Direct Contact Method Research Articles

Ultrasonic and thermographic studies for CFRP inspections with real and simulated defects

This paper deals with an overview of improved UT control procedures, related to defect investigation on advanced CFRP composite elements for aeronautical structures; the inspection procedures were evaluated with different frequency probes, employing direct contact, water stream and immersion methods. In this work, ultrasonic and thermographic controls of CFRP components are presented for detection of different types of defects (real and artificial) in order to evaluate sensitivity and detectability techniques. This work presents a preliminary ultrasonic study on CFRP components employing different probes and tools.For these aims, inspections of CFRP plates with artificial defects are optimized and compared to thermographic acquisitions with active pulsed technique, in order to calibrate Ultrasonic Technique tools and verify procedures for suitable results. In a second stage, improved ultrasonic scanning investigations are applied on real parts, containing real production defects in terms of small delamination and diffused porosity of T-shape stringer and resin/matrix excesses between layers, localized in the thin cap and web of structural civil aircraft stringers.

Evaluating antibacterial and surface mechanical properties of chitosan modified dental resin composites.

The antibacterial properties are beneficial and desired for dental restorative composite materials. The incorporation of various antimicrobial agents into resin composites may compromise their physical and mechanical properties hence limiting their applications. The aim of the current study is to evaluate the antibacterial activity and the hardness of microhybrid and flowable resin based composites (RBCs) modified using novel antimicrobial agent chitosan (CS). The antibacterial activity of microhybrid and flowable RBCs modified with 0, 0.25, 0.5 and 1% w/w chitosan (CS) against Actinomyces viscous bacteria was explored using agar diffusion test and direct contact methods. The hardness of control and experimental RBCs was determined by Vickers hardness (VH) tester. The results revealed that control and experimental flowable and microhybrid RBCs did not demonstrate growth inhibition zone in the lawn growth of Actinomyces viscous. The direct contact test revealed that colony forming unit (CFU) count of Actinomyces viscous was comparable among the experimental and control materials. The flowable RBCs containing 1% CS had significantly higher VH compared to control and other experimental flowable RBC groups. The microhybrid RBCs consisting of 0.50% CS exhibited significantly higher VH compared to experimental microhybrid RBC group containing 1% CS.

Assessment of the entomopathogenic nematode bacteria against the termite, Microtermes mycophagus D. (Isoptera: Termitidae)

The capability of symbiotic bacteria of entomopathogenic nematodes against the termite, Microtermes mycophagus D. (Isoptera: Termitidae), was assessed. Different fractions of Pakistani isolates of entomopathogenic bacteria viz., Xenorhabdus indica strain (Pak.S.B.50), X. indica strain (Pak.S.B.56), X. stockiae strain (Pak.S.B. 65), and X. steinernematis strain (C.B.10) were assessed against M. mycophagus by direct contact method (spraying method) and sand assay in laboratory conditions. Mortality response of cell-free filtrates after 24 h at 20 °C for X. indica (Pak.S.B.50), T2 = X. indica (Pak.S.B.56), T3 = X. stockiae (Pak.S.B. 65), and T4 = X. steinernematis (C.B.10) ranged (88.3–100%) as 33 ± 9.34, 98.33 ± 6.22, 88.33 ± 7.22, and 100.00% ± 0.00, respectively. In the case of sand assay, the most effective treatment was T4, where (100%) mortality rate was recorded 24 h post application of B.S. (bacterial suspension) (4 × 104 CFU/ml) and CFF (cell-free filtrate) (100 μl/10 ml) at 20 and 25 °C.

In vitro investigation of the antioxidant and antimicrobial effects of hydro-alcoholic and aqueous extracts of Globularia alypum L.

