Initial Sulfate Concentration Research Articles

Strength and self-desiccation of slag-cemented paste backfill at early ages: Link to initial sulphate concentration

This paper presents the results of an experimental study on the early age strength and changes in the self-desiccation process of cemented paste backfill (CPB) that contains blast furnace Slag (Slag-CPB) and sulphate. Slag-CPB samples with different initial sulphate concentrations (0, 5000, 15,000 and 25,000 ppm) are prepared and cured in well-sealed molds at early ages (1, 3, 7 and 28 days) in room temperature (∼23 °C). Mechanical and hydraulic conductivity tests are performed on the samples, in which the suction and electrical conductivity of the Slag-CPB specimens are monitored. Furthermore, microstructural analyses are conducted on the Slag-CPB and slag-cement paste samples. The results show that sulphate can have a positive or negative effect on the early age strength and self-desiccation of Slag-CPB, i.e., cause an increase or decrease in strength and acceleration or reduction in the amount and rate of self-desiccation, depending on the initial sulphate content and curing time. This study also shows that an understanding of the positive or negative effect of sulphate on the early strength and self-desiccation of Slag-CPB is critical for designing cost-effective CPB structures with high early strength, speeding up mining cycles or assessing the deterioration of CPB caused by high sulphate attack to ensure safety in mining.

Sulfur removal from model fuel by Zn impregnated retorted shale and with assistance of design of experiments.

There is global concern about acid rain and other pollution which is caused by the consumption of oil. By decreasing sulfur content in the oil, we can reduce unwanted emissions and acid rain. Shale was usedwhich is a solid waste generated in the pyrolysis of shale, impregnated with Zn as an adsorbent which removes sulfur present in fuels from the hexane/toluene model solution. An influence of the agitation time (60-180min), temperature (25-35°C), adsorbent mass (0.1-0.25g), and initial sulfur concentration (100-250ppm) factorial 24 with three central points totaling 19 experiments was applied to investigate the effect of the variables on the efficiency of sulfur removal in fuels. The values of the parameters tested for maximum sulfur removal were obtained as follows: contact time = 180min, temperature = 35°C, adsorbent mass = 0.25g, and initial sulfur concentration = 100ppm. The mathematical model proposed with R2 99.97% satisfied the experimental data. This may provide a theoretical basis for new research and alternative uses for tailings of schist industrialization in order to evaluate its potential.

Top-down freezing in a Fe–FeS core and Ganymede’s present-day magnetic field

Ganymede’s core most likely possesses an active dynamo today, which produces a magnetic field at the surface of ∼ 719 nT. Thermochemical convection triggered by cooling of the core is a feasible power source for the dynamo. Experiments of different research groups indicate low pressure gradients of the melting temperatures for Fe–FeS core alloys at pressures prevailing in Ganymede’s core ( < 10 GPa). This may entail that the core crystallizes from the top instead of from the bottom as is expected for Earth’s core. Depending on the core sulfur concentration being more iron- or more sulfur-rich than the eutectic concentration either snowing iron crystals or a solid FeS layer can form at the top of the core. We investigate whether these two core crystallization scenarios are capable of explaining Ganymede’s present magnetic activity. To do so, we set up a parametrized one-dimensional thermal evolution model. We explore a wide range of parameters by running a large set of Monte Carlo simulations. Both freezing scenarios can explain Ganymede’s present-day magnetic field. Dynamos of iron snow models are rather young ( < 1 Gyr), whereas dynamos below the FeS layer can be both young and much older ( ∼ 3.8 Gyr). Successful models preferably contain less radiogenic heat sources in the mantle than the chondritic abundance and show a correlation between the reference viscosity in the mantle and the initial core sulfur concentration.

