NL8000795A - PROCESS FOR THE PREPARATION OF A SYNTHETIC RHOMBOEDRICAL MAGNETITE AND SYNTHETIC RHOMBOEDRIC MAGNETITE, WHICH CAN BE PREPARED BY THIS PROCESS. - Google Patents

Description

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Process for the preparation of a synthetic rhombohedral magnetite, as well as synthetic rhombohedral magnetite, which can be prepared by this process.

The invention relates to magnetite, which can be used as a pigment. In particular, this relates to synthetic rhombohedral magnetite, which is useful as a black pigment and which can also be calcined in the presence of oxygen to form a red alpha-ferric oxide pigment. This magnetite is prepared from waste pickling liquor by addition of carbonate, preferably in the form of limestone or anhydrous sodium carbonate.

Numerous patents have been issued for the process of preparing iron oxide from pickling liquids. Representative prior art in this regard are U.S. Patents 1,269.M2, 1,882,936, 3,261,665, 3U3U.797, 3,617,560, 3,617,562, 3,927,173, U,090,888 and k.107.267 and British Patent 1,218,601. According to all of these patents 15, waste pickling liquid is treated with some base to prepare an iron oxide. In most cases, the iron oxide formed is a black oxide, which can be used as a pigment, and sometimes this black oxide can be further calcined to form a brown or red pigment.

According to the invention, for the first time, a synthetic rhombidahedral magnetite is prepared from waste pickling liquor and carbonate, which is superior in color strength and unique in particle size, as evidenced by the observed large specific surfaces. In addition, this 800 07 95 2 new magnetite can be calcined in the presence of oxygen to a red pigment with very acceptable color properties and at very low cost.

The invention relates to a process for the preparation of a synthetic rhombohedral magnetite, in which: A. Ferrochloride solution with an Fe ++ concentration of about 0.9 to 2.1 moles per liter is contacted with a stoichiometric amount of carbonate ion, B the mixture is heated to a temperature of about 10 T0 to 90 ° C, C. the mixture is aerated to oxidize the iron to magnetite with a Fe / total Fe and Fe ratio of about 0.25-0.30 and D. Magnetite thus formed wins, the process being characterized in that the carbonate is provided in the form of finely divided particles with an average size of less than 3.5 microns.

Preference is given to a method in which the magnetite is calcined at a temperature of 50-925 ° C and in the presence of oxygen to prepare alpha-ferric oxide, the ferrous chloride solution comprising waste pickling liquid from the steel preparation and the carbonate from calcium carbonate exists.

The invention also relates to a synthetic rhombohedral magnetite prepared according to the method of the invention.

A synthetic rhomboid magnetite with a BET surface area greater than 13 m / g and an average particle size of less than about 0.08 microns measured along the long axis is also part of the present invention. Such materials range in size from about 0.0k to 0.08 microns.

The novel synthetic rhombohedral magnetite of the invention is unique in the following manner and when compared to the known magnetite and to the currently available magnetite: (1) high relative color strength, (2) 35 low Y value of the color strength, (3) a large specific surface area and (U) a small particle size.

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A characteristic Y value of the color strength of the magnetite according to the invention is shown in Table A and is 15.78. The Y values of the color strengths of commercially available competing magnetites range from 17.73 to 25.05, as shown in Table A. This determination is made using the FMC-II color equation and with a Diano-Hardy spectrophotometer. The samples were prepared by mixing 0.5g of pigment and 1.5g of titanium dioxide in a dispersing oil on a Hoover grinder. Then 10g nitrocellulose lacquer (Fuller-1Q Obrien No. 813-0-1011) is added and mixed well. Then a draw-down of 0.15 mm is made on Morest White Cards and allowed to dry. As is known, a low value for Y is desirable because it amounts to a darker shade, which in this case indicates a deeper black color strength.

The relative color strength is a comparison of the novel magnetite of the invention and the commercially available BK-5000 premium magnetite from Pfizer, which has been assigned an arbitrary relative color strength of 100. The measurement is made using the Applied Color System "Q-check" 20 program and with a Diano-Hardy spectrophotometer. The samples are prepared in the manner described above to determine the value of Y. Table A shows that a typical magnetite according to the invention has a relative color strength of 109.7, while commercially available competitive product have the value 25. between 5 ^ 7 and 100.0.

