D. Zamboulis

Sorption of As(V) by Goethite Particles and Study of Their Flocculation

Arsenate oxyanions were removed from aqueous solutions by sorption onto synthetic goethite, which was applied as fine particulate suspension during laboratory experiments. The main parameters affecting this treatment process were investigated, namely the concentrations of goethite and of arsenic(V), contact time, temperature, solution pH values and ionic strength variations, and typical adsorption isotherms were calculated. The study of flocculation of goethite particulates in bench scale was subsequently carried out in presence of pentavalent arsenic (being a toxic pollutant), by applying an appropriate optical technique. The flocculation dynamics of dispersed goethite particles was examined, complemented by turbidity and electrophoretic mobility measurements.

POWDERED ACTIVATED CARBON SEPARATION FROM WATER BY FOAM FLOTATION

Abstract Powdered activated carbon was separated from dilute aqueous suspensions (200–1000 mg/L) by foam flotation using surfactants (anionic or cationic). The effects of surfactant type, pH value of the suspension, initial carbon and surfactant concentrations, flotation time, and air flow rate on the dispersed-air flotation of powdered activation carbon were investigated. In optimum conditions the powdered activated carbon separation was almost complete. The ζ-potential of powdered activated carbon was also measured in the presence and absence of surfactants. Finally, carbon flotation was examined after the carbon had adsorbed chromate ions from an acidic solution (pH 2). Almost complete separation of Cr(VI)-loaded carbon was obtained by using an anionic surfactant.

The application of sorptive flotation for the removal of metal ions

There is a stringent need for the control of toxic metals produced during various production processes and released into the aqueous environment in order to avoid damage relevant to soil or groundwater contamination. Among the available treatment technologies, sorption has been considered of particular importance. In the present study, a synthetic ultrafine zeolite was initially applied as sorbent (in suspension) for the removal of copper and zinc cations, and also chromium(VI) oxyanions — the latter less effectively. The removal of cations by zeolite particles depends mainly on the respective pH value, influencing the aquatic speciation during the process, as well as the zeta-potential values (surface charge) of the system. Flotation was subsequently applied for the efficient (more than 95%) solid/liquid separation of metal-laden sorbents. A suitable surface-active agent (acting as collector) should be added such as sodium dodecyl sulfate, dodecylamine or hexadecyl-trimethyl-ammonium bromide, depending on the specific experimental conditions in order to render hydrophobic and hence, to increase the floatability of solids. As a result, a foam concentrate is produced consisting of the metal-loaded zeolite particles and of purified water as underflow, which could be more easily subjected to further treatment (for instance, by membrane filtration), if necessary. Both the aforementioned technological stages, sorption and flotation, can be operated in the same unit, and the integrated innovative process was termed “sorptive flotation”.

Foam flotation of zeolites: Application for zinc ion removal

Abstract In this paper the solid/liquid separation of a NaY zeolite, a known cation exchanger, was investigated in the laboratory by foam flotation from aqueous suspensions. The main parameters affecting the process in batch experiments, such as the pH of the suspension, the type of collector, the cationic collector concentration, the zeolite concentration, and the ionic strength were examined. The optimum conditions for removal (flotation) of more than 95% of the zeolite were determined. Following flotation of the zeolite in the Na form, zinc ions were chosen to serve as an application for ion exchange by the zeolite (for metal recovery), followed by foam floatation of the exchanged form of the zeolite from solution.

Application of Flotation for the Separation of Metal‐Loaded Resins#

Abstract The separation of two typical Lewatit‐type ion exchange resins (TP208 and TP260) was studied by the application of flotation, following their preliminary use for ion exchange of zinc, a common heavy metal found in many wastewater streams. The major examined parameters were the specific type of resin and the respective ion exchange capacity, the required resin concentration for the efficient removal of metal, the influence of wetting on both processes (i.e., ion exchange and flotation), the effect of pH value on the removal of metal and on the regeneration of resin, the type and concentration of used surfactant (primary amine or quaternary ammonium were examined), as well as the effect of frother (ethanol) on flotation efficiency. The regeneration of resins was studied, with respect to the desorption of metal and to the elution of surfactant. The efficiency of combined process, which includes the removal of Zn(II) by ion exchange and the application of flotation for the subsequent solid/liquid separation of metal‐loaded resin, showed that almost 100% of zinc was removed and more than 95% of used resin was recovered by flotation in a single stage. The operation was also examined during multiple cycles, i.e., following regeneration of resin; the high efficiency of both processes remained rather constant. Many thanks are due to the European Union – Energy, Environment and Sustainable Development (5th Framework programme) for funding the METASEP research project (for more information see reference 28) with contract no EVK1‐CT‐2000‐00083 and to the coordinator Dr. V. Mavrov (Inst. Envir. Compatible Process Tech., Univ. Saarland). Also, to Ms. S. Pataroudi, chemist, for experimental collaboration.

Goethite Mineral as a Sorbent for Heavy Metal Ions

A toxic metal cation (cadmium) and an oxyanion (arsenic in III or V valence state) removed from dilute aqueous solutions by mineral goethite. The simultaneous removal of cations and anions is a great advantage of goethite as a sorbent material. The pure mineral sample was initially characterised by adsorption (and desorption) of nitrogen at liquid nitrogen temperature. The metal ion removal was strongly dependent on the solution pH. The modification of the mineral by potassium hydroxide was examined. Its removal capacity was compared to that of a synthetic goethite. The modelling of the sorption isotherm was discussed. An efficient solid/liquid separation technique, such as flotation preceded by flocculation, may be necessary downstream, when the material used is in an ultrafme state, as in the present study.

Foam flotation for fine particles removal from water: The example of zeolites

An experimental investigation is reported of the effects of several parameters on the foam flotation of fine zeolite particles, used here also as a model of fine particles. A general discussion is given relative to the application of the process to large‐scale clarification of turbid waters. Ion exchange of zinc, a typical heavy metal, by zeolite followed by flotation was also examined, resulting in the simultaneous removal (recovery) of zeolite and of heavy metal.

Application of powdered activated carbon (PAC) for membrane fouling control in a pilot-scale MBR system

Membrane fouling is considered to be the most serious drawback in wastewater treatment when using membrane bioreactors (MBRs), leading to membrane permeability decrease and efficiency deterioration. This work aims to develop an integrated methodology for membrane fouling control, using powdered activated carbon (PAC), which will enhance the adsorption of soluble microbial products (SMP) and improve membrane filterability, by altering the mixed liquors characteristics. Reversible fouling was assessed in terms of sludge filterability measurements, according to the standard time-to-filter (TTF) method, while irreversible fouling was assessed in terms of SMP removal. Results showed that the addition of PAC at the concentration of 3 g/L in the mixed liquor reduced SMP concentration and enhanced substantially the sludge filterability. Furthermore, the TTFPAC/TTFno PAC ratios were lower, than the corresponding SMPPAC./SMPno PAC ratios, indicating that the batch-mode, short-term addition of PAC promotes the reversible, rather than the irreversible fouling mitigation.