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’.     

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.     

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.     

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.     

Foam Separation of Mercury(II) and Cadmium(II) from Aqueous Systems

Abstract

Mercury(II) and cadmium(II) were separated from aqueous systems by a number of batch-type precipitate flotation and adsorbing colloid flotation techniques. HgS, CdS, and Cd(OH)₂ were removed by precipitate flotation; Fe(OH)₃, Al(OH)₃, FeS, and CuS were used as adsorbing colloids. Sodium lauryl sulfate and hexadecyltrimethylammonium bromide (HTA) were used as collectors. Dependence of separation efficiency on pH and ionic strength was investigated. Floc foam flotation of both metals with CuS and HTA was found to be quite effective, resulting in residual Hg(II) levels as low as 5 ppb and residual Cd(II) levels as low as 20 ppb. Floc foam flotation of Cd(II) with FeS and HTA yielded residual Cd(II) levels as low as 10 ppb.     

Precipitate flotation I. Removal of nickel from dilute aqueous solutions and its separation from cobalt

A new technique, called precipitate flotation of the second kind, in which no surfactant is used to float precipitates, is described. Nickel is completely removed from 1.5 × 10^?5 m-NiCl₂ solutions in 3 minutes using a tenfold excess of nioxime. Flotation improves with increasing temperature between 21° and 40° if the pH is in the range 8–11. Increase in ionic strength has no deleterious effect, unlike conventional precipitate flotation. Nickel can be completely separated from a hundredfold excess of cobalt by complexing the latter with nitroso-R-salt before flotation. Iron does not float on its own but recoveries of 50% can be achieved by entrainment of ferric hydroxide in nickel nioximate.     

Electrical Aspects of Adsorbing Colloid Flotation

Abstract

The Gouy-Chapman theory of the electric double layer is applied to the calculation of the interaction energy of a charged surface film and a solid surface of opposite charge immersed in a solution of electrolyte. This model is found to account for the decrease in efficiency of precipitate flotation and adsorbing colloid flotation which is observed when ionic strength is increased. The Gouy-Chapman theory is also used to predict the existence of analogs to the phenomena of electroosmotic flow and streaming potential in foams and surface films.     

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.     

Electrical Aspects of Adsorbing Colloid Flotation. XVI. Double-Layer Relaxation

Abstract

A mathematical model for studying relaxation processes in the electric double layer adjacent to a plane charged surface is developed and analyzed. The model is nonlinear and nonideal. A time constant of roughly 7 × 10^?8 s qualitatively describes the relaxation processes. Increased applied potentials yield nonlinear responses, which are investigated by Fourier analysis. The effects of ionic size are determined. The relaxation rate is fast enough so that the local equilibrium assumption in foam flotation is amply justified.     

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.     

Ion Flotation of Chromium(VI) Species: pH,Ionic Strength,Mixing Time,and Temperature

Abstract

Batch foam separation experiments of Cr(VI) anions with the cationic surfactant, ethylhexadecyldimethylammonium bromide, show a sharp increase in the flotation stoichiometry from 1.0 to 2.0⁺ over pH 6-8, corresponding to the conversion of Cr₂O₇ ^2?(HCrO₄ ^?) to CrO₄ ^2? with pH. In the acidic region for approximately 1.0×10^?3 M Cr(VI) solutions, the maximum increase in the flotation stoichiometry and decrease in the fractional removal of Cr₂O₇ ^2? is 12% over a fortyfold increase in ionic strength, varied with four different monoand divalent salts; the effect is produced by a small increase in the solubility of the (EHDA)₂Cr₂O₇ precipitate. In the basic region, a twentyfold increase in ionic strength with NaCl produces greater than 100% changes in the same flotation parameters, indicating a foam fractionation mechanism and competition between Br^?, Cl^? and CrO₄ ^2? for surfactant exchange sites. A temperature increase from 23 to 33°C in the acidic region has no effect on the flotation, and the lack of the effect of the mixing time between the Cr(VI) and surfactant solutions over the full range of variables permits all reported data points to be the average of four replicates, within ±3%.     

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).     

Mechanical Responses of 2-Hydroxyethyl Methacrylate-Methacrylonitrile and 2-Hydroxyethyl Methacrylate-Acrylonitrile Copolymer Networks

Abstract

The mechanical behaviour of 2-hydroxyethyl methacrylate-methacrylonitrile (HEMA-MAN)and 2-hydroxyethyl methacrylate-acrylonitrile (HEMA-AN) copolymer networks of various composition prepared in presence of 0.6 × 10^?4 mol cm^?3 ethylene dimethacrylate and 20 vol.-% dimethylformamide were investigated. The viscoelastic and stress-strain behaviour of samples swollen in water to equilibrium and the dynamic relaxation behaviour of dry polymers from liquid nitrogen temperature onwards was investigated.

