FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Process for the production of synthetic red iron oxide pigments from aqueous ferrous chloride waste
APPLICANTS
DCW LIMITED, Nirmal, 3rd Foor, Nariman Point, Mumbai 400 021,Maharashtra, India, an Indian Company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a process for the production of synthetic red iron oxide pigments from aqueous ferrous chloride waste.
This invention also relates to a process for the production of synthetic red iron oxide pigments and other valuable products from aqueous ferrous chloride waste.
This invention also relates to synthetic red iron oxide pigments and other valuable products obtained from aqueous ferrous chloride waste.
BACKGROUND OF THE INVENTION
Synthetic yellow and red iron oxides pigments have replaced their natural versions for the past several years. Both the synthetic iron oxide pigments are mostly produced from ferrous sulphate feed stock by the precipitation route. Ferrous sulphate as a feed stock is obtained from sources like titanium dioxide plants and steel pickling plants. Ferrous sulphate feedstock is becoming increasingly difficult to obtain for reasons like closure of titanium dioxide plants and steel pickling plants, especially in Western Europe and USA and increased use of it in cement industry as reducing agent for chromium (VI). Production of ferrous sulphate by dissolving scrap steel in sulphuric acid is increasingly costly and requires special reactors to manage hydrogen being liberated. There are also environmental problems associated with production of iron oxide pigments by the sulphate route. US 3946103 describes a process for the preparation of red iron oxide from aqueous iron (11) salt solution by the precipitation route using a modifying substance

like magnesium, calcium or aluminium. The pigments so produced have a goethetite content less than 15% by weight correspondingly reducing the purity and chroma of the pigments. Red iron oxide pigments are known to be produced by calcining yellow iron oxide pigments prepared from ferrous chloride by the precipitation route (US 6179908 Bl). Calcination is energy intensive and cumbersome to carry out.
W02009/100767 Al describes a process for producing red iron oxide with marginal goethite content from ferrous chloride feed stock comprising precipitating high surface area lepidocrocite seeds having a BET surface area greater than 175 m / g by mixing the ferrous chloride feedstock with an alkali and oxidizing the obtained mixture and growing the lepidocrocite seeds, whereby the lepidocrocite converts into red iron oxide. The ferrous chloride feedstock is diluted to ferrous iron concentrations of about 20 to 50 g/1. The ferrous chloride feedstock is first purified by reacting with iron or alkali. The lepidocrocite seed precipitation is carried out at about 5 to 25°C and the alkali is added in an amount that is sufficient to precipitate 90 to 110% of the iron present in the feedstock. The alkali is selected from sodium hydroxide, potassium hydroxide or ammonia and oxidation is carried out using oxidants selected from air, oxygen or hydrogen peroxide. The oxidation is carried out simultaneously with mixing of the alkali and ferrous chloride feedstock and is preferably rapidly carried out in 20 to 80 minutes. The growing of the lepidocrocite seeds is carried out at or above at least 80°C, preferably 90 to 95 °C by adding further ferrous chloride feedstock and alkali to the said mixture. The ferrous chloride feedstock is undiluted, having a ferrous iron concentration of about 5 to 23%, preferably about 15%. Alternatively, the growing of the lepidocrocite seeds is carried out by oxidizing the seeds at high temperatures in the presence of metallic iron. The above process does not effectively remove all

the impurities in the feedstock because of which the pigments still contain high levels of the impurities especially lead, manganese and zinc thereby reducing the colour value of the pigments. The process efficiency, productivity and yield and colour value of the pigments are also reduced because of the process conditions and process parameters employed.
Leach liquor and pickling liquor are cheap sources of ferrous chloride. Hydrochloric acid used in pickling steel and steel components or products in hot rolling plants is known as spent pickling liquor. Generally pickling liquor is discarded when hydrochloric acid concentration therein falls below 4% by weight. Disposal of pickling liquor is carried out either by neutralization with cheap alkali like lime or by spray roasting to decompose ferrous chloride hydrothermally into hydrochloric acid and iron oxide. Hydrochloric acid is recycled into the steel pickling process. Iron oxide has very limited applications due to contamination with impurities. Thus disposal of pickling liquor is uneconomical and problematic. Apart from acidic ferrous chloride and free hydrochloric acid, pickling liquor also contains trace metal impurities contained in the steel and steel components or products like aluminium, calcium, chromium, magnesium, manganese, sodium, lead, copper, silica, nickel, molybdenum and zinc. Iron chlorides waste generated in the process of manufacture of synthetic rutile from ilmenite ore is known as leach liquor. It contains ferrous chloride, ferric chloride and free hydrochloric acid apart from other metallic impurities associated with ilmenite mineral such as alumina, calcium, cobalt, copper, manganese, magnesium, nickel, lead, vanadium and zinc. Leach liquor is generally used for regeneration of hydrochloric acid in about 16-18% concentration by hydrothermal decomposition of the ferrous and ferric chlorides in a spray roaster. Iron oxide contaminated with the impurities present in the leach liquor, is left behind and is a waste creating disposal and environmental problems.

