METHOD FOR PRODUCING SULFUR FROM PHOSPHOGYPSUM

Abstract

The objective of the invention is the development of a new process for producing sulfur from phosphogypsum. During this process, the phosphogypsum is mixed with a source of carbon and hydrogen forming a slurry after mixing. This source of carbon and hydrogen is a natural or synthetic organic polymer, as an example that is not limiting, biomass, used tires or plastic, kerogen or tars. The granules undergo a heat treatment (100 to 150° C.) to evaporate the mixing water.

The product obtained undergoes a heat treatment (550 to 900° C.) under a neutral atmosphere and/or partially oxidizing. The generated gases are bubbled in deionized water, sodium hypochlorite solution or a basic aqueous solution which allows the trapping, among others, of organosulfur molecules and the precipitation of sulfur S8. Non-entrapped gases are recovered to extract volatile sulfur products.

Claims

1. A process for preparing elemental sulfur from phosphogypsum, characterized in that the process is carried out in four stages described below: Step 1: making a mixture of phosphogypsum and a source of carbon and hydrogen; Step 2: heat treatment of the mixture obtained at a temperature ranging from 80° C. to 150° C. to form an organic sulfatepolymer composite; Step 3: heat treatment of the organic sulfatepolymer composite in an inert or partially inert atmosphere at a temperature ranging from 550° C. to 900° C.; Step 4: recovery of elemental or combined sulfur.

2. The process according to claim 1, characterized in that the carbon source is chosen from synthetic or natural organic polymers, plant biomass, fossil resources such as heavy hydrocarbons, oil shales, or any residual organic matter.

3. The process according to claim 1, characterized in that the heat treatment of the organic sulfate polymer composite is preferably carried out at a temperature below 750° C.

4. The process according to claim 1, characterized in that the heat treatment of the organic sulphate polymer composite produces organo-sulphur compounds, sulfur and gaseous hydrogen sulphide from 550° C. accompanied by water vapor and carbon dioxide.

5. The process according to claim 4, characterized in that the gas formed is condensed in solid form, by precipitation, in the form of elemental or combined sulfur.

6. The process according to claim 4, characterized in that the gas formed is bubbled through an aqueous solution or a solution of sodium hypochlorite, alkali hydroxide, alcohol or H2O2,

7. The process according to claim 1, characterized in that the heat treatment of the organic sulphate polymer composite produces organo-sulphur compounds, sulfur and gaseous hydrogen sulphide from 550° C. accompanied by water vapor and carbon dioxide.

8. The process according to claim 4, characterized in that the gas formed is condensed in solid form, by precipitation, in the form of elemental or combined sulfur.

9. The process according to claim 4, characterized in that the gas formed is bubbled through an aqueous solution or a solution of sodium hypochlorite, alkali hydroxide, alcohol or H2O2,

Description

DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1: Diagram of the pyrolizer.

[0013] FIG. 2: X-ray diffraction diffractogram of the sulfur obtained

[0014] FIG. 3: Analysis by SEM-EDS.

[0015] FIG. 4: thermogravimetric analysis of the different residues for different pyrolysis temperatures.

[0016] FIG. 5: Evolution of the sulfur percentage/Calcium percentage ratio as a function of the pyrolysis temperature.

SUMMARY OF THE INVENTION

[0017] The object of the present invention is to implement a new process for producing sulfur from phosphogypsum. To do this, the invention aims to develop an efficient process for obtaining elemental sulfur S8 by reduction of the sulfate ion in the presence of a source of carbon and hydrogen (natural or synthetic organic polymer) at low temperatures from 550° C.

[0018] There are four stages in the production of S8 sulfur:

[0019] 1. Preparation of the mixture: The phosphogypsum is mixed with a source of carbon and hydrogen (synthetic or natural organic polymers).

[0020] 2. Treatment of the mixture: the mixture is treated, at a temperature ranging from 80 to 150° C., to form a sulfate-organic polymer composite.

