WO2022168110A1

WO2022168110A1 - A process for recovery of base metal from mill scale waste

Info

Publication number: WO2022168110A1
Application number: PCT/IN2021/051208
Authority: WO
Inventors: Uttamchand C. MEHTA; Tushar U. MEHTA
Original assignee: R & D Center, Mangalam Alloys Limited
Priority date: 2021-02-03
Filing date: 2021-12-27
Publication date: 2022-08-11

Abstract

The present invention provides a process for recovery of base metal of steel from mill scale waste. Said process coverts the mill scale waste into base metal of steel alloys along with the respective parent elements such as Fe, Ni, Cr, Mo and Cu with slightly higher carbon (C) percentage and lower manganese (Mn) percentage. The process uses byproducts of steel making operation as charge for arc furnace along with refiners' reducing agents and fluxing agents to enhance metal recovery with their parent elements.

Description

“A PROCESS FOR RECOVERY OF BASE METAL FROM MILL

SCALE WASTE”

FIELD OF INVENTION:

The present invention relates to a process for recovering base metal of steel. More particularly, it relates to the process for recovery of base metal of steel alloys from mill scale waste along with the respective parent element.

BACKGROUND OF INVENTION:

Steel is produced by refining hot metal from an arc / induction / blast furnace etc. After molten steel has been refined, it is solidified and then subjected to successive rolling operations during which the steel may be successively heated and cooled. During the successive heating and cooling of steel, or during storage between various rolling operations, surface of the steel oxidizes to form mill scale. This mill scale flakes off during handling and rolling of the steel.

It has been observed that 2.0 to 3.0 wt. % of metal is converted into oxide/ mill scale during storage between rolling operations and it tends to huge amount of mill scale generation in steel industries. It is difficult for industries to store and manage such huge mill scale. Mill scales generally include base metal chips, platelets and other fines, which are essential oxides of iron. Such oxides are primarily composed of ferrous/ ferric iron (FeO, Fe2O3 and Fe304) surrounding a core of the iron base material. Thus, mill scale is a prime candidate for recycling in steel making or arc furnace operations because mill scale is a relatively coarse, dense, waste oxide material of relatively high iron content and low in impurities such as alumina or silica. In addition, fines are generated from manufacturing units and the use of Direct Reduced Iron (DRI) pellets. DRI pellets are a primary material used by electric arc furnaces in the making of steel and a secondary material used by blast furnaces and cupolas. Many of the pellets are crushed during transportation to mill sites from production plants and during normal charging operations.

Numerous processes have been developed to treat and recycle mill scales but have met with varying success and are often costly. Some of these processes use plasma arc furnaces, briquetting machines and pelletizing systems. These processes are very expensive, inefficient, and require relatively clean mill scale. Therefore, there is a need for an efficient and inexpensive process for recovering iron/ steel from scrap mill scales.

PRIOR ART AND ITS DISADVANTAGES:

The European patent application EP20130772913 discloses a process for recovering iron/ steel from scrap mill scales and fines is disclosed. A process in accordance with embodiments of the present invention comprises mixing mill scales and fines with coke or other carbon containing fines and sealing the mixture in a container. The container is charged into a cupola or blast furnace, where the components react to form molten iron/ steel. The recovery process in accordance with an embodiment of the present invention is performed integral to cupola or blast furnace operations and the recovered metal is collected at the base of the furnace as molten iron/ steel. In said document, the container is charged into a cupola or blast furnace is also melted and thus effects the chemistry of elements recovered from mill scale. Further, there is a possibility of bursting of charged container due to the generation of CO2 from mix coal during reaction.

Another patent KR101164448B1 discloses a method for refining and recovering metal iron from base metal comprises the steps of: cutting base metal using a cutter with a diamond tip, boring the base metal using a drilling machine with a diamond drill tip or punching the base metal using a breaker to reduce the base metal to a specified size(SlOO), pulverizing the base metal to a size of 0.01-300mm(S200), sorting and separating the pulverized base metal to a size of 0.01- 20mm and a size of 20-300mm(S300), refining the separated base metal through shot-peening(S400), and sorting and selecting the base metal to a size of 0.01 -1mm and a size of l-300mm(S500).

Said document relates to a method for refining and recovering metal iron from base metal is followed various processes which increases losses of metal in each step and finally reduces yield of meal recover. It fails to provide the single step process for recovery of base metal steel from mill scale. Also the process disclosed in prior art utilizes gas during the melting process in order to refine the metal. This leads to make complex recovery system and thus increases refining cost.

