IL25249A - Process for the preparation of hydrated iron oxides - Google Patents

Description

n A process for the preparation of hydrated iron oxides 24096 This invention relates to a process for the preparation of hydrated iron oxide which has the chemical constitution whose structural formula can he ted as or PeOOH and which is known as This finds application various industrial It for be used advantageously as a yellow pigment of good quality as well as a raw material for the production of synthetic Many methods of preparation of such ferric compounds are already According to one of these an aqueous solution of ferrous sulphate is treated with sodium hydroxide to give a ferrous hydroxide which is then oxidised with air or other oxidising agents in suitable conditions of temperature and of pH of the solution to give hydrated ferric oxide According to another of these rather pure scrap iron is suspended in a solution of ferrous a small quantity of hydrated ferric oxide is then introduced as a nucleus and air is bubbled through the mixture which is heated to 70 to In this way oxidation of the ferrous iron into ferric iron is brought about at the pH tained by the ferrous precipitates as ferric oxide in the form of a yellow precipitate on the small quantity of the already present hydrated ferric oxide which acts as a The sulphuric acid which is formed from the ferrous sulphate under the reaction attacks the metallic iron present and restores the starting These methods of although leading to hydrated ferric oxides suitable for use as yellow ments of good general are not free from conveniences and These processes are particularly in only at the 2 to 4g per hour per litre of solution of precipitate can be excluding of course the quantity of ferric oxide which is introduced as a In the second mentioned process it is also of fundamental importance to use scrap iron of high such as for example soft iron in the form of in turns out to be rather Also a careful cleaning and degreasing of the metal is necessary and attacked iron residues must be systematically eliminated from the reaction It an object of the present invention to prepare hydrated ferric oxide which is particularly suited for use as yellow by a process in which these disadvan tages and drawbacks are eliminated or at least According to the invention there is provided a cess for the preparation of hydrated ferric oxide having the chemical constitution in which an aqueous solution of a ferric salt is added to an aqueous solution of a ferrous salt which contains hydrated ferric oxide having the chemical constitution as a nucleating agent for precipitating the hydrated ferric the mixture is maintained at a ture of 50 to and its is maintained at from 2 to 5 so that the ferric salt is and the hydrated ferric oxide formed is The process according to the invention haa the advantage that the formation of the hydrated ferric oxide occurs with a reaction velocity as the quantity of ferric oxide formed hour and per litre of solution of ferrous which is very much higher than the one obtained according to the It is possible to obtain the formation of 10 to of hydrated ferric oxide per litre of excluding of course any quantity of hydrated ferric oxide which may be used as the nucleating The pH is kept at from 2 to 5 preferably at tially By operating in accordance with the invention the ferric salt is hydrolysed to hydrated ferric in the form of a yellow deposits itself on the nucleating The chemical composition of this hydrated ferric oxide is The oxide has a fine yellow colour and can be represented by the formula or PeOOH The solid compound thus obtained is separated from the solution by hot filtration and the precipitate is then washed and dried in an oven at a temperature below to A particularly suitable hydrated ferric oxide ing agent is the suspension prepared by precipitation of ferrous hydroxide by adding to a solution of ferrous sulphate and then oxidising the hydroxide with an oxidising agen Suitable starting salts include the ferrous salts of sulphuric acid and of strong such as for example ferrous ferrous ammonium sulphate and ferrous example the product which obtained in the of iron or the product can be obtained by the treatment of by sulphuric Also ferrous chloride is particularly Similarly useful is the obtained in the reduction of nitrobenzene to aniline and hydrochloric The process acoording the invention is preferably effected with solutions of ferrous containing from 10 to 500 of ferrous per litre of Suitable as the ferric salts which are added in solution to the solution are the ferric salts of sulphuric acid and such as for ferric chloride and ferric iJarticularly suitable are the products obtained by treatment sulphuric or hydrochloric acid of pyrites ashes or the red slurries obtained in the preparation of alumina according to the Bayer and the product obtained by treatment with hydrochloric or sulphuric acid of the residue obtained during the preparation of electrolytic zinc starting from zinc According to the by roasting the sine blende one obtains besides ZnO a residue of ferric The mixture of the two oxides is attacked with and iron is separated by precip as process according to the invention is preferably effected with solutions of ferric containing from 50 to 600 of ferric salt per litre of The adjustment of the pH of the reaction medium to the values required to cause the hydrolysis of the ferric salt responsible for the precipitation of the hydra ed ferric is to add a base to the medium simultaneously with ferric In this way the acidity formed within the reactio medium by the precipitation of the ferric in of drated Oxide is immediately neutralised by the addition of the Operating in this the conditions ing the ferric ion as that is with a pH around remain The base which is added to adjust the pH can be a solution of an alkali or hydroxide or carbonate or a suspension of an earth metal hydroxide or ate or an organic It is preferable to ad a solution or suspension of a which is concentrated to avoid diluting the reaction but on the other hand the solution or suspension should not be too concentrated so to avoid any precipitation of iron hydroxides which will not redissolve and which are formed as a result of a great change in the region in drops of the solution or suspension of the baseare added to the aqueous reaction It is also possible to operate in the presence of buffers capable of maintaining the pH of the reaction medium to values very near to The colour and the covering power of the pigments obtained from the hydrated ferric oxide prepared according to the process of the present invention depend directly on a number of such the pH of the precipitation 2 to the reaction temperature 50 to the reaction time from 2 to 8 the ratio of the of from 1 to 0 the stirring A suitable choice of these variables allows the according to of the required type of yellow Another remarkable advantage connected with the process of the present invention is unlike the known the preparation of hydrated ferric oxide according to the invention can be carried out continuously in aa much while the solution of ferric salt is continuously the hydrated ferric which forms c n be separated continuously from the reaction A further advantage lies in the fact unlike some known it is not necessary to blow air or other oxidising gases into zone during the reaction according to the thus avoiding the use of complex and expensive Thanks to their structure the yellow pigments tained from the hydrated ferric oxide prepared according to the invention do not present any tendency to which is a considerable advantage in their use in the production of These yellow pigments are easily converted into red pigments with excellent eharaeteristics by simple calcination at temperatures of 400 to The invention will now be described by the following Examples to which it is not Example 1 Preparation of the of 25 to A suspension of the presence of excess sodium was Air was bubbled through this suspension until the mass passed from the colour of the ferrous hydroxide to the yellow colour of the goethite Preparation of the pigment 28 g of were dissolved in 250 ml of water and then 10 ml of the nucleus suspension prepared as above were added to the Part of the precipitated as while the pH rose to Air was bubbled through the mass which was kept at 20 to until the pH fell to and the colour became The bubbling of air through the mass was then At the same time the mass was heated to 70 to At this point a solution of 28 g of in 100 ml of water and a 2N solution of sodium hydroxide were added regulating the addition in such a way that the pH always remained around to the temperature being around 70 to The reaction was practically complete in about 5 hours and then the precipitate was washed and dried in an oven at g of a yellow pigment of excellent properties were Example 2 g of Fe were dissolved in 250 ml of water and 10 ml of the nucleating agent suspension prepared as previously described were The pH to with the precipitation of a small quantity of Air was bubbled through the mass which was simultaneously heated to 70 to The then fell to and the mass changed colour from green to bubbling of air through the mass was then At this point 29 g of dissolved in 100 ml of water and a solution of 2N sodium hydroxide were dripped into the the addition being regulated in such a way that the pH was kept between and The precipitate was washed dried at and g of a yellow pigment having excellent characteristics were Example 3 The process of the preceding Example was repeated except after the bubbling of air through the mass had been 29 g of dissolved in 100 ml of water and a suspension of calcium hydroxide in water were introduced taking care to keep the pH between and After washing and 10 g of a pigment of excellent characteristics were Example 4 14 of were in 250 ml of and 10 ml the previously prepared nucleating agent suspension were Air was bubbled through and the mass was simultaneously heated up to 70 to The bubbling of air was stopped and then 29 g of dissolved in 100 ml of water and a solution of sodium hydroxide were added in such a way as to keep the pH of the suspension between and After washing and g of a yellow pigment with excellent characteristics were Example The process was affected as in the preceding Example except of a pigment identical to the one previously Example 6 The process was effected as in Example 4 except that only g of were The yield was g of a yellow a little darker than the one obtained Example 7 Into a flask containing 250 ml of water at a temperature of 70 to 2g of the dry yellow pigment obtained from Example 1 and 14 g of were Then 15 g of in 50 ml of water and sodium hydroxide were added taking care that the pH was kept between and After washing and drying g of an pigment were When this procedure was repeated using as starting material the dry yellow pigment from any of Examples 2 to similar results were insufficientOCRQuality

