Method for enhancing dissolution and iron separation and recovery of monohydrate bauxite

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to a method for strengthening dissolution and iron separation and recovery of monohydrate bauxite. The method comprises the following steps: (1) preparing mixed ore pulp from the monohydrate bauxite, the sodium aluminate circulating mother liquor and an additive; the additive is chitin biomass or a derivative thereof; and (2) the mixed ore pulp obtained in the step (1) is heated to 190-280 DEG C for a dissolution reaction, dissolution slurry and dissolution residues are obtained, the dissolution residues are subjected to magnetic separation and recovery, and iron ore concentrate is obtained. According to the method, the bauxite can be efficiently dissolved out, the problem of combination of iron minerals and silicon minerals in the high-iron bauxite is solved, and the problem that iron resources in the high-iron bauxite are difficult to utilize is solved more efficiently at low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and particularly relates to a method for enhancing the digestion of boehmite-type bauxite and separating and recovering iron. Background Art

[0002] Compared with gibbsite-type bauxite, the digestion of boehmite-type bauxite requires higher temperature and alkalinity. During the digestion process of bauxite, due to the substitution of aluminum and iron isomorphs, aluminum-substituted goethite (Fe 1- x Al x OOH) may also exist in the ore. Under the digestion conditions of the Bayer process at high temperature (230-260°C), it is difficult to release the aluminum element therein, resulting in a decrease in the alumina digestion rate. At the same time, bauxite usually contains 2-4% titanium minerals, which exist in the forms of rutile, anatase and brookite. During the Bayer digestion process of diaspore-type bauxite, titanium minerals will significantly reduce the alumina digestion rate. Due to the blocking effect of titanium minerals on alumina digestion, lime is generally added in industry to eliminate its harm. However, adding lime brings problems such as an increase in alumina loss, an increase in the amount of red mud and washing water, and an increase in carbonate reverse causticization in alumina production. In addition, when producing alumina by the traditional bauxite digestion method, only the collection of single aluminum resources is emphasized, and the high-proportion iron minerals are generally discharged as components of red mud waste, bringing serious environmental problems and also causing great waste of iron resources.

[0003] Therefore, if it is possible to enhance the digestion of alumina in high-iron boehmite-type bauxite without adding lime during the bauxite digestion production process, and at the same time dissociate and separate iron minerals from silicon minerals and recover the iron components therein, not only can the discharge amount of red mud waste in alumina production be greatly reduced, but also high-grade iron minerals can be obtained for utilization, taking into account both environmental benefits and economic benefits. Therefore, it is necessary to improve the existing digestion method to achieve the efficient digestion of aluminum and the separation and recovery of iron in high-iron boehmite-type bauxite.

[0004] Patent CN107201441A discloses a comprehensive utilization method of high-iron bauxite and an additive for treating high-iron bauxite. This method first mixes, pelletizes, and dries the finely ground high-iron bauxite with the additive, and then performs reduction roasting using coal as a reducing agent. After roasting, the agglomerates are crushed, ground, and the iron component is separated by magnetic separation. This method requires an additional high-temperature roasting process, and the subsequent utilization of aluminum resources needs to be achieved through two-step wet processes of acid dissolution → alkali neutralization, with more steps, high production costs, and a large amount of low-value by-products. Patent CN102976375B discloses a high-pressure digestion method for diaspore-type bauxite, using at least one of iron powder and ether cellulose as an additive, which undergoes physicochemical interaction with the surface of titanium minerals to reduce the concentration of titanate ions in the solution, thereby eliminating the blocking effect of titanium minerals on the alumina digestion. This patent mainly focuses on promoting the digestion of alumina and does not involve promoting the dissociation and separation of iron minerals and silicon minerals. Patent CN102976377B discloses a digestion method for boehmite-type bauxite, introducing a mixture of one or more of alcohols, sugars, aldehydes, alkanes, activated carbon, graphite, coal, coal tar, and wheat bran as an additive during the bauxite digestion process to replace the traditional additive lime, to solve the hindrance of titanium minerals to bauxite digestion and simultaneously perform magnetic conversion on iron minerals. This method also does not notice the influence of silicon mineral impurities on the recovery of iron components, and the total iron (TFe) mass percentage content (56.30% - 62.12%) of the obtained iron concentrate and the recovery rate of iron in bauxite (37.82% - 50.26%) are not high. Patent CN117208946A discloses a digestion and iron recovery method for high-iron boehmite-type bauxite, using a mixture of one or more of organic bases, carboxylic acids, and amino acids as an additive, enriching iron minerals and removing silicon impurities during the bauxite digestion process, and converting them into easily separable magnetic iron minerals. The selected additives have strong volatility characteristics or high costs, and problems related to proper storage need to be considered in industrial applications.

