Biosorption of trace metals from aqueous multimetal solutions by green microalgae

Two strains of green microalgae C.reinhardti and C.pyrenoidosa were examined for their biosorption of Mn2+,Fe2+,Co2+,Ni2+,Cu2+,Zn2+,and Cd2+from aqueous multi-metal solutions.A wide range of biosorption capacities can be observed due to different strains of microalgae and different species of trace metals.This characteristic was ascribed to the distinct components and structures of algal cell walls and the different physicochemical properties of trace metals,such as atomic weight and ion density.C.pyrenoidosa showed higher uptake capacities than C.reinhardti and both of them had a preference for the uptake of cadmium over others in the trace metal solution,suggesting they can be a good biomaterial for biosorption of cadmium.Live microalgal cells displayed a more complex sorption process than dead microalgal cells because of cell assimilation.     

Biosorption of methylene blue from aqueous solutions by Typha angustata phytomass

The objective of this study was to investigate the biosorption of an azo dye (Methylene blue) by a wetland phytomass (Typha angustata) under post-phytoremediation scenario. Thus, the phytomass was used without any chemical modification. The batch adsorption experiments were conducted to evaluate the effects of contact time and temperatures (25–45 °C) on the adsorption of methylene blue (MB) from aqueous solution by cattail phytomass (CP). More than 80 % of MB dye was removed from the aqueous solution within first 10 min of the experiment. Langmuir isotherm was modeled to describe the monolayer adsorption of MB dye (R ² = 0.995) with the maximum adsorption capacity of 8.1 mg/g at 25 °C. Pseudo-second-order kinetic model adequately described the kinetics of absorption process (R ² = 0.999). The adsorption of MB on the cattail phytomass was a spontaneous and endothermic process that was governed by chemisorption. Hence, CP could be applied as a potential low cost biosorbent to treat dyeing wastewater.     

Hexavalent chromium removal from aqueous solutions by using low-cost biological wastes: equilibrium and kinetic studies

The batch removal of hexavalent chromium from aqueous solutions using almond shell, activated sawdust, and activated carbon, which are low-cost biological wastes under different experimental conditions, was investigated in this study. The influences of initial concentration, adsorbent dose, adsorbent particle size, agitation speed, temperature, contact time, and pH of solution were investigated. The adsorption was solution pH dependent and the maximum adsorption was observed at a solution pH of 2.0. The capacity of chromium adsorption under equilibrium conditions increased with the decrease in particle sizes. The equilibrium was achieved for chromium ion after 30?min. Experimental results showed that low-cost biosorbents are effective for the removal of pollutants from aqueous solution. The pseudo-second-order kinetic model gave a better fit of the experimental data as compared to the pseudo-first-order kinetic model. Experimental data showed a good fit with the Freundlich isotherm model. Changes in the thermodynamic parameters, including Gibbs free energy (??G_o), enthalpy (??H_o), and entropy (??S_o), indicated that the biosorption of hexavalent chromium onto almond shell, activated sawdust, and activated carbon was feasible, spontaneous, and endothermic in the temperature range 28?C50?°C.     

The kinetics of nucleation of solid solutions from aqueous solutions: a new model for calculating non-equilibrium distribution coefficients

The nucleation kinetics of binary solid solutions, with general formula B_xC_1−xA, crystallising from aqueous solution can be described using a generalised expression for the nucleation rate: the function, J(x), in which supersaturation, interfacial free energy and other parameters of the classical nucleation rate equation are considered as functions of the solid composition. As an example, we studied the behaviour of such J(x) functions for the case of the (Ba,Sr)SO₄ and (Ba,Sr)CO₃ solid solutions. J(x) functions are very sensitive to slight changes in the composition of the aqueous solution, which result in strong modifications of the nucleation kinetics. The implications of the relationship between supersaturation and nucleation rate functions for the general nucleation behaviour in solid solution-aqueous solution (SS-AS) systems are discussed. Finally, we present a method for constructing non-equilibrium Roozeboom diagrams based on the nucleation kinetics in SS-AS systems. Our Roozeboom diagrams calculated for different departures from equilibrium conditions are consistent with previous experimental work and they can be used to predict actual distribution coefficients.     

