Synthesis of plant-based biogenic jarosite nanoparticles using Azadirachta indica and Eucalyptus gunni leaf extracts and its application in Fenton degradation of dicamba

Bio-jarosite,an iron mineral synthesized biologically using bacteria,is a substitute for iron catalysts in the Fenton oxidation of organic pollutants.Iron nanocatalysts have been widely used as Fenton catalysts because they have a larger surface area than ordinary catalysts,are highly recyclable,and can be treated efficiently.This study aimed to explore the catalytic properties of bio-jarosite iron nanoparticles syn-thesized with green methods using two distinct plant species:Azadirachta indica and Eucalyptus gunni.The focus was on the degradation of dicamba via Fenton oxidation.The synthesized nanoparticles exhibited different particle size,shape,surface area,and chemical composition characteristics.Both particles were effective in removing dicamba,with removal efficiencies of 96.8%for A.indica bio-jarosite iron nano-particles(ABFeNPs)and 93.0%for E.gunni bio-jarosite iron nanoparticles(EBFeNPs)within 120 min of treatment.Increasing the catalyst dosage by 0.1 g/L resulted in 7.6%and 43.0%increases in the dicamba removal efficiency for EBFeNPs and ABFeNPs with rate constants of 0.025 min^(-1) and 0.023 min^(-1),respectively,confrming their catalytic roles.Additionally,the high efficiency of both catalysts was demonstrated through five consecutive cycles of linear pseudo-first-order Fenton oxidation reactions.

Making waste profitable: Efficient recovery of metallic iron from jarosite residues

To address the hazardous by-product of zinc smelting and resource utilization of jarosite residue,this study applies an electric field-assisted hot acid treatment to completely recycle iron(Fe).This innovative approach aims to enhance the leaching efficiency of Fe from jarosite residue.The introduction of an electric field changes the charge distribution on the surface of the particles to enhance ions and electrons exchange and promotes the collision between particles to strengthen reaction kinetics.Based on the above,the leaching efficiency of Fe in jarosite under sulfuric acid attack has improved observably.The result shows that Fe leaching efficiency reaches 98.83%,which is increased by 28%under the optimal experimental conditions:current density of 30 mA·cm^(-2),H_(2)SO_(4) concentration of 1.5 mol·L^(-1),solid-liquid ratio of 70 g·L^(-1),temperature of 80℃ and time of 12 h.Leaching kinetics calculations show that the apparent activation energy is 16.97 kJ·mol^(-1) and the leaching of jarosite residue is controlled by a mixture of chemical reaction and diffusion,as well as the temperature and concentration of the leaching solution have an influence on leaching.This work provides a feasible idea for the efficient leaching of Fe from jarosite residue.

Catalytic performance of biological method seeds on jarosite process

The catalytic performance on jarosite process of jarosite seeds via biosynthesis and chemical processes were studied, respectively. The SEM and XRD results showed that biosynthetic jarosite seeds （BIO seeds） had smooth surface and mainly consisted of potassium jarosite. The chemical synthesis jarosite seeds （CHM seeds） had a loose cauliflower-like surface and mainly consisted of hydronium jarosite. The catalytic performance of BIO seeds was better than that of CHM seeds on the formation of final jarosite product. The induction time can be shortened to 20 min, the reaction temperature can be reduced to only 75 ℃, and the initial reaction speed was enhanced obviously, up to 3.933%/min. The crystallinity of final jarosite product using BIO seeds can achieve 97.22%, while it was only 12.89% without seeds. This indicates that the precipitation process of jarosite is more complete with BIO seeds.

