CN102897812B - A kind of method of low-temperature bake doctor treatment activation processing high-sulfur bauxite - Google Patents

Abstract

The invention discloses a method for activating and treating high-sulfur bauxite by a low-temperature roasting desulfurization method. A method for oxidative desulfurization and roasting of bauxite with a sulfur content of 1-5wt% to make it a raw material suitable for the production of alumina by the Bayer process, characterized in that the oxidative desulfurization temperature is controlled within the range of 500-600°C. Specifically, hot air at 650-900° C. is used to heat the dry-milled ore powder in a fluidized fluidized furnace or a rotary kiln. After treatment, not only the sulfur content of the ore powder is reduced to below 0.5%, but also the organic matter in the ore is completely oxidized and decomposed. At the same time, the low roasting temperature avoids the transformation of activated alumina and is too stable. When the roasted bauxite is used for Bayer dissolution, the dissolution performance is improved, and the alumina dissolution rate is greater than 93%. For the tail gas containing SO ₂ produced by oxidative desulfurization, the content of SO ₂ can be reduced to below 300mg/m ³ after being purified by limestone suspension circulating spray desulfurization or red mud suspension spray desulfurization, which meets the emission standard.

Description

A kind of low-temperature roasting desulfurization method activation treatment method of high-sulfur bauxite

technical field

The invention belongs to the technical field of effective utilization of low-quality mineral resources, and mainly relates to a pre-desulfurization technical method for producing alumina by utilizing high-sulfur bauxite.

Background technique

Alumina is a bulk raw material for the production of aluminum metal. my country's annual output and consumption have exceeded 30 million tons, ranking first in the world. However, the high-quality bauxite resources used to produce alumina in my country are very limited, and about 200 million tons of high-sulfur diaspore-type bauxite with a sulfur content greater than 0.7wt% is urgently needed to be developed and applied. Sulfur in bauxite mainly exists in the form of pyrite (FeS ₂ ), and secondly in the form of sulfate. Such ores generally coexist with a large amount of humic acid organic matter. At present, the main problem in the production of alumina with high-sulfur bauxite is that organic matter hinders the dissolution of diaspore in lye, and the sulfur in the ore will be in the form of sulfate, sulfite or thiosulfate It enters the sodium aluminate solution and accumulates in the circulating mother liquor, which affects the control of the Bayer process alumina production process, the normal operation of equipment and the quality of alumina products. Among the pretreatment technologies related to high-sulfur bauxite at home and abroad, the Chinese invention patent CN102228869A discloses the method of simultaneously desulfurizing and desiliconizing the pyrite in bauxite by using the forward flotation desulfurization and reverse flotation desiliconization processes. The content of sulfur in the concentrated ore is lower than 0.3wt%. However, the flotation method has a large loss of ore, and the water brought in will cause a significant increase in energy consumption in the subsequent evaporation process. It has been reported that the method of desulfurization by adding barium salt process is not ideal for the removal of other valence sulfur in the circulating mother liquor in the form of thiosulfate and other non-sulfate radicals. Chinese invention patent ZL200810230200.0 discloses a method for the pretreatment of high-sulfur bauxite and the removal of SO ₂ in the tail gas. Powder desulfurization, activation and elimination of organic matter, roasting tail gas into the stirred red mud for SO ₂ removal. This method is easy to combine with the alumina production process, but there are the following problems: first, the use of fluidized bed roasting desulfurization has strict requirements on the uniformity of ore powder particles, which increases the cost; second, the roasting desulfurization temperature is too high, resulting in waste of energy and It is not conducive to the dissolution of aluminum; the third is to directly use the red mud slurry as the filler in the desulfurization packed tower for desulfurization of the roasting tail gas, the gas-liquid mass transfer efficiency is poor, and blockage is prone to occur.