Removal of zinc(II) from aqueous solutions using modified agricultural wastes: kinetics and equilibrium studies

In recent years, the need for safe and economical methods to eliminate heavy metals from contaminated waters has necessitated research on the production of low-cost alternatives to commercially available activated carbon. In the present work, in order to enhance the removal of heavy metals from contaminated water, Zizyphus vulgaris wastes were modified chemically to produce an adsorbent rich in carboxylic groups to enhance the removal of heavy metals from contaminated water. Adsorption of Zn(II) ions on the produced adsorbent was then optimized. The optimal ratio for esterification involved the treatment of Z. vulgaris wastes (1 g) with 0.0037 mmol malic acid in the presence of a very small amount of water for 2 h at 140 °C. The maximum values for adsorption capacity, q _max, were 28.7 and 164.6 mg/g on native and modified Z. vulgaris wastes, respectively, at pH 5 and 30 °C with a contact time 2 h and an initial metal ion concentration of 400 mg/L. The equilibrium data were well fitted by the Langmuir and Freundlich adsorption models and demonstrated the significant capacity for Z. vulgaris wastes in the removal of Zn(II) ions from aqueous solutions.     

Removal of diazinon pesticide from aqueous solutions using MCM-41 type materials: isotherms,kinetics and thermodynamics

In this research, ordered mesoporous silica, including MCM-41, was synthesized via sol–gel process and a propyl methacrylate-modified ordered mesoporous silica (MPS-MCM-41) was successfully synthesized via a postsynthesis grafting process. Then both MCM-41 and MPS-MCM-41 were characterized using FTIR, XRD, SEM and BET techniques. The synthesized materials were utilized as adsorbent for removal of diazinon pesticide from aqueous solutions. The effects of pH, contact time, adsorbent dose, initial concentration and temperature have been evaluated using removal efficiencies. Also, the kinetic, thermodynamic and isotherm models of diazinon adsorption were studied for the both MCM-41 and MPS-MCM-41. The results showed that the maximum adsorption capacities are 142 and 254 mg g^?1 for the MCM-41 and MPS-MCM-41, respectively, at the initial concentration of 50 mg L^?1, temperature of 298 K and adsorbent dose of 0.1 g L^?1. The highest percentages of diazinon removal are 56.4 and 87.2 (at adsorbent dose of 2 g L^?1 and the temperature of 318 K) for the MCM-41 and MPS-MCM-41, respectively. The Freundlich and Langmuir models are more compatible for describing equilibrium data of the diazinon adsorption capacity on the MCM-41 and MPS-MCM-41, respectively. Thermodynamic study indicated that the adsorption process of diazinon onto MCM-41 and MPS-MCM-41 is exothermic and has a spontaneous nature. The higher adsorption capacity and higher spontaneous nature of MPS-MCM-41 in comparison with MCM-41 might be due to the presence of the both hydrogen bonding and hydrophobic interaction between surface functional groups of MPS-MCM-41 (hydroxyl and propyl methacrylate) and diazinon functional groups.     

Biosorption of Cu(II) and Pb(II) from aqueous solutions by chemically modified spent coffee grains

In this research, spent coffee grains were modified with citric acid solutions (0.1 and 0.6 M) to increase the quantity of carboxylic groups improving its metal adsorption capacity. Added functional groups on modified and non-modified spent coffee grains were identified and quantified by attenuated total reflection Fourier transform infrared analyses and potentiometric titrations, respectively. These adsorbents were used for the removal of lead (II) and copper (II) from aqueous solutions at 30 °C and different pH in batch systems. In addition, adsorption–desorption experiments were conducted to evaluate the possibility of re-using the modified adsorbent. Potentiometric titrations data reveal that the quantity of carboxylic groups was increased from 0.47 to 2.2 mmol/g when spent coffee grains were modified with 0.1 and 0.6 M citric acid. Spent coffee grains treated with 0.6 M citric acid, achieved a maximum adsorption capacity of 0.77 and 1.53 mmol/g for lead (II) and copper (II), respectively, whereas non-modified spent coffee grains only reached 0.24 and 0.19 mmol/g for lead (II) and copper (II), respectively. Desorption of lead (II) and copper (II) achieved around 70 % using 0.1 N HCl for non-modified and modified spent coffee grains with 0.6 M citric acid. It is suggested that lead (II) and copper (II) species were adsorbed mainly on the carboxylic groups of modified spent coffee grains and these metals may be exchanged for hydrogen and calcium (II) ions during adsorption on non-modified spent coffee grains. Finally, the adsorption equilibrium was reached after 400 min for modified spent coffee grains with 0.6 M citric acid. Modified spent coffee grains are a promising option for removing metal cations from aqueous solutions due to its low cost and high adsorption capacity (about 10 times higher than the activated carbons).     