Relationship and effect of redox potential,jarosites and extracellular polymeric substances in bioleaching chalcopyrite by acidithiobacillus ferrooxidans

The changes of pH,redox potential,concentrations of soluble iron ions and Cu^2＋ with the time of bioleaching chalcopyrite concentrates by acidithiobacillus ferrooxidans were investigated under the different conditions of initial total-iron amount as well as mole ratio of Fe（III） to Fe（II） in the solutions containing synthetic extracellular polymeric substances （EPS）.When the solution potential is lower than 650 mV （vs SHE）,the inhibition of jarosites to bioleaching chalcopyrite is not vital as EPS produced by bacteria can retard the contamination through flocculating jarosites even if concentration of Fe（III） ions is up to 20 g/L but increases with increasing the concentration of Fe（III） ions;jarosites formed by bio-oxidized Fe3＋ ions are more easy to adhere to outside surface of EPS space on chalcopyrite;the EPS layer with jarosites acts as a weak diffusion barrier to further rapidly create a high redox potential of more than 650 mV by bio-oxidizing Fe^2＋ ions inside and outside EPS space into Fe^3＋ ions,resulting in a rapid deterioration of ion diffusion performance of the EPS layer to inhibit bioleaching chalcopyrite severely and irreversibly.

Preparation of ammonium jarosite from clinker digestion solution of nickel oxide ore roasted using(NH_4 )_2SO_4

To obtain the appropriate conditions for eliminating Fe3＋from NiSO4 solution, the digestion solution of the clinker was used as raw material, which was obtained from roasting the nickel oxide ore with （NH4）2SO4. The ammonium jarosite was successfully synthesized from the solution with analytic grade NH4HCO3. The effects of reaction temperature, reaction time, end pH value of reaction on the removal rate of iron were investigated, and the effect of the initial concentration of Fe3＋was also discussed. All of those factors had significant effects on the removal rate of Fe3＋, among which the reaction temperature was the most prominent. The appropriate reaction conditions were concluded as follows： reaction temperature 95 ℃ reaction time 3.5 h, end pH value of reaction 2.5 at initial concentration of Fe3＋19.36 g/L. The physical aspect of （NH4）2Fe6（SO4）4（OH）12 was cluster figure composed of sheet or prismatic particles with smooth surface.

Thermodynamics of leaching roasted jarosite residue from zinc hydrometallurgy in NH_4Cl system

The thermal decomposition process ofjarosite residue and the solubility of various oxides presented in the decomposed residue in NH4C1-H20 system were studied. The results of heat decomposition ofjarosite residue show that the insoluble ZnFe2O4 phase in the residue can be decomposed at temperatures ranging from 500 ℃ to 650 ℃ for 1 h. The OLI Systems software was used to study the thermodynamics of the solubility of various metal oxides existing in the decomposed residue in NH4CI-H20 system. The results show that the solubility ofZnO, PbO, CdO, CuO and Ag20 is high, while the solubility of Fe203 is less than 10-4 mol/L in the pH range from 4.0 to 9.0. The calculated data are in accordance with the experimental results.

Formation of jarosite and its effect on important ions for Acidithiobacillus ferrooxidans bacteria

The precipitation of jarosite adversely affects the bio-leaching of copper sulfides in the Sarcheshmeh heap bio-leaching process. The variables of the initial concentration of ferrous iron in the growth medium, pH, and temperature were examined in the laboratory to determine how they affect the precipitation of jarosite in the presence of Acidithiobacillus ferrooxidans bacteria. It was found that the maximum ferric precipitate occurred at a ferrous sulfate concentration of 50 g/L, a temperature of 32 ℃, and an initial pH value of 2.2. The effects of the precipitation of ferric iron on the quantities of ions that are important for A. ferrooxidans bacteria in aqueous phase, i.e., ferric, sulfate, potassium, phosphate, and magnesium ions, also were assessed. The results showed relatively similar patterns for the ferric and potassium ions, and then reason might have been the co-precipitation of these ions as constituent elements of jarosite mineral. At pH values greater than 1.6, the solubility of phosphate ions decreased dramatically due to the co-precipitation of phosphate ions with the jarosite precipitate and due to the significant growth rate of A. ferrooxidans bacteria in this pH range. Due to the dissolution of a gangue constituent in the ore, the magnesium levels increased in the first few days of the bio-leaching process;thereafter, it decreased slightly.

