CA1115932A

CA1115932A - Process for the preparation of pigment grade iron oxides from waste ferrous sulphate and the resulting fe.sub.2o.sub.3 pigments

Info

Publication number: CA1115932A
Application number: CA336,645A
Authority: CA
Inventors: Pierre J. Portes; Jean-Marie Trautmann; Daniel Hoffner
Original assignee: Thann and Mulhouse SA
Current assignee: Thann and Mulhouse SA
Priority date: 1978-10-04
Filing date: 1979-09-28
Publication date: 1982-01-12
Also published as: FR2438075B1; FR2438075A1; BE879146A; JPS5550069A; ZA795143B

Abstract

Abstract of the Disclosure This invention relates to a novel process for producing pigment grade Fe203 from waste ferrous sulfate by a roasting process. Waste ferrous sulfate is partially converted to the oxide by roasting and after elimination of soluble constituents by washing, the oxide is subjected to pigmentary calcination and then crushed and if desired, micronized. The process produces red pigments of excellent quality which are characterized by pure tints ranging from orange-red to purplish-red with low oil absorption levels. The pigments find a variety of uses and in view of their low toxicity, may effectively be used in foodstuffs.
The process provides a useful means to convert previously waste by-products into commercially viable products more effectively than any other prior art process. The products thus produced exhibit excellent qualities for use as pigments.

Description

S~3~

g This invention relates generally to the preparation of pigment grade iron oxides and more particularly, to the pre~
paration of pigment grade Fe2O3 from waste ferrous sulfate by a roasting process.
In the past, waste ferrous sulfate has presented a problem to many lndustries. In particular, waste ferrous sulfate is produced from pickling plants and from the production of titanium dioxide by tne sulfuric process as a by-product and its discharge and disposal creates many problems including ecological and handling problems for these industries.
The neutralization of this waste product is costly and generally results in unsaleable products, which also raises storage problems. For many years, processes have been proposed involvin~ roasting of the iron sulfate with the formation o~
sulfur oxides which can be recycled for the production o~ sulfuric acid, but the ferric oxide also produced by the roasting is coarse and possesses inadequate pigment grade properties (see for example, German Patent No. 921,264). The production of sulfuric acid by this method is only competitive if the iron oxide which ~O accompanies it is a high quality product which is utiliza'~le on the market, such as with red Fe2O3 pigments with good colour purity.
However, the iron sulfates with whicll this invention is concerned generally contain metallic impurities which, when roasted, com~ine with the iron oxide and lower its colour purity.
More recently, several processes have been proposed which are designed to eliminate these impurities. For example, re~erence is made to German Ausle~eschxift serial number ~ 2~8 (published on ~ovember 28,1963) whicll recites a process which includes roasting to convert 80 to 95% of the iron sulfate to the oxide, followed hy washin~, in the course of which certain ~5~a3~

1 cations such as ~n, which remain in the form of soluble salts, are eliminated. Following this treatment, pure ~ Fe203 oxide is effectively obtained, but it only has mediocre pigment properties, owing to the fact that the roasting time/ternperature combination required to elimina-te the harmful cations fails to i~part optimum dimensions to the oxide particles. Moreover, pigment preparatiOn is not the object of the German Ausleaeschrift serial nu~ber 1 144 248, as the purified ~ Fe2O3 oxide serves as a base for the subsequent preparation of ~ Fe203. Similar ob-servations can be made in connection with US Patents 2,184,738 and 2,416,138.
A further process also has been proposed ~see French Patent Number 2,296,671) in which the harmful metallic cations are eliminated by partial roasting followed by washing. I-lowever, this process applies to a raw material other than iron su7fate, jarosite. Moreover, the achievement of well defined pigment ; yrade properties is subject to the precise adjustment of the partial pressure of SO2 or oxygen in the ~urnace, and this is di~ficult to achieve on an industrial scale.
Accordingly, it is an object of the p~esent invention to at least partially overcome these disadvantages by providing a process for converting a previously-k~own pollu-tant by-product into a saleable product.
It is a ~urther object of this invention to provide a process for converting iron sul~ate to a commercially usable pigment grade iron oxide.
It is a still further o~ject of this invention to provide a pigment grade iron oxide from waste ferrous sulfate.
To this end, in one of its aspects, the invention provides a process for produci~g red Fe2O3 pig~ents from 3~

