SE445209B - PIGMENT OF SYNTHETIC ROMBOID MAGNETIT - Google Patents

Description

Soo1oso-9 1-2- tit with a ratio Fe ++ / total amount of Fe ++ and Fe +++ of between about 0.25 and about 0.38; and D. recovery of the magnetite thus formed.

The improvement according to the present invention is that the carbonate is used in the form of small particles with an average particle size of less than 3.5 μm.

It is preferred in the process that said magnetite is calcined at a temperature between 650 and 925 ° C in the presence of oxygen, so that K-iron (III) oxide is formed, that said iron (II) chloride solution comprises used pickling liquid from steelmaking and that said carbonate is calcium carbonate.

The synthetic rhomboid magnetite with a BET surface area greater than about 13 m 2 / gram and an average particle size less than about 0.08 microns measured along the longitudinal axis has a particle size between about 0.04 and about 0.08 microns.

The new synthetic rhomboid magnetite according to the invention is unique in the following respects in comparison with previously known magnetite and in comparison with currently commercially available magnetite: (1) it has a high relative color strength; (2) low Y value for color strength; (3) large surface area and (4) small particle size.

A typical, for the magnetite according to the present invention Y-value for color strength is, as shown in Table 1, 15.78. For commercially available competing magnetites, the Y-values for color strength are between 17.73 and 25.05, which is also shown in Table 1.

These values have been determined with the color equation FMC-II and a Diano-Hardy spectrophotometer. The samples were prepared by mixing 0.5 grams of pigment and 1.5 grams of titanium dioxide in dispersing oil in a hoover according to Hoover. Then 10 grams of nitrocellulose lacquer (Fuller-Obrien No. 813-C-1011) were added which was mixed well. A 0.1 mm thick film in the wet state was then prepared on Morest White Cards and left to dry. As is known, a lower Y-value is desirable with a lower Y-value, because this represents a darker shade, which, in this case, indicates stronger black color strength. V Relative color strength is a comparison between the new magnetite according to the invention and Pfizer's technical magnetite (BK-5000 premium magnetite) which is arbitrarily given the color strength value 100. The measurements are performed using the Applied Color System "Q-check" program and a spectrophotometer according to Diano-Hardy. The samples were prepared as above and the Y values were determined. Table 1 shows that a typical magnetite preparation according to the present invention has a relative color strength of 109.7, while technically competing products have values between 54.7 and 100.0.

Eabell 1 Y-value Relative color strength Typical preparation of the magnetite according to the invention 15.78 109.7 Pfizers magnetite BK-5000 17.73 100.0 Reichard-Coulston # 724 18.93 84.9 Pfizers magnetite BK-5099 19.89 78 Bayers # 306 23.49 60.9 Toda Kogyo KM-340 25.05 54.7 The average particle size of the magnetite of the present invention is substantially smaller than that of known magnetites and more particularly, the magnetite of the present invention has about half the particle size. size as technical synthetic magnetites, with which the magnetite according to the invention can be expected to compete on the market. Table 2 indicates that the magnetite according to the invention has a particle length of less than approximately 0.08 μm (measured along the longitudinal axis of the particle using the Quantimet Image technique; Cambridge Imanco "Quantimet 720, System 20 Image Analyzer" with a Chords technology on transmission electron micrographs at 35,000X) and that comparable technical magnetites generally have 10 15 20 25 30 35 40 8001030-9 + 4 - a particle length between 0.155 and 0.197 μm. Other technically competing magnetites have a particle length between 0.13 and 0.30 μm. The magnetite according to the invention has a uniform particle size which is better than products available on the market, which is evident from measurements of the particle size distribution according to Quantimet. Due to the small particle size and the narrow particle size range (high degree of particle size uniformity), the magnetite according to the invention has a peculiarly large surface area (determined according to the BET method), as shown in Table 2. The BET method is the standard method in the field in question and is described in full in "Adsorption, Surface Area, and Porosity", by SJ Gregg and KSW Sing, Academic Press, 1967: Chapter 2. Table 2 indicates that a typical preparation of the magnetite according to the invention has a BET area of 18.3 m2 / gram, while competing products have corresponding values around 8.6 m2 / gram.