Silver losses from ammoniacal solutions on complex sulphide and chalcopyrite ammonia leach residues

Extraction and subsequent loss of silver from leach liquor during oxidative ammonia leaching of complex sulphide and chalcopyrite concentrates have been observed. The lost silver value from the leach liquor was unrecoverable when the residues were treated with ammonia-ammonium sulphate buffer (pH=9.5) solutions at 27°C. However, when the same slurry was heated to 75°C in an autoclave under an atmosphere of oxygen, almost all the silver value could be redissolved. The leach residues lost their silver absorbance property from ammoniacal solutions on repeatedly heating and cooling the leached slurries in the presence of oxygen. In this work, silver losses from ammoniacal solutions on various leach residues, synthetic iron oxides, and freshly precipitated Fe(II) and Fe(III) hydroxides are reported. None of the major constituents present in the leach residues were responsible for the silver losses but small amounts of Fe(II) associated with the residues could take up silver from the leach solutions.     

Adsorption kinetics of herbicide paraquat in aqueous solution onto a low-cost adsorbent, swine-manure-derived biochar

Biochars have received increasing attention in recent years because of their significant properties such as carbon sequestration, soil fertility, and contaminant immobilization. In this work, the adsorptive removal of paraquat (1,1′-dimethyl-4,4′-dipyridinium chloride, one of the most widely used herbicides) from aqueous solution onto the swine-manure-derived biochar has been studied at 25 °C in a batch adsorption system. The adsorption rate has been investigated under the controlled process parameters including initial pH (i.e., 4.5, 6.0, 7.5, and 9.0), paraquat concentration (i.e., 0.5, 1.0, 2.0, 4.0, and 6.0 mg/L), and biochar dosage (i.e., 0.10, 0.15, 0.20, 0.25, and 0.30 g/L). Based on the adsorption affinity between cationic paraquat and carbon-like adsorbent, a pseudo-second order model has been developed using experimental data to predict the adsorption kinetic constant and equilibrium adsorption capacity. The results showed that the adsorption process could be satisfactorily described with the reaction model and were reasonably explained by assuming an adsorption mechanism in the ion exchange process. Overall, the results from this study demonstrated that the biomass-derived char can be used as a low-cost adsorbent for the removal of environmental cationic organic pollutants from the water environment.     

Adsorption kinetics of chromium(III) removal from aqueous solutions using natural red earth

Laboratory-scale-simulated experiments were carried out using Cr(III) solutions to identify the Cr(III) retention behavior of natural red earth (NRE), a natural soil available in the northwestern coastal belt of Sri Lanka. The effects of solution pH, initial Cr(III) concentration and the contact time were examined. The NRE showed almost 100 % Cr(III) adsorption within the first 90 min. [initial [Cr(III)] = 0.0092–0.192 mM; initial pH 4.0–9.0]. At pH 2 (298 K), when particle size ranged from 125 to 180 μm the Cr(III) adsorption data were modeled according to Langmuir convention assuming site homogeneity. The pH-dependent Cr(III) adsorption data were quantified by diffused layer model assuming following reaction stoichiometries: $$ \begin{aligned} 2\, {>}{\text{AlOH}}_{{({\text{s}})}} + {\text{ Cr }}\left( {\text{OH}} \right)_{{ 2\,({\text{aq}})}}^{ + } \, \to \, \left( { {>}{\text{AlO}}} \right)_{ 2} {\text{Cr}}_{{({\text{s}})}}^{ + } + {\text{ 2H}}_{ 2} {\text{O}} \quad {\text{log K 15}}. 5 6\\ 2\, {>}{\text{FeOH}}_{{({\text{s}})}} + {\text{ Cr}}\left( {\text{OH}} \right)_{{ 2\,({\text{aq}})}}^{ + } \, \to \, \left( { {>}{\text{FeO}}} \right)_{ 2} {\text{Cr}}_{{({\text{s}})}}^{ + } + {\text{ 2H}}_{ 2} {\text{O}}\quad {\text{log K 5}}.0 8.\\ \end{aligned} $$ The present data showed that NRE can effectively be used to mitigate Cr(III) from aqueous solutions and this method is found to be simple, effective, economical and environmentally benign.     