Abstract The aim of this work was to establish the antioxidant and antimicrobial activity of hydro-alcoholic and aqueous extracts prepared from the leaves of Globularia alypum L. The quantitative estimation of total polyphenols (by the Folin-Ciocalteu method) and total flavonoids (by the method of aluminium trichloride) showed that the aqueous and ethyl acetate extracts had the highest content of phenolic and flavonoid compounds. Moreover, the results of antioxidant power assessed by both method DPPH and phosphomolybdenum indicated that leaves extracts of G. alypum expressed a considerable activity. The evaluation of the antimicrobial effects, using the disc diffusion method from antibacterial screening and the direct contact method from the antifungal activity, indicated strong antibacterial and antifungal activity.

Antimicrobial efficacy of building material based on ZnO/palygorskite against Gram-negative and Gram-positive bacteria

This study investigated ZnO nanoparticles immobilized in palygorskite clay mineral (Pal) that acted as an inorganic antimicrobial agent in a commercial mortar aiming to control microorganisms and improve safety and stability for building applications. ZnO/Pal nanocomposites were obtained by sol-gel methods at pH 7 and 11 and were calcined at 250 °C and 400 °C to evaluate different synthesis parameters. The mortar/ZnO/Pal composite was obtained using 5% (by weight) ZnO/Pal hybrid mixed with a commercial mortar. The results show that pH and calcination temperature influenced the properties of ZnO/Pal. ZnO was observed in the ZnO/Pal samples during the wurtzite phase by analyzing the XRD patterns. FTIR spectra illustrated the interactions between ZnO nanoparticles and the fibrous clay mineral. TG-DTG analysis showed the thermal events of Pal before and after zinc incorporation. Scanning electron microscopy (SEM) evaluated ZnO morphology as spherical in shape and dispersed on the fibers of the clay minerals, which presented needle-like morphology. ZnO/Palygorskite showed a possible antibacterial effect when used in mortar formulation. The mortar/ZnO/Pal composites were effective against Escherichia coli and Staphylococcus aureus bacteria when tested by the direct contact method in darkness and in visible light and could be an alternative antimicrobial material for building surfaces.

Sensorial profile, content, and antioxidant activity in coffee beverages prepared by direct contact methods

Direct content coffee preparation methods may be used as alternative ways to obtain coffee beverages with varied cup profiles. In this investigation the antioxidant metabolites, antioxidant activity, and cup profiles were determined for coffee drinks prepared using five different direct contact methods. The method that registered greatest antioxidant retention was Ibrik, followed by French press, and Toddy. Antioxidant capacity was proportional to antioxidant component retention in the preparations made. It is recommended that coffee be prepared via the Ibrik, French press, and Toddy methods for high acceptance levels, as well as for retention of bioactive components with antioxidant properties and abilities. Key words: Tasting; antioxidants; barista; quality; cup.

Novel bioactive caries-detecting dye solution: Cytotoxicity, antimicrobial activity, scanning electron microscope, and stereomicroscopic analysis in diagnosis of dental caries.

AimThe aim was (1) to study the cytotoxicity of novel Bioactive Caries-detecting Dye solution (BCD) and its antimicrobial activity against Streptococcus mutans, Lactobacillus acidophilus, Actinomyces naeslundii, and Candida albicans and (2) comparative assessment of BCD and Carie-Care for efficient removal of caries (stereomicroscope) and dentin tubule occlusion (scanning electron microscope [SEM]).Materials and MethodsFor BCD cytotoxic study (direct contact method), colorimetric MTT assay, and cell line study(L929 mouse fibroblast NCTC clone 929 strain L) was performed. Xenetix 350, chitosan, nanohydroxyapatite (nHA), BCD, and Carie-Care solutions were subjected to the antimicrobial activity through blood agar well diffusion method, and the minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined. On 20 extracted human carious teeth a comparative pilot study was done for BCD (Group A, n = 10) and Carie-Care (Group B, n = 10), and evaluated visually and radiographically. After mechanical excavation of caries with a spoon excavator, teeth sectioned longitudinally and stereomicroscopically were evaluated (8x–40x) by two observers. The percentage of dentinal tubule occlusion was evaluated with SEM for both solutions. Statistical kappa analysis of agreement was 0.7–0.8 (P < 0.01). Mann–Whitney test ranks and Wilcoxon signed-rank test (P = 0.01) were applied.ResultsCytotoxicity test revealed BCD to be nontoxic and biocompatible. Antimicrobial tests (zone of inhibition) showed BCD > chitosan > chlorhexidine > Carie-Care > Xenetix 350 > nHA. MIC and MBC values suggested chlorhexidine > BCD > Carie-Care. Stereomicroscopic analysis showed effective mechanical removal of caries in BCD without residual dye in the dentinal tubules as compared to Carie-Care. Dentinal tubule occlusion (SEM analysis) was 80%–85% for BCD and 10% for Carie-Care.ConclusionsProfound synergistic effect for BCD was observed with advantage of radiographic assessment.

