Preparation method of environment-friendly iron-zinc-chromium brown pigment

Abstract

A preparation method of an environment-friendly iron-zinc-chromium brown pigment comprises the following steps: (1) adding a zinc source, an iron source and a chromium source into water, dissolving, adding EDTA and modified nano graphene oxide powder, and mixing under an ultrasonic condition; (2) adding an acid aqueous solution to be acidic, adding a sol agent at the same time, and carrying out gelation under heating and stirring conditions; (3) carrying out pre-calcination treatment, and then carrying out high-temperature calcination treatment on the obtained precursor powder; and (4) after ball milling treatment, adding stearic acid, heating and stirring to obtain the iron-zinc-chromium brown pigment. The method is simple in process, environmentally friendly, green, low in energy consumption, low in cost and suitable for industrial production, and the obtained iron-zinc-chromium brown pigment is small in particle size, free of granular sensation, uniform in quality, free of color difference and good in dispersity.

Description

Technical Field

[0001] The invention relates to a method for preparing an iron-zinc-chrome brown pigment, and in particular to a method for preparing an environmentally friendly iron-zinc-chrome brown pigment. Background Art

[0002] Iron-zinc-chrome brown pigment is one of the commonly used brown pigments, and its color is characterized by calmness, stability, and simplicity. The brown pigment presented by iron-zinc-chrome brown has been widely used in glazed tiles and antique tiles since ancient times. It has excellent chemical resistance, outdoor light and weather resistance, thermal stability, no color bleeding, no migration, and comprehensive performance. It can adapt to the high requirements of modern coatings and plastics, and is compatible with most thermoplastic and thermosetting resins. It is a non-toxic and environmentally friendly pigment; its color spectrum ranges from yellowish reddish brown to dark reddish brown, and it also has very excellent infrared reflection function, which is suitable for reflective heat insulation coatings and camouflage coatings, etc. It can be made into camouflage coatings for use in many military fields.

[0003] At present, the preparation of iron zinc chrome brown pigment mainly adopts high temperature solid phase method and gel solid phase method. The pigment products prepared by high temperature solid phase method have the problems of large particle size and unstable color, and the traditional high temperature solid phase has high energy consumption and poor environmental protection. The gel solid phase method uses heavy metal salt solution for preparation, the heavy metal reaction yield is low, and there is a problem of heavy metal dissolution in the pigment. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for preparing an environmentally friendly iron-zinc-chrome brown pigment with simple process, environmental friendliness, green environmental protection, low energy consumption, low cost, suitability for industrial production, small particle size, no granularity, uniform quality, no color difference and good dispersibility.

[0005] The technical solution adopted by the present invention to solve the technical problem is as follows: a method for preparing an environmentally friendly iron-zinc-chrome brown pigment comprises the following steps: (1) adding a zinc source, an iron source and a chromium source into water to dissolve them, then adding EDTA and modified nano graphene oxide powder, and mixing them under ultrasonic conditions to obtain a mixed suspension; (2) adding an acid aqueous solution to the mixed suspension obtained in step (1) until it becomes acidic, and simultaneously adding a sol, and performing gelation under heating and stirring conditions to obtain a gel; (3) pre-calcining the gel obtained in step (2), and then calcining the obtained precursor powder at high temperature to obtain iron zinc chrome brown powder; (4) After ball milling the iron zinc chrome brown powder obtained in step (3), stearic acid is added, and the mixture is heated and stirred to obtain an iron zinc chrome brown pigment.

[0006] The inventive concept of the method of the present invention is: through step (1), the dispersibility of heavy metal ions in the mixed system is improved, and the uniformity of the mixed material is increased, so as to facilitate the formation of a complex gel system with uniform heavy metal ion distribution during gelation in step (2); then, through step (3), a two-stage calcination treatment is performed to obtain zinc-iron-chromium oxide mixed phase crystals with impurities removed and stable lattice; finally, through step (4), surface modification is performed to improve the water resistance of the obtained pigment.

[0007] Preferably, in step (1), the mass ratio of the zinc source, the iron source and the chromium source is 1:1.2-1.5:1.5-2.0.