Although leach liquor and pickling liquor are cheap sources of ferrous chloride, they contain significant levels of impurities like aluminium, chromium, silica, manganese, zinc and lead which can have negative effects on red iron oxide pigments. There are also significant differences in the synthesis of red oxides from ferrous chloride and sul ate systems. In the case of ferrous chloride feed stock the goethite seeds will not transform to hematite but will persist as goethite throughout the growth reaction with a significant negative effect on the red colour quality.
We have described in our Indian Patent No 241113 (1152/MUM/2006) dated 19 July 2006, a process and equipment for the recovery of valuable products from leach liquor, namely yellow iron oxide pigments, ammonia and calcium chloride. The process comprises reacting the leach liquor with iron to convert free hydrochloric acid and ferric chloride in the leach liquor to ferrous chloride. Impurities in the leach liquor are precipitated by treating the leach liquor with an aqueous ammonia solution containing 8-12%ammonia at a pH of 2.5 to 5.0 under agitation. The precipitated impurities are flocculated by treating the leach liquor with a flocculating agent. The flocculated impurities are separated from the leach liquor to obtain a purified ferrous chloride solution. The pH of the ferrous chloride solution is optionally adjusted between 1.5 to 2.0 by treatment with hydrochloric acid. The ferrous chloride solution containing ferrous iron (Fe++) concentration of 2.0 to 4.0% is reacted with an aqueous solution of ammonia containing 8-12% ammonia in the presence of 8-15% ammonium chloride and chilled water under agitation to convert ferrous chloride to ferrous hydroxide. The ferrous hydroxide is oxidized with air at 18-35°C and a pH between 3.0 to 5.0 to form hydrated ferric oxide pigment seeds (yellow pigment seeds) and the pigment seeds are further oxidized with oxygen mixed with steam in the presence

of an aqueous ammonia solution containing 8-12% ammonia at 60-85°C under agitation and at pH at 3.0 to 5.0 to allow the seeds to grow to the require size. The pigment slurry is filtered to separate the pigment cake from the mother liquor containing ammonium chloride, the pigment cake is washed with water, dried and pulverized. Ammonia and calcium chloride are recovered from the mother liquor. Process for the production of yellow and red iron oxide pigments from ferrous chloride feed stock involve judicious and meticulous selection and critical control of process steps, process conditions and process parameters and are distinctly different. Process for the preparation of one does not lead to the other.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a process for the production of synthetic red iron oxide pigments from aqueous ferrous chloride waste, the process comprising:
a) enriching the aqueous waste with ferrous chloride by reacting and neutralizing the aqueous waste with iron to a pH0.5 to 1.5 and converting the free hydrochloric acid in the aqueous waste to ferrous chloride;
b) purifying the aqueous waste by treating the aqueous waste with aqueous ammonia in 5 to 15% concentration to adjust the pH of the aqueous waste to 3-5 and precipitate metallic impurities in the aqueous waste, flocculating the impurities in the aqueous waste with a polyelectrolyte and separating the flocculated impurities from the aqueous waste to

obtain purified aqueous solution of ferrous chloride containing ferrous iron (Fe++) 100 -200 gm/1;
c) producing red iron oxide (hematite-Fe203) seeds by reacting diluted purified ferrous chloride containing ferrous iron (Fe++) in 40-60 gm/1 and ammonium chloride in 50 to 80 gm/1 with aqueous ammonia in 5 to 15% concentration at 25 to 40°C and at acidic pH3.8-5.0 with simultaneous oxidation of the ferrous iron using an oxygen containing gas at the flow rate of 5.0 to 10.0 Nm3/hr under shear mixing of the seed slurry by intense agitation of the seed slurry;
d) conditioning and growing the red iron oxide seeds into red iron oxide pigments by treating the seed slurry at 85-95°C by injecting steam into the seed slurry with simultaneous oxidation and precipitation of the seeds with continuous feeding of an oxygen containing gas at the flow rate of 0.3 to 1 Nm3/hr and aqueous ferrous chloride in 20 to 35 % concentration to maintain the ferrous iron concentration in the seed slurry at 40 to 60 g/1 and with simultaneous pH adjustment of the seed slurry at 3 - 5 with an aqueous ammonia in 5 to 15% concentration and under shear mixing of the seed slurry by intense agitation of the seed slurry; and
(e) recovering the pigments from the pigment slurry.
In order to remove lead impurities from the aqueous, the aqueous ammonia treated aqueous waste of step (b) is optionally further purified by treating the aqueous waster with an aqueous

