Effects of sulfide and lead nitrate addition to a gold cyanidation circuit using potentiodynamic measurements

Corrosion potentiodynamic polarization experiments on a gold electrode in a cyanide solution with 0–30ppm lead addition and 0–20ppm sulfide were carried out. Solutions containing 300ppm NaCN, adjusted to a pH 11.1 by NaOH and bubbled with air were used at atmospheric pressure and room temperature. If the concentration of lead ions was equal or larger than the sulfide ions a change of potential towards the more negative potential (a potential drop) was observed and this was accompanied by a significant increase in the corrosion rate (up to 10mmy^-1 in certain circumstances). If lead nitrate was added to a solution with a gold electrode that had been previously passivated by sulfides, the corrosion rate typically rose from about 0.3 to 0.95mmy^-1. The addition of lead nitrate to sulfides in cyanide solution can create a synergetic effect which results in an increase in dissolution rates of gold in cyanide solutions and this is accompanied by a drop in the corrosion potential of gold and a dramatic decline in thiocyanate and free sulfide concentrations.     

Characterization of phosphorus availability in selected New Zealand grassland soils

Appropriate evaluation of phosphorus (P) availability in soil is aprerequisite for ensuring the productivity and long-term sustainable managementof agroecosystems. Fifteen soils presently under grassland were collected fromdifferent areas of New Zealand and soil P availability was assessed by isotopicexchange kinetics (IEK) and related to P forms obtained by chemicalfractionation (sequential extraction). Concentrations of total P determined inthe 15 soils ranged from 375 to 2607 mg kg^–1(mean1104 mg kg^–1). Mean concentrations of inorganic P(Pi) extracted by sequential extraction with ammonium chloride, sodiumbicarbonate, sodium hydroxide (first), hydrochloric acid and sodium hydroxide(second) were 1.2, 41, 205, 113 and 23 mg kg^–1,respectively. Mean concentrations of organic P (Po) extracted by sodiumbicarbonate, sodium hydroxide (first) and sodium hydroxide (second) were 133,417 and 105 mg kg^–1, respectively. Similarly,results from IEK analysis showed that the intensity (water soluble Pi (Cp)),capacity (R/r₁ and n), and quantity (E value,isotopically exchangeable P pools (E_{1 min},E_{1 min–24 h},E_{24 h–3 m},E_{>3 m})) factors varied markedlyamongst soils. Thus Cp concentrations ranged from 0.02–1.90 mgL^–1, while concentrations of Pi determined in theE_{1 min}, E_{1 min–24},E_{24 h–3 m},E_{>3 m} pools were 2–29 (mean 10), 10–321(76), 11–745 (152), and 8–498 (177) mgkg^–1, respectively. The corresponding values forR/r₁ and n were 1.0–17.7 (mean 4.5) and0.10–0.50 (mean 0.37), respectively. Regression analysis revealed that Cpconcentrations were exponentially and inversely proportional toR/r₁,n and P sorption index (PSI)(R²=0.806(P<0.01), 0.852 (P<0.01) and 0.660(P<0.01), respectively). Cluster analysis identified twobroad groups of soils, namely those with low P availability (mean Cp0.11 mg L^–1, E_{1 min} Pi 5mg kg^–1, R/r₁ 3.9,n 0.44), and those with high P availability (mean Cp 1.33mg L^–1, E_{1 min} Pi 20mg kg^–1, R/r₁ 1.21,n 0.16). Correlation analysis indicated thatE_{1 min} P i was significantly correlated with bicarbonateextractable Pi (BPi, R²=0.37,P<0.05) and thesum of ammonium chloride extractable Pi (APi) and BPi(R²=0.38,P<0.05). However, the concentration of Pi in theE_{1 min} pool was generally lower than the sum of APi andBPi. Sodium hydroxide extractable Pi (N₁Pi) was significantlycorrelated with the sum of the E_{1 min},E_{1 min–24 h},E_{24 h–3 m} Pi pools(R₂=0.974, P<0.01),indicating that N₁Pi fractioncould be considered as representing potentially available soil P for pasturespecies over a growing season.     

