WO2015198018A1

WO2015198018A1 - Process for producing free flowing ferrous sulphate

Info

Publication number: WO2015198018A1
Application number: PCT/GB2015/051744
Authority: WO
Inventors: Vittorio CARIA; Stefano FRANCARDI
Original assignee: Tioxide Europe Limited
Priority date: 2014-06-24
Filing date: 2015-06-12
Publication date: 2015-12-30
Also published as: GB201411204D0; TW201607893A

Abstract

The invention provides a process for producing a product comprising ferrous sulphate, the process comprising: (i) combining ferrous sulphate monohydrate, hemihydrate gypsum and ferrous sulphate heptahydrate to provide a reaction mixture; and (ii) mixing the reaction mixture to obtain a free flowing product comprising ferrous sulphate. The thus-obtained product may be used as a chromium (VI) reducing agent; as an additive for cement; in the production of ceramics; or (c) as a source of iron in a fertiliser.

Description

PROCESS FOR PRODUCING FREE FLOWING FERROUS SULPHATE

Field of the Invention The present invention relates to a process for producing a product comprising ferrous sulphate.

Background to the Invention It is widely known that ferrous sulphate, especially in monohydrate form, can be produced via thermal processing of copperas (ferrous sulphate heptahydrate) in order to reduce the level of water and to obtain a dry product with free-flowing characteristics. For example, WO 84/01942 discloses a drying process of ferrous sulphate heptahydrate using a combination of drying and addition of an absorbing material. In particular, the process required drying at temperatures between 20-60 °C to obtain a free flowing dry powder. US 2,771 ,342 also describes the drying of moist ferrous sulphate heptahydrate at a temperature below its melting point, followed by the addition of finely ground calcium carbonate and intensive mixing, to obtain a free-flowing product with no tendency to agglomerate. However, the disadvantage of these methods and other known methods in the art is that to get a free-flowing and apparently dry product, the ferrous sulphate heptahydrate has to be dried at certain temperatures to help the removal of water. This thermal process therefore involves high energy consumption, increases the production cost and may result in heat-related stability issues of the product thus obtained.

In view of the above, there is still a need to develop less expensive and more environmentally friendly processes, which require significantly less energy and equipment to manufacture useful ferrous sulphate products. In particular, there is a desire for a method that allows the production of a free- flowing ferrous sulphate product whilst avoiding or reducing one or more of the above problems.

Summary of the Invention The present invention provides, in a first aspect, a process for producing a product comprising ferrous sulphate, the process comprising: (i) combining ferrous sulphate monohydrate, hemihydrate gypsum and ferrous sulphate heptahydrate to provide a reaction mixture; and then (ii) mixing the reaction mixture to obtain a free flowing product that comprises ferrous sulphate .

The present invention thus involves a simple mixing process that utilises the ability of different components to react with the free water present in copperas products to produce a free-flowing ferrous sulphate product. The product obtained is relatively dry, as can be seen by the free-flowing nature of the product.

In the present invention a free-flowing product is one that meets one or both of the following criteria:

(a) when 1000 grams of the product is filled into a funnel with a ½ inch ( 1.27cm) neck at room temperature, the product takes a time of less than 2 minutes and 30 seconds to flow out of the neck of the funnel;

(b) when 1000 grams of the product is filled into a funnel with a 1 inch (2.54cm) neck at room temperature, the product takes a time of less than 40 seconds to flow out of the neck of the funnel. Preferably, the free-flowing product meets both criteria (a) and (b).

Suitably, the process of the present invention is carried out at or close to room temperature, e.g. at substantially room temperature. No heating is required. Unlike typical known processes, therefore, the process of the present invention improves the production of a product comprising ferrous sulphate without the need for thermal drying. A process that makes no use of externally provided heat for the preparation of such products is clearly more economic, environmentally friendly and easy to carry out. The resulting product comprising ferrous sulphate as obtained by the process of the present invention does not discolour or exhibit noticeable oxidation. It retains excellent long term flow properties, even after prolonged storage.

Additionally, the complete absence of needing to provide heat for dehydration also makes the product more stable than thermally dried ferrous sulphate products and less prone to re-hydration and caking. Thus the obtained ferrous sulphate product is suitable for all the typical applications of ferrous sulphate, particularly as a chromium (VI) reducing agent (e.g. in cement production) or as a fertiliser in agriculture. However, it also has additional benefits, e.g. in terms of long term stability. In one preferred embodiment the product comprising ferrous sulphate as obtained is in the form of a free-flowing powder.

As noted above, the free-flowing nature of the product can be assessed by a flow time through a ½ inch funnel and/or by a flow time through a 1 inch funnel. In each case the test is carried out at room temperature and pressure .

In one embodiment, criterion (a) is fulfilled. Thus when 1000 grams of the product is filled into a funnel with a ½ inch ( 1.27cm) neck, the product takes a time of less than 2 minutes and 30 seconds to flow out of the neck of the funnel. For example, the flow time may be from 5 seconds to 2 minutes and 30 seconds, e.g. from 10 seconds to 2 minutes and 30 seconds, or from 20 seconds to 2 minutes and 30 seconds, or from 25 seconds to 2 minutes and 30 seconds, or from 30 seconds to 2 minutes and 30 seconds, or from 35 seconds to 2 minutes and 30 seconds, or from 40 seconds to 2 minutes and 30 seconds.

In one such embodiment, when 1000 grams of the product is filled into a funnel with a ½ inch ( 1.27cm) neck, the product takes a time of less than 2 minutes and 20 seconds to flow out of the neck of the funnel. For example, the flow time may be from 5 seconds to 2 minutes and 20 seconds, e.g. from 10 seconds to 2 minutes and 20 seconds, or from 20 seconds to 2 minutes and 20 seconds, or from 25 seconds to 2 minutes and 20 seconds, or from 30 seconds to 2 minutes and 20 seconds, or from 35 seconds to 2 minutes and 20 seconds, or from 40 seconds to 2 minutes and 20 seconds.