solution of ammonium sulphide in 5 to 10% concentration at a pH4-6 to precipitate lead under agitation of the aqueous waste, the ammonium sulphide used being 400 to 800% excess of the stoichometric requirement for lead precipitation. The aqueous ferrous chloride waste is preferably pickling liquor or leach liquor. The aqueous waste is neutralized preferably with iron comprising carbon steel scraps selected from cuttings, punchings or trimmings of cold rolled carbon steel of low manganese content. Preferably the flocculated impurities are separated from the aqueous waste by filtration of the aqueous waste. The polyelectrolyte used for flocculation impurities is selected from acrylic polymer, polyacrylamide or polyacrylate and is preferably polyacrylate. The ammonium chloride treatment of step (c) aided with the ferrous chloride treatment of step (d) helps to form a soluble complex of Mn with the ammonium chloride and substantially reduce the Mn impurity level in the pigment and improve colour value of the pigment. The oxygen containing gas is oxygen or air and is preferably oxygen. Preferably the ammonium chloride is used in step (c) in 75 gm/1 concentration and the seed production in step (c) is carried out at 26 to 28°C to precipitate ferrous iron stoichiometrically.
According to an embodiment of the invention, the pigments are recovered from the pigment slurry by separating the pigment cake from the mother liquor,preferably, by filtration of the pigment slurry, washing the pigment cake with water, drying the cake and pulverizing the cake.
According to an embodiment of the invention, the process further comprises recovery of ammonia and calcium chloride from the mother liquor. Preferably the recovery of ammonia and calcium chloride from the mother liquor comprises:
i) reacting the mother liquor with lime to form ammonia and calcium chloride;

ii) recovering ammonia from the reaction mixture by subjecting the reaction mixture to steam distillation and dissolving the distilled off ammonia in water to form aqueous ammonia solution; and
(iii) recovering calcium chloride from the distillation residue by cooling the distillation residue, clarifying the distillation residue, concentrating the clear solution of calcium chloride by exporation and converting the concentrated calcium chloride to the required form or shape followed by calcination and cooling.
Preferably the concentrated calcium chloride is converted into flakes by flaking it at 170-175°C, calcining the flakes at 200 to 220°C and cooling the clacined flakes to 40 to 45°C.
According to the invention there is also provided synthetic red iron oxide pigments of high purity and chroma and optionally calcium chloride and ammonia obtained from aqueous ferrous chloride waste.
The separation of the flocculated impurities from the aqueous waste, separation of the pigment cake from the mother liquor and recovery of calcium chloride and ammonia from the mother liquor all can be carried out by other known methods also. The concentrated calcium chloride can be also recovered in other shapes and forms. Such variations of the invention are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention.

It has been found according to the invention by extensive research and experimentation that by judiciously selecting and controlling the process parameters and conditions like temperature, pH, oxygenation rate, agitation rate, concentrations and ratios of the reactants and reagents, the impurities in the aqueous ferrous chloride waste are effectively removed such that the process of the invention produces synthetic red iron oxide pigments of high purity and chroma from aqueous ferrous chloride waste. Besides, producing pigments of high purity and chroma, the process also recovers ammonia and calcium chloride thereby practically converting the entire waste into useful and valuable products and eliminating waste disposal and environmental problems and rendering the process economical. As the seed production temperature is 25-40°C, the chilling requirements for the seeds has been eliminated. The process is thus simple and easy to carry out. As the concentration of the ferrous iron in the purified ferrouos chloride used for seed production is 40-60 g/1, the process throughput and efficiency is very high. As the seed slurry is shear mixed by intense agitation at high rpm in steps (c) and (d), the oxygen gas is broken into tiny bubbles in the liquid phase. These tiny bubbles increase the number of solvated oxygen ions for faster oxidation with minimum wastage of oxygen to be bubbled out. This increases the reaction rate and maximizes utilization of oxygen in the seed formation and seed growth. Because of the maximum use of oxygen and rapid oxidation, the seed formation and growth ratio of the color value is increased thereby increasing production of pigments of high colour value. Maintentnace of ammonium chloride concentration at 50 to 80 gm /1 during seed production also improves the chroma and purity level of the pigments. Maintenance of ferrous iron concentration in the seed slurry at 40 to 60 also improves the process efficiency and throughput and the chroma and purity of the pigments. Utilisation of cheap and easily available aqueous ferrous chloride waste as the starting material also renders the process economical.

