WO1990000628A1

WO1990000628A1 - Pellets from highly enriched iron ore and a method for manufacturing the same

Info

Publication number: WO1990000628A1
Application number: PCT/SE1989/000343
Authority: WO
Inventors: Sten Forsmo; Lars Norman; Magnus Tottie
Original assignee: Luossavaara Kiirunavaara Ab, Lkab
Priority date: 1988-07-05
Filing date: 1989-06-16
Publication date: 1990-01-25
Also published as: SE8802516L; SE8802516D0

Abstract

The invention concerns pellets manufactured from highly enriched iron ore concentrate and a method for manufacturing of the same. Characterizing for the invention is that slag former added have been grinded into a degree of fineness which is much lower than what is used up to now.

Description

PELLETS FROM HIGHLY ENRICHED IRON ORE AND A METHOD FOR IvlANUFACTURI G THE SAME.

AREA The present invention concerns pellets manufac¬ tured from highly enriched iron ore concentrate and a method for its manufacturing. Characterizing for the in¬ vention is that slag formers, which have been added, have been grinded into a degree of fineness, which is much lower than what is used up to now. BACKGROUND TECHNIC

It is often necessary to grinde lump ore into fine grains in order to increase the iron content by en¬ richment. Highly enriched iron ore concentrate from e.g. the Kiruna-mine in Sweden can content more than 71 % iron (Fe) at a content of silicic acid (Si0₂) below 0.6 %. At the enrichment also is obtained that, beside a reduc¬ tion of gangue, also for the end product harmful substan¬ ces are used to a minimum in that way that the iron pro- duction process can be operated in an economically advan¬ tageous way that a sound end product will be achived. The grain size of a iron ore concentrate after grinding often can be the following:

100 % of the grains are not larger than 0,5 mm 92 % " 0,1 "

83 % " 0,07 "

70 % " 0,04 " ^•

Shortly this will often be expressed that "70 % of the concentrate has a grain size below 40 am".

In order to use the iron ore concentrate indu- ^' strially pellets are manufactured from the same by mixing the concentrate with some additives for slag forming and binders and water and rolling the mixture into pellets, which after that are dried and sintered. The binder above all is keeping the pellets together before sintering and is mostly consisting of bentonite, a clay including aluminium and silicium. As those substances have a pro¬ nounced drawbac in the following process it is desired to exchange the bentonite for organic binders.

The sintering is carried out at about 1300°C and is serving for transferring the iron oxide in the concentrate into hematite by oxidation and to create strong bindings. The hematite is the form iron oxide which is lighter but magnetite^* to reduce into iron. The drawback with the pellets sintered from highly enriched concentrate is that they easely disin¬ tegrate during the first phase of the reduction process, this as a result of that the hematite-bindings, which in this case give the pellets there strength, are subjected to too big stresses. By this reson slag formers must be added in order to give a sufficient binding-phase (slag-phase) during the reduction.

Depending on what additive which is added and in which amount, besides the binding-phase mentioned above, also other metallurgical characteristics will be achie- ved. The additive can consist of silica, olivine, lime stone, dolomite and others. Above all by economical rea¬ sons it is desirable to keep these contents down as much as possible. Normally about 4 % slag former must be ad¬ ded. The grain size has been kept on the same level as the iron ore concentrate (se the foregoing). The high ad¬ ditive has been settled by that the strength during the first reduction phase should be sufficiant. If the pel¬ lets should disintegrate the gas penetration for the re¬ ducing gas should be decreased and the reduction process should decrease quickly or stop completely.

In order to make tests of reduction speed and degree of metallisation at different mixtures of iron ore concentrate and slag former a method, which is a Japanese industrial standard (JIS) and indicated M8713-1972, is used and consists in reduction of sinter pellets in a furnace at 900°C in an atmosphere of 30 % carbon mon¬ oxide to a highest possible rate of metallisation. After reduction the pellets are cold down in an inert gas. According to another method, drawn up at the company LKAB in Malmberget, Sweden, the pellets from the JlS-test can be pressure-tested in a cold state in order to measure their strength after the reduction. This strength, which is mesasured in kilograms gives an excellent result for how the sintered pellets stand the load during the reduc¬ tion process.

The test apparatus is equipped with a pressure transmitter and an indicator BKI-2 from the company

Bofors, Sweden. The pressure device has a constante speed of 6,5 mm/min and is powered by an electrical motor by a gear. The indication of the pressure force is made by an scale instrument, at which the indicating needle stays in that position where the breaking load is reached. By that an exact reading can be done.

The test is carried out in that way that, after calibration and test pressing, 40 pellets are indivdually pressure-loaded into break at which the breaking load is indicated for each pellet. The mean value and the stan¬ dard deviation is calculated. It has been observed that a breaking load value of 30 kg is acceptable for sinter pellets which are to be reduced in a blast furnace. THE INVENTION Surprisingly it has shown that sinter pellets can be manufactured with an amount of slag former which is lower than earlier, in order to get acceptable values of the strength in the first critical phase of the reduc¬ tion at the iron manufacturing, by grinding the additives for the iron ore concentrate into grain sizes which are below 0,015 mm (15.um). s As mentioned earlier about 4 % slag former must have been added in order to reach an acceptable value for a breaking load of about 30 kg. By grinding to a lower value instead about 1-2 % can be sufficiant at which iron contents more than 68 % can be reached.

In order to prove this different amounts of slag former was mixed in into a highly enriched iron ore con¬ centrate, showing a grain size distribution according to what is mentioned on page 1, at which the grain size in the additive was below 14 um, manufactured pellets where reduced according to the JlS-test and where pressure tes¬ ted according to the method described in the foregoing. The result is declarated in the schedule below. Column 1 shows the amount and the kind of added material, column 2 the iron ore content in the pellets and column 3 the breaking load. The magnetite used at the tests is highly enriched but contents a certain amount of gangue. In this way it also is shown that even ore can be added, in order to increase the breaking load, if this is sufficiantly grinded.

All declarated values of the breaking load are substantially higher than the values reach with a coarser additive.

Claims

PATENT CLAIMS

1. Pellets concisting of highly enriched iron ore concentrate, slag former and binder, c h a r a c ¬ t e r i z e d in that the joining slag former has a grain size mainly below 0,014 mm.

2. A method for manufacturing pellets from highly enriched iron ore concentrate, c h a r a c t e ¬ r i z e d in that the slag former added is grinded into an grain size below 0,014 mm.