Treatment of alkaline bauxite residue

Patent metadata

Field	Value
Publication number	US-10494280-B2
Application number	US-201314441449-A
Country	US
Kind code	B2
Filing date	Oct 21, 2013
Priority date	Nov 7, 2012
Publication date	Dec 3, 2019
Grant date	Dec 3, 2019

Abstract

A process is disclosed for treating a Bayer process waste comprising a slurry containing bauxite residue and dissolved aluminum. The process comprises supplying the waste to a settling area to cause the bauxite residue to settle out of the slurry, thereby producing a supernatant liquor. The process further comprises neutralizing the supernatant liquor with a solution containing magnesium and calcium to produce a neutralized slurry containing precipitated hydrotalcites and thickening the neutralized slurry to produce a clarified effluent and a compacted slurry containing the precipitated hydrotalcites, part of said compacted slurry being recirculated to the supernatant liquor to be neutralized and/or directly to the neutralizing step. The clarified effluent and the compacted slurry are disposed of separately. Also disclosed is a plant for treating a Bayer process waste.

First claim

The invention claimed is:

1. A process for treating a Bayer process waste comprising a slurry containing bauxite residue and dissolved aluminium, the process comprising the steps of:
(a) supplying the waste to a settling area to cause the bauxite residue to settle out of the slurry, thereby producing a supernatant liquor, and blending the supernatant liquor with a Bayer process liquor stream to create a modified supernatant liquor with a desired composition;
(b) neutralizing the modified supernatant liquor with a solution containing magnesium and calcium in a single neutralization step in a mixing vessel to produce a neutralized slurry containing precipitated hydrotalcites;
(c) thickening the neutralized slurry in a thickener vessel to produce a clarified effluent and a compacted slurry containing the precipitated hydrotalcites;
(d) recirculating a stream of compacted slurry to the supernatant liquor fed to the neutralization step (b) and/or directly to the neutralization step (b); and
(e) disposing of the clarified effluent and the compacted slurry separately,
wherein the process further comprises the step of adding flocculant, selected to cause hydrotalcite interaction, to steps (b) and/or (c) or to one or more inputs to steps (b) and/or (c).

2. The process according to claim 1 , characterized in that a quantity of compacted slurry that is recirculated is selected to achieve a solids loading of at least 10 g/L in the neutralized slurry sent to the thickening step (c).

3. The process according to claim 1 , characterized in that the process further comprises recirculating a stream of the compacted slurry to the thickening step (c).

4. The process according to claim 1 , characterized in that the waste is supplied in step (a) to a plurality of ponds of the settling area, and characterized in that the process further includes selecting supernatant liquors from different ponds having different chemical compositions and blending the selected supernatant liquors for producing the modified supernatant liquor.

5. The process according to claim 1 , characterized in that the process further includes:
selecting the Bayer process liquor stream, such that the Bayer process liquor stream has a different chemical composition than the supernatant liquor produced in step (a).

6. The process according to claim 5 , characterized in that the Bayer process liquor stream is selected so that the modified supernatant liquor to be neutralized in step (b) has a molar ratio of carbonate to aluminium of at most 30:1.

7. The process according to claim 1 , characterized in that the flocculant is diluted to 0.5 to 2.0 g/L by adding flocculant directly to the solution input to neutralization step (b).

8. The process according to claim 1 , characterized in that the process further comprises initially diluting flocculant at a location remote from a plant for carrying out the process, transferring the diluted flocculant to the plant and then diluting the flocculant further to a required concentration prior to supply to the process.

9. The process according to claim 1 , characterized in that neutralization step (b) involves supplying the modified supernatant liquor and the solution to the mixing vessel and involves controlling conditions in the mixing vessel to produce the neutralized slurry that enables a settling rate at least 5 m/h in a thickening step.

10. The process according to claim 9 , characterized in that the conditions in the mixing vessel are controlled by adjusting a residence time of the modified supernatant liquor in the mixing vessel and/or by adjusting a mixing intensity.

