Elemental Sulfur Recovery Research Articles

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

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 120min 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.

Catalytic Recovery of Elemental Sulfur Using a Novel Catalytic Membrane Reactor at Room Temperature with a Layer of Dispersed Mo-Co/γ-Al2O3 Catalyst: Reaction Kinetics and Mass Transfer Study

The mass transfer rate of catalytic recovery of sulfur is investigated, enters through the catalyst-membrane interface (layer), accompanied by pseudo-first order irreversible reaction. Reaction kinetics is measured considering the system as a homogeneous system due to the consideration of mixed flow patterns of the reacting fluids, though the catalysis is a heterogeneous one. The multi-reactant mass transfer behaviour of the catalytic membrane reactor (CMR) is also studied on the basis of Maxwell-Stefan theory to understand the diffusion of reactants inside the membrane reactor. The mass transport behaviour and the performance of the fabricated CMR are strongly influenced by the reaction conditions, such as, reaction equilibrium constant ( K eq ) and membrane properties, namely, membrane area and reactor volume. An intermediate value with asymptotic nature of K eq as a function of time indicates appreciable performance of the catalytic membrane. On the other hand, the minimum value of k ij indicates a negligible effect on mass transfer over the reactor performance.

Catalytic Recovery of Elemental Sulfur Using a Novel Catalytic Membrane Reactor at Room Temperature with a Layer of Dispersed Mo-Co/γ-Al2O3 Catalyst: Reaction Kinetics and Mass Transfer Study

The mass transfer rate of catalytic recovery of sulfur is investigated, enters through the catalyst-membrane interface (layer), accompanied by pseudo-first order irreversible reaction. Reaction kinetics is measured considering the system as a homogeneous system due to the consideration of mixed flow patterns of the reacting fluids, though the catalysis is a heterogeneous one. The multi-reactant mass transfer behaviour of the catalytic membrane reactor (CMR) is also studied on the basis of Maxwell-Stefan theory to understand the diffusion of reactants inside the membrane reactor. The mass transport behaviour and the performance of the fabricated CMR are strongly influenced by the reaction conditions, such as, reaction equilibrium constant (Keq) and membrane properties, namely, membrane area and reactor volume. An intermediate value with asymptotic nature of Keq as a function of time indicates appreciable performance of the catalytic membrane. On the other hand, the minimum value of kij indicates a negligible effect on mass transfer over the reactor performance.

Enhanced performance of denitrifying sulfide removal process at high carbon to nitrogen ratios under micro-aerobic condition

The success of denitrifying sulfide removal (DSR) processes, which simultaneously degrade sulfide, nitrate and organic carbon in the same reactor, counts on synergetic growths of autotrophic and heterotrophic denitrifiers. Feeding wastewaters at high C/N ratio would stimulate overgrowth of heterotrophic bacteria in the DSR reactor so deteriorating the growth of autotrophic denitrifiers. The DSR tests at C/N=1.26:1, 2:1 or 3:1 and S/N =5:6 or 5:8 under anaerobic (control) or micro-aerobic conditions were conducted. Anaerobic DSR process has <50% sulfide removal with no elemental sulfur transformation. Under micro-aerobic condition to remove <5% sulfide by chemical oxidation pathway, 100% sulfide removal is achieved by the DSR consortia. Continuous-flow tests under micro-aerobic condition have 70% sulfide removal and 55% elemental sulfur recovery. Trace oxygen enhances activity of sulfide-oxidizing, nitrate-reducing bacteria to accommodate properly the wastewater with high C/N ratios.

Isolation, Identification and Metabolic Characteristics of a Heterotrophic Denitrifying Sulfur Bacterial Strain

Organics,sulfide and nitrogen compounds in industrial wastewater are significant challenges for wastewater treatment. These pollutants could be removed simultaneously from wastewater treatment system using biological technologies. In this study, a heterotrophic denitrifying sulfur bacterial strain HDD1 was isolated from wastewater treatment bioreactor. Strain HDD1 was identified as Thauera sp. based on the 16S rRNA gene phylogenetic analysis and physiological characteristics. Acetate and sulfide could be utilized as electron donors and nitrate as electron acceptor for respiration in Thauera sp. HDD1. The acetate (300 mg·L-1), sulfide (200 mg·L-1) and nitrate (487 mg·L-1) were completely metabolized and removed within 15 hours. The main product of sulfide oxidation was elemental sulfur as identified by scanning electron microscope and energy dispersive spectrometer. These results suggest that the newly isolated Thauera sp. HDD1 could be used for simultaneous industrial wastewater treatment and elemental sulfur resource recovery.