[0005] Therefore, there is an urgent need to develop a method for the digestion, iron separation, and recovery of boehmite-type bauxite with simple process, low production cost, low equipment requirements, cheap and easily available additives, and good industrialization prospects. Summary of the Invention

[0006] Aiming at the above-mentioned shortcomings and deficiencies of the prior art, the purpose of the present invention is to provide a method for enhancing the digestion, iron separation, and recovery of boehmite-type bauxite. The method of the present invention can achieve the efficient digestion of bauxite, solve the problem of the combination of iron minerals and silicon minerals in high-iron bauxite, and more efficiently and low-costly solve the problem of difficult utilization of iron resources in high-iron bauxite.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for strengthening the dissolution of gibbsite-type bauxite and the separation and recovery of iron comprises the following steps:

[0009] (1) preparing a mixed slurry of gibbsite-type bauxite, sodium aluminate circulating mother liquor and an additive; the additive is chitin biomass or its derivatives;

[0010] (2) The mixed ore pulp obtained in step (1) is heated to 190-280° C. to carry out a dissolution reaction to obtain a dissolution slurry and dissolution slag, and the dissolution slag is subjected to magnetic separation and recovery to obtain an iron ore concentrate.

[0011] Furthermore, the diaspore bauxite in step (1) refers to a high-iron diaspore bauxite whose main component is diaspore and whose iron mineral content is greater than 15% (in terms of the mass percentage of Fe2O3), including diaspore bauxite or boehmite bauxite.

[0012] Furthermore, the Na2O in the sodium aluminate circulating mother liquor in step (1) k The concentration is 160~280g / L, and the Al2O3 concentration is 75~140g / L.

[0013] Furthermore, the mass volume ratio of the added mass of the gibbsite bauxite in step (1) to the mass volume ratio of the sodium aluminate circulating mother liquor is 130 to 360 g / L.

[0014] Furthermore, the mass volume ratio of the additive added in step (1) to the circulating mother liquor is 0.5 to 50 g / L.

[0015] Furthermore, the chitosan biomass in step (1) includes at least one of shrimp shells and crab shells; and the derivative includes at least one of chitosan and chitosan.

[0016] It has been verified by the present invention that the additive in step (1) can promote the better dissolution of alumina in bauxite, and at the same time has good interface adjustment function and reducibility, which can significantly promote the reduction reaction of iron minerals in the ore to generate magnetic magnetite or iron element, and promote the dispersion and dissociation of iron minerals and silicon mineral impurities in high-iron gibbsite-type bauxite, thereby improving the iron recovery rate of bauxite and reducing the silicon impurity content in the iron concentrate obtained by magnetic separation of bauxite slag.

[0017] Furthermore, the dissolution reaction time in step (2) is 30 to 90 minutes, preferably 80 minutes.

[0018] Furthermore, the dissolution slurry described in step (2) is diluted and then finely filtered, and seed crystals are added to the obtained filtrate to promote the decomposition of sodium aluminate in the solution to generate aluminum hydroxide, and the solid-liquid separation is performed. The obtained aluminum hydroxide solid is calcined to obtain an alumina product, and the liquid is returned to the dissolution process for continued use.

