Electrochemical oxidation of cyanide on 3D Ti-RuO2 anode using a filter-press electrolyzer.

The novelty of this communication lies in the use of a Ti-RuO2 anode which has not been tested for the oxidation of free cyanide in alkaline media at concentrations similar to those found in wastewater from the Merrill Crowe process (100 mg L-1 KCN and pH 11), which is typically used for the recovery of gold and silver. The anode was prepared by the Pechini method and characterized by SEM. Linear sweep voltammetries on a Ti-RuO2 rotating disk electrode (RDE) confirmed that cyanide is oxidized at 0.45 < E < 1.0 V vs SHE, while significant oxygen evolution reaction (OER) occurred. Bulk oxidation of free cyanide was investigated on Ti-RuO2 meshes fitted into a filter-press electrolyzer. Bulk electrolyzes were performed at constant potentials of 0.85 V and 0.95 V and at different mean linear flow rates ranging between 1.2 and 4.9 cm s-1. The bulk anodic oxidation of cyanide at 0.85 V and 3.7 cm s-1 achieved a degradation of 94%, with current efficiencies of 38% and an energy consumption of 24.6 kWh m-3. Moreover, the degradation sequence of cyanide was also examined by HPLC.

Arsenopyrite weathering under conditions of simulated calcareous soil.

Mining activities release arsenopyrite into calcareous soils where it undergoes weathering generating toxic compounds. The research evaluates the environmental impacts of these processes under semi-alkaline carbonated conditions. Electrochemical (cyclic voltammetry, chronoamperometry, EIS), spectroscopic (Raman, XPS), and microscopic (SEM, AFM, TEM) techniques are combined along with chemical analyses of leachates collected from simulated arsenopyrite weathering to comprehensively examine the interfacial mechanisms. Early oxidation stages enhance mineral reactivity through the formation of surface sulfur phases (e.g., S n (2-)/S(0)) with semiconductor properties, leading to oscillatory mineral reactivity. Subsequent steps entail the generation of intermediate siderite (FeCO3)-like, followed by the formation of low-compact mass sub-micro ferric oxyhydroxides (α, γ-FeOOH) with adsorbed arsenic (mainly As(III), and lower amounts of As(V)). In addition, weathering reactions can be influenced by accessible arsenic resulting in the formation of a symplesite (Fe3(AsO4)3)-like compound which is dependent on the amount of accessible arsenic in the system. It is proposed that arsenic release occurs via diffusion across secondary α, γ-FeOOH structures during arsenopyrite weathering. We suggest weathering mechanisms of arsenopyrite in calcareous soil and environmental implications based on experimental data.

Chemical treatment of the intra-canal dentin surface: a new approach to modify dentin hydrophobicity.

OBJECTIVE: This study evaluated the hydrophobicity of dentin surfaces that were modified through chemical silanization with octadecyltrichlorosilane (OTS). MATERIAL AND METHODS: An in vitro experimental study was performed using 40 human permanent incisors that were divided into the following two groups: non-silanized and silanized. The specimens were pretreated and chemically modified with OTS. After the chemical modification, the dentin hydrophobicity was examined using a water contact angle measurement (WCA). The effectiveness of the modification of hydrophobicity was verified by the fluid permeability test (FPT). RESULTS AND CONCLUSIONS: Statistically significant differences were found in the values of WCA and FPT between the two groups. After silanization, the hydrophobic intraradicular dentin surface exhibited in vitro properties that limit fluid penetration into the sealed root canal. This chemical treatment is a new approach for improving the sealing of the root canal system.

Influence of the surface speciation on biofilm attachment to chalcopyrite by Acidithiobacillus thiooxidans.

Surfaces of massive chalcopyrite (CuFeS2) electrodes were modified by applying variable oxidation potential pulses under growth media in order to induce the formation of different secondary phases (e.g., copper-rich polysulfides, S n(2-); elemental sulfur, S(0); and covellite, CuS). The evolution of reactivity (oxidation capacity) of the resulting chalcopyrite surfaces considers a transition from passive or inactive (containing CuS and S n(2-)) to active (containing increasing amounts of S(0)) phases. Modified surfaces were incubated with cells of sulfur-oxidizing bacteria (Acidithiobacillus thiooxidans) for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the density of cells attached to chalcopyrite surfaces, the structure of the formed biofilm, and their exopolysaccharides and nucleic acids were analyzed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy coupled to dispersive X-ray analysis (SEM-EDS). Additionally, CuS and S n(2-)/S(0) speciation, as well as secondary phase evolution, was carried out on biooxidized and abiotic chalcopyrite surfaces using Raman spectroscopy and SEM-EDS. Our results indicate that oxidized chalcopyrite surfaces initially containing inactive S n(2-) and S n(2-)/CuS phases were less colonized by A. thiooxidans as compared with surfaces containing active phases (mainly S(0)). Furthermore, it was observed that cells were partially covered by CuS and S(0) phases during biooxidation, especially at highly oxidized chalcopyrite surfaces, suggesting the innocuous effect of CuS phases during A. thiooxidans performance. These results may contribute to understanding the effect of the concomitant formation of refractory secondary phases (as CuS and inactive S n(2-)) during the biooxidation of chalcopyrite by sulfur-oxidizing microorganisms in bioleaching systems.

