Summary of sulfur hazards in high­sulfur bauxite and desulfurization methods.

With the gradual depletion of high-grade bauxite, the development of the alumina industry has been seriously constrained. High­sulfur bauxite reserves are abundant and can be used as an effective supplement to bauxite resources. Therefore, the development of desulfurization and comprehensive utilization methods for high sulfur bauxite has been widely studied. Excessive sulfur content in bauxite and complex valence changes in the Bayer process have serious impacts on products and equipment. This paper will introduce pre-treatment desulfurization and post-treatment desulfurization methods such as roasting, flotation, electrochemical and biological methods. Roasting methods use oxidative roasting to convert sulfur to sulfur dioxide-containing flue gas; flotation methods enrich pyrite through flotation chemicals; biological methods use complex chemical reactions of microorganisms to remove sulfur; and electrolysis methods convert sulfur to sulfate through oxidants produced by electrolysis. Post-treatment methods add precipitants such as zinc oxide to treat small amounts of sulfur entering the Bayer process. The reaction mechanism and development of various desulfurization methods are summarized, and the problems of these desulfurization methods are analyzed. The aim is to combine their advantages to develop economical and environmentally friendly desulfurization methods, and propose suggestions for the future resource utilization of high­sulfur bauxite.

Removal of small elemental sulfur particles by polysulfide formation in a sulfidic reactor.

For over 30 years, biological gas desulfurization under halo-alkaline conditions has been studied and optimized. This technology is currently applied in already 270 commercial installations worldwide. Sulfur particle separation, however, remains a challenge; a fraction of sulfur particles is often too small for liquid-solid separation with conventional separation technology. In this article, we report the effects of a novel sulfidic reactor, inserted in the conventional process set-up, on sulfur particle size and morphology. In the sulfidic reactor polysulfide is produced by the reaction of elemental sulfur particles and sulfide, which is again converted to elemental sulfur in a gas-lift reactor. We analyzed sulfur particles produced in continuous, long term lab-scale reactor experiments under various sulfide concentrations and sulfidic retention times. The analyses were performed with laser diffraction particle size analysis and light microscopy. These show that the smallest particles (< 1 µm) have mostly disappeared under the highest sulfide concentration (4.1 mM) and sulfidic retention time (45 min). Under these conditions also agglomeration of sulfur particles was promoted. Model calculations with thermodynamic and previously derived kinetic data on polysulfide formation confirm the experimental data on the removal of the smallest particles. Under the 'highest sulfidic pressure', the model predicts that equilibrium conditions are reached between sulfur, sulfide and polysulfide and that 100% of the sulfur particles <1 µm are dissolved by the (autocatalytic) formation of polysulfides. These experiments and modeling results demonstrate that the insertion of a novel sulfidic reactor in the conventional process set-up promotes the removal of the smallest individual sulfur particles and promotes the production of sulfur agglomerates. The novel sulfidic reactor is therefore a promising process addition with the potential to improve process operation, sulfur separation and sulfur recovery.

Organic layer characteristics and microbial utilization of the biosulfur globules produced by haloalkaliphilic Thioalkalivibrio versutus D301 during biological desulfurization.

The haloalkaliphilic genus Thioalkalivibrio, widely used in bio-desulfurization, can oxidize H2S to So, which is excreted outside cells in the form of biosulfur globules. As by-product of bio-desulfurization, information on biosulfur globules is still very scant, which limits its high-value utilization. In this paper, the characteristics of biosulfur globules produced by Thioalkalivibrio versutus D301 and the possibility of cultivating sulfur-oxidizing bacteria as a high biological-activity sulfur source were studied. The sulfur element in the biosulfur globules existed in the form α-S8, which was similar to chemical sulfur. The biosulfur globule was wrapped with an organic layer composed of polysaccharides and proteins. The composition of this organic layer could change. In the formation stage of biosulfur globules, the organic layer was dominated by polysaccharides, and in later stage, proteins became the main component. We speculated that the organic layer was mainly formed by the passive adsorption of organic matter secreted by cells. The existence of organic layer endowed biosulfur with better bioavailability. Compared with those found using chemical sulfur, the growth rates of Acidithiobacillus thiooxidans ATCC 19377T, Thiomicrospira microaerophila BDL05 and Thioalkalibacter halophilus BDH06 using biosulfur increased several folds to an order of magnitude, indicating that biosulfur was a good sulfur source for cultivating sulfur-oxidizing bacteria.

Integration of a nitrification bioreactor and an anoxic biotrickling filter for simultaneous ammonium-rich water treatment and biogas desulfurization.

