Concentrated H2SO4 Solutions Research Articles

EXTRACTION OF CHROME FROM FERROCHROME PRODUCTION SLAG USING THE SULFURIC ACID METHOD

Currently, the development of industrial waste recycling processes that reduce the anthropogenic load on the biosphere and ensure the rational use of natural resources is an urgent task. Technogenic waste from ferrochrome production contains chromium, which is one of the most toxic components of industrial waste. To extract chromium from them, the most acceptable method is acid leaching. The purpose of the work is to study the influence of temperature, process duration and H2SO4 concentration on the extraction of chromium from high-carbon ferrochrome slag into a sulfuric acid solution. Using mathematical planning of a 3-factor experiment, experiments were carried out to extract chromium from the slags of high-carbon ferrochrome production. The H2SO4 concentration was varied from 5 to 95% by diluting the concentrated acid. The duration of the process ranged from 10 to 180 minutes at S:L = 1:30, the temperature varied from 22 to 90 °C. Results and discussion. The maximum transition of chromium into acid occurs at a temperature of 76-90 °C and a process duration of 145-180 minutes. The degree of extraction reaches 97.9%. The smallest amount of chromium, about 20 mg/L, passes into the weakly concentrated H2SO4 solution, the degree of leaching is low and equal to 20.6%. When using 50% H2SO4, the highest degree of transition of Cr (94.8%) from ferrochrome slag to sulfuric acid occurs at a high temperature of 90 °C in 150-180 minutes. Deeper extraction of chromium cations into acid occurs at 80-90 °C. The maximum content of Cr3+ in the acid is achieved in 46-107 minutes and amounts to (0.33-0.68)%. Conclusions. It was revealed that with increasing process duration and increasing temperature, the degree of extraction increases. The maximum transition of chromium into acid from high-carbon ferrochrome slag occurs at a temperature of 76-90 °C and a process duration of 145-180 minutes. The degree of extraction reaches 97.9%. An increase in the temperature of the process of leaching chromium from VUVC with concentrated sulfuric acid initiates the extraction of chromium from the raw material.

Wet and dry etching of ultrawide bandgap LiGa5O8 and LiGaO2

Crystalline thin films of LiGa5O8 have recently been realized through epitaxial growth via mist-chemical vapor deposition. The single crystal, spinel cubic LiGa5O8 films show promising fundamental material properties and, therefore, make LiGa5O8 a potential enabling material for power electronics. In this work, chemical resistance and etch susceptibility were investigated for the first time on crystalline LiGa5O8 thin films with various wet chemistries. It was found that LiGa5O8 is very chemically resistive to acid solutions, with no apparent etching effects observed when placed in concentrated acid solutions of HCl, H2SO4, HF, or H3PO4 at room temperature. In contrast, orthorhombic (010) LiGaO2 shows effective etching in HCl solutions at varying dilution concentrations, with etch rates measured between 8.6 [1000:1 (DI water: HCl concentration)] and 6092 nm/min (37 wt. % HCl). The inductively coupled plasma reactive ion etching (ICP-RIE) of LiGa5O8 using BCl3/Ar and CF4/Ar/O2 gas chemistries was investigated. The etching rate and surface morphology of etched surfaces were examined as a function of RIE and ICP power. Using a CF4/Ar/O2 gas chemistry with an RIE power of 75 W and an ICP power of 300 W resulted in smooth etched planar surfaces while maintaining an etch rate of ∼24.6 nm/min. Similar dry etching studies were performed for LiGaO2. It was found that the BCl3/Ar gas chemistry was better suited for LiGaO2 etching, with similar surface morphology quality being obtained after etching as prior etching when a RIE power of 15 W and an ICP power of 400 W is utilized.

OPTIMIZATION AND QUALITY ANALYSIS OF BIO-BUTANOL PRODUCTION FROM SUGARCANE (Saccharum officinarum) BAGASSE HYDROLYSATE

Several companies are currently investigating in development for the production of Biobutanol. This research was concerned with Biobutanol production from ABE (Acetone, Butanol, and Ethanol) fermentation of sugarcane bagasse hydrolysate by Clostridium Perfringens. The sample was hydrolyzed with concentrated H2SO4 solution for 1 hour at 121oC. Response surface designed by optimizing the fermentation parameters (Time, Temperature, and pH) by the used media (C. Perfringens) showed the highest Biobutanol yield at temperature (350C), Time 48 (Hhs), and pH 6.0 with 163 cm3 which is exactly around 0.543(g/L) by converted to a gram per liter as mostly represented by many researchers. The produced Biobutanol from the sugarcane bagasse hydrolysate was characterized using FT-IR and GC-MS analysis. Conclusively this work revealed the importance of sugarcane bagasse as a good potential feedstock of Biobutanol.

