Extraction of titanium (IV) from acidic media by tri-n-butyl phosphate in kerosene

The extraction of titanium (IV) from sulfate, and nitrate solutions has been studied using tri-n-butyl phosphate (TBP) in kerosene. Extraction of titanium was affected by acid concentration over the range of 0.5–4 mol L^?1. The titanium distribution coefficient reached a minimum between 1 and 2 mol L^?1 acid for both sulfate and nitrate solutions. Third phase formation was observed in the extraction of titanium from acidic media at all condition tested. At the next stage, the stripping of titanium was studied using H₂SO₄, H₂SO₄ + H₂O₂ and Na₂CO₃. The kinetics of the stripping were very slow for H₂SO₄. The use of complex forming stripping agents (H₂SO₄ + H₂O₂) and Na₂CO₃ significantly improved the kinetics of stripping. About 98% recovery was achieved by extracting titanium from an aqueous nitrate solution using TBP and stripping with sodium carbonate.     

Multicolumn solid phase extraction with hybrid adsorbent and rapid determination of Au,Pd and Pt in geological samples by GF-AAS

A novel hybrid adsorbent (HA) composed of cellulose fiber, activated carbon, and anion exchange resin Dowex 1 × 8 was prepared for the preconcentration and separation of noble metals, namely, gold (Au), palladium (Pd) and platinum (Pt), in geological samples. The optimal experimental parameters, such as flow rate, sample volume and interfering ions, were investigated. The accuracy of the method was confirmed by added/found method for tap and sea water, and evaluated by analyzing certified reference materials with good agreement. Under the optimal experimental conditions, the detection limits (3σ criteria) of the developed technique were 0.008 ng mL⁻¹ (Au), 0.017 ng mL⁻¹ (Pd) and 0.014 ng mL⁻¹ (Pt) and the sample throughput reach to 30 samples every eight hours. Moreover, the adsorption capacity of HA for Au, Pd and Pt was determined to be 48.2, 35.9 and 29.8 mg g⁻¹, respectively.     

Study on separation of heavy rare earth elements by solvent extraction with organophosphorus acids and amine reagents

The present work describes a study of the separation of rare earth elements (REE) from heavy REE concentrate through solvent extraction. Seven extractants were investigated: three organophosphorus acids (DEHPA, IONQUEST^®801 and CYANEX^®272), a mixture of DEHPA/TOPO (neutral ester) and three amines (ALAMINE^®336, ALIQUAT^®336 and PRIMENE^®JM-T). The organophosphorus extractants were investigated in hydrochloric and sulphuric media whereas the amines performance was assessed in a sulphuric medium. The variables investigated were: concentration of the extractant agent, aqueous phase acidity, aqueous/organic volumetric ratio, contact time, stripping agent concentration (hydrochloric acid solution) and the selective stripping step. In the extraction step, the best separation factors for the adjacent elements were obtained with DEHPA and IONQUEST 801. For 1.0 mol L⁻¹ DEHPA in an initial acidity of 0.3 mol L⁻¹ H⁺, the separation factor was 2.5 Tb/Dy, 2.1 Dy/Ho, 1.9 Ho/Er, 2.0 Ho/Y and 1.1 Y/Er; for 1 mol L⁻¹ IONQUEST 801 in 0.3 mol L⁻¹ of H⁺ it was 2.7 Tb/Dy, 2.4 Dy/Ho, 2.1 Ho/Er, 2.1 Ho/Y e 1.5 Y/Er. The study concluded that for the extractants investigated, IONQUEST 801 is the most indicated for the separation of heavy REE because it has lower affinity with the REE compared to the affinity of DEPHA/REE, which makes the strip of the REE from Ionquest 801 easier than from DEHPA. Moreover, the number of stages necessary for the stripping of the REE from IONQUEST 801 is much lower than that observed when DEPHA is employed.     

Simultaneous determination of Au(III) and Cu(II) with 1-phenyl-1,2-propanedione-2-oximethiosemicarbazone (PPDOT) on solid phase

A new method for the simultaneous determination of copper and gold was developed by derivative spectrophotometry using a previous preconcentration on solid phase. The method is based on the formation of Cu(II)-PPDOT and Au(III)-PPDOT complexes that are extracted from aqueous solution in only 20 min on cationic exchange SP Sephadex C25. In this simultaneous determination, the second derivative and the zero crossing method were used. The copper and gold determinations were carried out at 278.0 nm and 282.0 nm, respectively. The determination range for both analytes was 1.6 × 10⁻⁸–141 × 10⁻⁸ mol L⁻¹. Good levels of repeatability (RSD) of 1.3% and 1.4% were observed for copper and gold, respectively. The method was applied successfully for the copper and gold determination in mineral residuals, minerals and natural water samples. The results were consistent with those provided by ICP-mass spectrometry.     