Direct elemental sulphur recovery from gold acid mine drainage streams

The metal precipitates resulting from the neutralization and desalination processes of acid mine water with lime, limestone and barium carbonate are wastes identified as sludge. The composition of these sludges generally comprises hydrated manganese, magnesium hydroxides, gypsum and large amount of barite. Legislation requires that these sludges be disposed in an environmentally acceptable manner to prevent metals from leaching and entering the environment. However; the enormous volumes of sludge produced and the limited disposal spaces present major environmental and economic concerns for the development of a viable technology for acid mine water treatment. This paper assesses the conversion of CaSO4/Mg(OH)2 and BaSO4/CaCO3 generated in the water stage of the Alkali Barium Calcium desalination process into sulphur. Africa is a major importer of large tonnages of sulphur at high cost often inflated by the cost of transportation whilst sulphur itself remains a relatively cheap product. This paper investigates a) the reduction of BaSO4/CaCO3 and CaSO4/Mg(OH)2 sludges to barium and calcium sulphide; b) the stripping of the sulphide with CO2 gas and the production of sulphur. Thermal reduction study shows that BaSO4/CaCO3 and CaSO4/Mg(OH)2 sludges can be reduced to BaS/CaS with duff carbon in a muffle furnace operating at about 1100°C with BaS/CaS yield between 70 and 76%. The BaS/CaS formed was slurried in water and CO2 was used for the stripping of sulphide to form H2S gas and BaCO3/CaCO3 precipitate. The H2S generated was reacted with ferric sulphate to form elemental sulphur. Sulphur with purity between 95.2% and 99.1% was recovered from the sulphate rich wastes.

Recovery of high purity elemental sulfur from coal syngas by liquid redox catalytic process using tannin extracts

Liquid redox sulfur recovery (LRSR) processes using tannin extracts and vanadium pentoxide as dual redox catalysts are widely employed for removal of hydrogen sulfide and recovery of elemental sulfur from coal syngas in China. Difficulties in melting sulfur pastes, poor quality of sulfur and the running stability are the major concern of the process. In this study, tannin extracts obtained from valonia and black wattle and an industrial benchmark tannin extract designated as the LRSR's catalyst were investigated for their composition and the kinetics of sulfide oxidation. Industry samples of sulfur pastes from the LRSR processes were analyzed. The results demonstrate that the accumulation of impurities of tannin extracts along with byproducts of sulfide oxidation in scrubbing liquid prevents sulfur froth separation and affects the purity of sulfur. The pretreatment of sulfur pastes with nitric acid reduces the accumulation of the impurities and improves the purity of sulfur from 60% to 99%, leading to cleaner production of sulfur by the LRSR process.

Treatment of high-strength sulfate wastewater using an autotrophic biocathode in view of elemental sulfur recovery

Treatment of high-strength sulfate wastewaters is becoming a research issue not only for its optimal management but also for the possibility of recovering elemental sulfur. Moreover, sulfate-rich wastewater production is expected to grow due to the increased SO2 emission contained in flue gases which are treated by chemical absorption in water. Bioelectrochemical systems (BESs) are a promising alternative for sulfate reduction with a lack of electron donor, since hydrogen can be generated in situ from electricity. However, complete sulfate reduction leads to hydrogen sulfide as final sulfur compound. This work is the first to demonstrate that, in addition to an efficient sulfate-rich wastewater treatment, elemental sulfur could be recovered in a biocathode of a BES under oxygen limiting conditions. The key of the process is the biological oxidation of sulfide to elemental sulfur simultaneously to the sulfate reduction in the cathode using the oxygen produced in the anode that diffuses through the membrane. High sulfate reduction rates (up to 388 mg S-SO42− L−1 d−1) were observed linked to a low production of sulfide. Accumulation of elemental sulfur over graphite fibers of the biocathode was demonstrated by energy dispersive spectrometry, discarding the presence of metal sulfides. Microbial community analysis of the cathode biofilm demonstrated the presence of sulfate-reducing bacteria (mainly Desulfovibrio sp.) and sulfide-oxidizing bacteria (mainly Sulfuricurvum sp.). Hence, this biocathode allows simultaneous biological sulfate reduction and biological sulfide oxidation to elemental sulfur, opening up a novel process for recovering sulfur from sulfate-rich wastewaters.

