Title of Invention

A METHOD OF PROCESSING PHOSPHOGYPSUM

Abstract A method of processing phosphogypsum containing calciumsulphate and soluble impurities of phosphorus pentoxide , free phosphoric acid and/or other soluble phosphates and/or free fluoride and silico fluoride ions , whereby most of the soluble impurities are eliminated, to make phosphogypsum a suitable substitute for gypsum in commercial and industrial applications, by a process essentially comprising of: (a) preparing a homogenous mixture on wet/dry basis of phosphogypsum and additives comprising of reactive minerals and/or reactive minerals, having elements capable of forming insoluble phosphates and/or gaseous/volatile fluorides, in a proportion of 1:100 to 50:100 by weight; (b) Pyroprocessing the mixture in a furnace at a temperature ranging from 200°C to 600°C for a period of 5-10 seconds to 50-60 mins., depending xipon the type of pyroprocessing technique used, to form processed phosphogypsum, and optionally cooling the same; resulting in the soluble phosphoras pentoxides and free phosphoric acid being converted to insoluble phosphates and the sihcofluorides and fluorides being converted to gaseous or volatile fluorides and calcium sulphate being converted to calcium sulphate anhydrite.
Full Text THE PATENTS ACT 1970
COMPLETE SPECIFICATION
1. Title: A method of processing phosphogypsum.
2. APPLICANTS: , ACC Limited, an Indian Company registered under the Companies Act, 1913 and having their registered address at Cement House, 121 Maharshi Karve Road, Mumbai 400 020, Maharashtra, India.
3. The following specification particularly describes the nature of this invention and the manner in which it is to be performed:




Field of invention: The invention relates to a process for treatment of phosphogypsum so as to make it a suitable substitute for mineral or marine gypsum used in industrial and commercial applications.
BACKGROUND OF INVENTION. Gypsum, which is essentially CaS04.2H2O,is
an important and essential component of cement and constitutes 4-5 % of cement. It is added to regulate the extreme setting reaction of cement, which occur in the presence of water. Phosphogypsum is a cheap byproduct from the phosphoric acid industry. Its cost in about half to one third of the cost of gypsum. Phosphogypsum is essentially CaS04. 2H2O. It is unsuitable for the manufacture of cement and several other commercial and industrial applications because of the presence of impurities like soluble phosphorus pentaoxide_(P205) and free phosphoric acids, free soluble fluoride and silico fluoride ions and other organic compounds, These impurities when it exceeds minimal levels, severely restrict the use of phosphogypsum in commercial and industrial application especially in the manufacture of cement, since it retards the setting of cement when exposed to water, through the body of the cement. The soluble phosphorus pentoxide and free phosphoric acids reacts with calcium ions in the cement clinker and form insoluble calcium phosphate, which deposits on the surface of the hydrating grains of cement, thus hindering the penetration of water through the body of the cement and reaction of cement with water.
Similarly the fluoride ions and silico fluoride ions present in phosphogypsum, precipitate as calcium fluoride in the lime rich region of the hydrating cement grains, preventing the setting of cement in the presence of water.
Several methods have been used to reduce the impurities in phosphogypsum to make it equivalent to marine or mineral gypsum. The most popular process is by washing and leaching. Washing and leaching processes are cumbersome, since it involves handling of the slurry , and washing and drying the filtered cake. Another known method of treating phosphogypsum is with milk of lime (Ca(OH)2) which converts the soluble impurities into insoluble calcium phosphate and calcium fluorides.

The above processes only remove 50% of the water soluble impurities in
phosphogypsum.
The present invention describes a process by which phosphogypsum can be
processed, so that it can be used as a substitute for gypsum in the cement industry as
well as in other commercial and industrial applications where gypsum is used. By this
process, phosphogypsum is made equivalent to mineral and marine gypsum in the
performance in cement, in terms of setting characteristics and compressive strengths.
SUMMARY: In its main aspect, the invention describes a method of processing phosphogypsum, whereby the soluble phosphorus pentoxide and free phosphorieacid and soluble fluoride and silico fluoride impurities, contained in phosphogypsum are significantly eliminated, so as to make it a substitute for mineral or marine gypsum in commercial and industrial applications where gypsum is used. A homogenous mixture of phospho gypsum and reactive mineral elements capable of forming insoluble phosphates and volatile fluorides are prepared on a wet/dry basis, in the ratio of 1:100 to 50:100 by weight The mixture is pyroprocessed in a furnace at a temperature of 150°C to 600°C for a period of 5-10 seconds to 50-60 mins., depending upon the type of pyroprocessing technique used, to form processed phosphogypsum.
The pyroprocessing of phosphogypsum in the presence of reactive minerals, converts the soluble pentoxides and free phosphoric acid to insoluble metahc phosphates, which do not react with water during the process of hydration. The flouride ions and silico fluoride ions are converted to metalic fluorides which volatalise during the process of pyroprocessing.
In another aspect of the invention, one or more industrial byproducts or reactive minerals containing elements such as, aluminum, Manganese, Magnesium, Silica, Strontium, iron and barium are used. Reactive minerals such as alum, aluminium sulphates, Gibbisite, a -allumina, high alumina cements, aluminosilicate glasses, bauxite, or aluminous clays may be used.

