Flotation Mechanisms of Boron Minerals

Abstract

The development of reagent strategies for the flotation of boron minerals requires an understanding of flotation chemistry of reagent/mineral interactions. The floatability of a typical boron mineral, colemanite, was investigated in a microflotation cell by using anionic and cationic surfactants as collectors and tannic acid as a depressant. The results obtained with zeta potential measurements together with flotation tests reveal that colemanite is floatable with both anionic and cationic surfactants at its natural pH of 9.3. While the floatability of colemanite with anionic surfactants decreases with increasing pH, that with a cationic surfactant exhibits a maximum at pH 10.2, indicating the major role of electrostatic interactions in the system.     

Flotation Using Microgas Dispersions for the Removal of Pentachlorophenol from Aqueous Solutions

ABSTRACT

Microgas dispersions called colloidal gas aphrons (CGAs) were generated using cationic, anionic, and nonionic surfactants, and were used in an adsorptive bubble flotation process in a semibatch mode to remove pentachlorophenol (PCP) from the aqueous phase. The aqueous solution was maintained at pH values by using buffers. CGAs generated with Tergitol, which is a nonionic surfactant, were found to be the most efficient for the removal of PCP; the efficiency remained nearly independent of pH. In the case of an anionic surfactant, sodium dodecylbenzene sulfonate (DDBS), the efficiency of removal improved from 15 to 36% with a change in pH from 10.1 to 3.0. For a cationic surfactant, hexadecyltrimethylammonium bromide (HTAB), the removal at pH 10.1 was 81%, which decreased to 68.1% at pH 3.0. The charges on the encapsulating film of CGAs may explain the higher percentage of adsorption of PCP on the CGAs generated using HTAB as compared to CGAs generated using DDBS. For all the surfactants, an increase in concentration improved the removal efficiency. These results were compared with the removal efficiencies using conventional flotation techniques used by other researchers. Solvent sublation appears to be effective in the removal of PCP, but even in the presence of a surfactant it required 300% more air volume per volume of liquid when compared with CGA flotation.     

Foam separation of active carbon

An experimental investigation is presented of the foam separation of powdered active carbon, equilibriated with an aqueous, synthetic waste water containing phenol and a cationic (ethylhexadecyldimethylammonium bromide (EHDA-Br)), anionic (dodecyl sodium sulphate), or non-ionic (alkyl phenoxy polyethoxy ethanol) surfactant. The effect of surfactant, of pH, of initial carbon concentration, and of initial surfactant concentration on the flotation of carbon is investigated. At pH 3, 7, and 10, the cationic surfactant yields the best flotation of carbon, which increases with increasing pH. At pH 7, a suspension containing 800 mg/1 carbon can be reduced to 24 mg/1 in 10 min. with 0·37 mM EHDA-Br. The relative concentrations of carbon and of surfactant must be controlled carefully to yield sufficient free surfactant to obtain a foam but not excessive free surfactant to impair the foam separation process. Foam volumes are controlled by free (non-adsorbed) surfactant.     

Investigations of Kinetics of Removal of Trivalent Chromium Salts from Aqueous Solutions Using lon and Precipitate Flotation Methods

Abstract

Trivalent chromium salt solutions were flotated using cationic and anionic surfactants. The results indicate that the course of ion and precipitate flotation in the range of parameters investigated can be described by an equation analogous to a first-order rate equation. In the region of precipitate flotation the flotation rate constant reaches a maximum at a definite pH value. Increases in the surfactant concentration result in decreases in the flotation rate. Flotation of chromium at higher surfactant concentrations results in a delay effect which increases with the concentration of the surface-active agent. Increases in the flotation gas flow rate result in increases in the rates of ion and precipitate flotation.     

Coagulation and Flotation of Colloidal Titanium Dioxide

Abstract

The foam separation of dispersed and coagulated titanium dioxide was investigated using anionic and cationic collector surfactants in a batch flotation system. Aluminum sulfate was used as the coagulating agent, and ethanol served as the frother. Removal was studied as a function of pH with coagulant and collector concentrations as parameters.     