Designing selective stripping processes for Al-Cr-N hard coatings on WC-Co cemented carbides

Hard coatings like (Al,Cr)N are commonly used to protect cemented carbide cuttings tools from wear and corrosion. While such coatings increase the tool-lifetime, they also hinder the recycling effort of damaged tools. We report a new recycling strategy for coated cemented carbide tools by applying an interlayer between an arc evaporated Al0.7Cr0.3N coating and the WC-Co substrate. By selectively dissolving this interlayer in a concentrated basic solution, the coating spalls off the substrate, which is left intact. Four bases have been tested as saturated solutions: LiOH, NaOH, KOH, and CsOH, of which NaOH showed the highest reactivity. It was therefore used for subsequent investigations. Three different methods have been tested: (1) a metallic Al-doped interlayer region between substrate and coating can be removed in ▪ at ▪. Depositing an (2) Al0.7Cr0.3 or (3) Al0.9Cr0.1N interlayer leads to a significantly faster removal compared to the first method. Hereby a substrate could be fully de-coated in ▪ at only ▪. The reaction time was also decreased by pre-treating the samples in concentrated HCl, HNO3, or H2SO4 solutions at ▪ for ▪ before subjecting the samples to the NaOH bath. Such treated substrates were fully de-coated in ▪ at only ▪. While HNO3 oxidized the substrates significantly, HCl and H2SO4 caused only negligible substrate damage.

2,3,4,5,6-Pentabromobenzoic Acid

Pentabromobenzoate is a useful fragment in organic synthesis and in coordination chemistry. Among known synthetic approaches to pentabromobenzoic acid (PBA), we have assessed and identified exhaustive bromination of benzoic acid by using 1.3-dibromoisocyanuric acid in concentrated H2SO4 solution as the most efficient method for the preparation of PBA on a multigram scale. As the crude bromination product is typically contaminated with 3,4,5,6-tetrabromobenzoic acid (TBA) and pentabromobenzene, C6Br5H, a simple purification protocol for preparation of analytically pure PBA has been developed. The molecular structure and crystal packing of PBA established by single-crystal X-ray diffractometry suggests a pattern of H-bonding and halogen bonding in solid state.

Corrosion protection properties of Janus PTFE coatings in highly corrosive H2SO4 solutions

To improve the corrosion protection properties of polytetrafluoroethylene (PTFE) in highly corrosive H2SO4 solutions, Janus PTFE coatings (PDA/PEI@PTFE) were constructed. The modified side is achieved by co-deposition of polydopamine (PDA) and polyethyleneimine (PEI) on the sodium naphthalene etched side of PTFE. It not only has a 5-fold increase in interfacial adhesion with substrates via chemical bonds, but also exhibits improved barrier properties due to the coverage of dense PDA/PEI film, with corresponding corrosion resistance increase by ~2–3 orders of magnitude. Meanwhile, the untreated side is hydrophobic pristine PTFE and has good self-cleaning properties and excellent resistance in concentrated H2SO4 solutions.

Vanadium recovery by electrodialysis using polymer inclusion membranes

Industrial applications and environmental awareness recently prompted vanadium recovery spell from secondary resources. In this work, a polymer inclusion membrane containing trioctylmethylammonium chloride as carrier was successfully employed in electrodialysis for vanadium recovery from acidic sulfate solutions. The permeability coefficient of V(V) increased from 0.29 µm·s-1 (without electric field) to 4.10 µm·s-1 (with the 20 mA·cm-2 current density). The transport performance of VO2SO4-, which was the predominant species containing V(V) in the acidic region (pH <3), was influenced by the aqueous pH value and sulfate concentration. Under an electric field, a low concentrated H2SO4 solution (0.2 M) effectively stripped V(V) from the membranes, avoiding the requirement of a highly concentrated H2SO4 without electric field. Under the optimum conditions, the permeability coefficient and flux reached 6.80 µm·s-1 and 13.34 µmol·m-2·s-1, respectively. High selectivity was observed for the separation of V(V) and Mo(VI) from mixed solutions of Co (II), Ni (II), Mn (II), and Al (III). Additionally, the separation between Mo(VI) and V(V) was further improved by adjusting the acidity of the stripping solution. The V(V) selectivity for the resulting membrane was higher than that of commercial anion exchange membranes.