It was found that with increasing concentration of the MAN or AN component the equilibrium degree of swelling in water decreases, which on the other hand is accompanied by a simultaneous decrease in the glass transition temperature, T _g of copolymers in the dry state. T_g passes through a minimum in this case. The HEMA-AN copolymers become swollen to a higher degree; their T_g temperatures in the dry state are lower compared to the HEMA-MAN copolymers. The effect of the decreasing degree of swelling with increasing content of the MAN or AN comonomers is predominantly reflected in shifting the viscoelastic data toward the main transition region, that is in the increasing distance from the mechanical equilibrium of networks measured at room temperature. In the molar concentration range of nitrile comonomers n ? 0.2 a minimum of the equilibrium modulus was observed, probably related to changes in the effectivity of crosslinking reaction with increasing content of the MAN or AN groups.

The tensile strength increased with increasing content of acrylonitrile and metha-crylonitrile, while strain-at-break passed through a maximum, the position of which depended on temperature and on the strain rate. The failure envelopes plotted as [sgrave]_bΛ_tT_oT^?1 vs. log ?b+ log 3(C₁ + C₂) shows that the ultimate behaviour of both types of copolymers is very similar, while the differences in behaviour can be predominantly attributed to different distances from the equilibrium.     

Flotation of metal hydroxide precipitates. II. Flotation of zinc and cobalt hydroxides

Flotation of zinc and cobalt hydroxide precipitates was investigated at total initial metal concentrations of 1 × 10^?2 M with sodium dodecylbenzenesulphonate (DBSNa) and dodecyldimethylbenzylammonium bromide (DDMBABr), both at initial concentrations of 1 × 10^?4 M. In particular, the granulometric analysis of precipitates and measurements of their electrokinetic potential were carried out over a wide range of acidity of aqueous precipitate suspensions. Moreover, adsorption of the flotation collectors by the precipitates as well as the rate of their sedimentation were measured. It was found that the extent of collector sorption, changes in the electrokinetic potential of precipitate grains and their aggregation affected the flotability and course of flotation of the examined precipitates. These dependencies were irregular and could be discussed in terms of chemisorption of collectors on the surface of the precipitate grains.     

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     

Adsorbing Colloid Flotation of Pb(II). Feasibility of Utilizing Streaming Current Detector

Abstract

A feasibility study was conducted to assess the application of a streaming current detector (SCD) in the flotation of dissolved heavy metals. The adsorbing colloid flotation of Pb(II) with iron oxide and sodium dodecylsulfate was injvestigated. Both zeta potential and streaming current (SC) readings of each colloidal system were measured. For colloids of goethite or of amorphous iron oxide, the results show SC changed with pH values and can be well correlated to the zeta potential. The removal of Pb(II) increased with increasing pH. Judging from the experimental results, it is proposed that when pH is at 3.0 or lower, Pb(II) is mainly removed by foam fractionation. When pH values are between 4.0 and 7.0, Pb(II) removal can be attributed to both foam fractionation and adsorbing colloid flotation. When pH values are higher than 7.0, Pb(II) is mainly removed by precipitate flotation in the form of Pb(OH)₂(s) or Pb-Fe coprecipitate. Advantages and limits of utilizing SCD in flotation processes are discussed. Preliminary results show it is feasible for SCD to be utilized in the flotation of Pb(II).     

Electrical Aspects of Adsorbing Colloid Flotation. Y. Nonideal Flocs and Salts

Abstract

Three methods are developed for the calculation of adsorption isotherms in precipitate and adsorbing colloid flotation. The Gouy-Chapman model is used in all three, with corrections for the effective volumes of the ions in the ionic atmosphere and of the floc particles. The theories all predict a weak dependence of adsorption isotherm on temperature and a stronger dependence on ionic strength; increasing either variable decreases the surface adsorption. The effects of film surface potential, floc zeta potential, ion and floc effective volumes, and floc-floc screening are examined.     

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.     

Precipitate flotation. IV. Flotation of silver,uranium and gold

The conditions for the flotation of silver using α-nitroso-β-naphthol and β-nitroso-α-naphthol, that of uranium using α-nitroso-β-naphthol and benzoylacetone, and that of gold using phenyl-α-pyridylketoxime were examined. Recoveries of over 90% were possible from 5 × 10^?5 M solutions of silver, 10^?4 M solutions of uranium (VI) and 3 × 10^?4 M solutions of gold (III). Extractions were best in the pH range 7–9, 6–9 and 3–5 respectively. Silver could be separated from 10-fold molar excesses of copper, zinc and lead; uranium from 10-fold molar excesses of gold and iron and 100-fold molar excesses of sulphate and manganese: gold from a 10-fold molar excess of uranium. Methods are suggested whereby redispersion in precipitate flotation of the second kind can be avoided. The efficiency of this kind of flotation is considered.