Effect of Al(III) as an Activator for Adsorbing Colloid Flotation

Abstract

The effect of Al(III) on adsorbing colloid flotation using Fe(OH)₃ as the coprecipitant and sodium lauryl sulfate as the collector was studied, and the results of foam separation were compared with the zeta potential of the floc before and after Al(III) being added to the solution. It was found that when Al(III) is used as an activator, the zeta potential of the floc is more positive, which presumbly gives the floc a stronger affinity for anionic surfactant adsorption, resulting in better separation efficiency. The working range of pH for an effective separation is extended and good separation efficiency can be achieved at pH values closer to neutral with the aid of Al(III). Furthermore, the separation efficiency is significantly improved for solutions containing interfering ions, such as sulfate, by using Al(III) as an activator.     

As(V) Recovering‐Separation from Aqueous Systems by DAF Technique

Abstract

As(V) oxyanions removal from aqueous systems by dissolved air flotation (DAF) using Fe₂O₃ · xH₂O as solid support and sodium laurate as anionic surfactant was investigated. The influencing factors of the process: pH, support, surfactant, and As(V) concentrations, the presence of flocculant and foreign ions, conditioning time and dissolved air pressure were discussed, as they may affect in a great extent the separation efficiency. The systematic study aims to establish the optimum operating parameters of the process, to investigate the equilibrium and mechanism of separation.     

Mechanism of Selective Flotation of Sodium-Calcium Borates with Anionic and Cationic Collectors

Abstract

The major boron minerals, colemanite and ulexite, are frequently found together in boron deposits. Similarities in their chemical compositions create problems in the selective flotation of these minerals. The surface properties of the above boron minerals have been determined by solubility, microflotation, and zeta potential measurements using typical anionic and cationic surfactants. The isoelectric point (iep) of colemanite is 10.5, while ulexite exhibits no iep in a practical pH. Anionic surfactants thus easily float colemanite but fail to float ulexite at a natural pH. This knowledge is used to find the optimum conditions for the selective separation of colemanite from ulexite at a natural pH of 9.3. Cationic surfactants work well but are adversely affected by the presence of clay-type minerals in the boron ore which hinder the floatability of borates by the formation of a slime coating. The mechanism of slime coating onto boron minerals is also elucidated.     

Electroflotation Studies on Cu,Ni, Zn,and Cd with Ammonium Dodecyl Dithiocarbamate

Abstract

The concentration of Cu, Ni, Zn, and Cd ions by electroflotation using the ammonium salt of dodecyl dithiocarbamic acid as an anionic collector is examined. Quantitative studies reveal better separation efficiency by this method as compared to column flotation using dodecyl dithiocarbamic acid ligand as a chelating surfactant.     

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.     

Simultaneous Removal of Algae and Their Secondary Algal Metabolites from Water by Hybrid System of DAF and PAC Adsorption

Abstract

The feasibility of a hybrid system consisting of powdered activated carbon (PAC) adsorption and dissolved air flotation (DAF) processes was examined for the simultaneous removal of algae (anabaena and mycrocystis) and their secondary algal metabolites (2‐methylisoboneol and geosmin). Before studying the hybrid system, adsorption equilibrium and kinetics of organics (2‐methylisoboneol and geosmin) produced from algae on three powdered activated carbons (wood‐based, coal‐based, coconut‐based) were studied. The flotation efficiency of algae and PAC in DAF process was evaluated with zeta potential measurements. Interestingly, we found that the agglomerate of bubble and PAC particle can be successfully floated by DAF. In addition, the simultaneous removal of algae and organics (i.e., secondary algal metabolites) dissolved in water can be achieved by using the hybrid system of adsorption/DAF processes.     

