Adsorption of rhenium(VII) on 4-amino-1,2,4-triazole resin

The adsorption properties of 4-amino-1,2,4-triazole resin (4-ATR) for Re(VII) were investigated by static and dynamic adsorption–desorption measurements with ultraviolet–visible spectroscopy. The influence of conditions such as temperature, initial solution pH and contact time on the adsorption curve was studied. It was found that the 4-amino-1,2,4-triazole resin was suitable for adsorption of Re(VII). The saturated adsorption capacity was 354 mg·g^− 1resin at pH 2.6 in HAc–NaAc medium at 298 K. The adsorption rate constant was k₂₉₈ = 8.2 × 10^− 5 s^− 1. The adsorption behavior of 4-ATR for Re(VII) obeyed the Freundlich empirical equation; whilst changes in adsorption with temperature gave an enthalpy change ΔH  = − 11.8 kJ·mol^− 1. The molar ratio of the functional group of 4-ATR to Re(VII) was about 2:1. Re(VII) adsorbed on 4-ATR was eluted by 1.0 ~ 5.0 mol·L^− 1 HCl with 100% quantitative elution in 4.0 mol·L^− 1 HCl solution. The resin can be regenerated and reused without apparent decrease in adsorption capacity.     

Properties of electrolyte solutions relevant to high concentration chloride leaching. III. Solubility of pertinent solids and iron(III)/iron(II) redox potential measured in concentrated magnesium chloride solutions

Results of solubility measurements of nickel chloride, manganese chloride, iron(II) chloride, hematite and akaganeite in aqueous solutions of MgCl₂ (0.5–3.5 mol L^− 1) at temperatures of 60 and 90 °C are reported. Solubilities of metal(II) chlorides decrease almost linearly with MgCl₂ concentration due to the common ion effect. Nickel chloride and iron(II) chloride solubilities are very similar, while manganese chloride is about 30% more soluble.Hematite is more stable (i.e. less soluble) than akaganeite under all conditions investigated in this study, while ferrihydrite is considerably less stable. In other words, there is no change in the relative stabilities of these phases effected by the presence of high magnesium chloride concentrations. The solubility of all of these phases decreases with temperature and, for each temperature, the solubility constants increase linearly with the MgCl₂ concentration. The present results allow the prediction of the iron concentration as a function of the H⁺ and MgCl₂ molality at equilibrium with hematite or akaganeite.The Fe(III)/Fe(II) redox behaviour has been characterized in concentrated aqueous solutions of MgCl₂ (1.5–3.5 mol L^− 1) at a temperature of 25 °C. Standard redox potentials are ca. 100 mV lower than at infinite dilution and change linearly by only 13 mV in the range 2–4 mol L^− 1 MgCl₂.     

Palladium(II) complexes adsorption from the chloride solutions with macrocomponent addition using strongly basic anion exchange resins, type 1

The use of the strongly basic anion exchange resins, type 1 such as Lewatit MP-500 and Lewatit MP-500A for palladium(II) complexes adsorption has been investigated. The adsorption process was carried out from the chloride solutions with macrocomponent (sodium chloride) addition (x M HCl–1.0 M NaCl; x M HCl–2.0 M NaCl) where the concentration of hydrochloric acid was constant and equal to x = 0; 0.1; 0.5; 1.0; and 2.0 M, respectively. The breakthrough curves of Pd(II) were determined and the sorption parameters (weight and bed distribution coefficients, working anion exchange capacity) were calculated. The pseudo-second kinetic order was applied in kinetic studies as well as to calculate the kinetic parameters. The values of the working anion exchange capacities (0.029 g/cm³; 0.028 g/cm³) for Lewatit MP-500 and Lewatit MP-500A (0.028 g/cm³; 0.027 g/cm³) in the 1.0 M NaCl and 0.1 M HCl–1.0 M NaCl solutions, respectively are really close and in other solutions under discussion Lewatit MP-500 possess slightly higher values of capacities, and therefore is insignificantly more efficient in the adsorption process of palladium(II) ions than Lewatit MP-500A. The equilibrium adsorption capacities changed in the range 8.84–9.99 and 8.40–9.38 mg/g for Lewatit MP-500 as well as 8.12–9.57 and 7.26–8.85 mg/g for Lewatit MP-500A in the chloride x M HCl-1.0 M NaCl and x M HCl-2.0 M NaCl solutions, respectively. The adsorption process proceeds according to the pseudo-second kinetic order.     

