Claims:We Claim:
1. Hyper-activated clay binder comprising polymer and clay combination favouring in-situ polymerized inter-cum-intra molecular polymer chains in said clay as binder in the presence of water.

2. Hyper-activated clay binder as claimed in claim 1 comprising silico-aluminous clay binder including bentonite binder for pelletization of iron ore fines favouring improving the kinetics of green ball formation and increasing balling disc efficiency.

3. Hyper-activated clay binder as claimed in anyone of claims 1 or 2 comprising hyper-activating polymer containing bentonite adapted for formation of inters and intra networking chains of polymer on hydration.
4. Hyper-activated clay binder as claimed in anyone of claims 1 to 3 comprising poly acryl-amide co-polymer hyper activated clay preferably bentonite clay having higher water absorption capacity, which is swelled favouring multifold increased surface area through shearing mechanism and generating nucleation sites for gathering iron ore particles for effective binding, lower gelling time, high gel formation index with Intrinsic viscosity at room temp of 70-80 Cp and at higher temperature is 75-85Cp.
5. Hyper-activated clay binder as claimed in anyone of claims 1 to 4 wherein said polymer and clay favouring superior binder characteristics with respect to untreated clay binder including selectively:
a) swelling index increase from 18-24ml to 30-35 ml
b) plate water absorption improvement from 325-526% to 525-700%
c) value of gel formation index increase from 70-73 ml to 90-93ml
d) reduced gelling time from 80-90 sec to 30-45 sec.

6. Hyper-activated clay binder as claimed in anyone of claims 1 to 5 wherein said polymer clay combination comprises
polyacryl-amide co-polymer comprising an acrylamide polymeric backbone including sodium acrylate as chain activator, sodium carbonate as hardener, adapted for said copolymer having density of 0.66 gm/cc and particle size 95 % passes through a 200 mesh BSS sieve.

7. Hyper-activated clay binder as claimed in anyone of claims 1 to 6 comprising clay/bentonite 90 to 97 % and polymer 3 to 10 % by wt. adapted for a binder formulation/composition as pellets involving 0.01-0.05% polymer and 0.3-1% bentonite wherein lower binder (bentonite) dosage preferably reduced at 0.3% bentonite and 0.01% polymer reduce down the silica and alumina load inside the pellet in the range of 60 - 65% through binder only.

8. A process for the manufacture of said hyper-activated clay binder as claimed in anyone of claims 1 to 7 comprising:
step of hyper-activating clay binder involving a polymer in combination with said clay binder such as to favour in-situ polymerized inter-cum-intra molecular polymer chains in said clay binder in the presence of water.

9. A process as claimed in claim 8 comprises of providing a binder system having selectively clay/bentonite 90 to 97 to % and polymer 3 to 10 % by wt.

10. A process as claimed in anyone of claims 8 or 9 wherein the polymer used comprises poly acryl-amide co-polymer.

11. A process as claimed in anyone of claims 8 to 10 wherein the polymer is used to activate said clay binder involving acrylamide which is backbone of polymer, Sodium acrylate as chain activator, sodium carbonate as hardener, the polymer having density of 0.66 gm/cc and particle size preferably being 95 % passing 200 mesh BSS sieve.

12. Process as claimed in anyone of claims 8 to 11 wherein bentonite used is either Ca or Na treated and comprises of 40-45% SiO2, 16-18% Al2O3, 15-18% Fe2O3, 2-6% CaO, 2.5-3.5% MgO, 2-4 % Na2O, and 0.1-0.5% K2O by wt. and wherein Bentonite used is characterized by swelling index of 18-24 ml, Plate water absorption of 325-526%, Viscosity of 30-35 Cp at room temperature and 15-25 Cp at 4000C and fineness of 80-85% 200 mesh BSS sieve passing.

13. Process as claimed in anyone of claims 8 to 12 wherein said polymer used for hyperactivating clay binder is based on formation of inters and intra networking chains of polymer on hydration whereby in presence of said polymer the moisture absorbing capacity increases due to polymerization and forming of polymer chains between tetrahedral silica and octahedral alumina of clay binder to act as a bridge between two grains of bentonite thereby resulting in improved physical and rheological properties of said bentonite.

14. Process as claimed in anyone of claims 8 to 13 wherein the polymer is initially added with clay bentonite in dry form before subjecting to exposure to water and mixing for binding purposes.

15. Process as claimed in anyone of claims 8 to 14 wherein the clay/bentonite activation sequence followed is first bentonite and the polymer to be discharged on the bentonite layer to achieve better mixing and distribution and attachment of the polymer with bentonite particles.

16. Process as claimed in anyone of claims 8 to 15, wherein the Blain number (size of the particles) of the polymer used is 2200 to 2800 cm2/g preferably about ~ 200 mesh which is sufficient to take care of the hyper-activation of the bentonite binder irrespective of it’s own size (Blain no.) in the range of 2800 to 4000 cm2/g.

