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 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.     

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.     

Batch and continuous ion-flotation of hexavalent chromium

An experimental investigation is presented of the flotation of dichromate ion using a cationic surfactant, ethylhexadecyldimethylammonium (EHDA) bromide. Dichromate ion forms a colloidal complex with EHDA ion in a molar ratio of 1 : 2, which may be efficiently floated from solution and concentrated in a stable foam produced by excess surfactant. Batch experiments with feed solutions containing 5–100 mg/l of dichromate ion produced residual dichromate concentrations ranging from 0.004 to 0.198 of that of the feed, depending upon the concentration of surfactant in the feed. The effects of pH and of possible interfering anions were determined. Continuous experiments indicated the reduction of dichromate from 50 to 15 mg/l, producing a foam stream containing 450 mg/l of dichromate. The influence of retention time is discussed.     

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.     

内循环式泡沫浮选塔处理含铬废水

采用自制的内循环泡沫浮选塔处理含铬废水,考察pH值、Fe(NO3)3浓度、十二烷基硫酸钠(SDS)浓度、气体流量、分离时间等因素对分离效率的影响,并与常规泡沫塔比较. 结果表明,在12~35 min内,内循环式浮选塔分离效率更高,35 min时塔内铬离子浓度为0.6 mg/L,常规泡沫塔内铬离子浓度为10 mg/L. 内循环浮选塔最佳分离工艺条件为,对初始铬浓度为20 mg/L的废水,在pH 5.5、SDS 100 mg/L、Fe(NO3)3 60 mg/L、气体流量800 mL/min条件下处理效果最好,泡沫夹带率约为10%,Cr(III)脱除率可达97%以上.     

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.     

Foam fractionation of anions with a cationic surfactant: Orthophosphate

An experimental study has been conducted for the first time of the foam fractionation of orthophosphate using a cationic surfactant. For feed solutions 2.63×10⁻⁴ molar in phosphate and three surfactant concentrations, pH has a pronounced effect on residual concentrations of phosphate. A comparison with the ion flotation of dichromate and with the foam fractionation of phenolate shows dichromate flotation to be the most efficient.     

含十二烷基苯磺酸钠废水的多级泡沫分离研究

采用多级泡沫分离装置对水中十二烷基苯磺酸钠(SDBS)进行分离富集,考察了表面活性剂溶液的浓度、离子强度、pH值、分离时间、气体流速等因素对水中十二烷基苯磺酸钠脱除率的影响。进一步采用四因素三水平正交实验进行分离条件的优化,结果表明溶液浓度为20 mg/mL,气体流速为20L/min,pH=10,离子强度为2×10-5mol/L时,分离5 min,可使SDBS的脱除率最高达到97%,三次平行试验SDBS的脱除率分别为96.61%、97.04%和93.93%。与单级环流泡沫分离塔(其脱除率为82%)相比,多级泡沫分离装置具有能耗比低、分离效率高的优点,具有更好的推广应用价值。     

FOam separation of colloidal particulates: Rate studies

An experimental investigation is presented of the rate of foam separation of colloidal ferric oxide from aqueous suspension. A cationic surfactant in initial concentrations of from 0·05 to 0·13 mmole/1 is used with negatively charged ferric oxide at pH 10·8. An anionic surfactant in initial concentrations of from 0·03 to 0·10 mmole/1 is used with positively charged ferric oxide at pH 5·8. The initial concentrations of particulates are 2·38 and 1·67 mmole/1, as trivalent iron. The process involves variable volumes and a consideration of relative rates of adsorption and foam separation. The rates of removal of surfactant are directly proportional to the quantities of surfactant in the residual suspension and are independent of the quantities of particulates. The rates of removal of particles are directly proportional to the surfactant to particulate ratio in the residual suspension and are a power function of the quantity of particulates in the residual suspension. In one case, the initial surfactant concentration is significant. The relations obtained are accurate to about 15% for the surfactant removals and to about 24% for the particulate removals; these are reasonable considering process complexities.     

Foam separation of complexed cyanide: Studies of rate and of pulsed addition of surfactant

An experimental investigation is presented of the foam separation of cyanide complexed with ferrous iron, using a cationic surfactant, ethylhexadecyldimethylammonium bromide. With a 25 min. foaming time, an initial iron to total cyanide ratio of 0·351:1 and an initial surfactant to complexed cyanide ratio of about 0·34:1 suspensions containing from 1·54 to 3·08 mM total cyanide can be reduced to about 0·11 mM in complexed cyanide and 0·29 mM in non-complexed cyanide. The rate of surfactant removal was satisfied by a first-order relationship, similar to that obtained with colloidal ferric oxide. The rate of complexed cyanide removal was satisfied by a reversible, approximately first-order relationship eliminating the residual surfactant concentration. The pulsed addition of surfactant in three dosages during the course of an experiment, compared with a single dose at the beginning of an experiment, produced lower residual concentrations of complexed cyanide and higher foam volumes. At an iron to total cyanide ratio of 0·351:1,90% of the complexed cyanide concentration could be removed by one fifth less surfactant, using pulsed addition, compared with a single dose.     