[0019] The principle of the present invention is that by adding a reducing additive with the function of adjusting the surface and interface properties, during the digestion process of bauxite, the iron minerals in the ore undergo a reduction reaction to generate magnetic magnetite or elemental iron, and at the same time, the surface properties of the iron minerals are adjusted to disperse and dissociate the silicon mineral impurities closely connected thereto, so that the iron minerals can be enriched by simple magnetic separation. At the same time, the reducing additive undergoes physicochemical interactions with the surface of the titanium minerals, reducing the concentration of titanate ions in the solution, thereby eliminating the blocking effect of the titanium minerals on the alumina digestion.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) Compared with the traditional digestion method adding lime, the additive dosage of the method of the present invention is low, the alumina digestion efficiency is improved, the amount of discharged red mud is greatly reduced, and it has significant environmental protection advantages, realizing the full utilization of aluminum resources; during the bauxite digestion process, the enrichment of iron minerals and the removal of silicon impurities are realized, and they are transformed into magnetite that is easy to separate, greatly improving the recovery efficiency of iron resources.

[0022] (2) The present invention uses chitin-based biomass or its derivative additives to reduce iron minerals, expanding the scope of use of chitin-based biomass. Compared with other reducing biomass additives, it can better strengthen the digestion of alumina and the enrichment of iron minerals and the removal of silicon impurities, so as to achieve better digestion and separation and recovery efficiency.

[0023] (3) The selected additive of this method is safe, non-toxic, stable in nature, easy to store, cheap and easy to obtain. There is no need to add other large-scale equipment in the existing digestion production process, with low cost and simple operation. Specific Embodiments

[0024] The present invention will be further described in detail below in conjunction with embodiments, but the embodiments of the present invention are not limited thereto.

[0025] Example 1

[0026] A high-iron boehmite-type bauxite (mineral composition: Al2O3 60.60%, Fe2O3 25.61%, SiO2 10.76%), 200 mL of circulating mother liquor and additive shrimp shells are prepared into a mixed pulp. Among them, in the circulating mother liquor: Na2O kThe concentration is 230 g / L, the concentration of Al2O3 is 110 g / L, the ratio of the mass of bauxite added to the volume of the circulating mother liquor is 220 g / L, and the ratio of the mass of the additive added to the volume of the circulating mother liquor is 20 g / L; the mixed pulp is filled into a steel bomb and placed in a salt bath furnace for digestion reaction at 260 °C for 60 min to obtain a digested slurry and digested residue. Under these conditions, the obtained digested residue is subjected to magnetic separation at a magnetic field intensity of 160 kA / m. The mass percentage of total iron (calculated as Fe2O3) in the obtained iron concentrate is 81.51% (total iron mass percentage = mass of iron in the iron concentrate (calculated as Fe2O3) / mass of the iron concentrate × 100%), the mass percentage of silicon impurity (calculated as SiO2) is 8.68%, and the iron recovery rate in the bauxite is 71.66% (iron recovery rate = mass of iron in the iron concentrate (calculated as Fe2O3) / mass of iron in the bauxite × 100%). The relative dissolution rate of alumina is 98.53% (relative dissolution rate of alumina = (iron-silicon ratio of bauxite - iron-silicon ratio of digested residue) / (iron-silicon ratio of bauxite - 1) × 100%). The digested slurry is diluted and then subjected to fine filtration. The obtained filtrate is added with seeds to promote the decomposition of sodium aluminate in the solution to form aluminum hydroxide. After solid-liquid separation again, aluminum hydroxide solid is obtained, and further calcined to obtain alumina products, and the liquid is returned to the digestion process for continued use. The obtained alumina products meet the GB / T 24487-2022 standard.