Surface imaging based non-destructive assessment of concrete deterioration using hue-saturation-intensity colour space

This study presents a methodology for imaging-based quantification of deterioration in concrete structures due to various chemical attacks, using HSI colour space. In this study, M30 grade of concrete samples are exposed to various deterioration agents like 5% concentrated solutions of NaCl, HCl, H2SO4 and MgSO4 for a period of 3,7,14 and 28 days respectively. The changes in surface colour profiles over time, due to chemical attack, are quantified within the HSI space. The numerical values of H show a little variation in the range of chemical exposure studied in the research. However, when combined with the variations of S and I, the deterioration of concrete structures can be assessed. Further, the correlation between the change of surface colour and deterioration of compressive strength is established by destructive testing. The change in surface colour between any two time intervals enables identification of the specific attacking chemical and estimation of the duration of attack as well as the residual strength of concrete. This novel approach enables establishment of empirical relationships between HSI values and residual compressive strength, towards visual-spectrum based quantification of the extent and duration of deterioration.

Penetapan Kadar Flavonoid Total Ekstrak Buah Gambas (Luffa acutangula(L.) Roxb.) dengan Metode Spektrofotometri UV-Vis

Gambas or Oyong fruit has various benefits, namely it can overcome enlarged lymph nodes, diuretics, laxatives, antioxidants, hepatoprotective, inhibiting the growth of fungi and bacteria. The purpose of this study was to determine the levels of total flavonoid compounds in gambas (Luffa acutangula (L.) Roxb). Extraction methode using soxhletation with 96% ethanol as solvent. The extract obtained was used for qualitative and quantitative analysis. Phytochemical analysis of the flavonoid content in the sample using the Shinoda test, 10% NaOH solution, and concentrated H2SO4 solution, obtained positive results containing flavonoids. Quantitative analysis using UV-Vis Spectrophotometry with the maximum wavelength obtained is 429.5 nm and operating time is 30 minutes. The average total flavonoid content obtained was 9.897±0.11 mg/gram extract with %KV 1.14%.

Experimental study on durability characteristics of composite fiber reinforced high-performance concrete incorporating nanosilica and ultra fine fly ash

This study is aimed at investigating the durability properties of Composite Fiber Reinforced High-Performance Concrete. A 15% partial replacement of cement by weight was done with ultra-fine fly ash. The addition of nanosilica was in fractions of 0%, 1.5%, 3.0% and 4.5% by weight of cement. For each of the above combinations, 1.0% steel and 0.25% polypropylene fibers, respectively, by volume of the binders were added. A constant aggregate binder ratio of 2.0 and varying water binder ratios of 0.275, 0.300, 0.325 were used in this investigation.The sorptivity test was performed to assess the rate of absorption, and the rapid chloride permeability test (RCPT) was performed to assess the permeability of concrete. Test results revealed that all the mixes attained low to very low chloride permeability. The decrease in chloride ion permeability for mixes with nanosilica and ultra-fine fly ash ranged from 53.83% to 71.45% for 28 days curing period and 55.88% to 74.27% for 56 days curing period, as against the reference mix.‘Residual Compressive Strength’ and ‘Percentage Weight Loss’ for 28 and 56 days of immersion in 5% concentrated solutions of HCl, H2SO4, and MgSO4 were evaluated to study the effects of aggressive ions such as chlorides and sulfates on concrete. The weight loss observed ranged from 7.09% to 2.07% in the case of HCl, from 7.96% to 2.86% in the case of MgSO4, from 17.93% to 11.02% in case of H2SO4 for water binder ratio of 0.275 and 56 days of immersion. The percentage reduction in strength after 56 days of immersion for mixes with water binder ratio of 0.275 ranged from 14.39% to 8.92% in HCl, from 14.53% to 9.66% in MgSO4 and 14.81% to 10.92% in H2SO4.The outcomes of the study showed that a combination of 15% ultra-fine fly ash and 3% nanosilica is the optimum replacement level to achieve increased durability, reduced porosity and permeability due to improved macro and micrometer densities of concrete. In addition, steel and polypropylene fibers have also made a small contribution towards improving the durability of Composite Fiber Reinforced High-Performance Concrete.

