Studies on the Separation of Cadmium from Solutions by Foam Separation. II. Precipitate Flotation of Cadmium Hydroxide

Abstract

Foam separation of cadmium in relation to pH from solutions of different metal concentrations was carried out by means of lauryl sulfate. The effect of inert salt on the removal of cadmium hydroxide and cadmium cations by adsorbing colloid floation was also studied. The precipitate flotation results reflect the precipitation of the metal in the form of a hydroxide. The precipitation pH values calculated are approximately those at which cadmium removal over 50% is obtained. The presence of electrolyte has a negative effect on the results of precipitate flotation of cadmium hydroxide and adsorbing colloid flotation of cadmium cations with lauryl sulfate.     

Removal of Cadmium from Aqueous Solution Using Adsorptive Bubble Separation Techniques

Abstract

Cadmium ion was removed from aqueous solutions using adsorptive bubble separation techniques. The effect of pH, coagulant and activator concentrations, and ionic strength on separation efficiency was studied. Adsorbing colloid flotation using ferric hydroxide and aluminum hydroxide as the coprecipitant and sodium lauryl sulfate as the collector and frother was found to be very effective provided that the ionic strength of the solution was no greater than 0.01 M. The residual cadmium concentration was less than 0.02 ppm after foaming for 10 min from a solution containing 20 ppm cadmium initially. Effective separation can be achieved from solutions containing 0.1 M NaNO₃ or 0.05 M Na₂SO₄ when zinc ion is used as the activator. The results of foam flotation were compared with the zeta potential of the floc. It was found that the zeta potential of the floc decreases with increasing ionic strength of the solution. The zeta potential of the floc is more positive when activators (aluminum and zinc ions) were added, which presumably gives the floc a stronger affinity for anionic surfactant adsorption, resulting in better separation efficiency. Adsorbing colloid flotation becomes less effective with increasing inert salt concentration of the solution; this effect can be compensated for to quite a large extent with the aid of activators, and the applicability of foam separation techniques for heavy metal removal from wastewater is thus greatly extended     

Continuous Precipitate Flotation of CuS/ZnS

Abstract

The precipitate flotation of copper and zinc as sulfides in dilute aqueous solutions (50-250 ppm metal ion concentration) was investigated in the laboratory in continuous flow. The dispersed-air flotation technique was followed, leading to a selective recovery of copper sulfide of the order of 95% in a high acidic pH region (of 1.7) by a laurylamine ethanolic solution as collector and with the addition of cetyl-pyridinium chloride as frother. The precipitate flotation of zinc sulfide was then accomplished with the same method at pH 5.0 as a second separation stage (in the presence of minor amounts of copper).     

Bioremoval of Metal Ion and Water Treatment in a Hybrid Unit

Abstract

Several biomass types, such as yeast (in the present Saccharomyces, a brewery waste), have been reported to remove heavy metals (i.e., zinc) from aqueous solution. The separation of metal-loaded biomass and hence, the production of a clean water stream using a hybrid flotation-microfiltration unit were investigated. The hybrid cell consisted of a microfiltration module submerged directly into a flotation cell. Air bubbling, constituting the transport medium during flotation, meanwhile has been used in order to limit the membranes fouling. The effects of air sparging, the solid particle content, and the type and concentration of flotation reagents on the performance of the hybrid process were the main examined parameters.     

Investigation of the Column Performance of Cadmium(II) Biosorption by Cladophora crispata Flocs in a Packed Bed

ABSTRACT

In this study the biosorption of cadmium(II) ions to dried floes of Cladophora crispata, a kind of green algae, was investigated in a packed bed column. The cadmium(II) removal performance of the column was investigated as a function of the cadmium(II)-bearing solution flow rate and the inlet cadmium(II) concentration. Re- moval and total removal percentages of cadmium(II) related to flow volume were determined by evaluating the breakthrough curves obtained at three different flow rates for two different constant inlet concentrations. At the lowest flow rate the effect of inlet cadmium(II) concentration on the column capacity was also investigated. Data confirmed that early saturation and lower cadmium(II) removals were observed at higher flow rates and at higher cadmium(H) concentrations. Column experiments also showed that maximum specific cadmium(II) uptake values of C. crispata floes were as higher as those of other biomass sorbents.     

Foam Separation of Lead(ll) and Cad mi urn (II) from Waste Water

Abstract

Foam separation techniques are evaluated to determine if they would be feasible for removing lead(II) and cadmium(II) from highly contaminated waste water. Variables such as pH, ionic strength, collector concentration, and interfering ions were studied to determine their effects on ion flotation. Increased ionic strength, calcium(II), and phosphate interference made ion flotation impractical. Precipitate flotation of lead sulfide and cadmium sulfide left approximately 0.20 ppm lead(II) and 0.08 ppm cadmium(II) in the bulk solution under optimum conditions—somewhat above the levels considered safe to release into the environment. Adsorbing colloid flotation gave excellent results; lead sulfide and cadmium sulfide were adsorbed to ferrous sulfide which was then removed by foaming with hexadecyltrimethylam-monium bromide. Lead(II) levels were reduced from 0.80 to 0.025 ppm in 34 min foaming with 15 ppm iron(III) added. Cadmium(II) levels were reduced from 1.0 to 0.008 ppm in 45 min foaming with 25 ppm iron(III) added.     

Foam Separation of Mercury(II) and Cadmium(II) from Aqueous Systems

Abstract

Mercury(II) and cadmium(II) were separated from aqueous systems by a number of batch-type precipitate flotation and adsorbing colloid flotation techniques. HgS, CdS, and Cd(OH)₂ were removed by precipitate flotation; Fe(OH)₃, Al(OH)₃, FeS, and CuS were used as adsorbing colloids. Sodium lauryl sulfate and hexadecyltrimethylammonium bromide (HTA) were used as collectors. Dependence of separation efficiency on pH and ionic strength was investigated. Floc foam flotation of both metals with CuS and HTA was found to be quite effective, resulting in residual Hg(II) levels as low as 5 ppb and residual Cd(II) levels as low as 20 ppb. Floc foam flotation of Cd(II) with FeS and HTA yielded residual Cd(II) levels as low as 10 ppb.     

Selective Removal of Cadmium from Mixed Metal Solution by Carbonate Infusion

Abstract

The purpose of this study is to develop the technology of selective precipitation of a single metal from a mixed solution by carbonate infusion. Experiments were conducted in Pyrex reactors and jar testers. Synthetic wastewater of cadmium and copper mixed solution was used in this study. Initial cadmium and copper concentrations were 10^?5, 10^?4, and 10^?3 M, which are the concentrations commonly occurring in electroplating rinsewater. The effects of pH, carbonate concentration, and mixing rate on copper and cadmium hydrolysis were investigated. The optimum conditions of selective precipitation for the cadmium form mixed solutions were around pH 9, and the mixing rate was 100 rpm.     

Biosorption of heavy metals (Cd,Cu, Ni,Pb, Zn) by chemically-reinforced biomass of marine algae

Particles of two different sizes (0·105–0·295 mm and 0·84–1.00 mm diameter) of two marine algae, Sargassum fluitans and Ascophyllum nodosum, were crosslinked with formaldehyde (FA), glutaraldehyde (GA) or embedded in polyethylene imine (PEI), followed by glutaraldehyde crosslinking. They were used for equilibrium sorption uptake studies with cadmium, copper, nickel, lead and zinc. The metal uptake by larger particles (0·84–1·00 mm) was higher than that by smaller particles (0·105–0·295 mm). The order of adsorption for S. fluitans biomass particles was Pb > Cd > Cu > Ni > Zn, for A. nodosum copper and cadmium change places. Uptakes of metals range from q_max = 378 mg Pb g^?1 for S. fluitans (FA, big particles), to q_max = 89 mg Zn g^?1 for S. fluitans (FA, small particles) as the best sorption performance for each metal. Generally, S. fluitans is a better sorbent material for a given metal, size and modification, although there were several exceptions in which metal sorption by A. nodosum was higher. The metal uptake for different chemical modifications showed the order GA > FA > PEI. A comparison of different sorption models revealed that the Langmuir sorption model fitted the experimental data best.     

Removal of toxic metals from aqueous mixtures. Part 1: Biosorption

The biosorption of toxic metals from an aqueous mixture containing zinc, copper and nickel, in the presence of calcium and sodium ions (usual co‐existing cations in related systems) has been investigated. Industrial biomass samples of different origin have been examined batchwise as effective sorbents, including bacteria (Streptomyces rimosus), fungi (Penicillium chrysogenum) and yeasts (Saccharomyces carlsbergensis and Saccharomyces cerevisiae). The effect of solution pH was evaluated in the range of 3–11.5. Selectivity was observed, particularly for the removal of copper. The observed removal of metals by the application of biosorption was also compared in laboratory experiments with other more conventional separation techniques (filtration, centrifugation and flotation). © 1999 Society of Chemical Industry     

Adsorption and complexation mechanisms of heavy metal uptake in activated sludge

Differences were observed between the uptake of cadmium, copper, manganese and nickel by activated sludge biomass: their removal was studied when a range of metal concentrations was added to resuspended mixed liquor solids in the absence of possibly competitive organic ligands. The predominant mechanism of metal removal was passive uptake with some indication of binding site specificity for copper and possibly manganese. The data obtained were interpreted in the form of adsorption isotherms. The results were used to calculate conditional stability constants (K′) of the complexes formed, and the complexation capacity of the biomass for heavy metal uptake. Studies were conducted over a range of sludge ages from 3 to 12 days. Log₁₀K′ values between 4.6 and 6.7 were found. However, there was no direct relationship between sludge age and K′. EDTA was used to desorb bound metal: this provided a means of differentiating between the surface complexes and the unexchangeable metal such as that taken up intracellularly. There was a difference in the adsorption affinity series of the metals when EDTA was present. This indicated that more than one mechanism for metal uptake was operating, and that the relative importance of physical and chemical absorption varied with each metal.     

Assessment of Cadmium in Aquatic Sediment Using Dialysis Samplers with Ion-Exchangs-Resin Collection

ABSTRACT

Simultaneously extracted metals (SEM) and acid volatile sulflde (AVS) show the potential for toxicity on the basis of their ratio. Accordingly, we spiked cadmium in a range for which Cd/AVS ratios were from 0.2 to 10 in the sediment with its weight about 8 kg in each batch. Dialysis samplers with a cation ion-exchange resin (Dowex 50W-X4) collection were used in a laboratory for the determination of free cadmium concentrations in pore water of the collected sediment. When equilibrium was reached among cadmium in pore water, sediment, and ion-exchange resin, cadmium exchanged onto resin phase was regenerated with 1 N hydrochloric acid (OPTIMA grade) and determined using an atomic absorption spectrophotometer (Zeeman 5000) with a graphite furnace accessory. Cadmium determined using the dialysis sampler is considered as free cadmium which is related to the metal bioavailability toward aquatic biota. The developed methodology provides a new technique for assessment of free metal in aquatic sediment systems.     

Biosorption of Lead,Copper, and Cadmium with Continuous Hollow-Fiber Microfiltration Processes

Abstract

A hollow-fiber crossflow microfiltration membrane was utilized to retain a biomass of Pseudomonas aeruginosa PU21 for continuous biosorption of lead (Pb), copper (Cu), and cadmium (Cd) ions in single or ternary metal systems. The results obtained from the microfiltration systems showed that in both single and ternary biosorption, the metal removal efficiency based on a molar basis was clearly Pb > Cu > Cd. For a single-membrane process with an influent metal concentration of 200 μM and a flow rate of 350 mL/h, the effluent concentration of Pb and Cu satisfied the national regulations for an influent volume of 6.3 L. With a three-metal influent, the adsorption capacity of the biomass for Pb, Cu, and Cd was reduced 4,50, and 74% compared to that for single-metal adsorption. Selective biosorption with a three-column sequential microfiltration operation exhibited an enhancement of 40 and 57% of total metal removal for Cu and Cd, respectively, over the results from single-membrane operation. The multimembrane operation also enabled locally optimal accumulation of Pb, Cu, and Cd at the first, second, and third stage, respectively. The regeneration efficiency of the biomass was 70% after three repetitive adsorption/desorption cycles, whereas the Pb recovery efficiency was maintained at nearly 90%. A rapid-equilibrium model (Model A) and a mass-transfer model (Model B) were used to describe the results of single- and multimetal biosorption with the microfiltration processes. Model A exhibited excellent prediction for the results of single-metal biosorption, while Model B was more applicable to interpret the multimetal biosorption data.     

Cadmium(II) biosorption from aqueous solutions using Hydrilla verticillata

The kinetics and equilibrium of cadmium biosorption from aqueous solutions were investigated using fresh tissues of Hydrilla verticillata. The biosorptive characteristics of cadmium ions were studied with respect to well‐established effective parameters, including pH, temperature and contact time. The biosorptive capacity of H. verticillata for cadmium increased with increasing pH. In addition, the resulting isotherms were well‐described by Langmuir and extended Langmuir models (R² = 0.9794–0.9957 and 0.9880, respectively). The comparison between calculated and experimental q_e values showed that the extended Langmuir model had a better simulation for the cadmium biosorption by H. verticillata than the Langmuir isotherm model. The equilibrium biosorption data at a constant temperature were well‐interpreted by the Langmuir model. The maximum biosorptive capacity increased from 33.54 to 37.46 mg/g when the solution temperature was increased from 278 to 298 K. Other various thermodynamic parameters were also estimated. Biosorptive equilibrium was established within approximately 20 min. Moreover, the pseudo‐second‐order equation was more appropriate in predicting biosorptive capacity than the pseudo‐first‐order equation. In practical viewpoints, the abundant and inexpensive plant biomass H. verticillata can be used as an effective and environmentally friendly biosorbent for the detoxification of cadmium from aqueous solutions. © 2012 Canadian Society for Chemical Engineering     

Removal of Heavy Metals from a Chelated Solution with Electrolytic Foam Separation

Abstract

An experimental study was conducted on the chelation and electrolytic foam separation of trace amounts of copper, nickel, zinc, and cadmium from a synthetic chelated metal wastewater. Sodium ethylenediaminetetraacetate (EDTA), citrate, sodium diethyldithiocarbamate (NDDTC), and potassium ethyl xanthate (KEtX) were used with sodium dodecylsulfate (NaDS) as a foam-producing agent. Experimental results from an electrolytic foam separation process showed that chelating agents NDDTC and KEtX, due to their higher chelating strength and hydrophobic property, can efficiently separate Cu and Ni from chelated compounds (Cu, Ni/EDTA, and Cu, Ni/citrate). In a Cu-EDTA-NDDTC system with a chelating agent/metal ratio of 4, the residual Cu(II) concentration is 0.7 mg/L. The effects of chelating agent types and different chelating agents concentrations on the removal of metal ions were studied. The effect of NaDS dosage on flotation behavior and the efficiency of metal removal were also investigated.     

Preliminary Studies on Furfural Production from Lignocellulosics

This study focused on the production of furfural from agricultural and industrial biomass residues by a hydrodistillation process. Corncobs, sugarcane bagasse, and eucalypt wood were treated with sulfuric, hydrochloric, and phosphoric acids as catalysts, with different acid concentrations (1.5 to 5.2 mol.L ^?1). In addition, the eucalypt liquor from the auto-hydrolysis, kraft-dissolving pulp production process was also investigated as a source of furfural, using sulfuric and hydrochloric acids as a catalyst (0.9 and 3.9 mol.L ^?1) . Furfural yields of 30.2, 25.8, and 13.9% were achieved for corncob, sugarcane bagasse, and eucalypt wood, respectively, on the basis of biomass dry weight. The efficiency of conversion from pentose to furfural using eucalypt liquor from the auto-hydrolysis kraft process was 71.5% using HCl 3.9 mol.L ^?1 . Due to the presence of a high amount of pentose, corncob produced the highest amount of furfural, followed by sugarcane bagasse and then eucalypt wood.     

Modification of Pyrite and Sphalerite Flotation by Dextrin

Abstract

The role of dextrin in the xanthate flotation of pyrite and sphalerite was examined by means of flotation tests and microelectrophoretic measurements. Floatability and ζ-potential of both minerals were found to be depressed in a suitable pH range due to the formation of their respective superficial metal hydroxide layers. The influences of surface oxidation and flocculation of mineral particles were also discussed. The selective flotation of sphalerite from pyrite in an acidic medium in the presence of copper sulfate was found to be possible, as shown by artificial mixture separation studies. In this way, the possible exclusion of cyanides (for environmental reasons) may be advanced.     

Zinc uptake by Streptomyces rimosus biomass using a packed‐bed column

The ability of Streptomyces rimosus biomass to bind zinc ions in batch mode was shown recently. The aim of this study was to determine the zinc uptake capacity by Streptomyces rimosus biomass in continuous mode. Bacterial biomass was able to bind more Zn(II) after pretreatment with sodium hydroxide (1 mol dm⁻³) than without treatment. The maximum adsorption capacity and the adsorption capacity at the saturation point calculated by means of both the exchange zone model and the Thomas model were practically identical of about 2.9 mg_Zn(II) g⁻¹_biomass. This result was lower than the batch adsorption capacity of Streptomyces rimosus, indicating that the packed‐bed is not the most appropriate process to exploit the bacterial biomass adsorption capacity. The effect of zinc concentration in the range of 10 to 200 mg_Zn(II) dm⁻³ on the biosorption capacity of the packed‐bed was not significant. Biomass regeneration with 0.1 mol dm⁻³ HCl gave a 90% recovery of the adsorbed Zn(II). © 1999 Society of Chemical Industry     

Cadmium biosorption by a glyphosate-degrading bacterium,a novel biosorbent isolated from pesticide-contaminated agricultural soils

In this study, biosorption of cadmium (II) ions from aqueous solutions by a glyphosate degrading bacterium, Ochrobactrum sp. GDOS, was investigated in batch conditions. The isolate was able to utilize 3 mM GP as the sole phosphorous source, favorable to bacterium growth and survival. The effect of different basic parameters such as initial pH, contact time, initial concentrations of cadmium ion and temperature on cadmium uptake was evaluated. The adsorption process for Cd (II) is well fitted with Langmuir adsorption isotherm. Experimental data were also tested in terms of biosorption kinetics using pseudo-first-order and pseudo-second-order kinetic models. Maximum metal uptake q_max was obtained as 83.33 mg g⁻¹. The sorption process of cadmium onto the Ochrobactrum sp. GDOS biomass followed second-order rate kinetic (R² = 0.9986). A high desorption efficiency was obtained in pH 2. Reusability of the biomass was examined under successive biosorption–desorption cycle repeated thrice. The characteristics of the possible interactions between biosorbent and metal ions were also evaluated by scanning electron microscope (SEM), Fourier transform infrared (FT-IR) and X-ray diffraction analysis.     

Effects of Acylation and Crosslinking on the Material Properties and Cadmium Ion Adsorption Capacity of Porous Chitosan Beads

Abstract

Chitosan is a novel glucosamine biopolymer derived from the shells of marine organisms. This biopolymer is very attractive for heavy metal ion separations from wastewater because it is selective for toxic transition metal ions over less toxic alkali or alkane earth metal ions. Highly porous, 3-mm chitosan beads were prepared by an aqueous phase-inversion technique for casting gel beads followed by freeze drying. In the attempt to simultaneously improve material properties and adsorption capacity, chitosan was chemically modified by 1) homogeneous acylation of amine groups with nonanoyl chloride before bead casting, and 2) heterogeneous crosslinking of linear chitosan chains with the bifunctional reagent glutaric dialdehyde (GA) after bead casting but before freeze drying. The random addition of C₈ hydrocarbon side chains to about 7% of the amine groups on uncrosslinked chitosan beads via N-acylation improved the saturation adsorption capacity from 169 to 216 mg Cd²⁺/g-bead at saturation (pH 6.5, 25°C) but only slightly reduced solubility in acid solution. Crosslinking of the N-acylated chitosan beads with 0.125 to 2.5 wt% GA in the crosslinking bath increased the internal surface area from 40 to 224 m²/g and rendered the beads insoluble in 1 M acetic acid (pH 2.36). However, crosslinking of the N-acylated chitosan beads reduced the saturation adsorption capacity to 136 mg Cd²⁺/g-bead at 0.75 wt% GA and 86 mg Cd²⁺/g-bead at 2.5 wt% GA. Crosslinking also significantly reduced the compression strength. There was no clear relationship between internal surface area and adsorption capacity, suggesting that the adsorbed cadmium was not uniformly loaded into the bead.