Sulfuric Medium Research Articles

Characterization of the Solid Leach Residues from the Iodine-Assisted Chalcopyrite Leaching in Ferric Sulfate Media

Characterization of the Solid Leach Residues from the Iodine-Assisted Chalcopyrite Leaching in Ferric Sulfate Media

Solubility and solvation thermodynamics of glycine, dl-alanine and l-threonine in pure aqueous and aqueous (NH4)2SO4 solution

In this article the equilibrium saturated solubility of glycine, dl-alanine and l-threonine in aqueous ammonium sulphate media at various temperatures were estimated. The standard transfer Gibbs free energies and different thermodynamic parameters were also estimated. Different interactions were analysed for the solvation of the amino acids in the experimental media to explain the mechanism of solvation. For dl-alanine and l-threonine, salting-in effect is observed at lower electrolyte concentration while at higher electrolyte concentration salting-out effect is observed at a particular temperature. The chemical stability of the amino acids in aqueous electrolyte mixture was explained to justify the experimental results.

Recovery of Gold from Refractory Sulphide Concentrates by Means of Pressure Oxidation and Thiocyanate Leaching

The alternative method for gold recovery from POX cakes is thiocyanate leaching. This method has several advantages: thiocyanate is less toxic than cyanide; complex [Au(SCN)4]– is very stable (lgβ = 43.9); leaching of gold is carried out in sulfate media without CCD and neutralization of acidic POX slurry; high rate of this process; the gold oxidant is ferric ions which formed during POX of iron sulfides. The test work on pressure oxidation and thiocyanate leaching was carried out for refractory sulfide gold-copper flotation concentrate. The gold content in the concentrate was 31.8 g/t. Pressure oxidation tests at the temperature of 220 oC and the oxygen pressure of 0.7 MPa were carried out. The POX slurry to 90–95 oC was cooled and thiocyanate leaching of gold was carried out at atmospheric pressure. The concentration of thiocyanate ions was changed from 0.5 to 2 g/dm3. The recovery of gold from leaching solution was carried out by activated carbon. The loaded carbon to cyanide treatment, thermal reactivation and acidic treatment for copper and iron remove was subjected. The cyanide treatment was carried out with a sodium cyanide solution of 20 g/dm3. Thermal treatment was carried out at the temperature of 650–700 oC for 0.5 h. The acidic treatment was carried out with a hydrochloric acid solution of 20 g/dm3. After impurities removing the carbon in next experiments was used. 6 cycles gold adsorption and carbon regeneration were carried out. It was shown that thiocyanate gold leaching from POX products can be carried out in the CIP and CIL modes. Gold recovery was over 95%. 80–99% of copper, 65–88% of iron and 90–99% of sulfur were recovered from carbon during removing cycles. The gold adsorption process in each cycle had line nature. The content of gold in the loaded carbon after six cycles was 0.5 kg/t, and after long time CIP process was 3.9 kg/t. The gold stripping by alkaline solution was 97%. The gold content in the stripped carbon was 0.016 kg/t. The copper and iron content was 0.021 and 0.132 kg/t, respectively.

Iodine-assisted chalcopyrite leaching in ferric sulfate media: Kinetic study under fully controlled redox potential and pH

The addition of iodide has been found to significantly accelerate chalcopyrite leaching in ferric sulfate media at ambient conditions. Solution potential is the principal factor determining the leaching performance through controlling the iodine speciation. In order to develop a kinetic equation that incorporates the iodine speciation, a series of leaching tests were carried out in specially-designed sealed reactors that allows the solution potential together with other leaching parameters to be fully controlled. The experimental results showed that the rate of copper dissolution was increased by increasing the solution potential in the range of 669 to 769 mV vs. SHE), increasing the total iodide concentration in the range of 50 to 200 mg/L, and increasing the temperature between 25 and 40 °C. The formation of elemental sulfur and jarosite did not hinder the leaching reaction. A kinetic model was developed that relates the rate of copper extraction to the solution potential with a reaction order of 0.32, the diiodine concentration with a reaction order of 1.17, and temperature with an activation energy of 43.1 kJ/mol. The kinetic analysis supported that the leaching process was controlled by surface chemical reaction.