Bioleaching of indium from discarded liquid crystal displays

Abstract The present study is the first report on the bioleaching of indium (In) from discarded liquid crystal displays (LCDs) using adapted Acidithiobacillus thiooxidans. The adaptation of bacteria to the LCDs powder began with 1% (w/v) and continued up to 4% (w/v). Response surface methodology (RSM) was used to evaluate the effects of initial pH, pulp density, and initial sulfur concentration and optimize their values in order to maximize In and Sr recovery. Under optimum conditions of an initial pH of 2.6, pulp density of 1.6% (w/v) and initial sulfur concentration of 8.6 (g/l), 100% of In and 10% of Sr were recovered. The rate-controlling step in this process was determined using the shrinking core model, which suggests that both diffusion and chemical reaction play an important role in the overall bioleaching process. Scanning electron microscopy (SEM) analysis demonstrated the effectiveness of bacterial activity in bioleaching. In addition, the results confirmed that bioleaching was more effective than chemical leaching. The bioleaching from discarded LCDs by A. thiooxidans is a promising technology that can decrease the environmental hazard of this waste. The bioleaching results of present study supplied a method for large-scale industrial purposes.

Precipitation of silica from zinc process solution

Precipitation of silica in concentrated sulfuric acid solutions was studied with laboratory-scale batch experiments. The effects of initial silicic acid concentration, temperature, and sulfuric acid concentration were studied. It was observed also in this work that the high ionic strength of the leaching solution drastically decreased the solubility of silica. The solubility was also studied using Gibbs energy minimization method and Pitzer model using the ChemSheet program. Good agreement was obtained between the model and experimental results. The precipitation reaction of silica was observed to follow a pseudo-first-order rate law. Based on the rate law used, an activation energy of 61.7 kJ mol−1 was estimated. This implies a reaction-controlled mechanism of precipitation.

Iron snow in the Martian core?

The decline of Mars' global magnetic field some 3.8–4.1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core. The dynamo was probably powered by planetary cooling and so its termination is intimately tied to the thermochemical evolution and present-day physical state of the Martian core. Bottom-up growth of a solid inner core, the crystallization regime for Earth's core, has been found to produce a long-lived dynamo leading to the suggestion that the Martian core remains entirely liquid to this day. Motivated by the experimentally-determined increase in the Fe–S liquidus temperature with decreasing pressure at Martian core conditions, we investigate whether Mars' core could crystallize from the top down. We focus on the “iron snow” regime, where newly-formed solid consists of pure Fe and is therefore heavier than the liquid. We derive global energy and entropy equations that describe the long-timescale thermal and magnetic history of the core from a general theory for two-phase, two-component liquid mixtures, assuming that the snow zone is in phase equilibrium and that all solid falls out of the layer and remelts at each timestep. Formation of snow zones occurs for a wide range of interior and thermal properties and depends critically on the initial sulfur concentration, ξ0. Release of gravitational energy and latent heat during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies at least 400 km of the core. Snow zones can be 1.5–2 Gyrs old, though thermal stratification of the uppermost core, not included in our model, likely delays onset. Models that match the available magnetic and geodetic constraints have ξ0≈10% and snow zones that occupy approximately the top 100 km of the present-day Martian core.

Operando Spectromicroscopy of Sulfur Species in Lithium-Sulfur Batteries

In this study, a novel cross-sectional battery cell was developed to characterize lithium-sulfur batteries using X-ray spectromicroscopy. Chemically sensitive X-ray maps were collected operando at energies relevant to the expected sulfur species and were used to correlate changes in sulfur species with electrochemistry. Significant changes in the sulfur/carbon composite electrode were observed from cycle to cycle including rearrangement of the elemental sulfur matrix and PEO10LiTFSI binder. Polysulfide concentration and area of spatial diffusion increased with cycling, indicating that some polysulfide dissolution is irreversible, leading to polysulfide shuttle. Fitting of the maps using standard sulfur and polysulfide XANES spectra indicated that upon subsequent discharge/charge cycles, the initial sulfur concentration was not fully recovered; polysulfides and lithium sulfide remained at the cathodes with higher order polysulfides as the primary species in the region of interest. Quantification of the polysulfide concentration across the electrolyte and electrode interfaces shows that the polysulfide concentration before the first discharge and after the third charge is constant within the electrolyte, but while cycling, a significant increase in polysulfides and a gradient toward the lithium metal anode forms. This chemically and spatially sensitive characterization and analysis provides a foundation for further operando spectromicroscopy of lithium-sulfur batteries.