Supported gas membrane-based ammonia removal and recovery for a pH-dependent sink: Effect of water vapor transport

Sometimes NH3 is stripped from process/effluent streams through hydrophobic porous hollow-fiber-membranes (HFMs) via a supported-gas-membrane (SGM) process and recovered in concentrated H2SO4 solution as (NH4)2SO4. To recover relatively purified (NH4)2SO4, one can avoid excess H2SO4 with a more dilute H2SO4 strip solution. Neglect of strip-side mass-transfer resistance for low-pH strip H2SO4 solutions is not desirable with higher-pH H2SO4 strip solutions. Small hollow-fiber membrane modules (HFMMs) were used with a higher-pH H2SO4 strip solution. Mass transfer was successfully modeled using reaction-enhanced mass transport in higher-pH H2SO4 solution. Employing larger-scale crossflow HFMMs, time-dependent ammonia removal from a large tank having ammonia-containing process effluent was modeled for batch recirculation operation. The larger-scale modules employ shell-side feed liquid in crossflow with an overall countercurrent flow pattern and acid flow in the tube side. Modeling ammonia transport without water vapor transfer can cause substantial errors in batch recirculation method. Water vapor transport was considered here for low-pH and high-pH H2SO4 strip solutions for ammonia-containing feed in a large tank. Model results describe literature-based experimentally observed mass transfer behavior in industrial-treatment systems well. Model calculations were also made for continuous ammonia recovery from industrial effluents by a number of series-connected HFMMs without any batch recirculation.

Thermodynamic Modeling of Calcium Sulfate Hydrates in a CaSO4-H2SO4-H2O System from 273.15 to 473.15 K up to 5 m Sulfuric Acid.

To prevent scaling and to recycle aqueous solutions in industrial processes, the thermodynamic properties of the CaSO4–H2SO4–H2O system are studied by thermodynamic modeling with the Pitzer model. The published solubility data of calcium sulfate hydrates in sulfuric acid solutions were collected and reviewed critically. Then, the CaSO4–H2SO4–H2O system was modeled using the Pitzer activity coefficient approach from critically selected experimental data to obtain optimized parameters. The model reproduces the solubility data with good accuracy up to 5 m sulfuric acid at temperatures of 283.15–368.15, 283.15–473.15, and 298.15–398.15 K for gypsum (CaSO4·2H2O), anhydrite (CaSO4), and hemihydrate (CaSO4·0.5H2O), respectively. However, at temperatures above 398.15 K and sulfuric acid concentration above 0.5 mol/kg, the solubility of anhydrite predicted by our model deviates significantly from the literature data. Our model predicts that the solubility of anhydrite would first increase but then decrease in more concentrated sulfuric acid solutions, which is in disagreement with the experimental data showing constantly increasing solubilities as a function of increasing sulfuric acid concentration. This discrepancy has been discussed. The transformations of gypsum to anhydrite and hemihydrate were predicted in sulfuric acid solutions. With increasing H2SO4 concentration, the transformation temperatures of gypsum to anhydrite and hemihydrate will decrease. Thus, gypsum is stable at low temperatures in solutions of low H2SO4 concentrations and transforms to anhydrite at high temperatures and in concentrated H2SO4 solutions, while hemihydrate is always a metastable phase. Furthermore, the predicted results were compared with previous experimental studies to verify the accuracy of the model.

Compressive Behaviour of Steel Fiber Reinforced Concrete Exposed to Chemical Attack

In this modern age, Civil engineering constructions have their own structural and durability requirements, every structure has its own intended purpose and hence to meet this purpose, modification in traditional concrete has become mandatory. It has been found that steel fibers added in specific percentage to concrete improves durability of structure. The present study aims at comparing the durability in terms of weight loss and reduction in compressive strength of controlled concrete (with 0% steel fibers) and steel fiber reinforced concrete (with3% steel fibers), when exposed to acid, Sulphate and chloride attack. The grade of concrete designed for the study is M30. Hookend steel fibers with aspect ratio 50 at 0% and 3% of weight of cement are used. The specimens of 150 × 150 × 150 mm cubes are casted to find the weight loss and compressive strength of concrete. The specimens were demoulded after 24hours from the time of casting and the specimens are kept underwater for a period of 28days after that the specimens are immersed in the 5% concentrated solutions of H2So4, MgSo4 and Nacl for a period of 30, 60, 90, 120, 150 and 180days. The experimental studies revealed that the steel fiber reinforced concrete is performed better than that with controlled concrete after exposed to the chemical attack.

