Process for the recovery of elemental sulphur from residues produced in hydrometallurgical processes

Abstract

The present invention relates to a process for the recovery of elemental sulphur from residues produced in hydrometallurgical processes based on leaching with a solution of sodium sulphide in which the sulphur contained in the residues is selectively leached as sodium polysulphide. The sulphur leaching solution is conveniently regenerated and recycled to the process.

Description

EXAMPLE 1

A residue produced from the leaching of a lead concentrate has a content of elemental sulphur of 52%. 100 g of this residue are introduced into a reactor containing 0.85 l of a 60 g/l solution of sodium sulphide (Na₂S). After 1 h of leaching at 55° C., 46.85 g of dry residue washed residue are obtained, which contains 0.08 g of residual elemental sulphur and 1.0 l of a solution of sodium polysulphide (Na₂S_X wherein X is about 3.5) including the washing of the cake.

The solution is introduced into a closed reactor where approximately 43 g of CO₂ are fed. The dispersion produced is filtered, the cake washed and dried recovering 30.96 g of pure sulphur. Part of the sulphur is still in the aqueous phase as polysulphide.

The filtrate is treated with 55 g of lime (CaO) obtaining a dispersion which is filtered recovering 97.45 g of dry washed residue (CaCO₃) and 1.46 l of a solution containing about 49.6 g/l of sodium polysulphide (approximately Na₂S₂) to be recycled to the leaching.

EXAMPLE 2

Another portion of residue coming from the leaching of a lead concentrate, already used in Example 1, is adopted for this test and the end-solution of Example 1 evaporated to 0.85 l, is used as leaching solution. 60 g of residue are introduced into a reactor into which the regenerated solution of polysulphide is fed.

After 1 h of leaching at 55° C., 28.11 g of dry residue washed residue are obtained, which contains 0.06 g of residual elemental sulphur and 0.96 l of a solution of sodium polysulphide (Na₂S_X wherein X is about 3.5) including the washing of the cake.

The solution is introduced into a closed reactor where approximately 43 g of CO₂ are fed. The dispersion produced is filtered, the cake washed and dried recovering 31.39 g of pure sulphur.

The filtrate is treated with 55 g of lime (CaO) obtaining a dispersion which is filtered recovering 97.22 g of dry washed residue (CaCO₃) and 1.38 l of a solution containing about 55.2 g/l of sodium polysulphide (approximately Na₂S₂) to be recycled to the leaching.

Claims

1. A process for the of elemental sulphur from residues produced in hydrometallurgical processes comprises: a) leaching of residues containing sulphur with a solution of sodium sulphide wherein the sulphur contained in said residues is selectively leached as sodium polysulphide;b) separation of the residues from the solution containing polysulphide;c) treatment of said solution containing polysulphide with CO2 to obtain a dispersion containing elemental sulphur, acid sodium polysulphide and sodium bicarbonate;d) separation and recovery of the elemental sulphur from the solution containing acid sodium polysulphide and sodium bicarbonate;e) treatment of said solution of acid sodium polysulphide and sodium bicarbonate with CaO for regenerating the leaching solution;f) separation of a residue of CaCO3 from a solution of sodium sulphide which is recirculated to phase a) of the process.

2. The process according to claim 1 comprising a further phase g) for the roasting of the CaCO3 residue obtained in phase e) to produce CaO and CO2.

3. The process according to claim 2, wherein the CaO obtained from said phase g) is recycled to phase e) of the process and the CO obtained is recycled to said phase c).

4. The process according to claim 1, wherein the solution of sodium sulphide of the leaching phase a) has a concentration ranging from 20 to 300 g/l.

5. The process according to claim 1, wherein the leaching phase a) is carried out at a temperature ranging from 20 to 100° C. for a period of time ranging from 10 to 120 minutes.

6. The process according to claim 1, wherein the leaching phase a) is carried out in a stirred reactor.

7. The process according to claim 1, wherein the separation phases b), f) are effected by filtration.

8. The process according to claim 1, wherein said phase e) for treatment with CaO is carried out at a temperature ranging from 20 to 100° C. for a period of time ranging from 10 to 120 minutes.

9. The process according to claim 1, wherein said phase e) for treatment with CaO is carried out in a stirred reactor.

10. The process according to claim 1, wherein the residue separated in phase b) is substantially free of sulphur and is subjected to flotation or treatment for the extraction of the metals present therein.

11. The process according to claim 1, wherein the leaching phase a) is carried out in a stirred reactor.

12. The process according to claim 1, wherein the leaching phase a) is carried out in a stirred reactor.

13. The process according to claim 1, wherein the residues to be treated are produced from the leaching of a lead concentrate.