Properties of electrolyte solutions relevant to high concentration chloride leaching. II. Density, viscosity and heat capacity of mixed aqueous solutions of magnesium chloride and nickel chloride measured to 90 °C

Results of density and viscosity measurements for aqueous solutions of MgCl₂ (0.5–3.5 mol L^− 1) and MgCl₂ + 10% NiCl₂ (0.5–3.5 mol L^− 1) at temperatures of 25, 60 and 90 °C show an almost linear increase in density with total concentration, while low nickel contents and temperature have comparatively small effects. Viscosities of MgCl₂ solutions rise sharply at 25 °C but are significantly lower at 90 °C. The viscosity of 3–4 mol kg^− 1 MgCl₂ at 90 °C is similar to water at 25 °C. Nickel has no significant effect on the viscosity of these solutions.Results of heat capacity measurements for aqueous solutions of MgCl₂ (0.5–3.5 mol L^− 1) and MgCl₂ + 10% NiCl₂ (0.5–3.5 mol L^− 1) at temperatures of 60 and 90 °C show that the heat capacities of these solution decrease significantly with total concentration, while the effects of low nickel contents and temperature are again comparatively small.     

Extraction of Fe(III) from hydrochloric acid solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921)

Ferric ions were efficiently removed from HCl solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921). Iron was removed under the form HFeCl₄ through direct binding on the resin or by extraction with Cyanex 921 involving a solvation mechanism. High concentrations of HCl and intermediary extractant loadings were required for maximum sorption efficiency and rationale use of the extractant. At intermediary extractant loading (in the range 300–450 mg Cyanex 921 g^− 1) the maximum sorption capacity increased with extractant loading. Maximum sorption capacity slightly increased with temperature, the reaction is endothermic and the enthalpy change was found close to − 30.8 kJ mol^− 1. Sorption isotherms were fitted with the Langmuir equation and maximum sorption capacity reached values as high as 20–22 mg Fe g^− 1 in 3 M HCl solutions. Despite the good fit of experimental data with the pseudo second-order rate equation, sorption kinetics was controlled by the resistance to intraparticle diffusion. The intraparticle diffusion coefficient (D_e) varying in the range 1.2 × 10^− 11–4.7 × 10^− 10 m² min^− 1 was found to increase with metal concentration and with temperature, while varying the extractant loading it reached a maximum at a loading close to 453 mg Cyanex 921 g^− 1. The desorption of Fe(III) can be achieved using 0.1 M solutions of nitric acid, sulfuric acid, sodium sulfate and even water, maintaining high efficiencies for sorption and desorption for at least 5 cycles.     

Effect of phosphate on lead removal during a copper recycling process from wastes using ammoniacal chloride solution

Techniques for the removal of lead have been studied in order to develop a hydrometallurgical copper recycling process consisting of copper leaching from wastes using an ammoniacal chloride solution and subsequent copper electrowinning. The solubility of Pb(II) in the ammoniacal chloride solution increased with ammonia concentration; this was attributable to the formation of a lead ammine complex. The lead dissolution was depressed from the order of 10^− 3 M to the order or 10^− 5 M by the addition of phosphate into the leaching solution because of the precipitation of chloropyromorphite (Pb₅(PO₄)₃Cl), while no significant effect was observed by the addition of carbonate. Linear sweep voltammetry and potentiostatic electrolysis in the solution containing Pb(II) revealed that lead was deposited during the copper electrowinning, even in the potential region more positive than the equilibrium redox potential for the Pb/Pb(II) couple on the lead electrode, because of the alloy formation with copper. In a galvanostatic electrolysis, however, the lead content at the electrodeposited copper cathode was found to be lower than 5 ppm at the current density range of 125–400 A/m², when the Pb(II) concentration in the electrolyte was 5 × 10^− 5 M. Since this Pb(II) concentration was achieved by the phosphate addition, these results indicated the effectiveness of phosphate for lead removal in the copper recycling process using the ammoniacal chloride solution.     