In one embodiment, criterion (b) is fulfilled. Thus when 1000 grams of the product is filled into a funnel with a 1 inch (2.54cm) neck, the product takes a time of less than 40 seconds to flow out of the neck of the funnel. For example, the flow time may be from 1 second to 40 seconds, e.g. from 2 seconds to 40 seconds, or from 5 seconds to 40 seconds, or from 8 seconds to 40 seconds, or from 10 seconds to 40 seconds, or from 15 seconds to 40 seconds, or from 20 seconds to 40 seconds.

In one such embodiment, when 1000 grams of the product is filled into a funnel with a 1 inch (2.54cm) neck, the product takes a time of less than 35 seconds to flow out of the neck of the funnel. For example, the flow time may be from 1 second to 35 seconds, e.g. from 2 seconds to 35 seconds, or from 5 seconds to 35 seconds, or from 8 seconds to 35 seconds, or from 10 seconds to 35 seconds, or from 15 seconds to 35 seconds, or from 20 seconds to 35 seconds.

In one embodiment, both criteria (a) and (b) as described above are fulfilled. As noted above, the free-flowing nature of the product is indicative of the relative dryness of the product obtained by the present method.

The present invention is not limited to any particular water content in the free-flowing product as obtained. However, in one embodiment the free water content in the product comprising ferrous sulphate is 5% w/w or lower, such as 4.5% w/w or lower; more preferably 4% w/w or lower, such as 3.5% w/w or lower; even more preferably 3% w/w or lower, based on the total weight of the product. It may, e.g., be from 0 to 5%, or from 0.05 to 4.5%, or from 0.05 to 4%, %, or from 0. 1 to 3.5 %, or from 0. 1 to 3%, w/w %, based on the total weight of the product.

In all embodiments of the invention, where reference is made to a free water content this value may be determined by a Karl Fischer procedure. The procedure should be one that determines only free water content, not any the content of any water of crystallisation. In such a modified Karl Fischer procedure the measurement taken determines only the free water content, not any crystal moisture, because an initial extraction is carried out using propanol (dry propan- l -ol), to remove the free moisture from the sample, at room temperature. It is an aliquot of this propanol sample that is then titrated using a standard Karl Fischer volumetric titration procedure, to obtain a value for the free water content.

In particular, the Karl Fischer procedure as described in Annex A may be used. In this modified Karl Fischer procedure the measurement taken determines only the free water content, not any crystal moisture.

In one embodiment, the process for producing a product comprising ferrous sulphate comprises: (i) combining from 60% to 85 % w/w of ferrous sulphate heptahydrate, from 2% to 15% w/w of hemihydrate gypsum and from 5% to 35% w/w of ferrous sulphate monohydrate to provide a reaction mixture, where the amounts stated are based on the total weight of the reactants used to form the reaction mixture; and (ii) mixing the reaction mixture to obtain a product comprising ferrous sulphate . It may be that the level of free water in the thus-obtained product comprising ferrous sulphate is 5% w/w or less, e.g. from 0.01 to 5% w/w.

In one embodiment the product comprising ferrous sulphate is further mixed with one or more agriculturally acceptable carrier, agriculturally acceptable diluent and/or fertiliser material, to form a fertiliser product. In one embodiment the product comprising ferrous sulphate is further mixed with one or more cement additive, cement ingredient and/or cement binder, to form a cement mixture.

The present invention further provides, in a second aspect, a product comprising ferrous sulphate as obtainable by carrying out the process of the first aspect.

The product comprising ferrous sulphate as obtainable by carrying the process described herein suitably has a low free water content. Preferably, the ferrous sulphate product is substantially dry. It may, for example, have a level of free water of 5 % w/w or less, e .g. from 0.01 to 5% w/w. The product comprising ferrous sulphate is a free-flowing product. For example, in certain embodiments, the product comprising ferrous sulphate is a free-flowing powder.

In one embodiment, the product comprising ferrous sulphate as obtainable by carrying out the process of the first aspect is in admixture with one or more agriculturally acceptable carrier, agriculturally acceptable diluent and/or fertiliser material. Thus the product may be a fertiliser.

In one embodiment, the product comprising ferrous sulphate as obtainable by carrying out the process of the first aspect is in admixture with one or more cement additive, cement ingredient and/or cement binder. Thus the product may be a cement mixture . The cement may, for example, be hydraulic cement, such as Portland cement. Portland cement (also known as Ordinary Portland Cement or OPC) may be defined as a cementitious material meeting the requirements of ASTM C I 50 or the requirements of European Standard EN 197. 1. Other cements can, however, be used. In one embodiment, the cement mixture is further mixed with water, so as to form a hardened cement product.

In one such embodiment, the cement mixture is mixed with both aggregates (e.g. gravel and/or sand) and water, so as to form a concrete or mortar product. In one embodiment the cement mixture is mixed with aggregates (e.g. gravel and/or sand) before then being mixed with water.

In a third aspect, the present invention provides the use of a step of mixing ferrous sulphate monohydrate, hemihydrate gypsum and ferrous sulphate heptahydrate, to obtain a free-flowing product comprising ferrous sulphate, without the need for thermal drying.

The present invention further provides, in a fourth aspect, the use of the product of the second aspect as a chromium (VI) reducing agent. In one embodiment, the product comprising ferrous sulphate may be used to reduce the Cr (VI) content in cement, especially Portland cement.