Spontaneous separation of Pb from PbSO_(4)-coprecipitated jarosite using freeze-thaw cycling with thiourea

To separate Pb from PbSO_(4)-coprecipitated jarosite,a novel thiourea-induced freeze-thaw cycling(T-FTC)process was investigated.Results show that distributed PbSO_(4)particles are pressed and aggregated around the jarosite particles by T-FTC.Under the freezing-concentration effect of T-FTC,the reaction between PbSO_(4)and thiourea is also promoted,forming lead thiourea sulfate(Pb-tu).As the cycles of T-FTC increase,PbSO_(4)around jarosite disappears for the reaction of forming Pb-tu.After 12 cycles of T-FTC,a spontaneous separation is observed between Pb-tu and jarosite,i.e.,Pb-tu is separated into the upper layer while jarosite-rich phases remain in the lower layer.Due to this spontaneous separation,leaching toxicity of the jarosite coprecipitates is reduced by 73.7%.These results suggest that T-FTC process can achieve the separation of Pb from PbSO_(4)-coprecipitated jarosite and is a promising approach for removing and recovering metals from iron-rich jarosite residues.

Comprehensive recovery of lead, zinc, and iron from hazardous jarosite residues using direct reduction followed by magnetic separation

Lead, zinc, and iron were recovered from jarosite residues using direct reduction followed by magnetic separation. The influence of the coal dosage, reduction temperature, and reduction time on the volatilization rates of lead and zinc and the metallization rate of iron were investigated. The results show that the volatilization rates of lead and zinc were 96.97% and 99.89%, respectively, and the iron metallization rate was 91.97% under the optimal reduction roasting conditions of a coal dosage of 25.0 wt% and reduction roasting at 1250°C for 60 min. The magnetic concentrate with an iron content of 90.59 wt% and an iron recovery rate of 50.87% was obtained under the optimum conditions in which 96.56% of the reduction product particles were smaller than 37 μm and the magnetic field strength was 24 k A/m. Therefore, the results of this study demonstrate that recovering valuable metals such as lead, zinc, and iron from jarosite residues is feasible using the developed approach.

Preparation of jarosite by Acidithiobacillus ferrooxidans oxidation

The formation ofjarosite in the presence of Acidithiobacillusferrooxidans （A. ferrooxidans） was researched to ascertain the conditions of producing minimum precipitation. The effects of salt concentration and pH on the characteristics ofjarosite formed in K2SO4/（NHa）2SOa-FeSO4 inorganic salt solution and 9K medium were studied by using the measurements of scanning electron microscope, X-ray diffraction, Fourierism transform infrared analysis, thermogravity/differential thermogravity analysis and particle size analysis to evaluate the product. The results indicate that the formation of jarosite begins when A. ferrooxidans reaches logarithmic growth phase in 9K medium, and a higher pH value is beneficial to the formation of jarosite. The jarosite formed in 9K medium has smaller and more concentrative particle size and smoother surface than that formed in inorganic salt solution.

Mars exploration——In situ K-Ar dating of jarosite

To accurately determine the chronological framework of climatic variations recorded by various Martian terrains, the absolute ages of Martian events and cratering rate need to be constrained by either in situ dating or returned samples. In situ K-Ar dating is currently a more plausible dating technique as compared with sample return. Jarosite(KFe_(3)[SO_(4)]_(2)[OH]_(6)) is the only confirmed K sulfate mineral that is widely present on Mars, as indicated by in situ detection, orbital remote sensing, and meteorite studies. Jarosite can be used for precise K-Ar and (40)Ar/(39)Ar dating. The preservation of jarosite on Mars provides information about the nature and duration of aqueous processes on the Martian surface. Different ages of Martian jarosite represent the key to constraining the transition from Martian surface water activity to arid climatic conditions. This paper summarizes recent advances in our knowledge of the spatial distribution of Martian jarosite, its mineralogical properties and stability on Mars, the Ar diffusion kinetics of jarosite, and the current status of in situ K-Ar dating. Moreover, we examine the key scientific issues to be addressed for in situ K-Ar dating of jarosite and Martian sample return missions, and discuss future research directions.