17. Process of pelletization involving the hyper-activated clay binder as claimed in anyone of claims 1 to 7 carried out following:
a) providing the iron ore raw material sources for pelletization including preferably mixture of iron ore fines, coke, limestone, dolomite and ESP dust;
b) adding thereto the hyperactive clay/Bentonite binder having said polymer;
c) feeding the mixture to disc pelletizer for pellets formation.

18. Process as claimed in claim 17, wherein the hyper-activation of bentonite is accelerated by adding moisture into the mixture only and no water addition is done at disc pelletizer, and wherein the moisture level added is in of the order of 1.5-3 Nm3/hrs and depends on input moisture in feed concentrate to achieving a limiting final moisture of 9.8 - 10.2 %.

19. Process as claimed in anyone of claims 17 or 18 wherein the polymer with said clay/ bentonite is involved selectively to
(a) bring out the additional moisture to the surface of the pellet favoring evaporation of moisture on the surface and avoiding sticking of pellets and providing free flow during transportation on conveyors;
(b) maintaining the pellet surface dry thereby avoiding of sticking of material in lower and upper deck screening process of pelletization and increases the screening efficiency; and
(c) maintaining uniform moisture distribution resulting in lower thermal gradient from core to surface of the pellet in the drying zone of induration furnace and helps in reduction of crack generation.

20.Pellets obtained by the process according to anyone of the claims 17 to 19 having mean particle of 10 mm-11.5mm with Drop No 12-19, Green Compression Strength-0.96-1.38 kg/pellet and Dry Compression Strength 4.7-5.54 kg/pellet.

21. Pellets as claimed in claim 20 having the -10-micron particle size ranging from 30-40 % with 45 micron size of 62-73% and inherent moisture of 9.5-11%.

Dated this the 29th day of December, 2017
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
IN/PA-199

, Description:FIELD OF THE INVENTION
The present invention provides for hyper-activated clay binder preferably chemically treated/doped binder and binder formulation/composition and dosage of said binder formulation for pelletization of iron ore fines involving select chemical additive functioning based hyper-activation of clay preferably bentonite clay providing for enhanced physical properties of pellets such as improved drop strength, green compressive strength (GCS), dried compressive strength (DCS) and mean particle size (MPS) of pellets and shape factor of pellets thereby enhancing green pellets properties. More particularly, the present invention is directed to provide for said select polymer poly acryl-amide co-polymer based chemically doped/treated clay preferably bentonite clay comprising expanded clay with hydrated counter ion and including in-situ polymerized inter-cum-intra molecular polymer chains between tetrahedral silica and octahedral alumina of said clay adapted to act as a bridge between two grains of bentonite thereby favouring hyper-activated bentonite clay with numerous nucleation sites to catch and gather iron ore particles. Said hyper-activated clay binder and binder formulation/composition thereof including chemically doped/treated binder (preferably bentonite) of the present invention thus enhances the adhesive properties in combination with water forming inter-cum-intra molecular chains with expanded platelets of bentonite leading to improved gel formation index, reduced gelling time, higher swelling index & plate water absorption, increased viscosity of bentonite binder. Also provided are pellets and iron ore concentrate thereof from said binder composition of the present invention.

BACKGROUND OF THE INVENTION

Pelletization is a technique commonly used for agglomerating the iron ore fines/superfines wherein binder is used to develop strength for handling and transportation. The selection of proper binder and its dosage is of critical importance in producing good quality pellets. Binders accomplish very important functions in iron ore pelletization. Bentonite is primarily used for improving green compressive strength of iron concentrate pellets so that they go through the processes such as smelting without much damage. Ball et al. (1973) indicated that bentonite clay has the following effects.
? Bentonite absorbs moisture, allowing the high moisture concentrate feed to be pelletized. Moisture variations can be taken care of by altering bentonite dosages.
? As bentonite is mixed with iron ore concentrate it becomes wet so that clay layers expand and disperse by the hydration of exchangeable interlayer cations, transforming into a matrix that bonds the ore particles together.
? During balling, the pellets are formed by particles adhering to each other in layers, which are compacted by the weight of the other pellets into a spherical shape.

Bentonite, mostly used in iron ore pelletization, consists of silico-aluminous clay mineral having 50-60% silica and 13-17% alumina depending on other characteristics of the clay. Therefore, the use of bentonite as binder in the formation of pellets causes an increase in the content of silica and alumina, which leads to a drop in total iron content of the pellet. The pellet strength is dependent on the type of bonding produced by the binder. The bonding type can be classified as capillary forces, Van der Waals bonding and adhesive and cohesive forces. Capillary forces are strong but not sufficient for imparting required strength to finished pellets. Van der Waals bonding is very weak and only of minor importance for imparting sufficient pellet strength to finished pellets.

It is therefore necessary to use binders that will exert adhesive or cohesive forces for imparting sufficient strength to finished pellets. The adhesive and cohesive forces occur between solid particles when moisture (water) is present. Besides water, the presence of a binding agent is necessary in order to maintain the adhesive and cohesive forces and also after firing the pellets at temperatures above 1250°C.