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     

Electrochemical degradation of surfactants by intermediates of water discharge at carbon-based electrodes

The electrochemical oxidation of anionic (sodium dodecylbenzenesulfonate) and cationic (hexadecyltrimethyl ammonium chloride) aqueous dilute surfactant solutions at a BDD (boron-doped diamond) electrode has been studied by batch electrolysis experiments and potentiodynamic measurements. In the potential region of water decomposition (E>2.3 V vs. SHE), surfactants could be deactivated and oxidised with total organic carbon (TOC) removals up to 82% by the action of intermediates of water discharge (e.g. hydroxyl radicals). Of the investigated process parameters, the initial electrolyte pH had the highest impact on surfactant oxidation. An initial pH of 10 significantly enhanced the electrochemical oxidation of both surfactants. The process was not diffusion-controlled and instantaneous current efficiencies (ICE) for TOC removal were in all cases low, varying from 5 to 12% on average. The surfactant deactivation and oxidation potential of the BDD electrode was compared with other carbon-based electrodes. Applying an equal electrode surface, the BDD electrode showed much higher surfactant removals compared to plane graphite. Graphite granules and carbon felt suffered from abrasion, leading to additional carbon loading of the surfactant solutions. Based on the current electrolysis configuration, the specific energy requirement with the BDD electrode for the electrochemical oxidation of surfactants was estimated at 10-20 kW h m⁻³ effective wastewater.     

The foam separation of colloidal ferric oxide with an anionic and a cationic surfactant

An experimental investigation is presented of the foam separation of colloidal ferric oxide over the pH range 3 to 12 by using an anionic and a cationic surfactant. A sol containing 1.67 mmole/ liter (93 mg/liter) of trivalent iron can be reduced in concentration to 0.09 mmole/liter by 0.17 mmole/liter dodecyl sodium sulfate (anionic) over pH 4.5 to 8; and to 0.18 mmole/liter by 0.17 mmole/liter ethylhexadecyldimethylammonium bromide (cationic) over pH 10 to 12. Soluble iron species produce poorer separations. Between pH 8 and pH 10 the charge of the colloid is reversed from positive to negative, and for an efficient separation a two-step process should be used, first with an anionic surfactant and then with a cationic. The charge of the particulates has little effect on the foam separation of the surfactants although the presence of the particulates has a significant effect, as evidenced by residual surfactant concentrations and collapsed foam volumes.     

Two classes of anionic surfactants and their significance in hot water processing of oil sands

In hot water flotation of bitumen from Athabasca oil sands, two types of primary oil recovery response to sodium hydroxide addition are identified. Natural carboxylate surfactants can promote bitumen separation and flotation under certain process conditions, while a second, more polar, class of natural anionic surfactants can promote separation and flotation under different process conditions. As a result, some oil sands exhibit two recovery peaks as a function of sodium hydroxide addition. The phenomena are explained in terms of different sodium hydroxide additions required to reach critical surfactant concentrations specific to each surfactant class. The concept provides a means for interpreting a wide range of processibility phenomena.     

Recovery of Co2+ Ions from Aqueous Solutions by Froth Flotation

ABSTRACT

The recovery of Co(II) ions from aqueous solutions under acidic conditions (pH 5) was investigated in flotation columns with inside diameters of 4.0 and 8.0 cm. Three surfactants, dodecylamine, cetyl pyridinium chloride, and sodium dodecyl sulfate, were used as collectors. Sodium dodecyl sulfate was found to be the most efficient; all three, however, produced hydrated froths, leading to rather low recoveries and separation efficiencies. The volumetric gas flow rate was found to affect the process in relation to the amount of surfactant added and the column diameter. The scale-up of the column should be done in terms of the same superficial gas velocity in order to maintain similar levels of metal ion recovery.     

