Hexavalent Chromium Removal in a Foam Flotation Pilot Plant

Abstract

Hexavalent chromium was removed from dilute simulated wastewater in a continuous flow pilot scale foam flotation plant. Cr(VI) was reduced to Cr(III) with ferrous sulfate, and the floc resulting on pH adjustment was then removed by precipitate flotation. Sodium lauryl sulfate was used as the carrier surfactant. Effluent Cr concentrations below 0.5 mg/L are easily achieved over the pH range 4.5 to 7.0. The effects of varying the hydraulic loading rate and the ferrous sulfate dose were studied.     

Electrical Aspects of Adsorbing Colloid Flotation II. Theory of Rate Processes

Abstract

The kinetic and equilibrium factors affecting the rate of precipitate flotation are analyzed by means of the Gouy-Chapman model. Kinetic effects are found to be extremely rapid, and the rate of precipitate flotation is due to equilibrium considerations. Removal efficiency as a function of inert salt concentration goes through a maximum at about 10^?5 M for films 300 Å thick. Removal efficiency increases with increasing zeta potential of the film surface and with increasing charge on the precipitate particles.     

Precipitate Flotation of Complexed Cyanide

Abstract

Precipitated cyanide, complexed with Fe(II) at a molar Fe/CN ratio of 0.550, can be floated readily from aqueous suspension with a cationic surfactant, ethylhexadecyldimethylammonium bromide. The effects of three distinct mixing times of significance in preparing the precipitate and contacting it with surfactant, of pH, of initial cyanide concentration, of initial surfactant concentration, and of ionic strength have been established experimentally. Mixing times and the initial cyanide concentration have little influence on the flotation, while increases in pH and ionic strength have a most pronounced influence, part of which can be overcome with increased surfactant concentrations. At pH 6.0, 95% of the complexed cyanide can be foam separated from distilled water suspensions 1.5 to 3.1 mM in total cyanide. About 0.04 mole surfactant/mole complexed cyanide is required; about 0.08 mole/mole is required to increase the flotation to 99% or to overcome ionic strength effects.     

A kinetic study of precipitate flotation of Zinc(II), Cobalt(II) and Copper(II) hydroxides

An experimental kinetic study has been completed on precipitate flotation of Zn(II), Co(II) and Cu(II) hydroxides (initial metal concentration 1 × 10^?-2M) with the anionic surfactant, sodium dodecyl benzenesulphonate (1 × 10^?-4M), at varying equilibrium pH. An original radioactive isotope procedure was applied and proved to be sufficiently accurate. Kinetic equations of Rubin and co-workers were found to be relevant for precipitate flotation of hydroxides. From the flotation rate constant (k_p) determined at varying equilibrium pH of floated suspensions it appeared that the selective flotation of individual compounds from mixed precipitate was possible as a result of the ‘kinetic effect’.     

Flotation of Germanium from Dilute Solutions

Abstract

In laboratory experiments, ion flotation was found effective as a concentration method for germanium from dilute aqueous solutions. Removals over 90% were obtained at neutral pH conditions and stoichiometric addition of the flotation reagents, these being pyrogallol as activator for complex formation and laurylamine as cationic surfactant. Parameters investigated were initial and residual concentration, gas flow rate, pH of the solution, ionic strength, type of salts added, laurylamine concentration, retention time, ethanol addition, and surface tension on the germanium recovery.     

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).     

The low gas flow rate foam separation of cerium (III) from dilute aqueous solutions

Two low gas flow rate foam separation techniques, ion and precipitate flotation, have been investigated for the separation of trivalent cerium from solutions with initial cerium concentrations ranging from 1 × 10^?8 to 1 × 10^?4M in the pH range of 1.8–12 using the anionic collector sodium lauryl sulphate and the cationic surfactant cetyl trimethyl ammonium bromide. In addition to the type of collector, the pH and the cerium ion concentration, and other factors which can affect flotation results, viz. the time period of bubbling, the rate of gas flow, the ageing of both the cerium and the collector ions, the ionic strength, and the concentration of the collector ions have been investigated and optimum conditions have been established. Under optimum conditions removals as high as 98.5% can be achieved.     

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%.     