Adsorption behavior of rare earth elements using polyethyleneglycol (phosphomolybdate and tungstate) heteropolyacid sorbents in nitric solution

A new type of crystalline sorbent was prepared by the reaction of polyethyleneglycol (PEG) with phosphomolybdic (PMo) and phosphotungstic (PW) heteropolyacids. The morphology of the obtained sorbents was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It has been shown that a complexing reaction occurs between PEG and the heteropolyacids. By using these sorbents, the adsorption behaviors of rare earth elements in nitric solution were studied. The effects of temperature, contact time, nitric acid and initial metal ion concentration on the adsorption were investigated. In 0.1–5.0 mol L^− 1HNO₃, the adsorption percentage decreases with the increase of acid concentration. H,PEG400,PW and H,PEG400,PMo exhibited a different selectivity for rare earth metals, with H,PEG400,PW adsorbing in the order of La³⁺ > Y³⁺ > Pr³⁺ > Gd³⁺ > Sm³⁺, and H,PEG400,PMo in the order of Y³⁺ > La³⁺ > Pr³⁺ > Gd³⁺ > Sm³⁺. The experimental maximum adsorption capacities of the sorbents are in the range of 90–225 mg g^− 1 for Y³⁺, La³⁺, Pr³⁺, Sm³⁺ and Gd³⁺. In all cases, the maximum adsorption capacities of H,PEG400,PW are near to those of H,PEG400,PMo. The equilibrium data were evaluated according to the Freundlich and Langmuir isotherms and the Langmuir equation gave a better fit and modeled the adsorption well.     

Measurements of Enthalpy Change of Reaction of Formation, Molar Heat Capacity and Constant-Volume Combustion Energy of Solid Complex Yb（Et2dtc）3（phen）

A ternary solid complex Yb(Et2dtc)3(phen) was obtained from the reaction of hydrous ytterbium chloride with sodium diethyldithiocarbamate (NaEt2dtc), and 1, 10-phenanthroline (o-phen·H2O) in absolute ethanol.The bonding characteristics of the complex were characterized by IR.The result shows Yb3 bands with two sulfur atoms in the Na(Et2dtc)3 and two nitrogen atoms in the o-phen.The enthalpy change of liquid-phase reaction of formation of the complex ΔrHθm (l), was determined as being (-24.838±0.114) kJ·mol-1 at 298.15 K, by an RD-496 Ⅲ type heat conduction microcalormeter.The enthalpy change of the solid-phase reaction of formation of the complex ΔrHθm (s), was calculated as being (108.015±0.479) kJ·mol-1 on the basis of an appropriate thermochemistry cycle.The thermodynamics of liquid-phase reaction of formation of the complex was investigated by changing the temperature during the liquid-phase reaction.Fundamental parameters, the activation enthalpy, ΔHθ≠, the activation entropy, ΔSθ≠, the activation free energy, ΔGθ≠, the apparent reaction rate constant k, the apparent activation energy E, the pre-exponential constant A, and the reaction order n, were obtained by a combination of the reaction thermodynamic and kinetic equations with the data from the thermokinetic experiments.At the same time, the molar heat capacity of the complex cm, p, was determined to be (86.34±1.74) J·mol-1·K-1 by the same microcalormeter.The constant-volume combustion energy of the complex, ΔcU, was determined to be (-17954.08±8.11) kJ·mol-1 by an RBC-Ⅱ type rotating-bomb calorimeter at 298.15 K.Its standard enthalpy of combustion, ΔcHθm, and standard enthalpy of formation, ΔfHθm, were calculated to be (-17973.29±8.11) kJ·mol-1 and (-770.36±9.02) kJ·mol-1, respectively.     