Enhanced photoresponse in ZnO nanorod array/p-GaN self-powered ultraviolet photodetectors via coupling with CuO nanostructures

ZnO nanorod arrays (ZnO NRAs) coupled with coral-like CuO nanostructures (CuO CLNs) were prepared by low-temperature hydrothermal method. Self-powered ultraviolet (UV) photodetectors (PDs) based on ZnO NRAs/CuO CLNs/p-GaN heterostructure were fabricated via a direct-contact method. Under UV illumination (1.46 mW cm−2), the ratios of photocurrent to dark current (Iphoto/Idark), photo-responsivity and specific detectivity for the ZnO NRAs/CuO CLNs/p-GaN heterojunction self-powered PD were estimated to be 1143, 1.44 mA W−1 and 5.9 × 1010 cm H z 1 /2/W at 0 V, which were about ∼187, ∼104 and ∼153 times greater than those of the ZnO NRAs/p-GaN self-powered PD, respectively. Moreover, the PD displayed faster response time, excellent stability and repeatability by coupling with CuO CLNs. The mechanism of the enhanced photoresponse performance was discussed through the energy band diagram.

Direct-Contact Evaporation Using Different Refrigerants: A Review

The direct-contact evaporation method is characterized by its effectiveness in applications of heat exchangers, especially in cooling systems, due to the absence of any heat resistors that prevent the transfer of heat between the cold and hot medium. The direct contact heat transfer depends mainly on how quickly the heat is taken by the bubbles of the evaporative refrigerant from the liquid and the increase in its volume up to the top of the heat exchanger, which is usually a cylindrical liquid column so that the temperature drop therein is uniform and even. There is much research on the method of heat transfer by direct contact. In this research, we collected and summarized most of the theoretical and practical researches that examined this method with the most important findings.

In vitro Antifusarial Activity of a Tar Extracted from the Juniperus phoenicea L. Wild in Southwest of Algeria

The biological activities of medicinal plants have been recognized for centuries. Among them, Juniperus phoenicea is very commonly used for its medicinal virtues (respiratory, hepatic and renal infections). Its wood is used for heating and manufacture of coal and its vegetable tar is used to treat certain cases of eczema. The aim of the present study is focused on the evaluation of the in vitro antifungal activity of a tar extracted from Juniperus phoenicea L. The physicochemical analysis was performed first; then, the evaluation of antifusarial activity of the Juniperus phoenicea L. was carried out by using the dilution and the direct contact method to determine the minimum inhibitory concentration (MIC). Results of the physicochemical analysis show a density value of 1.10, a refraction index of about 1.5112, an acid pH (4.02) and the dries matter ratio of 36, 34% for the tested tar. The antifungal activity of the tar under study against six strains of Fusarium oxysporum f.sp. albedinis (FOA; S1, S2, S3, S4, S5, S6) revealed that Juniperus phoenicea L. tar has a great antifungal activity against all the investigated strains. The antifungal activity results reveal that the fungal growth was inhibited by the tar. S3 proved to be the most sensitive strain with a minimal inhibition concentration value of 0.006 mg/ml. The present study indicates that Juniperus phoenicea L. tar has antifungal activity against the different tested fungal strains.