The following comparative experimental examples are illustrative of the invention but not
limitative of the scope thereof:
Example 1
Chemical composition of the pickling liquor used in the Example as found out by Inductive
Coupled Plasma (ICP) spectrometry was as shown in the following Table 1:
Table 1

Composition Contents
FeC12 20.2 %
HC1 3.0%
Al 63 ppm
Ca 72ppm
Cr 41 ppm
Mg 24 ppm
Mn 390 ppm
Cu 35 ppm
Ni 24 ppm
Si02 33 ppm
(i) Experiment A
A 15 KL (kilo litre) iron scrap reactor fitted with recirculation arrangement was filled with cold rolled carbon steel (CRCS) iron scrap cuttings upto 2/3 of the height of the reactor. 12 KL of the pickling liquor was recirculated in the reactor at the rate of 30 m3/hr to neutralize free hydrochloric acid to ferrous chloride. After 8.00 hours circulation, acid concentration of the

pickling liquor reduced to pHl and the pickling liquor was further analysed by ICP spectrometry and the results were as shown in the following Table 2:
Table 2

Composition Contents
FeC12 24.9 %
HC1 PH0.7
Al 61 ppm
Ca 70 ppm
Cr 40 ppm
Mg 22 ppm
Mn 385 ppm
Cu 12 ppm
Ni 22 ppm
Sio2 31 ppm
Iron treated pickling liquor was purified in a purification tank fitted with agitator by adding 12% aqueous ammonia to precipitate impurities. Before additing aqueous ammonia, aqueous ferric chloride solution in 45% concentration was added to the iron treated pickling liquor to achieve a concentration of 2500 ppm and act as coagulating agent. The purification was carried out at pH4 and the impurities were coagulated using polyacrylamide as flocculating agent. ICP spectrometry analysis of the purified pickling liquor was as shown in the following Table 3:

Table 3

Composition Contents
FeC12 23.8%
Al 12 ppm
Ca 61 ppm
Cr 14 ppm
Mg 22 ppm
Mn 353 ppm
Cu 11 ppm
Ni 19 ppm
Sio2 10 ppm
Purified ferrous chloride was pumped into a pigment reactor of 50KL volume fitted with an agitator and was diluted using chilled water to a concentration of Fe 20 g/1. 34 KL diluted ferrous chloride was maintained at 15°C under agitation and 12% ammonia solution at 16°C was added in 20 minutes to precipitate 95% of the iron present in the dilute ferrous chloride and simultaneously oxidized for 60 minutes using oxygen gas at a flow rate 300 Nm3/hr. During the precipitation and oxidation pH of the solution ranged from 3.9 - 4.7 and temperature increased froml5°Cto22°C.
The seed slurry formed was heated for 3.5 hours under agitation to raise temperature to 90°C by directly injecting low pressure steam at 2 bar. Ferrous chloride solution was added to the seed slurry to make Fe iron concentration 1.0 g/1 and pH was adjusted to 3.8 to carry out crystal growth by simultaneous addition of 12% ammonia solution and oxygen at the flow rate 15 Nm3/hr to carry out simultaneous precipitation and oxidation. Fe iron concentration was maintained at 0.8 - 1.2 g/1 during crystal growth at pH- 3.8 - 4.0 by continuous dosing of ferrous

chloride. After 28 hours of crystal growth, ferrous chloride addition was stopped and residual ferrous iron was precipitated and oxidized to make iron content almost nil. The pH was slowly increased from 4.2 - 6 by adding ammonia and oxygen to neutralize the pigment slurry. The pigment slurry was filtered and cake was washed, dried and milled in a pulverizer.
The colour analysis of the pigments was carried out and was compared with a standard red pigment (Yuxing China Red - 120) by CIELAB method using MACBETH colour eye ® 7000 at natural day light illumination at D 65 and making draw down in acrylic resin in the weight ratio 1:8 (Pigment : Resin). Absolute colour values of both the pigments were as shown in the following Table 4:
Table 4

Red pigment L A B
Red-120 38.12 30.58 21.57
Red pigment of Experiment A 35.32 24.62 18.8
The deviations of L A B coordinates of the pigment of Experiment A with respect to the standard Red - 120 were measured to estimate the standard deviation DE (the square root of DL + DA + DB2).
DL = (L of Experiment A - L of standard) = -2.8 DA = (A of Experiment A - A of standard) = - 5.96 DB = ( B of Experiment A - B of standard) = .- 2.77 Standard Deviation DE = 7.17

