1,721,051 research outputs found
Gold reduction in batch and column experiments using silica gel derivates and seaweed biomass
No full textAbstract Gold recovery from aqueous solution was studied in the present work. Two synthetic materials composed of immobilized chelating agent on silica gel, and the brown seaweed Sargassum muticum were used as reducing agents inducing gold colloid nanoparticles formation. The results showed that there is no pH effect and no interference on gold recovery by the presence of other metals in solution, such as Co, Ni, and Cr(VI). A strong complexing reagent for gold leaching, such as thiourea, was able to recover a significant amount of the gold previously reduced over the surface of the materials. The investigated synthetic materials presented much faster rate than the algae for gold recovery. A first order model with respect to the oxidizable groups and gold concentrations accuracy described the entire kinetic process. The rate constant of the reaction and the concentration of oxidizable groups per gram of material were obtained from kinetic data fit. Column studies were conducted varying the flow rate and the quantity of material used. Under favourable conditions of flow rate (1 mL/min) and quantity of material in the column (?0.2 g), more than 95% of the gold was recovery from the inlet solution. A mechanism based on the experimental evidences was proposed. \{FTIR\} and \{SEM\} analysis supported the suggested mechanism. Based on the results showed it can be concluded that the gold removal from aqueous solution is mainly based on a reduction mechanism where gold colloid nanoparticles are produced
Gold recovery from artificial seawater using synthetic materials and seaweed biomass to induce gold nanoparticles formation in batch and column experiments
No full textGold recovery from artificial seawater was studied in the present work Two synthetic materials composed of silica gel joint to a strong chelating agent were used as reducing agents to induce gold colloid nanoparticle formation: ethylene diamine tetraacetic acid and diethylene triamine pentaacetic acid, together with brown seaweed Sargassum muticum. The mechanism and ideal conditions involving gold recovery from artificial seawater were investigated. The results showed that there is no pH effect within the range of 2-6. Moreover, the presence of other metals like Co, Ni, and Cr(VI) did not interfere the gold sorption/reduction reactions. Only thiourea showed significant regeneration percentages of the materials saturated with metallic gold. The absence of complete gold appearance in the effluent during column experiments could indicate that the sorption capacity of the materials was saturated, but not their reduction power. The shape of the obtained curves during the kinetic experiments revealed several stages occurring during the gold recovery from artificial seawater. Potentiometric titrations, FTIR, and SEM analysis provided decisive evidence supporting the proposed mechanism. A novel plausible three-step mechanism was suggested for the gold recovery from artificial seawater based on the experimental evidence. In a first stage, the adsorption of the anion species AuCl4- occurred. Following, the reduction of AuCl4- to Au(0), and the later oxidation of the metallic gold formed to the unstable AuCl2- arose. Finally, during the last stage metallic gold redissolution is not further favored, and probably only the reduction of the chloro-gold complexes to metallic gold occurred
Replication Data for: Seasonal variations in proton binding characteristics of dissolved organic matter isolated from the Southwest Baltic Sea
No full textThe file contains experimental data obtained from pH meaurements and data from calculations of the DOM charge, representing the experimental points of Figure 3 in the article, according to the legend of the figure. It also contains pH measurements and the corresponding NICA model simulations used in the Figure 3 of the article (solid lines). These data allow to represent Figure 3 of the article and test other binding models
Thermodynamic and kinetic aspects on the biosorption of cadmium by low cost materials: A review
No full textCadmium is internationally recognized as an important pollutant in the environment, and different methods for its removal from wastewaters (chemical precipitation being the most commonly used) have been reported in the literature. Those methods are in most cases oriented to situations with high concentrations of the pollutant. Thus, alternative removal and recovery methods are being considered for removing very low concentrations of cadmium. These methods are all based on biosorption, the passive adsorption and sequestration of metals by several natural materials of biological origin. In this review we have considered the biosorption of cadmium onto biomaterials from a physicochemical, thermodynamic, and kinetic perspective. The thermodynamic perspective is based on the characterization of the interactions of the binding sites of the biosorbents with cadmium species in aqueous solution. Traditionally, this approach has been quantified using different kinds of isotherms. In addition, the description is completed by taking into account electrostatic effects, and the influence of pH and ionic strength, which are associated with the negative charge developed, in most cases, by the biomaterial. The other point of view in this review is the kinetic one, which is necessary for a full physicochemical description of the sorbate - biosorbent system. Consequently, an updated description of the various approaches commonly employed in kinetic studies in biosorption has been carried out
Detection of silver nanoparticles in seawater at ppb levels using UV–visible spectrophotometry with long path cells
No full textSilver nanoparticles (AgNPs) are emerging contaminants that are difficult to detect in natural waters. UV–visible spectrophotometry is a simple technique that allows detection of AgNPs through analysis of their characteristic surface plasmon resonance band. The detection limit for nanoparticles using up to 10 cm path length cuvettes with UV–visible spectrophotometry is in the 0.1–10 ppm range. This detection limit is insufficiently low to observe AgNPs in natural environments. Here we show how the use of capillary cells with an optical path length up to 200 cm, forms an excellent technique for rapid detection and quantification of non-aggregated AgNPs at ppb concentrations in complex natural matrices such as seawater