Investigations show that the improvement in natural adhesion between the grains of iron ore caused by the organic binders is attributed to its increasing effect on the wettability on the surface of concentrates, besides an increase in the dispersion of ore fines. Organic binders act as dispersants for fines. The increase of the dispersion degree of fines when organic binders are used entails an increase in the pellet strength by filling up the empty spaces between the solid particles which form the pellets with a better finishing without dust deposition on the pellets’ surface. Organic binders also burnt-off during sintering thus causing an increase in the micro-porosity of the finished pellets, allowing the escape of gases and water vapor.

Guihong Han et al, ISIJ Int. Journal, Vol. 52 (2012) investigated that the functions and molecular structure of an ideal organic binder for iron ore pelletization had been expounded and the ideal structure and physical/chemical properties of organic binders can be summarized as: (1) acidic groups involving -COOH and -OH are ideal polar and hydrophilic groups of organic binders; (2) The cohesive force and adhesive force of organic binder are the most important indexes for deciding the binding strength of iron ore particles and binder; (3) The higher molecular weight, the greater cohesive force and mechanical strength of organic binder itself; (4) Good wettability of organic binder solution to the surface of iron ore particles is precondition for achievement of great adhesive force. However, the two most important factors influencing the performance of organic binder in iron ore pelletization are its acidic groups and molecular weight. Increasing the content of acidic groups and the molecular weight favors in enhancing the performance of organic binder. Since the viscosity of organic polymer solution is an indicative of molecular weight, the viscosity is generally considered as an alternative influencing factor.

US Patent 4728537 discloses organic polymer binders like cationic polymers from diallyl dimethyl ammonium chloride and quaternised dialkylamino alkyl (methyl) acrylates and quaternised dialkylamino alkyl (methyl) acrylamides.

US Patent 4767449 relates to a process of agglomerating, comprising a two component binder system, a first component being a binding polymer and a second one being clay. The polymer or copolymers is a derivative from monomer units of acrylamide, sodium acrylate, vinyl acetate and poly (ethylene oxide). The polymer can also be a polysaccharide, e.g. carboxymethyl cellulose, guar gum and hydroxyethyl cellulose.

US Patent 5294250 discloses a self-fluxing clay free binder composition comprising in admixture of a carrier selected from the group of synthetic or natural magnesium and/or calcium mineral (calcite, olivine, magnesite and dolomite) and one organic enhancer consisting of a natural polysaccharide of high viscosity (guar gum).

US Patent 5306327 discloses a binder for pelletizing particulate minerals. The binder comprises of (1) modified native starch, and (2) a water dispersible polymer. The polymer includes lingo-sulfonates, acrylic polymers, vinyl polymer, cellulose derivates, natural gums, guar gums and pectin.

US Patent 0033872 published in 2014 discloses the binder composition mainly consists of acrlyamide polymer with finely grounded wood fibers. The pellets are made with only as mentioned polymer without using bentonite as one of the binder. WO 2009109024 A1 the present invention refers to a binding composition containing bentonite for use in binding finely ground iron ore. The composition of this prior art comprises bentonite and molasses and also refers to a process for preparing iron ore pellets wherein a composition comprising bentonite and molasses is used as binder.

WO 2017/037207 A1 discloses the use of hydrophobically associative copolymers as binders for pelletizing metal containing ores such as iron containing ores. The copolymers comprise monomer units derived from at least one hydrophobically associative monomer, preferably at least one unsaturated hydrophobically associating monomer.

RU 2245930 describes a binding composition containing bentonite and an amount by weight of a polysaccharide as bentonite activator. In this prior art a polysaccharide-based polyelectrolyte polymer is added to the iron ore concentrate in the range of 1- 5% and it is disclosed that this amount should vary with the specific surface of the mineral concentrate. Considering the polymer additions in the range of 1 - 5%, the polymer besides being used in variable amounts according to the specific surface of the mineral, has an excessively high use proportion. By virtue of use of excessively high amounts of the polymer, a person skilled in the art would affirm that such high use of polymer would not justify activation of bentonite.

It thus the need of the day to explore for formulations/ compositions for hyper-activation of binder preferably bentonite binder for pelletization of iron ore fines to enhance the swelling index, plate water absorption, gel formation index and viscosity of the binder at high temperature such as to favour early ball formation with good surface finish and controlled size, which would further enable achievement of desired green pellets properties at either constant and/or reduced binder dosage without compromising the high temperature properties of pellets. Also, is the long felt requirement of the day to look for said binder formulation/composition which binder post water addition would aid in the enhancement of adhesive and cohesive forces even after firing the pellets at temperatures of above 1250°C and would thereby enable increased nucleation sites to catch and gather the iron ore particles for faster rate of pellet production to allow increment of disc speed.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide a binding formulation/composition for hyper-activation of clay binder preferably a silico-aluminous clay binder more preferably bentonite binder towards pelletization of iron ore fines for improving the kinetics of green ball formation and increasing balling disc efficiency.