Stability of 3CaO · Al2O3 · 6H2O in KOH + K2CO3 + H2O system for chromate production

In the novel clean chromate production process, the alkali liquor recycled to decompose the chromite ore mainly consists of KOH and K₂CO₃ which accumulates aluminium impurity and affects the quality of the product greatly. Aluminium impurity can be removed by adding CaO to precipitate as 3CaO · Al₂O₃ · 6H₂O (C₃AH₆). A study of the effects of various parameters, such as KOH concentration, K₂CO₃ concentration and temperature on the behaviour of C₃AH₆ show that C₃AH₆ is decomposed to 3CaO · Al₂O₃ · CaCO₃ · 11H₂O and CaCO₃ below 150 g L^− 1 KOH, and decomposed to Ca(OH)₂ above 150 g L^− 1 KOH. With K₂CO₃ concentration increasing, C₃AH₆ decomposes significantly, which results in more CaCO₃ or 3CaO · Al₂O₃ · CaCO₃ · 11H₂O produced. Temperature has a large positive effect on the decomposition of C₃AH₆ at 45 g L^− 1 KOH but has no significant effect at 150 g L^− 1 KOH. The optimal condition for removing aluminium impurity in the KOH + K₂CO₃ + H₂O system is 150 g L^− 1 KOH, 50 g L^− 1 K₂CO₃ and 80 °C.     

Study on microbial reduction of vanadium matallurgical waste water

The research employed microbial fuel cell (MFC) to domesticate dissimilatory metal reduction microorganisms, and to study the endurance to NaVO₃ of Rhodoferax ferrireducens (R.f). The effects of concentration of NaVO₃, pH, and temperature on the reduction of V⁺⁵ have also been observed. The maximum current output of the MFC is 0.318 mA when there is no vanadium compound in the MFC. While adding 300 mg/L NaVO₃ into the anode chamber, the current output reached 0.6 mA, the reduction ratio of NaVO₃ is 72%, and the total electron recovery of MFC is 64%. When the main operation parameters are as follows: 30 °C, 150 rpm stirring speed, pH 7.5, and vanadium wastewater with 300 mg/L NaVO₃, the reduction rate of V⁺⁵ is 75.8%, and bacteria density reached 1.1 × 10⁹ CFU/ml. The proper concentration of NaVO₃ in the wastewater promotes the formation of biofilm on the electrodes in MFC, and it also accelerates the rate of glucose conversion by the microbes.     

Synthesis and enhanced photoluminescence properties of red emitting divalent ion (Ca2+) doped Eu:Y2O3 nanophosphors for optoelectronic applications