In a fifth aspect, the invention provides the use of the product of the second aspect as an additive for cement, e.g. Portland cement.

The present invention further provides a cement mixture comprising the product of the second aspect. The invention also provides a hardened cement product comprising the product of the second aspect. The invention also provides a concrete or mortar product comprising the product of the second aspect.

The invention also provides a fertiliser comprising the product of the second aspect.

The present invention also provides a method of producing a fertiliser, wherein the method comprises: (i) producing a product comprising ferrous sulphate by carrying out the method of the first aspect, and (ii) mixing the product comprising ferrous sulphate with one or more agriculturally acceptable carrier, agriculturally acceptable diluent and/or fertiliser material. The present invention also provides a method of producing a cement mixture, wherein the method comprises: (i) producing a product comprising ferrous sulphate by carrying out the method of the first aspect, and (ii) mixing the product comprising ferrous sulphate with one or more cement additive, cement ingredient and/or cement binder.

The present invention also provides a method of producing a hardened cement product, wherein the method comprises: (i) producing a product comprising ferrous sulphate by carrying out the method of the first aspect, (ii) mixing the product comprising ferrous sulphate with one or more cement additive, cement ingredient and/or cement binder, to form a cement mixture, and (iii) mixing the cement mixture with water.

The present invention also provides a method of producing a concrete or mortar product, wherein the method comprises: (i) producing a product comprising ferrous sulphate by carrying out the method of the first aspect, (ii) mixing the product comprising ferrous sulphate with one or more cement additive, cement ingredient and/or cement binder, to form a cement mixture, and (iii) mixing the cement mixture with aggregates (e.g. gravel and/or sand) and water. In one embodiment the cement mixture is mixed with aggregates before then being mixed with water.

In the present invention, when reference is made to "at room temperature" or to "substantially at room temperature" this may, for example, be from 15 to 25 degrees C, such as from 16 to 25 degrees C and especially from 18 to 25 degrees C; such as from 18 to 24 degrees C or from 19 to 24 degrees C or from 19 to 23 degrees C or from 20 to 22 degrees C, e .g. at about 21 degrees C.

In the present invention, when reference is made to "at room pressure" or to "at atmospheric pressure" this may, for example, be from 95 to 105kPa, such as from 98 to 104kPa, e .g. from 99 to 103kPa or from 100 to 102kPa, e .g. at about l O lkPa.

Description of the drawings

Figure 1 is a spectra showing the elements detected in the ferrous sulphate product of Example 1 , using a JEOL T330A Scanning Electron Microscope with ED AX x-ray microanalysis attachment.

Figure 2 is a SEM image of the ferrous sulphate product of Example 1 , obtained using a JEOL T330A Scanning Electron Microscope with EDAX x-ray microanalysis attachment.

Figure 3 is a set of x-ray maps for the elements Fe, S, Ca and Ti, as detected in the ferrous sulphate product of Example 1.

Figure 4 is a spectra showing the elements detected in the ferrous sulphate product of Example 1 , using a JEOL T330A Scanning Electron Microscope with EDAX x-ray microanalysis attachment, as detected using a higher magnification scan than Figure 1.

Figure 5 is a SEM image of the ferrous sulphate product of Example 1 from a higher magnification scan than Figure 2, obtained using a JEOL T330A Scanning Electron Microscope with EDAX x-ray microanalysis attachment. Figure 6 is a set of x-ray maps for the elements Fe, S, Ca and Ti as detected in the ferrous sulphate product of Example 1 from a higher magnification scan than Figure 3. Detailed description of the invention

The present invention is directed to a process for making a product comprising ferrous sulphate . The process can be generally described as involving combining the following reactants: a) ferrous sulphate heptahydrate, b) ferrous sulphate monohydrate and, c) hemihydrate gypsum; and then mixing the reactants.

The reactants may, in one embodiment, be combined by adding the ferrous sulphate monohydrate and the hemihydrate gypsum to the ferrous sulphate heptahydrate, and mixing the reactants. However, the reactants may, ultimately, be combined in any order. They may optionally be all combined at once.

The reactants may be combined in any suitable manner depending on the technique used for mixing and the concentration of each reactant. All three of the aforementioned reactants can be mixed together using techniques known in the art, such as a front end loader or a solid mixer. The invention is not limited by the equipment or techniques used for mixing, which may be manual or automated.

The ingredients are mixed for a time period sufficient to allow the ingredients to react and form a ferrous sulphate product

The reactants may be allowed to react during the combining step, during the mixing step, and optionally may be allowed to react for a period of time after mixing. In general, the reactants may be allowed to react for a sufficient amount of time to form the ferrous sulphate product.

In certain embodiments, the ingredients are mixed for a period of 1 minute or more, such as 2 minutes or more or 5 minutes or more. The mixing may optionally be for a time period of up to 90 minutes, such as up to 60 minutes or up to 30 minutes, e .g. up to 25 minutes. The mixing may be for a time period of from 2 minutes to 90 minutes, such as from 5 minutes to 60 minutes and especially from 5 minutes to 30 minutes, e.g. from 10 to 20 minutes or from 15 to 25 minutes.

Optionally the reactants may be left to react for a period of time after mixing, e.g. for a period of 1 minute or more, such as 2 minutes or more or 5 minutes or more, such as from 1 minute to 30 minutes, or from 2 minutes to 25 minutes or from 5 minutes to 20 minutes.

The reaction is viewed as complete when the product meets one or both (preferably both) of the following criteria:

(b) when 1000 grams of the product is filled into a funnel with a 1 inch (2.54cm) neck at room temperature, the product takes a time of less than 40 seconds to flow out of the neck of the funnel.

