Versiane Albis Leão

Mine water treatment with limestone for sulfate removal

Limestone can be an option for sulfate sorption, particularly from neutral mine drainages because calcium ions on the solid surface can bind sulfate ions. This work investigated sulfate removal from mine waters through sorption on limestone. Continuous stirred-tank experiments reduced the sulfate concentration from 588.0mg/L to 87.0mg/L at a 210-min residence time. Batch equilibrium tests showed that sulfate loading on limestone can be described by the Langmuir isotherm, with a maximum loading of 23.7mg/g. Fixed-bed experiments were utilized to produce breakthrough curves at different bed depths. The Bed Depth Service Time (BDST) model was applied, and it indicated sulfate loadings of up to 20.0gSO(4)(2-)/L-bed as the flow rate increased from 1 to 10mL/min. Thomas, Yoon-Nelson and dose-response models, predicted a maximum particle loading of 19mg/g. Infrared spectrometry indicated the presence of sulfate ions on the limestone surface. Sulfate sorption on limestone seems to be an alternative to treating mine waters with sulfate concentrations below the 1200-2000mg/L range, where lime precipitation is not effective. In addition, this approach does not require alkaline pH values, as in the ettringite process.

Manganese and limestone interactions during mine water treatment.

Manganese removal from mining-affected waters is an important challenge for the mining industry. Addressed herein is this issue in both batch and continuous conditions. Batch experiments were carried out with synthetic solutions, at 23+/-2 degrees C, initial pH 5.5 and 8.3 g limestone/L. Similarly, continuous tests were performed with a 16.5 mg/L Mn(2+) mine water, at 23 degrees C, initial pH 8.0 and 20.8 g limestone/L. Calcite limestone gave the best results and its fine grinding proved to the most effective parameter for manganese removal. In either synthetic solutions or industrial effluents, the final manganese concentration was below 1 mg/L. A change in limestone surface zeta potential is observed after manganese removal and manganese carbonate formation was suggested by IR spectroscopy. The conclusion is that limestone can remove manganese from industrial effluents for values that comply with environmental regulations.

Implications of volatile fatty acid profile on the metabolic pathway during continuous sulfate reduction

Volatile fatty acid (VFA) profile is an important parameter in anaerobic reactors because it enables the assessment of metabolic pathways. Volatile fatty acids were monitored during sulfate reduction in a UASB (upflow anaerobic sludge blanket) reactor treating 2g/L sulfate concentration and with the organic loading increasing from 3.5 kg COD/m(3)d to 5.9 kg COD/m(3)d, for a 1-day residence time. In the absence of recirculation, the best outcome (65% reduction) was noticed with the lowest organic loading (3.55 kg/m(3)d). When recirculation was applied, sulfate reduction yields increased to 89%, corresponding to a sulfate removal rate of 1.94 kg SO(4)(2-)/m(3)d. The reactor performance was discussed in relation to microbial diversity and metabolic pathways. At high organic loading, two metabolic pathways account for lactate degradation: (i) lactate is oxidized to acetate and carbon dioxide by the incomplete-oxidizer SRB (sulfate-reducing bacteria) Desulfomonas, Desulfovibrio, Desulfolobus, Desulfobulbus and Desulfotomaculum spp.; (ii) lactate is converted to acetate by fermenting bacteria such as Clostridium sp. High propionate concentrations imply that there are low sulfate reduction efficiencies.

Copper extraction from coarsely ground printed circuit boards using moderate thermophilic bacteria in a rotating-drum reactor

The current work reports on a new approach for copper bioleaching from Printed Circuit Board (PCB) by moderate thermophiles in a rotating-drum reactor. Initially leaching of PCB was carried out in shake flasks to assess the effects of particle size (-208μm+147μm), ferrous iron concentration (1.25-10.0g/L) and pH (1.5-2.5) on copper leaching using mesophile and moderate thermophile microorganisms. Only at a relatively low solid content (10.0g/L) complete copper extraction was achieved from the particle size investigated. Conversely, high copper extractions were possible from coarse-ground PCB (20mm-long) working with increased solids concentration (up to 25.0g/L). Because there was as the faster leaching kinetics at 50°C Sulfobacillus thermosulfidooxidans was selected for experiments in a rotating-drum reactor with the coarser-sized PCB sheets. Under optimal conditions, copper extraction reached 85%, in 8days and microscopic observations by SEM-EDS of the on non-leached and leached material suggested that metal dissolution from the internal layers was restricted by the fact that metal surface was not entirely available and accessible for the solution in the case of the 20mm-size sheets.

A sulfate-reducing bacterium with unusual growing capacity in moderately acidic conditions.

The use of sulfate-reducing bacteria (SRB) is a cost-effective route to treat sulfate- contaminated waters and precipitate metals. The isolation and characterization of a SRB strain from an AMD in a Brazilian tropical region site was carried out. With a moderately acidic pH (5.5), the C.1 strain began its growth and with continued growth, modified the pH accordingly. The strain under these conditions reduced sulfate at the same rate as an experiment performed using an initial pH of 7.0. The dsrB gene-based molecular approach was used for the characterization of this strain and its phylogenetic affiliation was similar to genus Desulfovibrio sp. The results show an SRB isolate with unexpected sulfate reducing capacity in moderately acidic conditions, bringing new possibilities for the treatment of AMD, as acid water would be neutralized to a mildly acidic condition.