Effect of Electrolyte and Temperature on Volatile Organic Compounds Removal from Wastewater Using Aqueous Surfactant Two-Phase System of Cationic and Anionic Surfactant Mixtures

Abstract

Benzene, toluene, ethylbenzene, and xylene are frequently observed contaminants in industrial wastewaters causing concerns about environmental and health effects. An aqueous surfactant two-phase (ASTP) extraction system using mixtures of cationic and anionic surfactants have been shown to be a promising surfactant-based separation technique to concentrate solutes such as proteins and dyes from aqueous solution. A phase separation of a surfactant solution occurs at certain surfactant compositions and concentrations, forming two isotropic phases. One is rich in surfactant aggregates (surfactant-rich phase) and the other is lean in surfactant aggregates (surfactant-dilute phase). Most of the organic contaminants tend to solubilize and concentrate in the surfactant-rich phase, leaving the surfactant-dilute phase containing only small amounts of contaminants as remediated water. The effect of NaCl addition on the critical micelle concentration (CMC) and the extraction ability of ASTP formed by mixtures of cationic surfactant (dodecyltrimethylammonium bromide; DTAB) and anionic surfactant (alkyl diphenyloxide disulfonate; DPDS) at 50 mM total surfactant concentration with a 2:1 molar ratio of DTAB:DPDS was investigated; the CMC of the mixture slightly decreases with increasing NaCl concentration. The extraction and preconcentration of benzene are greatly enhanced by added NaCl. The higher the degree of hydrophobicity of contaminants, the greater the extraction into the surfactant-rich phases. At 1.0 M NaCl addition, about 95% of xylene, 92% of ethylbenzene, 90% of toluene, and 79% of benzene are extracted into the surfactant-rich phase within a single stage extraction and the contaminant partition ratios can be as high as 395 for xylene, 273 for ethylbenzene, 206 for toluene, and 84 for benzene, which are greater than those obtained from the conventional ASTP extraction system using nonionic surfactants.     

Surfactant Recovery from Water Using Foam Fractionation

Abstract

The purpose of this study was to investigate the use of foam fractionation to recover surfactant from water. A simple continuous mode foam fractionation was used and three surfactants were studied (two anionic and one cationic). The effects of air flow rate, foam height, liquid height, liquid feed surfactant concentration, and sparger porosity were studied. This technique was shown to be effective in either surfactant recovery or the reduction of surfactant concentration in water to acceptable levels. As an example of the effectiveness of this technique, the cetylpyridinium chloride concentration in water can be reduced by 90% in one stage with a liquid residence time of 375 minutes. The surfactant concentration in the collapsed foam is 21.5 times the feed concentration. This cationic surfactant was easier to remove from water by foam fractionation than the anionic surfactants studied.     

Removal of Trace Levels off Phenols from Aqueous Solution by Foam Flotation

Abstract

Peritachlorophenol (PCP) was removed from water by foam flotation with the cationic surfactant cetyltrimethylammonium bromide (CTAB). With initial PCP concentrations of 20 ppm or less, residual PCP concentrations of less than 0.05 ppm were obtained after 5 min flotation. The CTAB concentration and flotation time are directly related to the amount of PCP removed. PCP removal is most efficient at neutral to basic pH and at low ionic strength. PCP removal is less effective with sodium dodecyl sulfate. As much as 80% of the CTAB can be replaced by dodecylamine without inhibiting PCP removal. Alcohols up to 10% by volume do not affect PCP removal. Other phenols can also be removed equally well by foam flotation if the phenol is in the anionic form during flotation.     

Separation of Some Dyes from Aqueous Solutions by Flotation

Abstract

Separation of the dyes brilliant green, neutral red, eriochrome black T, and eosin from aqueous solutions by flotation was studied using oleic acid surfactant. Nearly 100% of the investigated dyes could be floated under the optimum conditions. The effect of pH on the flotation efficiency was studied in particular. At pH ≤ 2, 7.5, ≤ 5, and ≤ 6, the maximum flotation was achieved for brilliant green, neutral red, eriochrome black T, and eosin, respectively. The effects of oleic acid and dye concentrations, some ions, and temperature on the floatability were examined. Moreover, the selective separation of some dyes was attempted.