This work presents the synthesis of Y₂O₃:Eu³⁺,xCa²⁺ (x = 0 mol%, 1 mol%, 3 mol%, 5 mol%, 7 mol%, 9 mol%, 11 mol%) nanophosphors with enhanced photoluminescence properties through a facile solution combustion method for optoelectronic, display, and lighting applications. The X-ray diffraction (XRD) patterns of the proposed nanophosphor reveal its structural properties and crystalline nature. The transmission electron microscope (TEM) results confirm the change in the shape of the particle and aggregation of particles after co-doping with Ca²⁺. Fourier transform infrared spectroscopy (FTIR) and Raman vibrations also confirm the presence of Y–O vibration and subsequently explain the crystalline nature, structural properties, and purity of the samples. All the synthesized nanophosphors samples emit intense red emission at 613 nm (⁵D₀→⁷F₂) under excitation with 235, 394 and 466 nm wavelengths of Eu³⁺ ions. The photoluminescence (PL) emission spectra excited with 235 nm illustrate the highest emission peak with two other emission peaks excited with 466 and 394 nm that is 1.4 times higher than 466 nm and 1.9 times enhanced by 394 nm wavelength, respectively. The emission intensity of Y₂O₃:Eu³⁺,xCa²⁺ (5 mol%) is increased 8-fold as compared to Eu:Y₂O₃. Doping with Ca²⁺ ions enhances the emission intensity of Eu:Y₂O₃ nanophosphors due to an increase in energy transfer in Ca²⁺→Eu³⁺ through asymmetry in the crystal field and by introduction of radiative defect centers through oxygen vacancies in the yttria matrix. It is also observed that the optical band gap and the lifetime of the ⁵D₀ level of Eu³⁺ ions in Y₂O₃:Eu³⁺,xCa²⁺ nanophosphor sample gets changed with a doping concentration of Ca²⁺ ions. Nanophosphor also reveals high thermal stability and quantum yield as estimating activation energy of 0.25 eV and 81%, respectively. CIE, CCT, and color purity values (>98%) show an improved red-emitting nanophosphor in the warm region of light, which makes this material superior with a specific potential application for UV-based white LEDs with security ink, display devices, and various other optoelectronics devices.     

Facile synthesis and highly efficient selective adsorption properties of Y2Mo4O15 for methylene blue: Kinetics,thermodynamics and mechanical analyses

Y_2 Mo_4 O_(15) particles were prepared using a simple solution method(SSM) and used as a highly efficient selective adsorbent for methylene blue(MB) in aqueous solutions. The maximum adsorption capacity of the samples was determined based on the adsorption isotherms with different adsorbent doses at 298,318 and 338 K. The fittings of the temperature-dependent isotherms yield ΔrG_m~θ =-34.1 kJ/mol,Δ_rH_m~θ=-36.9 kJ/mol and Δ_rS_m~θ=-9.67 J/mol·K. The as-prepared Y_2 Mo_4 O_(15) has a very large maximum adsorption capacity(i.e., 198 mg/g) for MB at room temperature, and this value is only less than that of amorphous hardwood powder. Notably, 80 mg of adsorbent is able to completely decolorize 250 mL of30 mg/L MB aqueous solution. The kinetic parameters of the adsorption process were obtained from the temperature-dependent adsorption isotherm(i.e., E_1=26.9 kJ/mol and E_1 = 63.8 kJ/mol). The results of adsorption kinetics show that it is a pseudo-second-order reaction. The mechanism of the high selectivity and the large adsorption capacity is discussed based on competitive ion(CI) experiments and coordination theory.     

Separation and recovery of palladium(II) from base metal ions by melamine–formaldehyde–thiourea (MFT) chelating resin

Melamine–formaldehyde–thiourea (MFT) resin, a chelating resin, was synthesized by reaction with melamine, formaldehyde and thiourea in aqueous solution. This chelating resin was used in the separation and recovery of palladium(II) from copper(II) and zinc(II) base metal ions. Effect of initial acidity, adsorption capacities of the metal ions by batch method and adsorption, elution, separation factors and column adsorption capacity of the metal ions by column method were examined. The optimum initial acidity was determined as pH 4. Adsorption capacities of the MFT resin were found as 15.29 mg/g (0.144 mmol/g) for palladium(II), as 1.612 mg/g (0.025 mmol/g) for copper(II) and as 0.453 mg/g (0.007 mmol/g) for zinc(II). In addition the protonation capacity of the resin was found as 0.110 mmol H⁺/g. It was concluded that ionic interaction between protonated amines on the resin and chloro-palladate complex (PdCl₄^2?) was very effective as well as chelation. In the column studies, dynamic adsorption capacities were calculated as 1580 μg/g (14.85 μmol/g) for palladium(II), as 250 μg/g (3.93 μmol/g) for copper(II) and as 25 μg/g (0.38 μmol/g) for zinc(II). MFT resin showed higher affinity to palladium(II) ions according to copper(II) and zinc(II) ions. It was seen that palladium(II) can be separated from copper(II) and zinc(II) and concentrated by melamine–formaldehyde–thiourea chelating resin.     