[0008] Preferably, in step (1), the amount of water used is equivalent to 1.5 to 2.5 times the total mass of the zinc source, the iron source and the chromium source. In the method of the present invention, too little water is not conducive to the dispersion of the gel during the subsequent gelation, while excessive water is not conducive to the formation of a stable gel.

[0009] Preferably, in step (1), the amount of EDTA added is equivalent to 0.3-2.4% (more preferably 0.5-2.0%) of the total mass of the zinc source, the iron source and the chromium source. In the method of the present invention, the role of adding EDTA is that the amino and carboxyl groups in EDTA form stable complexes with heavy metal ions of zinc, iron and chromium, which can prevent the free dissolution of heavy metal ions, thereby improving the reaction yield of heavy metal ions when preparing iron-zinc-chrome brown pigment.

[0010] Preferably, in step (1), the mixing treatment time is 30 to 40 minutes.

[0011] Preferably, in step (1), the zinc source includes zinc nitrate, etc. When a hydrate is used, the amount used is converted based on zinc nitrate.

[0012] Preferably, in step (1), the iron source includes ferric nitrate, etc. When a hydrate is used, the amount used is converted based on ferric nitrate.

[0013] Preferably, in step (1), the chromium source includes chromium nitrate, etc. When a hydrate is used, the amount used is converted based on chromium nitrate.

[0014] Preferably, in step (1), the amount of the modified nano graphene oxide powder added is equivalent to 2-5% (more preferably 2-4%) of the total mass of the zinc source, the iron source and the chromium source. In the method of the present invention, the role of adding the modified nano graphene oxide powder is that it has high thermal conductivity and a two-dimensional structure composed of a single layer of carbon atoms, and the surface is rich in oxygen-containing functional groups such as hydroxyl and carboxyl groups, which can improve the dispersibility of heavy metal ions in the mixed system, improve the uniformity of the mixed material, overcome the agglomeration caused by uneven dispersion, and make the subsequent calcination local overheating, resulting in color difference and uneven quality of the iron zinc chrome brown pigment; in addition, the oxygen-containing groups of the modified nano graphene oxide powder assist in the adsorption of heavy metal ions based on electrostatic action, and cooperate with EDTA to further improve the reaction yield of heavy metal ions.

[0015] Preferably, in step (1), the modified nano-graphene oxide is obtained by blending polyvinyl pyrrolidone and nano-graphene oxide. In the method of the present invention, covalent bond modification is carried out by polyvinyl pyrrolidone to achieve covalent bond functionalization of the graphene surface. Compared with unmodified nano-graphene oxide, the modified nano-graphene oxide added by the method of the present invention has significantly improved dispersibility in water and better performance; in addition, the modified nano-graphene oxide has excellent conductivity and optical properties, which can enhance the absorption and reflection ability of iron zinc chrome brown pigment to light, and effectively improve the color brightness of the pigment.

[0016] Preferably, the mass ratio of the polyvinyl pyrrolidone to the nano-graphene oxide is 0.5-1.5:4-7. The above ratio is conducive to exerting the effect of polyvinyl pyrrolidone and obtaining a better dispersion effect.

[0017] Preferably, in step (1), the preparation method of the modified nano-graphene oxide is: 1) dispersing polyvinyl pyrrolidone solution and nano-graphene oxide in water, and mixing them under ultrasonic conditions to obtain a uniformly dispersed colloidal solution; 2) stirring the uniformly dispersed colloidal solution obtained in step 1) once, and then stirring it twice, and washing the colloid obtained by the reaction and drying it.

[0018] Preferably, in step 1), the amount of water used is equivalent to 1 to 2 times the total mass of the polyvinyl pyrrolidone solution and the nano-graphene oxide.

[0019] Preferably, in step 2), the temperature of the first stirring reaction is 32-38° C., the pH value is 7.6-8.0, and the time is 20-30 min. The main function of the first stirring is to perform preliminary mixing.

[0020] Preferably, in step 2), the temperature of the secondary stirring reaction is 25-30° C., the pH value is 6.8-7.2, and the time is 15-30 minutes. After lowering the temperature, the secondary stirring is continued to further eliminate bubbles and improve the homogenization effect.