[0021] 3. Pyrolysis of the precursor: the precursor is heat treated, in a furnace with conventional fixed, rotary or fluidized bed heating, in a totally or partially inert medium at a temperature between 550 and 900° C.

[0022] 4. Sulfur recovery: The gases produced are bubbled through an aqueous or organic solution (water, alcohol, sodium hypochlorite, alkaline hydroxide).

EXAMPLE

[0023] The following example is provided to describe the manufacturing process for S8 sulfur. However, the example should not be interpreted as limiting the manufacturing process which has been developed within the frame of the invention.

[0024] Preparation of the precursor: Different sources of carbon, synthetic or natural organic polymers, were tested for different mass ratios of the phosphogypsum mixture/source of carbon and hydrogen. The mixture was heat treated to form a sulfate-organic polymer composite. In fact, under the effect of temperature, water evaporates and thus allows the formation of organic polymer/phosphogypsum composites.

[0025] Pyrolysis of the precursor: This step consists of a heat treatment of the precursor in a tubular pyrolizer (FIG. 1).

[0026] The gaseous sulfur products formed are bubbled through an aqueous or organic solution (water, alcohol, sodium hypochlorite, alkaline hydroxide).

[0027] At the end of the reaction, the sulfur produced in the form of a solid precipitate can be recovered after filtration or decantation.

[0028] Organic solutions containing sulfur can be used as a raw material for the synthesis of sulfur compounds. Sulfur S8 has various applications in the synthesis of sulfur-based materials. Another application is in the production of high purity sulfuric acid.

[0029] Analysis by scanning electron microscope (FIG. 2) clearly showed that the material contains more than 99% sulfur, this result was confirmed by X-ray fluorescence. To determine the nature of the sulfur obtained, a study by diffraction of the X-rays.

[0030] Analysis of the X-ray diffraction diffractogram (FIG. 3) clearly showed the presence of a single phase which is none other than sulfur S8.

[0031] The thermogravimetric analysis of the various pyrolysis residues (FIG. 4) clearly shows that from 550° C., the loss of mass relating to the decomposition of calcium sulphate (from 990 to about 1150° C.) decreases depending on of the pyrolysis temperature and practically disappears for the treated residues from 650° C.

[0032] FIG. 5 illustrates the sulfur/calcium ratio of the residues as a function of the temperature of the pyrolysis, it is clearly seen that this ratio decreases as a function of the temperature. Above 650° C., this ratio is almost zero, thus showing that the majority of the sulfur contained in the gypsum is transformed into elemental or combined sulfur.

INDUSTRIAL APPLICATION

[0033] The reaction can be carried out at a much lower temperature than that by the conventional method, thus producing a great saving of energy. As application we can consider the production of pure sulfuric acid for different industrial uses.

BIBLIOGRAPHICAL REFERENCES

[0034] [1] L. Yang et al., “Utilization of phosphogypsum for the preparation of non-autoclaved aerated concrete,” vol. 44, p. 600-606, 2013.

[0035] [2] M. Zairi and M. Rouis, “Environmental impacts of the storage of phosphogypsum in Sfax (Tunisia).” flight. 219, p. pp 29-40, 1999.

[0036] [3] Chandler, R. H. and Isbell, R.A.C. 1976. The Claus Process. R. H. Chandler Ltd., Braintree, USA.

[0037] [4] N. R. Mbhele, W. Van der Merwe, J P Maree and D. Theron, recovery of sulfur from waste gypsum, Abstracts of the International Mine Water Conference, Proceedings ISBN: number 978-0-9802623-5-3, 19-23 Oct. 2009, Pretoria, South Africa

[0038] [5] Sandrine Marty, production of calcium oxide and sulfur dioxide from the decomposition of phosphogypsum, Master of Applied Science, Department of Chemical Engineering, École Polytechnique de Montréal.

[0039] [6] G. d. Canada. (2013, February 2014). Natural Resources Canada. Archived—Sulfur, http://www.nrcan.gc.ca/mines-materiaux/marches/annuaire-mineraux-canada/2009/8471.