Synthesis of Ag nanoparticles from waste printed circuit board

The amount of waste from electrical and electronic equipment has been growing every year. The printed circuit boards contained in this waste include metals that can be recovered through urban mining, adding value to this waste and minimizing environmental impacts with its incorrect disposal or treatment. In this work, memory boards obsolete with 0.053 wt% Ag were used. The extraction of all metals studied (Ag, Al, Cu, Fe, Ni, Sn, and Zn) involved the evaluation of the Pourbaix and speciation diagrams to identify the pH and redox potential conditions, considering the possible species formed with leaching agents: sulfuric, nitric, and hydrochloric medium. After the definition of the leaching agent, the extraction routes by hydrometallurgical processing were proposed from the parameters of temperature, s/l ratio, and reaction time previously studied. Route A was composed of sequential stages (the first leaching in a sulfuric medium and the second in an oxidizing sulfuric medium) and obtained 100% of Ag recovery. Route B consisted only of leaching in an oxidizing sulfuric medium, obtained about 94% of the Ag recovery, and could not contribute to the subsequent purification steps (if necessary) of this solution, as all metals would also be in the solution. These two routes showed that Ag can only be recovered in an oxidizing sulfuric acid medium, according to the conditions studied. Ag recovered in the leach liquor of the second stage of Route A was purified by chemical precipitation with NaCl, and the AgCl was solubilized in an NH4OH solution. This solution was used to synthesize silver nanoparticles by the Turkevich method in 25 min. The spherical nanoparticles synthesized an average size distribution of 67 nm.

Comparative study of the removal of direct red 23 by anodic oxidation, electro-Fenton, photo-anodic oxidation and photoelectro-Fenton in chloride and sulfate media

This study aims to compare the efficiency of anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), and their association with UV irradiation (photo anodic oxidation (PAO), and photo electro-Fenton (PEF) for the removal of Direct Red 23 from wastewater using a BDD/carbon felt cell in chloride and sulfate medium and in their combination. The effect of the supporting electrolyte was investigated in AO-H2O2 and EF processes. High discoloration efficiency was obtained in chloride media while a higher mineralization rate was achieved in sulfate media. The EF process reached higher total organic carbon (TOC) removal efficiency than AO-H2O2. 90% TOC removal rate was achieved by the EF against 82% by AO-H2O2 in sulfate media. The influence of using the mixt supporting electrolyte formed of 75% Na2SO4 + 25% NaCl was found to have beneficial effect on TOC removal, achieving 89% and 97% by AO-H2O2 and EF, respectively. High currents led to higher mineralization rates while low currents yielded to a higher mineralization current efficiency (MCE%) and lower energy consumption (EC). UV irradiation enhanced process efficiency. Mineralization efficiency followed the sequence: AO-H2O2 < PAO < EF < PEF. The PEF process was able to remove TOC completely at 5 mA cm−2 current density and 6 h of electrolysis with a MCE% value of 16.57% and EC value of 1.29 kWh g−1 TOC removed.

Ultrasound/Complexing Agent-Assisted Solvent Extraction Behavior of Zn2+ with D2EHPA from Sulfuric Media Containing Transition and Rare-Earth (Fe, Ni, Cd, La, and Ce) Metal Ions

Ultrasound/Complexing Agent-Assisted Solvent Extraction Behavior of Zn2+ with D2EHPA from Sulfuric Media Containing Transition and Rare-Earth (Fe, Ni, Cd, La, and Ce) Metal Ions

Influence of Media pH on Corrosion Behaviour of AZ31 Magnesium Alloy in Chloride and Sulphate Media