1 E'eSO~ 7 H2O which comprises roasting partly dehydrated ancl granulated FeSO4 7 H2O, washing the resulting product, followed by pigmentary calcination and cru.shing.
In another of its aspects, the invention furtller provides a process for producing red Fe2O3 pigments from FeSO4 7 lI2O which comprises (a) roasting partly dehydrated and granulated FeSO4 7 H2O to convert 90 + 5% of said FeSO~ 7H2O to the oxide in the presence of a reducing agent in an externally heated furnace in which the roasted material and the roasting gases are collected continuously at the same end of .said furnace, said reducing agent being added in an amQUnt between 0.1 and 2 times the stoichiometric amount; (b~ subjecting the resultant product to a washing treatment without mechanically destroying said granules, said washing comprising the steps of washing with wa~er, treating with a hot alkaline solution, then washing with water; (c) sub~ecting the resulting pxoduct to pigmentary calcination in a furnace flushed by a gas flowing in a countercurrent dlrecti.on to said iron oxide at a temperature of between abaut 750C. and about 1000C.; (d) crushlng the resulting product.
In yet another of its aspects, the invention further provides red Fe203 pigments with orange-red to purplish-red tonality characterized by the fact that they exhibit an oil absorption lower than 12.5.

Further objects and advantages o~ the invent.ion will appear from the following description.
The objects o~ tl~e present invention may be achieved by subjectincJ the waste ferrous sulfate to double roasting with intermecliate washing, followed by crushing and if desired, micronization, LSit~3~

1 The term double roasting refers to a process which in-cludes an initial roas~ing, which may be conducted in the presence of a reducing agent, carried out on partially dehydrated FeSO4 7H2O , washing of this roasted product, followed by a second roasting - corresponding to pigmentary calcination of the residue from the previous operations. The final result is a red Fe2O3 pigment dis~inguished by excellent pigment grade characteristics. The first roasting is per~ormed so that about 90% of the iron sulfate is converted to the oxide; the second roasting or pigmentary calcination is performed at temperatures ranging from about 750C. to about 1000C.
A preferred embodiment of the invention will now be described.
Ferrous sulfate is generally available in the form of the heptahydrate. The direct introduction o~ this salt into a furnace raises problems because, by melting at less than 100C., it easily forms crusts which are detrimental to the satisfactory operation of the furnace. Hence it is pre~erable to feed the roasting furnace with a partially ~e}lydrated salt, particularly the monoh~drate. The latter should be available preferab:Ly in the form of granules which are 0.5 to 3 mm in diameter.
Roasting is carried out preferably in an externally heated furnace in order to avoi~ dilution of the sulfur oxides ~SO2r SO3) by combustion gases tco2, N2, excess 2) so as to enable their use for the production o~ sul~uric acid. It may be assumed that t~le reaction occurs as follows:

2FeSO4 x E20 ~ Fe203 ~ S02 3 2 (l) The temperature/~urnace residence time combination is selected so that about 90 ~ 5% of the iron present is converted to the o~ide, the rest remaining in soluble form. This is a com-promise whereby almost all the harm~ul impurities such as Mn, Mg 3~

1 and Co remain in soluble form, while achieving a satisfactory conversion yield to Fe2O3. This result is obtainecl at -temperatures ranging ~rom about 650 to about 800C., and residence times ranging from about 10 minutes to about 10 hours.
Roasting is improved if a certain amount of reducing agent (hereinafter referred to as R) is incorporated with the iron sulfate, such as carbon, sulfur or a llydrocarbon. The role of the reducing agent is to shit the equilibrium relation (1) to the right by the elimination o-f SO3 by a reaction of the type:
SO3 + R- ~ So2 + RO (2) It is recon~nendea that the quantity of reducing agent used be between 1 and 1.5 times the stoichiometric amount. A
particularly advantageous reducing agent is sulfur. In this case, the roasting reaction becomes:
4FeSO4 x H2O + S -~2 Fe2O3 + 5SO2 f 4 ~ H2O (3) Within the limits of unavoidable air infiltration into the furnace, it can be seen that the use of sulfur helps to obtain gases which are especially rich in sulfur oxide because, due to the use of an indirectly heated furnace, the only diluent is