Inhibiting effects of benzotriazole on the corrosion of α-Al-bronze in saline water

The inhibiting effect of benzotriazole (BTA) on the corrosion of -Al-bronze (Cu-7% Al) in 3.4% NaCl was studied. BTA showed good inhibition effects from short up to extended periods of time (about six weeks). The morphologies of the alloy surface were monitored after various periods of corrosion in the absence and presence of BTA, using SEM. The corrosion products were identified by X-ray diffraction. Corrosive attack occurs very early in the absence of BTA, leading to general and pitting corrosion. BTA was found to have a stronger inhibiting effect on the anodic dissolution of copper than on the cathodic reduction of oxygen. The current-potential relation is divided into two regions: region I within which BTA has a strong effect on the charge transfer kinetics, and a limiting current region where BTA has no significant inhibiting effect. It is also shown that the interaction of BTA with a Cu₂0-covered alloy surface is faster than on reduced alloy surfaces, although the protection efficiency on the latter is slightly better than on the former.     

Kinetics and mechanism of the preparation of Raney® copper

Raney® copper is an active hydrogenation catalyst formed by the selective dissolution of aluminium from a Cu–Al alloy. The structure of Raney® copper is presented in a series of images taken using a focussed ion beam miller (FIB). The images show a structure consisting of a uniform three-dimensional network of fine copper ligaments. A rotating disc electrode, used to control the diffusion layer, enabled a study of the kinetics of the leaching reaction at 269–303K in 2–8m NaOH. Under these conditions, the reaction rate was constant and independent of hydroxide concentration. The activation energy for leaching was determined as 69±7kJmol^–1. The mixed corrosion potential of the dissolving alloy has been related to the exposed copper surface area, which in turn is dependent on the leaching rate and the mechanism of rearrangement. The overall mechanism of formation/rearrangement of the Raney® copper structure was found to be mainly dissolution/redeposition of copper atoms, with surface or volume diffusion, or possibly both, playing a minor role.     

A Sol–Gel Derived CuOx/Al2O3–ZrO2 Catalyst for the Selective Reduction of NO by Propane in the Presence of Excess Oxygen

Copper catalysts supported on alumina-doped zirconia were prepared by sol–gel processing followed by supercritical drying or aging in the mother solution at 100°C. After drying and calcination, the catalyst supports were impregnated with a copper(II) nitrate aqueous solution by the incipient wetness method to achieve a Cu loading of about 2%. The samples showed 90% NO conversion at 350–400°C. The catalytic performance of these systems appears to be determined by the degree of clustering of copper cations as probed by FTIR spectroscopy of adsorbed CO.     

Deactivation of ferrierite during the skeletal isomerization of linear butenes

Deactivation of ferrierite during the skeletal isomerization of 1-butene at atmospheric pressure and 0.15 atm 1-butene partial pressure was studied. At 300°C, the carbon content shows a sharp increase during the first 30 min-on-stream, with a slower growth thereafter. Temperature-programmed oxidation profiles corresponding to different times-on-stream are similar, showing two well-defined combustion peaks centered at about 325 and 640°C, respectively. When starting the 1-butene feed with the catalytic bed at 100 or 200°C and then increasing the temperature up to 300°C, no significant difference is observed, neither in carbon content nor in oxidation profiles. Important differences in the profiles are observed by comparing at the same time at each temperature. The lower the temperature, the higher the reactivity toward oxidation at low temperature. The carbonaceous deposit formed at 100°C shows the main combustion peak at the lowest temperature (135°C) and a more olefinic character; it could be related to a strong adsorption of reactant molecules. At 200°C, the proportion of saturated species associated to oligomers increases; while at 300°C, coke shows both aromatic and olefinic species.     

Rate oscillations during partial oxidation of methane over chromel–alumel thermocouples

A chromel–alumel thermocouple has been found to catalyse the methane/oxygen reaction, the main products being CO, H₂ with some CO₂ and H₂O. Regular oscillations in both reactants, products and temperature have been observed at temperatures around 700C. Similar behaviour has been obtained using nickel wires.     