Manganese impurity in the pigments of Experiment A as measured by ICP spectrometry was 367 ppm.
It is seen from the above data that the colour quality of the red pigment of Experiment A was much inferior as compared to Red - 120 as standard deviation DE was 7.17 which is much higher than commercially acceptable DE value of 1.0. The Mn impurity level was also high thereby reducing the colour quality of the pigment.
ii Experiment B
The pickling liquor (12KL) was enriched as described in Experiment A and purified in a purification tank fitted with agitator by adding 10% aqueous ammonia to raise pH to 4.2 and precipitate impurities. After agitation for 30 minutes polyacrylate was added to coagulate / flocculate the precipitates and the precipitates were filtered out. The ICP spectrometry analysis of the pickling liquor after purification was as shown in the following Table 5:
Table 5

Composition Contents
FeC12 24.6 %
Al 8 ppm
Ca 63 ppm
Cr 12 ppm
Mg 23 ppm
Mn 365 ppm
Cu 12 ppm
Ni . 23 ppm
Sio2 12 ppm

Purified ferrous chloride was pumped into a pigment reactor of 50 KL volume fitted with an agitator in such quantity that the ferrous chloride solution after addition of 20% aqueous ammonium chloride solution and dilution with chilled water measured 34 KL. The composition of diluted ferrous chloride was 42 gms/lr Fe iron and 75 gms /ltr ammonium chloride at 26°C. An aqueous ammonia solution of 10% concentration at 25 °C was added in 60 minutes to precipitate 100%) Fe iron. Simultaneously it was oxidized by passing oxygen gas at the flow rate 300 Nm3/hr for 65 minutes at pH3.8 - 4.2. At the end of the seed production, the temperature raised to 35°C and pH raised to 4.7. The seed production was carried out by shear mixing of the seed slurry by intense agitation.
The seed slurry was heated for 4 hrs to raise the temperature to 88°C by directly injecting steam and ferrous chloride solution was added to the slurry to make Fe iron concentration 1.2 g/1 and pH was adjusted to 3.8 to carry out crystal growth by simultaneous addition of ammonia solution of concentration 10% and oxygen at flow rate 15 Nm3/hr. Fe iron concentration was maintained 0.8 - 1.5 g/1 during crystal growth at pH3.8 - 4.2 by continuous dosing of ferrous chloride. After 30 hours of crystal growth, ferrous chloride addition was stopped and residual ferrous iron was precipitated and oxidized to make iron content almost nil. The pH was slowly increased from 4.2 - 6 by adding ammonia and oxygen to neutralize the pigment slurry. The slurry was intensely agitated throughout seed growth to effect shear mixing of the slurry. The pigment slurry was filtered and cake was washed, dried and milled in a pulveriser.

The colour coordinates of the pigments were measured as described in Experiment A and LAB values were compared with the standard Red - 120. Absolute colour values of both the pigments were as shown in the following Table 6:
Table 6

Red pigment L A B
Red-120 38.12 30.58 21.57
Red Pigment of Experiment - B 37.93 29.85 21.67
The deviations of L A B coordinates of the pigment of Experiment B were compared with the
standard pigment Red - 120 and standard deviation DE was estimated.
DL = (L of Experiment B - L of standard) = -0.19
DA = (A of Experiment B - A of standard) = - .73
DB = (B of Experiment - B of standard) = .-0.1
Standard Deviation DE = 0.76
Manganese impurity in the pigment of Experiment B as measured using ICP spectrometry was 86 ppm.
It is seen from above data that the colour values of the pigment of Experiment B were very good and close to a standard pigment, as DE is less than 1, which is commercially acceptable. The Mn impurity level was also considerably reduced thereby improving the colour quality and purity of the pigments.

Calcium chloride and ammonia were recovered from the mother liquor as described in Experiment D in Example 2.
Example 2
The leach liquor used in the Example had the chemical composition (as found out by ICP
spectrometry) as shown in the following Table 7:
Table 7

Composition Contents
FeC12 22.0 %
FeC13 4.0 %
HC1 4.5 %
Al 970 ppm
Cr 240 ppm
Cu 17 ppm
Mg 2660 ppm
Mn 1450 ppm
Ni 20 ppm
Pb 35 ppm
Zn 125 ppm
Si02 63 ppm
V 286 ppm
(i) Experiment C
A 15KL (Kilolitre) iron scrap reactor fitted with recirculation arrangement wa$ filled with cold rolled carbon steel (CRCS) iron scrap cuttings upto 2/3 of the height of the reactor. 10 KL of the leach liquor was recirculated through the iron scrap bed at the rate of 30 Cu.nVhr to neutralize free hydrochloric acid to ferrous chloride. After 20 hours, acid concentration of the leach liquor

reduced to about pH0.8 and the leach liquor was further analysed by ICP spectrometry as shown in the following Table 8.
Table 8