2~ water vapourO The advantage offered by the use of a reducing agent resides in tlle fact that the roasting temperature is lowered by some 100C., thus lengthening the service life of the refractory metal which is used to line the furnace interior to acilitate heat transEers. Another advantage lies in the pro--duction of a non-oxidizing atmosphere, which also enhances the behaviour oE the metallic lining. The use of sulfur is also especially advantageous because, apart rom its beneficial efEect on the hea-t balance, the costs of additional raw materials ar~ offset by the corresponding sulfuric acid obtained.
The solids and gases should preEerably be in concurrent 1 flow in the roasting furnace, so that the sulfur which is dis-tilled at the furnace inlet is able to oxidlze in contact with the solids, or in the ~as phase itself before being able to escape.
The substance obtained at the furnace outlet occurs in the form o~ granules with dimensions approaching those of the dry iron sulfate charged initially into the furnace, and mainly contains Fe2O3 accompanied by about 10% iron remaining in the soluble state. The harmful impurities such as Mn, Mg and Co remain in soluble form. After purification, the sulfur oxides leaving the furnace are recovered for the production of sulfuric acid.
The roasted product is washed with water, but in order to obtain neutral pigments more easily, it is more advantageous to supplement this washing by hot alkaline treatment, for example with 0.1 N caustic soda, followed by a second washing with water.
Washing may pre~erably be carried out in a stationary bed with upward water flow, or more preferably, on strip filters and, in a more general manner, with any suitable system which does not subject the granules to mechanical stresses which are liable to destroy them.
After washing and drying, the iron oxide generally con-tains over 97% Fe2O3. The only impurities remaining in signifi-cant proportions are Ti (in tne case of iron sulfate from ilmènite) and S. ~`he latter is eliminated by the final calcin-ation of the oxide. The presence of Tio2 up to concentrations o~ 2~ is not detrimental for the pigment grade properties oE
the finished product. The washed and dried prod-lct obtained at this stage still only possesses very inadequate pigment grade

3~ properties, because the oxide particles are not yet of suitable si,ze. It i5 well knowil that particle size is an important factor influencing pigment characteristics.
The second roasting which plays the role of pigmentary calcination is advantageously performed in a directly heated furnace, but any other furnace allowing gas flow above the product is suitable. The gases and solids should preferably be in countercurrent flow in this furnace, so as to evacuate the waste sulfur oxides satisfactorily, and thus to ensure that tlle finished product has satisfactory pH and resistivity. The tem-perature and residence time are selected in order to obtain the desired red pigment shade: lower temperatures (750 - 820C.
yield small orange-red crystals, and higher temperatures (900 - 1000C.) yield larger purplish-red crystals. Neutral red tints, lying between orange-red and purplish-red, are obtained at intermediate temperatures ~820 900C.~. ~ particu]arly interesting pigment range is obtained by calcination for 1 to 10 hours in the interval 750 - 1000C.
At the outlet of the calcination furnace, the product is cooled and undergoes crushing in routine conditions prevailing in the inorganic pigment industry. Micronization can be used to supplement grinding, to ensure excellent dispersibility of the pigment in binders, and greater brilliancy of the lacquers pig-mented with this oxide.
This invention thus solves the ecological problem raises by waste iron sulEate, because it permiks its utilization for the production of sulEuric acid and high pigment grade iron oxide.
One advantage o~ the process is that it produces a ~ide range of red pigment tints by means of variations in a parameter which is easy to control; that is, the final calcination temperature.
The elimination of harmful impurities by the process also offers 3L5~3~