Another object of the present invention is to provide for said formulation/composition whose effect on bentonite would be to increase the ability of bentonite to swell about four times more than its volume to thereby increase its water absorption capacity and such that such excessive swelling of bentonite in presence of said formulation/ composition including a chemical additive would be adapted to create numerous sites for the thus activated bentonite to catch and gather the iron ore particles towards the formation of pellets and iron ore concentrate thereof.

Yet another object of the present invention is to provide for said formulation/composition including select chemical additive that would be sensitive to moisture and such that hydration of the same in the presence of clay preferably bentonite would create inter-cum-intra molecular chains with expanded platelets of bentonite leading to better gel formation index, reduced gelling time, higher swelling index & plate water absorption, increased viscosity of bentonite binder.

Another object of the present invention is directed to the activation of bentonite that would produce a narrow size distribution in green pellets an important criterion for the pellet quality as high permeability in the pellet bed is beneficial for reduction of pellet in blast furnace, corex, and direct reduced iron making.

A further object of present invention is directed to the activation of bentonite by said select chemical additive based composition so as to increase the disc speed and produce pellets at higher rate of production also adapted to increase the nucleation sites for faster pellets production also particularly adapted for an iron ore concentrate.

Still another object of present invention is to control the green pellet properties such as drop number, GCS and DCS with varying Blaine number of iron ore fine at constant dosage of select chemical based composition and bentonite wherein the Blaine number is related to -10 micron size fraction of particle ranging from 28 - 40%.

Yet another object of the present invention is directed to counter the fluctuation in moisture of feed iron ore fines as in closed wet grinding circuit, the control on moisture is highly difficult and the chemical additive based composition helps in faster absorption of water and such that the fluctuation can be countered when the chemical additive based composition for its activation would work under variation of feed moisture in raw material to be finally limited to the range of from 9.5-11.5%.
SUMMARY OF THE INVENTION

According to a basic aspect of the present invention there is provided a hyper-activated clay binder comprising polymer and clay combination favouring in-situ polymerized inter-cum-intra molecular polymer chains in said clay as binder in the presence of water.

Preferably said hyper-activated clay binder comprises silico-aluminous clay binder including bentonite binder for pelletization of iron ore fines favouring improving the kinetics of green ball formation and increasing balling disc efficiency.

More preferably, said hyper-activated clay binder comprises hyper-activating polymer containing bentonite adapted for formation of inters and intra networking chains of polymer on hydration.
According to another aspect of the present invention there is provided said hyper-activated clay binder comprising poly acryl-amide co-polymer hyper activated clay preferably bentonite clay having higher water absorption capacity, which is swelled favouring multifold increased surface area through shearing mechanism and generating nucleation sites for gathering iron ore particles for effective binding, lower gelling time, high gel formation index with Intrinsic viscosity at room temp of 70-80 Cp and at higher temperature is 75-85Cp.
Advantageously in said hyper-activated clay binder said polymer and clay favouring superior binder characteristics with respect to untreated clay binder including selectively:
a) swelling index increase from 18-24 ml to 30-35 ml
b) plate water absorption improvement from 325-526 % to 525-700 %
c) value of gel formation index increase from 70-73 ml to 90-93 ml
d) reduced gelling time from 80-90 sec to 30-45 sec.

Preferably in said hyper-activated clay binder wherein said polymer clay combination comprises
polyacryl-amide co-polymer comprising an acrylamide polymeric backbone including sodium acrylate as chain activator, sodium carbonate as hardener, adapted for said copolymer having density of 0.66 gm/cc and particle size 95 % passes through a 200 mesh BSS sieve.

According to another preferred aspect of the present invention there is provided a hyper-activated clay binder comprising clay/bentonite 90 to 97 % and polymer 3 to 10 % by wt. adapted for a binder formulation/composition as pellets involving 0.01-0.05% polymer and 0.3-1% bentonite wherein lower binder (bentonite) dosage preferably reduced at 0.3% bentonite and 0.01% polymer reduce down the silica and alumina load inside the pellet in the range of 60 - 65% through binder only.

According to another aspect of the present invention there is provided a process for the manufacture of said hyper activated clay binder comprising:
step of hyperactivating clay binder involving a polymer in combination with said clay binder such as to favour in-situ polymerized inter-cum-intra molecular polymer chains in said clay binder in the presence of water.

Preferably said process comprises providing a binder system having selectively clay/bentonite 90 to 97 % and polymer 3 to 10 % by wt.

More preferably in said process said polymer used comprises poly acryl-amide co-polymer.

According to another preferred aspect of the process the polymer is used to activate said clay binder involving acrylamide which is backbone of polymer, Sodium acrylate as chain activator, sodium carbonate as hardener, the polymer having density of 0.66 gm/cc and particle size preferably being 95 % passing 200 mesh BSS sieve.

Preferably in said process said bentonite used is either Ca or Na treated and comprises of 40-45% SiO2, 16-18% Al2O3, 15-18% Fe2O3, 2-6% CaO, 2.5-3.5% MgO, 2-4 % Na2O, and 0.1-0.5% K2O by wt. and wherein Bentonite used is characterized by swelling index of 18-24 ml, Plate water absorption of 325-526%, Viscosity of 30-35 Cp at room temperature and 15-25 Cp at 4000C and fineness of 80-85% 200 mesh BSS sieve passing.