Charge transfer between biogenic jarosite derived Fe^3＋ and TiO2 enhances visible light photocatalytic activity of TiO2

In this work, we have shown that mining waste derived Fe^3＋can be used to enhance the photocatalytic activity of TiO2. This will allow us to harness a waste product from the mines, and utilize it to enhance TiO2 photocatalytic waste water treatment efficiency. An organic linker mediated route was utilized to create a composite of TiO2 and biogenic jarosite. Evidence of Fe／O／Ti bonding in the TiO2/jarosite composite was apparent from the FTIR, EFTEM, EELS and ELNEFS analysis. The as prepared material showed enhanced photocatalytic activity compared to pristine TiO2, biogenic jarosite and mechanically mixed sample of jarosite and TiO2 under both simulated and natural solar irradiation. The prepared material can reduce the electrical energy consumption by 4 times compared to pristine P25 for degradation of organic pollutant in water. The material also showed good recyclability. Results obtained from sedimentation experiments showed that the larger sized jarosite material provided the surface to TiO2 nanoparticles, which increases the settling rate of the materials. This allowed simple and efficient recovery of the catalyst from the reaction system after completion of photocatalysis. Enhanced photocatalytic activity of the composite material was due to effective charge transfer between TiO2 and jarosite derived Fe^3＋as was shown from the EELS and ELNEFS. Generation of OHU was supported by photoluminesence（PL） experiments.

Control method of chalcopyrite passivation in bioleaching

Passivation is a common phenomenon on the surface of chalcopyrite in the process of bioleaching. The ordinary leaching and strengthening leaching by adding glass beads were carried out. The results show that the passivation of chalcopyrite was greatly weakened in strengthening leaching due to the change of leaching conditions. The copper leaching efficiency was increased from 50% to 89.8% through adding beads. The SEM and X-ray diffraction （XRD） analyses illustrate that there are few jarosite precipitates and weak passivation on the surface of chalcopyrite in strengthening leaching. In contrast, there are thick and compact jarosite precipitate and obvious passivation in ordinary leaching, which hinders further dissolution of chalcopyrite.

Bioleaching and electrochemical property of marmatite by Sulfobacillus thermosulfidooxidans

Bioleaching and electrochemical experiments were conducted to evaluate marmatite dissolution in the presence of pure S.thermosulfidooxidans.The effects of particle size,p H controlling and external addition of Fe^3＋ ions on the zinc extraction were investigated.The results show that in the bioleaching process the best particle size range is 0.043-0.074 mm and adjusting p H regularly to the initial value has a profound effect on obtaining high leaching rate.External addition of Fe^3＋ ions could accelerate the bioleaching,while the concentration of additional Fe^3＋ over 2.5 g/L weakens the positive effect,and even hinders the dissolution of marmatite.SEM and XRD analyses of the leaching residues reveal that a product layer composed of elemental sulfur and jarosite is formed on the mineral surface,which results in a low leaching speed at later phase.The results of electrochemical measurements illustrate that additional Fe^3＋ ions could increase the corrosion current density,which is favorable to zinc extraction.The EIS spectra show that rate-limiting step does not change when Fe^3＋ ions are added.

Transformation of iron in pure culture process of extremely acidophilic microorganisms

Jarosite and extracellular polymer substance generated during pure culture and bioleaching process have been widely accepted the main transformation of decreasing iron in the medium.In the present work,acidophilus bioleaching organisms Ferroplasma thermophilum,Leptospirillum ferriphilum and Acidithioobacillus ferrooxidans were cultured.It was found that they can live in low pH environment,and more than10particles in each cell intracellular nano-particles are synthesized in the cells.By analyzing the morphology and chemical composition of nano-particles,they were found to contain iron,and the three microorganisms belonged to high-yielding strains.The results show that the transformation of the decreasing iron ions is not only generating jarosite,but also taken into cells and synthesizing ferruginous nano-particles.

