

[0126] Freshwater pearls (6-7mm in diameter) were bleached. The pretreatment, color classification, A solution, and subsequent soaking, drying, and bleaching methods were the same as in Example 3. The bleaching time was 16 days.

[0127] Solution B: Add 528g of 18-crown(ether)-6 per 10 liters of methanol, and stir until completely dissolved. Adjust the pH to 9.0 using ammonium chloride and ammonia (reagent grade).

[0128] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 9.1-9.3.

[0129] Table 9.1 Color grading of pearls before and after bleaching

[0130]

[0131]

[0132] Table 9.2 Grading of the luster of pearls before and after bleaching

[0133]

[0134] Table 9.3 Grading of Pearl Surface Damage Before and After Discoloration

[0135]

[0136] Control group 6 (pH of solution B adjusted to 6.0)

[0137] Freshwater pearls (6-7mm in diameter) were bleached. The pretreatment, color classification, A solution, and subsequent soaking, drying, and bleaching methods were the same as in Example 3. The bleaching time was 16 days.

[0138] Solution B: Add 528g of 18-crown(ether)-6 per 10 liters of methanol, and stir until completely dissolved. Adjust the pH to 6.0 using ammonium chloride and ammonia (reagent grade).

[0139] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 10.1-10.3.

[0140] Table 10.1 Color grading of pearls before and after bleaching

[0141]

[0142]

[0143] Table 10.2 Grading of the luster of pearls before and after bleaching

[0144]

[0145] Table 10.3 Grading of Pearl Surface Damage Before and After Discoloration

[0146]

[0147] Control group 7 (treated with potassium chlorate but not dried)

[0148] Freshwater pearls (6-7mm in diameter) were bleached. The pretreatment, color classification, A solution, B solution, and subsequent immersion soaking and bleaching methods were the same as in Example 3. The bleaching time was 16 days.

[0149] Immerse each of the samples in solution A at 50°C for 48 hours, then rinse them clean, and finally bleach them in solution B.

[0150] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 11.1-11.3.

[0151] Table 11.1 Color grading of pearls before and after bleaching

[0152]

[0153] Table 11.2 Grading of the luster of pearls before and after bleaching

[0154]

[0155] Table 11.3 Grading of Pearl Surface Damage Before and After Discoloration

[0156]

[0157] Control group 8 (potassium chlorate concentration higher than 3%)

[0158] Freshwater pearls (6-7mm in diameter) were bleached. The pretreatment, color classification, B solution, and subsequent soaking, drying, and bleaching methods were the same as in Example 3. The bleaching time was 16 days.

[0159] Solution A: Add 400g potassium chlorate and 300g polyethylene glycol (100) to every 10 liters of water, and stir until completely dissolved.

[0160] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 12.1-12.3.

[0161] Table 12.1 Color grading of pearls before and after bleaching

[0162]

[0163] Table 12.2 Grading of the luster of pearls before and after bleaching

[0164]

[0165] Table 12.3 Grading of Pearl Surface Damage Before and After Discoloration

[0166]

[0167]

[0168] Control group 9 (potassium chlorate concentration less than 1%)

[0169] Freshwater pearls (6-7mm in diameter) were bleached. The pretreatment, color classification, B solution, and subsequent immersion soaking, drying, and immersion bleaching methods were the same as in Example 3. The bleaching time was 32 days.

[0170] Solution A: Add 80g potassium chlorate and 300g polyethylene glycol (100) to every 10 liters of water, and stir until completely dissolved.

[0171] The color, luster, and damage of the pearl grains before and after bleaching were graded and statistically analyzed. The results are shown in Tables 13.1-13.3.

[0172] Table 13.1 Color grading of pearls before and after bleaching

[0173]

[0174] Table 13.2 Grading of the luster of pearls before and after bleaching

[0175]

[0176] Table 13.3 Grading of Pearl Surface Damage Before and After Discoloration

[0177]

[0178]

[0179] Control group 10 (bleached with hydrogen peroxide for 16 days using traditional methods)

[0180] Freshwater beads (6-7mm in diameter) were soaked in methanol and 0.1% ammonia for 48 hours respectively, and then sorted by color, with 200 beads of each color taken.

[0181] Preparation of bleach solution:

[0182] Solution A: For every 10 liters of water, add 300 ml of 30% hydrogen peroxide and 300 g of polyethylene glycol (100), and stir until completely dissolved.

[0183] Each was bleached by immersion in solution A.

[0184] The color, luster, and damage of the pearls before and after bleaching were graded and statistically analyzed. The results are shown in Table 1: 4.1-14.3.