According to yet another preferred aspect of the process said polymer used for hyperactivating clay binder is based on formation of inters and intra networking chains of polymer on hydration whereby in presence of said polymer the moisture absorbing capacity increases due to polymerization and forming of polymer chains between tetrahedral silica and octahedral alumina of clay binder to act as a bridge between two grains of bentonite thereby resulting in improved physical and rheological properties of said bentonite.

Preferably in said process the polymer is initially added with clay bentonite in dry form before subjecting to exposure to water and mixing for binding purposes.

More preferably in said process the clay/bentonite activation sequence followed is first bentonite and the polymer to be discharged on the bentonite layer to achieve better mixing and distribution and attachment of the polymer with bentonite particles.

According to another preferred aspect of the process the Blain number (size of the particles) of the polymer used is 2200 to 2800 cm2/g preferably about ~ 200 mesh which is sufficient to take care of the hyper-activation of the bentonite binder irrespective of it’s own size (Blain no) in the range of 2800 to 4000 cm2/g.

According to another aspect of the present invention a process for pelletization involving the hyper-activated clay binder is carried out based on the following:
a) providing the iron ore raw material sources for pelletization including preferably mixture of iron ore fines, coke, limestone, dolomite and ESP dust;
b) adding thereto the hyperactive clay/Bentonite binder having said polymer;
c) feeding the mixture to disc pelletizer for pellets formation.

Preferably in above said process the hyper-activation of bentonite is accelerated by adding moisture into the mixture only and no water addition is done at disc pelletizer, and wherein the moisture level added is in of the order of 1.5-3Nm3/hrs and depends on input moisture in feed concentrate to achieving a limiting final moisture of 9.8 - 10.2 %.

More preferably in said process leading to the formation of pellets the polymer with said clay/ bentonite is involved selectively to
(a) bring out the additional moisture to the surface of the pellet favouring evaporation of moisture on the surface and avoiding sticking of pellets and providing free flow during transportation on conveyors;
(b) maintaining the pellet surface dry thereby avoiding of sticking of material in lower and upper deck screening process of pelletization and increases the screening efficiency; and
(c) maintaining uniform moisture distribution resulting in lower thermal gradient from core to surface of the pellet in the drying zone of induration furnace and helps in reduction of crack generation.

According to another aspect pellets obtained by the process have mean particle of 10 mm-11.5mm with Drop No 12-19, Green Compression Strength-0.96-1.38 kg/pellet and Dry Compression Strength 4.7-5.54 kg/pellet.

Preferably said pellets have -10-micron particle size ranging from 30-40 % with 45 micron size of 62-73% and inherent moisture of 9.5-11%.

Thus another aspect of the present invention is to modify the binding mechanism of bentonite in iron ore pelletization. The chemical additive used for hyper-activation of bentonite is basically sodium acrylate based acrylamide polymer. The presence of sodium acrylate in chemical additive works as a hardening agent.

In presence of moisture, the acrylamide based polymer is activated forming numerous networks of polymer chain. These chains capture the octahedral and tetrahedral sites of bentonite by forming the inter-cum-intra networks. The binding mechanism of chemical additive is independent of chemical composition of bentonite. A further aspect of the present invention is directed to said bentonite comprise of 40-45% SiO2, 16-18% Al2O3, 15-18% Fe2O3, 2-4% CaO, 2.5-3.5% MgO, 3-4 % Na2O, and 0.1-0.5% K2O by wt.

Addition of chemical additive with bentonite plays a vital role in its hyper-activation. Firstly, the chemical additive along with bentonite goes to mixer and fluxes and fuel added thereafter. The addition of water is done at mixing stage for early activation of chemical additive enriched bentonite. Hyper activated bentonite creates numerous sites to catch and gather the iron ore particles and helps in binding high Blaine number iron ore fines consisting of hematite, magnetite, limonite, goethite and banded hematite quartzite (BHQ). The -10 micron size fraction is ranging from 28-40%. Based on fineness of iron ore the moisture content varies from 9.5-11.5%.

A further aspect of the present invention is directed to enhance the swelling index, plate water absorption, gel formation index and viscosity at high temperature. This helps in early ball formation with good surface finish and controlled size. Chemical additive improves the green pellets properties such as drop strength, GCS, DCS and MPS of pellets at varying Blaine number and moisture in pellet feed concentrate.