DISADVANTAGES OF PRIOR ARTS:

Existing methods used for recovering base metal of steel suffer from all or at least of the below mentioned disadvantages:

• Most of them fail to provide open and single stage process. • Conventional prior art requires closed container to recover metal from mill scale or from other waste and thus increases the cost.

• Many of the prior art uses cupola or blast furnace for melting thus makes the complex process.

OBJECTS OF THE INVENTION:

The primary object of the present invention is to provide a process for recovering base metal of steel from mill scale waste.

Another object of the present invention is to provide the process for recovering base metal of steel alloys along with the respective parent element.

Yet another object of the invention is to provide the process for recovering base metal of steel from mill scale waste, which reduces the storage cost of mill scale waste in industries.

Another object of the invention is to provide the process for recovering base metal of steel from mill scale waste, which is cost-effective and environment friendly.

Yet another object of the invention is to provide the process for recovering base metal of steel from mill scale waste, which is open and single stage process.

Another object of the invention is to provide the process for recovering base metal of steel from mill scale waste, which reduces the scrap consumption and production cost. Yet another object of the invention is to provide the process for recovering base metal of steel from mill scale waste, which is performed in arc furnace operations and the recovered metal is collected in mold.

Another object of the invention is to provide the process for recovering base metal of steel from mill scale waste, which uses byproducts of steel making operation as charge for arc furnace along with refiners’ reducing agents and fluxing agents to enhance metal recovery with their parent elements.

Yet another object of the invention is to provide the process for recovering base metal of steel from mill scale waste, which reduces energy utilization of recovery operations by taking advantage of the inherent solubility of agents in mill scale and other associated metallurgical interactions.

Another object of the invention is to provide the process for recovering base metal of steel from mill scale waste, which is used to improve economics of industries and make them free from waste pollution.

Yet another object of the present invention is to provide a process that obviates the disadvantages of prior art.

SUMMARY OF THE INVENTION:

In order to achieve the foregoing objects, the present invention provides a process for recovery of base metal of steel alloys from mill scale waste along with the respective parent element. Said process comprises steps of: 1. Preheating a mill scale waste material in an arc furnace at 300°C for 1 hr; 2. Mixing the mill scale with a reducing agent in a ball mill at 1000 RPM for 90 minutes; 3. Adding CaCO3 to the obtained mixture in the same ball mill; 4. Adding a fluxing agent to the mixture obtained from step 3; 5. Adding a binder and preparing the final mixture; 6. Compacting of final mix in designed die by automatic press at 250 kg/sqcm; 7. Drying compacts in muffle furnace at 300°C for half an hour; 8. Melting dried compacts at 1600 to 1700° C for 55 to 65 minutes and casted in designated mold. The process uses byproducts of steel making operation as charge for arc furnace along with refiners’ reducing agents and fluxing agents to enhance metal recovery with their parent elements.

DESCRIPTION OF THE INVENTION:

The present invention provides a process for recovery of base metal of steel from mill scale waste. Said process converts the mill scale waste into base metal of steel alloys along with the respective parent elements such as Fe, Ni, Cr, Mo and Cu with slightly higher carbon (C) percentage and lower manganese (Mn) percentage.

The process uses the following elements:

A reducing agent,

A fluxing agent,

A binder,

A graphite rod electrode,

An arc furnace,

A muffle furnace,

A ball mill; Wherein,

Said reducing agent is used to enhance metal recovery with their parent elements. The Ferro Alloys and Calcimined Petroleum Coke (CPC) are used as reducing agents. Wherein said Ferro alloy Fe-Si is taken in the range of 7.5 to 9.0 wt % (along with purity of 70 wt % Si and 30 wt% Fe) and said Calcimined Petroleum Coke (CPC) is taken in the range of 10 to 15 wt.% with particle size 1.5-2.5 mm.

Further, the Calcined Petroleum Coke (CPC) comprises:

Ash content : 0.5 %

Volatile matter content: 0.5 %

Fixed carbon: 98-99 %

Real densitv: 2.05 gm/cc min.

Sulphur content: 1.0 - 1.3

Silicon content: 0.5 %

Iron content: 0.04 %

Vanadium content: 0.03%

Said fluxing agent is also used to enhance metal recovery with their parents. A feldspar and a slag-30 powder is used as fluxing agents wherein said feldspar is taken in the range of 5 to 7 wt. % and said slag-30 powder is taken in the range of 0.5 to 1 wt%.

Said binder, sodium silicate is taken in the range of 2.0 to 3.0 wt%.

Said graphite rod electrode of rectangular cross section is used to generate arc.

Said arc furnace is used to perform process operations.

Said muffle furnace is used for drying compacts in the process. Said ball mill is used to grind and blend into nanosize using different sized balls.