Accurate prediction of liquid phase equilibrium adsorption of sulfur compound

This work highlights the application of two types of artificial neural networks namely PSO-RBF and CSA-LSSVM for prediction of equilibrium adsorption of sulfur compound in liquid phase of hydrocarbon solution of isotherm batch systems. The precision and reliability of developed models were investigated by various graphical and statistical approaches. Initial sulfur concentration, utilized adsorbent weights, molecular weights and densities of solvent and solute, average size of adsorbent particle, Si/Al ratio of adsorbent and temperature were used as input parameters of models and the amount of adsorption was considered as the output. Results show that the predictions of CSA-LSSVM model are a little more precise and reliable compared to the outcomes of PSO-RBF model. The overall values of R2 and AARD% for CSA-LSSVM model were 0.9920 and 0.55 that show precision and robustness of the applied model.

Coexistence and competition of sulfate-reducing and methanogenic populations in an anaerobic hexadecane-degrading culture

BackgroundOver three-fifths of the world’s known crude oil cannot be recovered using state-of-the-art techniques, but microbial conversion of petroleum hydrocarbons trapped in oil reservoirs to methane is one promising path to increase the recovery of fossil fuels. The process requires cooperation between syntrophic bacteria and methanogenic archaea, which can be affected by sulfate-reducing prokaryotes (SRPs). However, the effects of sulfate on hydrocarbon degradation and methane production remain elusive, and the microbial communities involved are not well understood.ResultsIn this study, a methanogenic hexadecane-degrading enrichment culture was treated with six different concentrations of sulfate ranging from 0.5 to 25 mM. Methane production and maximum specific methane production rate gradually decreased to 44 and 56% with sulfate concentrations up to 25 mM, respectively. There was a significant positive linear correlation between the sulfate reduction/methane production ratio and initial sulfate concentration, which remained constant during the methane production phase. The apparent methanogenesis fractionation factor (αapp) gradually increased during the methane production phase in each treatment, the αapp for the treatments with lower sulfate (0.5–4 mM) eventually plateaued at ~1.047, but that for the treatment with 10–25 mM sulfate only reached ~1.029. The relative abundance levels of Smithella and Methanoculleus increased almost in parallel with the increasing sulfate concentrations. Furthermore, the predominant sulfate reducer communities shifted from Desulfobacteraceae in the low-sulfate cultures to Desulfomonile in the high-sulfate cultures.ConclusionThe distribution of hexadecane carbon between methane-producing and sulfate-reducing populations is dependent on the initial sulfate added, and not affected during the methane production period. There was a relative increase in hydrogenotrophic methanogenesis activity over time for all sulfate treatments, whereas the total activity was inhibited by sulfate addition. Both Smithella and Methanoculleus, the key alkane degraders and methane producers, can adapt to sulfate stress. Specifically, different SRP populations were stimulated at various sulfate concentrations. These results could help to evaluate interactions between sulfate-reducing and methanogenic populations during anaerobic hydrocarbon degradation in oil reservoirs.

Urease activity in an autotrophic bacteria Thiobacillus thiooxidans

Urease activity was found in the fermented liquid of Thiobacillus thiooxidans. It was found that initial concentration of sulfur and urea, and initial pH influenced urease activity in Thiobacillus thiooxidans, and the maximum urease activity was noted after 96h of fermentation with 24g/L initial concentration of sulfur and 0.1g/L of urea, and nature pH 5.82. The experiment found that urease activity showed a steady change which follow along with the growth of Thiobacillus thiooxidans. It shows a possibility to determine the Thiobacillus thiooxidans attached on the sulfide surface.