Chemical treatment of the intra-canal dentin surface: a new approach to modify dentin hydrophobicity

Objective: This study evaluated the hydrophobicity of dentin surfaces that were modified through chemical silanization with octadecyltrichlorosilane (OTS). Material and Methods: An in vitro experimental study was performed using 40 human permanent incisors that were divided into the following two groups: non-silanized and silanized. The specimens were pretreated and chemically modified with OTS. After the chemical modification, the dentin hydrophobicity was examined using a water contact angle measurement (WCA). The effectiveness of the modification of hydrophobicity was verified by the fluid permeability test (FPT). Results and Conclusions: Statistically significant differences were found in the values of WCA and FPT between the two groups. After silanization, the hydrophobic intraradicular dentin surface exhibited in vitro properties that limit fluid penetration into the sealed root canal. This chemical treatment is a new approach for improving the sealing of the root canal system.

Evolution of biofilms during the colonization process of pyrite by Acidithiobacillus thiooxidans.

We have applied epifluorescence principles, atomic force microscopy, and Raman studies to the analysis of the colonization process of pyrite (FeS(2)) by sulfuroxidizing bacteria Acidithiobacillus thiooxidans after 1, 15, 24, and 72 h. For the stages examined, we present results comprising the evolution of biofilms, speciation of S (n) (2-) /S(0) species, adhesion forces of attached cells, production and secretion of extracellular polymeric substances (EPS), and its biochemical composition. After 1 h, highly dispersed attached cells in the surface of the mineral were observed. The results suggest initial non-covalent, weak interactions (e.g., van der Waal's, hydrophobic interactions), mediating an irreversible binding mechanism to electrooxidized massive pyrite electrode (eMPE), wherein the initial production of EPS by individual cells is determinant. The mineral surface reached its maximum cell cover between 15 to 24 h. Longer biooxidation times resulted in the progressive biofilm reduction on the mineral surface. Quantification of attached cell adhesion forces indicated a strong initial mechanism (8.4 nN), whereas subsequent stages of mineral colonization indicated stability of biofilms and of the adhesion force to an average of 4.2 nN. A variable EPS (polysaccharides, lipids, and proteins) secretion at all stages was found; thus, different architectural conformation of the biofilms was observed during 120 h. The main EPS produced were lipopolysaccharides which may increase the hydrophobicity of A. thiooxidans biofilms. The highest amount of lipopolysaccharides occurred between 15-72 h. In contrast with abiotic surfaces, the progressive depletion of S (n) (2-) /S(0) was observed on biotic eMPE surfaces, indicating consumption of surface sulfur species. All observations indicated a dynamic biooxidation mechanism of pyrite by A. thiooxidans, where the biofilms stability and composition seems to occur independently from surface sulfur species depletion.

Influence of the sulfur species reactivity on biofilm conformation during pyrite colonization by Acidithiobacillus thiooxidans.

Massive pyrite (FeS2) electrodes were potentiostatically modified by means of variable oxidation pulse to induce formation of diverse surface sulfur species (S(n)²â», S°). The evolution of reactivity of the resulting surfaces considers transition from passive (e.g., Fe(1-x )S2) to active sulfur species (e.g., Fe(1-x )S(2-y ), S°). Selected modified pyrite surfaces were incubated with cells of sulfur-oxidizing Acidithiobacillus thiooxidans for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the attached cells density and their exopolysaccharides were analyzed by confocal laser scanning microscopy (CLMS) and atomic force microscopy (AFM) on bio-oxidized surfaces; additionally, S(n)²â»/S° speciation was carried out on bio-oxidized and abiotic pyrite surfaces using Raman spectroscopy. Our results indicate an important correlation between the evolution of S(n)²â»/S° surface species ratio and biofilm formation. Hence, pyrite surfaces with mainly passive-sulfur species were less colonized by A. thiooxidans as compared to surfaces with active sulfur species. These results provide knowledge that may contribute to establishing interfacial conditions that enhance or delay metal sulfide (MS) dissolution, as a function of the biofilm formed by sulfur-oxidizing bacteria.

Galena weathering under simulated calcareous soil conditions.