Influence of Media pH on Corrosion Behaviour of AZ31 Magnesium Alloy in Chloride and Sulphate Media

Removal of Fe(III), Cd(II), and Zn(II) as Hydroxides by Precipitation–Flotation System

In this paper, a combined precipitation–flotation system is proposed for the removal of Fe(III), Zn(II), and Cd(II) as hydroxides. The efficiency of precipitation, as a function of pH, metal ion concentration, and dosage of the precipitating agent as the main variables, was evaluated. The results showed that 99% efficiency was attained from a mixture solution containing the three metal ions in sulfate media at pH 10.3 after 15 min of treatment. The sedimentation behavior showed that a larger precipitate facilitated solid/liquid separation at 30 min. The characterization of precipitates was performed by X-ray diffraction (XRD) identifying iron, zinc, and cadmium oxides; hydroxides; and sodium sulfate. For the flotation, a 20 mg/L solution of dodecylamine (DDA) was used as a collector. Such a solution allowed for the removal of 76% of precipitates in concentrate. An increase in the collector concentration diminished the float percentage due to the micelle formation and low adsorption of the collector on the surface of the precipitate. The results provide evidence of the effectivity of the removal of metal ions by the combined precipitation–flotation system as an alternative for the treatment of acid mine drainage (AMD) in less time in comparison with a sedimentation stage.

The Influence of the Type of Electrolyte in the Modifying Solution on the Protective Properties of Vinyltrimethoysilane/Ethanol-Based Coatings Formed on Stainless Steel X20Cr13.

The paper reports the results of the examination of the protective properties of silane coatings based on vinyltrimethoxysilane (VTMS) and ethanol (EtOH), doped with the following electrolytes: acetic acid (AcOH), lithium perchlorate LiClO4, sulphuric acid (VI) H2SO4 and ammonia NH3. The coatings were deposited on stainless steel X20Cr13 by the sol–gel dip-coating method. The obtained VTMS/EtOH/Electrolyte coatings were characterized in terms of corrosion resistance, surface morphology and adhesion to the steel substrate. Corrosion tests were conducted in sulphate media acidified up to pH = 2 with and without chloride ions Cl−, respectively. The effectiveness of corrosion protection was determined using potentiometric curves. It has been demonstrated that the coatings under study slow down the processes of corrosion of the steel substrate, thus effectively protecting it against corrosion.

A Novel Surfactant Sensitized Fluorescent Sensor for Co(II) Based on Nitrogen Doped Carbon Quantum Dots

A novel nitrogen-doped carbon quantum dots (N-CDs) were prepared by the microwave irradiation method. The fluorescence quenching effect of Co(II) on the N-CDs was studied in the sodium dodecyl sulfate (SDS) medium and the fluorescence quenching was sensitized in the SDS. The linear range of calibration curve for the determination of Co(II) was 0.17µg/mL-11.8µg/mL and the limit of detection was 0.052µg/mL. The method has been applied for the determination of Co(II) in samples with satisfactory results.

Pilot-Scale Lanthanide Precipitation from Sulfate-Based Spent Ni-MH Battery Leachates: Thermodynamic-Based Choice of Operating Conditions

Access to critical metals required for high-performance technologies, particularly, the light rare earth elements (REEs = La, Ce, Nd, Pr), has become a major challenge for import-dependent economies such as the European Union. In this regard, the recycling of spent nickel metal hydride (Ni-MH) batteries by hydrometallurgical processes can serve as an attractive secondary source of REEs. In such processes, precipitation of REEs from pregnant leach solutions (PLS) in sulfate media using Na2SO4 is often reported. However, little consideration is given as to whether and how sodium ions influence the precipitation efficiency and selectivity. This work focuses on a better understanding of the precipitation process by coupling pilot-scale (2 L) experiments on industrially sourced PLS containing 50 g/L of Ni and 17 g/L of REEs, with thermodynamic modeling, to assess the influence of temperature (25 °C < T < 60 °C) and the Na/REEs molar ratio (0.8:1 < Na/REEs < 3.2:1). Equilibria calculations were performed using OLI Systems Inc. software whose database covers rare earth sulfate compound properties and an accurate description of the aqueous electrolytes. Highly selective precipitation was obtained at 60 °C and for a Na/REEs molar ratio of 4:1. A lanthanide-alkali solid solution was identified by multianalytical characterization.