Removal of Trace Levels of Aromatic Amines from Aqueous Solution by Foam Flotation

Abstract

Aromatic amines, including 4-(t-butyl)pyridine, 4-(n-butyl)aniline, benzylamine, 4-aminobiphenyl, 1- and 2-aminonaphthalene, and 2,6-xylidine, were effectively removed from water by foam flotation with the anionic surfactant sodium dodecylsufate (SDS). With initial amine concentrations of 10 mg/L or less, residual amine concentrations of less than 0.1 mg/L were generally obtained after 10–30 min of flotation. The SDS concentration and flotation time are directly related to the amount of amine removed. Amine removal is most efficient at pH values low enough so that the amine is protonated (usually about 3), and at low ionic strength. Alcohols up to 10% by volume do not appreciably affect amine removal. The mechanism of removal is dominated by ion-ion attraction between the surfactant and the protonated amine; there is also apparently some contribution from ion-dipole attraction. Benzidine is not removed effectively; evidently it is insufficiently hydrophobic.     

铁盐共沉淀泡沫浮选法去除废水中Cr(VI)的应用研究

采用铁盐共沉淀泡沫浮选法去除废水中Cr(VI),用FeSO4将六价铬还原成三价状态,考察了还原剂用量、捕捉剂品种及pH对总铬去除率的影响。结果表明,对浓度为10 mg/L的含Cr(VI)模拟废水,使用FeSO4作还原剂,LAS作捕捉剂,铁铬摩尔比为7∶1,pH=10,鼓泡10 min的条件下,Cr(VI)去除率可达99.1%。     

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     

表面活性剂处理浮选分离ABS和PC塑料的研究

研究了聚碳酸酯(PC)和丙烯腈-丁二烯-苯乙烯(ABS)两种密度相近的塑料在非离子表面活性剂仲醇聚氧乙烯醚(Tergitol 15-S-7)存在下的可浮性。通过调节表面活性剂浓度、起泡剂浓度以及浮选时间等因素,最终表面活性剂浓度60 mg/L、起泡剂浓度10 mg/L、浮选时间40 min时,ABS/PC混合塑料体系的浮选分离效果最佳,ABS的纯度和回收率接近100%,PC的纯度达到72.34%。实验结果表明,表面活性剂处理选浮分离有利于塑料的回收利用。     

Study on Riboflavin Recovery from Wastewater by a Batch Foam Separation Process

Abstract

A batch recovery of riboflavin via foam separation from industrial simulative wastewater was studied using a cationic surfactant, cetyltrimethyl ammonium bromide (CTAB). The experimental parameters examined were the surfactant concentration, air flow rate, pH, and foam height. Under optimal operating conditions obtained through an orthogonal experiment, the maximum enrichment ratio of 48.7 was achieved for riboflavin along with 99.3% removal efficiency. The optimal operating conditions had the concentration of CTAB at 0.3 g/L, air flow rate at 400 ml/min, foam height at 90 cm, and pH at 12. Therefore foam separation proved to be an effective method to recover the riboflavin in terms of the good enrichment and removal efficiency.     

含铜和含锌稀溶液的吸附泡沫分离技术的研究

运用自制的泡沫分离塔,以十二烷基硫酸钠为表面活性剂对泡沫吸附分离含铜及含锌溶液的操作参数进行了研究。考察了料液浓度、pH值、气体流量、表面活性剂浓度等因素对含铜和含锌溶液泡沫分离效果的影响。结果表明：最佳操作参数为pH值5．0,料液浓度0．125mmol／L,进料流速50mL/min,气体流量100mL/min,表面活性剂浓度0．25mmol／L。同时从理论上推算出泡沫吸附分离铜离子的最佳pH值范围为5．0左右。实验还通过改变孔板的孔径大小以改变气泡的尺寸,特别研究了泡沫尺寸对泡沫吸附分离的影响。     

Study on Streptomycin Sulfate Recovery by Batch Foam Separation

The feasibility of foam separation as a technique was assessed for the recovery of streptomycin sulfate from the waste solution by using an anionic surfactant sodium dodecyl sulfate (SDS). The experimental parameters examined were SDS concentration, superficial gas velocity, initial pH, and liquid loading volume. The results showed that sodium dodecyl sulfate as the surfactant for foam separation had good foaming quality and could effectively concentrate streptomycin sulfate of the aqueous solution by technology of foam separation. The enrichment ratio and the recovery rate of streptomycin sulfate were 4.0 and 85%, respectively under the best operating conditions of sodium dodecyl sulfate concentration 0.4 g/L, superficial gas velocity 300 mL/min, liquid loading volume 300 mL and initial pH 6.0 when streptomycin sulfate concentration was 0.5 g/L.     

Foam separation and precipitate flotation. The problem of surfactant recovery and reuse

An experimental investigation is presented on the recovery of cationic [dimethyl-benzyldodecylammonium bromide (DMBDA-Br)] and anionic [sodium dodecyl-benzylsulphonate (Na-DBS)] surfactants from foam separation and precipitate flotation concentrates. DMBDA-Br was recovered and reused fr m the concentrate of foam separation of perrhenates with recovery of over 90% by applying coacervation by potassium thiocyanate. Na-DBS was recovered and reused from the concentrate of precipitate flotation of copper hydroxide with recovery over 90% by applying precipitation with dodecylbenzylsulphonic acid from solution of concentrate dissolved in sulphuric acid at pH range from 1.0 to 2.5. Recovered surfactants were found efficient for subsequent flotation processes.     

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%.