1 the advantage of giving these pigments a colour purity whicll ma]ces them at least comparable to the best red pigments available on the market. The pigments thus obtained have a colourant power equal to or greater than currently marketed Fe2O3 pigments.
Other charact~ristics of the pigments produced by the invention process are far superior to those of existing pigments. Thus oil absorption represents less than half of that of available pig-ments: this of~ers the user an economic and ecological benefit, because he can consequen-tly use less solvent in paints containing this oxide, while obtaining the same visc~sity. The cl~emlcal composition of the pigments is another important advantage of this invention. Using iron sulfate produced by the titanium pigment industry, the only imp~rity which can remain in a signi-ficant concentration is ~iO2. As it so happens, TiO2, within the 2~ limit encountered in practice, is not harmful to colour purity.
Tllis is particularly important if the pigments obtæined are used to colour foodstuffs, packings and plastics~ These pigments are subject to maximum concentrations of toxic imp~rities established for foodstuffs, by various governmental authorities.
For example, in France, these are set by Article 8 of the Decree of 15 October 1964 published in the Journal Officiel dated

4 November 1964. The purification treatment inherent in the invention contributes to eliminate some of these impurities con-tained in the waste iron sulfate which served as a raw material, so that the pigments obtained largely satisfy the legal purity requirements, whereas these limits are sometimes exceeded in com-rnercially available pigments. The fact that the red pigments produced by the invention porcess satisfy legal purity requirements for their use in foodstuffs is a significant advantage over pig-ments currently available on the market.

3~2 1 These different advantayes are illustrated by the following examples. Most testing ~ethods employed are standard practice forprofessionals.
However, some of them have been specially developedand are clarified below.
For iron oxides, the determination of certain colouri-metric properties is more sensitive if, ins-tead of pigmen-ting resin with pure Fe203, a mixture of pigments is added to the resin, this mixture consi~ting in the same Fe203 with a Tio2 pigment in given proportions.
This gives rise to so-called "shaded off" paint in which the TiO2 plays the role of enhancing the colourimetric characteristics of the iron oxide. ~he rate of shading is defined by the weight ratio Fe~03 / Tio2 ~ Fe203. ~11 the comparative tests were performed with a shading rate of 25%. The use of a second pigment such as TiO2 in addition to ~e203 is also necessary to determine the tinting strength of this Fe203. The tinting strength may be defined by the equation:

TS = 100 x 25 ~ .
where-t is the shading rate which must be used with the test sample for the corresponding paint, checked by means of a colouri-meter, to have the same Y filter raflectance as the reference piyment to whicll it is compared, the latter itself contained in a 7.5~ shaded paint. For example, in order to obtain the same Y
tint inte~sity as the re~erence oxide in the 25% shaded paint, the sample must be shaded off by Z2%, so that the tining strength of this sample in comparison with the reference is:
100 ~ 25 = 113.6%