Contents of the invention

In view of the problems and deficiencies in the above-mentioned desulfurization technology using high-sulfur bauxite to produce alumina, the present invention provides a high-sulfur bauxite desulfurization pretreatment method that can be perfectly combined with the current alumina production process, and is energy-saving, environmentally friendly, economical and practical . Specifically, dry-grind sulfur-containing bauxite to a certain particle size range, put it into a fluidized fluidized furnace or a rotary kiln, and blow in hot air at 650-900°C to heat the ore powder to 500-600°C and keep it for 5- After 40 minutes, the sulfur content in the treated mineral powder was reduced to below 0.5%; the cooled tail gas containing SO ₂ was sprayed with limestone or red mud suspension, and the SO ₂ content in the treated tail gas was reduced to below 300mg/m ³ . The high-sulfur bauxite pretreatment method of the present invention is characterized in that:

(1) Control the temperature of oxidative roasting at 500~580℃, not only to achieve the effect of oxidative desulfurization, but also to completely oxidize and eliminate the organic matter in the ore powder, and avoid over-burning and agglomeration of the ore powder, so that the dissolution performance of the ore powder is improved. improved. The alumina dissolution rate of the treated mineral powder in the caustic alkali solution at 200-240 °C is over 93%.

(2) The use of a fluidized fluidized furnace is conducive to maintaining sufficient contact between the surface of the mineral powder and the hot air and rapid heat exchange to avoid over-burning and agglomeration. The disadvantage is that the required hot air volume is large and needs to be strictly controlled; There can be enough time for heat exchange between mineral powder and hot air, which can effectively reduce the amount of hot air and reduce the intensity of dust removal. The disadvantage is that the relative probability of mineral powder agglomeration increases.

(3) The use of coal-fired hot blast stoves to indirectly provide hot air can reduce the cost of heat sources by using cheap coal; the air flowing into the air inlet of the hot blast stove can be preheated by roasting and desulfurization tail gas to further reduce energy consumption.

(4) Use limestone or red mud suspension to spray SO ₂ in the tail gas. The limestone suspension can be recycled, and the alkalinity of the red mud can be used for farmland rehabilitation after neutralization.

In the high-sulfur bauxite pretreatment method of the present invention, the oxidation desulfurization treatment temperature is controlled to be 500-600°C, which is proposed based on the research on the thermochemical behavior of high-sulfur bauxite with a sulfur content of 1-5%. of.

At around 460°C and in the presence of oxygen, FeS ₂ can undergo an exothermic reaction with oxygen in the air as shown in formula (1):

FeS ₂ + 11/4 O ₂ = 1/2 Fe ₂ O ₃ + 2 SO ₂ + 826 kJ/mol (1)

At the same time, a small amount of organic matter contained in bauxite will also be completely mineralized.

When the temperature reaches 500°C, the gibbsite in the mineral powder begins to undergo the dehydration transformation and activation reaction shown in formula (2):

Al ₂ O ₃ H ₂ O → Al ₂ O ₃ + H ₂ O (2)

When the temperature is higher than 535°C, FeS ₂ in high-sulfur bauxite can also rapidly undergo the self-decomposition reaction shown in formula (3) under oxygen-poor conditions, so under oxygen-enriched conditions, it can undergo the self-decomposition reaction shown in formula (1). The oxidation reaction shown can be carried out quickly without further raising the oxidation roasting desulfurization temperature.

_FeS2 = FeS+ S↑ (3)

Therefore, theoretically, when the aerobic roasting temperature reaches 500°C, the oxidative roasting desulfurization and crystal transformation activation of high-sulfur bauxite can be realized. Increasing the aerobic roasting temperature can significantly increase the reaction rate of oxidative roasting desulfurization and crystal form conversion activation, and shorten the time of oxidative desulfurization and crystal form conversion, but the required energy consumption will also increase significantly; if the temperature is too high, the mineral powder will The crystallization of amorphous alumina in the bauxite is not conducive to the dissolution of aluminum. Obviously, it is appropriate to control the upper temperature limit of the roasting desulfurization and activation treatment of high-sulfur bauxite below 600 °C, and it should not be too high. Therefore, the present invention proposes that the suitable temperature range for roasting desulfurization and activation treatment of high-sulfur bauxite is 500-580°C. At the same time, in order to achieve the smooth progress of desulfurization, the mineral powder is pre-ground to a certain particle size to increase the reaction area, accelerate mass transfer, and ensure rapid oxidation of sulfur.

