1,721,068 research outputs found
Olive mill solid residues as heavy metal sorbent material: a preliminary study
No full textBiosorption of heavy metals is an innovative and alternative technology to remove these pollutants from aqueous solutions using inactive and dead biomasses such as agricultural and industrial wastes, algae and bacteria. In this study olive mill solid residue was used as heavy metal adsorbent material for its wide availability as agricultural waste and also for its cellulosic matrix, rich of potential metal binding active sites. Preliminary studies concerned with the removal of different heavy metals (Hg, Pb, Cu, Zn and Cd), the effect of pre-treatments by water and n-hexane and the regeneration possibility. Olive mill solid residue resulted able to remove heavy metals from aqueous solutions with an affinity series reflecting the hydrolytic properties of the metallic ions, but also a particular affinity for copper. It can be supposed that biosorption phenomenon occur by a general ion exchange mechanism combined with a specific complexation reaction for copper ions. Water pre-treatment is sufficient to reduce COD release in the effluent according to the law limit, while n-hexane pre-treatment strongly reduces also the adsorption properties of this material. Experimental isotherms obtained under different operating conditions were fitted using a nonlinear regression method for the estimation of the Langmuir parameters. Moreover a simple Scatchard plot analysis was performed for a preliminary investigation of the active sites, showing the presence of two different site affinities depending on the metal concentration, according to the previous hypothesis of two kinds of uptake mechanisms for copper biosorption, Regeneration tests gave good results in terms of yield of regeneration and also concentration ratios. (C) 2002 Elsevier Science Ltd. All rights reserved
Preliminary screening of purification processes of liquor leach solutions obtained from reductive leaching of low-grade manganese ores
No full textIn this paper, the purification of liquor leach solutions obtained from low-grade manganese ores leached by carbohydrates in sulfinic medium was studied and developed. In particular, purification was made acting directly during the leaching process (simple or hydroalcoholic medium) and also using different down-stream purification technologies such as precipitation, solvent extraction and adsorption onto active carbon. The complexity of the aqueous system (due to the high concentration and heterogeneity of inorganic ionic species, but also to the presence of organic compounds as intermediates of glucose oxidation) affects metal speciation in solution in contrast with theoretical predictions. Leaching performed in hydroalcoholic medium combined with adsorption onto active carbon permits obtaining, after an evaporation phase, a final solution with specification concentrations of manganese, calcium and iron for food-additive production. (C) 2004 Elsevier B.V. All rights reserved
Leaching of low-grade manganese ores by using nitric acid and glucose: Optimization of the operating conditions
No full textManganese extraction from low-grade ores was investigated by using glucose as a reducing agent in dilute nitric acid medium. Ore characterisation by X-ray and SEM denoted that manganese is present as a mixed oxide Mn7O 13 (6MnO2·MnO) surrounding and joining together aluminosilicate fragments. The effects of temperature, particle size, glucose and nitric acid concentrations were investigated and compared with previous results using H2SO4. The operating conditions of leaching were optimised to obtain maximum manganese extraction and purity by performing sequential factorial designs and evaluating the statistical significance of the different factors by analysis of variance (ANOVA). The optimised conditions are 90°C, stoichiometric nitric acid, -20% below stoichiometric glucose and 295-417 μm size fraction. The stoichiometric reagent concentrations were evaluated according to the following reaction assuming all manganese in the ore as Mn(IV): C6H12O6+12MnO2+24H +=6CO2+12Mn2++18H2O Optimised leaching conditions with HNO3 give up to 99% manganese extraction, <0.05% iron dissolution and reduced reagent consumption compared to previous tests using H2SO4. © 2004 Elsevier B.V. All rights reserved
Copper and cadmium biosorption onto Sphaerotilus natans: Application and discrimination of commonly used adsorption models
No full textIn this paper, the experimental data of copper and cadmium biosorption onto Sphaerotilus natans obtained under different operating conditions of pH (3divided by6 units) and biomass concentration (0.5divided by2 g/L) were reported. These experimental data, showing the good separative performances of S. natans and the strong effect of the selected operative factors, were represented by three different empirical models: Langmuir. Freundlich, and Redlich-Peterson isotherms. A statistical representation of the characteristic model parameters (parameter standard deviation and regression coefficient) along with a model discrimination analysis (model residual variance, F-test and residual analysis) were proposed in order to suggest a standardized procedure for treating the biosorption data
A methodological approach for dynamic modelling of membrane integrated biosorption: a case study on Sphaerotilus natans as biosorbent
No full textThis work is a review of the study performed on heavy metals biosorption by Sphaerotilus natans confined in an ultrafiltration membrane module. A methodological approach has been applied aiming at the dynamic modelling of the process: i) firstly, biosorbent was characterised according to acid-base properties of binding sites; ii) then, equilibrium studies were performed both in single metal and multimetal systems in order to evidence any competition for binding sites and to find mechanicistic models that are able to describe biosorption equilibrium; iii) finally, biosorption in membrane processes was investigated in laboratory scale, in the case of both single- metal and two- metal systems, and a dynamic model was developed accounting for binding site competition and for binding ability of cell's fragments generated by tangential flow shear stress
“Acidogenic phase of anaerobic digestion of the organic fraction of MSW as a way to improve the reliabity of the BNR processes”
No full textTreatment of concentrated arsenic(V) solutions by micellar enhanced ultrafiltration with high molecular weight cut-off membrane
No full textIn this work arsenic removal by micellar enhanced ultrafiltration (MEUF) was investigated using cetylpyridinium chloride (CPC) and a cross-flow polyethersulphone (PES) membrane apparatus. The effects of some operating factors on permeate flux, arsenic and CPC rejections were investigated and, in particular, transmembrane pressure, pH, CPC concentration, As concentration and ionic strength. The novel aim of this work is evaluating the possible advantages of using large molecular weight cut-off membrane (100 kDa) and reduced surfactant concentrations (1-3 mM) for treating high fluxes of concentrated arsenic-bearing solutions (6-10 ppm). The experimental results reported in this paper show that PES membrane apparatus with high molecular weight cut-off allowed to treat large fluxes of concentrated arsenic-bearing solutions (6-10 ppm) even by using low surfactant concentration (1-3 mM). In particular arsenic removal ranged from 93-98% to 70-74% depending on initial As concentration (6 and 10 ppm, respectively). In addition surfactant leakage in the permeate was always below CMC due to presieving of concentration polarisation layer. The favourable combination of high MWCO membranes and low surfactant concentration can benefit to overall process economics for the lower membrane area requirement (due to greater flux) and the reduced surfactant consumption. © 2007 Elsevier B.V. All rights reserved
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