Influence of Sulphate Attack on Properties of Modified Cement Composites

Monitoring the condition of building structures based on composite materials in aggressive environments shows that the deterioration of basic properties occurs under the influence of various factors such as temperature and humidity changes, in addition to changes in the chemical composition of air environment. In addition, the composite materials during the operation must retain not only the mechanical properties laid down at the design stage, but also the electro-physical characteristics, regardless of the type of destructive effects. In the current study, the quantitative assessment of the result of the interaction of an aggressive sulphate-containing medium with composites modified with conductive and dielectric additives was carried out. The effect of sulphate attack on the specific electrical conductivity of cement composites was studied. The nature of the interaction was evaluated by changing the properties of the samples of the developed compositions under the influence of a single-normal solution of sodium sulphate. The analysis was carried out by means of potentiometric titration using the exchange interaction method by fixing the degree of absorption of sulphate ions and determining the concentration of calcium ions in the solution. The measurement of the solution potential allowed determination of the quantitative indicators of the rate of calcium hydroxide leaching from the sample structure, which is necessary to assess the intensity of the destruction process and determine the nature of the change in strength properties. Measurements of the electrical resistivity of samples under the constant influence of sulphate aggression were taken during 28 days of observation. A method for quantifying the effect of a sulphate medium on a cement matrix was proposed that enables the material durability to be predicted. The features of changes in the morphology of structural components after exposure to aggressive solution were determined by physical and chemical methods.

Comparative study on extraction of copper(II) cations from highly saline media using 2-((phenylimino)methyl)phenol chelating mono-Schiff base /kerosene as novel extractant system

The present investigation reports a fundamental extraction- recovery studies of high amount of copper(II) cations from different concentrated saline aqueous solutions including sulphate, chloride, and mixed chloride/ sulphate media with 2-((phenylimino)methyl)phenol extractant (HPIMP) in kerosene at 25 °C. The acid-dissociation constant (Ka) and distribution constant (Kd) between kerosene and various saline aqueous solutions of (HPIMP) were determined. The influence of different parameters namely contact time, organic to aqueous phase (O/A) ratio, pH-value, extractant concentration, and temperature, as well as the effect of anions on the extraction recovery process has been studied. The experimental results revealed that the extraction ability of the (HPIMP) towards Cu(II) ions depends on the nature of inorganic salt. A maximum extraction efficiency of 99.76% was obtained from a 1 M chloride medium, which is significantly higher than those obtained from the sulphate medium (E(%) = 79.13%) or the mixed chloride/sulphate medium (E(%) = 81.75%). The trends in the values of extraction constants were explained in terms of acidity and distribution constants of (HPIMP). From the thermodynamic analysis it is inferred that the extraction process is endothermic and favorable at high temperatures, leading to stable, extractable Cu-HPIMP complexes.

A study on the biosorption kinetics of Cu (II) and Zn (II) ions from aqueous phase (sulphate medium) using waste sawdust generated from Acacia nilotica wood carpentry.

In the present study, the natural biosorption capacity of Acacia nilotica sawdust (wood biomass) was studied for the removal of copper (Cu) and zinc (Zn) heavy metal ions. The process was optimized for several important factors such as pH, contact time, biomass amount, and metal ion concentration. The maximum biosorption of Zn onto Acacia nilotica sawdust was 66.092% at pH 7.0, contact time 20 min, biomass concentration 0.4 g, and initial Zn concentration 8.4 mg/L. The maximum Cu biosorption to Acacia nilotica sawdust was 66.097% at pH 4, contact time 45 min, biomass 0.8 g, initial metal ion concentration 27 mg/L. The experimental data were analyzed by two different adsorption isotherms i.e. Langmuir and Freundlich models. Based on the regression coefficient the Freundlich isotherm model showed the best fit for Zn whereas Cu metal ion adsorption gave a favorable fit for Langmuir isotherm. Both metal ions followed pseudo-second-order kinetics in the adsorption process using sawdust of Acacia nilotica.