Selective and direct sorption of zirconium from acidic leach liquor of zircon concentrate by rice bran

A new method for extraction of zirconium from leach liquor of zircon concentrate is proposed. The procedure is based on the adsorption of Zr(IV) ions on rice bran. The sorption capacity of the biomass for zirconium is 50 mg g^?1. Adsorption equilibrium was achieved in less than 1 min and slightly affected by solution acidity. In the optimum conditions, the adsorption efficiencies of other associated metal ions such as Ti⁴⁺, Fe³⁺, Al³⁺, La³⁺, Ce³⁺ were significantly lower than Zr(IV) ion and this biomass is excellent sorbent for the selective uptake of zirconium from acidic aqueous solutions.     

A simple spectrophotometric method for determination of gold (III) in aqueous samples

A simple method for rapid determination of trace Au in natural water was presented by using UV–vis spectrophotometry after reaction of gold (III) with 3,3′, 5,5′-tetramethylbenzidine hydrochloride (TMBH) in acidic solution. Under the optimum conditions, in a concentration range of 100–2000 μg L^?1 of Au (III) a good linear calibration graph was obtained (r = 0.9969, n = 7). The percent relative standard deviation (RSD) for determination of 1000 μg L^?1 Au was 10% (n = 3) and limit of detection based on a signal-to-noise ratio (S/N) of 3 (3S_bl) was 50 μg L^?1. The proposed method has been successfully applied to the determination of gold spiked and real aqueous samples.     

Palladium(II) removal from chloride and chloride–nitrate solutions by chelating ion-exchangers containing N-donor atoms

The chelating ion-exchangers of functional iminodiacetate (Amberlite IRC-718), amidoxime (Duolite ES-346) and aminophosphonic (Duolite C-467) groups have been applied for Pd(II) removal from the model chloride (0.1–6.0 M HCl) and chloride–nitrate (0.1–0.9 M HCl and 0.9–0.1 M HNO₃ and 0.1–1.5 M HCl and 1.9–0.5 M HNO₃) solutions. The total ion-exchange capacities as well as recovery factors of Pd(II) were determined by the batch method. The influence of acid concentrations, phase contact time and macrocomponent addition (AlCl₃, CuCl₂, NiCl₂) was studied. The results show that the ion-exchangers of functional amidoxime and iminodiacetate groups can be widely recommended for Pd(II) ion removal from anodic slimes, and used up catalysts, as well as Pd(II) trace analysis due to their high selectivity.     

Solvent extraction of tetravalent hafnium from acidic chloride solutions using 2-ethyl hexyl phosphonic acid mono-2-ethyl hexyl ester (PC-88A)

Solvent extraction of Hf(IV) from acidic chloride solutions has been carried out with PC-88A as an extractant. Increase of acid concentration decreases the percentage extraction of metal indicating the ion exchange type mechanism. The plot of logD vs log[extractant], M is linear with slope 1.8 indicating the association of two moles of extractant with the extracted metal species. Plot of logD vs log[H⁺] gave a straight line with a negative slope of ∼2 indicating the exchange of two moles of hydrogen ions for every mole of Hf(IV). The effect of Cl⁻ ion concentration at constant concentration of [H⁺] did not show any change in D values. Addition of sodium salts enhanced the percentage extraction of metal and follows the order NaSCN > NaCl > NaNO₃ ∼ Na₂SO₄. Stripping of metal from the loaded organic (LO) with different acids indicated sulphuric acid as the best stripping agent. Regeneration and recycling capacity of PC-88A, temperature, extraction behavior of associated elements was studied.     