The reduced MPS and improved shape factor of pellets help in maintaining the bed permeability during firing in induration furnace and hence reducing the deviation in CCS of pellets. Suction pressure of induration furnace also improves due to better shape factor of pellets.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1- illustrates schematic diagram of process flow for iron ore pelletization indicating the sequence of chemical additive and raw material additions.
Figure 2a- illustrates photograph of the chemical treated bentonite gel formation index value against normal bentonite. (A-Bentonite, B- Bentonite with 0.01% Chemical additive);
(C – Only Bentonite and D- Bentonite with 0.01% Chemical additive both dried at 1200C)
Figure 2b- represents graphically the plate water absorption value (%) of treated and untreated bentonite;
Figure 3a- represents graphically the mean particle size (MPS) distribution of pellets made with normal bentonite and effect of -10-micron size on pellet size at constant binder dosage;
Figure 3b- represents graphically the mean particle size (MPS) distribution of pellets made with activated bentonite effect of -10-micron size on pellet size at constant binder dosage;
Figure 4- illustrate the result of EPMA (electron probe micro analyzer) analysis of chemical treated bentonite (JXA-8230 wherein the photomicrographs of pellets taken at 100X,200X,500X,1000X,2000X and 3000X represent from a-f).

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES

As discussed hereinbefore the present invention provides for hyper-activated clay binder preferably a chemically treated/doped clay binder and binder formulation/composition thereof suitable for pelletizing iron ores comprising least from 90 to 97% by weight of binder preferably bentonite based on the total weight of the binder, and from 3% to 10% by weight of chemical additive preferably an in-situ formed polymer based on the total weight of the binder adapted for modification or enhancement of binding mechanism of clay preferably normal bentonite. Preferably the montmorillonite based bentonite is treated/doped with chemical additive (polymer) with the minor dosage of 0.01 to 0.05%.

It is a significantly special finding of the present invention that the select poly acryl-amide co-polymer based chemically treated/doped clay preferably bentonite clay reveals swelling, lower gelling time, high gel formation index. Higher water absorption capacity of the binder formulation of the present invention causes the quick absorption of water at lower binder dosage. The hydration of the binder/clay of the present invention stretched the voids (tetrahedral and octahedral) aided by in-situ polymerized inter-cum-intra molecular polymer chains between tetrahedral silica and octahedral alumina of said clay adapted to act as a bridge between two grains of clay preferably bentonite clay that resulted in excessive swelling leading to multifold increased surface area through shearing mechanism thereby creating many nucleation sites for gathering iron ore particles.

According to a preferred aspect of the present invention the select chemical additive of the present invention that is added to the binder comprises polyacryl-amide co-polymer comprising an acrylamide polymeric backbone including sodium acrylate as chain activator, sodium carbonate as hardener, adapted for said copolymer having density of 0.66 gm/cc and particle size 95 % passes through a 200 mesh BSS sieve.

In present invention, addition of water in the mixture of binder and said chemical additive plays a pivotal role for achieving the aforementioned physical properties. The chemical additive enables the bentonite not only improving the green pellet properties but also helps in achieving thermo-thickening behavior of binder during curing of pellets. As the pellet gets dried, the chemical additive increases the viscosity of the binding fluid and adhesion of the particles.

However, normal known organic binders (both cellulose and poly-acryl-amide based) behave other way around, i.e., adhesion is lost as temperature increases. The dried pellets of the present invention are hard enough to withstand the forces acting on pellets during its transfer from one zone to another in induration furnace. The improved shape-factor of green pellets enhances the exposure of hot gases in firing zones resulting in improved fire pellet properties.

Accompanying Figure 1 shows a schematic diagram of material flow and various equipment required for iron ore pelletization. The modified circuit for raw material addition consists of a bunker containing chemical additive 201 and bentonite 101 which is feed to belt conveyor with screw dozer 211. Other raw material like iron ore fine, Coke and Limestone, Dolomite, and ESP dust fed from bunker 103,104,105, and 106 respectively. The overall non-homogenous material fed to high speed mixer 401. For activation of the select chemical additive, the moisture added in mixture itself. During whole process of pelletization the moisture added in mixture only and not in disc pelletizer. Addition of moisture in Disc pelletizer results in bigger size of ball and difficulty in maintaining the final moisture of green pellet. Addition of water in mixer activated the chemical additive and helps in early formation of ball. This helps in generating nuclei for pellet formation even at higher disc speed.

Accompanying Figure 2a- shows a photograph of the actual performance of chemical additive on gelling behavior of normal bentonite clay. The un-treated bentonite (100% bentonite) and chemical treated/doped bentonite (0.01% chemical additive and 0.3% bentonite) were put in the glass funnel and the test is carried out as per IS 12446-2007. The value of gel formation index for normal bentonite clay was found to be 70-73 ml while that for treated bentonite was 90-93 ml. The higher gelling index of treated bentonite with the time helps in reduce the total binder consumption around 60 - 62%.
The fully swelled bentonite samples with and without chemical additive were subjected to heating at temperature of 120 0C. Photograph 2a-C shows that the lumpy mass of bentonite is formed after moisture removal whereas the chemical additive treated bentonite shows spongy mass of bentonite in Figure 2a-D

