J. Telegdi

Bioleaching - a result of interfacial processes caused by extracellular polymeric substances (EPS).

Abstract Extracellular polymeric substances (EPS) seem to play a pivotal role in bioleaching—the winning of precious metals as well as acid rock drainage. For a better control of both processes structure and function of extracellular polymeric substances from leaching bacteria are of crucial importance. Our research focussed on Acidithibacillus ferrooxidans, the composition of its extracellular polymeric substances and further deduction of their function. The extracellular polymeric substances of Acidithiobacillus ferrooxidans consist mainly of neutral sugars and lipids. The functions of the extracellular polymeric substances of this leaching bacterium seem to be (i) to mediate attachment to a (metal) sulfide surface, (ii) to concentrate iron(III) ions by complexation through uronic acids or other residues at the mineral surface and, thus, allowing for an oxidative attack on the sulfide. Consequently, dissolution of the metal sulfide is enhanced, which may result in an acceleration of 20- to 100-fold over chemical leaching. Experiments were performed to elucidate the importance of the iron(III) ions complexed by extracellular polymeric substances for strain-specific differences in oxidative activity for pyrite. The preliminary data indicate that strains of Acidithiobacillus ferrooxidans, with a high amount of iron(III) ions in their extracellular polymeric substances, possess a higher oxidation activity than those with less iron(III) ions. These data provide new insight into the function of extracellular polymeric substances and the consequent advantage conferred to bacteria involved in bioleaching.

Influence of cations on the corrosion inhibition efficiency of aminophosphonic acid

Abstract The iron/electrolyte interphase has been studied in the presence of N , N -di(phosphonomethyl)glycine (DPMG) inhibitor with or without the bivalent cations. In electrochemical measurements, inhibition was assumed by the formation of a complex in the presence of DPMG. In situ atomic force microscopy provided direct insight into changes in the surface morphology at several hundred nanometres when topographical changes owing to the breakdown of the passive layer, and initiation of corrosion were monitored. Section analysis has revealed the degree of deterioration. Bivalent cations (Ba 2+ , Sr 2+ , Ca 2+ and Zn 2+ ) synergically improved the activity of DPMG, though the mechanism was different. Barium, strontium and calcium ions in blends hindered the anodic iron dissolution, while zinc ions influenced both the anodic and cathodic processes. Composition of the surface layer was analysed by X-ray photoelectron spectroscopy (XPS). The 2:1 Ba 2+ /Sr 2+ /Ca 2+ /DPMG molar ratio in the solution resulted in a surface layer with a composition of about 1.3:1 of cation/DPMG. In the case of Zn 2+ /DPMG mixture the surface layer was composed of a mixture of slightly soluble Zn 2+ /DPMG (∼3:l) and zinc hydroxide.

An investigation of copper corrosion inhibition in chloride solutions by benzo-hydroxamic acids

Benzo-hydroxamic acids (BHA) are investigated as potential copper corrosion inhibitors in chloride solution. The BHAs investigated were: p-chloro-benzo-hydroxamic (p-Cl-BHA), o-chloro-benzo-hydroxamic acid (o-Cl-BHA), P-nitro-benzo-hydroxamic acid (p-N-BHA) and o-methyl-benzo-hydroxamic acid (o-M-BHA). Electrochemical measurements, potentiostatic polarization and ac impedance spectroscopy were carried out to evaluate the inhibition effect of the investigated BHAs. An Electrochemical Quartz Crystal Microbalance (ECQM) was used to measure electrode corrosion and inhibitor adsorption or layer formation processes. A poorly soluble layer consisting of the inhibitor and copper corrosion products is proposed to account for the protective effect in chloride solutions.

EQCM study of copper and iron corrosion inhibition in presence of organic inhibitors and biocides

Attention has been devoted to the application of quartz crystal microbalance (QCM) in the field of corrosion and corrosion inhibition. In-situ measurements were performed on copper and iron surfaces. Copper corrosion inhibition by the application of several inhibitors was followed by QCM. Copper corrosion inhibition in different electrolyte solutions such as acidic sodium sulphate and neutral sodium chloride were investigated. Different inhibitor compounds were tested for protection against copper corrosion. Three different groups of inhibitors were investigated; aromatic sulfoxides, benzo-hydroxamic acid derivatives, and azole derivatives. Among the tested sulfoxides, di-benzyl-sulfoxide (DBSO) produced the best protection, while p-chloro-benzo-hydroxamic acid showed excellent protection among the benzo-hydroxamic acid derivatives. Among the tested azole derivatives, 5-mercapto-1-phenyl-tetrazole (5-McPhTT) and 5-(4′-isopropylbenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (5-IPBDT) showed excellent inhibition properties against copper corrosion in acidic media. The effect of biocides, namely N-hydroxyalkylated amino acids, on biofilm formation has been investigated, too. From the attained results, it is clear that QCM is an essential tool for obtaining important information on corrosion inhibition and its mechanism.