Table 2 Particle size, BET surface area, μm m2 / gram Typical preparation of the magnetite according to the invention 0.077 18.3 Pfizers BK-5000 0.197 8.6 Pfizers BK-5599 0.155 8.6 It is known in the field in question that the smaller the particle size is the larger the surface area must be. In the works on which the present invention is based, BET surfaces of up to 32.5 m2 / gram and particle sizes down to 0.048 μm have been observed.

The shape of magnetite particles according to the present invention has been determined by transmission electron microscopy; By applying this technique, it has been possible to determine that the particles are rhomboids with angles of 60 °. 7 The new material according to the present invention can be prepared from used pickling liquid of the hydrochloric and sulfuric acid type, i.e. ferric chloride or ferrous sulphate. A typical pickling liquid generally has an Fe ++ concentration of 0.9 - 2.4 moles per liter. The pickling liquid can be used as obtained from the steel rolling mill or it can be neutralized or concentrated by heating in the presence of scrap metal or by adding base. Sometimes it may be desirable to dilute the pickling liquid to the desired concentration. When using neutralized liquid, only a stoichiometric amount of alkali is required. In fact, preferably no more than this amount is used, because excess carbonate causes carbonate contamination of the black oxide. When using pickling liquid that has not been neutralized, a sufficient amount of additional alkali must be used to neutralize the free acid.

You can choose alkali from calcium carbonate, barium carbonate, sodium carbonate and strontium carbonate.

These carbonates can be natural products or they can be produced (precipitated) to the extent that they have a particle length of less than about 3.5 μm. Preferred alkalis are limestone with a particle size of up to about 3.5 microns, and soda. In general, the process can be summarized as follows: a) a stoichiometric amount of carbonate is added to the agitator; b) after heating the mixture to an aqueous solution of iron salt (pickling liquid) about SOOC, start inhaling; c) stirring, aeration and heating are continued until the reaction is complete. This can be determined by titrating the percentage of Fe ++ compared to the total amount of Fe ++ and Fe +++ in the magnetite slurry (nominal 33%) or by electro-analytical technique, ie measuring the oxidation-reduction potential using an electrometer with a platinum combination electrode; d) the magnetite thus obtained is extracted (for example by filtration), washed and subjected to possible drying, after which the product can be used as black ~ - ~~ - »- ff ~ ~ ~ -» V e -__ -. _.-..-- ~ _-... ~ ._...__.... 10 15 20 25 30 35 40 together ¿~ ß - pigment or it can be calcined, generally at a temperature above approx. GSOOC and below 925 ° C in the presence of air to give a red pigment; e) the red pigment may, if desired, be subsequently subjected to further processing by grinding.

One of the advantages of the present invention is that the expensive hydrochloric acid used in the steel pickling can be regenerated and returned to the pickling plant. If desired, the filtrate obtained after removal of the black pigment can be acidified with H 2 SO 4 to regenerate HCl. The following reaction takes place: znzo + caclz + Hzsot + caso; - znzo + zuci The waste product gypsum can be used as a building material or as a landfill. When working with pickling liquid containing H2SOt, CaCO3 and BaCO3 cannot be used as alkali, because these carbonates would form insoluble gypsum (CaSOt ° 2H2O) or BaSOt, which would precipitate together with the magnetite and contaminate the black pigment. . Instead, it is advisable to use Na3CO3.

When the pickling liquid contains H2SOt and Na2CO3 is used as the base, the soluble salt Na2SOr which usually remains after the FeSOt and Na2CO3 reaction is usually discarded for economic reasons and consequently non-acid regeneration is generally applied in the FeSOq / Na2CO3 scheme.