In all the above steps of the process no external heat is applied. Thus the process is suitably carried out substantially at room temperature. The process is preferably carried out at atmospheric pressure .

After the reaction is complete, the product can be stored. It may be stored in bulk or may be stored in individual bags or other containers, as known in the art. The product may, for example, be stored in sealed bags or other containers.

It has been surprisingly discovered that by use of the disclosed process a stable product comprising ferrous sulphate is formed. This product is less dusty than a conventional ferrous sulphate monohydrate product. The product is a fine powder. The product has improved free-flowing characteristics. The product has also a low free water content, despite the fact that thermal drying is not involved.

Accordingly, the product comprising ferrous sulphate produced can be stored, handled, and dispensed more readily when compared to other ferrous sulphate products known in the industry. As used herein, "free-flowing", "free-flowing form" or "free-flowing characteristics" means that no adhesion is apparent. As discussed above, the flow behaviour is measured by a flow time test which consists of measuring the length of time for a standard quantity of powder sample to completely empty from a specified funnel. A funnel suitable for testing powder flow has a discharge spout opening or neck with a specified exit orifice dimension and is mounted vertically and in an outlet level with the horizontal. Such a funnel can be filled with 1000 grams of a sample of the product and the flow time of said sample through the neck is then measured. The measurements are carried out at room temperature and pressure .

The ferrous sulphate product as made by the method of the invention is substantially dry and therefore the product may have a free water content below 5% w/w. In a preferred embodiment, the free water content in the product comprising ferrous sulphate is below 4.5% w/w, more preferably below 4% w/w, e.g. below 3.5% w/w and even more preferably below 3% w/w, based on the total weight of the product. It may, e.g., be from 0 to 5% w/w, or from 0.5 to 4% w/w, or from 1 to 3% w/w. It may be that the free water content in the product comprising ferrous sulphate is from 0. 1 % to 5% w/w, or from 0. 1 % to 4% w/w, or from 0. 1 % to 3% w/w, based on the total weight of the product.

Any source of ferrous sulphate monohydrate can be used in the present invention. For example, the ferrous sulphate monohydrate compound used in the process described herein can be one that has been obtained by conventional drying of ferrous sulphate heptahydrate .

The ferrous sulphate monohydrate used in the process is preferably provided in substantially dry form. Accordingly it is preferred that a ferrous sulphate monohydrate product is provided that has a low free water content, e.g. below 4% w/w free water, or below 3.5% w/w; preferably below 3% w/w, e.g. below 2.5% w/w, or below 2% w/w free water, based on the total weight of this reactant. It may, e.g., have a free water content of from 0.01 % to 3% w/w or from 0.01 % to 2% w/w. In one embodiment it has below 1.5% w/w, or even below 1 % w/w, free water. It may, e.g., have a free water content of from 0. 1 % to 3% w/w or from 0. 1 % to 2.5% w/w; preferably from 0. 1 to 2% w/w; most preferably from 0. 1 to 1.5% w/w or from 0. 1 to 1 % w/w. It may be that the ferrous sulphate monohydrate reactant has a free water content of from 0.3% to 3% w/w, or from 0.3% to 2.5% w/w; preferably from 0.3% to 2% w/w; most preferably from 0.3 to 1.5% w/w or from 0.3% to 1 % w/w, based on the total weight of the ferrous sulphate monohydrate. In one embodiment the free water content is from about 0.5 to about 1 % w/w based on the total weight of this reactant.

In one embodiment, the ferrous sulphate monohydrate compound can be used in an amount ranging from 5% to 35% w/w based on the total weight of the reactants used to form the reaction mixture . For example, in certain embodiments, the ferrous sulphate monohydrate compound is used in amount ranging from 10% to 30% w/w, such as from 15% to 25 % w/w, or from 18% to 22% w/w. It may be that the ferrous sulphate monohydrate is used at a level of from 5% to 30% w/w, or from 5% to 28% w/w, or from 5% to 23% w/w, or from 5% to 22% w/w, based on the total weight of the reactants used to form the reaction mixture. In a preferred embodiment, the ferrous sulphate monohydrate has a concentration from 10% to 35% w/w, such as from 15% to 35% w/w, or 15% to 30% w/w, or from 18% to 30% w/w, or from 18% to 25% w/w.

Any source of hemihydrate gypsum may be used in the present invention. Hemihydrate gypsum is also known as calcium sulfate hemihydrate or plaster of Paris, or may be referred to as CaS04 nH20, where n is in the range from 0.5 to 0.8.

For example, the hemihydrate gypsum may be red hemihydrate gypsum or white hemihydrate gypsum, or combinations thereof. The hemihydrate gypsum used in the present invention may be natural or may be synthetic. The alpha-hemihydrate and/or the beta-hemihydrate can be used.