In yet another aspect of the invention, the pyroprocessing is done in a furnace which may be a kiln, fluidized furnace, trolley furnace or a stationary furnace, which may fired by fossil fuel, nuclear energy or hydrogen power or thermal power.
In the final aspect of this invention, the industrial application of this invention can be in the cement industry or any other industry where gypsum is used as a set regulator.
DESCRIPTION: The following is a brief description of working of this invention. In its main embodiment, a homogenous mixture of phosphogypsum and additives containing reactive minerals and/or industrial byproducts having elements capable of forming insoluble metallic phosphates and volatile metallic fluorides, is prepared, on a wet / dry basis. The phosphogypsum is usually obtained as a byproduct from the phosphoric acid production. This phosphogypsum is sun dried before industrial use. The proportion of additives to phosphogypsum would depend upon the extent of impurities in phosphogypsum and the composition of the additives used. Usually phosphogypsum and additives are in the range of ratio of 1:100 to 50:100 by weight. The elements in the reactive mineral would include aluminum, barium, magnesium, manganese, strontium and silica. The homogenous mixture is pyroprocessed in a furnace at a temperature ranging from 150°C to 600°C for a period of 5-10 seconds to 50-60 mins., depending upon the type of pyroprocessing technique used.
The furnace may be a kiln, fiuidized furnace, stationary furnace or trolley furnace, and
may be fired by coal, gas, oil or other type of fossil fuel or nuclear fuel or hydrogen or thermal power.
During the process of pyroprocessing, amongst others, three simultaneous reactions takes place:
1. The soluble phosphorus pentoxide and free phosphoric acid impurities are converted to insoluble metallic phosphates, which are inert to cement hydration reactions.
2. The fluorine ions form metallic fluorides volatalise during the pyroprocessing.
3. The Calcium sulphate dihydrate present in phosphogypsum is converted to soluble Calcium sulphate anhydrite.

In its preferred embodiment, one or more minerals are chosen from among the group consisting of reactive minerals such as alum, aluminum sulphates, a alumina, Gibbisite, high alumina cements, aluminosiiicate glasses, bauxite and aluminous clays. The mixture of phosphogypsum and reactive minerals are pyroprocessed in a appropriate pyroprocessing system.
Thus during the process of pyroprocessing the homogenous mixture of phosphogypsum and aluminum based reactive minerals, various reactions take place to give the following end products amongst others:

The following examples give the comparative levels of soluble and insoluble Phosphorus pentoxide and free phosphoric acid and fluoride impurities in phosphogypsum and processed phosphogypsum at different levels of impurities in phosphogypsum.
EXAMPLE -1 - for preparing Processed Gypsum from phosphogypsum-S_A


EXAMPLE - 2 for preparing Processed Gypsum from phospho gypsum- B


Soluble phosphorus pentoxide and free phosphoric acid and free fluoride and sihco
fluoride impurities below the level of 0.06%. and fluorine ions below the level of
.05% do not interfere in the hydration process
The processed phosphogypsum is a cheap substitute for gypsum in any industrial or commercial application. It finds specific use in the cement industry, where normally gypsum is added to cement clinker to regulate the setting reaction of cement in the presence of water. The setting of cement involves the reaction of clinker minerals with water to form a system of interlocking crystals which lock the material together. The setting of cement is primarily due to the reaction of tri-calcium aluminate (Ca3Alt>4) which is the most reactive of the clinker minerals present in cement.
The set regulating action of gypsum is primarily due to its reaction with tri-calcium
aluminate. Calcium sulphate is soluble in water and aides in the setting process when
it reacts with tri-calcium aluminate as given by the following reaction:
Ca3A10 4+ CaS04 +H20 ► CaO.Al 20 3.3CaSO 4.32H 2O(Ettringite).
The ettringite is usually formed as a very fine grained crystal which forms a coating on the surface of tricalcium aluminate particles. These crystals are too small to bridge the gaps between the particles of cement. The cement mix therefore remains plastic. After the initial hydration reaction of cement, a dormant period occurs during which the rate of hydration of cement is usually reduced. During this dormant period, ettringite crystals continue to grow and eventually are large enough to impede the mobility of cement particles. At mis stage setting occurs. Thus processed phosphogypsum, without ihe impurities of soluble phosphorus pentoxides, free phosphoric acid and free fluoride and sihco fluoride ions > is made a cost effective equivalent to mineral or marine gypsum, for use in industrial application.