Cytotoxicity Evaluation of The Bioresorbable and Titanium Plates/Screws Used in Maxillofacial Surgery on Gingival Fibroblasts and Human Mesenchymal Bone Marrow Stem Cells.

Objective Bioresorbable and titanium plates/screws are considered as a standard treatment for fixation of the bone segments of craniofacial area and paying attention to their biocompatibility is an important issue along with other aspects of application. The purpose of the study was to evaluate the cell viability of two types of plate and screw used in maxillofacial surgeries in contact with gingival fibroblasts and bone marrow stem cells. Materials and Methods In this experimental study after extraction and cultivation of cells from healthy human gingival tissue and alveolar bone of jaw, cytotoxicity of device was evaluated. In direct contact method, samples had near vicinity contact with the both cell lines and in indirect contact method, by-products released, like ions, from samples after 8 weeks were used to assess cytotoxicity. Then cytotoxicity was evaluated on the 2nd, 4th and 6th day with MTS tests and microscopy. The data were analyzed by one-way ANOVA and independent t tests. Results There was a statistically significant difference between the German plate and screw and all the samples studied on day 6 (P<0.05). Furthermore, a statistically significant difference was observed between both metal samples and both bio-absorbable samples on day 6 and both cell lines (P<0.05). Comparisons between the two groups with each other for both cell lines on the 6th day were statistically significant (P<0.05). ConclusionOur results suggest that that cytotoxicity of biomaterial, from different brands, were not similar and some of the biomaterial showed lower degree of toxicity compared to others and specialist using these products showed be aware of this differences. Our investigation indicates more biocompatibility of bioresorbable plates and screws compared to titanium. In addition our results suggest that biomaterials were not completely neutral.

Water Quality Index Score in River Water Treatment Plant at Upper Klang and Gombak River Catchment

National River Water Plants are located along upper Klang and Gombak river catchment to purify the polluted river using direct contact methods. As the current water quality situation in the study area is poor due to the contribution of anthropogenic activities on the water quality degradation in these urban rivers, the investigation was performed using the Water Quality Index. This paper gives the overall performance of RWTP using Water Quality Index (WQI) calculation methods. The WQI act as the basis of environment assessment towards to river water quality classification under Malaysia National Water Quality Standards. As an overall result, 57 percent from the total effluents achieve target Class II and above and another 43 percent achieve Class III and below regardless of two (2) RWTPs are under target from the average monitoring; RWTP Sg Gisir and RWTP Sg Sentul. However, the result for RWTP Sg Sentul is not yet conclusive since the monitoring duration is less than 2 years. Certainly, RWTP Sg Gisir needs to be taken into consideration for more frequent maintenance of the RWTP or upgrading of the RWTP oxidation tank as suggested in several MBBR/IFAS operation. As to improve the RWTP performance to score higher WQI, the introduction of recycling sludge in the biological tank so it will be a shorter reaction time. Additionally, the RWTP owner should implement a frequent maintenance work into RWTP component especially clarifier, sludge collector, biological oxidation tank and rubbish trap collector.

Ionic Liquid-Impregnated Metal–Organic Frameworks for CO2/CH4 Separation

A large set of distinct ionic liquid (IL)-impregnated metal–organic framework (MOF) composites were produced by a direct-contact method to study their performance as sorbents for gas separation app...

Presodiation Strategies and Their Effect on Electrode-Electrolyte Interphases for High-Performance Electrodes for Sodium-Ion Batteries.

