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CA-3202734-C - PROCESS FOR RECOVERING MATERIALS FROM BAUXITE RESIDUE, MICROWAVE REACTOR FOR HEATING MINING PRODUCTS AND METHOD FOR HEATING A MINING PRODUCT

CA3202734CCA 3202734 CCA3202734 CCA 3202734CCA-3202734-C

Abstract

The present invention refers to a technically and economically viable process for recovery of metallic and non-metallic content of interest from mining residues, particularly bauxite residue, using it in its integral form. Such a process uses energy from microwaves, assisted leaching and logical sequencing of steps to allow a technically and economically viable extraction of components from the bauxite residue, particularly the residue from the Bayer process. The invention also refers to a microwave reactor that is appropriate for performing the above-mentioned process, as well as to a method for heating a mining product.

Inventors

  • LUCAS ARANTES ARAUJO

Assignees

  • WAVE ALUMINIUM BRASIL S.A.

Dates

Publication Date
20260505
Application Date
20211217
Priority Date
20201218

Claims (14)

  1. 32 CLAIMS 1. A process for recovering materials derived from bauxite residue, wherein the process comprises the steps of: - mixing the bauxite residue to a reducing agent to obtain a residue mixture; - heating the residue mixture in a microwave reactor to obtain a reduced bauxite residue; - magnetically separating the reduced bauxite residue to obtain portions of magnetic and non-magnetic materials; - leaching the portion of the non-magnetic material with sulfuric acid to obtain a leaching liquor, and subsequently decanting said leaching liquor for silica extraction (SiO2); - precipitating the leaching liquor after the silica (SiO2) extraction to obtain titanium dioxide (TiO2); - evaporating the leaching liquor after the titanium dioxide (TiO2) precipitation to obtain a saturated liquor and an alumina-rich retained solid; and - calcining the alumina-rich retained solid obtained from the evaporation step to obtain alumina (Al2O3).
  2. 2. The process for recovering materials derived from bauxite residue according to claim 1, wherein the reducing agent comprises particle size lower than 75 µm, and that the mixing takes place between 10 and 30 minutes up to formation of a carbothermal mixture of bauxite residue and reductor, at ratios from 5 to 50% of reductor.
  3. 3. The process for recovering materials derived from bauxite residue according to claim 1, further comprising a pelletizing step of the residue mixture obtained from the mixing step, prior to the heating step.
  4. 4. The process for recovering materials derived from bauxite residue according to claim 1, wherein in the heating step, the bauxite residue is irradiated 33 from 10kW.h to 100kW.h of power per ton of carbothermal mixture, for a time ranging from 2 to 18 minutes, with temperature being kept above 80% of the temperature of conversion into magnetic phases for, at least, twice the time spent to reach the temperature of conversion to the magnetic phases.
  5. 5. The process for recovering materials derived from bauxite residue according to claim 1, further comprising the steps of: - performing a first milling of the bauxite residue of the heating step; - performing a size separation of the bauxite residue milled in the first milling for obtaining a gross portion and a fine portion of the bauxite residue.
  6. 6. The process for recovering materials derived from bauxite residue according to claim 5, - wherein magnetically separating the reduced bauxite residue to obtain the portions of magnetic and non-magnetic materials occurs after performing the size separation; - wherein the magnetic separation is carried out separately for the gross portion and the fine portion; and - wherein the magnetic separation of the gross portion obtains magnetic and non-magnetic gross portions, and the magnetic separation of the fine portion obtains magnetic and non-magnetic fine portions.
  7. 7. The process for recovering materials derived from bauxite residue according to claim 6, wherein a second milling is performed in the fine portion prior to the magnetic separation of the fine portion.
  8. 8. The process for recovering materials derived from bauxite residue according to claim 5, wherein the size separation comprises: - forwarding the bauxite residue resulting from the first milling to a first cyclonic separator, that separates the bauxite residue into two portions of 34 material, a first portion with sizes less than 0.149mm and a second portion with sizes greater than 0.149mm; - forwarding the first portion separated by the first cyclonic separator to a second cyclonic separator; - separating the first portion, through the second cyclonic separator, further into a third portion with sizes below 0.074mm and a fourth portion with sizes above 0.074mm, wherein the third portion is the fine portion; and - gathering the second portion that is separated by the first cyclonic separator, with the fourth portion that is separated by the second cyclonic separator to obtain the gross portion.
  9. 9. The process for recovering materials derived from bauxite residue according to claim 1, wherein the leaching step takes place at a solid-liquid ratio from 1 to 10 grams of the portion of non-magnetic material for 10 mL of the sulfuric acid at concentrations from 2 mol/L to 6 mol/L.
  10. 10. The process for recovering materials derived from bauxite residue according to claim 1, wherein the leaching step takes place within a time ranging from 30 to 120 minutes, at a temperature from 30º to 90ºC, and agitation speed from 400 to 600 RPM.
  11. 11. The process for recovering materials derived from bauxite residue according to claim 1, wherein the precipitation step comprises: - adding a TiO2 seed to the liquor; and - adding sodium hydroxide solution to increase the pH of the liquor from 1.5 to 2.5 to precipitate the titanium dioxide (TiO2).
  12. 12. The process for recovering materials derived from bauxite residue according to claim 1, wherein the precipitation step takes place at an agitation 35 speed from 50 to 200 RPM, at temperatures from 10º to 90ºC, within a period ranging from 30 to 120 minutes.
  13. 13. The process for recovering materials derived from bauxite residue according to claim 1, wherein the evaporation step comprises: - evaporating the leach liquor after the titanium dioxide (TiO2) precipitation up to a density from 10 to 16 degrees Baumé, and - adding stoichiometric amounts of sodium sulfate and adjusting the pH of the leach liquor after the titanium dioxide (TiO2) precipitation from 6 to 12 by adding of 50% (w/v) sodium hydroxide solution.
  14. 14. The process for recovering materials derived from bauxite residue according to claim 1, wherein the calcination step comprises: - calcining the retained solid at a temperature from 400º to 800ºC, within a period from 30 to 120 minutes.