11. The process according to claim 1 , characterized in that neutralizing step (b) further comprises controlling a supply of the modified supernatant liquor and solution such that the inputs of the modified supernatant liquor and the solution provide a molar ratio of magnesium to aluminium in a range of at least 4:1.

12. The process according to claim 1 , characterized in that the solution is seawater, and the seawater and the modified supernatant liquor are supplied in a volume ratio in excess of a required volume ratio to achieve substantially full hydrotalcite precipitation.

13. The process according to claim 1 , characterized in that the thickening step (c) is controlled to produce the compacted slurry with a hydrotalcite loading of >100 g/L.

14. The process according to claim 1 , characterized in that thickening step (c) is controlled to produce the compacted slurry with a hydrotalcite loading of 110 to 130 g/L.

15. The process according to claim 1 , characterized in that the process further comprises recirculating a stream of compacted slurry to a decanter that receives the neutralized slurry from neutralization step (b) such that a hydrotalcite loading of the combined neutralized slurry and the compacted slurry fed to the decanter is >15 g/L.

16. The process according to claim 1 , characterized in that the thickening step (c) is further controlled to produce a clarified effluent having a hydrotalcite loading of <10 mg/L.

17. The process according to claim 1 , characterized in that the process further comprises operating steps (b) and (c) on a continuous basis.

18. The process according to claim 1 , characterized in that disposal step (d) involves removing hydrotalcite from the compacted slurry by dewatering a stream of the compacted slurry produced in thickening step (c).

19. The process of claim 1 , wherein the neutralized slurry has a pH of less than 9.

20. The process of claim 1 , wherein the blending of the supernatant liquor with the Bayer process liquor stream is performed in a pre-mixing vessel upstream from the mixing vessel.

21. The process of claim 1 , wherein the blending of the supernatant liquor with the Bayer process liquor stream is performed in the mixing vessel.

22. A plant for treating a Bayer process waste comprising a slurry containing bauxite residue and dissolved aluminium, the plant comprising:
(a) a settling area for receiving the Bayer process waste, wherein the settling area is adapted to cause the bauxite residue to settle out of the slurry, thereby producing a supernatant liquor;
(b) means for blending the supernatant liquor with a Bayer process liquor stream to create a modified supernatant liquor with a desired composition;
(c) a single neutralization mixing vessel adapted to mix the modified supernatant liquor and a solution containing magnesium and calcium such that a neutralized slurry is formed in a single neutralization step with precipitated hydrotalcites in a form and in quantities suitable for separating the hydrotalcites from the neutralized slurry by a thickening process;
(d) a thickener vessel for receiving the neutralized slurry and for producing a clarified effluent and a compacted slurry containing the precipitated hydrotalcites; and
(e) supply lines for recirculating compacted slurry from the thickener vessel to one or more of the mixing vessel, the thickener vessel, or a supplying line for conveying the neutralized slurry from the mixing vessel to the thickener vessel, wherein the supply lines directly connect the thickener vessel to the one or more of the mixing vessel, the thickener vessel, or the supplying line for conveying the neutralized slurry from the mixing vessel to the thickener vessel,
wherein the plant is configured for adding flocculant, selected to cause hydrotalcite interaction, to the mixing vessel and/or the thickener vessel or to one or more inputs to the

Assignees

• Rio Tinto Alcan Int Ltd

Inventors

• Anderson John Victor
• Rousseaux Jean-Marc
• Peloquin Guy
• O'Brien Ben

Classifications

• A62D2101/43

  containing heavy metals, in the bonded or free state · CPC title

• A62D2101/24

  containing heavy metals · CPC title

• A62D3/33 Primary

  by chemical fixing the harmful substance, e.g. by chelation or complexation · CPC title

• C01F7/066

  Treatment of the separated residue · CPC title

• C02F2103/16

  from metallurgical processes, i.e. from the production, refining or treatment of metals, e.g. galvanic wastes · CPC title