Kinetic and thermodynamic studies on biosorption of Cu（ Ⅱ ） by chemically modified orange peel

Cu(II) biosorption by orange peel that was chemically modified with sodium hydroxide and calcium chloride was investigated. The effects of temperature, contact time, initial concentration of metal ions and pH on the biosorption of Cu(II) ions were assessed. Thermodynamic parameters including change of free energy), (ΔG^θ), enthalpy (ΔH^θ) and entropy (ΔS^θ) during the biosorption were determined. The results show that the biosorption process of Cu(II) ions by chemically treated orange peel is feasible, spontaneous and exothermic under studied conditions. Equilibrium is well described by Langmuir equation with the maximum biosorption capacity(qm) for Cu(II) as 72.73 mg/g and kinetics is found to fit pseudo-second order type biosorption kinetics. As the temperature increases from 16 °C to 60 °C, copper biosorption decreases. The loaded biosorbent is regenerated using HCl solution for repeatedly use for five times with little loss of biosorption capacity.     

Effect of strontium on the grain refining efficiency of Mg–3Al alloy refined by carbon inoculation

The effect of Sr on the grain refining efficiency of the Mg–3Al alloy refined by carbon inoculation has been investigated in the present study. A significant grain refinement was obtained for the Mg–3Al alloy treated with either 0.2% C or 0.2% Sr. The Al–C–O particles were found in the sample refined by 0.2% C, and the element O should come from reaction between Al₄C₃ nuclei of Mg grains and water during the process of sample preparation. The grain size of the sample refined by carbon inoculation was further decreased after the combined addition of Sr. The grain size decreased with increasing Sr content. Much higher refining efficiency was obtained when the Sr addition was increased to 0.5%. Sr is an effective element to improve the grain refining efficiency for the Mg–Al alloys refined by carbon inoculation. The number of Al₄C₃ particles in the sample refined by the combination of carbon and Sr was more than that in the sample refined by only carbon. No Al–C–O–Sr-rich particles were obviously found in the sample refined by the combination of carbon and a little (<0.5%) Sr addition.     

Effect of 2,2′ benzothiazolyl disulfide on the corrosion of mild steel in acid media

2,2′ benzothiazolyl disulfide (BTDS) has been synthesised and their inhibiting action on mild steel corrosion in 1 M HCl and 0.5 M H₂SO₄ at 308 K has been investigated using weight loss, EIS, polarization and SEM study. BTDS showed better efficiency in 0.5 M H₂SO₄ compared to 1 M HCl. Polarization studies revealed that BTDS is a mixed type inhibitor in both acids predominantly cathodic in 1 M HCl where as predominantly anodic in 0.5 M H₂SO₄. Thermodynamic parameters i.e. free energy of adsorption, enthalpy, entropy and activation energy were calculated, the values of these parameters showed good interaction.     

Microstructure and grain refining performance of a new Al–Ti–C–B master alloy

A kind of Al–Ti–C–B master alloy with a uniform microstructure is prepared using a melt reaction method. It is found that the average grain size of α-Al can be reduced from 3500 to 170 μm by the addition of 0.2 wt.% of the prepared Al–5Ti–0.3C–0.2B and the refining efficiency does not fade obviously within 60 min. It is considered that the TiC_xB_y and TiB_2−mC_n particles found at the grain center are the effective and stable nucleating substrates for α-Al during solidification, which accounts for the good grain refining performance.     

Sorption behavior of iminodiacetic acid resin for indium

In（Ⅲ） was quantitatively adsorbed by iminodiacetic acid resin （IDAAR） in the medium of pH = 4.52. The statically saturated sorption capacity of IDAAR is 235.5 mg·g^-1. 1.0 mol·L^-1 HCl can be used as an eluant. The elution efficiency is 97.9%. The resin can be regenerated and reused without apparent decrease of sorption capacity. The sorption rate constant is k298 = 1.94 × 10-5 s^-1. The apparent sorption activation energy of IDAAR for In（Ⅲ） is 20.1 kJ·mol^-1. The sorption behavior of IDAAR for In（HI） obeys the Freundlich isotherm. The enthalpy change is AH= 17.2 kJ·mol^-1.     

Removing Al and regenerating caustic soda from the spent washing liquor of Al etching

Spent liquor from washing of aluminum section materials after etching with caustic soda (NaOH) has been treated. Aluminum was removed from the liquor and caustic soda was regenerated by adding precipitating agents to hydrolyze sodium aluminate (Na₂AlO₂), separating the aluminumprecipitate, and concentrating free NaOH in the resulting solution for reuse in the etching process. Four systems were investigated: hydrated lime [Ca(OH)₂], hydrogen peroxide (H₂O₂), H₂O₂/Ca(OH)₂ mixture, and dry lime (CaO). Results revealed that CaO was more efficient in the removal of aluminum from the spent liquor with a higher hydrolyzing rate of Na₂AlO₂ than Ca(OH)₂, H₂O₂, or their mixture. For more information, contact M.A. Barakat, Central Metallurgical R&D Institute, P.O. Box 87 Helwan 11421, Cairo, Egypt; fax: +20-2-501-0639; e-mail: mabarakat@gmail.com.     