[0021] Preferably, in step 2), the colloid is washed with deionized water and ethanol for 3 to 4 times. The purpose of washing the colloid obtained by the reaction multiple times is to remove unreacted polyvinyl pyrrolidone to facilitate subsequent drying.

[0022] Preferably, in step 2), the drying temperature is 50-70°C.

[0023] The method of the invention optimizes the conditions during the modified mixing and stirring reaction to ensure that the polyvinyl pyrrolidone and the nano-graphene oxide fully react, so that the particle size of the obtained modified nano-graphene oxide powder is uniform and the properties are stable.

[0024] Preferably, in step (2), an acid aqueous solution is added until the pH value is 4 to 6. When the pH value is too low after the acid aqueous solution is added, an ammonia aqueous solution with a concentration of 0.5 mol / L is used to adjust the pH value.

[0025] Preferably, in step (2), the concentration of the aqueous acid solution is 1 to 2 mol / L.

[0026] Preferably, in step (2), the acid aqueous solution includes citric acid aqueous solution, etc. In the method of the present invention, citric acid can coordinate with metal cations to form a gel.

[0027] Preferably, in step (2), the amount of the sol agent added is equivalent to 0.5-1.0% of the volume of the mixed suspension. In the method of the present invention, the sol agent can reduce agglomeration, improve the stability of the gel, and help obtain a uniform and transparent gel.

[0028] Preferably, in step (2), the sol agent includes ethylene glycol or the like.

[0029] Preferably, in step (2), the gelation temperature is 85-95°C, the stirring speed is 200-400 r / min, and the time is 4-8 hours. The citric acid coordinates with the metal cation to gelate, and in the above process, the reaction is uniformly stirred by slow stirring.

[0030] In step (3) of the method of the present invention, a two-stage calcination treatment including pre-calcination and high-temperature calcination is carried out, and a staged temperature-controlled calcination system is established to react and generate zinc-iron-chromium oxide mixed-phase crystals with a spinel structure, which can better control the crystal structure and properties of the iron-zinc-chrome brown pigment, and compared with direct high-temperature solid phase calcination, energy consumption is reduced and environmental protection is improved. More preferably, the two-stage calcination treatment is carried out in a muffle furnace.

[0031] Preferably, in step (3), the pre-calcination treatment is carried out under the following conditions: heating to 400-600°C at a rate of 5-15°C / min under a protective atmosphere, and then calcining for 1-3 hours. The pre-calcination treatment in the method of the present invention is a low-temperature and slow calcination of the gel obtained in step (2), which can fully remove organic matter and is conducive to the formation of the crystal structure of the powder.

[0032] Preferably, in step (3), the conditions of the high temperature calcination treatment are: in a protective atmosphere, heating to 1100-1300°C at a rate of 50-150°C / min, and then calcining at this temperature for 30-50 minutes. The high temperature calcination treatment in the method of the present invention is a rapid high temperature calcination of the precursor powder obtained by the pre-calcination treatment to achieve a crystal phase transformation, complete crystal reconstruction, and form a more stable structure.

[0033] Preferably, in step (3), the protective atmosphere includes nitrogen and / or argon.

[0034] Preferably, in step (4), the diameter of the grinding balls used in the ball milling treatment is 20 to 40 mm, and the grinding balls are equivalent to 40 to 50% of the mass of the iron zinc chrome brown powder. The particle size of the pigment particles is refined by optimizing the ball milling conditions.

[0035] Preferably, in step (4), the rotation speed of the ball milling treatment is 60 to 80 r / min, and the time is 2 to 4 hours. The method of the present invention refines the particle size of the pigment particles by optimizing the ball milling conditions, so that the obtained iron zinc chrome brown pigment has a small particle size, no granularity, uniform quality, no color difference and good dispersibility. The ball milling treatment is carried out in a ball mill.