The low-temperature roasting desulfurization method of the present invention activates the high-sulfur bauxite method, mainly comprising:

(1) High-sulfur bauxite is crushed and dry-milled before roasting. The high-sulfur bauxite with a sulfur content of 1~5wt% is properly dried first, and then crushed and dry-ground, which can reduce adhesion and improve crushing efficiency. The particle size range of the required mineral powder varies depending on the roasting method used: if a fluidized fluidized furnace is used, the particle size of the mineral powder should be controlled below 0.3mm, preferably 0.075~0.18mm; if a rotary kiln is used, the particle size of the mineral powder should be controlled The particle size should be below 0.85 mm, preferably below 0.3 mm.

(2) Carry out oxidative roasting desulfurization and dehydration transformation and activation reactions of high-sulfur bauxite in fluidized fluidized furnace or rotary kiln.

In the fluidized fluidized furnace, hot air at 650-900°C is fed into the high-sulfur bauxite ore powder for fluidized heating and roasting, so that the ore powder is kept at a temperature range of 500-580°C for 5-20 minutes to reduce its sulfur content to below 0.5%.

In the rotary kiln, hot air at 650-900°C is introduced to heat and roast the high-sulfur bauxite ore powder, keeping the ore powder at a temperature range of 500-565°C for 15-40 minutes, and reducing its sulfur content to 0.5 %the following. .

The hot air required for desulfurization and activation of high-sulfur bauxite can be generated by a variety of hot air stoves. Prioritize the use of coal-fired hot air stoves to generate cheap hot air at 650~900°C to reduce the cost of heat sources.

(3) Use limestone suspension spray or red mud suspension spray method to absorb SO ₂ in roasting tail gas:

The limestone suspension spray method absorbs SO ₂ in the roasting tail gas, and the specific description is as follows: the cooled roasting tail gas is passed into the desulfurization tower, and the limestone suspension spray liquid film is used to absorb SO ₂ in the tail gas. The chemical reactions shown in formula (4) and formula (5) mainly occur:

CaCO ₃ +2H ₂ O +2SO ₂ = Ca(HSO ₃ ) ₂ +CO ₂ ↑ (4)

Ca(HSO ₃ ) ₂ +CaCO ₃ + O ₂ = 2CaSO ₄ ↓+CO ₂ ↑ (5)

This desulfurization technology method has been widely used in power plant flue gas desulfurization, and the technology is mature. The method has high efficiency, low cost, good process stability, desulfurization rate>95%, and can reduce the SO2 content to below 300 _mg / ^m3 to meet the emission standards; the disadvantage of this method is that it consumes a large amount of limestone powder and produces Large amounts of carbon dioxide gas are released into the atmosphere.

The invention proposes a red mud suspension spraying method to absorb SO ₂ in the roasting tail gas, cool the roasting tail gas and pass it into a desulfurization tower, and use the red mud suspension spraying liquid film to absorb and desulfurize. The chemical reaction mainly occurs as shown in formula (6):

NaOH + SO ₂ = NaHSO ₃ (6)

A considerable part of the NaHSO ₃ produced by the reaction can also be absorbed and fixed by the solid alkaline substances in the red mud.

The technical key of this desulfurization method is to properly adjust the relative stability of the red mud slurry and the structure of the desulfurization tower to avoid premature destabilization and fouling during spray desulfurization. This method has fast desulfurization speed and simple post-treatment, reduces the sulfur content in the tail gas to below 300 _mg /m ³ , and the desulfurization rate is >95%. Environment friendly.

(4) Dissolution of aluminum in bauxite after desulfurization and activation treatment:

In the eluate with a caustic concentration of 6.5~7.7M, the roasted desulfurized ore powder is mixed according to the sodium-aluminum ratio of 1.3~1.6, and dissolved at 220~240°C for 60~90 minutes, and the dissolution rate of alumina is >93%.

Description of drawings

Fig. 1 is a process flow diagram of low-temperature roasting oxidative desulfurization and activation treatment of high-sulfur bauxite in the present invention. 1, high-sulfur bauxite; 2, crushing and grinding; 3, fluidized fluidized furnace or rotary kiln; 4, heat exchange; 5, bauxite after roasting; 6, tail gas; 7, red mud absorption device; 8, air; 9 , hot stove; 10, fuel.