[0027] Example 2

[0028] The high-iron boehmite-type bauxite (mineral composition is the same as that in Example 1), 200 mL of circulating mother liquor and the additive crab shell are prepared into a mixed pulp. Among them, in the circulating mother liquor: Na2O k The concentration is 260 g / L, the concentration of Al2O3 is 125 g / L, the ratio of the mass of bauxite added to the volume of the circulating mother liquor is calculated as 360 g / L, and the ratio of the mass of the additive added to the volume of the circulating mother liquor is calculated as 12.2 g / L; the mixed pulp is filled into a steel bomb and placed in a salt bath furnace for digestion reaction at 270 °C for 90 min to obtain a digested slurry and digested residue. Under these conditions, the obtained digested residue is subjected to magnetic separation at a magnetic field intensity of 160 kA / m. The mass percentage of total iron (calculated as Fe2O3) in the obtained iron concentrate is 72.28%, the mass percentage of silicon impurity (calculated as SiO2) is 8.17%, and the iron recovery rate in the bauxite is 70.18%. The relative dissolution rate of alumina is 98.76%. The digested slurry is diluted and then subjected to fine filtration. The obtained filtrate is added with seeds to promote the decomposition of sodium aluminate in the solution to form aluminum hydroxide. After solid-liquid separation again, aluminum hydroxide solid is obtained, and further calcined to obtain alumina products, and the liquid is returned to the digestion process for continued use. The obtained alumina products meet the GB / T 24487-2022 standard.

[0029] Example 3

[0030] The high-iron boehmite-type bauxite (mineral composition is the same as that in Example 1), 200 mL of recycled mother liquor, and the additive chitosan are formulated into a mixed pulp. In the recycled mother liquor: Na2O k The concentration is 250 g / L, the Al2O3 concentration is 125 g / L. The mass ratio of the added bauxite to the volume of the recycled mother liquor is 224 g / L, and the mass ratio of the added additive to the volume of the recycled mother liquor is 22.4 g / L. The mixed pulp is loaded into a steel bomb and placed in a salt bath furnace for digestion reaction at 270 °C for 80 min to obtain a digested slurry and digested residue. Under these conditions, the obtained digested residue is subjected to magnetic separation at a magnetic field intensity of 160 kA / m. The mass percentage of total iron (calculated as Fe2O3) in the obtained iron concentrate is 75.37%, the mass percentage of silicon impurity (calculated as SiO2) is 8.68%, and the iron recovery rate in the bauxite is 69.23%. The relative digestion rate of alumina is 101.32%. The digested slurry is diluted and then subjected to fine filtration. The obtained filtrate is added with seeds to promote the decomposition of sodium aluminate in the solution to form aluminum hydroxide. After solid-liquid separation again, aluminum hydroxide solid is obtained, and further calcined to obtain alumina product, and the liquid is returned to the digestion process for continuous use. The obtained alumina product meets the GB / T24487-2022 standard.

[0031] Example 4

[0032] The high-iron boehmite-type bauxite (mineral composition is the same as that in Example 1), 200 mL of recycled mother liquor, and the additive chitin are formulated into a mixed pulp. In the recycled mother liquor: Na2O k The concentration is 280 g / L, the Al2O3 concentration is 140 g / L. The mass ratio of the added bauxite to the volume of the recycled mother liquor is 180 g / L, and the mass ratio of the added additive to the volume of the recycled mother liquor is 25 g / L. The mixed pulp is loaded into a steel bomb and placed in a salt bath furnace for digestion reaction at 280 °C for 70 min to obtain a digested slurry and digested residue. Under these conditions, the obtained digested residue is subjected to magnetic separation at a magnetic field intensity of 160 kA / m. The mass percentage of total iron (calculated as Fe2O3) in the obtained iron concentrate is 75.88%, the mass percentage of silicon impurity (calculated as SiO2) is 9.47%, and the iron recovery rate in the bauxite is 74.66%. The relative digestion rate of alumina is 94.64%. The digested slurry is diluted and then subjected to fine filtration. The obtained filtrate is added with seeds to promote the decomposition of sodium aluminate in the solution to form aluminum hydroxide. After solid-liquid separation again, aluminum hydroxide solid is obtained, and further calcined to obtain alumina product, and the liquid is returned to the digestion process for continuous use. The obtained alumina product meets the GB / T24487-2022 standard.

[0033] Comparative Example 1

[0034] In this comparative example, compared with Example 1, an equal amount of CMC (carboxymethyl cellulose) additive is used to replace the shrimp shell, and the rest is the same.