WE CLAIM:
1. A method of processing phosphogypsum containing calciumsulphate and soluble impurities of phosphorus pentoxide , free phosphoric acid and/or other soluble phosphates and/or free fluoride and silico fluoride ions , whereby most of the soluble impurities are eliminated, to make phosphogypsum a suitable substitute for gypsum in commercial and industrial applications, by a process essentially comprising of:
(a) preparing a homogenous mixture on wet/dry basis of phosphogypsum and additives comprising of reactive minerals and/or reactive minerals, having elements capable of forming insoluble phosphates and/or gaseous/volatile fluorides, in a proportion of 1:100 to 50:100 by weight;
(b) Pyroprocessing the mixture in a furnace at a temperature ranging from 200°C to 600°C for a period of 5-10 seconds to 50-60 mins., depending xipon the type of pyroprocessing technique used, to form processed phosphogypsum, and optionally cooling the same;
resulting in the soluble phosphoras pentoxides and free phosphoric acid being converted to insoluble phosphates and the sihcofluorides and fluorides being converted to gaseous or volatile fluorides and calcium sulphate being converted to calcium sulphate anhydrite.
2. A method as claimed in claim 1, wherein reactive minerals or the industrial bi-products contain one or more of the elements form the group consisting of aluminum, barium, ferrous iron, magnesium, manganese, silica and strontium.
3. A method as claimed in claim 2, where in the pyroprocessing is done in a furnace, which may be a kiln, stationary furnace, trolley furnace, fluidized furnace fired by one or more types of fossil fuel, nuclear power or hydrogen power or thermal power.

4. A method as claimed in claim 3, where in the reactive minerals contain aluminum and are one or more from among the group consisting of alum, amminixun sulphates, Gibbisite, a -allumina, high alumina cements, aluminosihcate glasses, bauxite, and aluminous clays *
5. A process as claimed in claim 4, which is used in the manufacture of cement.
Dated this 24th day of Navember 2003 at Mumbai

To,
The {Controller Of Patents
Patent Office
Mumbai

Documents:

1335-mum-2003-cancelled pages(16-12-2004).pdf

1335-mum-2003-claims(granted)-(16-12-2004).doc

1335-mum-2003-claims(granted)-(16-12-2004).pdf

1335-mum-2003-correspondence(06-12-2004).pdf

1335-mum-2003-correspondence(ipo)-(29-09-2004).pdf

1335-mum-2003-form 1(16-12-2004).pdf

1335-mum-2003-form 19(13-07-2004).pdf

1335-mum-2003-form 2(granted)-(16-12-2004).doc

1335-mum-2003-form 2(granted)-(16-12-2004).pdf

1335-mum-2003-form 26(31-12-2003).pdf


Patent Number 207857
Indian Patent Application Number 1335/MUM/2003
PG Journal Number 32/2007
Publication Date 10-Aug-2007
Grant Date 29-Jun-2007
Date of Filing 24-Nov-2003
Name of Patentee ACC LIMITED
Applicant Address CEMENT HOUSE, 121 MAHARSHI KARVE ROAD, MUMBAI,
Inventors:
# Inventor's Name Inventor's Address
1 MR. MANISH VASANT KARANDIKAR RESEARCH & CONSULTANCY DIRECTORATE DEPT. THE ACC LIMITED, CENTRAL RESEARCH STATION, LAL BAHADUR SHASTRI MARG, THANE 400 604,
2 MR. RUSTOM MINOCHER CURSETJI RESEARCH & CONSULTANCY DIRECTORATE DEPT. THE ACC LIMITED, CENTRAL RESEARCH STATION, LAL BAHADUR SHASTRI MARG, THANE 400 604,
3 MR. ABHAY KANT PATHAK RESEARCH & CONSULTANCY DIRECTORATE DEPT. THE ACC LIMITED, CENTRAL RESEARCH STATION, LAL BAHADUR SHASTRI MARG, THANE 400 604,
4 MR. SHREESH ANANT KHADILKAR RESEARCH & CONSULTANCY DIRECTORATE DEPT.., THE ACC LIMITED, CENTRAL RESEARCH STATION, LAL BAHADUR SHASTRI MARG, THANE - 400 604
PCT International Classification Number C04B 11/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA