Separation of Hg(II) by foam fractionation in the acidic range: effect of complexation

Removal of trace hexavalent chromium from aqueous solutions by ion foam fractionation

Ion foam fractionation is a green and cost-effective technology where separation of molecules exploits the difference in surface affinity. In this work, a batch ion foam fractionation system was designed and optimized for the separation of trace hexavalent chromium (Cr(VI)) from aqueous solutions. The effect of surfactant head groups (collectors) on the adsorption dynamics was analyzed. Cetyl trimethyl ammonium bromide (CTAB), a cationic surfactant showed high efficiency for the removal of Cr(VI) from aqueous solutions. An experimental investigation of the effect of different operational parameters on the separation characteristics is presented. The recovery of Cr(VI) increased with the increase in CTAB/Cr(VI) molar ratio and reached a maximum of 92.5% at optimum operating conditions. However, with CTAB concentrations close to the critical micelle concentration (CMC) wet foams were produced resulting in high liquid hold-up and poor enrichment ratio. The presence of Cr(VI) at the gas-liquid interface significantly improved the drainage characteristics of the foam decreasing the liquid hold-up. Further, a three-stage ion foam fractionation unit was developed with Cr(VI) removal efficiency of more than 99%. The concentration of Cr(VI) in the residue after the three-stage operation was less than 0.02 mg/L which is below the USEPA recommended standards for drinking water.

Single- and Dual-Stream Foam Fractionation of Protein – Exploring a Simple and Effective System to Improve Fundamental Understanding

In this paper, a single-/dual-stream foam separation device was constructed to simplify the conventional foam fractionation process (CFFP), by minimizing interactions between bubbles. This was expected to help reveal mechanisms in a ‘neat’ way. Results have shown negligible productivity of single-stream foam fractionation (SSFF) for the protein enrichment ratio (E) under conditions tested, whereas dual-stream foam fractionation (DSFF) was established as a reasonable basic unit of CFFP. The influence of DSFF operating conditions, such as the inlet protein concentration and gas velocity, were examined. Calculations of protein concentration and liquid volume were performed via foam thickness measurement, which is very difficult with CFFP. It was evident that the middle drainage channel played a key role in enrichment phenomena. The current DSFF system provides a control case for evaluating principles of foam fractionation. Furthermore, a simple mass-balance model has been proposed to represent the column-wide behavior of DSFF.

Removal of Cu, Pb and Zn by foam fractionation and a soil washing process from contaminated industrial soils using soapberry-derived saponin: a comparative effectiveness assessment

The feasibility of using the eco-friendly biodegradable surfactant saponin (a plant-based surfactant) from soapberry and surfactin from Bacillus subtilis (BBK006) for the removal of heavy metals from contaminated industrial soil (6511mgkg(-1) copper, 4955mgkg(-1) lead, and 15090mgkg(-1) zinc) by foam fractionation and a soil flushing process was evaluated under variation of fundamental factors (surfactant concentration, pH, temperature and time). The results of latter process showed that 1-2% Pb, 16-17% Cu and 21-24% Zn was removed by surfactin after 48h, whereas the removal of Pb, Cu and Zn was increased from 40% to 47%, 30% to 36% and 16% to 18% in presence of saponin with an increase from 24 to 72h at room temperature by the soil washing process at pH 4. In the foam fractionation process, the metal removal efficiencies were increased with increases in the saponin concentration (0.075-0.15gL(-1)) and time (24-72h), whereas the efficiency was decreased with increasing pH (4-10) and temperature (>40°C). The removal efficiencies of Pb, Cu and Zn were increased significantly from 57% to 98%, 85% to 95% and 55% to 56% with an increase in the flow rate from 0.2 to 1.0Lmin(-1) at 0.15gL(-1) saponin (pH 4 and 30°C). The present investigation indicated that the foam fractionation process is more efficient for the removal of heavy metal from contaminated industrial soil in comparison to the soil washing process. The plant-based eco-friendly biodegradable biosurfactant saponin can be used for environmental cleanup and pollution management.

Recovery of Hg(0) from the Aqueous Hg(I/II) Present in Analyte Solution after Quantitative Determination of Iron

An easy and feasible approach to recover HgCl2, used in quantitative determination of iron values, as Hg(0) was described. Both Hg(I) and Hg(II), present in the solution after quantitative determination of iron, was completely reduced to Hg(0) by the addition of aluminium chips in more slightly excess than the stoichiometric amount. The purity of recovered Hg(0) was verified by comparing the value of density with pure mercury. This simple method may be useful to remove the mercury from other waste aqueous solutions before their discharge into the environment.