A preferred embodiment of the invention is carried out as follows: to a neutralized aqueous solution of ferric chloride containing about 111 to 381 grams of FeCl 2 per liter is added a stoichiometric amount of fine-grained calcium carbonate with moderate stirring of the mixture. The preferred average particle size for the calcium carbonate is between about 0.6 and about 3.5 microns. The temperature of the ferric chloride solution should be kept below 65 ° C and may be the room temperature at the time of the alkali addition.

After the calcium carbonate is added, the mixture is heated rapidly to 80 DEG C., after which air is introduced. The stirring speed is suitably increased and the aeration is continued until the reaction is complete. The solid components are separated (for example by filtration), washed and dried. The dried black product can then be ground to the final product.

According to a particularly preferred embodiment, the Fe ++ concentration in the pickling liquid varies between 1.4 and 2.4 moles per liter and, of course, a stoichiometric amount of calcium carbonate is used. Calcium carbonate has a particle size between 0.68 and 2.5 microns. The precipitation and oxidation are carried out at 20-65 and 75-8500, respectively. For economic reasons, a shorter oxidation time is usually applied and this is determined by means of the air flow rate, stirring and temperature.

At a preferred air flow rate between about 14 and about 42 liters per minute and a preferred agitation between 300 and 600 revolutions per minute using a pitch angle turbine paddle, the reaction is usually complete in the course of between about 230 and about 815 minutes. .

If it is desired to convert the magnetite to a red pigment, the magnetite is charged in the form of a wet filter cake or a dry powder in an oven and calcined in the presence of oxygen. After the calcination, the red iron oxide is suitably ground to the desired fineness, namely a particle size between about 0.1 and about 1.0 μm, which is usually. determined using a Micromeritics 5000 D sedigraph.

The following examples illustrate the invention, which of course is not limited to the measures and details set forth in the examples but encompasses everything that falls within the scope of the claims.

Example 1 45 liters of an iron (II) chloride solution containing 300 grams of FeCl 2 per liter were charged to a 75 liter reaction container equipped with a stirrer. The solution was heated to 6500 with stirring. When said temperature was reached, a stoichiometric amount was added in the course of 10 minutes, namely 10.662 kg of precipitated calcium carbonate with an average particle size of 1.8 μm. The mixture was aerated at 28 liters per minute and the stirring was increased to 600 rpm. The mixture was heated to 83 ° C and stirred and aerated while maintaining the temperature between 78 and 83 ° C until the reaction was complete. The total reaction time since the addition of the alkali was complete was 360 minutes. The slurry solid was filtered off, washed and dried at 70 ° C. The product thus obtained had a BET surface area of 25.7 m2 / gram, a relative color strength of 105.9 and an average particle size (harmonic) of 0.052 μm. 10 grams of the dried magnetite was charged to a stainless steel vessel and the vessel was placed in a laboratory size muffle furnace (Thermolyne model 2000) previously heated to 816 ° C. The sample was heated for 30 minutes, after which it was taken out and desaglomerated. Standard films were prepared in the manner indicated above for the magnetite and the samples were found to have a medium shade of red, clear, light characteristic.

Example 2 41.8 liters of ferric chloride solution containing 171.8 grams of FeCl 2 per liter were charged to a 75 liter reaction vessel equipped with a stirrer. While stirring at 300 rpm, the solution was heated to 65 ° C. 19.5 liters of a slurry containing 5.672 kg of ground natural limestone with an average particle size of 1.8 μm were then added. The mixture was heated to 80 ° C and kept at 78 - 8100 with stirring at 300 rpm and aeration with 14 liters of air per minute, until the reaction was complete. The total reaction time after completion of the alkali addition was 444 minutes. The solids were filtered off, washed and dried at 70 ° C. The product thus obtained had a BET surface area of 22.0 m 2 / gram, a relative color strength of 116.1 and an average particle size (harmonic) of 0.066 μm.