Composition Contents
FeC12 34.1 %
FeC13 0.3 %
HC1 pH0.8
Al 945 ppm
Cr 233 ppm
Cu 11 ppm
Mg 2556 ppm
Mn 1485 ppm
Ni 18 ppm
Pb 34 ppm
Zn 125 ppm
Si02 61 ppm
V 272 ppm
Iron treated leach liquor was purified in a purification tank fitted with an agitator by adding aqueous ammonia solution of concentration 10% to maintain pH4.2 and precipitate the impurities. The impurities flocculated using polyacrylate and removed by filtration to give purified ferrous chloride. The composition of the purified ferrous chloride as found out by ICP spectrometry was as shown in the following Table 9:

Table 9

Composition Contents
FeC12 32.2 %
pH 4.2
Al 43 ppm
Cr 23 ppm
Cu 10 ppm
Mg 2506 ppm
Mn 1436 ppm
Ni 16 ppm
Pb 32 ppm
Zn 113 ppm
Si02 9 ppm
V 22 ppm
Purified leach liquor (34 KL) was pumped into a pigment reactor of 50 KL volume fitted with an agitator and was diluted using chilled water to iron concentration 20 gm/ltr and temperature of 17°C under agitation at 120 rpm. 10% ammonia solution was added in 25 minutes to precipitate 96% Fe iron present in diluted ferrous chloride solution and simultaneously oxidised for 60 minutes using oxygen at the flow rate 340 Nm3/hr. During the precipitation and oxidation, pH of the solution ranged from 3.9 to 4.5 and temperature increased from 17°C to 25°C.
The seed slurry was heated for 4 hours under agitation to raise the temperature to 90°C by directly injecting low pressure steam at 2 bar. Ferrous chloride was added to the seed slurry to maintain Fe iron concentration 1 g/1 and pH was adjusted to 4 to carry out crystal growth by simultaneous addition of ammonia solution of 10% concentration and oxygen at the rate of 12

Nm3/ hr to carry out simultaneous precipitation and oxidation. Fe iron concentration was maintained in the range 0.5 - 1.0 g/1 by dosing FeC12. The slurry was continuously intensely agitated during seed growth to effect shear mixing. After 30 hours of crystal growth, ferrous chloride was stopped and residual ferrous iron was precipitated and oxidized to make iron content almost nil. The pigment slurry was filtered and cake was washed, dried and milled in a pulveriser.
The colour analysis of the pigments was done to compare the colour coordinates L, A, B with respect to the standard Red - 120 as stated in Experiment A of Example 1. Absolute colour values of the both the pigments were as shown in the following Table 10 :
Table 10

Red pigment L A B
Red-120 39.02 30.65 22.87
Red Pigment of Experiment - C 37.45 25.82 20.58
The deviations of L A B coordinates of the pigment of Experiment C with respect to the
standard Red - 120 were measured to estimate the standard deviation DE.
DL = (L of Experiment C - L of standard) = - 1.57
DA = (A of Experiment C - A of standard) = - 4.83
DB = ( B of Experiment C - B of standard) = .- 2.29
Standard Deviation DE = 5.56

Manganese and lead impurities in the pigment were measured using ICP spectrometry and were as given below: Mn - 572 Pb = 98
The colour values were very poor as the standard deviation DE was much higher than the commercially acceptable limit of 1.0. Mn and Pb impurities were also very high thereby adversely affecting the colour value and purity of the pigments.
ii) Experiment D
The leach liquor (10KL) was enriched as described in Experiment C and the enriched ferrouos chloride of Table 8 was purified in a purification tank fitted with an agitator by adding aqueous ammonia solution of concentration 10% to raise pH to 4.2 and 8% solution of ammonium sulphide was added in excess of 500% of stoichiometric requirement for Pb precipitation as lead sulphide. After agitation for 30 minutes polyacrylate was added to cogulate / flocculate the precipitates. Precipitates were filtered out and the purified ferrous chloride had the composition as given in the following Table 11 as found out by ICP spectrometry:

Table 11

Composition Contents
Fel2 31.6%
pH 4.2
Al 37ppm
Cr 19ppm
Cu lOppm
Mg 2498 ppm
Mn 1402 ppm
Ni 15 ppm
Pb 6 ppm
Zn 103 ppm
Si02 13 ppm
V 24 ppm
Purified Ferrous chloride was pumped into a pigment reactor of 50 KL volume fitted with an agitator in such quantity that the ferrous chloride solution after addition of 20% aqueous ammonium chloride solution and dilution with chilled water measured 34 KL. The composition of diluted ferrous chloride was 42 gm/1 Fe iron and 75 gms /ltr ammonium chloride at 28°C. An aqueous ammonia solution of 10% concentration at 25°C was added in 55 minutes to precipitate 99% Fe iron. Simultaneously the seed slurry was oxidized by passing oxygen gas at the flow rate 320 Nm3/hr for 60 minutes at pH4.0 - 4.2. The slurry was intensely agitated and shear mixed during seed production. At the end of the seed production, the temperature raised to 35°C and pH raised to 4.7.