Exploitation of polymetallic deposits from calcareous mining sites exposes galena and others sulfides to weathering factors. Galena weathering leads to the formation of lead phases (e.g., PbSO(4), PbCO(3)) with a higher bioaccessibility than galena, thus increasing the mobility and toxicity of lead. Despite the environmental impacts of these lead phases, the mechanisms of galena oxidation and the transformation of lead secondary phases, under neutral-alkaline carbonated conditions, have rarely been studied. In this work, an experimental approach, combining electrochemical and spectroscopic techniques, was developed to examine the interfacial processes involved in the galena weathering under simulated calcareous conditions. The results showed an initial oxidation stage with the formation of an anglesite-like phase leading to the partial mineral passivation. Under neutral-alkaline carbonated conditions, the stability of this phase was limited as it transformed into a cerussite-like one. Based on the surface characterization and the formation of secondary species, the weathering mechanisms of galena in calcareous soil and its environmental implications were suggested.

Propriedades físico-químicas da água potencialmente oxidativa e sua capacidade de remoção da camada residual de instrumentação / Physico-chemical properties of the potentially oxidative water and its capability of the instrumentation residual layer remotion

O objetivo deste estudo foi elaborar a água potencialmente oxidativa (APO) e analisar algumas de suas propriedades físico-químicas: pH, densidade, tensão superficial, ângulo de contato, condutividade e potencial ação de oxidorredução. Além disso, buscou-se comparar sua capacidade de remoção de matéria orgânica e inorgânica à do hipoclorito de sódio a 1% associado ao EDTA a 17%. A APO foi obtida por processo de eletrólise, e foram determinadas suas propriedades físico-químicas em 0, 1, 3, 5 e 7 dias. Para avaliar a capacidade de remoção da camada residual de instrumentação utilizaram-se 30 pré-molares unirradiculares extraídos de humanos, por razões periodontais divididos em três grupos: controle positivo (NaOCL+EDTA), controle negativo (água destilada) e experimental (APO). Após o preparo, as amostras foram observadas sob microscopia eletrônica com aumento de 2.500x nos terços médio e apical, tendo sido utilizada a escala Rome (quantidade de túbulos dentinários abertos) por um pesquisador que não participou do estudo. Para a análise estatística aplicaram-se o teste de qui-quadrado e a prova exata de Fisher r. Na análise dos resultados foi possível observar que, de acordo com os valores obtidos das propriedades físico-químicas determinadas, a solução se mantém constante nos diferentes tempos de avaliação. De acordo com a comparação dos valores obtidos na avaliação das amostras no terço médio e apical baseados no sistema Rome, houve diferença estatística entre os grupos controle negativo (água destilada) e positivo (p<0,05 ­ exata de Fisher), assim como entre o grupo controle negativo (água destilada) e experimental [APO (p<0,05 ­ exata de Fisher)]. Não houve diferença estatística entre grupo controle positivo (NaOCl associado ao EDTA) e grupo experimental (APO). Conseguiu-se a obtenção eletrolítica da APO, que, de acordo com as propriedades físico-químicas determinadas, tem uma estabilidade de até 7 dias. Os resultados da análise sob microscopia permitiram observar que a APO atingiu 75% de túbulos dentinários permeáveis, e assim se demonstra que tal solução tem a capacidade de remover matéria orgânica e inorgânica. Sem dúvida, para poder propor o uso da APO como solução irrigadora em Endodontia é imperiosa a realização de estudos de citotoxicidade e biocompatibilidade

The purpose of the study was to elaborate the potentially oxidative water (POW) and analyze some of the physico-chemical properties: pH density, superficial stress, contact angle, conductivity and REDOX potential; besides comparing its POW organic as well as non-organic matter removal capacity with hypochlorite sodium at 1% plus 17% EDTA. For the methodology the POW elaboration an electrolysis process was used and the physico-chemical properties were determined in 0, 1, 3, 5 and 7 days. For the removal capacity of teeth tartar evaluation, 30 extracted uniradicular premolars were used, divided in three groups: positive control (NaOCl at 1% + EDTA at 17%), negative control (distilled water) and experimental (POW). Afterwards, the samples were observed under electronic microscopy with 2500x magnifying at the middle thirds and apical, analyzing them with the Rome scale (amount of open dental tubes). For the statistical analysis the Chi-square and the Fisher Exact Proof was used. The results showed that the solution was constantly maintained at all times during the evaluation and there was found statistical difference between negative control and positive control and between negative control and the experimental group. With regards to the dental tartar removal it was found that there was no statistical difference between the control group and the experimental group (POW); reason why it is concluded that the POW has the capacity to remove dental tartar. Nevertheless, to be able to propose the use of the POW as an irrigator solution in Endodontics it is necessary to do further studies to evaluate its cytotoxicity and biocompability