Electrostatic Effects in Biosorption: The Role of the Electrochemistry
No full textBiosorption is the passive sequestration of pollutants by non-metabolizing non-living biomass. The technique emerged in 1980?s as a possible alternative method for wastewater treatments in an environmentally friendly manner. In this paper it is shown that a basic research in biosorption processes is closely related to the field of Electrochemistry according to the conceptual division of this area in Ionics and Electrodics
Aluminium removal from wastewater by refused beach cast seaweed. Equilibrium and dynamic studies
No full textAluminium removal has been investigated in synthetic and real wastewaters provided by an aluminium surface treatment plant. Marine algae, obtained as beach cast seaweed (a refuse substance) were used as adsorption material. The influence of pH, metal concentration and time for aluminium elimination was studied by use of synthetic solutions. The optimum pH value was 4.0, which provided a maximum adsorption capacity of 22.5 mg g(-1). The adsorption percentage surpassed 80\% in less than 30 min of contact time. Real solutions from the industrial unit were fully characterized and tested in two different fixed-bed columns. One column was filled with 27.5 g of dried beach cast seaweed. Three cycles of adsorption and two of desorption were carried out. The first cycle (12 mg g(-1) maximum sorption capacity) was enough to reach the maximum adsorption capacity at 15 mL min(-1) flow rate. The second column was packed with 1100 g of seaweed and its behaviour was compared to another column filled with activated charcoal, following both the same experimental procedure. Maximum sorption capacity was 14 mg g(-1) for seaweed, whereas the activated charcoal only reached 1.6 mg g(-1) (flow rate of 250 mL min(-1))
Cr(VI) removal from synthetic and real wastewaters: The use of the invasive biomass Sargassum muticum in batch and column experiments
Full text linkThe macroalgae Sargassum muticum was selected for the treatment of solutions containing Cr(VI). Very acidic pH values were established as optimal for Cr(VI) reduction. Algae chemical modification reduced equilibrium time to 4 h. First order kinetic model was used to describe the reduction kinetic of Cr(VI). A column experiment allowed to distinguish the processes occurring during Cr(VI) elimination: its reduction to Cr(III) and the subsequent adsorption of this species formed. Under the selected conditions the biomass was capable of reducing all the incoming Cr(VI) during 77 h. Industrial wastewaters from chrome plating industry were also tested for chromium removal
Biosorption of Cadmium by Fucus spiralis
No full textCadmium biosorption properties of nonliving, dried brown marine macroalga Fucus spiralis from Galician coast (northwest Spain) have been investigated. The biosorption capacity of the alga strongly depends on solution pH; the uptake is almost negligible at pH <= 2 and reaches a plateau at around pH 4.0. Cadmium biosorption kinetics by F. spiralis is relatively fast, with 90\% of total adsorption taking place in less than one hour. A pseudo second order mechanism has been proved to be able to predict the kinetic behaviour of the biosorption process. The effect of initial cadmium ion concentration, alga dose, solution pH, and temperature on the biosorption kinetics has been studied. The Langmuir, Freundlich, Langmuir-Freundlich, and Toth isotherms were used to fit the experimental data and to find out the adsorption parameters. Acid-base properties of the alga have been studied potentiometrically in order to calculate the number of acidic groups and the apparent pK value by using Katchalsky model. The pK obtained is comparable with typical values associated to the ionization of carboxyl groups of alginates, supporting the implication of these groups in the biosorption process
Acid-base properties of brown seaweed biomass considered as a Donnan gel. A model reflecting electrostatic effects and chemical heterogeneity
No full textBrown seaweeds are interesting materials to be used as biosorbents for heavy metals due to their high binding ability and low cost. The study of the passive biosorption of protons on this kind of materials and its dependency on pH, ionic strength, and medium composition is essential for the practical application of brown algae in wastewater treatment. This work reports the results of the study of the proton binding equilibria of dead biomass from the seaweeds Sargassum muticum, Cystoseira baccata, an Saccorhiza polyschides by potentiometric titration with glass electrode in the pH range between 2 and 8. Two different salts, NaCl and KNO3, in concentrations ranging from 0.05 to 2 mol(.)L(-1), were used as background electrolytes. The influence of the ionic strength was accounted for by means of the Donnan model in combination with the master curve approach. Different empirical expressions to describe the swelling behavior of the biosorbent were tested. On the basis of the intrinsic affinity distribution analysis a unimodal Langmuir-Freundlich isotherm was selected to describe the proton binding properties. The results show very little influence of the type of salt. The ionic strength dependency of the proton binding is very similar for the three species, and average empirical expressions of the Donnan volume are proposed. The maximum proton binding capacities obtained ranged between 2.4 and 2.9 mol(.)kg(-1), with average intrinsic proton affinity constants between 3.1 and 3.3, and heterogeneity parameters of ca. 0.5 for S. muticum and C. baccata, and slightly higher (ca. 0.7) for S. polyschides. The combined Langmuir-Freundlich equation and Donnan model allowed a good description of the experimental charge vs pH curves obtained
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