Flotation of metal hydroxide precipitates. I. Flotation of copper hydroxide

Flotation of copper hydroxide precipitate has been investigated at total initial copper concentration 10^?2M with sodium dodecylbenzenesulphonate (DBSNa) and dodecyldimethylbenzylammonium bromide (DDMBABr), both at initial concentration 10^?4M. In particular, granulometric analysis of the precipitate and measurement of its electrokinetic potential were carried out over a wide range of the acidity of aqueous precipitate suspension in order to establish essential factors governing flotation of the precipitate. Moreover, adsorption of the flotation collectors by the precipitate as well as the rate of precipitate sedimentation were measured. The cationic collector (DDMBABr) neither influenced the electrokinetic potential of copper hydroxide precipitate nor adsorbed on its surface. Consequently, no flotation of copper hydroxide was observed with (DDMBABr). On the other hand, the anionic collector (DBSNa) influenced the electrokinetic potential of copper hydroxide within the same pH range where adsorption of DBSNa on the precipitate was observed and flotation was effective. The rate of flotation varied with the pH of the aqueous suspension. This dependence was irregular and presumably governed by the aggregation of precipitate grains since the rate of flotation increased with the size of the aggregates.     

Foam Fractionation and Precipitate Flotation of Zinc(II)

Abstract

The hydrolytic behavior of a metal can be related to its removal by foaming. In this study the effect of pH and ionic strength on the foam separation of 0.1 mM zinc (II) was investigated using different concentrations of sodium lauryl sulfate as the collector. At low pH Zn²⁺ ion was removed by foam fractionation while above pH 8 Zn(OH)²(s) was removed by precipitate flotation. The results demonstrate that precipitate flotation is a more efficient removal process than the foam separation of soluble metal species.     

Removal of Molybdate and Arsenate from Aqueous Solutions by Flotation

Abstract

Ion flotation and adsorbing colloid flotation have been studied in this paper for the effective removal of molybdenum(VI) and arsenic(V) from dilute aqueous solutions. These different flotation methods were also compared. Ion flotation using a cationic surfactant (dodecylamine) as collector, as well as adsorbing colloid flotation using ferric hydroxide as coprecipitant (or sorbent) and an anionic surfactant (sodium dodecyl sulfate) as collector were examined. Laboratory-scale experiments were conducted in order to assess the effects of the following parameters on the efficiency of the process: pH value, dosages of chemical reagents, initial concentrations of arsenic and molybdenum, and the presence of foreign anions, such as Cl^- and SO² ₄ ^-. In practical applications, ion flotation or adsorbing colloid flotation may be selected according to the concentration of arsenic, molybdenum, and also the initial [Mo]/[As] molar ratios in solution.     

A new kinetic model for Ni(II) ion flotation based on gene expression programming

ABSTRACT

The Ni(II) ion flotation kinetics with sodium dodecylsulfate as collector was studied with the aim of developing new models to predict the flotation rate constant (k) of Ni(II) ions and water removal during the process of Ni(II) ion flotation. In this regard, the most influential parameters on Ni(II) ion flotation efficiency including the ratio of collector concentration on the Ni(II) ion concentration, impeller speed, activity coefficient, and pH were used to develop predictive models. The results show that the proposed gene expression programming models can be used to predict the flotation rate constant of Ni(II) ions and water removal.     

Electrical Aspects of Adsorbing Colloid Flotation. XV. Adsorption Isotherms of Mixed Surfactants

Abstract

A theory is developed for the calculation of absorption isotherms of binary mixtures of surfactants A and B on solid-water interfaces. The effects of the relative magnitudes of the interaction energies of A-A, A-B, and B-B nearest neighbor pairs are explored. The theory makes use of the random approximation in order to overcome mathematical difficulties which arise in the general case. The possibility of reducing surfactant costs in precipitate and adsorbing colloid flotation by the use of mixed surfactants is suggested.     

Precipitate flotation. V. Extractive solvent sublation

The new technique of precipitate flotation of the second kind is unique amongst flotation processes in that it requires no surfactant. This does have the disadvantage that the floated material is not supported on the surface and tends to redisperse into the solution. A layer of immiscible organic solvent containing either a surfactant, a complexing agent, or the original precipitant, leads to solubilisation and retention of the floated material. As this is quantitative, spectrophotometric examination of the organic layer may provide a means of analysis for the ion originally precipitated. Complete removal from solutions as dilute as 10^?5 M is possible.     

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.     