In one embodiment, the hemihydrate gypsum compound can be used in an amount ranging from 2% to 15% w/w based on the total weight of the reactants used to form the reaction mixture . For example, in certain embodiments, the hemihydrate gypsum compound is used in amount ranging from 2% to 14% w/w, such as from 2% to 13% w/w, or from 2% to 12% w/w. In one embodiment, the hemihydrate gypsum is used in an amount of from 3% to 15% w/w, such as from 3 % to 14% w/w, or from 3% to 13% w/w, or from 3% to 12% w/w. In certain embodiments, the hemihydrate gypsum compound is used in an amount ranging from 4% to 14% w/w, such as from 4% to 12% w/w, or from 4% to 10% w/w. For example, it may be that the hemihydrate gypsum compound is used in an amount from 2% to 10% w/w or from 2% to 8% w/w; or from 3% to 10% w/w or from 3% to 7% w/w; e.g. from 4% to 8% w/w or from 4% w/w to 6% w/w, based on the total weight of the reactants used to form the reaction mixture. Ferrous sulphate heptahydrate has the chemical formula FeS0₄"7H₂0. Any source of ferrous sulphate heptahydrate compounds can be used in the process described herein. For example, the ferrous sulphate heptahydrate compound used may be a by-product of the steel and titanium industries. There is a great deal of interest in the use of ferrous sulphate heptahydrate byproducts, as the cost is low and they are produced in large quantities. However, the perceived problem with these by-products is that they contain considerable amounts of humidity, i.e. they have a high residual free water content. However, these products have surprisingly been found suitable for use in the present process, which permits an end product to be obtained that is free flowing and that has a low free water content without requiring the use of thermal drying. Therefore, wet ferrous sulphate heptahydrate is preferred as a reactant in the present process for obtaining ferrous sulphate products. In one embodiment the ferrous sulphate heptahydrate used in the process is substantially wet or damp, i.e. it has a free water content that is not negligible . In one embodiment the ferrous sulphate heptahydrate has a free water content of 6% or more, such as 6.5 % or more, or 7% or more or 8% or more, w/w, based on the total weight of this reactant. In a preferred embodiment the ferrous sulphate heptahydrate has a free water content up to 15% w/w, preferably up to 14% w/w, e.g. up to 13%, or up to 12%; more preferably the water content is up to 1 1 %; most preferably the water content is up to 10% w/w. It may be from 6 to 15%, such as from 7 to 15% or from 8 to 15%, w/w, based on the total weight of the ferrous sulphate heptahydrate. For example, in certain embodiments, the free water content in the ferrous sulphate heptahydrate is from 6% to 13%, or from 6% to 12% or from 6% to 1 1 %; preferably from 7% to 12% or from 7 to 1 1 %, e.g. from 8% to 10%, w/w, based on the total weight of this reactant.

In some embodiments, the ferrous sulphate heptahydrate used as a reactant has an iron content ranging from 18wt % to 20wt%, such as from 18 to 19wt%. In one embodiment, the ferrous sulphate heptahydrate is used in an amount in the range from 60% to 85 % w/w, based on the total weight of the reactants used to form the reaction mixture . In one preferred embodiment, the ferrous sulphate heptahydrate is used in amount ranging from 60% to 80% w/w, e.g. from 65% to 80% w/w, such as from 70% to 78% w/w. It may be that the ferrous sulphate heptahydrate has a concentration in the reactant mixture of from 65% to 85% w/w, or from 70% to 80% w/w, e.g. from 72% to 78% w/w. In one embodiment, the ferrous sulphate heptahydrate has a concentration from 68% to 78% w/w, or from 70% to 78% w/w, or from 73 % to 77% w/w, based on the total weight of the reactants used to form the reaction mixture.

In a preferred embodiment, the process of the invention comprises: (i) combining from 60% to 85% w/w (such as from 60 to 80%) of ferrous sulphate heptahydrate, from 2% to 15% w/w (such as from 2 to 10%) of hemihydrate gypsum and from 5% to 35% w/w (such as from 10 to 30%) of ferrous sulphate monohydrate to provide a reaction mixture, where the amounts stated are based on the total weight of the reactants used to form the reaction mixture; and (ii) mixing the reaction mixture to obtain a product comprising ferrous sulphate.

In a preferred embodiment, the process of the invention comprises: (i) combining from 70% to 80% w/w (such as from 72 to 78%) of ferrous sulphate heptahydrate, from 2% to 8% w/w (such as from 3 to 7%) of hemihydrate gypsum and from 15% to 25% w/w (such as from 17 to 23%) of ferrous sulphate monohydrate to provide a reaction mixture, where the amounts stated are based on the total weight of the reactants used to form the reaction mixture; and (ii) mixing the reaction mixture to obtain a product comprising ferrous sulphate .

In one preferred embodiment, the process for producing a product comprising ferrous sulphate comprises: (i) combining 75% w/w of ferrous sulphate heptahydrate, 5% w/w of hemihydrate gypsum and 20% w/w of ferrous sulphate monohydrate to provide a reaction mixture, where the amounts stated are based on the total weight of the reactants used to form the reaction mixture; and (ii) mixing the reaction mixture to obtain a product comprising ferrous sulphate . In one embodiment the ferrous sulphate monohydrate, hemihydrate gypsum and ferrous sulphate heptahydrate are the only reactants used to form the reaction mixture . Thus the amount of ferrous sulphate monohydrate plus the amount of hemihydrate gypsum plus the amount of ferrous sulphate heptahydrate equals 100% (by weight).

In another embodiment, further reactants may be present and/or there may be low levels of impurity. Preferably the amounts of any reactants/impurities that are not ferrous sulphate monohydrate, hemihydrate gypsum and ferrous sulphate heptahydrate is 5% wt/wt or less, based on the total weight of the reactants used to form the reaction mixture, such as 4% or less or 3% or less or 2% or less or 1 % or less. For example, the amounts of any reactants/impurities that are not ferrous sulphate monohydrate, hemihydrate gypsum and ferrous sulphate heptahydrate may be from 0 to 3% wt/wt, such as from 0.01 to 2% or from 0.05 to 1 % or from 0.05 to 0.5% or from 0.1 to 0.3%.

The product comprising ferrous sulphate obtained by the process is substantially a free-flowing product and optionally has a low free water content. Preferably, the free- flowing ferrous sulphate product is substantially dry. In a preferred embodiment, the free water content in the free-flowing product comprising ferrous sulphate is below 5% w/w, more preferably below 4.5% w/w and even more preferably below 4% w/w and even more preferably below 3.5% w/w or below 3% w/w. It may, e.g., be from 0 to 5% w/w, or from 0.5 to 4% w/w, or from 1 to 3% w/w. It may be that the free water content in the free-flowing product comprising ferrous sulphate is from 0. 1 % to 5 % w/w, or from 0. 1 % to 4% w/w, or from 0. 1 % to 3% w/w, based on the total weight of the free-flowing product.

