Inventor: Thammanur Venkatesan Sivaraman, Director, SNAM Alloys P Ltd.
Title: This invention relates a special process to increase the recovery of magnesium in Ferro Silicon Magnesium production using different fluxes as cover material.
Abstract: A process for manufacturing Ferro Silicon Magnesium from Ferro Silicon comprises of melting Ferro Silicon in an arc furnace and tapping out liquid Ferro Silicon into a ladle to a pre¬determined weight,. ,addirtg the Mild Steel scrap to the liquid Ferro Silicon and thoroughly stirring the same, adding the Calcium and Rare earth metal, plunging Magnesium ingot in to the liquid Ferro Silicon, adding additional Mild Steel scrap and stirring to keep the Silicon percentage between 45% to 48% , pouring the liquid Ferro silicon~Magnesium there after into a ladle and allowing the same to cool in the ingots.
The recovery of Magnesium in the Ferro Silicon Magnesium production process is 80-85% .There is no work done for increase in recovery of Magnesium in Ferro Silicon Magnesium production. This invention relates to a process to increase the recovery of Magnesium to 92% to 95% by adding flux material during the plunging of Magnesium and addition of scrap which cover the upper surface of the melt. This avoids the oxidation of Magnesium and increases the vapor pressure of the melt and the melting point of Magnesium, which increase the Magnesium recovery.

Ferro Silicon Magnesium is used as a nodulizer in ductile iron production. Magnesium is the most popular nodularizing agent,and is usually added as a multi-component alloy form called Ferro Silicon Magnesium. This multi-component alloy contain additions other than Magnesium to reduce the reaction violence, promote Graphite spheroidization, neutralize the effect of impurities on graphite morphology, and control the matrix structure.
Ferro Silicon Magnesium modifies the solidification structure so that the graphite phase precipitates and grows as spheroids, instead of flakes, thus resulting in a cast iron with significantly improved mechanical properties. The nodularizing action can be regarded as a simultaneous desulphurization and deoxidation treatment, where the elements having strong affinity to both Sulphur and-oxygen are added. When dissolved Sulphur and Oxygen are removed from the liquid, the graphite growth will proceed as nodules, according to its crystallographic features.
Magnesium is an essential element for nodulariization in ductile iron so it's recovery is the most important aspect of Ferro Silicon Magnesium production.
Ferro Silicon Magnesium is generally produced in accordance with the following reaction,
FeSi + Mg FeSiMg
Usually the reaction is made to take place between Ferro Silicon and Magnesium in an induction furnace. Molten Ferro Silicon alloy (65% Si, 1-2% Ca, 1.2-2% Rare earth and balance Iron) is taken in an amount of 930 Kg in the ladle shown at 5 at temperature of about 1400 degree Celsius. At this temperature, magnesium metal in the amount of 60-100 Kg is plunged into the Ferro Silicon by attaching Magnesium ingots shown at 2 each weighing 1.5 Kg to 2 Kg into the Steel bars (2.5 m long and 20 mm diameter) shown at 1 and holding the ingots beneath the surface of the bath until the Magnesium ingots are dissolved (patent No: 1794960,patented by SNAM alloy Pvt. Ltd: 8/01/1992). The temperature after plunging is about 1290 degree Celsius. Steel scrap, weighing about 120- 136 Kg is added to increase the Iron content, causing practically no temperature change. The alloy is then cast and analyzed to contain about 3-11% Magnesium, 44-50% Silicon,42-44% Iron. The magnesium recovery is found to be around 80-85%.
The Ferro Silicon Magnesium contains Silicon about 44-50%, iron about 42% to 44% and a Magnesium content of 3-11%. Bath is at least 60% of Silicon prior to the Magnesium addition,with iron being subsequently added to adjust the final alloy composition to its desired value. Magnesium recoveries can be increased to 80% and higher. Reason for this is believed to be the higher Silicon content in the starting Ferro - Silicon which provides Silicon available for the formation of Mg2Si,

