FIELD OF INVENTION
The present invention relates to a process to upgrade the low grade ferruginous ores using chemical leaching, heat treatment and low intensity magnetic separation. More particularly the process relates to chemical leaching of ore fines using oxalic acid to recover iron oxalate as a byproduct and creates a magnetic coating on the residue iron particles by controlled heat treatment to separate the magnetized iron particles from manganese particles. BACKGROUND OF THE INVENTION
Manganese ores are primarily used in the manganese ferroalloy making. These ferroalloys are used in steel making process to refine the steel. Quality of manganese alloys depend on the feed grade ores. Manganese ore of different grade (Mn: 30-60%, Mn/Fe: 2.5-12) are mixed to prepare a feed blend with Mn: 38, Mn/Fe: 2.5 to produce different grade silicomanganese alloys and Mn: 46, Mn/Fe: 5 for production of high carbon ferromanganese. The mined high-grade manganese ore lumps (+10mm) are used in the submerged arc furnace at manganese ferroalloy plants. The low-grade fines generated in the mining and sizing of the high grade manganese ores, are disposed at waste dumps. These fines usually contain Mn: 10-30% and Mn/Fe: 0.2-1. The high-grade manganese ore resources are depleting rapidly and there is an economic sense to beneficiate the low-grade manganese ore fines/lumps to

generate the usable grade ores. The process utilize low-grade manganese ore fine (Mn : 15-35%, Fe :20-40%, Si02 : 1-5%, Al2O3 :2-10%) to recover the iron oxalate byproduct and ore concentrate for manganese alloy production process. The recovered ore concentrate can be briquetted/sintered to use into manganese alloy making process to replace the high grade lumpy ores as well as to maintain the better slag properties.
The iron, silica and alumina are found as impurities in manganese ores but presence of impurities show huge variation depending upon geographical distribution and geological formation of ore deposits. These impurities are mainly beneficiated by gravity and magnetic separation methods (US3864118). Reduction roasting and high intensity magnetic separation are preferred methods to remove iron impurities. Magnetite is ferromagnetic mineral and can be efficiently separated by magnetic separator but hematite and goethite are paramagnetic minerals and high intensity (10k Gauss) magnetic separator shown limited applicability. Reduction roasting is a pyrometallurgical route and paramagnetic hematite is reduced into ferromagnetic phase magnetite and further separation is carried out using magnetic separator as reported in various patents (US5270022 A, US 4985216 A). But the techno-economics of this process is not very attractive and new process is still under exploration at various research labs.

Problems with the Prior Art
1. Density difference in iron and manganese minerals is very narrow which makes the conventional gravity separation process unsuitable for beneficiation of ferruginous manganese ores.
2. Both hematite and pyrolusite are paramagnetic minerals and it is a limiting factor for efficient separation of iron and manganese in ferruginous manganese ores using high intensity magnetic separator at commercial scale.
3. Reduction Roasting is a high temperature process and need higher energy to convert hematite to magnetite which makes this process less attractive.
4. Hydrometallurgical characteristics of iron and manganese minerals are similar which makes selective leaching of any one element less viable.
5. There is no known process which recovers a high value byproduct to make the process economically more attractive.
Selective leaching of iron or manganese from the low grade fines using different kinds of acids (H2S04, HN03, HCI, etc.) has also been reported in various patents (US 5932086 A, US4150091, RU2174156, SU1740474, SU1328397). But these methods are very complex and many of these are still under development. So, a process is needed which can be relatively fast and techno-economic.

OBJECT OF THE INVENTION
Therefore, it is an object of the invention to propose a techno-economic process
for upgradation of low grade manganese ores to recovery a valuable iron bearing
byproduct and ore concentrate which can be used into ferroalloy production
process.
Another object of the invention is to propose a robust process which can deal
with the huge variation in the grade of low grade ores and can produce a tailing
with Mn <10% which can be disposed of as a reject.
Yet another object of the invention is to propose a process to produce iron oxalate and ferrite (Y Hematite) using low grade manganese ores to make the ore process flow sheet techno-economic. SUMMARY OF THE INVENTION
A hydrometallurgical process flow sheet has been developed to upgrade the low grade ferruginous manganese ores. The low grade manganese ores fines of 0-3mm have been leached using oxalic acid solution of 1 molarity, 4 hours, 10% solid density and at 60 Deg. Centigrade. The filtered liquid is further photoreduced for 4 hours to achieve the valuable by-products (ferrous oxalate & maghemite). The residue was heat treated at 200-500 Deg. Centigrade for 4 hours in a closed container to produce magnetic coating on iron particles which are further separated by low intensity magnetic separator to produce concentrate which can be used in manganese ferroalloy production.