A preliminary assessment has been carried out on the integration of an anoxic biotrickling filter and a nitrification bioreactor for the simultaneous treatment of ammonium-rich water and H2S contained in a biogas stream. The nutrient consumption in the biotrickling filter was as follows (mol-1 NO3--N): 6.3·10-4 ± 1.2·10-4 mol PO43--P, 0.04 ± 0.05 mol NH4+-N and 0.04 ± 0.03 mol K+-K. Furthermore, it was possible to supply a mixture of biogenic NO3- and NO2- into the biotrickling filter from the nitrification bioreactor to obtain a maximum elimination capacity of 152 gH2S-S m-3 h-1. The equivalence between the two compounds was 1 mol NO3--N equal to 1.6 mol NO2--N. The biotrickling filter was also operated under a stepped variable inlet load (30-100 gH2S-S m-3 h-1) and outlet H2S concentrations of less than 150 ppmV were obtained. It was also possible to maintain the outlet H2S concentration close to 15 ppmV with a feedback controller by manipulating the feed flow (in the nitrification bioreactor). Two stepped variable inlet loads were tested (60-111 and 16-102 gH2S-S m-3 h-1) under this type of control. The implementation of feedback control could enable the exploitation of biogas in a fuel cell, since the H2S concentrations were 15.1 ± 4.3 and 15.0 ± 3.4 ppmV. Finally, the anoxic biotrickling filter experienced partial denitrification and this implied a loss of the desulfurization effectiveness related to SO42- production.

[Inhibition of biological desulfurization by organosulfur: a review].

As a green and economic emerging technology, biological desulfurization is popular. However, biological desulfurization is inhibited by organosulfur in the treatment gases which cannot be ignored. This article summarizes relevant studies on the influence of organosulfur on biological desulfurization in recent years, including the types and physicochemical characteristics of organosulfur, the influence of organosulfur on the desulfurization process, the reaction mechanism of organosulfur, the interplay between organosulfur and some operating conditions, and species of microorganisms that are tolerant to organosulfur. Methods for mitigating the effect of organosulfur on the desulfurization process are discussed, to provide references for the stable and efficient operation of biological desulfurization.

Inhibition of biological desulfurization by organosulfur: a review / 生物工程学报

As a green and economic emerging technology, biological desulfurization is popular. However, biological desulfurization is inhibited by organosulfur in the treatment gases which cannot be ignored. This article summarizes relevant studies on the influence of organosulfur on biological desulfurization in recent years, including the types and physicochemical characteristics of organosulfur, the influence of organosulfur on the desulfurization process, the reaction mechanism of organosulfur, the interplay between organosulfur and some operating conditions, and species of microorganisms that are tolerant to organosulfur. Methods for mitigating the effect of organosulfur on the desulfurization process are discussed, to provide references for the stable and efficient operation of biological desulfurization.

[Determination of sulfur compounds in biological desulfurization system by high performance liquid chromatography].

Biological desulfurization is a process in which sulfur compounds are removed from gas and oil using microorganisms. It is a simple process that has mild operating conditions, high desulfurization efficiency, low energy consumption and less environmental pollution. However, there is still a lack of simple and efficient analytical methods for quantitatively analyzing the sulfur compounds in the biological desulfurization process. In order to solve this problem, the analytical method for the simultaneous determination of sulfite, thiosulfate and sulfide in biological desulfurization solutions by pre-column fluorescence derivation using high performance liquid chromatography (HPLC) was developed. The standard curves of sulfur species in this analytical method had good linear relationships with correlation coefficients of 0.999 5, 0.999 7, and 0.999 7 for sulfite, thiosulfate and sulfide, respectively. The detection limits of these sulfur compounds were 0.000 6, 0.000 7 and 0.001 1 µmol/L; the range of recovery rates were 98.17 to 101.9%, 100.9 to 102.6%, and 101.1 to 104.2%; which had good repeatability and stability. The analytical method was simple, efficient and accurate, and could be used to simultaneously determine the sulfur compounds in different biological desulfurization systems.

Determination of sulfur compounds in biological desulfurization system by high performance liquid chromatography / 生物工程学报

Biological desulfurization is a process in which sulfur compounds are removed from gas and oil using microorganisms. It is a simple process that has mild operating conditions, high desulfurization efficiency, low energy consumption and less environmental pollution. However, there is still a lack of simple and efficient analytical methods for quantitatively analyzing the sulfur compounds in the biological desulfurization process. In order to solve this problem, the analytical method for the simultaneous determination of sulfite, thiosulfate and sulfide in biological desulfurization solutions by pre-column fluorescence derivation using high performance liquid chromatography (HPLC) was developed. The standard curves of sulfur species in this analytical method had good linear relationships with correlation coefficients of 0.999 5, 0.999 7, and 0.999 7 for sulfite, thiosulfate and sulfide, respectively. The detection limits of these sulfur compounds were 0.000 6, 0.000 7 and 0.001 1 μmol/L; the range of recovery rates were 98.17 to 101.9%, 100.9 to 102.6%, and 101.1 to 104.2%; which had good repeatability and stability. The analytical method was simple, efficient and accurate, and could be used to simultaneously determine the sulfur compounds in different biological desulfurization systems.