A 10 gram sample of the magnetite was calcined in the manner set forth in Example 1. In this case, the oxide was found to have a light shade of bright red (chromium).

Example 3 45 liters of an iron (II) sulphate solution containing 257.9 grams of FeSO 2 per liter were charged to a 75 liter 15 9 40-9-8001039-9 liter reaction vessel equipped with a stirrer. The solution was heated to 65 DEG C. with stirring at 300 rpm and then 8.106 kg of technical grade sodium carbonate were added over the course of 22 minutes. The mixture was heated to 80 ° C and air was introduced into the mixture at 14 liters per minute. The mixture was stirred and aerated while maintaining the temperature between 77 and 82 ° C, until the reaction was complete. The total reaction time since the addition of the alkali was 815 minutes.

The solids were filtered off, washed and dried at 70 ° C. The product obtained had a BET surface area of 15.8 m2 / gram, a relative color strength of 109.6 and an average particle size (harmonic) of 0.078 μm.

Example 4 45 liters of (unneutralized) ferric chloride solution (pH 0.5) containing 250 grams of FeCl 2 per liter were charged to a 75 liter reaction vessel equipped with a stirrer. To neutralize the free hydrochloric acid, 1,172 kg of ground natural limestone with an average particle size of 2.5 μm was added with stirring at 65 ° C. The mixture was heated to BOOC and air was introduced into the mixture at 42 liters per minute. In the course of 5 minutes, an additional 8,878 kg of the limestone described above was added. After the alkali addition, the mixture was stirred and aerated while maintaining the temperature between 79 and 81 ° C, until the reaction was complete (741 minutes). The solids were filtered off, washed and dried at 70 ° C. The magnetite product thus obtained had a BET surface area of 20.6, a relative color strength of 110.1 and an average particle size (harmonic) of 0.065 μm.

A sample of 10 grams of the magnetite was calcined in the manner set forth in Example 1. In this case, a medium red pigment was obtained.

Example 5 Magnetite was prepared by precipitation in the manner set forth in Example 1. The iron salt solution used was ferric chloride and the alkali used was precipitated calcium carbonate with an average particle size of 2.2 μm. The procedure was repeated seven times, the slurries thus obtained were combined, after which the solids were filtered off, washed, washed and dried. The process conditions are given in the following table.

FeC12-Con- Precipitation- Oxidationf Oxidation- Stirring Liter air concentration temperature temperature time, revolutions per minute grams / liter OC OC minutes minute 280,3 2 room temperature- '80 345 600 28 temperature 280,3 "" sno' "" 234 , 6 "" 232 f "" 234,6 "" 249 "" 243,8 "7 '244' V" 243,8 "" 269 "," 244,8 "" 619 "" The composite product had a relative color strength of 109.6, an area of 18.3 m2 / gram and an average particle size (harmonic) of 0.071 μm.

Example gel 6 45 liters of an iron (II) chloride solution containing 229 grams of FeCl 2 per liter were charged to a 75 liter reaction vessel equipped with a stirrer. While stirring at 300 rpm, the solution was heated to 65 ° C.

For 4 minutes, 10.639 kg of precipitated calcium carbonate with an average particle size of 0.68 μm was added.

The mixture was heated to 8000 and air was introduced, during which the mixture was kept at BOOC and under stirring. Aeration was continued until the reaction was complete. The stirring speed was 600 rpm and 28 liters of air were blown in per minute. The total reaction time was 264 minutes. The solids were filtered off, washed and dried at 70 ° C.

The obtained magnetite product had a BET surface area of 31.5 m2 / gram, a relative color strength of 134.6 and an average particle size (harmonic) of 0.048 μm.

Claims (1)

1. -11- 8001030-9 PATENTK RAV Synthetic rhomboid magnetite is characterized in that it has angles of 600, a Y-value of the color strength not exceeding 15.78, a BET surface area exceeding 13 mz / g and an average particle size less than 0.08 mm measured along the land axis.