The kinetics of the dissolution of chrysocolla in acid solutions

The dissolution of liberated chrysocolla particles in dilute (0.033 to 0.15 mol L−1) sulfuric acid solutions has been shown to be relatively rapid and the kinetics of dissolution are consistent with rate-determining diffusion of acid through the silica layer that is formed around the particles from which the copper has been dissolved. The rate is inversely proportional to the square of the particle size and increases linearly with increasing acidity. The effect of the addition of chloride ions on the rate is negligible at concentrations below 70 g/L chloride. Addition of sulphate ions results in reduced rates of dissolution due to complexation of the proton by sulphate ions. The effect of temperature is relatively small as expected for a process for which the rate is controlled by diffusion. The rate of dissolution in dilute acid is slower than malachite but faster than tenorite under the same conditions. These results suggest that heap leaching of chrysocolla in dilute acid may be slow relative to malachite but should present no chemical problems and that there is no advantage to be gained from the addition of chloride ions. High sulphate concentrations (100 g/L) in the raffinate solution to the heap could reduce the rate by up to one-half

Investigation of complexation and solubility equilibria in the copper(I)/cyanide system at 25°C

The complexation of copper(I) by cyanide ions (CN−) in aqueous solution has been studied by glass electrode potentiometry at 25 °C and ionic strengths (I) of 1, 3 and 5 M in NaCl media. Overall formation constants, βn, for the equilibria: Cu+(aq) + nCN−(aq) ⇌ Cu(CN)n(n − 1)−(aq) with n = 2, 3 and 4, were quantified, along with the ionization constant (Kw) of water and the acid dissociation constant (Ka) of HCN(aq). The solubility constants *Ksn for the equilibria: CuCN(s) + (n − 1)HCN0(aq) ⇌ Cu(CN)n(n − 1)−(aq) + (n − 1)H+(aq) were also determined from a re-analysis of published solubility data for CuCN(s) in acidic cyanide solutions at I = 1 M(NaCl) and 25 °C. Because of the instability of uncomplexed Cu+(aq) and parameter correlations in the data, neither β1 nor the solubility product Ks0 (CuCN(s) ⇌ Cu+(aq) + CN−(aq)) could be reliably determined from the present data although estimates are presented

Engineered expression of the invertebrate‐specific scorpion toxin AaHIT reduces adult longevity and female fecundity in the diamondback moth Plutella xylostella

Background: Previous Genetic Pest Management (GPM) systems in diamondback moth (DBM) have relied on expressing lethal proteins (‘effectors’) that are ‘cell‐autonomous’ i.e. do not leave the cell they are expressed in. To increase the flexibility of future GPM systems in DBM, we aimed to assess the use of a non cell‐autonomous, invertebrate‐specific, neurotoxic effector – the scorpion toxin AaHIT. This AaHIT effector was designed to be secreted by expressing cells, potentially leading to effects on distant cells, specifically neuromuscular junctions. Results: Expression of AaHIT caused a ‘shaking/quivering’ phenotype which could be repressed by provision of an antidote (tetracycline); a phenotype consistent with the AaHIT mode‐of‐action. This effect was more pronounced when AaHIT expression was driven by the Hr5/ie1 promoter (82.44% of males, 65.14% of females) rather than Op/ie2 (57.35% of males, 48.39% of females). Contrary to expectations, the shaking phenotype and observed fitness costs were limited to adults where they caused severe reductions in mean longevity (‐81%) and median female fecundity (‐93%). qPCR of AaHIT expression patterns and analysis of piggyBac‐mediated transgene insertion sites suggest that restriction of observed effects to the adult stages may be due to influence of local genomic environment on the tetO‐AaHIT transgene. Conclusion: We have demonstrated the feasibility of using non cell‐autonomous effectors within a GPM context for the first time in the Lepidoptera, one of the most economically damaging orders of insects. These findings provide a framework for extending this system to other pest Lepidoptera and to other secreted effectors

Effect of halides in the electrowinning of zinc. II. Corrosion of lead-silver anodes

This paper summarizes experimental results obtained from a series of laboratory scale electrowinning tests conducted over 5 months to quantify the effects of halides (chloride, fluoride and bromide) on the performance and corrosion of lead-silver anodes under conditions similar to those used during the electrowinning of zinc. The parameters investigated include operating anode potential, corrosion rate and anode scale/cell mud generation rates. Information was also obtained on the consumption of halides and manganese ions and the composition of the anode scale and cell mud. The results have confirmed plant observations of excessive anode corrosion and chlorine emissions at a chloride concentration of 400 mg/L but not at a concentration of 200 mg/L. It has also confirmed the importance of maintaining a suitable manganese(II) concentration in the electrolyte. Bromide and fluoride ions, albeit at lower concentrations, do not have measurable effects on anode corrosion. Although a definitive explanation for enhanced local corrosion at high chloride concentrations has not been advanced, the nature of the accelerated corrosion suggests that a crevice-like corrosion process is responsible for localized massive corrosion. This has been attributed to the presence of high acidity and permanganate ions between the manganese oxide layer and the alloy surface