Electrochemical oxidation of ciprofloxacin in different aqueous matrices using synthesized boron-doped micro and nano-diamond anodes

The present work investigates the electrocatalytic performance of two different morphologies of boron doped-diamond film electrode (microcrystalline diamond - MCD, and nanocrystalline diamond - NCD) used in electrochemical oxidation for the removal of the antibiotic ciprofloxacin (CIP). A thorough study was conducted regarding the formation of the MCD and NCD films through the adjustment of methane in CH4/H2 gas mixture, and the two films were compared in terms of crystalline structure, apparent doping level, and electrochemical properties. The physicochemical results showed that the NCD film had higher sp2 carbon content and greater doping level; this contributed to improvements in its surface roughness, as well as its specific capacitance and charge transfer, which consequently enhanced its electrocatalytic activity in comparison with the MCD. The results obtained from CIP removal and mineralization assays performed in sulfate medium also showed that the NCD was more efficient than the MCD under all the current densities investigated. The effects of CIP concentration and the evolution of the final by-products, including short-chain carboxylic acids and inorganic ions, were also investigated. The electrochemical performance of the NCD was evaluated in different aqueous matrices, including chloride medium, real wastewater and simulated urine. The application of the NCD led to complete or almost complete CIP degradation, regardless of the medium employed. The kinetic constant rates obtained under the different media investigated were as follows: synthetic urine (0.0416 min−1 – R2 = 0.991) < real wastewater (0.0923 min−1 R2 = 0.997) < synthetic matrix containing chloride (0.1992 min−1 – R2 = 0.995); this shows that the pollutant degradation was affected by the type of aqueous matrix and the oxidants that were electrogenerated in situ. The results obtained from the analysis of electrical energy per order (EE/O) showed that the treatment of simulated urine spkiked with required the highest energy consumption, followed by the real effluent and synthetic matrix containing chloride. The present study proves the viability of electrocatalytic nanostructured materials to the treatment of antibiotics in complex matrices.

Extraction of copper from chalcopyrite with potassium dichromate in 1-ethyl-3-methylimidazolium hydrogen sulfate ionic liquid aqueous solution

Developing new and sustainable leaching system with limited release of pollutant and low acid and energy consumption is a challenge for copper extraction from chalcopyrite. In this work, a hydrometallurgical process for chalcopyrite dissolution in 1-ethyl-3-methyl-imidazolium hydrogen sulfate ([EMIm]HSO4) media with potassium dichromate (K2Cr2O7) was developed, and the leaching behavior of chalcopyrite with various parameters, such as kinds of ionic liquids (ILs), concentrations of [EMIm]HSO4 and K2Cr2O7, stirring speed, leaching temperature, and particle size were discussed in detail. The result show that the most effective ILs medium for chalcopyrite dissolution was varied with the specific oxidant. The leaching rate of chalcopyrite was significantly enhanced by increasing temperature, concentrations of K2Cr2O7 and [EMIm]HSO4, and decreasing particle size, while it has little to do with the increasing of stirring speed. The maximum copper extraction yield of 90.2% was reached within 90 min under the following optimized conditions: 10 g/L of solid/liquid ratio, 10 vol% of [EMIm]HSO4 concentration, 0.1 M of initial K2Cr2O7 concentration, stirring speed of 200 rpm, the temperature of 70 °C and particle size of −45 µm. The leaching process of chalcopyrite in [EMIm]HSO4-K2Cr2O7 aqueous solution follows an empirical kinetic model 1-2/3x-(1-x)2/3=kdt with the apparent activation energy of 36.26 kJ/mol, which was limited by the diffusion through a protect layer of elemental sulfur and pyrite.