(Invited) Mechanistic Study of PEMFC Reversible Voltage Degradation through Experiment and Modeling

Fuel cell durability has been a research focus towards successful commercialization of hydrogen-powered fuel cell vehicles. Voltage degradation that defines cell durability must be understood to design the fuel cell system for automotive application and to mitigate voltage loss during cell operation. Voltage degradation is irreversible if it results from permanent damage of cell components. Reversible degradation is caused by certain contaminants that deactivate catalyst surface and can be recovered by contaminant removal. Previous studies indicate that adsorption of mobile anions such as sulfate generated by membrane chemical degradation causes reversible voltage degradation;1 and fixed anions like sulfonate group in the electrode ionomer side chain can also adsorb onto the platinum surface, thus reducing catalyst specific activity at dry operating conditions.2 The purpose of this work is two-fold: (1) to further identify reversible degradation mechanisms by design of experiments; and (2) to develop a mathematical model for assisting development of voltage recovery strategies. We have used a design of experiments (DoE) to quantify the effect of cathode Pt loading, membrane type (and thickness), and Cerium (Ce) level in membrane. A number of 53 cm2 cells were built using a membrane-electrode-assembly (MEA) made of different membranes, cathodes with various Pt loadings, and identical anodes with Pt/Gr-C catalyst. Other cell components were kept the same. A standardized test protocol which includes a voltage recovery procedure (at low V, low T, and over 100%RH) was employed. Cell polarization curves were measured before and during voltage recovery. Water was collected at cell outlet to calculate cell water balance and analyze anion species. Figure 1 compares the reversible voltage losses with different level of Ce used to mitigate membrane chemical degradation, showing a significantly higher reversible voltage loss for MEAs with unmitigated membrane, and nearly the same cell performance is achieved after voltage recovery. The fluoride release rate (FRR) corresponding to Ce level is greatly reduced with a mitigated membrane. However, the related reversible voltage loss does not decrease further as Ce level is doubled from current level, implying that a portion of reversible voltage loss should be due to fixed anion adsorption. The DoE results show clear difference in the reversible voltage loss between Ce-mitigated and non-mitigated cases, suggesting that the reversible voltage degradation could be de-convoluted into two parts: the membrane chemical-degradation-rate-dependent portion (i.e. sulfate adsorption) and the chemical-degradation-rate-independent portion (or the adsorption of sulfonate end group from electrode ionomer). We have developed a mathematical model to simulate the voltage recovery process considering that sulfate anion and sulfonate end group adsorption onto Pt surface takes place independently and hence effectively reduces the electrochemical active area (ECA). Sulfonate adsorption-desorption kinetics is derived from the most recent experimental study showing continuous decrease in specific activity when an electrode operates at dry conditions,2 which is strongly dependent on electrode potential and relative humidity (RH). The kinetics for sulfate anion adsorption-desorption is obtained by utilizing the published (bi)sulfate coverage on a Pt(1,1,1) electrode as a function of electrode potential and sulfate concentration in a solution of HClO4 and H2SO4 mixture,3 with one adjustable parameter to be determined by fitting to the measured reversible voltage loss with respect to recovery time. Sulfate anion transport is governed by the dilute-solution theory, or the Nernst-Planck equation. It is assumed that sulfate anion leaves the electrode only with liquid water during voltage recovery. Initial sulfate concentration and sulfate coverage are evaluated by the correlation of reversible voltage loss in terms of sulfate coverage obtained from experiments. The reduction in ECA due to sulfate and sulfonate adsorption onto the Pt surface has two effects on cell performance: one is the kinetic effect reflecting a lower specific activity; and the other relates to oxygen transport local to Pt/ionomer interface, which shows a higher impact on cell voltage with increasing current density. Figure 2 shows that the model agrees well with the measured recovered voltage loss during an 8-hour voltage recovery. As cell performance at high load is sensitive to the amount of Pt embedded in the carbon support particles, accurate catalyst morphology information is required for the model input. With further improvement, the model can be used to assist in developing voltage recovery strategies. References J. Zhang, B. A. Litteer, F. D. Coms, and R. Makharia, J. Electrochem. Soc., 160, F1067 (2013).S. Jomori, K. Komatsubara, N. Nonoyama, M. Kato, and T. Yoshida, J. Electrochem. Soc., 160, F1067 (2013).A. Kolica and A. Wieckowski, J. Phys. Chem. B, 105, 2588 (2001). Figure 1