Kinetics of reductive leaching of manganese oxide ore with molasses in nitric acid solution

The kinetics of reductive leaching of manganese from a low grade manganese ore in dilute nitric acid in the presence of molasses is examined. The rate is controlled by diffusion through the “product” layer composed of the associated minerals. The leaching process follows the kinetic model 1 − 2/3X − (1 − X)^2/3 = kt with an apparent activation energy of 25.7 kJ/mole. It is concluded that the concentration of HNO₃ and molasses as well as temperature are the main factors influencing the leaching rate. The results indicate a reaction order of 1.2 for HNO₃ concentration and 1.9 for molasses concentration.     

Effects of Microalloying on Glass Forming Ability and Thermodynamic Fragility of Cu-Pr-Based Amorphous Alloys

The effects of microalloying of Ti and B on the glass formation of Cu60Pr30Ni10Al10-2xTixBx（x = 0, 0.05% （atom fraction）） amorphous alloys was investigated using differential scanning calorimetry （DSC） and X-ray diffraction （XRD）. XRD analysis showed that mieroalloying with 0.05% Ti and 0.05% B improved the glass forming ability （GFA）. The smaller difference in the Gibbs free energy between the liquid and crystalline states at the glass transition temperature （△G1-X（Tg）） and the smaller thermodynamic fragility index （△Sf/Tm, where ASf is the entropy of fusion, and Tm is the melting temperature） after mieroalloying correlated with the higher GFA.     

Properties of electrolyte solutions relevant to high concentration chloride leaching I. Mixed aqueous solutions of hydrochloric acid and magnesium chloride

A computer code based on a Pitzer model has been developed for the comprehensive prediction of the thermodynamic properties of MgCl₂–HCl aqueous solutions over a wide range of conditions from 25 to 120 °C and from 0–350 g L^− 1 chloride. This code was applied to the calculation of (i) water activities and mean ionic activity coefficients for mixed aqueous solutions of hydrochloric acid and magnesium chloride over a wide range of concentrations and to 100 °C, (ii) solubilities of MgCl₂·6H₂O in MgCl₂–HCl solutions to 80 °C, (iii) partial pressures of HCl(g) and H₂O(g) over MgCl₂–HCl aqueous solutions at various temperatures and (iv) partial pressures of HCl(g) at the normal boiling point of these mixed electrolyte solutions. The model predictions are in excellent agreement with available experimental data and confirm evidence from the literature that MgCl₂(aq) and HCl(aq) mix almost ideally at constant water activity.     

Study of extraction and purification of Ni, Co and Mn from spent battery material

In spent battery material, there are plenty of valuable metals, such as copper, nickel, cobalt, manganese. Recovery of valuable metals from spent battery material not only protects the environment but also improves the utilization of resources and decreases the cost of battery material. In this study, hydrochloric acid is used as lixivant with characteristics of faster leaching rate and being recycled easily. The optimal conditions are that hydrochloric acid concentration is 6 mol/L, reaction temperature is exactly 60 °C, liquid/solid ratio is 8:1, (H₂O₂)_mol/(MeS)_mol = 2, and the leaching time is 2 h, the results show that the dissolution yields of Ni, Co and Mn can be 95 wt.% at least. The basic purification concept of the leaching solution includes that copper is removed through replacement by iron powder followed by iron precipitation in goethite method. The results show that Cu and Fe can be removed 99 wt.% at the least. At the same time, the loss of Ni, Co and Mn is not beyond 2 wt.%, 3 wt.％ and 2 wt.%, respectively. This method makes the preparation of pure Ni_xCo_yMn_z ternary system precursor economical. The process seems to be able to claim base metals from waste in a reliable and feasible way.     

