WO1994002252A1 - Flotation method - Google Patents

Flotation method Download PDF

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Publication number
WO1994002252A1
WO1994002252A1 PCT/AU1993/000373 AU9300373W WO9402252A1 WO 1994002252 A1 WO1994002252 A1 WO 1994002252A1 AU 9300373 W AU9300373 W AU 9300373W WO 9402252 A1 WO9402252 A1 WO 9402252A1
Authority
WO
WIPO (PCT)
Prior art keywords
liquor
aerated
suspended solids
tank
flocculent
Prior art date
Application number
PCT/AU1993/000373
Other languages
French (fr)
Inventor
Geoffrey Robert Browne
Kevin John Lobb
Original Assignee
Hoefer, Dawn, Annette
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hoefer, Dawn, Annette filed Critical Hoefer, Dawn, Annette
Priority to AU45505/93A priority Critical patent/AU4550593A/en
Publication of WO1994002252A1 publication Critical patent/WO1994002252A1/en

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/14—Flotation machines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/02—Froth-flotation processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/14—Flotation machines
    • B03D1/24—Pneumatic
    • B03D1/247—Mixing gas and slurry in a device separate from the flotation tank, i.e. reactor-separator type
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D3/00—Differential sedimentation
    • B03D3/06—Flocculation

Definitions

  • the present invention relates to a method of separating suspended solids from a liquor by flotation.
  • the suspended solids must have an affinity for gas bubbles, usually, a collector, such as xanthates, dithiophosphates, fatty acids, soaps, and amine salts, is added to the liquor to coat the suspended solids so that the surfaces of the suspended solids become hydrophobic.
  • a collector such as xanthates, dithiophosphates, fatty acids, soaps, and amine salts
  • the suspended solids and gas bubbles must come into contact so that the gas bubbles can adhere to and raise the suspended solids to the surface of the liquor.
  • liquids as used herein are understood to include aqueous and non-aqueous liquids.
  • liquids such as emulsions.
  • sustained solids as used herein is understood to include organic and inorganic material in particulate form or in colloidal form.
  • An object of the present invention is to provide an improved method of separating suspended solids from a liquor by flotation.
  • a method of separating suspended solids from a liquor by flotation comprising:
  • the floes formed by the above method float to the surface of the liquor and thereby separate the suspended solids from the liquor. It is believed by the applicant that the aeration of the liquor prior to the addition of the flocculent in accordance with the above method promotes a situation in which air bubbles are trapped interstitially between particles of the suspended solids as the particles agglomerate to form the floes and thereby provide sufficient buoyancy to cause the floes to float to the surface of the liquor.
  • the flocculent be a polyelectrolyte flocculent.
  • polyelectrolyte flocculent as used herein is understood to mean any suitable cationic, non-ionic and anionic flocculent. It is preferred that the method be carried out on a continuous basis.
  • the method comprises, aerating the liquor in an aeration tank, transferring the aerated liquor from the aeration tank into a flotation tank, and allowing floes of the suspended solids to form and float to the surface of the flotation tank.
  • the method comprises adding the flocculent to the aerated liquor in an outlet section of the aeration tank or as the aerated liquor flows between the aeration tank and the flotation tank.
  • the method comprises transferring the aerated liquor containing the flocculent into a draft tube having open upper and lower ends located in the flotation tank.
  • the height and the diameter of the draft tube be selected to provide sufficient residence time to allow the floes to form and to float upwardly in the draft tube before the suspended solids reach the lower end of the draft tube.
  • Figure 1 illustrates schematically an apparatus for carrying out a preferred embodiment of the method of the invention
  • Figure 2 is a top plan view of the apparatus shown in Figure 1;
  • Figure 3 illustrates schematically an apparatus for carrying out another preferred embodiment of the method of the inventio .
  • a liquor containing suspended solids is fed into an aeration tank 5 and is aerated by any suitable means (not shown) .
  • the inlet feed of liquor may be sprayed onto the surface of the liquor in the aeration tank 5.
  • a motor- driven impeller 7 is located in the aeration tank 5 and is operated to mix the aerated liquor.
  • the aerated liquor is discharged from the aeration tank 5 through a conduit 9 and is introduced into an upper section of an open-ended draft tube 11 located centrally in a settling tank 13.
  • a predetermined amount of a polyelectrolyte flocculent is added to the aerated liquor through a line 10 as the aerated liquor flows through the conduit 9.
  • the aerated liquor dosed with flocculent flows downwardly after being introduced into the draft tube 11 and progressively floes of the suspended solids and air bubbles form and float towards the upper end of the draft tube II.
  • the floes are periodically skimmed from the surface by means of a motor-driven radial scraper blade 17 which feeds the floes into a radial launder 19.
  • the amount and type of the polyelectrolyte flocculent and the height and diameter of the draft tube 11 are selected so that substantially all the suspended solids agglomerate to form floes prior to reaching the lower end of the draft tube 11.
  • the clarified liquor flows downwardly from the lower end of the draft tube 11 and is discharged continuously from an outlet 21 positioned in a lower section of the settling tank 13.
  • a liquor containing suspended solids is fed into and aerated in an aeration tank 31, the aerated liquor is dosed with a predetermined amount of a polyelectrolyte flocculent delivered by means of a circuit 34 into the aeration tank 31, and thereafter the dosed and aerated liquor is transferred by means of a conduit 33 into a settling tank 35.
  • a settling tank 35 floes of suspended solids and air bubbles form and float to the surface and are periodically skimmed from the surface by means of a motor driven radial scraper blade 35 into a discharge chute 37.
  • a particular feature of the embodiment shown in Figure 3 is that the aeration tank 31 is divided by means of a baffle 39 into a feed chamber 41 and an aeration chamber 43.
  • the liquor containing suspended solids is fed into an upper section of the feed chamber 41 through the line 36 and mixed therein by means of an agitator (not shown) , and the mixed liquor containing suspended solids is transferred by means of a pump 45 through a circuit 47 to a cyclone 49 positioned above the aeration chamber 43.
  • the cyclone 49 directs a spray of the mixed liquor containing suspended solids into the aeration chamber 43 such that the action of the spray contacting the surface of the liquor in the aeration chamber 43 promoted aeration of the liquor.
  • the liquor level in the aeration tank 31 is controlled so that liquor can flow over the upper edge of the baffle 39 between the aeration chamber 43 and the feed chamber 41.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Biotechnology (AREA)
  • Physical Water Treatments (AREA)