How to minimize iron loss while decontaminating converter dust from lead

The purpose of this work was to decontaminate a converter flue dust from lead while minimizing the iron loss from the dust matrix. A physicochemical method based on a leaching cascade was applied to remove lead impurities with HCl. Finally, the lead-rich wastes generated at the end of the operations were further treated in order to meet the standards of waste disposal sites. The results show that lead could be removed from the dust with efficiencies of better than 90%. However, some iron was lost in these operations. It was noticed that under optimum conditions 8.5 g of iron would be lost as leachate per each gram of removed lead. It was also noticed that the lead-treated dust was more concentrated in iron and had less calcium. A number of parameters that could affect the amount of iron loss, such as acid dose, exposure time and temperature, were identified and the extent of the effects are presented. It was concluded that the lead content in the flue dust could practically be lowered to any level. It was also concluded that the difference between the solubility of lead chloride in cold and hot water, as well as the affinity of certain ligands such as Cl- and OH- to form stable complexes with lead ions, played a key role in this study. The lead-containing complexes in the leachate were identified to be predominantly PbCl3- and PbCl+.

Removal of mercury by foam fractionation using surfactin, a biosurfactant

The separation of mercury ions from artificially contaminated water by the foam fractionation process using a biosurfactant (surfactin) and chemical surfactants (SDS and Tween-80) was investigated in this study. Parameters such as surfactant and mercury concentration, pH, foam volume, and digestion time were varied and their effects on the efficiency of mercury removal were investigated. The recovery efficiency of mercury ions was highly sensitive to the concentration of the surfactant. The highest mercury ion recovery by surfactin was obtained using a surfactin concentration of 10 × CMC, while recovery using SDS required < 10 × CMC and Tween-80 >10 × CMC. However, the enrichment of mercury ions in the foam was superior with surfactin, the mercury enrichment value corresponding to the highest metal recovery (10.4%) by surfactin being 1.53. Dilute solutions (2-mg L⁻¹ Hg²⁺) resulted in better separation (36.4%), while concentrated solutions (100 mg L⁻¹) enabled only a 2.3% recovery using surfactin. An increase in the digestion time of the metal solution with surfactin yielded better separation as compared with a freshly-prepared solution, and an increase in the airflow rate increased bubble production, resulting in higher metal recovery but low enrichment. Basic solutions yielded higher mercury separation as compared with acidic solutions due to the precipitation of surfactin under acidic conditions.

Removal of trace Cd2+ using continuous multistage ion foam fractionation: part I--The effect of feed SDS/Cd molar ratio

In this research, a continuous multistage ion foam fractionation column with bubble-cap trays was employed to remove cadmium ions from simulated wastewater having cadmium ions at a low level (10 mg/L). In this study, sodium dodecyl sulfate (SDS) was used to generate the foam. An increase in feed SDS/Cd molar ratio enhanced the removal of Cd. However, the SDS concentration above a certain level resulted in wetter foams, leading to having a high volume of generated foam that lowered both the enrichment ratio and separation factor of the Cd. The SDS recovery tended to increase with increasing feed SDS/Cd molar ratio. The molar ratio of SDS/Cd in foamate was found to be close to the theoretical adsorption molar ratio of 2/1 on the air-water interface of foam when the system was operated at a feed SDS/Cd molar ratio in the range of 2/1-7/1. Ion foam fractionation has been demonstrated in this study to be a promising technique for high heavy metal removal (more than 99%) for a feed having a low heavy metal concentration in the ppm (mg/L) level.

Removal of color from textile dyeing wastewater by foam separation

The feasibility of foam separation for color removal from direct dyes-containing wastewater was assessed using actual textile wastewater as the research system and cetyl trimethyl ammonium bromide (CTAB) as the collector. The influences of liquid loading volume, air flow rate, surfactant concentration, and initial pH on the removal efficiency and reuse of CTAB in the foamate were studied. The results indicated that using CTAB as a collector for foam separation can provide good foaming quality and effectively remove color from textile wastewater. Under optimum operational conditions (liquid loading volume 450 mL, gas flow rate of 500 mL/min, CTAB concentration 20 mg/L, and an initial pH of 7.0), the removal efficiency reached 88.9%. The residual dye content met the discharge standard for the dyeing and finishing textile industry (GB4287-92) published by the Ministry of Environmental Protection of the People's Republic of China. Using recycled foamate in untreated wastewater, the removal efficiency of 87.5% was obtained with CTAB concentration 10 mg/L of the wastewater.

Silica coated magnetite particles for magnetic removal of Hg2+ from water

The magnetic removal of Hg(2+) from water has been assessed using silica coated magnetite particles. The magnetite particles were first prepared by hydrolysis of FeSO(4) and their surfaces were modified with amorphous silica shells that were then functionalized with organic moieties containing terminal dithiocarbamate groups. Under the experimental conditions used, the materials reported here displayed high efficiency for Hg(2+) uptake (74%) even at contaminant levels as low as 50 μg l(-1). Therefore these eco-nanomagnets show great potential for the removal of heavy metal ions of polluted water, via magnetic separation.