Table A

Y value Relative color strength

Typical Magnetite Preparation of the Invention 15.78 109.7 BK-5000 Magnetite (Pfizer) 17.73 100.0 ™ Reichard-Coulston $ J2k 18.93 8.9 BK-5099 Magnetite (Pfizer) 19.89 78 , 7

Bayer jf 306 23, 9 60.9

Toda Kogyo ΚΜ-3 ^ 0 25.05 5 ^, 7

The average particle size of the magnetite according to the invention is considerably smaller than that of the known magnetites. The magnetite according to the invention has about half the size of the commercially available synthetic magnetites, with which it is commercially available. must compete. Table B shows that the magnetite of the invention has a length of less than about 0.08 microns (measured along the long axis of the 5 particles using the Quantimet Image technique (Cambridge Imanco "Quantimet 720, System 20 Image Analyzer" using a Chords technique in transmission electron micrography and a magnification of 35000 times) and that comparable commercially available magnetites are generally between 0.155 and 0.197 microns in length Other commercially available competing magnetites range in length from 0, 13 and 0.30 microns.

The uniformity of the size of the present magnetite is superior to commercially available products, as indicated by determinations of the Quantimet particle size distribution.

Due to the small size and the narrower particle size distribution (a strong uniformity of the particle size), the magnetite according to the invention has a uniquely large specific surface area (measured according to the BET method), as can be seen from table B. The BET method is a standard method in the art and a full description thereof is found in "Adsorption, Surface Area, and Porosity" by SJGregg and KSWSing, Academic Press, 1967, chapter 2. Table B shows that a characteristic magnetite according to the invention has a BET surface area of 18.3 m / g, while competing products have a value of about 8.6 m / g.

Table B

Particle size BET surface (microns) (m2 / g) 30 - - -

Typical Magnetite Preparation of the Invention 0.077 18.3 BK-5000 (Pfizer) 0.197 8.6 BK-5599 (Pfizer) 0.155 8.6 It is known that the smaller the particle area, the larger the specific surface area. Specific BET-80 0 0 7 95 * u 5 o surfaces of 32.5 m / g and particle sizes of only 0.0U8 micron have been observed.

The shape of the magnetite particles according to the invention was determined by transmission electron microscopy. With this technique it was determined that the particles are rhombohedral and have angles of 60 °.

The new material according to the invention can be prepared from waste pickling liquor of both the hydrochloric acid (ferrous chloride) and sulfuric acid (ferrous sulfate) type. Typical pickling liquids generally have an Fe ++ concentration of 0.9 to 2.1+ moles per liter. The pickling liquid can be used as obtained from the steel mill or it can be pre-neutralized or concentrated by heating in the presence of waste iron or by adding a base. Sometimes it may be desirable to dilute the pickling liquid to obtain the desired concentration. When using neutralized liquid, only a stoichiometric amount of alkali is required; in fact, preferably no more than that amount is used because an excess of carbonate results in contamination of the black oxide with carbonate. When using pickling liquor, which has not been pre-neutralized, enough additional alkali must be added to neutralize the free acid.

The alkali used can be selected from calcium carbonate, barium carbonate, sodium carbonate or strontium carbonate.

These carbonates can be natural products or they can be prepared (precipitated) provided their length is less than about 3.5 microns. Preferred alkali products are limestone with a particle size up to about 3.5 microns and anhydrous soda. In general, the process can be summarized as follows: a) a stoichiometric amount of carbonate is added to an aqueous iron salt solution (pickling liquid) with stirring, b) after heating the mixture to about 80 ° C, aeration is started, c stirring, aeration and heating are continued until the reaction is complete. This can be determined by either determining the percentage of Fe by titration compared to the total of Fe ++ and Fe +++ in the magnetite slurry (nominal 33%) or by electro-analytical techniques, for example, measuring the oxidation reduction potential using an electrometer with a platinum combination electrode, d) the magnetite formed is recovered (eg by filtration), washed and optionally dried, after which the product can be used as a black pigment or calcined, generally at temperatures above about 650 and below about 950 ° C and in the presence of air to obtain a red pigment and e) the red pigment may be further processed by milling if desired.

One of the advantages of the invention is that the expensive hydrochloric acid used in pickling steel can be regenerated and returned to the pickling device.

If desired, the filtrate remaining after removal of the black pigment is acidified with H 2 SO 2 to regenerate HCl. The following reaction proceeds: 2H20 + CaCl2 + H2SO ^ - ^ CaS0 ^ .2H20 + 2HCl.

The waste product, gypsum, can be used as a building material or, if desired, as a bottom filler.