The removal of zinc from liquid streams by electroflotation

The removal of heavy metals from dilute aqueous solutions (in the range of 10⁻⁷–10⁻⁴ mol dm⁻³) is often not acceptable using classical methods, which do not achieve levels in accordance with environmental quality standards. Electroflotation has certain desirable characteristics, compared to dissolved and dispersed air flotation, particularly in regard to the small bubble size distribution of the process. The aim of this work was to develop an electroflotation (EF)/electrocoagulation (EC) cell to study this combined process and the influence of some relevant parameters/variables, such as collector concentration, tension and current density variation, on the removal of zinc from synthetic solutions containing 20 mg l⁻¹ of the metal. A platinum gore (5 mm) anode and stainless steel mesh cathode were used in the electroflotation cell. The work showed that it was possible to remove zinc by electroflotation, 96% removal being achieved using sodium dodecyl sulfate (SDS) as collector in the stoichiometric ratio 1:3, current density of around 8 mA/cm² and an inlet pH of about 7.0.     

Kinetics of saprolitic laterite leaching by sulphuric acid at atmospheric pressure

Mineralogical analyses of the saprolitic laterite material have been characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermal analysis, scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDAX). Results showed that the saprolitic laterite material consists mainly of nickel-substituted lizardite showing the pebble-like morphology and traces of magnetite and phlogopite. Leaching results showed that as much as 84.8% nickel could be leached under the experimental conditions of 10% (v/v) H₂SO₄, 90 °C reaction temperature, leached within 5 min, particle size d₅₀ = 25 μm, stirring at 500 rpm and liquid to solid ratio 3:1. The kinetics of nickel and magnesium leaching from the saprolitic laterite material have been investigated in a mechanically stirred reactor and the activation energies were determined to be 53.9 kJ mol^?1 for nickel and 59.4 kJ mol^?1 for magnesium respectively, which are characteristic for a chemical reaction controlled process. The similarity of the activation energies of nickel and magnesium leaching from the saprolitic laterite material by sulphuric acid means that nickel in lizardite is loosely bound within the octahedral layer and almost all of the nickel could be leached simultaneously with magnesium but without complete decomposition of the silicate structure.     

Solvent extraction separation and recovery of cobalt and nickel from sulphate medium using mixtures of TOPS 99 and TIBPS extractants

We report in this paper the solvent extraction separation of cobalt and nickel from synthetic sulphate solutions using TOPS 99 and TIBPS mixtures diluted in kerosene. The feed contains 1.061 g/L Co and 1.187 g/L Ni. Extraction experiments with synergistic mixture of extractants showed highest separation factor of 12,245 with 0.1 M TOPS 99 and 0.05 M TIBPS at pH 1.1. McCabe–Thiele plot for Co extraction with 0.1 M TOPS 99 and 0.05 M TIBPS extractants mixture indicated the necessity of three theoretical stages for >99% Co extraction at an aqueous to organic phase (A/O) ratio of 2. A three stage counter current extraction simulation test conducted at pH 1.1 with 0.1 M TOPS 99 and 0.05 M TIBPS mixture, confirmed Co extraction of 99.5% with Ni co-extraction of 0.02%. The results demonstrated that the addition of TIBPS–TOPS 99 acts as a synergist for Co extraction and antagonist for Ni.     

Ionic liquid-based modified cold-induced aggregation microextraction (M-CIAME) as a novel solvent extraction method for determination of gold in saline solutions

Modified-cold-induced aggregation microextraction (M-CIAME) was used for determination of gold in saline solutions. It is robust against the much higher concentration of salt (up to 40%). In this method sodium hexafluorophosphate (NaPF₆) was added to the sample solution containing Au-TMK complex and a very small amount of 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF₄]. Afterward the solution was cooled in an ice bath and a cloudy solution was formed. After centrifuging, the extractant phase was analyzed using a spectrophotometric detection method. Under the optimum conditions, the limit of detection (LOD) was 0.7 ng mL^?1 and the relative standard deviation (RSD) was 1.65% for 50 ng mL^?1 gold. The method was applied for the determination of trace amount of Au in mineral and seawater with satisfactory results.     