[0035] The total iron mass percentage content of the iron concentrate obtained by dissolution and magnetic separation recovery in this comparative example is 66.32%, the silicon impurity mass percentage content is 11.57%, the iron recovery rate in bauxite is 59.84%, and the relative dissolution rate of alumina is 82.92%.

[0036] Comparative Example 2

[0037] Compared with Example 1, in this comparative example, an equal amount of wheat bran additive is used to replace the shrimp shell, and the rest is the same.

[0038] The total iron mass percentage content of the iron concentrate obtained by dissolution and magnetic separation recovery in this comparative example is 68.15%, the silicon impurity mass percentage content is 10.39%, the iron recovery rate in bauxite is 61.70%, and the relative dissolution rate of alumina is 87.26%.

[0039] Comparative Example 3

[0040] Compared with Example 1, in this comparative example, an equal amount of starch additive is used to replace the shrimp shell, and the rest is the same.

[0041] The total iron mass percentage content of the iron concentrate obtained by dissolution and magnetic separation recovery in this comparative example is 65.48%, the silicon impurity mass percentage content is 11.45%, the iron recovery rate in bauxite is 59.55%, and the relative dissolution rate of alumina is 80.46%.

[0042] From the comparison results of the above Comparative Examples 1-3 and the examples, it can be seen that compared with the conventional reducing biomass additives, the use of chitin-based biomass or its derivative additives in the present invention can better strengthen the dissolution of alumina and the enrichment and removal of silicon impurities from iron minerals, thereby achieving better dissolution and separation recovery efficiency.

[0043] The above examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above examples. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for strengthening the dissolution of diaspore-type bauxite and the separation and recovery of iron, characterized in that: The steps include: (1) preparing a mixed slurry of gibbsite-type bauxite, sodium aluminate circulating mother liquor and an additive; the additive is chitin biomass or its derivatives; (2) The mixed ore pulp obtained in step (1) is heated to 190-280° C. to carry out a dissolution reaction to obtain a dissolution slurry and dissolution slag, and the dissolution slag is subjected to magnetic separation and recovery to obtain an iron ore concentrate.

2. The method for strengthening the dissolution of diaspore-type bauxite and the separation and recovery of iron according to claim 1, characterized in that: The gibbsite bauxite in step (1) refers to a high-iron gibbsite bauxite whose main component is gibbsite and whose iron mineral content is greater than 15%.

3. The method for strengthening the dissolution of diaspore-type bauxite and the separation and recovery of iron according to claim 1, characterized in that: The Na2O of the sodium aluminate circulating mother liquor in step (1) k The concentration is 160~280g / L, and the Al2O3 concentration is 75~140g / L.

4. The method for strengthening the dissolution of diaspore-type bauxite and the separation and recovery of iron according to claim 1, characterized in that: The mass volume ratio of the added mass of the gibbsite bauxite to the sodium aluminate circulating mother liquor in step (1) is 130 to 360 g / L.

5. The method for strengthening the dissolution of diaspore-type bauxite and the separation and recovery of iron according to claim 1, characterized in that: The mass volume ratio of the added mass of the additive described in step (1) to the circulating mother liquor is 0.5 to 50 g / L.

6. The method for strengthening the dissolution of diaspore-type bauxite and the separation and recovery of iron according to claim 1, characterized in that: The chitosan biomass in step (1) includes at least one of shrimp shells and crab shells; and the derivative includes at least one of chitosan and chitosan.

7. The method for strengthening the dissolution of diaspore-type bauxite and the separation and recovery of iron according to claim 1, characterized in that: The dissolution reaction time in step (2) is 30 to 90 minutes.

8. The method for strengthening the dissolution of diaspore-type bauxite and the separation and recovery of iron according to claim 1, characterized in that: The dissolution slurry described in step (2) is diluted and then finely filtered. Seed crystals are added to the obtained filtrate to promote the decomposition of sodium aluminate in the solution to produce aluminum hydroxide. The solid-liquid separation is carried out. The obtained aluminum hydroxide solid is calcined to obtain an alumina product, and the liquid is returned to the dissolution process for continued use.