In one embodiment step (i) is carried out substantially at room temperature and step (ii) is carried out substantially at room temperature. In one embodiment the entire process is carried out substantially at room temperature .

Thus in one embodiment step (i) is carried out without the application of any external heat and step (ii) is carried out without the application of any external heat. In one embodiment the entire process is carried out without the application of any external heat. One advantage of the present invention is that when the ferrous sulphate heptahydrate (copperas) is combined with ferrous sulphate monohydrate and hemihydrate gypsum, these components utilise or take up the free water present in the copperas starting material, thereby resulting in a substantially dry product. As explained above, this product has surprisingly been found to have excellent free flowing characteristics. Further, it is easily handled, dispensed, and stored.

While not wishing to be bound by any particular theory, it is believed that the hemihydrate gypsum reacts with free water present in the free copperas, reducing water content and leading to the free flowing nature of the product. In addition, it is believed that a coating may form on the particles of ferrous sulphate heptahydrate, e.g. as the hemihydrate gypsum converts to gypsum, and that this coating may serve to reduce friction and so makes the particles more free flowing and easier to handle. Additionally, the fact that the product can be obtained without the application of any external heat for drying/ dehydration also makes the product more stable versus those produced by a thermal process. The product is also less prone to re-hydration and caking than prior art products. This product is also less dusty than a conventional ferrous sulphate monohydrate product.

Another advantage of the present invention is that the ferrous sulphate product can be used in a variety of industries, such as those needing some form of iron. For example, the ferrous sulphate mixture may be used as a reducing agent, e.g. it could be used to reduce the Cr (VI) content of products, especially in the cement industry. It can, therefore, be used as an additive in cement mixtures. For example, it can be added to Portland cement mixtures to reduce Cr(VI). Additionally, the ferrous sulphate product can be used in ceramics production. The ferrous sulphate product can also be used as a source of iron in the agriculture industry, e.g. in fertilisers.

Another advantage of the present invention is that the process makes no use of externally applied heat for the production of the ferrous sulphate product. The product is, instead, chemically dried. Therefore very basic equipment is needed for the production of the product. Essentially, all that is required is standard mixing machinery. This results in a less expensive process, which requires significantly less energy and is more environmentally friendly.

The invention will now be further described, in a non-limiting fashion, in the following examples.

Examples

Example 1 : Manufacture of ferrous sulphate product

The reactants described in Table 1 were used to prepare a free flowing ferrous sulphate mixture.

Table 1

The ferrous sulphate heptahydrate was one that was obtained from a titanium dioxide plant (Tioxide Europe' s Huelva plant) . This was added into a mixer.

Then ferrous sulphate monohydrate and hemihydrate gypsum were added to the mixer. The ferrous sulphate monohydrate which was used in this example was also obtained from a titanium dioxide plant (Tioxide Europe 's Huelva plant). The hemihydrate gypsum was obtained from Fibran SpA, Italy.

The reaction mixture was stirred for approximately 15 minutes at room temperature to achieve a homogenous mixture.

The end of the reaction between damp ferrous sulphate heptahydrate, ferrous sulphate monohydrate and hemihydrate gypsum was determined by a flow time method. The evolution of the free flowing ability of the final product is observed by sampling the product at different times after the reaction has started. The flow time of the sample through a funnel at room temperature is measured. The reaction is considered ended when one or both of the following criteria are met:

(b) when 1000 grams of the product is filled into a funnel with a 1 inch (2.54cm) neck at room temperature, the product takes a time of less than 40 seconds to flow out of the neck of the funnel. When both of the conditions are met, the reaction was ended and the product was ready to be stored.

The ferrous sulphate product produced is substantially dry, as determined in Example 2. It is free-flowing, as determined in Example 3.

Example 2: Determination of free water content

A modified Karl Fischer procedure was used to determine the free water content in the reagents used in Example 1 and in the ferrous sulphate product as produced in Example 1.

The standard Karl Fischer procedure (Angew. Chem. 1935, 48 (26): 394-396) titrates both free water and crystal moisture . In the present invention it is just the free water content that is relevant. The Karl Fischer procedure used has therefore been modified from the standard Karl Fischer procedure to ensure that the measurement taken determines only the free water content, not any crystal moisture. This is achieved by an initial extraction using propanol, to remove the free moisture from the sample, at room temperature. It is then an aliquot of this propanol sample that is titrated using the standard Karl Fischer volumetric titration procedure, to obtain a value for the free water content.

The modified Karl Fischer procedure is set out in Annex A below.

The free water content of the ferrous sulphate heptahydrate and ferrous sulphate monohydrate compounds used in Example 1 was measured with this modified Karl Fischer procedure. The free water content of the ferrous sulphate product produced was also determined in this way.

The results are summarized in Table 2.

Table 2

Example 3: Determination of flow time The free flowing ability was confirmed by measuring the flow time of the ferrous sulphate product produced in Example 1.

A 2kg sample of the ferrous sulphate product produced in Example 1 was sieved (at 4mm; 5 mesh) to eliminate the coarse material.

Two funnels with a discharge spout opening (neck) are filled with one kilogram each of the sieved material (one with ½ inch neck and one with 1 inch neck). Then, the time required to completely empty the funnels flowing the product through the two necks is measured.

The flowing time was less than two minutes and thirty seconds in the ½ inch funnel and less than 40 seconds in the one inch funnel.