Fig. 2 is an XRD spectrum of a high-sulfur bauxite sample in southwest my country before and after being treated by the low-temperature roasting oxidative desulfurization and activation treatment method of the present invention. Curve 1 is the XRD diffraction pattern of the raw ore sample; Curve 2 is the XRD diffraction pattern after treatment; Curve 3 is the standard XRD diffraction pattern of AlO(OH); Curve 4 is the standard XRD diffraction pattern of Al ₂ O ₃ .

specific embodiment

The following introduces the embodiment of high-sulfur bauxite oxidative desulfurization and dehydration transformation and activation treatment by low-temperature roasting of high-sulfur bauxite using the present technology. The high-sulfur bauxite selected in the following embodiment is high-sulfur bauxite from Southwest my country.

Example 1 Oxidative Roasting Desulfurization and Activation of High-sulfur Bauxite Powder Fluidized Furnace and Limestone Wet Purification of Roasting Tail Gas

Dry and grind the high-sulfur bauxite with an aluminum-silicon ratio of 7.1 and a sulfur content of 3.7%, and pass through 50 meshes to take the ore powder with a particle size of <0.30mm; heat the preheated air to 800~ 900°C hot air; after the ore powder is added to the fluidized bed, hot air is added from the lower side of the fluidized furnace, and the hot air is used to heat and ignite the FeS ₂ in the ore powder in the fluidized bed, so that the ore powder is in a fluid state within the temperature range of 560~580°C Oxidative desulfurization and dehydration transformation activation, keep in the fluidized bed furnace for 5~10 minutes, the sulfur content of the ore powder after roasting will drop to 0.43%; mix the roasted desulfurization ore powder according to the sodium-aluminum ratio of 1.6, add the equivalent of bauxite content of 4 % lime, dissolved in a solution with a caustic concentration of 240g/L at 240°C for 60 minutes, and the dissolution rate of alumina was 93.4%; use cold air to cool the roasting desulfurization tail gas through a heat exchanger to reduce the temperature of the desulfurization tail gas to 70~80°C, then spray limestone suspension into the desulfurization tower for desulfurization, the SO ₂ content in the tail gas is reduced to 300mg/m ³ and then discharged.

Example 2 Oxidative roasting desulfurization and activation of high-sulfur bauxite powder rotary kiln and purification of roasting tail gas by red mud method

Dry and grind the high-sulfur bauxite with an aluminum-silicon ratio of 8.1 and a sulfur content of 4.1%, and pass through 20 meshes to obtain ore powder with a particle size of <0.85mm; heat the preheated air to 650~ Hot air at 750°C; add mineral powder from the high end of the rotary kiln, add hot air from the low end of the rotary kiln, use hot air to heat and ignite FeS ₂ in the mineral powder in the rotary kiln, so that the mineral powder is at a temperature of 500~535°C Within the range of fluidized oxidative desulfurization and dehydration transformation activation, keep it in the rotary kiln for 30~40 minutes, the sulfur content of the slag after roasting will drop to 0.31%; mix the roasted desulfurization slag according to the sodium-aluminum ratio of 1.45, add equivalent to Lime with a bauxite content of 4% is dissolved in an eluate with a caustic concentration of 200g/L at 220°C for 90 minutes, and the dissolution rate of alumina is 93.1%; use cold air to cool the roasting desulfurization tail gas through a heat exchanger , the temperature of the desulfurized tail gas is lowered to 70~80°C, and then the red mud suspension is sprayed into the desulfurization tower for desulfurization, and the SO ₂ content in the tail gas is reduced to 260mg/m ³ before being discharged.