Investigation of the electrochemical behaviour of lead dioxide in aqueous sulfuric acid solutions by using the in situ EQCM technique

The charge-discharge characteristics and the aging mechanism of PbO2 layers in contact with sulfuric acid solutions of different concentrations (1.5–5.0 M) were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers were electrodeposited on gold substrate from aqueous solutions of Pb(NO3)2 dissolved in nitric acid. Based on the electrochemical and the mass change responses, it was found that in more concentrated solutions of H2SO4, the main reduction reaction was the transformation of lead dioxide to lead sulfate. However, in less concentrated sulfuric acid media, the transformation of lead dioxide to lead(II) ion became the main reaction. These Pb2+ ions transformed into lead sulfate crystals later by a chemical reaction. Because the electrochemical oxidation of lead sulfate is less favourable in sulfuric acid medium of higher concentrations, thus, PbO2 layers cannot be tested by continuous cyclization, which is necessary to study their aging parameters. Therefore, a delay step before each cyclic voltammogram was applied while the non-conductive lead sulfate dissolves or alternatively, by applying a pre-oxidation step prior to each cyclic voltammetry experiment to produce electrochemically significant amount of lead dioxide which can be reduced during the following negative potential sweep.

Thermal Stability of Ordered Mesoporous Carbon Based Catalyst and Its Application in Conversion of Linseed Oil to Methyl Esters

Ordered mesoporous carbon based catalyst (MCC catalyst) derived from microalgal waste biomass was prepared through condensation and hydrothermal post-treatment process at 90 °C and 120 °C, respectively. Biochar obtained from pyrolysis of the waste was sulfonated in concentrated H2SO4 solution at 150 °C for 15 h to introduce sulfonic groups to the biochar’s structure consisting of condensed polycyclic aromatic rings. This process modified biochar to sulfonated biochar (SBP) which was then applied as precursor in the MCC catalyst preparation. The MCC catalyst structure was demonstrated for its ordered mesoporous structure. The thermal behavior of the catalyst was then investigated by heating process with and without using oxygen for estimating its thermal stability. The acidity of the catalyst was also considered through propylamine-TPD established in TG–MS machine. The catalysts activity was tested in conversion of linseed oil to methyl ester under mild conditions of 120 °C for 3.5 h, and the yield of methyl esters was up to 94.6% proving its high activity and selectivity in the conversion. In this study, TG–DSC coupled with MS, XRD, TEM, NH3-TPD, BET-BJH, techniques were applied to characterize the catalyst, and GC–MS was used for determining the methyl ester composition of the product.

Acid pretreatment optimization for xylose production from Agave tequilana Weber var. azul, Agave americana var. oaxacensis, Agave karwinskii, and Agave potatorum bagasses using a Box-Behnken design

There is a growing interest in the use of lignocellulosic biomass for biofuel production leading to by-products with high added value such as xylitol, a sweetener obtained from chemical synthesis or fermentative pathways, characterized by high degree of sweetness, recommended for people with diabetes, making it a product of great interest in the industrial market. The objective of this study was to use the bagasse of four agave plants from Mexico: Agave tequilana Weber var. azul (AT), Agave Americana var. oaxacensis (AA), Agave karwinskii (AK), and Agave potatorum (AP) to obtain xylose as an alternative for xylitol or ethanol production. The dilute acid pretreatment was optimized to obtain the maximum concentration of xylose and the minimum concentration of acetic acid, using a Box-Behnken design, where H2SO4 concentration, hydrolysis time, and liquid-to-solid ratio were evaluated. Xylose concentrations of 23.18 g/L (AT), 27.63 g/L (AA), 31.8 g/L (AK), and 24.42 g/L (AP) were achieved. It was also observed that by using more concentrated H2SO4 solutions, higher concentrations of xylose were obtained, but also high concentrations of acetic acid (1.02 g/L in AT, 2.3 g/L in AA, 3.46 g/L in AK, and 2.01 g/L in AP). This study shows that AT, AA, AK, and AP are a promising alternative feedstock for bioethanol or xylitol production using xylose as substrate.

Modified activated carbon as a promising adsorbent for quinoline removal

Abstract Activated carbon from coconut shell (Elaeis guineensis), in crude form and as forms chemically modified with concentrated solutions of HNO3 and H2SO4, were initially tested for their ability to remove quinoline from an organic medium. The adsorbents were characterised by techniques such as adsorption/desorption of N2 at 77 K, the point of zero charge, the Boehm method, infrared spectroscopy, thermogravimetric/differential thermal analysis, X-ray photoelectron spectroscopy and CHNOS elemental analysis. The best results of contaminant removal were achieved using sulfuric acid-treated activated carbon (SAAC). With regard to its potential in quinoline removal, SAAC was evaluated in a closed batch system by a phenomenological investigation of the adsorption process, using experimental data and mathematical modelling of kinetics and equilibrium. The maximum adsorption capacity (qmax) obtained by the Langmuir model was 56.6 mg g−1. The kinetic results obtained for different concentrations of quinoline showed that the internal resistance model, with variable mass transfer coefficient, suitably describes the quinoline adsorption process in a batch system. Therefore, such model should be used for the optimisation and design of industrial-scale columns for the investigated, and similar, systems.