In processes using HgSO 2 for steel pickling, CaCO 2 and BaCO 2 cannot be used as an alkali because insoluble gypsum (CaSO 2 .2H 2 O) or BaSO 2 will precipitate along with the magnetite and contaminate the black pigment. In cases where HgSO 2 is used as a pickling liquid and NagCO 2 is the base, the soluble NagSO 2 salt remaining after the reaction between FeSO 2 and Na 2 O 2 is generally discharged and regenerated for economic reasons. Acid is therefore generally not used in the FeSO2 / NagCOg scheme.

A preferred embodiment of the invention proceeds as follows: To a neutralized aqueous ferrous chloride solution containing about 111 to 381g FeCl 2 per liter, a stoichiometric amount of calcium carbonate is added with moderate stirring of the mixture . The preferred average particle size of the calcium carbonate is between about 0.6 and 3.5 microns. The ferrous chloride temperature should be kept below about 65 ° C and may be equal to room temperature during the addition of alkali. After the calcium carbonate is added, the mixture is quickly heated to 80 ° C, after which air is introduced into the mixture. The stirring speed 1 q is preferably increased and aeration is continued until the reaction is complete. The solids are then separated (e.g., by filtration), washed and dried. The dried black can then be ground to a finished product.

In a particularly preferred embodiment of the invention, the Pe concentration m the pickling liquid is between 1, ¾ and 2, olen moles per liter and, of course, a stoichiometric amount of calcium carbonate used. The calcium carbonate particles range in size from 0.68 to 2.5 microns. The precipitation is carried out between 20 and 65 ° C and the oxidation is carried out between 75 and 85 ° C. Economic considerations generally dictate a shorter oxidation time.

The time for the oxidation is determined by the air velocity, the degree of stirring and the temperature. Preferably, air velocities from about 1¾ to liter2 liters per minute and stirring speeds (from 300 to 600 revolutions per minute using a "pitched" blade turbine) the reaction is usually completed in about 230 to 815 minutes.

If one wants to convert the magnetite to a red pigment, it is placed in an oven in the form of a filter cake or as a dry powder and calcined in the presence of oxygen.

After calcination, the red iron oxide is then preferably ground to the desired fineness, with a particle size of about 0.1 to 1.0 microns being common, determined according to a micromeritics 5000 D sedigraph.

35 The following examples are illustrative and not intended to be limiting.

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Example I

1 + 5 liters of ferrous chloride solution, containing 300g FeClg per liter, was placed in a Jé liter reactor equipped with a stirrer. The solution was heated to 65 ° C with stirring.

Once a temperature of 65 ° C was reached, a stoichiometric amount, 10,662 kg, of a precipitated calcium carbonate with an average particle size of 1.8 microns was added over 10 minutes. The mixture was aerated at a rate of 28 liters per minute and the stirring was increased to 60 revolutions per minute. The mixture was heated to 83 ° C

and was stirred and aerated, keeping the temperature between 78 and 83 ° C until the reaction was completed. The total reaction time after addition of alkali was 360 minutes. The slurry was filtered off, washed and dried at 70 ° C. The resulting product had a BET surface area of 25.7 m / g, a relative color strength of 105.9 and an average (harmonic) particle size of 0.052 microns.

10g of the dried magnetite was placed in a stainless steel dish and placed in a laboratory 20 µm muffle furnace, model Thermolyne 2000, which was pre-set at a temperature of 816 ° C. The sample was heated for 30 minutes, after which it was removed from the oven and de-agglomerated. Standard subtractions were prepared as described above for the magnetite and the sample was found to be an intermediate shade of red with clear, light properties.

Example II

1 + 1.8 liters of ferrous chloride solution, containing 171.8g FeCl2 per liter, were placed in a 76 liter reactor equipped with a stirrer. The solution was heated to 65 ° C with stirring at 300 revolutions per minute. Then 19.5 liters of a slurry containing 5.672 kg of ground natural limestone with an average particle size of 1.8 microns was added. The mixture was heated to 80 ° C and held at 78 to 81 ° C with stirring at 300 revolutions per minute and aeration with 14 liters of air per 35 minutes until the reaction was complete. The total reaction time after the addition of alkali was 1 + 41 + minutes. The solids were filtered off 80 0 0 7 95 * 9, then washed and dried at 70 ° C. The resulting product had a BET surface area of 22.0 a / g, a relative color strength of 116.1 and an average (harmonic) particle size of 0.066 microns.

A 10g magnetite sample was calcined as described in Example 1. In this case, the oxide was a light-colored, high "chroma" red.

Example III

1 + 5 liters of ferrous sulfate solution, containing 257.9g FeSO 4 per 10 liters, were placed in a 76 liter reactor equipped with a stirrer. The solution was heated to 65 ° C with stirring at 300 rpm and then 8.106 kg of technical commercially available sodium carbonate (NagCOg) was added over 22 minutes. The mixture was heated to 80 ° C and air 15 was introduced into the mixture at a rate of 1l + liter per minute. The mixture was stirred and aerated, keeping the temperature between 77 and 82 ° C until the reaction was completed.

The total reaction time after the addition of alkali was 815 minutes. The solids were filtered off, washed and dried at 70 ° C. The product obtained had a BET surface area of p 15.8 m / g, a relative color strength of 109.6 and an average (harmonic) particle size of 0.078 microns.

Example IV

1 + 5 liters (non-neutralized) ferrous chloride solution 25 (pH 0.5), containing 250g FeCl 2 per liter, was placed in a 76 liter reactor 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 microns was added with stirring at 65 ° C. The mixture was heated to 80 ° C and air was introduced into the mixture at a rate of 1 + 2 liters per minute.

An additional 8.878 kg of the above-described limestone was then added over 5 minutes. After the addition of alkali, the mixture was stirred and aerated at a temperature between 79 and 81 ° C until the reaction was complete (7l + 1 minutes). The solids were filtered, washed and dried at 70 ° C. The resulting magnetite product had a BET surface area of 20.6, a relative 800 0 7 95-10 color strength 110.1, and an average (harmonic) particle size of 0.065 microns.

A 10g sample of magnetite calcined as described in Example 1. In this case, a red pigment 5 with intermediate color was obtained.

Example V

Magnetite was prepared by precipitation as in Example 1. The iron salt solution used was ferrous chloride and the alkali was a precipitated calcium carbonate with an average particle size of 2.2 microns. The operation was repeated seven times, the resulting slurry solutions were combined, then the solids were filtered off, washed and dried. The operating conditions are summarized in the following table.

FeClp Precip. Oxyd. Oxyd. Stirring Air speed 15 _ 2 Temp. * Temp. Time (OPM) (l / min.) (G / 1) (° c) (° c) <““ ·> 280.3 Room Temp. 80 345 600 28 280.3 "" 300 20 234.6 "" 232 "" 234.6 "" 249 243.8 "" 244 243.8 "" 269 21 + 4.8 "" 619 25 --—-

The composite product had a relative color strength of 2 109.6, an area of 18.3 m / g, and an average (harmonic) particle size of 0.071 microns.

Example VI

1 + 5 liters of ferrous chloride solution, containing 229g FeCl 2 per liter, were placed in a 76 liter reactor equipped with a stirrer. The solution was heated to 65 ° C with stirring at 300 revolutions per minute. 10.639 kg of precipitated calcium carbonate with an average particle size of 0.68 micron was added over 4 minutes.

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The mixture was heated to 80 ° C and air was introduced into the mixture. The mixture was kept at 80 ° C with stirring and aeration until the reaction was completed. The stirring speed was 600 revolutions per minute and the air speed 28 liters per minute. The total reaction time was 2h minutes. The solids were filtered, washed and dried at T0 ° C. The magnetite product obtained had a BET surface area of 31.5 m / sec, a relative color strength of 13.6 and an average (harmonic) particle size of 0.08 micron.

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Claims (5)

1. A process for the preparation of a synthetic rhombohedral magnetite, wherein A. ferrous chloride solution with an Fe ++ concentration of about 0.9 to 2.1 moles per liter is contacted with a stoichiometric amount of carbonate ion, B. the mixture heated to a temperature of about 70 to 90 ° C, C. the mixture aerated to oxidize the iron to magnetite with an Fe / total Fe and Fe ratio of about 0.25 to 0.38, and D. the thus formed magnetite recovered, characterized in that the carbonate is provided in the form of finely divided particles with an average size of less than 3.5 microns. A method according to claim 1, characterized in that the magnetite is calcined at a temperature of 650 to 925 ° C and in the presence of oxygen to form alpha ferric oxide. 3. Process according to claim 1, characterized in that the ferrous chloride solution consists of waste pickling liquid from the steel preparation. h. Process according to claim 3, characterized in that the carbonate consists of calcium carbonate. 5. Synthetic rhombohedral magnetite obtained according to the method of any one of the preceding claims. 6. Synthetic rhombohedral magnetite with a BET surface area greater than about 13 m / g and an average particle size less than about 0.08 microns, measured along the long axis. J 800 0 7 95