upon the addition of Magnesium, where by the vapour pressure of Magnesium is lowered and losses are reduced.
Since Magnesium provides the nodularization effect so increment in the recovery of Magnesium in production process is beneficial for the quality of finished product. This invention proposes the flux material that can increase the recovery of Magnesium.
To increase the recovery of Magnesium in Fe-Si-Mg production, various fluxes are used as the cover material shown at 6 during plunging of Magnesium such as MgO, CaO, MgCCb, CaC03, SiCte, AI2O3, CaF2, Na2B40?. IOH2O, CaF2 and Talc(Mg3Si40io(OH)2).
To further illustrate the present invention, tests were conducted by making 10 heats
Heat 1 was taken in a conventional manner without any addition of flux/slag cover.
Heat 2 was taken by adding a mixture of MgO(45%), CaO(50%)& borax (5%)as a cover material.
Heat 3 was taken by adding a mixture of MgC03 (45%), CaC03 (50%) & borax(5%) as cover material
Heat 4 was taken by adding CaO(95%) & CaF2 (5%) as cover.
Heat 5 was taken by adding MgO (35%), CaO(35%) & Talc (30%).
Heat 6 was taken by adding a mixture of MgO(30%), CaO(30%), Talc (35%) & Borax(5%)
Heat 7 was taken by adding a mixture of CaCOa (33.33%), MgC03 (33.33%) & Talc (33.33%).
Heat 8 was taken by adding a mixture of CaCO3(30%), MgCO3(30%), Talc(35%) & Borax(5%).
Heat 9 was taken by adding a mixture of Dolomite(45%), Talc(50%) & Borax (5%).
Heat 10 was taken by adding a mixture of Si02(35%), CaCO3(30%), MgCO3(30%) & Borax(5%).
In all the heats mentioned above, we have added the flux in the ratio of 7 Kg/1100 Kg of the melt.
The heats were taken in an induction furnace by melting the charge material in a Graphite crucible. For plunging magnesium, magnesium ingot was attached to a steel bar and submerged in the melt such that the ingot is 2-3 inch below the metal surface and held in that position until it dissolved completely.

From the above experiments it can be concluded that mixture of CaC03, MgC03 ,CaO, MgO, Dolomite,Talc & borax was found to give good recovery.
Technical aspect of the invention Mechanism of working of flux
1- Talc, Calcium Carbonate, Magnesium Carbonate ,Calcium Oxide ,Magnesium Oxide and Boric acid form a cover over the surface of the melt. This cover provides enough surface tension to the surface that prevents Magnesium vapors to come out of the melt. These Magnesium vapours remain trapped in the melt and hence increase the recovery of magnesium.
2- The flux cuts off the supply of atmospheric oxygen to the melt, which helps in preventing the oxidation of magnesium to Magnesium oxide.
3- The dissociation of carbonates release Carbon di-oxide which acts as a cover to prevent the oxidation of Magnesium.
4- There is also some chance of getting Magnesium in a small quantity from the dissociation of Magnesium Carbonate which may help increase the recovery.
5- The flux reduces the temperature of the surface of melt, which prevents boiling of Magnesium at the surface.
6- Boric acid and Calcium Fluoride help in coagulation of the oxides (from Talc & Dolomite) at the surface by reducing the melting temperature of the Oxides which helps in formation of a uniform cover over the surface.
What the claim is
Modified process for Ferro Silicon Magnesium manufacturing:
Process for adding Magnesium to Ferro Silicon produces an alloy containing substantially equal amount of Iron and Silicon and 3 to 11% Magnesium where by high recoveries of Magnesium are obtained. The said process comprises of:
1- Providing molten bath containing at least 60% Silicon.
2- Plunging Magnesium metal below the surface of molten Ferro Silicon causing the Magnesium to dissolved therein.

3- After the dissolution of the Magnesium, adding Iron to molten bath in a form that sinks beneath the surface of the iron bath to provide up to dissolution of the added Iron, an alloy containing substantially equal amounts of Iron and Silicon i.e 45%.
4-During plunging of Magnesium and Mild steel scrap addition, adding flux material having a mixture of CaC03, MgC03 ,CaO, MgO, Dolomite,Talc & borax to increase the recovery of Magnesium up to 95%.

We Claim
1) A Process for the manufacture of Ferro Silicon Magnesium from Liquid Ferro Silicon comprising the provision of a molten bath containing at least 60% Silicon; Plunging of Magnesium metal ingots below the surface of molten Ferro Silicon causing the Magnesium to dissolved therein; after the dissolution of Magnesium, adding mild steel scrap to the molten bath to sink beneath the surface of melt to provide complete dissolution of scrap, an alloy containing substantially equal amounts of iron and Silicon i.e. 44 - 45%; during plunging of Magnesium and addition of Mild steel scrap, adding flux material either having a mixture of CaC03 (30 - 35%), MgC03 (30 - 35%), Tale (30 - 35%) and Borax (5 -10%) in ratio 2 - 12kg / 1100 kg or (2) to increase the recovery of Magnesium up to 92 -98%;or CaC03 (30 - 35%), MgO (30 - 35%), Tale (30 - 35%) and Borax (5 - 10%)