N. K. Lazaridis

Hybrid flotation-membrane filtration process for the removal of heavy metal ions from wastewater

A promising process for the removal of heavy metal ions from aqueous solutions involves bonding the metals firstly to a special bonding agent and then separating the loaded bonding agents from the wastewater stream by separation processes. For the separation stage, a new hybrid process of flotation and membrane separation has been developed in this work by integrating specially designed submerged microfiltration modules directly into a flotation reactor. This made it possible to combine the advantages of both flotation and membrane separation while overcoming the limitations. The feasibility of this hybrid process was proven using powdered synthetic zeolites as bonding agents. Stable fluxes of up to 80l m(-2)h(-1) were achieved with the ceramic flat-sheet multi-channel membranes applied at low transmembrane pressure (<100 mbar). The process was applied in lab-scale to treat wastewater from the electronics industry. All toxic metals in question, namely copper, nickel and zinc, were reduced from initial concentrations of 474, 3.3 and 167mg x l(-1), respectively, to below 0.05 mg x l(-1), consistently meeting the discharge limits.

Flotation of metal-loaded clay anion exchangers. Part I: the case of chromates

Synthetic hydrotalcite-like layered materials are known for their ability to remove anions, like the chromates. These sorbents usually exist in powder form, thereby exhibiting high surface area and rapid kinetics for adsorption, but presenting appreciable problems in the subsequent solid/liquid separation process. Almost complete removals were obtained in this paper, from batchwork dispersed-air flotation in presence of a flocculant. Due to the experienced difficulty of flotation of thermally activated (at 500 degrees C) hydrotalcite metal-loaded particles, the application of various surfactants was studied. Continuous-flow laboratory runs certified also the effectiveness of this combined process of sorptive flotation, a promising innovative treatment technology.

Selective Separation of Cu, Zn, and As from Solution by Flotation Techniques

Abstract The selective precipitation and flotation of copper, zinc, and arsenic ions from dilute aqueous solutions were investigated. Phase separation was accomplished effectively by the dissolved-air technique for the production of fine gas bubbles, and a short-chain xanthate was applied as the collector for copper ions, dialkyldithiocarbamate for zinc, and ferric sulfate for the pentavalent arsenic. The procedures followed were ion flotation for copper and zinc, and adsorbing colloid flotation for arsenic (without a surfactant).

A study and modelling of liquid-phase mixing in a flotation column

Abstract The mixing process of the liquid phase in a gas-liquid flotation column and the effect of the flowrates on it have been investigated. The increase of the gas and liquid flowrates had opposite effects: the former enhanced the mixing process, whereas the latter caused the behaviour of the column to approach plug flow. A mixed zones-in-series model is proposed for interpreting the experimental results, which involves two parameters: the number of zones and the ratio of backwards to net liquid flow. In this way, the mixing was related to the backflow and the increase in mixing was due to an intense internal recirculation. The model was able to predict accurately the column behaviour in the experimental range investigated. Its major advantage lies in its structured description of the column contents.

A statistical approach to precipitate flotation of CuSZnS

Abstract The precipitate flotation of copper and zinc, as sulphides, by cationic surfactants (mainly laurylamine) was studied at a pH of about 2, as a selective separation method for the two dissolved metals from dilute aqueous solutions. The dissolved-air flotation technique was used to produce fine bubbles and copper sulphide was found in the foam layer. The applied laurylamine was also chemically determined, in parallel with copper and zinc. The laboratory tests were scheduled by a full factorial experiment based on previous experience in flotation and the results were treated statistically for optimization of the process. Two series of batch experiments were carried out: an initial (first-order) series having as basic parameters the copper-ion concentration, pH, and concentrations of sodium sulphide and amine added; and a second-order series, with the concentrations of copper and zinc ions and the preliminary stirring speed as parameters. The obtained separation results were considered promising; copper recovery was over 90%, while an amount of about 10–20% of zinc was occluded in the concentrate.

Simultaneous Removal of Nickel(II) and Chromium(VI) from Aqueous Solutions and Simulated Wastewaters by Foam Separation

The present investigation was carried out to study the feasibility of foam separation for simultaneous removal of two types of inorganic hazardous contaminants, nickel(II) cations and chromium(VI) anions, from aqueous solutions and simulated wastewaters. The effects of pH of the solution, Ni/Cr ratio, collector and frother concentrations, induction and flotation time, and solution ionic strength on the co-removal efficiency of nickel(II) and chromium(VI) were studied. At the optimum conditions, removals more than 99.5% were obtained for nickel(II) and chromium(VI). The concerned contaminants were effectively removed when they coexisted at low as well as at high concentrations. Coflotation of nickel(II) and chromium(VI) from tap water and simulated electroplating wastewater resulted in removal percentages higher than 99.5% with residual concentrations below their permissible limits in potable water. High removal percentages, DFs, ERs, and VRs were achieved for their radionuclides, 63Ni(II) and 51Cr(VI), from simulated radioactive process wastewater. The results obtained in this study suggest the feasibility of the developed foam separation process for treatment, in a single-step, of wastewaters contaminated with cationic and anionic inorganic pollutants.

Removal and Recovery of Metals from Dilute Solutions

Dilute aqueous solutions, generated or used by mineral industry, generally contain several metal species; the latter are known to be non-biode-gradable substances. For this reason, various processes suitable for metal ions removal from water and effluents will be briefly reviewed, among them the conventional ones such as precipitation, sorption and ion exchange. Nevertheless, attention will be mainly paid to the application of innovative processes, particularly aiming for metals recovery. In today’s world of water shortage, water reuse in the mineral processing plants is also of great importance. Stress will be given to the necessary solid-liquid separation technique applied downstream, following the metals removal. The important aspect of applying industrial by-products (i.e. mineral fines, etc.) as efficient sorbents, including the biosorbents, will be discussed. Finally, the chemistry of pyrite flotation will be reported.

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).

A Study of Flotation Column Performance for the Recovery of Fine Particles

The performance of a laboratory-scale flotation column has been experimentally investigated for the recovery of fine particles (-200 mesh). The column operation has been found to be exceptionally stable, and the solid particles (calcite) recovery to depend upon the pulp, gas, and washwater flow rates. An optimum performance can be achieved for a range of operating variables which depends upon the physical-chemical characteristics of the mineral system and also the geometrical features of the particular column in use.

A New Hybrid Flotation-Microfiltration Cell

Abstract The investigated hybrid cell combines the advantages of both flotation and membrane separation, while overcoming their limitations and having as an outcome clean water from a industrial wastewater. Hence, metals recovery from dilute aqueous solutions was a promising application of this innovative process, further to solid/liquid separation. The specific objective was to apply the process for the efficient separation of effluents containing metals (here, zinc). The main examined parameters were the following: the metal initial concentration, flotation surfactant applied, and air flowrate. The successful contribution of precipitate flotation was highlighted, while the observed metal removals were of the order of ∼100%.