_ 9 _ In a qualitative manner, thls may be summarized by saying that a sample of red has greater tinting strength if it is mixed in smaller amounts with a given mass of TiO2 to obtain the same reference pink.
Another important characteristic of a pig~ent is the colour deviation (~C) which it exhibits in comparison with existing good quality products. A new oxide is considered to be satisfactory if, in;relation to one of the existing commercial grades, it exhibits colour deviation not exceeding the limit corresponding to measurement accuracy ~or ac about 1.5) and if, moreover, its tinting strength is greater than or equal to that of the known pigment. Colour deviations ~C taken into considera-tion in the following examples have been established as follows:
alkyd resin base paint samples are prepared with a 25~ shading rate with each of the known oxides, and the corresponding tri-chromatic coordinates X,Y, Z are measured. Using the same formulation, the pigment obtained by the invention process is added to the binder, and -the reflectances are measured with tri-stimuli filters X, Y, Z. The colour deviation ~C is then determined ~ in MacAdam units, National ~ureau of Standards, Draft Standard ASTM D 2244-64T) between the sample and the dif-ferent known oxides. Among known pigments, the one against which the oxide prepared by the invention process can be compared is the one which most closely approaches i-t in chromaticity, i.e.
the one which exhibits the smallest colour deviation in relation to it~ This determination of the known pigment which most closely approaches a given sample re~uires time-consuming calculations which we carried out successPully with the use of a microcomputer.
If ~C is lower than 1.5~ it is considered that the difference 3~ between the sample and the reference is insignificant, i.e. that 1 the colour purity of the sample is as good as that of the corresponding pigment existing on the market. All comparisons presented in the examples deal with pigments prepared in accordance with the state of the technique, or by the invention process, with their commercial co~nterpart with the nearest chromaticity.
One of the particularly interesting elements of this comparison is the value of the Z component given by the colourimeter, because this is characteris~ic of the tonality of the red obtained.
With 25% shading, quality pigments currently available on the market cover an interval ranging from about Z = 15 (for orange tonalities) to Z = 38 (for the most purplish tonality~.
The dispersibility of the pigments, expressed in microns, is measured by a North gauge after 5 and 30 minutes of crushing of the oxide in alkyd medium, in the presence of 4 mm diameter glass balls. The lower these values, the better the fineness of the crushing and hence the dispersibility.
The pH of the pigments is measured in accoxdance with AFNOR Standard T 30-035. It is generally considered that pi~nents of which the aqueous extract has a pX from S to 9 are satisfactory.
The aqueous sùspensions obtained by working in accordance with this Standard have also served to determine indirectly the soluble salt content o~ the finished product. ~o do this, the resistivityof the aqueous extract is measured: the higher the resistivity, the lower the soluble salt content.
Oil absorption is determined in accordance with AFNOR
Standard T 30-022. The fi~ures expressin~ the oil absorption represent the rate o oil required to obtain a firm, smooth paste with 100 g of pigment.
Brilliancy is measured with a Zeiss GP 2 brilliancy meter, at an angle of incidence of 20 , on OVen-baked alkyd paints, g with a volumetric pigment concentration of 16. The higher this figure, the better the brilliancy.
Exampl_ l The raw material employed was a ferrous sulfate ob-tained from Tio2 production by the sulfuric me~hod, characterized by a Mn/Fe2O3 ratio of 0~63%. Its more complete analysis is the following:
FeSO~ 7H2O 94% Fe 19% SO4 34.75~
Mn 0~18~ Ti 0.13% Mg 0.20% Zn 0.02%
Co 0.003%
An iron oxide free of solubilizable impurities was prepared in accordance with the German Patent ~ No.
11 44 248. The previously dehydrated salt aggregated in 3 mm diameter granules was roasted until a conversion rate to Fe2O3 of 91.7% was obtained; roasting lasted 15 minutes at 800C. The roasted product was subjected to intensive washing with water, dried and crushed, then subjected to tlle series of pigment and analytical tests. The results are given in Table l (example l, Column e). It may be seen that the chemical purity is satis-~actory. On the other hand, certain essential pig~ent yradeprop~rties are clearly deficient. The comparison with an existing range of commercial high quality red p~gments shows that the ~ ,~bl/'cc2f.c~1 sample prepared by the German Patenti~}h~x~ ll 44 248 most closely resembles the most orange pigment (Z = 14) (Column h), but that, even in comparison with this pigmellt, it exhLbits a high chromatic deviation ( ~C - 2.6). The procedure described in this patent fails to produce p:igments characterized by Z values higher than about 14~ The neutral or purplish reds are therefore un-obtainable. It may also be observed that the pll falls outside the standard limits, and the soluble salt content is fairly hi~h, 3~

1 so that the oxide thus obtained fails to meet the objective set in this invention.
Example 2 FeS04 7H2O from the same source as that of Example 1 was partially dehydrated and granulated in a Niro Atomi~er (Copenhagen) spray granulator. The 1 to 3 mm diameter FeS04 H20 spherules obtained were introduced by a worm screw continuously at the rate of 4 kg per hour into a 2 meter long horizontal rotary furnace. The solids travel in a 20 cm diameter NS 30 refractory steel 'tube, externally heated by gas by means of a Meker burner rack subjected to automatic temperature control. The partially roasted iron sulfate and roasting gases are withdrawn at the same end of the furnace. The average residence time of the solid in the furnace is 1. 5 hours The furnace temperature was regulated to 790C. The oxide obtained was crushed and sub-]ected to di'fferent tests. The resul~s in Table 1 show that the commercial pi~ment most closely approaching this oxide is char-acterized by a Z of 17.5 with 25% shading. In comparison with this commercial oxide, the pigment prepared in Example 2 exhibits a large chromatic deviation (AC = 3.9) which reflects the lack of purity caused by foreign cations. Furthermore, this oxide has a sharply acidic pH and a high soluble salt content. It may ~e noted that owing to its high Zn content, this oxide does not meet the maximum concentrati.on requirements imposed by the Decree of 15 October 1964. The product thus obtained is consequently'not a quality pigment.
Exam~le 3 Ferrous sul~ate from the same source as that used in Examples 1 and 2 was dried and granulated as indicated in Example 2. The granules were mixed with crushed sulfur in the ratio - 13 ~