Most active materials for sodium-ion batteries suffer from the problem of low-energy efficiency in the first cycle because of the loss of active sodium ions consumed for the formation of a solid electrolyte interface. To make up for the lost sodium ion, presodiation treatments have been applied, which are effective ways to mitigate the low initial efficiency. Here, we developed a direct-contact method to achieve the presodiation for cathode and anode electrodes and demonstrated the enhanced Coulombic efficiency of the first cycle with improved cyclability and reversible capacity. Moreover, we proved the formation of a thick passivation layer at the cathode-electrolyte interface during the presodiation process; this contributes to the improved cycle stability by preventing the dissolution of the active material and its deposition on the anode surface. The direct-contact method is a simple and cost-effective way to complete presodiation, and this simple process will be widely applicable for practical battery manufacturing.

Predictors Linking Obesity and the Gut Microbiome (the PROMISE Study): Protocol and Recruitment Strategy for a Cross-Sectional Study on Pathways That Affect the Gut Microbiome and Its Impact on Obesity.

BackgroundThe prevalence of obesity has increased substantially over recent decades and is associated with considerable health inequalities. Although the causes of obesity are complex, key drivers include overconsumption of highly palatable, energy-dense, and nutrient-poor foods, which have a profound impact on the composition and function of the gut microbiome. Alterations to the microbiome may play a critical role in obesity by affecting energy extraction from food and subsequent energy metabolism and fat storage.ObjectiveWe report the study protocol and recruitment strategy of the PRedictors linking Obesity and the gut MIcrobiomE (PROMISE) study, which characterizes the gut microbiome in 2 populations with different metabolic disease risk (Pacific and European women) and different body fat profiles (normal and obese). It investigates (1) the role of gut microbiome composition and functionality in obesity and (2) the interactions between dietary intake; eating behavior; sweet, fat, and bitter taste perception; and sleep and physical activity; and their impact on the gut microbiome, metabolic and endocrine regulation, and body fat profiles.MethodsHealthy Pacific and New Zealand (NZ) European women aged between 18 and 45 years from the Auckland region were recruited for this cross-sectional study. Participants were recruited such that half in each group had either a normal weight (body mass index [BMI] 18.5-24.9 kg/m2) or were obese (BMI ≥30.0 kg/m2). In addition to anthropometric measurements and assessment of the body fat content using dual-energy x-ray absorptiometry, participants completed sweet, fat, and bitter taste perception tests; food records; and sleep diaries; and they wore accelerometers to assess physical activity and sleep. Fasting blood samples were analyzed for metabolic and endocrine biomarkers and DNA extracted from fecal samples was analyzed by shotgun sequencing. Participants completed questionnaires on dietary intake, eating behavior, sleep, and physical activity. Data were analyzed using descriptive and multivariate regression methods to assess the associations between dietary intake, taste perception, sleep, physical activity, gut microbiome complexity and functionality, and host metabolic and body fat profiles.ResultsOf the initial 351 women enrolled, 142 Pacific women and 162 NZ European women completed the study protocol. A partnership with a Pacific primary health and social services provider facilitated the recruitment of Pacific women, involving direct contact methods and networking within the Pacific communities. NZ European women were primarily recruited through Web-based methods and special interest Facebook pages.ConclusionsThis cross-sectional study will provide a wealth of data enabling the identification of distinct roles for diet, taste perception, sleep, and physical activity in women with different body fat profiles in modifying the gut microbiome and its impact on obesity and metabolic health. It will advance our understanding of the etiology of obesity and guide future intervention studies involving specific dietary approaches and microbiota-based therapies.Trial RegistrationAustralian New Zealand Clinical Trials Registry ACTRN12618000432213; https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=370874International Registered Report Identifier (IRRID)RR1-10.2196/14529

Nanoenabled Direct Contact Interfacing of Syringe-Injectable Mesh Electronics.

