Additive for reducing the roasting temperature of fluxed magnetite pellets and a method of using it

Abstract

The present invention discloses additive for reducing the roasting temperature of fluxed magnetite pellets and a method of using it, consisting of components: B.sub.2O.sub.3, Mn.sub.2O.sub.3, the B.sub.2O.sub.3 and Mn.sub.2O.sub.3 are pure chemical reagents, the mass of the additive is 0.8%, 4% of the dry basis mass of the magnetite concentrate, respectively, the magnetite concentrate, bentonite clay, calcium flux and additives will be dosed with 12-14% water of the dry base mass ratio of the mixture, prepared into green pellets of 10-12.5 mm in diameter in a disc ball making machine, After the pellets are completely dried, preheat them for 1520 min at 6001000 C. to ensure that Mn.sub.2O.sub.3 is fully decomposed, then roasting is carried out for 15 min at 1200 C., and after roasting, the pellets are cooled to room temperature to obtain the finished pellets.

Claims

1. An additive for reducing a roasting temperature of fluxed magnetite pellets, comprising components: B.sub.2O.sub.3 and Mn.sub.2O.sub.3; the B.sub.2O.sub.3 and Mn.sub.2O.sub.3 being chemical analytical reagents, and the additive being formed by mixing B.sub.2O.sub.3 with Mn.sub.2O.sub.3; a mass percentage of B.sub.2O.sub.3 being 0.8% of a dry base mass of magnetite concentrate, and a mass percentage of Mn.sub.2O.sub.3 being 4% of the dry base mass of the magnetite concentrate; and a preheating time of a preheating temperature stage of 600-1000 C. being extended to cause Mn.sub.2O.sub.3, at 600-1000 C., to lose weight and be decomposed to release O.sub.2, promoting the oxidation and recrystallization of magnetite from an interior, and the roasting temperature being set below a melting point temperature of 1200 C. of a low melting point substance.

2. A using method for an additive for reducing a roasting temperature of fluxed magnetite pellets according to claim 1, comprising following steps: mixing magnetite concentrate, bentonite, calcium flux, and the additive into a mixture, then adding water accounting for 12-14% of a dry base mass of the mixture, preparing a same into green pellets with a diameter of 10-12.5 mm in a disc balling machine, preheating the green pellets at 600-1000 C. for 15-20 minutes after completion of drying the green pellets to ensure that Mn.sub.2O.sub.3 is fully decomposed, then roasting a same at 1200 C. for 15 minutes, and after roasting, cooling the pellets to a room temperature to obtain finished pellet ore.

3. The using method for an additive for reducing a roasting temperature of fluxed magnetite pellets according to claim 2, wherein a dosage of the bentonite is 0.7% of the dry base mass of the mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart of a pellet production process according to the present disclosure; and

(2) FIG. 2 is a TG graph of a thermogravimetric analysis experiment according to the present disclosure.

DETAILED DESCRIPTION

(3) Referring to the FIG. 1, a pellet ore production process is performed.

Example 1

(4) Local high-silica magnetite concentrate (66.3% of TFe and 6.17% of SiO.sub.2) was used as raw material, 0.7% of bentonite and calcium flux CaO were added and uniformly mixed, no B.sub.2O.sub.3 and Mn.sub.2O.sub.3 were added, after adding 12-14% of water, and green pellets with a diameter of 10-12.5 mm were prepared in a disc balling machine. A shatter strength of the green pellets was 5 times/pellet (0.5 m), and a compressive strength of the green pellets was 8.2 N. After the green pellets were dehydration and dried, the preheating was performed at 900 C. for 15 minutes, and the roasting was performed at 1200 C. for 15 minutes. An average strength of a roasted finished pellet was 1980 N/pc, and a strength of the pellet ore was lower at this time.

Example 2

(5) Local high-silica magnetite concentrate (66.3% of TFe and 6.17% of SiO.sub.2) was used as raw material, 0.7% of bentonite, calcium flux CaO, and 4% of Mn.sub.2O.sub.3 were added and uniformly mixed, no B.sub.2O.sub.3 was added, after adding 12-14% of water, and green pellets with a diameter of 10-12.5 mm were prepared in a disc balling machine. A shatter strength of the green pellets was 5 times/pellet (0.5 m), and a compressive strength of the green pellets was 8.4 N. After the green pellets were dehydration and dried, the preheating was performed at 600-1000 C. for 15 minutes, and the roasting was performed at 1200 C. for 15 minutes. An average strength of a roasted finished pellet was 2274 N/pc, and a strength of the pellet ore was slightly higher at this time.