Iron-Speciation Control of Chalcopyrite Dissolution from a Carbonatite Derived Concentrate with Acidic Ferric Sulphate Media

The mechanisms involved in the dissolution of chalcopyrite from a carbonatite concentrate in a ferric sulphate solution at pH 1.0, 1.5 and 1.8, and temperatures 25 °C and 50 °C were investigated. Contrary to expectations and thermodynamic predictions according to which low pH would favour high Cu dissolution, the opposite was observed. The dissolution was also highly correlated to the temperature. CuFeS2 phase dissolution produced intermediate Cu rich phases: CuS, Cu2S and Cu5FeS4, which appeared to envelop CuFeS2. Thermodynamic prediction revealed CuS to be refractory and could hinder dissolution. CuFeS2 phase solid-state dissolution process was further discussed. Free Fe3+ and its complexes (Fe(HSO4)2+, Fe(SO4)2– and FeSO4+ were responsible for Cu dissolution, which increased with increasing pH and temperature. The dissolution improved at pH 1.8 rather than 1.0 due to the increase of (Fe(HSO4)2+, Fe(SO4)2– and FeSO4+, which were also the predominating species at a higher temperature. The fast and linear first dissolution stage was attributed to the combined effect of Fe3+ and its complex (Fe(HSO4)2+, while Fe(SO4)2– was the main species for the second Cu dissolution stage characterised by a slow rate.

Electro-Fenton process for the removal of Direct Red 23 using BDD anode in chloride and sulfate media

• Degradation of dye DR23 by EF using BDD or DSA anode in chloride and sulfate media. • BDD/carbon graphite cell achieved efficient discoloration and mineralization. • Rapid and complete discoloration was obtained in chloride medium. • Sulfate medium led to the higher mineralization rates. • Combination of chloride and sulfate as supporting electrolyte provided a beneficial effect. This paper aims to study the degradation and mineralization of the dye Direct Red 23 (DR23) by electro-Fenton (EF) process for the first time using BDD and DSA anode and carbon graphite (CG) cathode in NaCl and Na 2 SO 4 media. The effect of different parameters such as the nature, concentration, and combination of the supporting electrolyte, the nature of the anode, the concentration of the catalyst and DR23 and the current density on H 2 O 2 generation and mineralization rate was investigated. The best treatment efficiencies were achieved by BDD/CG cell. The degradation of DR23 solution was faster in NaCl medium. The mineralization was more efficient in Na 2 SO 4 , where the main oxidizing species were the hydroxyl radicals, generated both in the bulk solution ( • OH) and at the anode surface (M( • OH)). The TOC removal, the energy consumption, and electrical cost per m 3 were 90%, 2.41 kWh g −1 TOC, and 3.21 US $ m −3 , respectively, after 6 h of electrolysis in sulfate medium while lower mineralization rate (83%) and higher energy consumption (2.86) and electrical cost per m 3 (3.27 US $ m −3 ) were achieved in chloride medium. As the textile wastewater contain generally sulfate and chloride ions, experiences were also performed in a medium formed of Na 2 SO 4 and NaCl. The following combination of these salts (75% Na 2 SO 4 + 25% NaCl) as supporting electrolyte was beneficial to further increase the mineralization rate of DR23 solution, current efficiency and reduce the energy consumption. Degradation of DR23 in the presence of different scavengers (methanol, 2-propanol, and tert-butanol) asserted that the elimination of DR23 is mainly attributed to the action of • OH/M( • OH) on the target pollutant.

The Evaluation of Sphalerite Surface Formed During Oxidative Leaching in Acidic Ferric Sulfate Media

The Evaluation of Sphalerite Surface Formed During Oxidative Leaching in Acidic Ferric Sulfate Media