Example 4: Electron Microscopy Microanalysis

The ferrous sulphate product of Example 1 was analysed at Huntsman Pigment Innovation Centre using a JEOL T330A Scanning Electron Microscope with EDAX x- ray microanalysis attachment.

Figure 1 is a spectra showing the elements detected Figure 2 is an SEM image of the product

Figure 3 is a set of x-ray maps for the elements Fe, S, Ca and Ti

The main elements detected were iron, sulphur, carbon, oxygen and calcium. Also present at lower concentrations were some titanium, manganese, aluminium and magnesium. The particle appears to consist mostly of iron, sulphur and calcium. The calcium appeared to be present as smaller particles adhered to the surface of the larger crystal. An image and elemental scan was therefore obtained at a higher magnification to see if this could be determined more clearly.

Figure 4 is a spectra showing the elements detected from the higher magnification scan

Figure 5 is an SEM image of the product from the higher magnification scan

Figure 6 is a set of x-ray maps for the elements Fe, S, Ca and Ti from the higher magnification scan

The spectra at higher magnification makes it clearer that the calcium is present in particles on the surface of the larger crystal. The circled areas on the elemental x-ray maps show particles that have a high calcium content but do not appear to have any iron and they correspond with particles on the micrograph that appear to be adhered to the surface. The overlay image shows these particles are distributed over most of the crystal surface. It does therefore appear that the particles of ferrous sulphate heptahydrate have a coating of calcium sulphate. This coating may be serving to reduce friction and so is making the particles more free flowing and easier to handle.

Example 5: Reduction capability of ferrous sulphate in cement Experiments were carried out in order to determine the percentage of abatement of hexavalent chromium in three different Portland cement samples.

The tests were carried out for three different addition rates (0. 1 %w/w; 0.2 w/w; 0.3% w/w) where no reducing agent was added during production.

A 1 gram sample of each cement, free from any reducing agent, was obtained from a cement mill, was mixed with the ferrous sulphate product of Example 1 , and analyzed with the following procedure .

Each sample was extracted with 10ml of distilled water and centrifuged (3500 rpm for 3 minutes). The water was separated and collected. This procedure was repeated three times with fresh water. The extraction water was collected in a 50ml flask and HC1 10% v/v was added up to pH 2±0.5.

A 10ml sample of this solution was then analyzed with a standard colorimetric determination of violet complex with 1 ,5 DPC ( 1 ,5-Diphenylcarbazide) at 540 nm (UV-VIS instrument).

The procedure was repeated for the three addition rates and for the three different cement samples. The percentage of abatement is reported in Table 3.

Addition rate Cr(VI) percent abatement

Cement sample

(% w/w) (%)

0. 1 92

1 0.2 96

0.3 98

0. 1 90

2 0.2 95

0.3 97

3 0. 1 93 0.2 95

0.3 98

Table 3

Annex A - Modified Karl-Fischer process used to determine free water content of products containing water of crystallisation

Instrumentation: Autotitrator

Analytical Range: 0.0001 - 100%

Carried out at room temperature and pressure

1. Scope

This procedure is used to determine the free water content of products containing water of crystallisation. This procedure uses Karl-Fischer (KF) titration to determine the amount of water. The sample is dissolved in methanol.

ROH + S0₂ + R'N [R'NH] S0₃R (Reaction 1) where R 'N = base, ROH = alcohol, typically methanol The water within the sample is titrated quantitatively at room temperature with anhydrous solution of sulphur dioxide and iodine in the presence of a buffer that reacts with hydrogen ions.

[R 'NH] S0₃R + H₂0 + h + 2R'N -> 2[R'NH]I + [R'NH] S0₄R (Reaction 2)

The end point is determined electrometrically with a current applied to a two pin platinum electrode.

The oxidation of alkylsulfite to alkylsulfate in Reaction 2 consumes water, which should come only from the sample . Since water and iodine (I₂) are consumed in a 1 : 1 stoichiometric ratio, the amount of water in the original sample is calculated by measuring the concentration of I₂ remaining after the reaction is complete . The I₂ is measured volumetrically. 2. Reagents

• Hydranal® - Composite 5 = Reagent for volumetric one-component Karl Fischer titration (methanol free), titer: 1 mL to 5 mg water, as available from Sigma Aldrich. This contains iodine, sulfur dioxide and a mixture of imidazole and 2-methylimidazole, dissolved in diethyleneglycol monoethyl ether (DEGEE) (see note A)

• Hydranal® - Methanol dry = reagent for volumetric one-component Karl Fischer titration (working medium), as available from Sigma Aldrich. This is methanol with <0.01 % water, (see note A)

• Dry propan- l -ol

3. Standard

Demineralised Water

4. Equipment/Apparatus

Metrohm USA Inc. volumetric Karl Fischer titrator: "Karl-Fischer 890 Titrando" Double Platinum Wire Electrode

Balance O. lmG

Syringe Ι ΟΟμΙ

Centrifuge Tube

Centrifuge

Micro-pipette 1ml 5. Calibration

Standardisation:

• Turn on KF Titrando.

• Select KF titre method on software .

• Input sample ID information.

· Flush the titration cell with fresh dry methanol using the pump leaving approximately 25 -30ml in the cell. Press START button on software to start the conditioning process. Once the methanol in the cell is conditioned the Conditioning OK appears on the screen. Tare the Ι ΟΟμΙ syringe containing 50μ1 of demineralised water, and add this to the titration cell. Reweight the syringe and work out the water added to the titration cell. Enter the weight of the water added and press START.

On completion of the titration the % water results will be displayed.

Perform the titre determination in triplicates.

6. Validation

Apura® 1 % solid standard for KF oven method (see note B) 7. Method

• Turn on KF Titrando.