[0036] Preferably, in step (4), the amount of stearic acid added is equivalent to 1-3% of the mass of the iron zinc chrome brown powder. Stearic acid can react with the surface of metal oxides through carboxyl groups. The method of the present invention reduces the surface energy of the iron zinc chrome brown pigment by adding stearic acid to coat the pigment surface, forming a hydrophobic protective layer to improve hydrophobicity; while enhancing the water resistance of the iron zinc chrome brown pigment, it also improves the dispersibility of the pigment particles, avoids particle agglomeration, and further enhances the tinting power and hiding power of the iron zinc chrome brown pigment; at the same time, the iron zinc chrome brown pigment treated with stearic acid has metal ions stabilized in the crystal structure, reducing heavy metal exposure and reducing the risk of dissolution.

[0037] Preferably, in step (4), the heating and stirring temperature is 80-100° C., the stirring speed is 200-600 r / min, and the time is 1-2 h. Heating and stirring are beneficial to the melting of stearic acid and the formation of a hydrophobic layer on the surface of the iron zinc chrome brown powder.

[0038] The beneficial effects of the method of the present invention are as follows: (1) The method of the present invention can avoid the free dissolution of heavy metal ions, thereby improving the reaction yield of heavy metal ions in the preparation of iron-zinc chrome brown pigment; (2) The method of the present invention improves the dispersibility of heavy metal ions in the mixed system, improves the uniformity of the mixed material, and overcomes the problem of agglomeration due to uneven dispersion, which causes local overheating during subsequent calcination, resulting in color difference and uneven quality of the iron-zinc-chrome brown pigment; (3) The method of the present invention establishes a staged temperature-controlled calcination system to react and generate spinel-structured zinc-iron-chromium oxide mixed-phase crystals, which can better control the crystal structure and properties of the iron-zinc-chrome brown pigment. Compared with direct high-temperature solid phase calcination, the energy consumption is reduced and the environmental protection is improved; (4) The method of the present invention is simple in process, environmentally friendly, green and environmentally friendly, has low energy consumption, low cost, and is suitable for industrial production. The obtained iron-zinc chrome brown pigment has small particle size, no granularity, uniform quality, no color difference and good dispersibility. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with the embodiments.

[0040] Unless otherwise specified, the raw materials or chemical reagents used in the examples and comparative examples of the present invention were obtained through conventional commercial channels.