Effects of chloride, bromide and iodide ions on internal stress in films deposited during high speed nickel electroplating from a nickel sulfamate bath

The effects of chloride, bromide and iodide additions on the internal stress developed in nickel films deposited during high speed electroplating from nickel sulfamate baths operated close to the nickel ion limiting current density were investigated. The variations in internal strain in the films were detected in situ using a resistance wire-type strain gauge placed on the reverse side of the copper substrate. The film resistance on the as-plated electrodes was measured using an electronic current interrupter technique. The effects of chloride, bromide, and iodide additions could be classified into two groups: (a) chloride and bromide ions, and (b) iodide ions. For chloride and bromide additions over the concentration range of 0.1 to 0.5M, the nickel deposits exhibited a block- and pyramid-like texture with a (200) crystal orientation. The internal tensile stress developed in 20m thick nickel films deposited in the presence of these two halides was as low as 140–170MPa. Conversely, for additions of iodide, at iodide concentrations greater than 0.1M the deposited nickel exhibited a fine granular texture of disordered crystal orientation. The internal tensile stress developed in 20m thick nickel films deposited from these latter baths tended to rise with increasing iodide concentration to values considerably higher than those observed at similar concentrations of NiCl₂ or NiBr₂.     

Synthesis of ternary Li–Mn–O phase at a temperature of 260 ∘C and electrochemical lithium insertion into the oxide

A lithium–manganese oxide, Li _x MnO₂ (x=0.30.6), has been synthesized by heating a mixture (Li/Mn ratio=0.30.8) of electrolytic manganese dioxide (EMD) and LiNO₃ in air at moderate temperature, 260 C. The formation of the Li–Mn–O phase was confirmed by X-ray diffraction, atomic absorption and electrochemical measurements. Electrochemical properties of the Li–Mn–O were examined in LiClO₄-propylene carbonate electrolyte solution. About 0.3 Li in Li _x MnO₂ (x=0.30.6) was removed on initial charging, resulting in characteristic two discharge plateaus around 3.5V and 2.8V vs Li/Li⁺. The Li _x MnO₂ synthesized by heating at Li/Mn ratio=0.5 demonstrated higher discharge capacity, about 250mAh (g of oxide)^–1 initially, and better cyclability as a positive electrode for lithium secondary battery use as compared to EMD.     

原子力显微镜研究苯并三氮唑对铜的缓蚀作用

铜以及铜合金由于其优良的抗腐蚀性能,广泛用在冷却水系统中,苯并三氮唑(BTA)常常作为铜的缓蚀剂。将传统电化学方法和原子力显微镜(AFM)测试技术相结合,对人造海水中BTA作用于铜电极的缓蚀行为进行了研究。结果表明,BTA能够有效减缓铜在海水中的腐蚀,且随着缓蚀剂浓度的增加,缓蚀效果越明显,100 mg/L的BTA就能够高效的保护铜。电化学结果表明,BTA能够在铜的表面形成致密的保护膜[CuBTA]n;AFM测试表明,随着时间的进行,保护膜越来越致密,保护性能也越好。     

Highly selective propene epoxidation with hydrogen/oxygen mixtures over titania-supported silver catalysts

Silver supported on titania was found to be active for propene epoxidation using hydrogen/oxygen mixtures at 50°C. The dependence of the activity on the preparative method is pronounced, i.e., only catalysts prepared by using deposition–precipitation exhibit activity. Optimum performance was found for 2 wt% Ag/TiO₂ calcined at 400°C. The propene epoxidation activity, the activity in the low-temperature CO oxidation, in propane oxidation and deactivation behavior of these silver catalysts strongly resemble the results obtained for the Au/TiO₂ catalysts developed by Haruta.     