Example 3 Oxidative roasting desulfurization and activation of high-sulfur bauxite powder fluidized furnace and purification of roasting tail gas by red mud method

Dry and grind the high-sulfur bauxite with an aluminum-silicon ratio of 6.5 and a sulfur content of 2.1%, and pass through 80 mesh and 200 mesh respectively to obtain mineral powder with a particle size of 0.075~0.18mm; The air is heated by hot air at 750~850°C; after the ore powder is added to the fluidized bed, the hot air is added from the lower side of the fluidized furnace, and the FeS ₂ in the ore powder is heated and ignited in the fluidized furnace by hot air, so that the ore powder is heated at 540~580°C Fluidized oxidative desulfurization and dehydration transformation and activation within the temperature range, kept in the fluidized furnace for 10 to 15 minutes, the sulfur content of the ore powder after roasting was reduced to 0.22%; Lime with a bauxite content of 4% is dissolved in an eluate with a caustic concentration of 220g/L at 220°C for 60 minutes, and the dissolution rate of alumina is 93.2%; use cold air to cool the roasting desulfurization tail gas through a heat exchanger , the desulfurization tail gas is cooled to 70~80°C, and then the red mud suspension is sprayed into the desulfurization tower for desulfurization, and the SO ₂ content in the tail gas is reduced to 180mg/m ³ before being discharged.

Example 4 High-sulfur bauxite powder rotary kiln oxidative roasting desulfurization, activation and limestone wet purification of roasting tail gas

Dry and grind the high-sulfur bauxite with an aluminum-silicon ratio of 6.4 and a sulfur content of 1.3%, and pass through 50 meshes into mineral powder with a particle size of <0.30mm; heat the preheated air to 700~800mm with a fuel-fired hot air stove ℃ hot air; add the ore powder from the high end of the rotary kiln, add hot air from the low end of the rotary kiln, use the hot air to heat and ignite the FeS ₂ in the ore powder in the rotary kiln, so that the ore powder is in the temperature range of 535~565°C Internal fluidized oxidative desulfurization and dehydration transformation activation, kept in the rotary kiln for 15 to 25 minutes, the sulfur content of the ore powder after roasting was reduced to 0.19%; Lime with a soil ore content of 4% is dissolved in an eluate with a caustic concentration of 220g/L at 200°C for 75 minutes, and the dissolution rate of alumina is 93.1%; use cold air to cool the roasting desulfurization tail gas through a heat exchanger, Cool the desulfurization tail gas to 70~80°C, and then blow it into the red mud suspension spray desulfurization tower for desulfurization. The SO ₂ content in the tail gas is reduced to 160mg/m ³ and then discharged.

Claims (5)

1. a method for high-sulfur bauxite pretreatment, uses the bauxite warp that oxidation sweetening mode makes sulfur content be 1 ~ 5wt% After process, sulfur content is less than 0.5wt%, meets process for making alumina requirement, it is characterised in that: oxidation sweetening process is at fluidized bed furnace In carry out, it is desirable to breeze particle diameter is less than 0.30 mm, is passed through the hot-air of 650-900 DEG C, and heating breeze, to 540 ~ 580 DEG C, keeps 5 ~ 20 minutes.

2. a high-sulfur alum clay preprocess method, the bauxite using oxidation sweetening mode to make sulfur content be 1 ~ 5wt% is treated Rear sulfur content is less than 0.5wt%, meets process for making alumina requirement, it is characterised in that: oxidation sweetening process is entered in rotary kiln OK, it is desirable to breeze particle diameter is less than 0.85 mm, being passed through the hot-air of 650-900 DEG C, heating breeze, to 500 ~ 565 DEG C, keeps 5 ~ 40 Minute.

3. high-sulfur bauxite preprocess method as claimed in claim 1 or 2, wherein the hot-air of 650-900 DEG C is by coal fuel heating Wind furnace provides, and selects cheap coal-fired reduction thermal source cost.

4. high-sulfur bauxite preprocess method as claimed in claim 1 or 2, wherein produced tail gas during oxidation sweetening In containing SO₂, use limestone suspension spray method to process described tail gas, and recycle limestone suspension.

5. high-sulfur bauxite preprocess method as claimed in claim 1 or 2, wherein produced tail gas during oxidation sweetening In containing SO₂, use red mud suspension liquor nebulization to process described tail gas, use rear red mud alkalescence to be neutralized, for farmland second ploughing.