[0041] Example 1 (1) After dissolving 60 g zinc nitrate, 72 g ferric nitrate and 90 g chromium nitrate in 500 mL water, 2.0 g EDTA and 4.5 g modified nano-graphene oxide powder were added, and mixed under ultrasonic conditions for 30 min to obtain a mixed suspension; The preparation method of the modified nano-graphene oxide is as follows: 1) dispersing a polyvinyl pyrrolidone solution and nano-graphene oxide in a mass ratio of 0.7:4 in water equivalent to 1.5 times the total mass of the polyvinyl pyrrolidone solution and the nano-graphene oxide, and mixing under ultrasonic conditions to obtain a uniformly dispersed colloidal solution; 2) subjecting the uniformly dispersed colloidal solution obtained in step 1) to a stirring reaction for 25 minutes at 35° C. and a pH value of 7.8, and then to a second stirring reaction for 20 minutes at 28° C. and a pH value of 7.0, and washing the colloid obtained by the reaction with deionized water and ethanol three times in succession, and then drying at 60° C. to obtain the modified nano-graphene oxide powder; in the embodiment of the present invention, the conditions during the modified mixing and stirring reaction are optimized to ensure that the polyvinyl pyrrolidone and the nano-graphene oxide fully react, so that the particle size of the obtained modified nano-graphene oxide powder is uniform and the properties are stable; and covalent bond modification is performed by polyvinyl pyrrolidone to realize the covalent bond functionalization of the graphene surface. Compared with unmodified nano-graphene oxide, the modified nano-graphene oxide added in the embodiment of the present invention has significantly improved dispersibility in water and has better performance; in addition, the modified nano-graphene oxide has excellent conductivity and optical properties, can enhance the absorption and reflection ability of iron-zinc-chrome brown pigment to light, and effectively improve the color brightness of the pigment; In the embodiment of the present invention, the role of adding EDTA is that the amino and carboxyl groups in EDTA form stable complexes with heavy metal ions of zinc, iron and chromium, which can prevent the free dissolution of heavy metal ions, thereby improving the reaction yield of heavy metal ions when preparing iron-zinc-chrome brown pigment; In the embodiment of the present invention, the role of adding modified nano graphene oxide powder is to improve the dispersibility of heavy metal ions in the mixed system, improve the uniformity of the mixed material, overcome the agglomeration caused by uneven dispersion, and cause local overheating during subsequent calcination, resulting in color difference and uneven quality of the iron-zinc-chrome brown pigment; in addition, the oxygen-containing groups of the modified nano graphene oxide powder assist in the adsorption of heavy metal ions based on electrostatic action, and cooperate with EDTA to further improve the reaction yield of heavy metal ions; (2) Adding a 1 mol / L citric acid aqueous solution to the mixed suspension obtained in step (1) until the pH value is 5.0, and adding ethylene glycol equivalent to 1% of the volume of the mixed suspension, heating and stirring in a water bath at 90° C. and a stirring speed of 300 r / min for 6 h to obtain a gel; when the pH value is lower than 5.0 after adding the citric acid aqueous solution, adjusting the pH value with a 0.5 mol / L ammonia aqueous solution; In the embodiment of the present invention, citric acid can coordinate with metal cations to form gel; ethylene glycol as a sol can reduce agglomeration, improve the stability of the gel, and help to obtain a uniform and transparent gel; (3) placing the gel obtained in step (2) in a muffle furnace and pre-calcining the gel: heating the gel to 400°C at a rate of 10°C / min under an argon atmosphere, and then calcining the gel for 3 hours; then calcining the obtained precursor powder at a high temperature: heating the gel to 1100°C at a rate of 100°C / min under an argon atmosphere, and then calcining the gel for 50 minutes to obtain an iron-zinc-chrome brown powder; In the embodiment of the present invention, a staged temperature-controlled calcination system is established to react and generate zinc-iron-chromium oxide mixed-phase crystals with a spinel structure, which can better control the crystal structure and performance of the iron-zinc-chrome brown pigment, and compared with directly performing high-temperature solid phase calcination, energy consumption is reduced and environmental protection is improved; the pre-calcination treatment is a low-temperature slow calcination of the gel obtained in step (2), which can fully remove organic matter and is conducive to the formation of the crystal structure of the powder; the high-temperature calcination treatment is a rapid high-temperature calcination of the precursor powder obtained by the pre-calcination treatment to achieve crystal phase transformation, complete crystal reconstruction, and form a more stable structure; (4) The iron zinc chrome brown powder obtained in step (3) is placed in a ball mill, wherein the diameter of the grinding balls is 20 mm and the grinding balls are equivalent to 40% of the mass of the iron zinc chrome brown powder, and the ball milling treatment is carried out at a speed of 60 r / min for 4 h, and then stearic acid equivalent to 1% of the mass of the iron zinc chrome brown powder is added, and then the mixture is transferred to a mixer, heated and stirred at 80° C. and a stirring speed of 200 r / min for 2 h to obtain 1# iron zinc chrome brown pigment; In the embodiment of the present invention, the particle size of the pigment particles is refined by optimizing the ball milling conditions, so that the obtained iron zinc chrome brown pigment has a small particle size, no granular feeling, uniform quality, no color difference and good dispersibility; the surface energy of the iron zinc chrome brown pigment is reduced by adding stearic acid to perform surface coating treatment on the pigment, and a hydrophobic protective layer is formed to improve the hydrophobicity; while enhancing the water resistance of the iron zinc chrome brown pigment, the dispersibility of the pigment particles is also improved, and the particle agglomeration is avoided, thereby enhancing the tinting power and hiding power of the iron zinc chrome brown pigment; at the same time, in the iron zinc chrome brown pigment treated with stearic acid, the metal ions are stabilized in the crystal structure, which reduces the exposure of heavy metals and reduces the risk of dissolution.