Alkylation of benzene with ethane over platinum-loaded zeolite catalyst

Alkylation of benzene with ethane was carried out using various zeolite catalysts at temperature ranges of 400–550°C. Loading of platinum onto zeolite greatly enhanced the yield of ethylbenzene. Among the zeolites tested, H-ZSM5 and H-MCM22 showed catalytic activities. By contrast, mordenite did not yield ethylbenzene. Moderate acid strength distribution is the key factor of zeolite catalysts. Optimum catalyst and conditions for this reaction are as follows. The platinum-loaded H-ZSM5 catalyst containing 6.8 wt% Pt, at a reaction temperature of 500°C, afforded ethylbenzene and styrene formation rates of 14.2 and 0.8 mmolh^–1g-cat^–1, respectively (benzene-based yields 7.3 and 0.4%). In the alkylation of benzene with ethane over platinum-loaded H-ZSM5, ethene was initially formed from ethane over the metallic platinum. Then the alkylation proceeded over the acid sites of H-ZSM5.     

Effect of benzotriazole (BTA) addition on Polypyrrole film formation on copper and its corrosion protection

Benzotriazole (BTA) was added in a conducting Polypyrrole (PPy) film prepared on copper in oxalic acid aqueous solution containing pyrrole monomer to improve corrosion protection by the PPy film and reduce copper corrosion. When BTA was added in the preparation solution, the copper surface was covered by a BTA–Cu complex layer before the anodic polymerization of PPy was started. On the copper surface with the BTA layer, the initial dissolution of copper was inhibited and the PPy polymerization-deposition was started immediately after the anodic current was imposed. The PPy film thus formed was doped with oxalic ions and ionized BTA and was homogeneous in thickness and strongly adhesive. The PPy film containing BTA protected the copper from corrosion in 3.5 wt.% NaCl solution. In 400 h of immersion, copper dissolution was inhibited with 80% protection efficiency relative to that of bare copper.     

苯并三氮唑及其衍生物对铜的协同缓蚀效应

以苯并三氮唑(BTA)和溴代正丁烷为原料,采用一步法合成了N-丁基苯并三氮唑(N-BBTA),研究了BTA、N-BBTA以及N-BBTA与BTA的复配体系对铜在3％(质量分数)NaC1溶液中的缓蚀行为.结果表明,单一N-BBTA和BTA对铜均具有一定的缓蚀能力.当N-BBTA、BTA浓度为10 mmol/L时,缓蚀率分...     

The effect of benzotriazole on mass transfer in the corrosion of a copper rotating disk electrode

The effect of benzotriazole, BTA, on mass transfer in dissolution-corrosion of the copper rotating disk electrode in 0.02 M Fe(III)–0.5 M H₂SO₄ has been studied by means of atomic absorption spectrometry. The mass transfer coefficient, K, was determined from the slope of ln(C ₀/C)_Fe(III) vs. time plots. In the absence of BTA the corrosion process can be described by the correlation Sh = KR/D = 4.47Re ^0.5. The difference in values between Sh and Sh _Levich, and the change in slope in the Arrenhius plot points to mixed control for the cathodic process Fe³⁺ + 1e^– Fe ²⁺ and charge transfer control for the anodic process, Cu Cu²⁺ + 2e. The average activation energies were 7.7 kJ mol^–1 and 19.5 kJ mol^–1 at (500–1500) and (2000–3000) rpm, respectively. At low concentration of BTA the inhibiting action of BTA increases with concentration and with rotation speed. For [BTA] 5 × 10^–3 M, the K value, 10^–4 cm s^–1, remains constant and is independent of rotation rate. The morphology of the copper rotating disk after corrosion in the absence and presence of BTA was examined using scanning electron microscopy (SEM).     

Thermally stable alumina–gallia aerogel as a catalyst for NO reduction with C3H6 in the presence of excess oxygen

In order to improve thermal stability, an alumina–gallia aerogel was prepared and the catalyst performance for NO reduction with C₃H₆ was compared with that of an alumina–gallia xerogel. Basically, both were prepared by a sol–gel method with supercritical drying for the former, while with oven drying for the latter. Upon heating at 800, 900, and 1000°C, the aerogel exhibited higher NO conversion than the xerogel at reaction temperature <400°C, while NO conversion was lower on the former than on the latter at >500°C. At 450°C, NO conversion was almost the same for these two catalysts. A marked difference was observed upon heating them at 1100°C: the aerogel still maintained quite a high activity, while the xerogel greatly lost it. After heating the aerogel at 1100°C, -phase alumina remained untransformed with its surface area of 80 m²/g, while the xerogel was completely transformed to -alumina with its surface area of 6 m²/g. The high activity remaining on the aerogel heated at 1100°C was ascribed to its large surface area.     