Batch and fixed-bed assessment of sulphate removal by the weak base ion exchange resin Amberlyst A21

This paper investigated sulphate removal from aqueous solutions by Amberlyst A21, a polystyrene weak base ion exchange resin. Both the pH and initial sulphate concentration were observed to strongly affect sorption yields, which were largest in acidic environments. Working under optimum operational conditions, sulphate sorption by Amberlyst A21 was relatively fast and reached equilibrium after 45 min of contact between the solid and liquid phases. Sorption kinetics could be described by either the pseudo-first order (k1=3.05 × 10(-5)s(-1)) or pseudo-second order model (k2=1.67 × 10(-4)s(-1)), and both the Freundlich and Langmuir models successfully fitted the equilibrium data. Sulphate uptake by Amberlyst A21 was a physisorption process (ΔH=-25.06 kJ mol(-1)) that occurred with entropy reduction (ΔS=-0.042 kJ mol(-1)K(-1)). Elution experiments showed that sulphate is easily desorbed (∼ 100%) from the resin by sodium hydroxide solutions at pH 10 or pH 12. Fixed-bed experiments assessed the effects of the initial sulphate concentration, bed height and flow rate on the breakthrough curves and the efficiency of the Amberlyst A21 in the treatment of a real effluent. In all studied conditions, the maximum sulphate loading resin varied between 8 and 40 mg(SO4(2-))mL(resin)(-1).

Adsorção de metais pesados em serragem de madeira tratada com ácido cítrico

In the present work, the exchange capacity of Manilkara longifolia sawdust, chemically modified, was studied. The modification was carried out by a chemical treatment with citric acid, which introduced carboxilate groups in the material surface. The introduction of these groups was confirmed by infrared spectroscopy. Cadmium and copper sorption was studied batchwise. Isotherms were drawn and adjusted to the Langmuir model. Maximum loadings of 0.56 mmolCd/g and 0.94 mmolCu/g were achieved in single metal adsorption. Cadmium uptake was reduced from 0.56 mmolCd/g to 0.21 mmolCd/g as the copper concentration increased in the reaction system. These results show that there is a competition between the two metals for the exchange sites.

The dependence of sorbed copper and nickel cyanide speciation on ion exchange resin type

The present study investigates the influence of functional group structure and resin matrix on the speciation of copper and nickel cyanides sorbed onto two commercially available ion exchange resins. Batch experiments were performed using synthetic copper and nickel solutions containing 50 and 200 mg/L free cyanide, respectively. Despite the presence of Cu(CN)32− and Cu(CN)43− in solution, it has been found using Raman spectroscopy that the Imac HP555s resin, which has a polystyrene–divinylbenzene matrix, loads predominantly the Cu(CN)32− complex. In contrast, the polyacrylic resin, Amberlite IRA958, sorbed significant amounts of both Cu(CN)32− and Cu(CN)43−. It has been found that the speciation of nickel cyanide sorbed onto each resin was the same. A recently developed mathematical model based on statistical thermodynamic principles has been used as a tool to understand further the equilibrium sorption of copper and nickel cyanide complexes onto each resin studied. A higher sorption energy for nickel compared to copper has been observed for the sorption onto Imac HP555s. In contrast, the sorption energy for copper was found to be higher than for nickel for the polyacrylic resin, Amberlite IRA958. The values of the model parameters obtained were correlated with the chemical features of each complex in solution as well as sorbed onto the resins.

Hydrogels of cellulose acetate crosslinked with pyromellitic dianhydride: part I: synthesis and swelling kinetics

This work describes the synthesis of hydrogels of cellulose acetate (AC) crosslinked with 1,2,4,5-benzenotetracarboxylic dianhydride (PMDA). The crosslinking reaction was monitored by FTIR. Analysis of aromatic fragments from the alkaline hydrolysis of the gels by UV spectroscopy indicated that an increase in the stoichiometric ratio of dianhydride resulted in higher degrees of crosslinking. The non-porous nature of the gels was confirmed by analysis of nitrogen adsorption. Water absorption isotherms showed that as the temperature and degree of crosslinking increased, the percentage of water absorbed at equilibrium (%Seq) also increased. The hydrogels presented second order swelling kinetics.

Indirect Manganese Removal by Stenotrophomonas sp. and Lysinibacillus sp. Isolated from Brazilian Mine Water

Manganese is a contaminant in the wastewaters produced by Brazilian mining operations, and the removal of the metal is notoriously difficult because of the high stability of the Mn(II) ion in aqueous solutions. To explore a biological approach for removing excessive amounts of aqueous Mn(II), we investigated the potential of Mn(II) oxidation by both consortium and bacterial isolates from a Brazilian manganese mine. A bacterial consortium was able to remove 99.7% of the Mn(II). A phylogenetic analysis of isolates demonstrated that the predominant microorganisms were members of Stenotrophomonas, Bacillus, and Lysinibacillus genera. Mn(II) removal rates between 58.5% and 70.9% were observed for Bacillus sp. and Stenotrophomonas sp. while the Lysinibacillus isolate 13P removes 82.7%. The catalytic oxidation of Mn(II) mediated by multicopper oxidase was not properly detected; however, in all of the experiments, a significant increase in the pH of the culture medium was detected. No aggregates inside the cells grown for a week were found by electronic microscopy. Nevertheless, an energy-dispersive X-ray spectroscopy of the isolates revealed the presence of manganese in Stenotrophomonas sp. and Lysinibacillus sp. grown in K medium. These results suggest that members of Stenotrophomonas and Lysinibacillus genera were able to remove Mn(II) by a nonenzymatic pathway.