Selection of a synergistic solvent extraction system to remove calcium and magnesium from concentrated nickel sulfate solutions

Synergistic solvent extraction of Ca and Mg from concentrated Ni sulfuric solutions was assessed using extractants Cyanex 272, D2EHPA, and naphthenic acid. D2EHPA has a strong preference for extracting Ca; however, Ca was crowded out by Ni at pH>3.5. Cyanex 272 has a higher affinity for Mg at pH>5, while both earth alkaline metals are rejected by naphthenic acid at pH=2–6 as well as by the system Cyanex 272+naphthenic acid. The system D2EHPA+naphthenic acid has affinity only for Ca. The system D2EHPA+Cyanex 272 can extract Ca and Mg simultaneously; however, selectivities Ca/Ni and Mg/Ni are dependent on the liquor pH and D2EHPA concentration in organic mixture solution. In this system, a strong synergistic effect was found for Ca and Mg, whereas contradictory behavior was observed for Ni. To avoid crud formation, the selective extraction of Ca and Mg should be performed at pH<6. Ni can be selectively stripped from the loaded D2EHPA+Cyanex 272 using diluted H2SO4 solution, whereas Ca and Mg can be completely stripped with concentrated H2SO4 solution.

Effluent valorization in copper hydrometallurgy plant

Copper is commonly produced by hydrometallurgical processes. The production of this metal results in the formation of emissions (unwanted solids, liquids and gases). In this paper, an effluent from a Cu producer company is valorized by means of Fe and Cu recovery.In the current process, an effluent from the secondary solvent extraction (secondary raffinate) was sent to neutralization plant to be discharged. In this paper a modification of the process is proposed. The secondary raffinate was contacted with TP207 resin for Fe3+ and Cu recovery. Metals were eluted from the resins using another real effluent (primary raffinate, effluent from the primary solvent extraction) from the same plant.Experiments for the uptake and elution were carried out in batch and in columns. The effect of pH, resin dosing, and temperature onto metals retention are analyzed. Retention efficiencies (loading capacities) were 50.1% (8.1mg·g−1) for Cu and 54.8% (23.2mg·g−1) for Fe3+ under the optimal operational conditions (pH=0.45 and T=65°C). These values were confirmed in column tests. It is possible to recover Fe3+ and Cu from the secondary raffinate, leaving most of Fe2+ and other elements in solution. The experimental affinities that TP207 showed are: Cu>Fe3+>Fe2+>Zn.The elution of Fe and Cu was quantitatively achieved with concentrated H2SO4 solution. When acidified primary raffinate was used as eluting solution, an enriched solution containing 14.3g Cu·L−1, 20.3g Fe2+·L−1, and 18.6 de g Fe3+·L−1 was obtained. This enriched primary raffinate can be reintroduced in the process as leaching solution.So, after the modification of the process, using secondary raffinate as loading solution and acidified primary raffinate as eluting solution, the ion-exchange stage could substitute the external FeSO4 addition. In addition, 30–80kgCu·h−1 are reintroduced in the process.

Dual photo-electrochromic diimides derived from aliphatic aminothiols and π-electron deficient aromatic dianhydrides

The reaction of aliphatic 2-aminothiols with pyromellitic and benzophenone-3,3′,4,4'-tetracarboxylic dianhydrides endowed dual-response diimides with photo- and electrochromic properties in concentrated sulfuric acid solution. Upon stimulation, the yellow color photo-isomeric materials turned in a few seconds to dark blue or red color and subsequently reverted back within a few minutes. The color change was ascribed to the generation of radical-cation species which may be formed through a reversible photo-induced electron-transfer process from the thiol group to the proton-activated dianhydride moiety. Spectroelectrochemistry measurements in concentrated H2SO4 solution of the specified diimides were accompanied by a quite similar UV-vis spectral response as observed in photochromic process, indicating the equality of the created chromic centre in both phenomena. The two chromic activities showed a great sensitivity to the structure of the donor-acceptor couples.