Arsenic removal from copper ores and concentrates through alkaline leaching in NaHS media

Removal of arsenic impurity in ores and concentrates containing copper (Cu) through alkaline leaching in NaHS media was investigated in this work. Samples containing Cu from 10 to 40 wt.% and arsenic from 0.8 to 14 wt.% with enargite (Cu₃AsS₄) as main arsenic bearing mineral were used as starting materials and all leaching tests were conducted at 80 °C under normal atmospheric pressure. Solution and/or slurry potential and pH were maintained consistently below − 500 mV (SHE) and above 12.5 respectively with the addition of NaHS and NaOH, creating a reducing environment for arsenic dissolution and conversion of Cu₃AsS₄ to Cu₂S. Pulp density ranged from 100 to 1000 g/L, NaHS and NaOH reagents were added at 50–200 g/L each and leaching time varied from 10 min to 10 h.Characterization of solid samples (original and leach residue) by XRD and XRF analyses and chemical analysis of both solid and solution samples by ICP analysis showed that Cu₃AsS₄ in the starting material was completely decomposed or transformed to Cu₂S and arsenic released into solution as As (III)/As³⁺ ions (Na₃AsS₃). Over 90% of arsenic in the starting materials was removed within 1–3 h for materials with arsenic content from 1 to 4 wt.% and within 3–6 h for materials with arsenic content over 4–10 wt.%. Dissolution and analysis of leach residues obtained after leaching by ICP indicated that arsenic in the starting materials has been reduced in all cases to below 0.5 wt.%. In all test conditions dissolution of Cu and Fe into solution was not detected, indicating selective leaching of arsenic. NaHS application for removal of arsenic in Cu-ores and/or concentrates was demonstrated in this work and further research is in progress to develop a process to include treatment of arsenic leached into solution.     

Selective adsorption of chromium(VI) from zinc(II) and other metal ions using persimmon waste gel

An adsorption gel was prepared from persimmon waste, a cellulosic material, rich in polyphenolic compounds, which exhibits a high affinity for chromium(VI). It was prepared by cross-linking persimmon waste with concentrated sulphuric acid. Adsorption tests for different metal ions such as Cr(VI), Cr(III), Fe(III), Zn(II), Cd(II) and Pb(II) from aqueous solution at pH values ranging from (pH 1 to 5) found Cr(VI) to be selectively adsorbed on the cross-linked gel over the other metal ions studied. The adsorption isotherm of Cr(VI) followed the Langmuir type of adsorption and exhibited a maximum loading capacity of 7.18 mol kg^− 1 at pH 1. Selective removal of Cr(VI) from Zn(II) was successfully demonstrated by using a column packed with the persimmon waste gel.     

Dissolution kinetics of spent petroleum catalyst using two different acidophiles

Leaching studies using spent petroleum catalyst containing Ni, V and Mo were carried out using two different acidophiles, iron oxidizing (IOB) and sulfur oxidizing (SOB) bacteria. XRD analysis proved the existence of V in oxide form, Ni in sulfide form, Mo both in oxide and sulfide forms, and sulfur in elemental state. Both bacteria showed similar leaching kinetics at the same leaching parameters, such as pH, nutrient concentration, pulp density, particle size and temperature. The dissolution kinetics for Ni and V was much higher than Mo. Bioleaching kinetics was observed to follow dual rates, initially faster followed by a slower rate. So, dissolution mechanism was based on surface- and pore-diffusion rate. The dissolution process was found to follow 1st order kinetics. Unified dissolution rate kinetics equations were developed using 1st order rate kinetics. Various thermodynamic parameters were also calculated. Rate determining step for both the bacteria were evaluated and the average D₁ (surface) and D₂ (pore) values were found to be around 7 × 10^− 9 and 1 × 10^− 10 cm² respectively. The lower value of D₂ suggested that the pore diffusion is the rate determining step during bioleaching process.