Optimization of sulfate removal by sulfate reducing bacteria using response surface methodology and heavy metal removal in a sulfidogenic UASB reactor

Biological treatment using sulfate reducing bacteria (SRB) has been found out to have the potential for treatment of wastewaters containing sulfate and heavy metals. In the present study, in addition to the investigation of carbon source effect on the growth and sulfate removal, a statistical model using the design of experiments methodology has been developed to optimize the removal of sulfate by the obtained consortium from the anaerobic digested. All parameters were selected in three levels. Investigating the data collected from experiments using response surface methodology proved that the interactions between parameters were insignificant and could be neglected. The optimum removal conditions were achieved at pH of 7.19, initial sulfate concentration of 2153.15mg/L, COD (Chemical Oxygen Demand) to initial sulfate concentration ratio (COD/SO42−) of 2.72 and the COD related to ethanol to total COD ratio (CODethanol/CODtotal) of 1 which led to sulfate removal of 98%. In five different batch experiments done in UASB reactor, the optimum conditions were applied to evaluate SRB performance in real and synthetic wastewater treatment mostly in all experiments. The differences of experiments were in real or synthetic wastewater, having an extra stage of treatment by H2S, using organic wastewater as carbon source and presence of heavy metal in bacteria medium. The maximum obtained removal percentage for Zn and Ni were 99.996 and 96.87, respectively.

Adsorptive removal of sulfate from acid mine drainage by polypyrrole modified activated carbons: Effects of polypyrrole deposition protocols and activated carbon source

Polypyrrole modified activated carbon was used to remove sulfate from acid mine drainage water. The polypyrrole modified activated carbon created positively charged functionality that offered elevated sorption capacity for sulfate. The effects of the activated carbon type, approach of polymerization, preparation temperature, solvent, and concentration of oxidant solution over the sulfate adsorption capacity were studied at an array of initial sulfate concentrations. A hardwood based activated carbon was the more favorable activated carbon template, and this offered better sulfate removal than when using bituminous based activated carbon or oak wood activated carbon as the template. The hardwood-based activated carbon modified with polypyrrole removed 44.7 mg/g sulfate, and this was five times higher than for the pristine hardwood-based activated carbon. Various protocols for depositing the polypyrrole onto the activated carbon were investigated. When ferric chloride was used as an oxidant, the deposition protocol that achieved the most N+ atomic percent (3.35%) while also maintaining the least oxygen atomic percent (6.22%) offered the most favorable sulfate removal. For the rapid small scale column tests, when processing the AMD water, hardwood-based activated carbon modified with poly pyrrole exhibited 33 bed volume compared to the 5 bed volume of pristine activated carbons.

Removal of sulfate by fluidized bed crystallization process

This study investigated the behavior of sulfate removal and gypsum crystallization in an FBR with varying seed dosage, initial sulfate concentration and calcium to sulfate concentration ratio. The effect of recycling and use of silica carriers were also evaluated. A bench-scale glass fluidized-bed reactor (FBR) with gypsum seed crystals was used. Results showed that sulfate removal and gypsum crystallization increased with the tested parameters. Sulfate conversion increased from 70.29% to 77.69% and sulfate removal from 52.34% to 65.87% when seed dosage was increased from 4.0g/L to 11.0g/L. Similar trend was observed when the initial sulfate concentration was increased from 80mM to 160mM, sulfate conversion also increased from 75.05% to 85.40% and removal from 55.29% to 77.88%. When calcium to sulfate concentration ratio was increased from 1.0 to 2.0, sulfate conversion increased from 70.40% to 79.19% and removal increased from 49.45% to 65.08%. Product crystals and silica sand carriers were found to be as effective as fresh gypsum seed crystals, hence, the potential for economic recovery of sulfate.