[0042] Example 2 (1) 60 g of zinc nitrate, 78 g of iron nitrate and 96 g of chromium nitrate were added to 500 mL of water and dissolved, and then 2.0 g of EDTA and 7.02 g of modified nano-graphene oxide powder were added, and mixed under ultrasonic conditions for 30 minutes to obtain a mixed suspension; The preparation method of the modified nano-graphene oxide is as follows: 1) dispersing a polyvinyl pyrrolidone solution and nano-graphene oxide in a mass ratio of 0.8:5 in water equivalent to 1.5 times the total mass of the polyvinyl pyrrolidone solution and the nano-graphene oxide, and mixing under ultrasonic conditions to obtain a uniformly dispersed colloidal solution; 2) the same as step 2 of the preparation method of the modified nano-graphene oxide in Example 1); (2) Same as step (2) in Example 1; (3) placing the gel obtained in step (2) in a muffle furnace and pre-calcining the gel: heating the gel to 450°C at a rate of 10°C / min under an argon atmosphere, and then calcining the gel for 2.5 hours; then calcining the precursor powder: heating the gel to 1200°C at a rate of 90°C / min under an argon atmosphere, and then calcining the gel for 40 minutes to obtain an iron-zinc-chrome brown powder; (4) The iron zinc chrome brown powder obtained in step (3) is placed in a ball mill with a grinding ball diameter of 30 mm and a grinding ball amount equivalent to 45% of the mass of the iron zinc chrome brown powder. After ball milling for 3 h at a rotation speed of 70 r / min, stearic acid equivalent to 2% of the mass of the iron zinc chrome brown powder is added. The powder is then transferred to a mixer and heated and stirred at 90° C. and a stirring speed of 400 r / min for 1.5 h to obtain 2# iron zinc chrome brown pigment.

[0043] Example 3 (1) 60 g of zinc nitrate, 84 g of iron nitrate and 102 g of chromium nitrate were added to 500 mL of water to dissolve, and then 3.9 g of EDTA and 9.8 g of modified nano-graphene oxide powder were added, and mixed under ultrasonic conditions for 35 minutes to obtain a mixed suspension; The preparation method of the modified nano-graphene oxide is as follows: 1) dispersing a polyvinyl pyrrolidone solution and nano-graphene oxide in a mass ratio of 1:4 in water equivalent to twice the total mass of the polyvinyl pyrrolidone solution and the nano-graphene oxide, and mixing under ultrasonic conditions to obtain a uniformly dispersed colloidal solution; 2) the same as step 2 of the preparation method of the modified nano-graphene oxide in Example 1); (2) Same as step (2) in Example 1; (3) Same as step (3) in Example 2; (4) Same as step (4) in Example 2.

[0044] Example 4 (1) After dissolving 60 g zinc nitrate, 90 g ferric nitrate and 108 g chromium nitrate in 500 mL water, 2.5 g EDTA and 9.0 g modified nano-graphene oxide powder were added, and the mixture was mixed under ultrasonic conditions for 35 min to obtain a mixed suspension; The preparation method of the modified nano-graphene oxide is as follows: 1) dispersing a polyvinyl pyrrolidone solution and nano-graphene oxide in a mass ratio of 1.4:7 in water equivalent to twice the total mass of the polyvinyl pyrrolidone solution and the nano-graphene oxide, and mixing them under ultrasonic conditions to obtain a uniformly dispersed colloidal solution; 2) stirring the uniformly dispersed colloidal solution obtained in step 1) for a first reaction at 38° C. and a pH value of 7.6 for 20 minutes, and then stirring the colloidal solution for a second reaction at 30° C. and a pH value of 6.8 for 25 minutes, washing the colloid obtained by the reaction with deionized water and ethanol four times in succession, and drying it at 70° C. to obtain the modified nano-graphene oxide; (2) Adding a 2 mol / L citric acid aqueous solution to the mixed suspension obtained in step (1) until the pH value is 4.5, and simultaneously adding ethylene glycol in an amount equivalent to 0.8% by volume of the mixed suspension, heating in a water bath at 85° C. and a stirring speed of 400 r / min for 5 h to perform gelation to obtain a gel; when the pH value is lower than 4.5 after adding the citric acid aqueous solution, adjusting the pH value with a 0.5 mol / L ammonia aqueous solution; (3) placing the gel obtained in step (2) in a muffle furnace and pre-calcining the gel: heating the gel to 600°C at a rate of 10°C / min under an argon atmosphere, and then calcining the gel for 1 hour; then calcining the precursor powder: heating the gel to 1300°C at a rate of 80°C / min under an argon atmosphere, and then calcining the gel for 30 minutes to obtain an iron-zinc-chrome brown powder; (4) The iron zinc chrome brown powder obtained in step (3) is placed in a ball mill with a grinding ball diameter of 40 mm and a grinding ball amount equivalent to 50% of the mass of the iron zinc chrome brown powder. After ball milling for 2 h at a rotation speed of 80 r / min, stearic acid equivalent to 3% of the mass of the iron zinc chrome brown powder is added. The powder is then transferred to a mixer and heated and stirred at 100° C. and a stirring speed of 600 r / min for 1 h to obtain 4# iron zinc chrome brown pigment.