Example 3

(6) Local high-silica magnetite concentrate (66.3% of TFe and 6.17% of SiO.sub.2) was used as raw material, 0.7% of bentonite, calcium flux CaO, 0.8% of B.sub.2O.sub.3 were added and uniformly mixed, no Mn.sub.2O.sub.3 was added, after adding 12-14% of water, and green pellets with a diameter of mm were prepared in a disc balling machine. A shatter strength of the green pellets was 6 times/pellet (0.5 m), and a compressive strength of the green pellets was 9.1 N. After the green pellets were dehydration and dried, the preheating was performed at 900 C. for 15 minutes, and the roasting was performed at 1200 C. for 15 minutes. An average compressive strength of the pellet ore was 2631 N/pc, and a strength of the pellet ore was high at this time.

Example 4

(7) Local high-silica magnetite concentrate (66.3% of TFe and 6.17% of SiO.sub.2) was used as raw material, 0.7% of bentonite, calcium flux CaO, 0.8% of B.sub.2O.sub.3, and 4% of Mn.sub.2O.sub.3 were added and uniformly mixed, after adding 12-14% of water, and green pellets with a diameter of 10-12.5 mm were prepared in a disc balling machine. A shatter strength of the green pellets was 6 times/pellet (0.5 m), and a compressive strength of the green pellets was 9.3 N. After the green pellets were dehydration and dried, the preheating was performed at 600-1000 C. for 15 minutes, and the roasting was performed at 1200 C. for 15 minutes. An average strength of a roasted finished pellet was 2962 N/pc, and a strength of the pellet ore was very high at this time.

Example 5

(8) Local high-silica magnetite concentrate (66.3% of TFe and 6.17% of SiO.sub.2) was used as raw material, 0.7% of bentonite, calcium flux CaO were added and uniformly mixed, no B.sub.2O.sub.3 and Mn.sub.2O.sub.3 were added, after adding 12-14% of water, and green pellets with a diameter of 10-12.5 mm were prepared in a disc balling machine. A shatter strength of the green pellets was 6 times/pellet (0.5 m), and a compressive strength of the green pellets was 9.5 N. After the green pellets were dehydration and dried, the preheating was performed at 900 C. for 15 minutes, and the roasting was performed at 1280 C. for 15 minutes. An average strength of a roasted finished pellet was 3063 N/pc, and a strength of the pellet ore was the highest at this time.

(9) A macro strength indicates: B.sub.2O.sub.3 and Mn.sub.2O.sub.3 have a promoting effect on oxidation and recrystallization processes of magnetite at a low temperature, but promotion methods are different. Mn.sub.2O.sub.3 promotes the oxidation and recrystallization of magnetite in the gas phase, and B.sub.2O.sub.3 promotes the movement of Fe.sup.2+ in the liquid phase and accelerates the consolidation of solid phase. The combined promotion effect of the additives is greater than that of a single additive, and the macro strength results indicates that the compressive strength of the pellet ore at 1200 C. after adding the additives is basically the same as the compressive strength of roasted sample pellet ore at 1250-1280 C.

(10) The traditional method for reducing a bonding rate of fluxed pellets during high temperature roasting is to add MgO flux into the pellets to produce a high melting point substance, which makes it unsuitable for bonding at high temperatures. Traditional oxidation roasting of the magnetite pellets is performed layer by layer from outside to inside.

(11) Calcium ferrate systems, such as CaO.Math.Fe.sub.2O.sub.3, CaO.Math.2Fe.sub.2O.sub.3, CaO.Math.Fe.sub.2O.sub.3CaO.Math.2FeO eutectic mixtures, all have low melting points of 1216 C., 1226 C. and 1205 C., which can play a role in promoting the bonding of iron ore particles and increasing the strength of the pellets with an appropriate amount of liquid phase during the high temperature oxidation roasting of the pellets. However, during the roasting of the pellets, the amount of liquid phase not only needs to be strictly controlled, but also the amount of calcium ferrate liquid phase is difficult to control. Too much liquid phase will lead to pellet bonding and porosity reduction, contrarily, the metallurgical property of the pellets is deteriorated.

(12) According to the disclosure, oxide additives are mixed into pellet raw materials to cause the same to be fully decomposed during the preheating roasting to generate O.sub.2, which is performed from inside and outside to promote the oxidation and recrystallization of the magnetite, ensuring that the roasting strength of the magnetite at a high temperature (1250-1280 C.) can be maintained at a low temperature (1200 C.) and reducing the bonding rate of the pellet ore at the same time.

(13) According to the disclosure, starting from a root cause, the strength of the pellets is increased as much as possible by adding other additives while appropriately lowering the roasting temperature of the pellets. The amount of liquid phase generation at high temperatures is fundamentally controlled to avoid bonding problems. While the reduction of the roasting temperature of the pellet ore is also conducive to energy saving and consumption reduction, prolong the service life of a device and ensure the smooth roasting process, which is of great significance to the industrial production of the pellet ore.