WO2009048363A1

WO2009048363A1 - Metallurgical process for producing magnesium

Info

Publication number: WO2009048363A1
Application number: PCT/SE2008/000543
Authority: WO
Inventors: Ye Guozhu; Erik BURSTRÖM; Nils-Olov Lindfors; Johannes Eriksson
Original assignee: MEFOS-METALLURGICAL RESEARCH INSTITUTE AB
Current assignee: MEFOS-METALLURGICAL RESEARCH INSTITUTE AB
Priority date: 2007-10-09
Filing date: 2008-10-06
Publication date: 2009-04-16
Anticipated expiration: 2010-04-09
Also published as: SE0702250L; SE531428C2

Abstract

In a metallurgical process for producing liquid Mg, dolomite is burnt to give a mixed oxide CaO MgO and a production furnace (11) is charged with this mixed oxide together with an FeAl alloy and gaseous Mg is withdrawn from the furnace at atmospheric pressure and condensed to give liquid Mg. A second furnace (13) is charged with coal and with slag from the first furnace (11), whereby liquid FeAl alloy is reduced out in this second furnace and returned to the first furnace and calcium carbide, CaC2, is tapped from the second furnace. The calcium carbide formed in this manner can be used to produce gaseous Mg in a third furnace (17).

Description

Metallurgical process for producing magnesium

Technical field

This invention relates to a carbothermic metallurgical process for producing liquid primary Mg, in which dolomite is burnt to give a mixed oxide CaO MgO and a production furnace is charged with this mixed oxide together with an FeAl alloy and gaseous Mg is withdrawn from the furnace at atmospheric pressure and condensed to give liquid Mg.

Background of the invention and object of the invention

In known pyrometallurgical processes for the production of Mg, FeSi is used as a reducing agent to reduce burnt dolomite (CaO-MgO) to gaseous Mg. This is condensed in vacuo to the solid phase and then it has to be melted for refining. The necessity for a vacuum in the processes makes the processes complicated and unreliable. Using FeSi means that the processes are expensive with high energy consumption and high emission of greenhouse gases.

One aim of the invention is to be able to produce magnesium in a simpler and more reliable process with lower energy consumption, lower processing costs and lower emission of greenhouse gases.

The process according to the invention involves that a second furnace is charged with coal and with slag from the first furnace, whereby liquid FeAl alloy is reduced out in this second furnace and returned to the production furnace and calcium carbide is tapped from the second furnace, and in that the calcium carbide formed in the second furnace is fed together with minerals of the magnesium silicate type to a third furnace and evaporated Mg from this furnace is condensed to liquid Mg under atmospheric pressure.

The invention is defined by the claims.

Brief description of the drawing

Figure 1 shows a process flow diagram for one embodiment of the invention. Detailed description of the example of the invention shown

An electric furnace 11, e.g. a direct-current furnace, is charged with granulated FeAl, advantageously containing 25 % by weight Al, and burnt dolomite. The crushed burnt dolomite and granulated FeAl are charged together. The burnt dolomite originates from a calcining furnace 12 in which the dolomite is burnt to give CaO-MgO (calcined) and FeAl originates from an electric furnace 13 which can be, e.g. a D. C. furnace or a ferro-alloy furnace, such as a shaft furnace for CaC₂ production. This furnace 13 is charged with anthracite (coal) and slag from the furnace 11. The slag consists of CaO and Al₂O₃, with the remainder MgO and FeAl (e.g. 5 % by weight Al) which has been granulated at 19. The FeAl tapped from the furnace 13 is granulated at 20 before it is fed to the furnace 11. Calcium carbide is formed in the furnace 13 and tapped off. Residual magnesium in the slag from the furnace 11 is evaporated in the furnace 13 together with CO and is led through an off-gas flue 14 with a cooler 15 and an electric filter 16. Mg and CO in the off gases react upon cooling back to MgO and C, which are collected in the electric filter as solids. The mixture of magnesium oxide and coal collected is mixed with the dolomite fed to the calcining furnace. This leaves CO, which is recovered from the off-gas flue and can be used as fuel, as indicated by a flame.

Magnesium vapour under atmospheric pressure formed in the furnace 11 is conveyed to a condenser 18 in which it condenses to give liquid primary magnesium for further refining directly in its liquid state.

The calcium carbide, CaC₂, formed in the furnace 13 can be used directly for the production of magnesium gas in a furnace 17 (e.g. an induction furnace) which is charged with a mixture of crushed magnesium silicate (e.g. olivine) and the calcium carbide crushed at 22, advantageously in the form of briquettes. The furnace 17 may be an induction furnace. Magnesium in the gas phase from the furnace 17 is led to the condenser 18 for condensation together with the magnesium in the gas phase originating from the furnace 11. Other by-products are calcium silicate, Ca₂SiO₂ in the solid phase and coal in the solid phase. The coal may optionally be separated from the calcium silicate and fed to the furnace 13 as fuel. Calcium silicate is a valuable mineral.

Fe and Al circulate between the furnaces 11 and 13 without being consumed. The furnace 17 forms one separate process for the production of magnesium and the furnaces 11 ,

12, 13 form another separate process for the production of magnesium. CaC₂ used in the furnace 17 can be removed from the furnace 13 and granulated at 21. As the production process for producing magnesium with the furnace 17 requires calcium carbide and the process for the production of magnesium with the furnaces 11, 12 and 13 produces calcium carbide, it is advantageous to integrate the two processes so as to obtain an internal cycle of calcium carbide. Both of the processes operate under atmospheric pressure, which simplifies the processes and makes them more reliable.

The carbothermic process for the production of magnesium described has the following overall reaction:

2CaO MgO (burnt dolomite) + Mg₂SiO₄ (olivine sand) + 4 C = 4 Mg (product 1) + Ca₂SiO₄

(product 2) + 4 CO (energy)

Claims

1 A carbothermic metallurgical process for producing liquid primary Mg, in which dolomite is burnt to give a mixed oxide CaO MgO and a production furnace (11) is charged with this mixed oxide together with an FeAl alloy and gaseous Mg is withdrawn from the furnace at atmospheric pressure and condensed to give liquid Mg, characterised in that a second furnace (13) is charged with coal and with slag from the first furnace, whereby liquid FeAl alloy is reduced out in this second furnace and returned to the production furnace (11) and calcium carbide is tapped from the second furnace (13), and in that the calcium carbide formed in the second furnace (13) is fed together with minerals of the magnesium silicate type to a third furnace (17) and evaporated Mg from this furnace is condensed to liquid Mg under atmospheric pressure.

2 A process according to claim 1, characterised in that the magnesium silicate consists of olivine sand.

3 A process according to claim 2, characterised in that crushed calcium carbide and olivine sand are mixed and formed into briquettes which are fed to the third furnace (17).

4 A process according to any one of the preceding claims, characterised in that the off- gases from the second furnace (13) are conveyed to a cooler (15) where evaporated Mg and CO react back to MgO and C and are collected in a filter (16) and returned to a furnace (12) to be burnt together with the dolomite.