Figure 2b shows the graphical representation of plate water absorption values with respect to time. Bentonite which is basically montmorillonite, which has the ideal composition: (Na, Ca)0.33(Al 1.67,Mg 0.33)Si4O10(OH)2.nH2O. The tetrahedral silica and octahedral alumina Platelets are loosely bonded by counter ions (typically sodium or calcium) between them. In the presence of water, the counter ions hydrate, causing the clay to expand. However up to certain extent the bentonite can absorb moisture, but in presence of the chemical additive of the present invention the moisture absorbing capacity increase due to polymerization of chemical additive and it quickly form polymer chains between tetrahedral silica and octahedral alumina and acts as a bridge between two grains of bentonite. The plate water absorption (PWA) value increases from 1 to 11 hours after that there is no significant increase in PWA value similarly due to the absence of bridge in un- treated bentonite the PWA values are very ranging from 325-526% against 525-700%

Figure 3a and 3b show the comparative performance results of Mean Particle Size (MPS) of pellets with and without chemical additives. The chemical additive is sensitive to the moisture and it is confirmed from PWA test, higher absorption of water along with excessive swelling around boost the formation of ball in less time. The MPS of green ball made with normal bentonite varies from 11 to 12.6 mm with 0.8% bentonite in the blend against 10mm-11.5mm with 0.3% bentonite binder and 0.01% chemical additive.
Even at lower fraction of -10-micron particle size of iron ore fine and at constant dosage of binder and chemical additive, the +8-12 mm size fraction of pellets is largely controlled. Similarly, with increase in Blaine no (lager -10-micron particle size <35%) the generation of +16 and +12 mm pellets size is also controlled which results in better MPS irrespective of Blaine number of iron ore fines.

Figure 4 represents the EPMA image of dried Bentonite and chemical additive treated bentonite sample. The bentonite along with 0.01% chemical additive is thoroughly mixed and hydrated with water to form thick slurry. The slurry is then dried at temperature of 120 0C to get dried mass of bentonite and the sample is analyzed under EPMA. It is clearly revealed that the chemical additive is thoroughly surrounds the bentonite grains. Similarly, due to hydration of chemical additive the inter-cum-intra molecular layer formation helps in making dried mass more stretchable and foamy. At 3000X, it clearly reveals that the excessive swelling of bentonite occurs.

Experimental Results:
The process of the present invention has been established by conducting series of laboratory scale experiments to produce pellets from different combination of dosage of binder, moisture in green mix, and -10 micron size particles of iron ore fines (Blaine number). As discussed earlier in closed wet grinding circuit, large fluctuations in concentrate moisture and -10 micron size (Blaine number) were observed. To counter the problem of fluctuation it is important to control the binder dosage to make good green pellets. Series of trials are conducted in disc pelletizer to investigate the effect of moisture in green mix and -10 microns in feed.

The formed pellets are subject to physical tests such as drop no, Green Compression Strength (GCS), Dry Compression Strength (DCS) and fired pellet properties such as CCS, and high temperature properties such as RDI, abrasion index (AI) and characterization in scanning electron microscope. Higher the -10 micron particles in the feed higher will be the inherent moisture. Pellets formed under such condition will have higher MPS. Similarly, higher the Blaine number higher will be the surface area of particles and so binder consumption increases. However, treating the bentonite with select chemical additive of the present invention enhances its properties and gives better green and higher temperature properties.

Based on selective dosage of 0.01 % of chemical additive and 0.3% bentonite the plant based trial results shows that fluctuation of -10 micron feed size in the blend and the moisture, the green pellets properties are comparable or even higher compared to only bentonite made pellet. At constant dosage of binder composition, the higher temperature properties are also comparable and better then bentonite made pellets. Pellets produced with select binder and chemical dosage helped in obtaining the improved mean particle size which in turn helps to maintain the bed permeability and burn through temperature inside induration machine.

Chemical additive decomposes at temperature of 400-450 0C inside induration machine and thus strengthen the bentonite structure which results in increase in Dry Compression Strength (DCS) of pellets. The decomposition product mainly CO2, of chemical additive helps in maintaining uniform porosity inside the produced pellets. Maintaining MPS of green pellets in the range of 10 - 11.5 mm reduces the recirculation load in pelletization circuit.
Recirculation load basically calculated as; [(A-B) / A]*100
where, A - Balling disc discharge (tons per hour), and
B - Feed to induration machine (tons per hours)
Due to lower binder dosage, silica and alumina load inside the pellet reduced down for example at 0.3% bentonite and 0.01% chemical additive reduce down the silica and alumina load 60 - 65% through binder only.