Description

CA 03202734 2023-6-19 1 Specification of the Patent for "PROCESS FOR RECOVERING MATERIALS FROM BAUXITE RESIDUE, MICROWAVE REACTOR FOR HEATING MINING PRODUCTS AND METHOD FOR HEATING A MINING PRODUCT." 5 [001] This invention refers to a technically and economically feasible recovery process of relevant metals and non-metals of mining residues, particularly the bauxite residue, by using it in its whole. Such process route uses microwave energy, assisted leaching and logic sequencing of steps to allow a technically and economically feasible removal of components from the 10 bauxite residue, particularly the one derived from the Bayer process. Using electromagnetic radiation within the spectrum of microwaves leads to an improved efficiency in the treatment and processing of these materials and residues. This invention also provides a microwave reactor, whose construction and operation are particularly efficient for application in the recovery of min- 15 ing residues, and more particularly the bauxite residue resulting from the Bayer process. [002] Further, this invention refers to a microwave reactor for heating mining products, that is specifically adapted for heating mining products to the recovery of materials of interest, being applicable to perform a recovery 20 process of materials derived of the aforesaid bauxite residue. Background [003] In the technological field of mining process-derived products, one of the famous processes, mostly used by the mining industry to extract aluminum from iron ore (bauxite) is the Bayer process. 25 [004] The Bayer process, developed in 1888, is the most used worldwide to alumina production. This process consists in promotion a digestion of bauxite under temperature and pressure by using sodium hydroxide as leaching agent. The digestion stage enables the aluminum contained in the bauxite in the form of gibbsite, boehmite and diaspore to reach with the sodi- 30 um hydroxide, thus forming the soluble compound sodium aluminate. So, it is possible to separate this liquor containing sodium aluminate from the Bayer process residue, both by thickening and decantation. The liquor is forwarded CA 03202734 2023-6-19 2 to a crystallization step for alumina recovery; the material resulting from decanters are tailings the Bayer process, that are deposited in disposal lagoons. [005] This residue from the Bayer process (known as bauxite residue, 5 or red mud) is primarily composed of iron contents in the form of hematite and goethite, aluminum in the form of gibbsite and Bayer socialite, titanium in the form of anatasium and other minor elements, such as scandium, uranium, thorium, and zircon, among others. This tailing from Bayer process is insoluble at the digestion step, and results from the precipitation of kaolinite in 10 the form of Bayer Socialite. This sodalite contains aluminum, as well as iron, sodium and hydroxide. This tailing also contains a range of metals of strategic interest to the industry, such as zircon, scandium and titanium. [006] Nevertheless, the bauxite residue generated from alumina processing by Bayer is highly pollutant: it is reactive and corrosive due to its high 15 pH; contains heavy metals, particularly uranium and thorium; it is fine and light, thus requiring constant monitoring; irrigated and compact; requires soil waterproofing to avoid contamination. Therefore, such bauxite residue implies high maintenance costs, being highly harmful to be environment and likely to cause environmental catastrophes, such as the disaster at Ajka 20 plant, in Hungary. [007] In view of the above, the state of art intends to provide solutions to the treatment of products and residues for further obtaining materials of interest, including bauxite residue processing. However, such processes currently known lack efficiency in eliminating the residue, being limited to what is 25 possibly extracted as material of interest, as explained below. [008] Conceptually, solutions to the treatment of mining products and to the recovery of materials of interest mostly comprise converting or processing products or residue for subsequent separation through other procedures (such as magnetic separation or leaching), thus allowing the extraction 30 of elements of interest from that product or residue. [009] The conversion of products or residues traditionally uses the application of heat to force the change of phases of elements present therein CA 03202734 2023-6-19 3 and to allow their separation and use. Such heat results from the coal burning, also usually employed as reducing agent in conversion processes. The above comments disclose a first concern of the state of art: a conversion through heat generated by pollutant sources such as coal, whose burning 5 produces CO2 that is knowingly harmful to the environment. [001 O] The state of art proposes solutions based on the use of microwaves for energy supply, with a consequent heating of products and residues. So, the need of coal burning to t