Corrosion behaviour of Zn–Co compositionally modulated multilayers electrodeposited from single and dual baths

The corrosion behaviour of Zn–Co compositionally modulated multilayers (CMM) was studied using corrosion potential measurement and the neutral salt spray (NSS) method. It was established that the corrosion potentials of the CMM, deposited from a single bath, are significantly more positive than those deposited from a dual bath. The best corrosion resistance was found for multilayers consisting of four sublayers, each 3.0m thick, deposited both from a dual bath and from a single bath (with an oversublayer of Zn–Co1%).     

Titania–silica epoxidation catalysts modified by mono- and bidentate organic functional groups

Amorphous, mesoporous titania–silica mixed oxides with covalently bound mono- and bidentate acetoxyalkyl and aminoalkyl functional groups were prepared using the solution sol–gel process and ensuing low temperature supercritical extraction with CO₂. Titanbisacetylace-tonatediisopropoxide, tetramethoxysilane and amino- or acetoxyalkyl-trimethoxysilane precursors were used for the syntheses of hybrid aerogels with a constant Ti:Si atomic ratio of 1:12. The mixed oxides were characterized by thermal analysis, N₂physisorption, ¹³C- and ²⁹Si-CP-MAS NMR spectroscopy, and electron microscopy. The amorphous mesoporous structure of the aerogels depended markedly on the nature of the modifier. Organic modification enhanced remarkably the rate of epoxidation of cyclohexene and cyclohexenol. The highest selectivity in the more demanding epoxidation of cyclohexenol, 91% at 80% TBHP conversion, was achieved with a bidentate (diaminoalkyl)-modified aerogel.     

Impedance spectroscopy study of electrochromism in sputtered iridium oxide films

The a.c. impedance response of sputtered iridium oxide films (SIROFs) was studied at room temperature in 1M H₂SO₄ between 1mHz and 50mHz. The spectra were recorded as a function of applied potential in the range of electrochromic properties from 0.0 to 1.0V vs SCE and before and after an electrochemical treatment consisting of alternatively colouring and bleaching the electrode. The spectra were analysed with help of an equivalent circuit. Between 0.4 and 1.0V, the spectra can be interpreted as due to electrochemical proton insertion in a single phased compound. From the data, hydrogen chemical diffusion coefficients with values ranging from 2 × 10^–8 to 1.1 × 10^–7cm²s^–1 are found. It is shown that this parameter increases fourfold after the cycling treatment and significantly decreases with the amount of inserted hydrogen. Below 0.4V spectrum changes are observed over the intermediate frequency range studied, indicating some changes of the interfacial reactivity which remain to be clarified.     

Inhibition of mild steel corrosion in groundwater by pyrrole and thienylcarbonyl benzotriazoles

The inhibition efficiency of Zn²⁺, 3-phosphonopropionic acid (3-PPA), benzotriazole (BTA) and two synthesized benzotriazole derivatives namely 1-(2-pyrrole carbonyl) benzotriazole (PCBT) and 1-(2-thienylcarbonyl) benzotriazole (TCBT) were evaluated as inhibitors for the corrosion of mild steel in ground water. The inhibition efficiencies of PCBT and TCBT in combination with Zn²⁺ and 3-PPA were also investigated and the results were compared with BTA. In order to study the corrosion rate and inhibition efficiency we employed potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Further characterization using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) demonstrates the adsorption of inhibitor and the formation of corrosion products on the mild steel surface, respectively. Combination of PCBT along with Zn²⁺ and 3-PPA shows better corrosion inhibition efficiency than other inhibitor combinations and the individual inhibitors.