The effects of halides in the electrowinning of zinc. I. Oxidation of chloride on lead-silver anodes

A study of the kinetics of the anodic oxidation of chloride ions on the surface of lead-silver anodes used for the electrowinning of zinc has shown some interesting and practically important results. Oxidation of chloride does not occur on a PbSO4 surface but occurs readily on a PbO2 surface. Oxidation of chloride occurs at the mass-transport controlled rate at the operating potentials of anodes during the electrowinning of zinc in the absence of manganese in the electrolyte. However, the rate of oxidation of chloride ions is significantly lower in the presence of manganese ions in the concentration range 1 to 5 g/L. These results have been compared with plant observations that confirm the lower rate of chlorine generation in the presence of manganese. The use of periodic current reversal does not increase the rate of oxidation of chloride ions in the presence of manganese ions. The rate of anodic oxidation of chloride in the presence of manganese ions is too low to be of practical value in controlling the chloride levels during the electrowinning of zinc

Kinetics of the oxidation of iron(II) by oxygen and hydrogen peroxide in concentrated chloride solutions – A re-evaluation and comparison with the oxidation of copper(I)

The kinetics of the oxidation of iron(II) in 4 M sodium chloride solutions has been studied in order to resolve differences in the rates and rate equations from previously published studies. It has been confirmed that the rate is second order in iron(II) and first order in dissolved oxygen. The presence of trace concentrations of copper in the iron(II) solutions and catalysis by platinum metal used to monitor the solution potentials in previous studies have been experimentally identified as points of difference. The rates of oxidation of iron(II) and copper(I) by peroxide under similar conditions have been studied and the rate equations shown to be first order in both metal ion and peroxide. It is shown that peroxide is not a detectable intermediate in the reduction of oxygen by iron(II). Comparison with published data for the oxidation of copper(I) and that of iron(II) by oxygen in the presence of strongly complexing anions for iron(III) suggests that both outer-sphere and inner-sphere mechanisms are involved in the oxidation of iron(II) depending on the equilibrium for the transfer of the first electron to oxygen. This interpretation is supported by thermodynamic calculations and published kinetic data for the oxidation of iron(II) and copper(I) by the perhydroxyl radical

A potentiometric study of the association of copper(II) and sulfate ions in aqueous solution at 25 °C

A study of the association between copper(II) and sulfate ions in aqueous solution has been made using copper ion-selective electrode potentiometry at constant ionic strengths (I) of 0.05, 0.1, 0.25, 0.5, 1.0, 3.0 and 5.0 mol·L-1 in NaClO4 media at 25 °C. Only one complex was detected, corresponding to the equilibrium: (Formula presented.) No higher order complexes were detected even at sulfate/copper(II) concentration ratios of up to 1,000. The present potentiometric values of log10K1(I) are shown to be consistently higher than those obtained by UV-Vis spectrophotometry because of the failure of the latter technique to detect all of the solvent-separated ion pairs present. Extrapolation of log10K1(I) to infinite dilution using an extended Guggenheim equation yielded a standard state value of log10(Formula presented.), which is in excellent agreement with a recent IUPAC-recommended value

Ion association and hydration in aqueous solutions of copper(II) Sulfate from 5 to 65 °C by dielectric spectroscopy

Aqueous solutions of copper(II) sulfate have been studied by dielectric relaxation spectroscopy (DRS) over a wide range of frequencies (0.2 ≲ v/ GHz ≤ 89), concentrations (0.02 ≤ m/mol kg-1 ≲ 1.4), and temperatures (5 ≤ t/°C ≤ 65). The spectra show clear evidence for the simultaneous existence of double-solvent-separated, solvent-shared, and contact ion pairs at all temperatures, with increasing formation especially of contact ion pairs with increasing temperature. The overall ion association constant KA0 corresponding to the equilibrium: Cu2+(aq) + SO42-(aq) ⇌ CuSO40(aq) was found to be in excellent agreement with literature data over the investigated temperature range. However, the precision of the spectra and other difficulties did not allow a thermodynamic analysis of the formation of the individual ion-pair types. Effective hydration numbers derived from the DRS spectra were high but consistent with simulation and diffraction data from the literature. They indicate that both ions influence solvent water molecules beyond the first hydration sphere. The implications of the present findings for previous observations on copper sulfate solutions are briefly discussed