Anaerobic Dechlorination of Tetrachlorobisphenol A in River Sediment and Associated Changes in Bacterial Communities

Tetrachlorobisphenol A (TCBPA) is a widely used flame retardant and a potential endocrine disruptor. We estimated the role of the microbial community in degradation of TCBPA in river sediment from the vicinity of an E-waste processing facility. The effects of different anaerobic conditions on degradation efficiency of TCBPA were investigated, and differences in bacterial communities among these conditions were analyzed by 16S ribosomal RNA (rRNA) gene sequencing. The most effective dechlorination of TCBPA occurred under methanogenic conditions followed by electron donor-enhanced conditions and sulfate-reducing conditions with initial sulfate concentrations of 1, 10, and 20 mM. The extent of TCBPA removal under these conditions mentioned above was 65, 44, 43, 23, and 23%, respectively. 16S rRNA gene sequence analysis indicated that five dominant genera in the phylum Chloroflexi and another five species of Bacteroidetes, Chlorobi, and Firmicutes in these five systems were largely involved in TCBPA dechlorination. The initial sample had a total relative abundance of autochtonous potential dechlorinating bacteria of 12%. After 160 days, these values increased to 29–43% under above conditions. Addition of TCBPA decreased bacterial diversity. Efficiency of TCBPA degradation depends on the abundance and metabolism of dechlorinating bacterial guilds. The effectiveness of dechlorinating microbes in degradation of TCBPA was reduced by high sulfate concentrations.

Electrocoagulation treatment of mine water from the deepest working European metal mine – Performance, isotherm and kinetic studies

Abstract Electrocoagulation was investigated for the removal of copper, silicon, manganese, aluminum, iron and zinc as well as sulfate from real mine water. Batch experiments with monopolar iron anode and stainless steel cathode as well as monopolar aluminum anode and stainless steel cathode were conducted separately to identify the best electrocoagulation conditions. The removal efficiency in mine water increased with increasing reaction time and increasing current density and the type of electrodes affected the metals and sulfate removal as could be shown by the adsorption isotherms. Copper and silicon were obeying a Langmuir isotherm with an iron anode, whereas they were following a Freundlich isotherm when an aluminum anode was applied. The aluminum electrode resulted in a higher Langmuir constant q max for all metals, while the iron electrode showed a better efficiency for removing the metals. This might be a result of the higher kinetic rate of iron compared to aluminum. Sulfate removal was better with aluminum electrodes resulting in removal rates of up to 41%, removing up to 5700 mg/L sulfate from the initial sulfate concentrations, whereas iron could only remove 3833 mg/L of sulfate from the real mine water. Furthermore, sulfate removal by aluminum electrode was faster compared to iron electrode.

A statistical experimental design to remove sulfate by crystallization in a fluidized-bed reactor

Abstract This study used crystallization in a fluidized-bed reactor as an alternative technology to the conventional chemical precipitation to remove sulfate. The Box-Behnken Design was used to study the effects and interactions of seed dosage of synthetic gypsum, initial sulfate concentration and molar ratio of calcium to sulfate on conversion and removal of sulfate. The optimum conditions of conversion and removal of sulfate were determined and used to treat the simulated acid mine drainage (AMD) wastewater. The effect of inorganic ions CO 3 2 − , NH 4 + and Al3+ on sulfate conversion was also investigated. Experimental results indicated that seed dosage, initial sulfate concentration and molar ratio of calcium to sulfate are all significant parameters in the sulfate removal by fluidized-bed crystallization. The optimal conditions of 4 g seed L−1, 119.7 mM of initial sulfate concentration and [ Ca 2 + ] / [ SO 4 2 − ] molar ratio of 1.48 resulted in sulfate conversion of 82% and sulfate removal of 67%. Conversion and removal of sulfate in the simulated AMD wastewater were 79 and 63%, respectively. When ammonium or aluminum was added to the synthetic sulfate wastewater, significant conversion of sulfate was achieved.