50 kg samples of two different kinds of low grade manganese ores ((Mn>25%, Fe<25%) & (Mn<25% & Fe>25%) were collected from mines and crushed into 0-3 mm and 0.5mm sizes. Acidic solution of 0.01 to 2 Molarity were prepared using oxalic acid and ore fines were added 5, 10, 20% of solution weight. The slurry was stirred (200-400rpm) and heated at 30, 60 & 90 Deg. Centigrade for 2, 4, 6 hours. The solution was filtered to separate residue and solution. The solution was passed through photoreduction for 4, 6 & 12 hours to reduce the ferric oxalate into ferrous oxalate which is water insoluble and precipitates. The precipitate was further heat treated into in a closed container for 2, 4 & 6 hours to convert it into ferrite (Y maghemaite). The residue samples were heat treated in a closed container for 2,4 & 6 hours to converted the iron oxalate coating into maghemite coating on partially leached iron particles. The heat threated samples were passed through low intensity magnetic separator (0.5, 1 & 1.5 ampere) to separate the magnetic and nonmagnetic product fraction. The nonmagnetic fraction can be used into silico or ferromanganese alloy production and the rejects can be discarded or recirculate depending up on the Mn content in it.

Schematic process flow sheet is given in figure 1. The major outcomes are as follow:
(a) Ferrous oxalate dihydrate (Purity >80%, Yield: 15-20%) can be produced by partial leaching of low grade ferruginous manganese ores and it can be separated and purified from the solution using photochemical reduction process.
(b) Maghemite can be produced by heat treatment of ferrous oxlate dihydrate produced by leaching of low grade manganese ores.
(c) Magnetic coating of maghemite can be created on the particles surfaces by heat treatment at 300-500° C for 2 to 4 hours in a closed container which can impart magnetism ~15emu/gm for efficient magnetic separation.
(d) Ferromanganese grade product (Mn >46%, Mn/Fe~5) with yield ~33% can be achieved using this process by processing of low grade manganese ore which contain Mn 31.1% & Fe: 23.6%. The tailings with Mn >10% can be recirculate to achieve the rejects with Mn <10 %.
(e) Silico-manganese grade product (Mn >38%, Mn/Fe~3) with yield ~33% can be achieved using this process by processing of low grade manganese ore which contain Mn 19.3% & Fe: 39.9 %. The tailings contain Mn <10% which can be discarded.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - Shows physicochemical process flow sheet to treat low grade manganese ores.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Present invention comprises a methodology for continuous treatment of low grade manganese ore fines in an acidic solution to recover an iron oxalate solution and partially leached ore fines. The low grade ferruginous manganese ores of Joda contain iron mainly in the form of hematite (Fe+3) and manganese is in the form of pyrolusite (Mn+4). Manganese in the form of Mn+4 state (Mn02) is difficult to leach out and need a reducing agent to convert it into Mn+2 whereas Fe+3 in hematite (Fe203) is easy to dissolve and follow different dissolution mechanism also. Acidic solution of 0.01 to 2 Molarity were prepared using oxalic acid and ore fines were added 5, 10, 20% of solution weight. The slurry was stirred (200-400rpm) and heated at 30, 60 & 90 Deg. Centigrade for 2, 4, 6 hours. The solution was filtered to separate residue and solution. The solution was passed through photoreduction for 4, 6 & 12 hours to reduce the ferric oxalate into ferrous oxalate which is water insoluble and precipitates. The precipitate was further heat treated into in a closed container for 2, 4 & 6 hours to convert it into ferrite (Y maghemite). The residue samples were heat treated in a closed container for 2,4 & 6 hours to converted the iron oxalate coating into

maghemite coating on partially leached iron particles. The heat threated samples were passed through low intensity magnetic separator (0.5, 1 & 1.5 ampere) to separate the magnetic and nonmagnetic product fraction. The nonmagnetic fraction can be used into silico or ferromanganese alloy production and the rejects can be discarded or recirculate depending up on the Mn content in it. Oxalic acid solutions of different molarity were tested and found that higher molarity solutions can produce water soluble ferric oxalate. Solid and liquid were separated by filtration and liquid was photoreduced to reduce the water soluble ferric oxalate into water insoluble ferrous oxalate. The precipitated is tested and found that product purity is >70 % and it contain some amount of manganese oxalate also. The oxalic acid remained is recycled to make the process more economic. This process is able to recycle almost three fourth of the oxalic acid rest is consumed by the process. The solid residue contains iron particles which have coating of iron oxalates or ligands. The material was heated in the closed container to convert it into magnetic material which was further separated by low intensity magnetic separator. We developed and optimized a methodology for physicochemical processing of low grade ferruginous manganese ores to recover a valuable byproduct and ferroalloy grade ore concentrate with disposable rejects. There are seven major steps in this methodology:

(i) Feed Preparation and Charging: Physical and chemical properties of ores play very critical role during leaching. ROM of ores of two different grade ((Mn>25%, Fe<25%) & (Mn<25% & Fe>25%) has been crushed to two different sizes 0-0.5mm and 0-3mm. Finer sizes is always preferred for leaching but the subsequent magnetic separation process is not able to separate the iron particles very efficiently for fines sizes as studies indicated. So, suitable feed sizes identified for current process is 0-3mm.
(ii) Leaching of Ore Fines: Leaching is an established process for various kinds of ores fines. But it requires very fine size particles for complete leaching of metallic material. We tested 0-0.5mm and 0-3mm size particles. Acidic solution of 0.01 to 2 Molarity were prepared using oxalic acid and ore fines were added 5, 10, 20% of solution weight. The slurry was stirred at 200-400rpm and heated at 30, 60 & 90 Deg. Centigrade for 2, 4, 6 hours in closed container. The leached solution was separated using filtration technique and weight of the residue and solution were taken. It was observed that leaching at 1 -2 molarity is found the best operating molarity and a greenish and yellowish solution is achieved. The lower molarity solutions are not able to leach out the significant iron in the solution in the tested conditions. The 10-20% solid density of solution found optimum. Leaching temperature was optimum between 60-90 Deg C and further increase in temperature was no very suitable for process. It was found that considering the optimum conditions for leaching and magnetic separation 4 hour leaching time was found suitable for the process flow sheet. Weight of the residue varies between 75 to 90% depending upon the material fineness, physical and chemical properties as well as on leaching conditions.

(iii) Filtration: The slurry is filtered to separate the solution and residue for further processing.
(iv) Photo-reduction of solution: The ferrous oxalate is insoualbe in water and during leaching it mostly report in residue which create problem to separate it. So, higher molarity solutions are used to generate ferric oxalate which is water soluble. When the solution of ferric oxalate is photo reduced in sunlight for 4, 6 and 12 hours it get converted into ferrous oxalate which is water insoluble and precipitates. The precipitate is separated and remaining oxalic acid solution is recirculating. 15 to 25 kg ferrous oxalate can be produced by processing of 100kg of ore fines in the optimum process conditions. The optimum time for photo reduction was found between 4 to 6 hours where almost 90% material can recovered.
(v) Heat Treatment: The residue of leaching contains iron and manganese particles which are partially leached and particles carry ferrous oxalate and ligands on the surfaces. Heated treatment of these particles in a closed container can develop a magnetic coating on the particles surfaces which can be helpful magnetic separation of iron from manganese minerals. Heat treatment of recovered ferrous oxalate and partially leached ore fines was carried out in the next stage of process flow sheet.

(a) Heat Treatment of Ferrous Oxalate: The recovered ferrous oxalate can be converted into ferrite. Heat treatment of ferrous oxalate was carried out 250-500 Deg. C for 2-6 hours in a closed container. Chemical analysis, Magnetometer and XRD studies were carried out and found that iron ferrite can be produced by this method. It was found that 3-6kg ferrite and manganese ferrite can be produced by processing of low grade ore by existing process flow sheet. These ferrites can be used in soft magnet manufacturing.
(b) Heat Treatment of Residue: The heat treatment of residue will convert the iron oxalate coating on iron particles into maghemite coating. The residue fines were heat treated at 200-500 Deg. C in a closed container for 2 to 6 hours. Characterization studies revealed that magnetic coating is created at particles surfaces. The magnetic coating on iron particles facilitate efficient magnetic separation of iron particles from manganese particles to produce a ferroalloy grade ore concentrate.
(vi) Magnetic separation: The heat treated residue material was passed on a wet low intensity magnetic separator. The magnetic separation was carried out between 4-10k gauss by adjustment of current (0.5, 1 and 1.5 Amp.) in a low intensity magnetic separation. Magnetic separation test indicate that