Biosorption of hexavalent chromium from aqueous solution onto pomegranate seeds: kinetic modeling studies

Hexavalent chromium has been proved to be the reason of several health hazards. This study aimed at evaluating the application of pomegranate seeds powder for chromium adsorption (VI) from aqueous solution. Chromium adsorption percentage (VI) increased with increasing the adsorbent dosage. Chromium adsorption capacity (VI), at pH = 2 and 10 mg/L initial metal concentration, decreased from 3.313 to 1.6 mg/g through increasing dosage of adsorbent from 0.2 to 0.6 g/100 ml. The adsorption rate increased through increase in chromium initial concentration (VI). However, there was a removal percentage reduction of chromium (VI). Chromium adsorption kinetics by different models (pseudo-first-order, modified pseudo-first-order, pseudo-second-order, Elovich, intraparticle diffusion, Boyd kinetic) was investigated as well. Studies on adsorption kinetic indicated that the experimental data were matched by pseudo-second-order model (R ² = 0.999) better. Obtained results demonstrated the pomegranate seeds can be used as an effective biomaterial and biosorbent for hexavalent chromium adsorption from aqueous solutions.     

Adsorption phenomena in hydrometallurgy, 2. Electrophoretic behavior of oxides in aqueous ammoniacal solutions of copper,nickel and cobalt

The electrophoretic mobilities of finely divided oxides in aqueous ammoniacal solutions of copper, nickel, and cobalt have been measured. The solids used were rutile, alumina, quartz, and hematite. The effects of pH, ammonia-ammonium concentration, and metal-ion concentration on the electrophoretic behavior were investigated. The experimental results indicate that oxide colloids may undergo as may as five charge reversals in aqueous ammoniacal solutions of hydrolyzable ammine-forming metal ions.     

Adsorption phenomena in hydrometallurgy, 1 The uptake of copper,nickel and cobalt by oxide adsorbents in aqueous ammoniacal solutions

The uptake or adsorption of copper, nickel and cobalt by finely divided oxide solids in aqueous ammoniacal medium has been investigated experimentally in order to determine how adsorption on leach residues can affect the recovery of leachable metals. Hematite, rutile, alumina and quartz were used as model solid adsorbents. In the case of ammoniacal leach solutions the controlling metal species appears to be the aqueous neutral hydroxo species. Adsorption behavior was found to have maxima and minima as a function of pH, the magnitude of which depends on ammonia concentration, the metal cation, and the adsorbent.     

Removal of dyes from aqueous solutions using low-cost sorbents made of solid residues from olive-mill wastes (JEFT) and solid residues from refined Jordanian oil shale

The effectiveness of processed solid residue from olive-mill waste (JEFT) and solid residue of pyrolyzed oil shale in removing methylene blue as a cationic dye and methyl orange as an anionic dye from aqueous solutions has been investigated and compared with that of a commercial activated carbon, namely coconut-shell carbon. All three sorbents showed significant methylene-blue removal, but only the coconut granular-activated carbon showed notable methyl-orange removal. The oil-shale sorbent showed no removal and the olive carbon showed poor removal of methyl orange. The removal of both methylene blue and methyl orange increases with the lapse of time, and attains equilibrium in 100 min. Received: 12 May 1999 · Accepted: 1 November 1999     

Modeling the kinetics of silica nanocolloid formation and precipitation in geologically relevant aqueous solutions