The seed slurry was heated at 90°C for 3 1/2 hours under agitation to raise temperature to 90°C by directly injecting low pressure steam at 2 bar pressure Ferrous chloride solution was added to the slurry to make Fe Iron concentration 1.2 g/1 and pH was adjusted to 3.9 to carry out crystal growth by simultaneous addition of ammonia solution of concentration 10% and oxygen at the flow rate 12 Nm3/hr. Fe iron concentration in the solution was maintained at 0.8 - 1.5 g/1 during crystal growth at pH3.8 - 4.2 by continuous dosing of ferrous chloride. The slurry was intensely agitated and shear mixed during seed growth. After 30 hours of crystal growth, ferrous chloride addition was stopped and residual ferrous iron was precipitated and oxidized to make iron content almost nil. The pH was slowly increased from 4.2 - 6 by adding ammonia and oxygen to neutralize the pigment slurry. The pigment slurry was filtered and cake was washed, dried and milled in a pulverizer.
The colour coordinates of the pigments were measured as described in Experiment A and LAB values were compared with the standard Red - 120. Absolute colour values of both the pigments were as shown in the following Table 12 :
Table 12

Red pigment L A B
Red-120 39.02 30.65 22.87
Red pigment of Experiment D 38.82 30.58 22.58
The deviations of L A B coordinates of the pigments of Experiment D with respect to the Red -120 were measured to estimate the standard deviation DE. DL = (L of Experiment D - L of standard) = -0.2

DA = (A of Experiment D - A of standard) = - 0.07 DB = (B of Experiment D - B of standard) = .- 0.29 Standard Deviation DE = 0.35
Manganese and lead impurities in the pigments of Experiment D were measured by using ICP spectrometry as below. Mn = 68 ppm Pb =16 ppm
It is seen from the above data that red iron pigments of Experiment D were of high quality in colour as it was very close to the standard and DE was 0.3, very low as compared to commercially acceptable limit of 1.0. Mn and Pb contents were also very low thereby increasing the colour quality and purity of the pigments.
(iii) Experiment E
The mother liquor (filtrate) obtained from the Alteration of pigment cake was agitated with quick lime in a reactor to dissociate ammonium chloride into ammonia and calcium chloride. The slurry was distilled in a bubble cap distillation column using low pressure steam to recover ammonia as aqueous solution and calcium chloride as distiller effluent. Ammonia was dissolved in cooled ammonium chloride brine to make 10% aqueous ammonia solution for reuse in the red iron oxide pigment production. Ammonia recovery was 99%. The distiller effluent was cooled and passed through a clarifier to recover clear calcium chloride solution which was concentrated in multiple effect evaporation system to a concentration of 71% CaC12. The concentrated calcium chloride solution was passed through a flaker unit to make flakes. The flakes were

calcined at 210°C and cooled to 45°C. Recovery of calcium chloride flakes was 95%. Composition of calcium chloride flakes of thickness 1 -2mm and length < 20 mm recovered was as given in the following Table 13.
Table 13

Composition Contents
CaC12 78%
MgC12 0.3 %
Alkali Chlorides as NaCl% 1.0%
Sulphate as CaS04 0.1 %
Water Insolubles 0.2 %
pHof 10% solution 9.0 %

We Claim:
1. A process for the production of synthetic red iron oxide pigments from aqueous ferrous
chloride waste, the process comprising:
a) enriching the aqueous waste with ferrous chloride by reacting and neutralizing the aqueous waste with iron to a pH0.5 to 1.5 and converting the free hydrochloric acid in the aqueous waste to ferrous chloride;
b) purifying the aqueous waste by treating the aqueous waste with aqueous ammonia in 5 to 15% concentration to adjust the pH of the aqueous waste to 3-5 and precipitate metallic impurities in the aqueous waste, flocculating the impurities in the aqueous waste with a polyelectrolyte and separating the flocculated impurities from the aqueous waste to obtain purified aqueous solution of ferrous chloride containing ferrous iron (Fe++) 100 -200 gm/1;
c) producing red iron oxide (hematite-Fe203) seeds by reacting diluted purified ferrous chloride containing ferrous iron (Fe++) in 40-60 gm/1 and ammonium chloride in 50 to 80 gm/1 with aqueous ammonia in 5 to 15% concentration at 25 to 40°C and at acidic pH3.8-5.0 with simultaneous oxidation of the ferrous iron using an oxygen containing gas at the flow rate of 5.0 to 10.0 Nm3/hr under shear mixing of the seed slurry by intense agitation of the seed slurry;