Polymer-based electronics with low bending stiffnesses and high flexibility, including recently reported macroporous syringe-injectable mesh electronics, have shown substantial promise for chronic studies of neural circuitry in the brains of live animals. A central challenge for exploiting these highly flexible materials for in vivo studies has centered on the development of efficient input/output (I/O) connections to an external interface with high yield, low bonding resistance, and long-term stability. Here we report a new paradigm applied to the challenging case of injectable mesh electronics that exploits the high flexibility of nanoscale thickness two-sided metal I/O pads that can deform and contact standard interface cables in high yield with long-term electrical stability. First, we describe the design and facile fabrication of two-sided metal I/O pads that allow for contact without regard to probe orientation. Second, systematic studies of the contact resistance as a function of I/O pad design and mechanical properties demonstrate the key role of the I/O pad bending stiffness in achieving low-resistance stable contacts. Additionally, computational studies provide design rules for achieving high-yield multiplexed contact interfacing in the case of angular misalignment such that adjacent channels are not shorted. Third, the in vitro measurement of 32-channel mesh electronics probes bonded to interface cables using the direct contact method shows a reproducibly high yield of electrical connectivity. Finally, in vivo experiments with 32-channel mesh electronics probes implanted in live mice demonstrate the chronic stability of the direct contact interface, enabling consistent tracking of single-unit neural activity over at least 2 months without a loss of channel recording. The direct contact interfacing methodology paves the way for scalable long-term connections of multiplexed mesh electronics neural probes for neural recording and modulation and moreover could be used to facilitate a scalable interconnection of other flexible electronics in biological studies and therapeutic applications.

Inducing apatite pre-layer on titanium surface through hydrothermal processing for osseointegration.

Commercially available titanium (Ti) having high mechanical strength and a low area of cross-section can be adequately exploited for minimally invasive dental implantation. Current directions in clinical dental implant therapy focus on endosseous dental implant surfaces with nanoscale topographies using easy and economical processing approaches. The present study describes the generation of a novel nanolayer nucleating agent on the surface of Ti implant for early endosseous after implantation. The strategy is to modify the surface of Ti implant using Ca(OH)2 via hydrothermal technique (Ti-HT). The X-ray photoelectron spectroscopy analysis confirmed the presence of chemically bonded Ca ions on the Ti surface in the form of CaTiO3. In vitro studies are carried out to confirm the bone bonding ability of calcium enriched Ti surface. The apatite deposition on the surface after exposure to SBF for 7 days is confirmed via scanning electron microscopy, X-ray powder diffraction, Fourier-transform infrared spectroscopy and energy-dispersive X-ray spectroscopy techniques. The cell viability of Ti-HT was evaluated using direct contact method and MTT assay. The potential of Ca2+ ion on Ti surface via hydrothermal pre-treatment to enhance osseointegration of Ti has been proposed for achieving early stability for dental implants.

Effect of the Essential Oil of Mentha Piperita and Thymus Numidicus on the Growth of Fusarıum Sp

The polluting substances are of industrial or agricultural origin, at the level of the different ecosystems. These are the effects of synthetic products on the fauna and flora we are interested in. So our use of biopesticides based on plant extracts, namely essential oils as a natural insecticide is our concern. These bioactive substances or molecules are of great ecological interest because they are very harmful to the ecosystem. The objective of this study is the use of the essential oil of Mentha peperita harvested from the area of Larabaa (Blida) and Thymus numidicus recovered from the area of Bouira as biofungicides with respect to a fungal strain isolated and identified from the leaves of the zucchini crop in Boudouaou-El Bahri (Boumerdes). The isolated species belongs to the genus Fusarium. The extraction method is the hydraudistilation which allowed us to have yields of essential oil of 2.02% for M. peperita and 1.2% for T. numidicus. The study of the antifungal activity of these two oils tested was carried out by the direct contact method. The evaluation of the antifungal effect of these two extracts shows that the essential oil of T. numidicus has an inhibitory capacity on mycelial growth. T. numidicus oil is moderately active for concentrations; 400 μl 700 μl is inhibition rates; 43.33% and 50%. This natural substance is active with the 1000 μl dose, with an inhibition rate of 53.33%. It appears from this study that M. piperita oil is not very active on Fusarium sp with the following concentrations; 400 μl 700 μl and 1000 μl are inhibition rates respectively of 23%, 21.66%, and 23%. The essential oil of Peppermint has a slightly inhibitory activity on Fusarium sp with an inhibition zone diameter of 4.6 cm, 4.7 cm and 4.6 cm respectively for doses 400 μl 700 μl and 1000 μl. So, it is found that the increase in M. piperita oil concentration has no effect on the growth of Fusarium sp. Fusarium sp also shows an allergy to T. numidicus oil, while this plant pathogen is resistant to M. piperita oil.