Foam Fractionation and Ion Flotation of Simple and Complex Anions with Cationic Surfactants

Experimental data are presented and interpreted on the foam fractionation of an extensive series of simple and complex anions from dilute (of the order 10⁻⁶−10⁻⁴ molar) aqueous solutions, utilizing a quaternary ammonium surfactant with which the anions form soluble ion pairs in competition with the surfactant's counterion. Selectivity coefficients, based on a bubble-interface, ion exchange model, are established in a single-equilibrium-stage, continuous-flow, foam fractionation unit for each of a series of 13 anions and oxyanions versus the surfactant's bromide counterion. Three additional series of batch experiments with multi-metal solutions establish the separation and concentration in the foam of the oxyanions of Re(VII), Mo(VI), Cr(VI), W(VI), and V(V); of the cyanide complex anions of Zn(II), Cd(II), Hg(II), and Au(III); and of the chloride complex anions of Zn(II), Cd(II), Hg(II), and Au(III). The metal oxyanions and metal cyanide and chloride complex anions can be separated from each other and from competing chloride, cyanide, or nitrate. Ion flotation of anionic species with a cationic surfactant involves an entirely different mechanism, in which a precipitation reaction occurs and particle flotation follows. Hexavalent chromium (primarily HCrO⁻₄) is ion-floated with each of a series of variable chain length quaternary ammonium surfactants, elucidating the effects of temperature, the surfactant/Cr(VI) feed ratio, mixing time, and surfactant chain length in terms of the roles of the surfactant as precipitant, dispersant, collector, and frother.     

Diesel Oil Removal by Froth Flotation Under Low Interfacial Tension Conditions II: Continuous Mode of Operation

Abstract

The objective of this study was to investigate the relationship between interfacial tension (IFT) and foam characteristics and the efficiency of diesel oil removal from water in a continuous froth flotation column. The effects of operational parameters, including surfactant concentration, salinity, oil-to-water ratio, foam height, air flow rate, and hydraulic retention time (HRT) on the oil removal were investigated in the continuous mode of a froth flotation operation and compared to batch operation results. Unlike the batch system, for the continuous system used in the present study, having only branched alcohol propoxylate sulfate sodium salt surfactant (C_14–15(PO)₅SO₄Na) and NaCl present in the solution yielded such poor foam characteristics that a stable froth which overflowed the flotation column could not be produced, so the addition of sodium dodecyl sulfate (SDS) as a froth promoter was used to improve the foam stability. Unlike the batch froth flotation system with only C_14–15(PO)₅SO₄Na, the continuous froth flotation with the mixture of C_14–15(PO)₅SO₄Na and SDS, it was not possible to find a SDS and a NaCl concentration at which both ultralow IFT and good foaming were both achieved. Foam formation, stability, and production rate were found to be crucial parameters to the froth flotation efficiency. The continuous froth flotation system offers a high diesel oil removal of 96% in the single stage unit. Demonstration of efficient operation in the continuous mode in this work is important to the practical application of froth flotation in large scale processing.     

The Elimination of Channeling and Foam Overturning in Continuous Mode Adsorbing Colloid Flotation with a Sodium Dodecylsulfate/Dodecanoic Acid Mixture

Abstract

The effect of hydraulic loading, surfactant concentration, and air flow rate on the removal of Cr(III), Ni(II), and Zn(II) from chromium stream electroplating wastewater by adsorbing colloid flotation using a sodium dodecylsulfate/dodecanoic acid mixture was investigated. Typically, heavy metal concentrations of 81 ppm Cr(III), 55 ppm Ni(II), and 3.3 ppm Zn(II) were reduced to 1.2 ppm Cr(III), 3.2 ppm Ni(II), and 0.05 ppm Zn(II) at a hydraulic loading of 22.9 m³/m²·h (3 L·min^?1), an air flow rate of 45.8 m³/m²·h (6 L·min^?1), 40 ppm dodecanoic acid, and 80 ppm sodium dodecylsulfate, and using a 10-cm inner diameter column. A novel mode of operation (high liquid carryover) was used whereby a large proportion of the liquid entering the column leaves the column with the foam.     

Removal of Cu(II) from Aqueous Solutions by the Foam Separation Techniques of Precipitate and Adsorbing Colloid Flotation

Abstract

Experimental investigations on the removal of Cu(II) from aqueous solution were carried out through two foam separation techniques: precipitate flotation and adsorbing colloid flotation with Fe(III). The optimum pH for good removal was found to be about 9 for the former and about 7 for the latter. The effects of surfactant (sodium lauryl sulfate), foreign ions (Na⁺, Ca²⁺, NO^? ₃, and SO^2- ₄), and Al(III) addition on the efficiency of Cu(II) removal are discussed.     

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).