Effect of hexamethylpararosaniline chloride (crystal violet) on mild steel corrosion in acidic media

The corrosion inhibition of mild steel in 0.5 M H₂SO₄ and 1 M HCl by hexamethylpararosaniline chloride (HMPC) was investigated using the gravimetric technique in the temperature range 303–333 K. The results indicate that HPMC inhibited the corrosion reaction in both acid media at all temperatures and inhibition efficiency increased with HMPC concentration. The inhibiting action is attributed to general adsorption of protonated and molecular HPMC species on the corroding metal surface. Adsorption followed a modified Langmuir isotherm and the Temkin isotherm, with very high negative values of the free energy of adsorption (). An increase in temperature reduced the inhibition efficiency of HPMC in 0.5 M H₂SO₄ but increased efficiency in 1 M HCl. Activation parameters such as activation energy (E_a), activation enthalpy (ΔH^∗) and activation entropy (ΔS^∗) as well as the adsorption heat (Q_ads) were evaluated from the effect of temperature on corrosion and inhibition processes.     

Triazolyl blue tetrazolium bromide as a novel corrosion inhibitor for steel in HCl and H2SO4 solutions

The inhibition effect of triazolyl blue tetrazolium bromide (TBTB) on the corrosion of cold rolled steel (CRS) in 1.0 M HCl and 0.5 M H₂SO₄ solution was investigated for the first time by weight loss, potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS) methods. The results show that TBTB is a very good inhibitor, and is more efficiency in 1.0 M HCl than 0.5 M H₂SO₄. The adsorption of TBTB on CRS surface obeys Langmuir adsorption isotherm. Polarization curves reveal that TBTB acts as a mixed-type inhibitor in both acids.     

2,5-Bis(4-dimethylaminophenyl)-1,3,4-oxadiazole and 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole as corrosion inhibitors for mild steel in acidic media

2,5-Bis(4-dimethylaminophenyl)-1,3,4-oxadiazole (DAPO) and 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole (DAPT) have been synthesised and their inhibiting action on the corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄ at 30 °C has been investigated by various corrosion monitoring techniques. At constant acid concentration, the inhibitor efficiency of both the compounds is found to increase with inhibitor concentration. DAPT is slightly more efficient in 0.5 M H₂SO₄ than in 1 M HCl whereas DAPO is more efficient in 1 M HCl. Of the two, DAPT appears to be a better inhibitor. Potentiostatic polarisation studies show that both are mixed-type inhibitors in 1 M HCl but cathodic-type in 0.5 M H₂SO₄. The inhibitors function through adsorption following Langmuir isotherm in both the acids. The electronic properties of DAPO and DAPT, obtained using the AM1 semi-empirical quantum chemical approach, have been correlated with their experimental inhibition efficiencies using the linear resistance model (LR). These inhibitors are considered as a non-cytotoxic substances.     

Electrochemical behavior and electrolytic preparation of lead in eutectic NaCl−KCl melts

A novel molten salt extraction process consisting of chlorination roasting and molten salt electrolysis was proposed to develop a more efficient and environmental friendly technology for recovering lead from spent lead acid batteries (LABs). The feasibility of this process was firstly assessed based on thermodynamics fundamentals. The electrochemical behavior of Pb(II) on a tungsten electrode in the eutectic NaCl−KCl melts at 700 °C was then investigated in detail by transient electrochemical techniques. The results indicated that the reduction reaction of Pb(II) in NaCl−KCl melts was a one-step process exchanging two electrons, and it was determined to be a quasi-reversible diffusion-controlled process. Finally, potentiostatic electrolysis was carried out at −0.6 V (vs Ag/AgCl) in the NaCl−KCl−PbCl₂ melts, and the obtained cathodic product was identified as pure Pb by X-ray diffraction analysis. This investigation demonstrated that it is practically feasible to produce pure Pb metal by electrochemical reduction of PbCl₂ in eutectic NaCl−KCl melts, and has provided important fundamental for the further study on lead recovery from spent LABs via molten salt extraction process.     

Regeneration and decontamination of a nickel citrate complex in spent electroless nickel plating solutions

The possibility of citrate precipitation by excess metal ions in alkaline solutions suggests the use of Ni(II) together with OH^? to precipitate a Ni(II)-citrate complex from spent electroless plating solutions. After treatment of the precipitate with acid, excess Ni(II) can be removed in the form of insoluble Ni(OH)₂. The solution of the Ni(II)-citrate complex can then be reused for electroless nickel plating. During this procedure the additive adipate is not regenerated. For decontamination of spent electroless nickel plating solutions Fe(III) can be used as Ni(II)-citrate complex precipitant.     