Adsorptive removal of arsenic from river waters using pisolite

This work presents the experimental results for arsenic removal from aqueous solutions using pisolite as a natural inorganic sorbent, a waste mineral product from Brazilian manganese ore mines. A pisolite sample was submitted to physical and chemical characterization; particle size analysis by screening, X-ray diffractometry, X-ray fluorescence, surface area determination by the Brunauer–Emmett–Teller (BET) method and atomic absorption spectrophotometry (AA) for the determination of the species concentration in the pisolite and in the aqueous solution samples from the experiments.Column and batch tests to contact pisolite and aqueous feed solutions were carried out for evaluation of the pisolite’s performance as a natural sorbent for arsenic removal. Experiments using activated pisolite and aqueous feed solutions prepared with Velhas River water were also performed. In the column system, 1.0 g of pisolite removed 1.41 mg of As (4.05% As extraction) from 630 ml of the aqueous feed solution and 1.0 g of activated pisolite extracted 3.51 mg of As (11.6% As extraction). Results for the batch tests with 100 ml of aqueous feed solution and 1.0 g of pisolite removed 1.29 mg of As (24.7% As extraction) and 1.0 g of activated pisolite extracted 3.17 mg (58.2% As extraction).     

Review of rate constants for thiosulphate leaching of gold from ores,concentrates and flat surfaces: Effect of host minerals and pH

A review of literature data for different types of sulphide concentrates and gold ores has been carried out to examine the impact of host minerals and pH upon gold leaching. Analysis of initial rate data over the first 30–60 min of gold leaching from sulphide concentrates or silicate ores over a range of ammonia, thiosulphate, and copper(II) concentrations, pH (9–10.5) and temperatures up to 70 °C shows the applicability of a shrinking sphere kinetic model with an apparent rate constant of the order k_ss = 10⁻⁶–10⁻³ s⁻¹. The dependence of apparent rate constant on pH and initial concentrations of copper(II) and thiosulphate is used to determine a rate constant k_Au(ρr)⁻¹ of the order 1.0 × 10⁻⁴–7.4 × 10⁻⁴ s⁻¹ for the leaching of gold over the temperature range 25–50 °C (ρ = molar density of gold, r = particle radius). These values are in reasonable agreement with rate constants based on electrochemical and chemical dissolution of flat gold surfaces: k_Au = 1.7 × 10⁻⁴–4.2 × 10⁻⁴ mol m⁻² s⁻¹ over the temperature range 25–30 °C. The discrepancies reflect differences in surface roughness, particle size and the effect of host minerals.     

Single and binary component sorption of the fission products Sr2+, Cs+ and Co2+ from aqueous solutions onto sulphate reducing bacteria

This study investigates the removal of the fission products Sr²⁺, Cs⁺ and Co²⁺ in single and binary metal solutions by a sulphate reducing bacteria (SRB) biomass. The effect of initial concentration and pH on the sorption kinetics of each metal was evaluated in single metal solutions. Binary component equilibrium sorption studies were performed to investigate the competitive binding behaviour of each metal in the presence of a secondary metal ion. Results obtained from single metal equilibrium sorption studies indicated that SRB have a higher binding capacity for Sr²⁺ (q_max = 416.7 mg g^?1), followed by Cs⁺ (q_max = 238.1 mg g^?1), and lastly Co²⁺ (q_max = 204.1 mg g^?1). Among the binary systems investigated, Co²⁺ uptake was the most sensitive, resulting in a 76% reduction of the sorption capacity (q_max) in the presence of Cs⁺. These findings are significant for future development of effective biological processes for radioactive waste management under realistic conditions.     

Simplified cloud point extraction-inductively coupled plasma mass spectrometry for the preconcentration/analysis of ultra-trace gold

A new cloud point extraction method for the preconcentration of ultra-trace gold as a prior step to its determination by inductively coupled plasma mass spectrometry (ICP-MS) has been developed. The method is based on the cloud point extraction (CPE) of gold in the non-ionic surfactant Triton X-114 without a chelating agent. The parameters of CPE were investigated in detail. At optimum conditions, the linear range of 5.0–200.0 ng L^?1 of Au(III) and the detection limits of 1.1 ng L^?1 for Au(III) along with enrichment factors of 7.5, were obtained. The proposed method was applied to determination of ultra-trace amounts of gold in water samples with satisfactory results.     