[0185] Table 14.1 Color grading of pearls before and after bleaching

[0186]

[0187] Table 14.2 Grading of the luster of pearls before and after bleaching

[0188]

[0189]

[0190] Table 14.3 Grading of Pearl Surface Damage Before and After Discoloration

[0191]

[0192] Control group 11 (bleached with hydrogen peroxide for 6 days using traditional methods)

[0193] Freshwater beads (6-7mm in diameter) were soaked in methanol and 0.1% ammonia for 48 hours respectively, and then sorted by color, with 200 beads of each color taken.

[0194] Preparation of bleach solution:

[0195] Solution A: For every 10 liters of water, add 300 ml of 30% hydrogen peroxide and 300 g of polyethylene glycol (100), and stir until completely dissolved.

[0196] Each was bleached by immersion in solution A.

[0197] The color, luster, and damage of the pearls before and after bleaching were graded and statistically analyzed. The results are shown in Tables 15.1-15.3.

[0198] Table 15.1 Color grading of pearls before and after bleaching

[0199]

[0200] Table 15.2 Grading of the luster of pearls before and after bleaching

[0201]

[0202] Table 15.3 Grading of Pearl Surface Damage Before and After Discoloration

[0203]

[0204] Control group 12 (bleached directly with bleaching powder for 3 days)

[0205] Freshwater beads (6-7mm in diameter) were soaked in methanol and 0.1% ammonia for 48 hours respectively, and then sorted by color, with 200 beads of each color taken.

[0206] Preparation of bleach solution:

[0207] Solution A: Add bleaching powder to every 10 liters of water, which is equivalent to a solution containing 0.1% hypochlorous acid and 300g polyethylene glycol (100), and stir until completely dissolved.

[0208] The pearls were bleached with solution A. The color, luster, and damage of the pearls before and after bleaching were graded and statistically analyzed. The results are shown in Tables 16.1-16.3.

[0209] Table 16.1 Color grading of pearls before and after bleaching

[0210]

[0211]

[0212] Table 16.2 Grading of the luster of pearls before and after bleaching

[0213]

[0214] Table 16.3 Grading of Pearl Surface Damage Before and After Discoloration

[0215]

[0216] This invention employs a crown ether-controlled phase transfer catalytic method for bleaching solid potassium chlorate pearl particles. First, potassium chlorate, which has no bleaching ability, is allowed to fully penetrate the pearl layer. Then, the solid is dried and precipitated. Next, an alcohol organic solution containing 18-crown(ether)-6 is penetrated into the pearl layer, catalyzing the oxidation ability of chlorate anions and achieving a better bleaching effect.

[0217] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A pearl bleaching process based on phase transfer catalyzed oxidation, characterized in that, The method comprises the following steps: Step S1: preparing a potassium chlorate aqueous solution with a concentration of 1.0-3.0%, soaking the pretreated pearl particles in the potassium chlorate aqueous solution, taking out the pearl particles after the solution fully penetrates into the pearl layer to the deep layer of the pearl, cleaning, drying, and waiting for use; Step S2: drying the pearl particles to dehydrate the solution in the pearl layer, and making the potassium chlorate into solid powder adhered in the pearl layer, and waiting for use; Step S3: preparing an 18-crown-6 ether alcohol organic solution with a mass / volume ratio of 50.0-60.0 mg / mL by using an alcohol as a solvent, and adjusting the pH of the alcohol organic solution to 7-8; Step S4: soaking the pearl particles dried in step S2 in the 18-crown-6 ether alcohol organic solution, bleaching until complete decolorization, taking out the pearl particles, cleaning after soaking in clean water, and drying to obtain a finished product.

2. The phase transfer catalyzed oxidation based pearl bleaching process according to claim 1, characterized in that: In the step S1, the pearl particle pretreatment is respectively soaked in methanol and ammonia water.

3. The phase transfer catalyzed oxidation based pearl bleaching process according to claim 1, characterized in that: In the step S1, an appropriate amount of a surfactant is added to the potassium chlorate aqueous solution.

4. The phase transfer catalyzed oxidation based pearl bleaching process according to claim 3, characterized in that: The surfactant is polyethylene glycol, SDS, or Tween.

5. The phase transfer catalyzed oxidation based pearl bleaching process according to claim 1, characterized in that: In the step S2, the drying mode is reduced-pressure drying.

6. The phase transfer catalyzed oxidation based pearl bleaching process according to claim 5, characterized by: The drying temperature is 40-80 °C.

7. The phase transfer catalyzed oxidation based pearl bleaching process according to claim 1, characterized in that: In the step S3, the alcohol is methanol or ethanol.

8. The phase transfer catalyzed oxidation based pearl bleaching process according to claim 1, characterized by: In the step S3, the method for adjusting the pH of the alcohol organic solution is adjusting by using ammonium chloride and ammonia water.

Images