Mechanism and Kinetics of Corrosion Decomposition of Iron–Vanadium Alloys in Solutions of Acids and Salts

Corrosion of iron–vanadium alloys containing 0 to 100% of vanadium is studied in dilute HCl and H₂SO₄ solutions by gravimetric method and by taking anodic polarization curves. Alloys containing no less than 30% of vanadium are readily passivated in sulfuric acid solution. Local passivity breakdowns (pitting or intergranular corrosion) are observed in HCl solutions. Apparent values of number of electrons, transfer coefficients, exchange currents, and corrosion currents are determined for active alloys. Catalytic action of V(II, III) and V(III) ions in cathodic process in aerated solutions is demonstrated.     

Enhancement of CaMoO4 calcine decomposition and recovery of calcium resource by HCl cycle leaching

The thermodynamic equilibrium diagrams of CaMoO₄–CaSO₄–H₂SO₄–H₂O, CaMoO₄–HCl–H₂O and CaSO₄–CaCl₂–HCl–H₂O systems at 298 K were established. The calculation results demonstrated that HCl displays a much higher solubility of CaSO₄ than H₂SO₄. The leaching mechanism of Mo from CaMoO₄ calcine was systematically investigated from the perspective of the micro particle properties variation. HCl exhibits an excellent leaching performance for Mo from CaMoO₄ calcine due to the elimination of surface coating and the dissolution of a mass of Mo embedded in CaSO₄ matrix. Excellent Mo leaching efficiency of 99.7% was achieved under the optimal conditions of decomposing CaMoO₄ calcine by 2.4 mol/L HCl with a liquid/solid ratio of 10:1 at 50 °C for 60 min. Based on the experimental results, a highly efficient and green cycle leaching process of molybdenum from molybdenite was proposed, which eliminated surface coating and physical entraining, and converted most of the calcium from CaMoO₄ calcine into high purity gypsum by-product.     

Nanocomposites based on magnetite modified by chelate groups for a solid-phase concentration of heavy-metal ions from aqueous solutions

A nanocomposite material with an EDTA counterpart, ethylenediamine triacetate (ED3A), covalently fixed on the surface according to the core–shell technique is obtained in order to develop adsorbents for reversible analytical concentration of heavy-metal ions from solutions. The material is characterized using the methods of IR spectroscopy, X-ray phase analysis, elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. It is shown that magnetite nanocrystallites with a size of 8–10 nm in Fe₃O₄@SiO₂@ED3A are coated by a layer of silicon oxide that enhances 200- to 10-fold the stability of nanoparticles in the aqueous solutions in the range of pH 1–8. It is shown that the separation time of nanocomposites using a NbFeB magnet does not exceed 10 s. According to the data of elemental analysis, the concentration of functional groups on the nanocomposite surface is 0.32 mmol/g. Sorption isotherms of a number of metals on Fe₃O₄@SiO₂@ED3A are studied. They indicate the chemical character of the metal adsorption processes due to their complexation with functional groups. The conditions of sorption concentration of the Fe(II?), Cu(II), Pb(II), Zn(II), and Cd(II) ions from aqueous solutions and their desorption are studied. The affinity of the obtained nanocomposite to heavy-metal ions decreases in the series of Fe(II?) > Cu(II) > Pb(II) > Cd(II) ~ Zn(II). It is shown that all the studied metals (except for Zn(II)) are quantitatively recovered on Fe₃O₄@SiO₂@ED3A from weakly acidic aqueous solutions and are completely desorbed into the solution of 1.0 M HCl or HNO₃.     

Comparison of inhibition efficiency of some azoles on corrosion of type 304 stainless steel in acidic solutions

Abstract

Inhibition efficiencies have been investigated for two types of azole, namely 2-mercaptobenzoazole (CBA) and 2-methylbenzoazole (MBA), containing nitrogen, sulphur, oxygen, or selenium atoms, on the corrosion of type 304 stainless steel in 2M sulphuric acid (H₂SO₄) and 3M hydrochloric acid (HCl). The study was conducted using weight loss, gasometry, and polarisation methods. It was shown that some of the compounds tested provide 90% inhibition efficiency at a concentration of 5 × 10^-4M and that the efficiency depends on the heteroatom and decreases in the order Se > S > N > O. These inhibitors were more efficient in H₂SO₄ than in HCl whereas the opposite is true for inhibitors with nitrogen alone. Adsorption isotherms were fitted to the experimental findings and some thermodynamics functions were obtained.     