Corrosion and scale inhibitors with systematically changed structure

Abstract The corrosion inhibiting properties of some substituted carboxylic acids were studied with respect to the corrosion of mild steel in neutral solutions. Corrosion inhibition varied with the nature of the substituted components. The concentration dependence of inhibition was determined for the most efficient compounds.

The effect of calcium ions on the adsorption of phosphonic acid: a comparative investigation with emphasis on surface analytical methods

Abstract The influence of calcium ions on the adsorption of 1-hydroxy-ethane-1,1-diphosphonic acid (HEDP) on Fe electrodes has been examined. Surface analytical methods (XPS and XAES) have been applied in order to obtain direct information on the structure of the surface layer. On the surfaces of electropolished samples, various Fe 2+ , Fe 3+ and FeOOH compounds as well as the metallic state of Fe could be identified in the surface layers. HEDP was adsorbed on the iron surface in almost the same extent, when the basic solutions were bidistilled water or 0.5 mol dm −3 NaClO 4 , respectively. The presence of Ca 2+ cations increased the quantity of phosphonate adsorbed on the metal surface considerably. Varying the Ca/HEDP molar ratio in the solution between 0.5 and 4.0, the Ca/HEDP molar ratio on the metal surface remained under a limit close to one, corresponding to what could be expected on the basis of the results obtained by radiotracer method.

Nanolayer barriers for inhibition of copper corrosion

Abstract Protective nanolayers of alkyl hydroxamic acids deposited on a copper surface as a Langmuir-Blodgett film (LB) or as a self assembled molecular layer (SAM) were studied in acidic and neutral sodium chloride and sodium sulphate solutions. The LB film deposition and SAM formation on copper substrate were followed by a surface visualisation technique and by contact angle measurement. Following exposure to aggressive electrolytes the anticorrosion abilities of the monolayers and multilayers were characterised by image analysis, by the roughness of the copper surface, and by an electrochemical method.

Inhibition efficiency of N-containing carboxylic and carboxy-phosphonic acids

Abstract Organic compounds for protection against corrosion—mainly amino carboxylic acids and their N -phosphonomethyl derivatives -with or without additives (zinc or metavanadate ion) have been studied in neutral solution by three different methods via impedance spectroscopy, weight loss and potentiostatic polarization in order to show the significance of CH 2 -PO 3 H 2 substitution and to detect a synergism in the presence of metals. For understanding the synergistic effect the stability of the zinc ion complex with organic acids was determined pH-metrically.

Adsorption of a PEO–PPO–PEO triblock copolymer on metal oxide surfaces with a view to reducing protein adsorption and further biofouling

Abstract Biomolecule adsorption is the first stage of biofouling. The aim of this work was to reduce the adsorption of proteins on stainless steel (SS) and titanium surfaces by modifying them with a poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–PEO triblock copolymer. Anchoring of the central PPO block of the copolymer is known to be favoured by hydrophobic interaction with the substratum. Therefore, the surfaces of metal oxides were first modified by self-assembly of octadecylphosphonic acid. PEO–PPO–PEO preadsorbed on the hydrophobized surfaces of titanium or SS was shown to prevent the adsorption of bovine serum albumin (BSA), fibrinogen and cytochrome C, as monitored by quartz crystal microbalance (QCM). Moreover, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry were used to characterize the surfaces of the SS and titanium after competitive adsorption of PEO–PPO–PEO and BSA. The results show that the adsorption of BSA is well prevented on hydrophobized surfaces, in contrast to the surfaces of native metal oxides.

Influence of poly(ethylene oxide)-based copolymer on protein adsorption and bacterial adhesion on stainless steel: Modulation by surface hydrophobicity

The aim of the present work is to study the adhesion of Pseudomonas NCIMB 2021, a typical aerobic marine microorganism, on stainless steel (SS) substrate. More particularly, the potential effect on adhesion of adsorbed poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer is investigated. Bacterial attachment experiments were carried out using a modified parallel plate flow chamber, allowing different surface treatments to be compared in a single experiment. The amount of adhering bacteria was determined via DAPI staining and fluorescence microscopy. X-ray photoelectron spectroscopy (XPS) was used to characterize the surface chemical composition of SS and hydrophobized SS before and after PEO-PPO-PEO adsorption. The adsorption of bovine serum albumin (BSA), a model protein, was investigated to test the resistance of PEO-PPO-PEO layers to protein adsorption. The results show that BSA adsorption and Pseudomonas 2021 adhesion are significantly reduced on hydrophobized SS conditioned with PEO-PPO-PEO. Although PEO-PPO-PEO is also found to adsorb on SS, it does not prevent BSA adsorption nor bacterial adhesion, which is attributed to different PEO-PPO-PEO adlayer structures on hydrophobic and hydrophilic surfaces. The obtained results open the way to a new strategy to reduce biofouling on metal oxide surfaces using PEO-PPO-PEO triblock copolymer.