The kinetics of the formation and precipitation of nanocolloidal silica from geologically relevant aqueous solutions is investigated. Changes in monomeric (SiO_2(mono)), nanocolloidal (SiO_2(nano)) and precipitated silica (SiO_2(ppt)) concentrations in aqueous solutions from pH 3 to 7, ionic strengths (IS) of 0.01 and 0.24 molal, and initial SiO₂ concentrations of 20.8, 12.5 and 4.2 mmolal (reported in [Icopini, G.A., Brantley, S.L., Heaney, P.J., 2005. Kinetics of silica oligomerization and nanocolloid formation as a function of pH and ionic strength at 25 °C. Geochim. Cosmochim. Acta69(2), 293-303.]) were fit using two kinetic models. The first model, termed the concentration model, is taken from Icopini et al. (2005) and assumes that the rate of change of SiO_2(mono) as a function of time has a fourth-order dependence on the concentration of SiO_2(mono) in solution. The second model, termed the supersaturation model, incorporates the equilibrium concentration of amorphous silica and predicts that polymerization will be a function of the degree of silica supersaturation in solution with respect to amorphous silica. While both models generally predicted similar rate constants for a given set of experimental conditions, the supersaturation model described the long-term equilibrium behavior of the SiO_2(mono) fraction more accurately, resulting in significantly better fits of the monomeric data. No difference was seen between the model fits of the nanocolloidal silica fraction. At lower pH values (3-4), a metastable equilibrium was observed between SiO_2(mono) and SiO_2(nano). This equilibrium SiO_2(mono) concentration was found to be 6 mmolal, or three times the reported solubility of bulk amorphous silica under the experimental conditions studied and corresponds to the predicted solubility of amorphous silica colloids approximately 3 nm in diameter. Atomic force microscopy was used to determine the average size of the primary nanocolloidal particles to be ∼3 nm, which is in direct agreement with the solubility calculations. Larger aggregates of the primary nanocolloids were also observed to range in size from 30 to 40 nm. This work provides the first kinetic models describing the formation and evolution of nanocolloidal silica in environmentally relevant aqueous solutions. Results indicate that nanocolloidal silica is an important species at low pH and neutral pH at low ionic strengths and may play a more important role in geochemical cycles in natural aqueous systems than previously considered.     

Murmanite and lomonosovite as Ag-selective ionites: kinetics and products of ion exchange in aqueous AgNO3 solutions

Products and kinetics of ion exchange of heterophyllosilicate minerals lomonosovite and murmanite with aqueous AgNO₃ solutions under low-temperature conditions have been studied using scanning electron microscopy, electron microprobe analysis, single-crystal X-ray diffraction, infrared spectroscopy, ²³Na nuclear magnetic resonance spectroscopy and dynamic calorimetry. Both minerals show strong affinity for silver in cation exchange. Simplified formulae of Ag-exchanged forms of murmanite and lomonosovite are (Ag_3.0Ca_0.5Na_0.5) (Ti,Nb,Mn,Fe)_3.7?4 (Si₂O₇)₂O₄·4(H₂O,OH) and (Ag_8.2Na_1.2Ca_0.3) (Ti,Nb,Mn,Fe)_3.9?4 (Si₂O₇)₂ (PO₄)_1.9O₄·xH₂O, respectively. The reaction of ion exchange for murmanite follows the first-order kinetic model up to ca. 70–80 % conversion. The rate of the process is described by the equation k(h^?1) = 10^7.64±0.60 exp[?(12.2 ± 0.9)·10³/RT]. The average heat release value in the temperature range 39.4–72 °C is 230 J g^?1. The cation exchange is limited by processes in solid state, most probably binding of silver.     

The selective removal of Co(II) from Ni(II) by coprecipitation with manganese in ammoniacal solutions

The coprecipitation of cobalt(II) and nickel(II) with manganese in ammoniacal solutions has been studied. It was found that cobalt and nickel were precipitated with the aid of manganese at pH 9.3–10.2. However, the rate of precipitation of manganese was about five times that of cobalt. The recovery of these divalent ions by precipitation increased as the pH of the solution increased, while the selectivity of cobalt against nickel decreased with the increase of pH. The partial pressure of oxygen had also an important role in the precipitation of manganese and cobalt but little effect on the up-take of nickel. As the oxygen pressure increased, manganese and cobalt oxidized at a fast rate and the rate of coprecipitation of cobalt with manganese increased. Typically, more than 90% of cobalt was recovered readily by coprecipitation with manganese, while very little nickel was removed from the solution.     

Biosorption of metal dye from aqueous solution onto Agave americana (L.) fibres

In this research, a new low cost and abundant biosorbent; Agave americna (L.) fibres has been investigated in order to remove metal dye (Alpacide yellow) from aqueous solutions. In order to optimize the biosorption process, the effect of pH, temperature, contact time and initial solution concentration was investigated in batch system. The results indicated that acidic pH=2 was favourable for metal dye removal. The increase of temperature increases the velocity of the biosorption reaction. The biosorption kinetics of alpacide yellow were closer to the pseudo-second order than to the first order model for all concentrations and temperature. The calculated thermodynamic parameters such as dGG°, dGH° and dGS° indicated a spontaneous and endothermic biosorption process of metal dye onto Agave americana fibres. The equilibrium data were analysed using the Langmuir and Freundlich isotherms and showed a good fit with Langmuir model at lower temperatures and with Freundlich model at 50 °C.