Recovery of elemental sulphur from anaerobic effluents through the biological oxidation of sulphides

ABSTRACTThe aim of the present study was to evaluate the biological oxidation of sulphide in two different UASB reactors by assessing the occurrence of oxidized forms of sulphur in the effluents and the amount of S0 that could be recovered in the process. The bioreactors employed were an anaerobic hybrid (AH) reactor employing porous polyurethane foam as support media and a micro-aerated UASB reactor equipped with an aeration device above the digestion zone. The AH reactor produced a final effluent containing low concentrations of S2– (3.87% of total sulphur load). It was achieved due to a complete oxidation of 56.1% of total sulphur. The partial biological oxidation that occurred in the AH reactor allowed the recovery of 30% of the sulphur load as S0. The effluent from the micro-aerated UASB reactor contained 5% of the sulphur load in the form of S2–, while 20.9% was present as dissolved SO42– and 46% was precipitated as S0. It is concluded that the AH reactor or micro-aeration carried out above the digestion zone of the UASB reactor favoured the biological oxidation of S2– and the release of odourless effluents. Both technologies represent feasible and low-cost alternatives for the anaerobic treatment of domestic sewage.

Solution pH Manipulates Sulfur and Electricity Recovery From Aqueous Sulfide in an Air‐Cathode Fuel Cell

The air‐cathode fuel cell has great potential for simultaneous elemental sulfur (S0) and electricity recovery from aqueous sulfide. This work demonstrates the electrochemical oxidation of sulfide in the air‐cathode fuel cell can be manipulated by controlling solution pH. Below pH 7 the sulfide oxidation produces S0 as the main product, while in alkaline solution another product thiosulfate is formed together with S0. Elevating solution pH improves the fraction of sulfide converted to thiosulfate by moving the equilibrium shift from H2S(aq) to polysulfide. In addition, electron transfer from aqueous sulfide to the carbon electrode is facilitated at high pH values. However, the passivation of electrode surface by S0 deposition is aggravated at increased pH values, thus slowing down the electrochemical oxidation rate of sulfide. The operation of the air‐cathode fuel cell at pH 7 obtained the highest sulfur recovery efficiency of 71.3%, meanwhile the coulombic efficiency achieving as high as 55%.

Elemental sulfur recovery and spatial distribution of functional bacteria and expressed genes under different carbon/nitrate/sulfide loadings in up-flow anaerobic sludge blanket reactors

To characterize the impact of influent loading on elemental sulfur (S0) recovery during the denitrifying and sulfide oxidation process, three identical, lab-scale UASB reactors (30cm in length) were established in parallel under different influent acetate/nitrate/sulfide loadings, and the reactor performance and functional community structure were investigated. The highest S0 recovery was achieved at 77.9% when the acetate/nitrate/sulfide loading was set to 1.9/1.6/0.7kgd−1m−3. Under this condition, the genera Thauera, Sulfurimonas, and Azoarcus were predominant at 0–30, 0–10 and 20–30cm, respectively; meanwhile, the sqr gene was highly expressed at 0–30cm. However, as the influent loading was halved and doubled, S0 recovery was decreased to 27.9% and 45.1%, respectively. As the loading was halved, the bacterial distribution became heterogeneous, and certain autotrophic sulfide oxidation genera, such as Thiobacillus, dominated, especially at 20–30cm. As the loading doubled, the bacterial distribution was relatively homogeneous with Thauera and Azoarcus being predominant, and the nirK and sox genes were highly expressed. The study verified the importance of influent loading to regulate S0 recovery, which could be achieved as Thauera and Sulfurimonas dominated. An influent loading that was too low or too high gave rise to insufficient oxidation or over-oxidation of the sulfide and low S0 recovery performance.

Perspectives on Biological Treatment of Tannery Effluent

Leather processing is an important economic activity around the world and uncontrolled release of tannery effluents to natural water bodies causes environmental degradation and increases health risks to human beings. The treatment of tannery effluent is a complex technological challenge because of the presence of high concentrations of organic and inorganic pollutants of both conservative and non conservative nature. In this review paper information relevant to tannery effluents and its prospective on biological treatment processes and other recent potential biological processes are discussed. Emphasis is laid on the removal of organic matter (COD/BOD), NH4-N and sulphide/sulphate from tannery effluent. Though the aerobic process is efficient in treating tannery effluent, it requires an extended aeration time at low organic loading rates and thereby increasing the overall treatment cost. Anaerobic process is not effective because of sulphide inhibition problems. Sulphide inhibition control is essential for successful anaerobic treatment of tannery effluent. Sequencing Batch Reactor (SBR) and membrane reactor technologies are found to be effective for removal of organic matter and ammonia, but they are having very high operational cost. A recent development is the employment of alternate electron acceptor/donor already present in tannery effluent for simultaneous removals of COD/BOD, NH4-N and sulphide/sulphate with possibility of elemental sulphur recovery at higher organic loading rates. The recent development shows possibility of high rate treatment of tannery effluent in an alternate and an effective way suitable to both developing and developed countries.