d) conditioning and growing the red iron oxide seeds into red iron oxide pigments by treating the seed slurry at 85-95°C by injecting steam into the seed slurry with simultaneous oxidation and precipitation of the seeds with continuous feeding of an oxygen containing gas at the flow rate of 0.3 to 1 Nm3/hr and aqueous ferrous chloride in 20 to 35 % concentration to maintain the ferrous iron concentration in the seed slurry at 40 to 60 g/1 and with simultaneous pH adjustment of the seed slurry at 3 - 5 with an aqueous ammonia in 5 to 15% concentration and under shear mixing of the seed slurry by intense agitation of the seed slurry; and
(e) recovering the pigments from the pigment slurry.
2. The process as claimed in claim 1, wherein the purification step (b) comprises further treating the aqueous ammonia treated aqueous waste with an aqueous solution of ammonium sulphide in 5 to 10% concentration at a pH4-6 to precipitate lead under agitation of the aqueous waste, the ammonium sulphide used being 400 to 800% excess of the stoichometric requirement for lead precipitation.
3. The process as claimed in claim 1 or 2, wherein the aqueous ferrous chloride waste is pickling liquor or leach liquor.
4. The process as claimed in anyone of claims 1 to 3, wherein the aqueous waste is neutralized with iron comprising carbon steel scraps selected from cuttings, punchings or trimmings of cold rolled carbon steel of low manganese content.

5. The process as claimed in anyone of claims 1 to 4, wherein the flocculated impurities are separated from the aqueous waste by filtration of the aqueous waste.
6. The process as claimed in anyone of claims 1 to 5, wherein the polyelectrolyte is selected from acrylic polymer, polyacrylamide or polyacrylate, preferably polyacrylate.
7. The process as claimed in anyone of claims 1 to 6, wherein the oxygen containing gas used in steps (c) and (d) is oxygen or air, preferably oxygen.
8. The process as claimed in anyone of claims 1 to 7, wherein the ammonium chloride is used in step(c) in 75 gm/1 concentration and the seed production in step (c) is carried out at 26 to 28°C.
9. The process as claimed in anyone of claims 1 to 8, wherein the pigments are recovered from the pigment slurry by separating the pigment cake from the mother liquor, washing the pigment cake with water, drying the cake and pulverizing the cake.
10. The process as claimed in claim 9, wherein the pigment cake is separated from the pigment slurry by filtration.
11. The process as claimed in claim 9 or 10, wherein the process further comprises recovery of ammonia and calcium chloride from the mother liquor.

12. The process as claimed in claim 11, wherein the recovery of ammonia and calcium
chloride from the mother liquor comprises:
i) reacting the mother liquor with lime to form ammonia and calcium chloride;
ii) recovering ammonia from the reaction mixture by subjecting the reaction mixture to steam distillation and dissolving the distilled off ammonia in water to form aqueous ammonia solution; and
iii) recovering calcium chloride from the distillation residue by cooling the distillation residue, clarifying the distillation residue by concentrating the clear solution of calcium chloride by exporation and converting the concentrated calcium chloride to the required form or shape followed by calcination and cooling.
13. The process as claimed in claim 12, wherein the concentrated calcium chloride is converted into flakes by flaking it at 170-175°C calcining the flakes at 200 to 220°C and cooling the clacined flakes to 40 to 45°C.
14. Synthetic red iron oxide pigments of high purity and chroma obtained from aqueous ferrous chloride waste.
15. Synthetic red iron oxide pigments of high purity and chroma and ammonia and calcium chloride obtained from aqueous ferrous chloride waste.

16. Synthetic red iron oxide pigments as claimed in claim 14 or 15, which have colour coordinates L 37.93, A 29.85 and B 21.67 and DE 0.76 and Mn content of 86ppm and are obtained from pickling liquor.
17. Synthetic red iron oxide pigments as claimed in claim 14 or 15, which have colour coordinates L 38.82, A 30.58 and B 22.58 and DE 0.35 and Mn and Pb contents 68 ppm and 16 ppm, respectively and are obtained from leach liquor.