The iron oxide compounds produced by the process of this invention are well known articles of commerce.
They are used not only for pigmenting paints and lacquers, but also in rubber, plastic, paper, cement, emulsions, plaster and in cosmetics.
They are used in the production of catalysts, magnetic and electronic components and in polishing compounds.
For these purposes, control of particle size, and color is required, particularly for pigment applications where reproducible hiding power, tinctorial strength and color tone are essential.
The process yields yellow and red ferric oxides of big quality and purity in uniform particle size of excellent color and color strength.
The process of this invention allows the production of ferric oxide and ferric oxide hydrates at a higher production rate and thus, more economically than heretofore possible.
The oxidation and precipitation processes of this invention are conducted in the presence of a starting slurry of a hydrated ferric oxide present in minor amounts.
If a yellow ferric oxide hydrate slurry is employed, a yellow oxide will be produced analyzing 86.5 to 88.5% F6203.
If a red oxide slurryis used, a red oxide analyzing 96 to 99% Fe O will be formed.
Both the red and yellow oxides produced by the process of this invention have excellent color shades and are of fine uniform particle size in the range of about 0.25 to 5 mircons.
When the process of this invention is of short duration, such as for 2 or 3 days, a light shade of the red or yellow oxide is produced.
Longer processing yields progressively deeper shades such as dark orange and purple colors of the larger particle size oxide hydrates.
the oxidation of a ferrous salt solution by means of anhydrous ammonia and a free-oxygen containing gas. In US.
, a method for the production of yellow iron oxides is disclosed which comprises the alkaline precipitation of hydrated iron oxide produced by the oxidation of ferrous salts by air in the presence of a seed slurry of hydrated ferric oxide.
The preparation of a red iron oxide is disclosed in US.
oxidizing iron with air in the presence of a ferrous salt solution and a red hydrated ferric oxide seed slurry.
The process of this invention contemplates the production of ferric oxide by oxidation of a ferrous salt solution and the oxidation of metallic iron, in the presence of a minor amount of a slurry of hydrated ferric oxide, by the action of air and ammonia.
The process of this invention offers important advantages over the above-mentioned prior art in that I have obtained an unobvious and unpredictable increase in yield which would not be apparent in considering the combination of yields from a process employing the oxidation of ferrous salts in the presence of a seed slurry of hydrated ferric oxide, by the action of oxygen and anhydrous ammonia, and a process employing the oxidation of metallic iron by heating and oxidizing an aqueous ferrous salt solution in the presence of metallic iron
The process makes possible greatly increased yields from plant production facilities.
For example, tests in five commercial yellow oxide production tanks, each in excess of 10,000 gallons capacity, using the process of this invention, averaged 42.5% greater yield over five tanks operating under the same conditions using the metallic iron oxidation process. Of this greater product yield, 12% was due to the stoichiometric yield from the oxidation of the ferrous salt by air and ammonia as measured by the salt and ammonia consumed.
The balance of the increased yield, 30.5%, was due to the unexpected potentiating effect of the ammonia on the oxidation of iron.
Another advantage is a greater tank slurry fluidity or mobility for any given solid concentration which improves mixing and circulation of tank liquids and thereby improves the production rate and lowers processing costs.
Moreover, since shade development is faster by the process of this invention, the processing time to reach a given commercial shade is reduced by up to 50%, making possible more finished tank batches in a given time than possible With former commercial processes.
Still another advantage of this invention is the preparation of products of increased purity over the processes due in part to the less acidic conditions of the tank and also to the use of proportionately less metallic iron.
The metallic iron of the commercial processes is usually scrap iron, a commodity which fluctuates in quality and which can adversely affect the purity of the oxide made there-from.
Another very important advantage of this invention lies in the ammonia neutralization aspect wherein the iron salt concentration in the final tank slurry is lowered, thereby lowering the processing cost and decreasing the pollution hazard of process effiuent.
While the above advantages of this invention apply to both yellow and red oxide production, in the latter case, it is observed that the overall increase in productivity is proportional to the amount of ammonia used.
This invention has demonstrated a 21 to 30% greater rate of production of red oxide compared to the oxidation process when scrap iron is used alone under the same conditions.
A specific embodiment of the process of this invention as it relates to the production of yellow ferric oxide comprises adding a minor amount of a yellow ferric oxide seed slurry prepared by any method and preferably prepared by precipitating ferrous hydroxide from an aqueous ferrous salt solution with alkali and oxidizing said ferrous hydroxide with air.
the art that a greater concentration produces a lighter colored product and a. lesser concentration produces a darker product.
An intermediate range is one wherein the concentration of seed is in the range of about 0.1 to 0.3 pound per gallon based on the total reaction mixture volume.
To the seed slurry is added an aqueous ferrous salt solution.
The ferrous salt can be any water-soluble ferrous salt such as ferrous chloride, ferrous sulfate or ferrous acetate. Ferrous sulfate, copperas, is preferred because of its low cost and availability.
A range of from about 0.5 to 1.0 pound per gallon based on the total operating volume is preferred onthe basis of process control and economy.
While other concentrations are effective, less than the preferred range decreases the reaction rate and more than the preferred range is uneconomical since unreacted ferrous salt is obtained in the processing effluent.
To the mixture of ferrous salt solution and seed slurry is added scrap iron. The amount of scrap iron is also not critical.
However, we have found a range of about 2 to 6 tons for a processing tank of 12,000 gallons operating volume to be an economical range.
The tank slurry temperature is adjusted to from about 150 to 200 F. and preferably about 175 F.
by any heating means.
In usual practice, steam coils in the tank are used. Air and ammonia gas are introduced through separate sparge rings in the tank at such a rate as to maintain the acidity of the reaction mixture at a pH of from about 3 to 4.5 and preferably at about pH 4.0.
The pH of the process slurry may be adjusted higher by decreasing the volume of air or by increasing the amount of ammonia.
While air is the most convenient gas to use, pure oxygen, oxygen-enriched air and other oxygen-containing gases may be used efiectively in the process of this invention.
The ammonia of this invention is preferably in the form of ammonia gas.
However, ammonia in aqueous solution or anhydrous liquid ammonia may also be effectively used.
As the process is continued, the yield is monitored by analysis of the tank slurry.
Additional scrap iron and ferrous salt are added to maintain production and to prevent raw ma terials becoming exhausted.
The process is shut down when the desired shade of oxide is obtained. A medium red oxide shade is obtained by using a red oxide seed slurry by the process of this invention in about 100 hours.
The product is collected by the usual rotary vacuum filtration, washing and conveyor drying.
Other methods for collecting, filtering and drying are well known to those skilled in the art.