Heavy metals removal from solution by palygorskite clay

The possible use of palygorskite clay, mined in the Dwaalboom area of the Northern Province of South Africa, as an adsorbent for the removal of metal ions such as lead, nickel, chromium and copper from aqueous solution, was investigated. In this work, adsorption of these metals onto palygorskite has been studied by using a batch method at room temperature. The results of adsorption were fitted to both the Langmuir and Freundlich models. Satisfactory agreement between experimental data and the model-predicted values was expressed by the correlation coefficient (R²). The Langmuir model represented the sorption process better than the Freundlich one, with correlation coefficient (R²) values ranging from 0.953 to 0.994. The adsorption capacity (Q₀) calculated from the Langmuir isotherm was 62.1 mg Pb(II) g⁻¹, 33.4 mg Ni(II) g⁻¹, 58.5 mg Cr(VI) g⁻¹ and 30.7 mg Cu(II) g⁻¹ at a pH of 7.0 at 25 ± 1 °C for a clay particle size of 125 μm. Kinetic investigations were performed to investigate the rate of adsorption of metal ions. The Lagergren’s first-order rate constants were calculated for different initial concentrations of metal ions. In batch mode adsorption studies, removal increased with an increase of contact time, adsorbent amount and solution pH. Adsorption of metals from the single-metal solutions was in the order: Pb > Cr > Ni > Cu. Data from this study proved that metal cations from aqueous solution can be adsorbed successfully in significant amounts by palygorskite. This opens up new possibilities and potential commercial uses in the palygorskite market.     

Electrocoagulation as a remediation tool for wastewaters containing arsenic

This work shows results of electrocoagulation of solutions containing arsenic. The continuous flow treatment consisted of an electrocoagulation reactor with two parallel iron plates and a sedimentation basin.The results showed that the electrocoagulation process of a 100 mg/L As(V) solution could decrease the arsenic concentration to less than 2 mg/L in the effluent with a current density of 1.2 A/dm² and a residence time of around 9 min. Liquid flow was 3 L/h, and the DC current was reversed each 2 min.Increasing the current density from 0.8 to 1.2 A/dm², the Fe³⁺ and OH⁻ dosages increase too, and thereby favouring the As removal. On the other hand, it seems that increasing the current density beyond a maximum value, the electrocoagulation process would not improve further. This could probably be explained by passivation of the anode.     

Surface characteristics and flotation behaviour of platinum and palladium tellurides

The telluride minerals, moncheite ((Pt,Pd)(Bi,Te)₂ and PtTe₂) and merenskyite ((Pd,Pt)(Bi,Te)₂ and PdTe₂), contribute between 20% and 45% of the PGMs present in the Platreef ore which is located in the northern limb of the Bushveld Complex of South Africa. There is evidence of these minerals reporting to the tailings and the present investigation was aimed at determining their flotation behaviour and to relate this to their surface characteristics.Microflotation, zeta potential determinations, ToF-SIMS analyses (time of flight-secondary ion mass spectrometry) and X-ray photoelectron spectroscopy (XPS) were used to characterise the flotation and surface behaviour of the synthesised samples. Copper activation of both moncheite and merenskyite samples reduced the flotation response compared with xanthate on its own. When xanthate is added on its own, it is adsorbed on the mineral surfaces at a higher concentration compared to the copper activated minerals.Oxidation of the PGE telluride minerals negatively affects the flotation performance of the Pt and Pd bismuth telluride samples respectively but not the Pt and Pd telluride samples. Grinding finer reduced recoveries and increasing the calcium ion concentration from 80 ppm to 500 ppm in the synthetic water did not negatively affect the flotation response of the PdTe₂ mineral.     

Performance and selectivity of the new column flotoextraction method

The main difference between the new Column Flotoextraction (CFE) method and the conventional SX and SPRAY methods is the substitution of organic phase bubble dispersion, instead of its drop dispersion into the aqueous phase. This substitution is intended to increase the contact area of phases and to enhance the buoyancy force of the organic phase. The main aims of this study are the introduction of the CFE method and the comparison of its performance and selectivity with SX and SPRAY methods. The results indicated ∼10% and ∼20% increase of cobalt (Co) extraction from dilute (100 mg Co/l) synthetic solution in A/O = 40 and ∼1% and ∼6% increase of Co extraction from concentrated (1000 mg Co/l) synthetic solution in A/O = 30 for the CFE method compared to SX and SPRAY methods, respectively, due to improved contact surface of the phases. In the same extraction time (1 min), the increase of Co extraction from dilute and concentrated solutions in the CFE method compared to the SX method were ∼16% and ∼4%, which demonstrate improved kinetics of the extraction process in CFE method. Improvement of separation factors in the CFE method relative to SX and SPRAY methods warrants the better performance of this innovative method.