~s~

1 S/FeSO4 H2O = 5%. This mixture was introduced continuously by means of a suitable worm screw into the roasting furnace already used in Example 2. The furnace temperature was 670C.
and average residence time was 1.5 hours. The fraction insolubili~ed Fe/total Fe was 91%. The roasted granules ~ere placed on a Buchner, where they under~7ent washing by upward water flow up to total elimination of the soluble iron. The product was then placed in contact with boiling 0.lN caustic soda, and then washed again with water~ The washed product was oven dried and then calcined in a second horizontal furnace pro~ided with vigorous countercurrent air flushing. The temperature was 820C, average residence time was 1-1/2 hours, and the washed and dried oxide feea rate was 2 kg/hour. After cooling, the oxide was crushed in a ball mill and micron.ized.
Table 1 shows that the pigment obtained has a chroma-tlcity closely approaching ~ C - 0.6) that of a commercial quality pigment with a tonality leaning towards orange ( Z = lS).
However, the tinting strength of the sample prepared by the invention process is greater (113). The oil absorption of 10.1 ZO is much more favorable than that of the similar pigment available on the market ~28~. A clear advantage ~n bri.lliancy can also be observed. Very large diferences also appear in harmful element contents, for which maximum allowa~le limits in pigments intended for colouring foodstuffs are established by the ~inisterial Decree of 15 October 1964. Contrary to the corresponding com-mercial p.igment, the impurity concentrations of the oxide in Example 3 are lower than the maximum concentrations. (mhese maximum concentrations are noted in the right-hand column o Tables 1 and 2).
Thus, it may be seen that the pigment prepared by the 3~

1 inventlon process exhibits significant advantages over a corresponding good quality pigment currelltly available on the marketO
Example 4 Example 3 was repeated except that the only difference was that the temperature of pigmentary calcination was 845C.
instead of 820C. The chemical and pigment grade characteristics of this sample, shown in Table 2, show that, as in the previous example, the slighly orange-red pigment obtained offers significant 1Q advantages over its equivalent known before the invention .
Example 5 Examples 3 and 4 were repeated except that the only difference was that the pigmentary calcination temperature was ~80~. The pigment obtained was crushed in a ball mill but not micronized. T~is yielded a red pigment offering the advantages already mentioned in Example 3 over a standard pigment (see Table 2).

Example S was repeated except that the calcination tem-2~ perature was 960C. The pigment thus obtained i5 a clearly purplish-red, corresponding to the other extreme of the Fe2O3 reds on the market. ~ere again, Table 2 shows the many charac-teristics for which the pigment produced by the invention process is superior to its known equivalents.

~:3hs~3~

Table 1 . characteristlcc Example 1 ~ Example 3 (~) . _ . . ~_ . .. __. ___ ~
e h e h e h corcen~
.~ . _ _ _ ~ _ ~ tra~ion~
A : shaded off 21.9 25 26.1 25 22.2 25 B : coordinates .
Y 22.9 22.9 20.0 20.0 21.0 21.0 X 30.2 29.6 25.4 26.0 27.9 27.8 Z 13.0 ~.4.0 15.~ 17.5 ~.5.1 15.0 . . _ , _ _ - . -.-.- ------I
C . chromatic deviation~C 2.6 3.9 0.6 __ .___ . , ...
D : tinting strength 114100 96 100 113 100 E : oil absorption 2S.429 10.5 26 10.128 F : brilliancy 29 21 28 30 58 20 G : fineness in

5 min 95 75 90 65 80 80 30 min 40 37 35 35 35 40 }I : pH 2.67.4 2.9 5.7 6.37.5 I : resistivity 0.77.2 1.0 5.1 4.67.0 kohm ~ cm _ ._ ._, _ _ _ ._ ._ __ _ % Fe2O3 96.196 96.0 96 97. a 96 :~
~ Mn 0~01 ~.07 0.6 0.09 0.02 0.09 As mg/kg 0.1150 4 95 1- 140 5 Pb mg/kg ~2 7~ 2 72 ~ ~ 79 2~
Sb mg/kg <25<25 <25 <25 <2S <25 100 Cu mg/kg 5524 6 690 4 520 100 Cr mg/kg 855S 7 835 ~5 500 100 Zn mg/kg 6437 600 420 <5 405 loO
5O4Ba mg/k~ <5LG00 <51 O O < 5 9S0 100 .