The present invention also provides a process for recovery of base metal of steel from mill scale waste. Wherein the process comprises steps of:

1 . Preheating the mill scale waste material in an arc furnace;

2. Mixing the mill scale with reducing agents in a ball mill;

3. Adding CaCOs in mix from ii step in same ball mill;

4. Adding fluxing agent to the mixture obtained from step 3;

5. Adding binder and preparing the final mixture;

6. Compacting of final mix in designed die by automatic press;

7. Drying compacts in muffle furnace;

8. Charging arc furnace with pure metal scrap.

Step 1: Preheating the mill scale waste material in an arc furnace

The first step is to preheat the mill scale waste material in the arc furnace at 300°C for 1 hr.

Step 2: Mixing the mill scale with reducing agents in a ball mill

The next step is to mix the mill scale with reducing agents CPC (Calcinated Petroleum Coke) and Ferro alloys in the ball mill at 1000 RPM for 90 minutes where mill scale to ball ratio is 5: 1.

Step 3: Adding CaCo3 to the obtained mixture in the same ball mill

After mixing with reducing agents, add CaCOs to the obtained mixture from step 2 in the same ball mill. Step 4: Adding fluxing agents to the mixture obtained from step 3

The next step is to add fluxing agents feldspar and slag-30 powder in two steps: 50 percent of total fluxing agent is added before recovery process and remaining 50 percent is added into charge in two steps to maximize recovery of parent elements. From remaining 50% wt, first 30 wt. % of fluxing agent is added into semi melted mixture in the furnace after 30 minutes of initiation of melting process and then slag is removed out. Remaining 20 wt. % of fluxing agent is added to the mixture after 15 minutes and slag is separated out.

Step 5: Adding binder and preparing the final mixture

After adding fluxing agents, add sodium silicate as binder and prepare the final mixture.

Step 6: Compacting of final mixture in designed die by automatic press

The next step is to compact the final mixture in designed die by an automatic press at 250 kg/sqcm.

Step 7: Drying compacts in a muffle furnace

The next step is to dry the compacts in muffle furnace at 300°C for half an hour.

Step 8: Melting dried compacts and casted in designated mold

The next step is to use the dried compacts as charge for arc furnace where it is melted at 1600 to 1700° C for 55 to 65 minutes and casted into designed mold. ADVANTAGES OF THE INVENTION:

The advantages of the present invention are:

• The present invention provides a process for recovering base metal of steel from mill scale waste.

• It provides recovery of base metal of steel alloys along with the respective parent elements.

• It reduces the storage cost of mill scale waste in industries.

• It reduces the scrap consumption and production cost.

• It is open and single stage process.

Claims

CLAIMS,

1. A process for recovery of base metal of steel from mill scale waste, wherein the process comprises steps of: a. Preheating a mill scale waste material in an arc furnace at 300°C for 1 hr; b. Mixing the mill scale with a reducing agent in a ball mill at 1000 RPM for 90 minutes; c. Adding CaCO3 to the obtained mixture in the same ball mill; d. Adding a fluxing agent to the mixture obtained from step c; e. Adding a binder and preparing the final mixture; f. Compacting of final mix in designed die by automatic press at 250 kg/sqcm; g. Drying compacts in muffle furnace at 300°C for half an hour; h. Melting dried compacts at 1600 to 1700° C for 55 to 65 minutes and casted in designated mold.

2. The process for recovery of base metal of steel from mill scale waste as claimed in claim 1, wherein said reducing agents are Ferro Alloys and Calcimined Petroleum Coke (CPC).

3. The process for recovery of base metal of steel from mill scale waste as claimed in claim 1 and 2, wherein said Ferro alloy Fe- Si is taken in the range of 7.5 to 9.0 wt percent (along with purity of 70 wt % Si and 30 wt% Fe).

4. The process for recovery of base metal of steel from mill scale waste as claimed in claim 1 and 2, wherein said Calcimined Petroleum Coke (CPC) is taken in the range of 10 to 15 wt percent with particle size 1.5 -2.5 mm.

5. The process for recovery of base metal of steel from mill scale waste as claimed in claim 1, wherein said fluxing agents are feldspar and slag-30 powder.

6. The process for recovery of base metal of steel from mill scale waste as claimed in claim 1 and 5, wherein said feldspar is taken in the range of 5 to 7 wt. percent and said slag-30 powder is taken in the range of 0.5 to 1 wt percent.

7. The process for recovery of base metal of steel from mill scale waste as claimed in claim 1, wherein said binder is sodium silicate taken in the range of 2.0 to 3.0 wt percent.