[0045] Comparative Example 1 The difference between this comparative example and Example 3 is that in step (1), EDTA is not added. The rest is the same as Example 3 to obtain 5# iron zinc chrome brown pigment.

[0046] Comparative Example 2 The difference between this comparative example and Example 3 is that in step (1), no modified nano graphene oxide powder is added. The rest is the same as Example 3, and 6# iron-zinc-chrome brown pigment is obtained.

[0047] Comparative Example 3 The difference between this comparative example and Example 3 is that in step (4), stearic acid is not added for surface modification. The rest is the same as Example 3, and 7# iron-zinc-chrome brown pigment is obtained.

[0048] The commercially available Ranbar Brown I3660 iron-zinc-chrome brown pigment was used as a control group (marked as 0#) and the iron-zinc-chrome brown pigments obtained in Examples 1 to 4 of the present invention and Comparative Examples 1 to 3 (marked as 1# to 7#) were used to perform water resistance testing based on the provisions of GB / T5211.5-1985 "Method for Determination of Water Resistance of Pigments"; based on the method of EPA3060A, dissolution solutions dissolved in 0# to 7# pigments were prepared respectively, and the presence of heavy metal dissolution in the dissolution solutions was determined by diphenylcarbazide absorption photometry; the average particle size of the pigments and the appearance were measured based on microscopy; the results are shown in Table 1.

[0049] Table 1 Performance comparison of 0-7# iron-zinc-chrome brown pigments obtained in the control group, examples and comparative examples of the present invention

[0050] Note: In the table, the higher the water resistance level from 1 to 5, the better the water resistance.

[0051] As can be seen from Table 1, by comparing Example 3 of the present invention with Comparative Examples 1 to 3, it can be seen that the method of the present invention can avoid the dissolution of heavy metal ions in the pigment by adding EDTA, thereby avoiding heavy metal pollution; and by adding modified nano graphene oxide powder, a pigment product with uniform particle size, no color difference, and no granularity can be obtained; the water resistance of the pigment can be significantly improved by surface modification with stearic acid; in addition, since modified nano graphene oxide powder was not introduced in Comparative Example 2, a trace amount of heavy metal ions was detected in the obtained pigment (6#) during the dissolution test, indicating that graphene has a synergistic effect of inhibiting the precipitation of heavy metals.

Claims

1. A method for preparing an environmentally friendly iron-zinc chrome brown pigment, characterized in that: The following steps are involved: (1) adding a zinc source, an iron source and a chromium source into water to dissolve them, then adding EDTA and modified nano graphene oxide powder, and mixing them under ultrasonic conditions to obtain a mixed suspension; (2) adding an acid aqueous solution to the mixed suspension obtained in step (1) until it becomes acidic, and simultaneously adding a sol, and performing gelation under heating and stirring conditions to obtain a gel; (3) pre-calcining the gel obtained in step (2), and then calcining the obtained precursor powder at high temperature to obtain iron zinc chrome brown powder; (4) After ball milling the iron zinc chrome brown powder obtained in step (3), stearic acid is added, and the mixture is heated and stirred to obtain an iron zinc chrome brown pigment.