The de-tailed key corresponding to this table is gi.ven in Table 3.

5~

Table 2 . _ ~ _ __ Exa~ple 4 Example 5 Exa~p~e 6 . .
characteristics max.
e h e h e h concen-trations ___ _ ~ ._ _ A : shaded off 22.4 2523~0 25 23.3 25 B : coordinate Y 20.1 20.122.2 22.2 30.3 30.3 X 25.7 26.026.6 26.7 32.7 32.7 Z 17.~ 17.824.3 2g.5 37.5 38.0 _ ._ __ ._ _ ..
C : chromatic deviation ~C 1.1 0.6 O.S
... _ . ._ . .. _ _ D :tinting 111 100109 100 107 lOC
strength absorption 9.4 2S 9.0 22 9.5 15 F :brilliancy 76 35 50 29 32 16 G : fineness . .
: in ~
5 min 60 60 80 55 62 37 . - 30 min 22 30 30 27 37 27 H : plI 6.5 5.7 6.2 5.4 7.67.0 I : resistivit~ .
kohm x cm 5.1 7.0 16 10 18 18 .~ . ~_ ~ ~ ............... ~
~ Fe23 97.2 96 97.2 96 97 96 % Mn 0.03 o,oC 0.01 0.1~ 0.04 0.07 As mg/kg l.S 100 2 80 1.8 75 5 Pb mg/kg <2 63 <2 70 ~2 64 20 Sb mg/kg ~25 <25 <25 <25 <25 <2S 100 Cu mg/kg 6 727 5 415 6 354 100 Cr mg/kg <5 869 <S 612 <5 426 100 Zn mg/kg <5 424 <5 395 <5 211 100 BaSO4 my/ky <5 50 <5 1500 <5 3200 100 . . ~ ~ .. _ _ _ . _ The detailed key corresponding to this tabl is given in Table 3 ~f~

Table 3 De ~ to ~ables 1 and 2 A ShadincJ rate t ~in ~) to be used with tl~e sample (e) to obtain the same Y as for the equivalent commercial pigment with 2S% shading off ~h~
B trichromatic coordinates at t shading ~ for -the sample (e~ and with 25~ shadiny for i.ts corNmercial e~uivalent (h) C chromatic deviation ~C betwean the sample in the example (e) and its commercial equivalent ~h) D tinting strength of the sample (e) in comparison ~ith its commercial equivalent ~h) : TS = 2500/t E oil absorption tg of oil per 100 y of pigment~
F brilliancy G crushing fineness in microns.measured after 5 and 30 minutes of crushing in the presence of balls H pE determined in accordance with AFNOR Standard I resistivity of the aqueous extract expressed in kilohms cm .e characteristics of the pigment described in the exarnple h characteristics of the commercial pigment with the closest chromaticity a maximum concentrations of toxic impurities imposed by Ministerial Decree of lS October 1964 ~ournal Officiel date 4 November 1964) relative to substances usable for coloring foodstuffs For all the pigments presented in Tables 1 and 2, the impurities Cd, Hg, Se, Tl U, CrO~2~, Ba2+ and organic constituents are either undetectable or in a concentration lower than the miximum limits imposed by the Decree.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for producing red Fe203 pigments from FeS04 7H20 which comprises roasting partly dehydrated and granulated FeS04 7H2O in which 90 ? 5% of said FeSO4 7H20 is converted to the oxide by the roasting, washing the resulting product, followed by pigmentary calcination at temperatures of from about 75 a to about 100 a °C and crushing.