Efficient regulation of elemental sulfur recovery through optimizing working height of upflow anaerobic sludge blanket reactor during denitrifying sulfide removal process

In this study, two lab-scale UASB reactors were established to testify S0 recovery efficiency, and one of which (M-UASB) was improved from the previous T-UASB by shortening reactor height once S2− over oxidation was observed. After the height was shortened from 60 to 30cm, S0 recovery rate was improved from 7.4% to 78.8%, and while, complete removal of acetate, nitrate and S2− was simultaneously maintained. Meanwhile, bacterial community distribution was homogenous throughout the reactor, with denitrifying sulfide oxidization bacteria predominant, such as Thauera and Azoarcus spp., indicating the optimized condition for S0 recovery. The effective control of working height/volume in reactors plays important roles for the efficient regulation of S0 recovery during DSR process.

Synthesis of high-purity precipitated calcium carbonate during the process of recovery of elemental sulphur from gypsum waste

We recently showed that the production of elemental sulphur and calcium carbonate (CaCO3) from gypsum waste by thermally reducing the waste into calcium sulphide (CaS) followed by its direct aqueous carbonation yielded low-grade carbonate products (i.e. <90mass% as CaCO3). In this study, we used the insight gained from our previous work and developed an indirect aqueous CaS carbonation process for the production of high-grade CaCO3 (i.e. >99mass% as CaCO3) or precipitated calcium carbonate (PCC). The process used an acid gas (H2S) to improve the aqueous dissolution of CaS, which is otherwise poorly soluble. The carbonate product was primarily calcite (99.5%) with traces of quartz (0.5%). Calcite was the only CaCO3 polymorph obtained; no vaterite or aragonite was detected. The product was made up of micron-size particles, which were further characterised by XRD, TGA, SEM, BET and true density. Results showed that about 0.37 ton of high-grade PCC can be produced from 1.0 ton of gypsum waste, and generates about 0.19 ton of residue, a reduction of 80% from original waste gypsum mass to mass of residue that needs to be discarded off. The use of gypsum waste as primary material in replacement of mined limestone for the production of PPC could alleviate waste disposal problems, along with converting significant volumes of waste materials into marketable commodities.

Microbial community structure and function in response to the shift of sulfide/nitrate loading ratio during the denitrifying sulfide removal process

Influence of acetate-C/NO3−-N/S2− ratio to the functional microbial community during the denitrifying sulfide removal process is poorly understood. Here, phylogenetic and functional bacterial community for elemental sulfur (S0) recovery and nitrate (NO3−) removal were investigated with the switched S2−/NO3− molar ratio ranged from 5/2 to 5/9. Optimized S2−/NO3− ratio was evaluated as 5/6, with the bacterial genera predominated with Thauera, Enterobacter, Thiobacillus and Stappia, and the sqr gene highly expressed. However, insufficient or high loading of acetate and NO3− resulted in the low S0 recovery, and also significantly modified the bacterial community and genetic activity. With S2−/NO3− ratio of 5/2, autotrophic S2− oxidization genera were dominated and NO3− reduction activity was low, confirmed by the low expressed nirK gene. In contrast, S2−/NO3− ratio switched to 5/8 and 5/9 introduced diverse heterotrophic nitrate reduction and S0 over oxidization genera in accompanied with the highly expressed nirK and sox genes.

Enhanced elementary sulfur recovery with sequential sulfate-reducing, denitrifying sulfide-oxidizing processes in a cylindrical-type anaerobic baffled reactor

Simultaneous removal of COD, SO42− and NO3− and recovery of elemental sulfur (S0) were evaluated in a four-compartment anaerobic baffled reactor (ABR) with separated functional units of sulfate reduction (SR) and denitrifying sulfide removal (DSR). Optimal SO42−-S/NO3−-N ratio was evaluated as 5:5, with a substantial improvement of S0 recovery maintained at 79.1%, one of the highest level ever reported; meanwhile, removal rates of COD, SO42− and NO3− were approached at 71.9%, 92.9% and 98.6%, respectively. Nitrate served as a key factor to control the shift of SR and DSR related populations, with the possible involvement of Thauera sp. during SR and Sulfurovum sp. or Acidiferrobacter sp. during DSR, respectively. DsrB and aprA genes were the most abundant during SR and DSR processes, respectively. Cylindrical-type ABR with the improved elemental sulfur recovery was recommended to deal with sulfate and nitrate-laden wastewater under the optimized SO42−/NO3− ratio.