Bioleaching of pyrrhotite by Sulfobacillus thermosulfidooxidans

The bioleaching of pyrrhotite was investigated using Sulfobacillus thermosulfidooxidans.The effects of pH,pulp concentration,inoculation amount,external addition of ferrous and ferric ions were examined.The pH is found to exert a profound effect on the leaching process for controlling the bacterial activity and precipitation of ferric ions mainly as jarosite.The results show that low pulp content increases the leaching rate of iron.The inoculation amount from 1×107 cell/mL to 1×108 cell/mL has positive effects on the leaching rate.The results also imply that addition of ferrous sulfate(1 g/L) is required for the bacteria to efficiently drive the extraction of iron,however,the leaching efficiency has no obvious enhancement when 2 g/L ferrous sulfate was added.Comparatively,addition of ferric sulfate(2 g/L) significantly inhibits the bioleaching process.At the end of bioleaching,jarosite and sulfur are observed on the surface of pyrrhotite residues by using XRD and SEM.With the passivation film formed by jarosite and sulfur,the continuous iron extraction is effectively blocked.

Bioleaching of chalcopyrite by Leptospirillum ferriphilum

Chalcopyrite oxidation rates were examined under various conditions in the presence of Leptospirillum ferriphilum,in which the effects of different pulp content,inoculation amount,external addition of Fe3+ and initial pH value were studied.The bioleaching residues were investigated by X-ray diffractograms(XRD),scanning electron microscopy(SEM) and energy dispersion spectrum(EDS) analysis.The results show that low pulp concentration increases the leaching rate of copper,and external addition of Fe3+ is also beneficial to leaching chalcopyrite.The changes of inoculation amount and initial pH from 1.6 to 2.5 have a little effect on the final leaching rate.The results also imply that Fe3+ ions are important for bioleaching of chalcopyrite.At the end of bioleaching,jarosite and sulfur are observed on the surface of chalcopyrite residues by using XRD,SEM and EDS.With the passivation layer formed by jarosite and sulfur,the continuous copper extraction is effectively blocked.

Synthesis of Ni-Zn ferrite and its microstructure and magnetic properties

Nanometer Ni0.5Zn0.5Fe2O4 powders with spinel phase were prepared by the hydrothermal method using purified FeSO4 solution from sodium jarosite＇s slag as materials. The results show that the spinel phase of Ni0.5Zn0.5Fe2O4 powders begins to form at a relatively low temperature （130 ℃） and a shorter holding time （1 h） when pH=8. The crystallization kinetics equation at 200℃ is ln[-ln（1-x）] =-0.78＋0.951n t. The growth activation energy of Ni0.5Zn0.5Fe2O4 grains is 41.6 kJ/moL in hydrothermal synthesis process. With the increase of sintering temperature, the density and diameter shrinkage of ferrite circulus increase, whereas its pores decrease. The results of magnetic measurements show that saturation magnetic flux density Bs increases and the coercivity Hc decreases with the increase of their sintering temperature. Magnetic parameters of all the investigated samples satisfy the character demand of high Bs, low Br and low Hc of soft magnetic ferrite materials.

Leaching of nickel laterite ore assisted by microwave technique

The application of microwave technique in the hydrometallurgy of nickel laterite ores was described.The mixture of nickel laterite ores and sulfuric acid was pre-treated by microwave irradiation.The dissolving of nickel was conducted in hot water at the atmospheric pressure.The effects of factors,such as microwave power,microwave irradiation time,and sulfuric acid dosage, were investigated.In microwave field,the migration of ionic species and/or rotation of dipolar species promote the liquid?solid reaction process due to the increased contact area of reactants and leaching reaction rate constant.Thanks to the strengthening action of microwave,the microwave-assisted leaching process has its advantages,such as higher extracting rate than conventional atmospheric leaching,and no need for high-pressure operation as high pressure acid leaching(HPAL).The ferric iron in leaching solution could be effectively removed by sodium jarosite process with a little loss of nickel in the jarosite precipitate.