Hemocompatibility of biodegradable Zn-0.8 wt% (Cu, Mn, Li) alloys.

Zinc alloys have been explored as potential materials for biodegradable vascular stents due to their tolerable corrosion rates and tunable mechanical properties. However, the performances of Zn alloys were not supported with enough toxicity or biological compatibility evaluation, particularly hemocompatibility for vascular scaffolding application. In this work, the hemocompatibility of three zinc alloys (Zn-0.8Cu, Zn-0.8Mn and Zn-0.8Li) was evaluated with 316 L stainless steel and pure zinc as controls. The hemolysis ratios of 316 L stainless steel, pure Zn, Zn-0.8Cu, Zn-0.8Mn and Zn-0.8Li were 0.38 ± 0.08%, 1.04 ± 0.21%, 0.47 ± 0.21%, 0.57 ± 0.14% and 0.52 ± 0.22%, respectively, for direct contact method. Platelets aggregation on the 316 L stainless steel was observed, while the adhered platelets on the Zn alloys exhibited round shape with few pseudopodia spreading. The number of adhered platelets on the three zinc alloys (Zn-0.8Cu, Zn-0.8Mn and Zn-0.8Li) had no statistically difference compared with 316 L stainless steel, while significant fewer than the pure Zn group. None remarkable platelet activation, hematocyte aggregation, coagulation or complement activation was observed in any Zn alloy group. Furthermore, the Zn alloys prolonged prothrombin time and partial thromboplastin time, demonstrating a potential function of anticoagulation. The results demonstrated that Zn alloys presented in this work are indeed meeting the hemocompatible requirements of implant and showing the promise for perspective application as biodegradable stent.

Bioleaching behaviors of silicon and metals in electrolytic manganese residue using silicate bacteria

Electrolytic manganese residue (EMR) is a kind of solid waste generated along with the production of electrolytic manganese, with a high content of quartz and metals. The former can be used as silicon fertilizer for crops after activation, while the latter may cause harm to surrounding environment due to their toxicity. The aim of this study was to investigate the effects of bacterial on the activation of silicon and fixation of heavy metals in EMR by using microbe-mineral direct contact and indirect contact methods. Mixed cultures of Bacillus mucilaginosus (BM) and Bacillus circulans (BC) were used to achieve activation of silicon in EMR, and the leaching concentration of Mn, Co and Ni and their chemical forms in the leaching residue were also investigated. The results show that the microbe-mineral direct contact method has better performance for the activation of silicon in EMR with the available silicon in the leaching solution up to 163.27 mg L−1 than the indirect contact method. The metals (Mn, Co and Ni) remaining in the residue mainly exist as the stable state after bioleaching, with lower leaching concentration after bioleaching of 20 d. And the effect of silicon bacteria on activation of silicon and the fixation mechanism of metals including the effect of silicate and silicate bacteria is confirmed, and it is verified by the identification of metabolites and the analysis of chemical reaction process. This study investigates the treatment of EMR by using mixed silicate bacteria, and reveals the mechanisms of bacteria on the activation of silicon and fixaion of heavy metals in EMR. The bioleaching method not only provides silicon source for soil but also can realize the reclamation of EMR.