• Select KF determination method on software .

• Place approximately l Og of sample into a centrifuge tube .

• Add 25ml of propan- l -ol to the centrifuge tube and mix thoroughly using a glass stirrer.

• Place the tube in the centrifuge and separate the sample at 7500rpm for 1 minute.

• Input sample ID information and enter the weight of sample. Weight = weight taken/ volume of propan- l -ol added multiplied by the volume titrated into the titration cell.

• Flush the titration cell with fresh dry methanol using the pump leaving approximately 25-30ml in the cell. Press START button on software to start the conditioning process. Once the methanol in the cell is conditioned the Conditioning OK appears on the screen.

· When the centrifuge has stopped, remove the centrifuge tube and pipette 1ml of supernatant into the titration cell and press OK. (see note C)

• On completion of the titration the % water results will be displayed.

• Edit the sample information and add correct weight and recalculate the % water.

· Perform the titration in duplicates (see note D).

• No calculations are required as the results are read directly from the PC.

8. Expression of Results

Recording results: 2 decimal places

Reporting results: 2 decimal places Units: %

9. Method Validation

• 8 replicates carried out by one operator

10. Notes

A - Shelf life of the Hydranal® solutions is 3 years once opened.

B - See water content of Ti0₂ by Karl-Fischer method SPMM

C - Ensure sample is added to the titration cell without touching the surface of the titration cell and solution.

D - After a titration is completed the instrument/software automatically starts the conditioning process ready for the next sample .

Claims

1. A process for producing a product comprising ferrous sulphate, the process comprising: (i) combining ferrous sulphate monohydrate, hemihydrate gypsum and ferrous sulphate heptahydrate to provide a reaction mixture; and (ii) mixing the reaction mixture to obtain a free flowing product comprising ferrous sulphate .

2. The process according to claim 1 , wherein in step (i) the ferrous sulphate heptahydrate has a concentration in the range from 60% to 85 % w/w based on the total weight of the reactants used to provide the reaction mixture .

3. The process according to claim 1 or claim 2, wherein in step (i) the ferrous sulphate monohydrate has a concentration in the range from 5% to 35% w/w based on the total weight of the reactants used to provide the reaction mixture .

4. The process according to any one of claims 1 to 3, wherein in step (i) the hemihydrate gypsum has a concentration in the range from 2% to 15% w/w based on the total weight of the reactants used to provide the reaction mixture .

5. The process according to any one of claims 1 to 4, wherein in step (i) the ferrous sulphate monohydrate has below 3% w/w free water, based on the total weight of this reactant.

6. The process according to any one of claims 1 to 5, wherein in step (i) the ferrous sulphate heptahydrate has a free water content of 6% or more, based on the total weight of this reactant.

7. The process according to any one of claims 1 to 6, wherein step (i) involves combining from 60 to 80% w/w of ferrous sulphate heptahydrate, from 2 to 10% w/w of hemihydrate gypsum and from 10 to 30% w/w of ferrous sulphate monohydrate .

8. The process according to any one of claims 1 to 7, wherein the process is carried out at a temperature in the range of from 15 to 25 degrees C.

9. The process according to any one of claims 1 to 8, wherein the free flowing product comprising ferrous sulphate is further mixed with one or more cement additive, cement ingredient and/or cement binder.

10. The process according to any one of claims 1 to 9, wherein the free flowing product comprising ferrous sulphate is further mixed with one or more agriculturally acceptable carrier, agriculturally acceptable diluent and/or fertiliser material.

1 1. A product comprising ferrous sulphate as obtainable by carrying out the process of any one of claims 1 to 10.

12. The product according to claim 13, wherein the product has a free water content of 5% w/w or less.

13. The use of a step of mixing ferrous sulphate monohydrate, hemihydrate gypsum and ferrous sulphate heptahydrate, to obtain a free flowing product comprising ferrous sulphate without the need for thermal drying.

14. Use of the product of claim 1 1 or claim 12 as a chromium (VI) reducing agent.

15. Use of the product of claim 1 1 or claim 12:

(a) as an additive for cement; or

(b) in the production of ceramics; or

(c) as a source of iron in a fertiliser.

16. A cement mixture comprising the product of claim 1 1 or claim 12 together with one or more cement additive, cement ingredient and/or cement binder.

17. A fertiliser comprising the product of claim 1 1 or claim 12 together with one or more one or more agriculturally acceptable carrier, agriculturally acceptable diluent and/or fertiliser material.

18. A method of producing a fertiliser, wherein the method comprises: (i) producing the product comprising ferrous sulphate by carrying out the process of any one of claims 1 to 10, and (ii) mixing the product comprising ferrous sulphate with one or more agriculturally acceptable carrier, agriculturally acceptable diluent and/or fertiliser material.

19. A method of producing a cement mixture, wherein the method comprises: (i) producing a product comprising ferrous sulphate by carrying out the process of any one of claims 1 to 10, (ii) mixing the product comprising ferrous sulphate with one or more cement additive, cement ingredient and/or cement binder.

20. A method of producing a hardened cement product, wherein the method comprises: (i) producing a product comprising ferrous sulphate by carrying out the process of any one of claims 1 to 10, (ii) mixing the product comprising ferrous sulphate with one or more cement additive, cement ingredient and/or cement binder, to form a cement mixture, and (iii) mixing the cement mixture with water.

21. A method of producing a concrete or mortar product, wherein the method comprises: (i) producing a product comprising ferrous sulphate by carrying out the process any one of claims 1 to 10, (ii) mixing the product comprising ferrous sulphate with one or more cement additive, cement ingredient and/or cement binder, to form a cement mixture, and (iii) mixing the cement mixture with aggregates and water.