Control of zinc corrosion in acidic media: Green fenugreek inhibitor

Fenugreek seeds extract was examined as a green corrosion inhibitor for Zn in 2.0 mol/L H₂SO₄ and 2.0 mol/L HCl solutions by mass loss and electrochemical measurements. Scanning electron microscope (SEM) images show that the surface damage is decreased in the presence of the inhibitor. X-rays photoelectron spectroscopy (XPS) analysis was performed to identify the corrosion product, ZnO, and to prove the inhibitor adsorption mechanism. The maximum inhibition efficiency values are 90.7% after 1 h and 66.6% after 0.5 h by 200 mL/L of fenugreek extract in H₂SO₄ and HCl solutions, respectively. Addition of I⁻ ion greatly improves the inhibition efficiency of fenugreek seeds extract for Zn corrosion in HCl due to the synergistic effect. Potentiodynamic polarization and EIS measurements prove the inhibition ability of fenugreek for Zn corrosion in HCl as indicated by the decreased corrosion current density and increased charge transfer resistance values in the presence of fenugreek.     

Emulgin as an Inhibitor of Corrosion and Hydrogenation of Carbon Steel in Weakly Acidic H2S-Containing Solutions

The protection effect of emulgin (a technological mixture of some primary and secondary aliphatic amines) in concentrations of 0.078 to 0.625 mmol/l from acid, carbon dioxide, and hydrogen sulfide corrosion and hydrogenation of carbon steel St3 was studied. In a 0.005–0.05 M solution of HCl saturated with hydrogen sulfide, the protective value was 97%, no local damage being observed. At higher concentrations of HCl and H₂S, the anodic reaction is inhibited more effectively. The simultaneous presence of H₂S and CO₂ produces virtually the same (or only slightly reduced) effect. Under optimum conditions, steel hydrogenation is suppressed almost completely, especially at high concentrations of HCl and H₂S and at elevated temperatures.     

Effect of Hydroxyethylated Amines on the Corrosion and Hydrogenation of Carbon Steel

Mixtures of hydroxyethylated amines with hydrocarbon radicals C₁₀–C₁₃ and C₁₇–C₂₀ containing 2, 5, and 14 ethyleneoxy groups were tested as inhibitors of general carbon dioxide and hydrogen sulfide corrosion and hydrogenation of carbon steel in weakly acidic hydrochloric media and a simulated highly mineralized stratal water. In electrolytes containing H₂S or CO₂ + H₂S, the protective values of the mixtures were 90 (5 mM HCl) and 96% (50 mM HCl). The hydrogen diffusion through a steel membrane was reduced five times or even suppressed completely by the test compounds.     

Evaluation of hydrogen absorption behaviour during acid etching for surface modification of commercial pure Ti, Ti-6Al-4V and Ni-Ti superelastic alloys

The hydrogen absorption behaviour during acid etching for the surface modification of commercial pure Ti, Ti-6Al-4V and Ni-Ti superelastic alloys has been investigated on the basis of the surface morphology, electrochemical behaviour and hydrogen thermal desorption analysis. To simulate the conventional acid etching for the improvement of the biocompatibility of Ti alloys, the specimens are immersed in 1 M HCl, 1 M H₂SO₄ or 0.5 M HCl + 0.5 M H₂SO₄ aqueous solution at 60 °C. Upon immersion, commercial pure Ti absorbs substantial amounts of hydrogen irrespective of the type of solution. In H₂SO₄ or HCl + H₂SO₄ solutions, the hydrogen absorption occurs for a short time (10 min). For Ti-6Al-4V alloy, no hydrogen absorption is observed in HCl solution, whereas hydrogen absorption occurs in other solutions. For Ni-Ti superelastic alloy, the amount of absorbed hydrogen is large, resulting in the pronounced degradation of the mechanical properties of the alloy even for an immersion time of 10 min, irrespective of the type of solution. The hydrogen absorption behaviour is not necessarily consistent with the morphologies of the surface subjected to corrosion and the shift of the corrosion potential. The hydrogen thermal desorption behaviour of commercial pure Ti and Ni-Ti superelastic alloy are sensitively changed by acid etching conditions. The present results suggest that the evaluation of hydrogen absorption is needed for each condition of acid etching, and that the conventional acid etching often leads to hydrogen embrittlement.     

Corrosion behaviour of carbon steel in different concentrations of HCl solutions containing H2S at 90 °C

The corrosion behavior of SAE-1020 carbon steel in H₂S-containing solutions with different concentration of HCl at 90 °C was investigated by weight loss, electrochemical measurements, SEM and XRD analysis. The results showed that the corrosion rate of carbon steel increased with increasing HCl concentration. Uniform corrosion was found on the carbon steel surface in H₂S + HCl solutions, while corrosion cavities were observed in the solution only containing H₂S. The ratio of Faradaic process of total corrosion process increased with the increase of HCl concentration. The corrosion products were solely composed of mackinawite in the H₂S-containing solutions with or without HCl.