Table 1a
11 % moisture in Feed
Binder dosage, % 0.8 B 0.01 (C)+0.5(B) 0.02 (C)+0.3(B) 0.01 (C)+0.3(B)
-10 µm in feed (%) Drop No GCS DCS Drop No GCS DCS Drop No GCS DCS Drop No GCS DCS
30.26 12 0.92 3.4 14 0.86 4.82 15 1 4.78 12 0.98 4.62
33.25 13 0.94 3.6 14 0.92 4.97 15 1.12 5.1 12 1 4.98
35.46 13 0.98 3.7 15 0.98 5.18 17 1.22 5.18 13 1.12 5.16
37.25 16 1 4 17 1 5.2 19 1.3 5.27 16 1.28 5.18
40.15 19 1.12 4.2 19 1.38 5.44 21 1.4 5.42 19 1.42 5.39

Table 1b
10 % moisture in Feed
Binder Dosage % 0.8B 0.01 (C)+0.5(B) 0.02 (C)+0.3(B) 0.01 (C)+0.3(B)
-10 µm
in feed Drop No GCS DCS Drop No GCS DCS Drop No GCS DCS Drop No GCS DCS
30.26 10 0.75 3.6 11 0.83 4.77 13 0.92 4.96 11 0.96 4.95
33.25 11 0.85 3.7 12 0.88 4.89 15 1.1 5.1 11 0.98 4.98
35.46 12 0.9 3.8 13 0.91 5.12 15 1.12 5.19 12 1.13 5.15
37.25 14 0.96 3.96 15 1.1 5.26 17 1.26 5.29 14 1.23 5.28
40.15 15 0.98 4.18 18 1.39 5.43 19 1.41 5.46 18 1.38 5.42

Table 1c
10.5% moisture in Feed
Binder Dosage % 0.8B 0.01 (C)+0.5(B) 0.02 (C)+0.3(B) 0.01 (C)+0.3(B)
-10 µm
in feed Drop No GCS DCS Drop No GCS DCS Drop No GCS DCS Drop No GCS DCS
30.26 11 0.85 3.5 12 0.83 4.75 14 0.98 5.1 11 0.96 4.95
33.25 11 0.89 3.7 13 0.87 4.83 16 1.12 5.24 12 1.12 5.1
35.46 13 0.94 3.75 15 0.98 4.98 16 1.18 5.26 12 1.12 5.12
37.25 14 0.97 3.9 16 1.12 5.18 18 1.29 5.32 15 1.26 5.31
40.15 16 1 4.1 19 1.42 5.4 20 1.48 5.5 18 1.39 5.46
*C-Chemical additive, B-Bentonite

Table 1d

9.5% moisture in Feed
Binder Dosage % 0.8 (B) 0.01 (C)+0.5(B) 0.02 (C)+0.3(B) 0.01 (C)+0.3(B)
-10 µm
in feed Drop No GCS DCS Drop No GCS DCS Drop No GCS DCS Drop No GCS DCS
30.26 9 0.72 3.54 11 0.83 4.78 13 0.91 4.94 10 0.94 4.9
33.25 9 0.85 3.64 12 0.89 4.9 14 0.98 5 11 0.98 4.98
35.46 10 0.86 3.85 12 0.9 4.98 15 1.16 5.2 11 1.1 5.11
37.25 12 0.89 3.97 15 1.16 5.27 17 1.22 5.28 14 1.18 5.24
40.15 15 0.9 4.2 18 1.4 5.42 19 1.39 5.44 18 1.37 5.39

Table 2
Binder Dosage CCS RDI
(-6.3mm) AI
(-3.15mm) Tumbler index
(+6.3mm) Porosity
0.01C+0.3B 265 12.5 7.5 93.3 24.32
262 12.8 7.9 93.1 25.2
259 13.1 8.2 92.5 25.6
256 13.25 8.6 92.1 25.8

Table3
Binder Dosage Balling disc Discharge (TPH) Recirculation load Suction pressure (mmWc) Burn through Temp
0.01C+0.3B 250 10.6 -220 309
350 12.6 -250 281
450 14 -275 257
480 15 -320 232
*C-Chemical additive, B-Bentonite

It is thus possible for the present advancement to provide for a hyper-activated clay binder that is chemically doped and binder formulation/composition thereof and dosage of said binder for pelletization of iron ore fines and for enhancing green pellets properties by enabling hyper-activation of clay binder preferably bentonite clay resulting in improved physical and rheological properties of bentonite. It was found that addition of 0.01-0.05% of select chemical of poly acryl-amide based co-polymer in pellet making circuit helps in enhancing drop strength, green compressive strength (GCS), dried compressive strength (DCS) and mean particle size (MPS) of pellets at varying Blaine number (-10 micron particles ranging from 28 - 40%) and moisture in pellet feed concentrate (9.5 – 11.5%). The variation in Blaine number and moisture demands for varying dosage of binder. However, present invention achieved desired green pellets properties at either constant and/or reduced binder dosage without compromising the high temperature properties of pellets. The binder composition of the present invention reduces the input gangue load coming through binder by 65%. The said chemical surprisingly enhances the adhesive properties of the binder clay with addition of water due to its ability to form inter-cum-intra molecular chains with expanded platelets of bentonite clay leading to better gel formation index, reduced gelling time, higher swelling index & plate water absorption, increased viscosity of bentonite binder. Chemically activated binder of the present invention resulted in reduction of consumption of bentonite from 1.0% to 0.30% leading to the pellets. The reduced MPS of pellets helped in maintaining the bed permeability and reduces the deviation in cold compression strength (CCS) of pellets, which pellets also provides for improved iron ore concentrate.