Successful sulfur recovery in low sulfurate compounds obtained from the zinc industry: Evaporation–condensation method

doi:10.1016/j.jhazmat.2017.04.051

Journal of Hazardous Materials

Volume 336, 15 August 2017, Pages 168-173

https://doi.org/10.1016/j.jhazmat.2017.04.051 Get rights and content

Highlights

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Industrial residue coming from a zinc obtaining plant is used for sulfur recovery.
•
An evaporation–condensation method is successfully employed for low sulfur content samples.
•
The obtained sulfur has a high purity and is comparable to commercial sulfur.

Abstract

The improvement of an evaporation–condensation method allows for successful recovery of elemental sulfur from sulfide concentrates from the zinc industry. Elemental sulfur can be obtained with this method in samples with a low (60%) sulfur content. The effects of heating temperature between 150 °C and 250 °C and heating time up to 120 min on the recovery of sulfur are also studied. Elemental sulfur obtained in this way is of high purity and therefore, there is no need for further purification. The treatment of these industrial residues would help removing sulfur from the environment.

Introduction

Sulfur and its derivatives are used in many chemical and industrial processes, being particularly important in the manufacture of phosphate fertilizers. Sulfur is therefore important to industrial economies, but unlike other chemicals, it is not produced intentionally as a primary product. Sulfur is derived as a by-product from operations such as petroleum refining, tar sands recovery, heavy oil and natural gas processing, and from coking and metallurgical plants [1], [2]. One of the ways of obtaining sulfur is in the zinc industry.

The zinc industry has routinely achieved a high hydrometallurgical extraction of zinc (higher than 98%) [3]. Zinc is mainly recovered from primary sulfide concentrates; sulfide compounds are also obtained during this process and are usually converted into sulfuric acid. The recovery of pure sulfur is sometimes difficult.

Zinc concentrate is usually roasted as pretreatment in zinc hydrometallurgy, and the produced SO₂ is converted into sulfuric acid.

To avoid the release of SO₂ in the treatment of zinc ores, direct leaching can be performed in such a way that the sulfuric phases transform into elemental sulfur that remains in the residue after leaching. One of these processes is known as the Albion Process™.

The Albion Process™ is a combination of ultrafine grinding and oxidative leaching at atmospheric pressure. The fine grinding of the concentrate introduces a high degree of strain into the sulfide mineral lattice, increasing the number of fractures in the mineral and enabling leaching under atmospheric conditions. The feed to the Albion Process™ is a concentrate containing metals, and this process is used to oxidize the sulfide minerals in the concentrate and liberate these metals for recovery by conventional means.

The zinc sulfur concentrate is finely ground and slurried, and afterwards, it is pumped to an oxidative leaching circuit. Oxygen is injected at high pressure. The acid pressure oxidation is a way to obtain metals such as Zn, Cu, Ni, Pb and precious metals from sulfates [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15].

Different methods have been developed for sulfur recovery in pressure leaching of zinc concentrate [16], [17], [18], which are based in a floating process of the leaching residue followed by melting and filtration processes. If the flotation concentrate contains less than 70% elemental sulfur, it is difficult to obtain a melted fluid in the next stage of the fusion, which can cause difficulties in the filtration process.

The sulfide concentrates employed in this study contain approximately 60% elemental sulfur for which the melting-filter procedure is difficult to carry out. Although as a solution, the concentrate could be enriched with pure elemental sulfur until the sulfur content is high enough to obtain a melted fluid, this study will look at recovering elemental sulfur with other methods.

The aim of this work is to find a more appropriate method for the reuse of the residue of atmospheric pressure leaching of zinc concentrates with a high content of lead, with the specific goal of sulfur recovery. With that aim, the evaporation–condensation method of Watanabe et al. [19] is considered. According to this method, high-purity sulfur can be efficiently recovered from sulfurous compounds at temperatures below the boiling point of sulfur (445 °C). Sulfur has an unexpectedly high vapour pressure even in the liquid phase at temperatures near its melting point. To recover the sulfur, the float is heated to a temperature higher than sulfur's melting point (119 °C) and less than its boiling point. An inert gas is used as a carrier; the gas containing the evaporated sulfur is cooled to condense the sulfur. The cooling temperature is lower than sulfur's melting point. The Watanabe method did not show the expected results and the system was improved as explained below.

The method presented here is a way of removing hazardous sulfur from industrial residue that are collected in industrial dumps, and therefore, chemical weathering could occur, involving the alteration of ion sulfides, and the release of dissolvable sulfides and toxic metal ions.

Section snippets

Experimental setup

Our samples were obtained from the zinc plant AZSA, (Asturiana de Zinc S.A.). The material coming from the leaching residue at atmospheric pressure and afterwards the resultant sulfur and tailing residue coming from our evaporation–condensation experiments were characterized using different techniques, in order to observe changes in composition. An elemental analysis was performed in order to determine the elemental sulfur in the minerals. The determination of metals was also carried out by

Characterization of the flotation concentrate

The samples coming from the leaching residue at atmospheric pressure are characterized using several techniques, with the aim of determining the amount and structure of sulfur in them. The samples had the state of dry powder and were first treated during 2 h with heat in an oxidizing atmosphere in order to determine their weight loss with temperature.

Fig. 2 shows this weight loss with increasing temperature. It can be seen that the weight loss starts to be appreciable above 150 °C and has its

Conclusions

Elemental sulfur has been successfully recovered for the proposed evaporation–condensation method. It has the advantage that recovered sulfur in all cases is of high purity and a further purification treatment is not needed. Additionally, it does not depend on the content of sulfur in the sample, which is an advantage compared to other methods such as melting-filtration, which needs a minimum quantity of 70% of sulfur to work properly.

Working at the optimal conditions (250 °C, 120 min) will

Acknowledgements

The authors appreciate support from the Spanish Economics and Competitiveness Ministry through grant AYA2014-57648-P and the Government of the Principality of Asturias (Consejería de Economía y Empleo) through grant FC-15-GRUPIN16-017.

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Successful sulfur recovery in low sulfurate compounds obtained from the zinc industry: Evaporation–condensation method

Highlights

Abstract

Introduction

Section snippets

Experimental setup

Characterization of the flotation concentrate

Conclusions

Acknowledgements

Eur. J. Agron.

Miner. Eng.

Int. J. Miner. Process

Hydrometallurgy

Turkey. Miner. Eng.

Int. J. Miner. Process.

Hydrometallurgy

Miner. Eng.

Hydrometallurgy

J. Miner. Mater. Character. Eng.

Earth-Sci. Rev.

J. Hazard. Mater.