Claims (1)

1. - 11 - 2524*/2 CLAIMS ^ 1$ A process for the preparation of hydrated ferric oxide having the chemical constitution FeOgH in which an aqueous solution of a ferric salt is added to an aqueous solution of a ferrous salt which also contains hydrated ferric oxide having the chemical constitution eOgH as a nucleating agent for precipitating the hydrated ferric oxide, the mixture is maintained at a temperature of 50 to 100°C, and its pH is maintained at from 2 to 5 so that the ferric salt is hydro-lysed and the hydrated ferric oxide formed is precipitated,, 2* A process as claimed in claim 1 in which the precipitated oxide is separated by filtration and dried at a temperature below 300°C. 3· A process as claimed in claim 1 or claim 2 in which the pH is kept at substantially 3* 4e A process as claimed in any preceding claimSatt which the a .queous solution of the ferrous salt contains from 10 to 500 g of ferrous salt per litre of solution* 5· A process as claimed in any preceding claim in which the aqueous solution of the ferric salt contains from 50 to 600 g of ferric salt per litre of solution* 6« A process as claimed in any preceding claim in which the molecular ratio of the concentrations of ferrous ions to ferric ions is from 1 to 30, 7· A process as claimed in any preceding claim in which the ferrous salt is a salt of sulphuric acid or of a strong non-oxidising acid* 8* A process as claimed in any preceding claim in which the ferrous salt is ferrous sulphate, ferrous ammonium sulphate, or ferrous chloride* 25249/2 - 12 -ferric salt is ferric sulphate, ferric chloride or ferric alum. W 10, A process as claimed in any preceding elaim in which the pH is adjusted by the addition of a base to the reaction medium at the same time as the addition of the ferric salt solution, 11, A process as claimed in any preceding claim in which the hydrated ferric oxide nucleating agent has been prepared by precipitation of ferrous ihydroxide with NaOH from a solution of ferrous sulphate and oxidation of the hydroxide with an oxidising agent, 12, A process for the preparation of hydrated fer ic oxide having the chemical constitution FeOgH in accordance with claim 1 and substantially as herein described, 13, A process for the preparation of hydrated ferric oxide having the chemical constitution PeOgH, substantially as herein described with reference to the Examples· 14» Hydrated ferric oxide having the chemical constitution FeOgH prepared by a process as claimed in any preceding claim, 15", Yellow pigments prepared from the hydrated ferric oxide as claimed in Claim 14· 16, Red pigments prepared by calcination of the hydrated ferric oxide as claimed in claim 14 at a temperature of from 400