2. The method for preparing the environmentally friendly iron-zinc-chrome brown pigment according to claim 1, characterized in that: In step (1), the mass ratio of the zinc source, the iron source and the chromium source is 1:1.2-1.5:1.5-2.0; the amount of water used is equivalent to 1.5-2.5 times the total mass of the zinc source, the iron source and the chromium source; the amount of EDTA added is equivalent to 0.3-2.4% of the total mass of the zinc source, the iron source and the chromium source; the mixing treatment time is 30-40 minutes; the zinc source includes zinc nitrate; the iron source includes ferric nitrate; and the chromium source includes chromium nitrate.

3. The method for preparing the environmentally friendly iron-zinc-chrome brown pigment according to claim 1 or 2, characterized in that: In step (1), the amount of the modified nano-graphene oxide powder added is equivalent to 2-5% of the total mass of the zinc source, the iron source and the chromium source; the modified nano-graphene oxide is obtained by blending polyvinyl pyrrolidone and nano-graphene oxide; the mass ratio of the polyvinyl pyrrolidone to the nano-graphene oxide is 0.5-1.5:4-7.

4. The method for preparing the environmentally friendly iron-zinc chrome brown pigment according to claim 3, characterized in that: In step (1), the preparation method of the modified nano-graphene oxide is as follows: 1) dispersing a polyvinyl pyrrolidone solution and nano-graphene oxide in water, and mixing them under ultrasonic conditions to obtain a uniformly dispersed colloidal solution; 2) subjecting the uniformly dispersed colloidal solution obtained in step 1) to a first stirring reaction, and then to a second stirring reaction, washing the colloid obtained by the reaction, and drying the colloid to obtain the modified nano-graphene oxide; in step 1), the amount of water used is equivalent to 1 to 2 times the total mass of the polyvinyl pyrrolidone solution and the nano-graphene oxide; in step 2), the temperature of the first stirring reaction is 32 to 38° C., the pH value is 7.6 to 8.0, and the time is 20 to 30 minutes; the temperature of the second stirring reaction is 25 to 30° C., the pH value is 6.8 to 7.2, and the time is 15 to 30 minutes; washing with deionized water and ethanol for 3 to 4 times in sequence; and the drying temperature is 50 to 70° C.

5. The method for preparing the environmentally friendly iron-zinc-chrome brown pigment according to claim 1 or 2, characterized in that: In step (2), an acid aqueous solution is added until the pH value is 4 to 6; the concentration of the acid aqueous solution is 1 to 2 mol / L; the acid aqueous solution includes a citric acid aqueous solution; the amount of the sol added is equivalent to 0.5 to 1.0% of the volume of the mixed suspension; the sol includes ethylene glycol; the gelation temperature is 85 to 95° C., the stirring speed is 200 to 400 r / min, and the time is 4 to 8 hours.

6. The method for preparing the environmentally friendly iron-zinc-chrome brown pigment according to claim 1 or 2, characterized in that: In step (3), the conditions for the pre-calcination treatment are: in a protective atmosphere, heating to 400-600°C at a rate of 5-15°C / min, and then calcining at this temperature for 1-3 hours; the conditions for the high-temperature calcination treatment are: in a protective atmosphere, heating to 1100-1300°C at a rate of 50-150°C / min, and then calcining at this temperature for 30-50 minutes; the protective atmosphere includes nitrogen and / or argon.

7. The method for preparing the environmentally friendly iron-zinc-chrome brown pigment according to claim 1 or 2, characterized in that: In step (4), the diameter of the grinding balls used in the ball milling treatment is 20-40 mm, and the grinding balls are equivalent to 40-50% of the mass of the iron zinc chrome brown powder; the rotation speed of the ball milling treatment is 60-80 r / min, and the time is 2-4 h; the amount of stearic acid added is equivalent to 1-3% of the mass of the iron zinc chrome brown powder; the temperature of the heating and stirring is 80-100° C., the stirring speed is 200-600 r / min, and the time is 1-2 h.

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