Green fuel through green route by using a task-specific and neutral phosphonium ionic liquid: A joint experimental and theoretical study

Extractive desulfurization (EDS) is one of the most important techniques for the removal of the sulfur compounds (present in liquid fuels), which are one of the main sources to produce air pollutions, for instance: SOx. Because of environmental considerations, the use of organic solvents is limited for this process. Ionic liquids have unique properties, which broaden the applications of these types of solvents for EDS. In continuation of our previous work on the application of task-specific and acidic phosphonium ionic liquids (PIL) for EDS, tri-n-butyl-(2-hydroxyethyl)phosphonium bromide ([TBHEP][Br]) was synthesized, then, the EDS performance of it, as a neutral PIL with alcoholic moiety, was studied in details. At first, the effect of various parameters, such as: the reaction time, temperature, the volume ratio of [TBHEP][Br]/fuel, the initial concentration of sulfur in the liquid fuel and the types of the sulfur compounds on the extraction efficiency were investigated. The obtained results of experimental investigations show that [TBHEP][Br] (with the values of the extraction efficiency about 56, 70 and 41% for benzothiophene (BT), dibenzothiophene (DBT) and dimethyldibenzothiophene (DMDBT), respectively) acts as a suitable extractant for removal of the sulfur compounds from liquid fuel. Also, the theoretical calculations demonstrate that hydrogen of alcohol, as well as alpha-hydrogens of the methylene groups, connecting to phosphonium, can provide interaction between dibenzothiophene and PIL in the extraction process. However, it is concluded that [TBHEP][Br] is more suitable extractant than our previous report, PIL with acetic acid tag for EDS of the liquid fuel, because of low corrosivity and price. So, the results of this work support the idea of rational design, synthesis and application of task-specific ionic liquids for the green EDS.

Efficient adsorption of thiophene from model fuel by pyrolysed rice husks: factors of influence

ABSTRACTRice husks pyrolysed at different temperatures in the range of 250–700°C were investigated as adsorbents for thiophene removal from a model fuel. The adsorption ability of the samples was evaluated under both static and dynamic conditions. It was found that pyrolysed rice husks without any pretreatment are a promising adsorbent for the removal of sulphur-containing molecules from the model fuel. Removal of 92% of the sulphur from the fuel was achieved. The adsorption capacity of the pyrolysed rice husks correlates with their textural and chemical characteristics which strongly depend on the pyrolysis temperature. The adsorption of thiophene is influenced by the initial sulphur concentration level, the fractional composition of the adsorbent, the temperature and the adsorbent/fuel volume ratio. The adsorption capacity of the pyrolysed rice husks is higher under static than under dynamic conditions.

Bioleaching and selective biorecovery of zinc from zinc metallurgical leach residues from the Três Marias zinc plant (Minas Gerais, Brazil)

BACKGROUND Gradual depletion of high-grade ores for heavy metals has encouraged industries to search for alternative methods to recover metals. Wastes generated from metallurgical industries can be used as a secondary resource as it contains high concentrations of metals. RESULTS The bioleaching kinetics and biorecovery of zinc from Zn-plant leach residues (ZLR), collected from a currently operating Zn-plant in Tres Marias (Minas Gerais, Brazil) were investigated using sulfuric acid producing Acidithiobacillus thiooxidans (A. thiooxidans). Response surface methodology (RSM) with full factorial central composite design (CCD) was applied to optimize Zn bioleaching by A. thiooxidans. The experiments were performed by varying the initial elemental sulfur concentration (5–30 g L−1), pulp density (5–50 g L−1) and initial pH (3.0–4.0 pH units). More than 75% of Zn was extracted from ZLR by A. thiooxidans under optimized conditions (sulfur concentration 25.1 g L−1, pulp density 21.5 g L−1 and initial pH 3.3). The leaching efficiencies of culture supernatant (biogenic sulfuric acid) and chemical sulfuric acid were compared to understand the leaching kinetics. The Zn leaching kinetics of ZLR followed the shrinking core diffusion model. Zn was selectively recovered from the Fe-rich acidic bioleachate by biogenic sulfide precipitation. Fe was first removed (more than 85% of total Fe in the leachate) by adjusting the initial pH to 5.0, followed by selective Zn biorecovery. CONCLUSIONS Zn (>95%) was selectively recovered from Fe-depleted ZLR by biogenic sulfides (with 1:1, Zn:biogenic sulfide mass ratio). Biohydrometallurgy can be a potential alternative resource recovery strategy for the selective recovery of Zn from ZLR. © 2016 Society of Chemical Industry