NO136187B - - Google Patents

Description

The present invention relates to a method for the production of free-flowing iron (II) sulfate heptahydrate from iron (II) sulfate heptahydrate as it occurs in industrial processes.

Iron(II) sulfate heptahydrate occurs in large quantities in various industrial processes, for example, in the production of titanium dioxide pigment after the sulfuric acid process. It contains small amounts of adhered water and sulfuric acid and is therefore, when it comes from the process, not free-flowing and can therefore only be handled with difficulty.

U.S. patent no. 2,771,342 suggests drying the iron (II) sulfate heptahydrate to an FeSO^ content of 5° to 60% and then mixing the dried crystals with finely divided calcium carbonate.

Although a free-flowing iron (II) sulfate heptahydrate-containing product is obtained in this way, the method exhibits several disadvantages. The drying must take place very carefully so that the product does not melt, and during the drying part of the hydrate water is split off. For this reason, expensive precautions to control the drying process are necessary and the separation of hydrate water leads to increased energy costs.

During drying, aggregation occurs so that the product must in some cases be ground. In order to achieve an even distribution of the calcium carbonate in the iron sulphate, it is necessary that the mixing process is very intensive.

A new method has now been found for the production of free-flowing iron (II) sulfate heptahydrate from iron (II) sulfate heptahydrate from industrial processes where iron (II) sulfate heptahydrate is freed from adhering water in a fluidized layer at 5 to 65° C using air as fluidizing gas. The method is characterized by the fact that the iron (II) sulfate heptahydrate is simultaneously treated with up to 10 wt? gaseous ammonia, calculated on the iron (II) sulphate heptahydrate used. Preferably, the ammonia is supplied in amounts of 0.3 to 0.6% by weight, calculated on the iron (II) sulfate heptahydrate used.

The procedure can be carried out easily and simply, whereby expenditure on equipment is small. It can preferably be continuous. In contrast to known methods, drying and treatment of the iron dl) sulfate heptahydrate are carried out simultaneously in one operational step. No significant splitting off of water of hydrate occurs. The dosing of ammonia can be easily carried out by supplying it, for example, at the same time as the fluidizing gas, but it can also be supplied separately. Only small amounts of ammonia are required and painting of the product is not required. The obtained product shows good flowability and doseability and is storage stable. It is, for example, usable as an additive to precursors, fertilizers and cement. Due to its good dissolution properties in water, it is well suited as a flocculant in chemical sewage treatment.

It is important that the iron (II) sulfate heptahydrate that comes from the industrial process is as dry as possible, that is to say that it generally does not contain more than 2 to 5% by weight of hardened water.

Such iron(II) sulfate heptahydrate can be obtained by centrifugation or by other suitable means. Furthermore, care must be taken that the iron (II) sulfate heptahydrate is free of lumps when it is introduced into the fluidized layer.

During the treatment in the fluidized bed, three processes take place at the same time: 1) evaporation of adhered water, 2) neutralization of adhered free acid and 3) partial oxidation of divalent iron to trivalent iron.

Essential for carrying out the method according to the invention is the amount of added ammonia. If this quantity is too small, the product's fluidity and storage stability are reduced. On the other hand, with increasing amounts of ammonia, water-insoluble products are formed in increasing amounts, which can have a disruptive effect on the product's further processing. The appropriate amount of ammonia can easily be determined experimentally.

In order to create the fluidization state, arbitrary, per se known devices can be used. The choice of fluidizing gas is also largely freely selectable. Air is particularly suitable.

Example

Iron (II) sulfate heptahydrate which had been prepared from a titanium sulfate solution by centrifugation was treated in a fluidized bed with a diameter of 490 mm and a layer thickness of 620 mm at a temperature of 30°C. The throughput was 50 kg/h. As fluidizing gas, air was used in a quantity of 200 Nm/h, which was mixed with 0.25 kg/h of ammonia for introduction into the fluidizing layer. To achieve the required temperature in the fluidized layer, the air was preheated to approx. 60°C. Calculated on the free cross-section in the fluidized layer, the gas velocity was 30 cm/sec.

A yellow to light brown, free-flowing and storage-resistant product of sand-like consistency was formed, of which & 6% had a particle size greater than 0.2 mm. The experiment was discontinued after 1±0 hours of continuous, satisfactory operation.

Claims (2)

1. Procedure for the production of free-flowing iron (II) sulfate heptahydrate from iron (II) sulfate heptahydrate from industrial processes, where iron (II) sulfate heptahydrate is freed from adherent water in a fluidized layer at a temperature of 5 - 65°C, below use of air as fluidizing gas, characterized in that the iron (II) sulfate heptahydrate is simultaneously treated with up to 10 wt? gaseous ammonia, calculated on the iron (II) sulphate heptahydrate used. 2. Procedure according to claim 1, characterized in that the ammonia is added in an amount of 0.3 to 0.6 wt?, calculated on the iron (II) sulfate heptahydrate used.