2. A process as claimed in claim 1 where said roasting is conducted in the presence of a reducing agent.

3. A process as claimed in claim 1 or 2 wherein said roasting is conducted continually in an externally heated furnace in which the solid roasted material and roasting gases are col-lected continuously at the same end of the furnace.

4. A process as claimed in claim 1 or 2 wherein said roasting is conducted continually in an externally heated furnace in which the solid material and roasting gases are collected continuously at the same end of the furnace, said gases being used for the production of sulfuric acid.

5. A process as claimed in claim 2 wherein said reducing agent is sulfur.

6. A process as claimed in claim 5 wherein said sulfur is added in an amount between 0,1 and 2 times the stoichiometric amount.

7. A process as claimed in claim 5 wherein said sulfur is added in an amount between 1 and 1.5 times the stoichiometric amount.

8. A process as claimed in claim 1, 2 or 5 wherein said granules are not mechanically destroyed by said washing.

9. A process as claimed in claim 1, 2 or 5 wherein said washing comprises treating with water, treating with a hot alkaline solution, then treating with water.

10. A process as claimed in claim 1 or 2 wherein the pig-mentary calcination is carried out in a furnace flushed by a gas flowing in a countercurrent direction to the iron oxide.

11. A process as claimed in claim 1 or 2 wherein said pimen-tary calcination is carried out between about 750°C. and about 82°C.

12, A process as claimed in claim 1 or 2 wherein said pig-mentary calcination is carried out between about 820°C, and about 900°C.

13. A process as claimed in claim 1 or 2 wherein said pig-mentary calcination is carried out between about 900°C, and about 1000°C.

14. A process as claimed in claim 1 or 2 wherein the pigment is micronized subsequent to crushing.

15. A process for producing red Fe2O3 pigments from FeSO4 7H2O which comprises (a) roasting partly dehydrated and granulated FeSO4 ? 7H2O to convert 90 -? 5% of said FeSO4 ? 7H2O to the oxide in the presence of a reducing agent in an externally heated furnace in which the roasted material and the roasting gases are collected continuously at the same end of said furnace, said reducing agent being added in an amount between 0.1 and 2 times the stoichi-ometric amount;

Claim 15 continued ....

(b) Subjecting the resultant product to a washing treatment without mechanically destroying said granules, said washing comprising the steps of washing with water, treating with a a hot alkaline solution, then washing with water;

(c) subjecting the resulting product to pigmentary calcination is a furnace flushed by a gas flowing in a countercurrent direction to said iron oxide at a temperature of between about 750°C. and about 1000°C;

(d) crushing the resulting product.

16. A process as claimed in claim 15 wherein said roasting gases are used for the production of sulfuric acid.

17. A process as claimed in clam 15 wherein said reducing agent is sulfur.

18. A process as claimed in claim 17 wherein said sulfur is added in an amount between 1 and 1.5 times the stoichiometric amount.

19. A process as claimed in claim 15 wherein said pigment is micronized subsequent to crushing,

20. Red Fe2O3 pigments with orange- red to purplish-red tonality characterized by the fact that they exhibit an oil absorption lower than 12.5.

21. Red Fe2O3 pigments with orange-red to purplish-red tonality characterized by the fact that they exhibit an oil absorption lower than 10.5.

22. Pigments as claimed in claim 20 with orange-red to red tonality characterized by the fact that, when incorporated in an oily binder, the paint film obtained has a brilliance greater than 50.

23. Pigments as claimed in claim 20, 21 or 22 characterized by a resistivity exceeding 4000 ohm x centimeter,

24. Red iron oxide pigments as claimed in claim 20, 21 or 22 prepared from ferrous sulfate heptahydrate containing more than 0.15% Mn or more than 0.01% Zn characterized by the fact that they contain less than 0,05% Mn or less than 5 mg/kg of Zn.

25. A method of using red Fe2O3 pigments as claimed in claim 20, 21 or 22 which comprises mixing said pigments with.
a foodstuff.

26. A method of using red Fe2O3 pigments as claimed in claim 20, 21 or 22 which comprises mixing said pigments with packing material.

27. A method of using red Fe2O3 Pigments as claimed in claim 20, 21 or 22 which comprises mixing said pigments with a plastic.