Separation and enrichment of elemental sulfur and mercury from hydrometallurgical zinc residue using sodium sulfide

The separation and enrichment of mercury and the recovery of elemental sulfur from flotation sulfur concentrate in zinc pressure leaching process were carried out by sodium sulfide leaching and carbon dioxide precipitating. The results show that the leaching rate of elemental sulfur is more than 98%, and 98.13% of mercury is enriched in the residue, under the optimized conditions of sodium sulfide concentration 1.5 mol/L, liquid/solid ratio 6:1 and leaching time 30 min at room temperature. In addition, the content of mercury is enriched 5.23 times that in the leaching residue. The elemental sulfur is precipitated from leaching solution under conditions of carbon dioxide flow rate 200 mL/min and blowing time 150 min, while solution is stirred adequately. The recovery efficiency of elemental sulfur reaches 97.67%, and the purity of elemental sulfur is 99.75%, meeting the requirements of industrial first-rate product standard according to the national standard of GB/T 2449–2006 (PRC).

Recovery of elemental sulphur via selective catalytic reduction of SO2 over sulphided CoMo/γ-Al2O3 catalysts

This study aimed to develop sulphided CoMo/γ-Al2O3 catalysts to recover elemental sulphur via selective reduction and to understand the catalytic mechanism of the selective catalytic reduction (SCR) of SO2 into sulphur when CO is used as the reducing agent. A series of catalysts were prepared based on Taguchi’s L9 orthogonal array and were evaluated in terms of their SO2 conversion efficiency, selectivity of SO2 reduction to elemental sulphur, elemental sulphur yield, and selectivity of COS formation. It is found that the catalyst sulphided at 400°C with a ratio of Co/(Co+Mo)=0.31 and supported on γ-Al2O3 had the best performance among all the catalysts studied. In addition, the physical–chemical properties and catalytic activities of this catalyst were studied systematically. The mechanism of selective reduction of SO2 to elemental sulphur using CO as the reducing agent was therefore proposed.

Separation of elemental sulfur from zinc concentrate direct leaching residue by vacuum distillation

Properly disposal and reutilization of direct leaching residue (DLR) from metal production industries can reduce environmental pollution as well as better conserve resources. In this study, recovery of elemental sulfur from zinc concentrate DLR using vacuum distillation was thoroughly investigated. The results show that elemental sulfur recovery using vacuum distillation was over 98% with a high purity under optimized conditions. The low temperature requirement (200–300°C) of vacuum distillation may reduce the energy consumption comparing to traditional distillation under ambient pressure. Effects of parameters (distillation time, vacuum, temperature, particle size and distillation area) on sulfur recovery rate were presented. High sulfur recovery rate was observed with relative pressure lower than −0.09 megapascal (MPa). Sulfur recovery rate increased sharply with temperature in the range of 140–220°C, while temperature above 220°C only slightly promoted sulfur recovery. Smaller DLR particle size and larger distillation area facilitated mass and heat transportation, and resulted in higher sulfur recovery rates. The vacuum distillation separation technology reveals an alternative method to efficiently and economically separate elemental sulfur from zinc concentrate DLR. The impacts of operation parameters on the sulfur recovery rate were well documented in this study, and they are important for further optimizing the process and strategically applying the technology in a larger scale scenario.

Conversion of calcium sulphide to calcium carbonate during the process of recovery of elemental sulphur from gypsum waste

The production of elemental sulphur and calcium carbonate (CaCO3) from gypsum waste can be achieved by thermally reducing the waste into calcium sulphide (CaS), which is then subjected to a direct aqueous carbonation step for the generation of hydrogen sulphide (H2S) and CaCO3. H2S can subsequently be converted to elemental sulphur via the commercially available chemical catalytic Claus process. This study investigated the carbonation of CaS by examining both the solution chemistry of the process and the properties of the formed carbonated product. CaS was successfully converted into CaCO3; however, the reaction yielded low-grade carbonate products (i.e. <90mass% as CaCO3) which comprised a mixture of two CaCO3 polymorphs (calcite and vaterite), as well as trace minerals originating from the starting material. These products could replace the Sappi Enstra CaCO3 (69mass% CaCO3), a by-product from the paper industry which is used in many full-scale AMD neutralisation plants but is becoming insufficient. The insight gained is now also being used to develop and optimize an indirect aqueous CaS carbonation process for the production of high-grade CaCO3 (i.e. >99mass% as CaCO3) or precipitated calcium carbonate (PCC).