SiMn Grade concentrate (Mn >36, Mn/Fe ~2) and FeMn Grade product (Mn>46,
Mn/Fe: ~5) can be produced from low grade ores (Mn <25%, Fe>25%) and
medium grade ores (Mn>25%, Fe<25%), respectively.
(vii) Handling of Tailing: Conservation of natural resources is an important subject for development of the mankind. The material or process rejects which contain Mn>10% are not considered as rejects and need to store. This process is able to recycled the tailing and can produce rejects with Mn
<10%. Example 1: 100 gm of low grade manganese fines of 0-3mm size were collected/prepared from the mined ores. These ores contain Mn 19.3 %, Fe: 39.9 %, Si02: 2.6 %, Al203: 6.55 %. One morality solution of oxalic acid was prepared and it was stirred at 200 rpm and solution temperate was set at 60 Deg. C. Low grade fines were added in the solution as soon as it attains the set temperature. After four hours solution and solid were separated using filtration technique. The green color solution is photoreduced in sunlight for 4 hours and precipitate is separated and characterized. The molarity of solution was measured and found that it can be recirculating for leaching. During the process 22gm iron oxalate and 8 gm manganese ferrite have been recovered. Product quality was established by XRD and chemical analysis. The residue was further heat treated in a closed container for four hours at 500 Deg. C and passed through a low intensity magnetic separator. Magnetic separation results shown that a product with Mn : 42.9 % and Fe : 14.8% can be recovered. The weight recovery was found around 33 % and it can be further improved with slight compromise with product grade. The tailings generated in the process contain Mn: 7.9 % and Fe: 56.75% and can be disposed as a waste.

Example 2: 100 gm of low grade manganese fines of 0-3mm size were collected/prepared from the mined ores. These ores contain Mn 31.1 %, Fe: 23.6 %, Si02: 4.81 %, Al203: 1.61 %. One morality solution of oxalic acid was prepared and it was stirred at 300 rpm and solution temperate was set at 60 Deg. C. Low grade fines were added in the solution as soon as it attains the set temperature. After four hours solution and solid were separated using filtration technique. The green color solution is photoreduced in sunlight for 6 hours and precipitate is separated and characterized. The molarity of solution was measured and found that it can be recirculating for leaching. During the process 17 gm iron oxalate and 6 gm manganese ferrite have been recovered. Product quality was established by XRD and chemical analysis. The residue was further heat treated in a closed container for four hours at 500 Deg. C and passed through a low intensity magnetic separator. Magnetic separation results shown that a product with Mn : 54.3 % and Fe : 11.9% can be recovered. The weight recovery was found around 33 % and it can be further improved with slight compromise with product grade. The tailings generated in the process contain Mn: 24.21 % and Fe: 35.38% and it was recirculated to produce a waste with Mn <10%.

We Claim:
1. A process for beneficiating low grade ferruginous manganese ores to
recover valuable products, the process comprising;
crushing and grinding the ferruginous manganese ore fines/lumps;
leaching the crushed and grinded ferruginous manganese ore fines/lumps
with oxalic acid solution;
reducing filtered solution photochemical to recover iron oxalate byproduct;
heat treating underflow residue at 350 to 500 centigrade; and
separating magnetic and non-magnetic fractions by low intensity magnetic
separation.
2. The process as claimed in claim 1, wherein the low grade ferruginous manganese ores comprises two different grades, grade Fl with Mn>25 weight %, Fe<25 weight % and grade F2 with Mn<25 weight % and Fe>25 weight%.
3. The process as claimed in claim1 and claim 2, wherein grade Fl & F2 are crushed to a size range of 0 to 3 mm.
4. The process as claimed in claim 1, wherein concentration of oxalic acid
solution is in the range of 0.01 to 2 Molar.

5. The process as claimed in claim 4, wherein ore fines were added in the range of 5 to 20 % of solution weight and residue was stirred at 200 to 400 rpm and heated at 30 to 90 Deg. Centigrade for 2 to 6 hours in a closed container.
6. The process as claimed in claim 1, wherein filtrate of the leached solution is subjected to photo reduction in sunlight for 4 to 12 hours to precipitate the ferrous oxalate.
7. The process as claimed in claim 6 further comprising heating ferrous oxalate at 250 to 500 Deg. C for 2 to 6 hours in closed container to produce iron and manganese ferrite.
8. The process as claimed in claim 1, wherein underflow of the leached solution is roasted at a temperature range of 250 to 500 Deg. C for 2 to 6 hours in a closed container.
9. The process as claimed in claim 8, wherein roasted residue is exposed to a low intensity magnetic separator of 4 to 10 kilo gauss to separate magnetic fraction from non-magnetic fraction.
10. The process as claimed in claim 9, wherein magnetic fraction comprises 50 to 67 weight percentage of the roasted residue and non-magnetic fraction comprises 33 to 50 weight percent of the roasted residue.

11. The process as claimed in claim 10, wherein non-magnetic fraction comprises Mn in the range of 7.93 to 24.21 weight percent and Fe in the range of 35.38 to 56.75 weight percent, the remaining portion comprises of silica and alumina.
12. The process as claimed in claim 10, wherein magnetic fraction comprises Mn in the range of 42.9 to 54.3 weight percent and Fe in the range of 14.8 to 11.9 weight percent, the remaining portion comprises of silica and alumina.