Abstract

A method of separating suspended solids from a liquor by flotation comprises, aerating the liquor, thereafter adding a flocculent to the aerated liquor to form flocs of the suspended solids and air bubbles in the liquor, and allowing the flocs to float to the surface of the liquor.

Description

FLOTATION METHOD
The present invention relates to a method of separating suspended solids from a liquor by flotation.
There are two fundamental requirements of conventional flotation methods for separating suspended solids from a liquor.
1. The suspended solids must have an affinity for gas bubbles, usually, a collector, such as xanthates, dithiophosphates, fatty acids, soaps, and amine salts, is added to the liquor to coat the suspended solids so that the surfaces of the suspended solids become hydrophobic.
2. The suspended solids and gas bubbles must come into contact so that the gas bubbles can adhere to and raise the suspended solids to the surface of the liquor.
The term "liquor" as used herein is understood to include aqueous and non-aqueous liquids. In this regard, it is noted that the term "liquor" as used herein is understood to include mixtures of aqueous and non-aqueous liquors, such as emulsions.
The term "suspended solids" as used herein is understood to include organic and inorganic material in particulate form or in colloidal form.
An object of the present invention is to provide an improved method of separating suspended solids from a liquor by flotation.
According to the present invention there is provided a method of separating suspended solids from a liquor by flotation comprising:
(a) aerating the liquor;
(b) thereafter adding a flocculent to the aerated liquor to form floes of the suspended solids and air bubbles in the liquor; and
(c) allowing the floes to float to the surface of the liquor.
It has been found by the applicant that the floes formed by the above method float to the surface of the liquor and thereby separate the suspended solids from the liquor. It is believed by the applicant that the aeration of the liquor prior to the addition of the flocculent in accordance with the above method promotes a situation in which air bubbles are trapped interstitially between particles of the suspended solids as the particles agglomerate to form the floes and thereby provide sufficient buoyancy to cause the floes to float to the surface of the liquor.
It is preferred that the flocculent be a polyelectrolyte flocculent.
The term "polyelectrolyte flocculent" as used herein is understood to mean any suitable cationic, non-ionic and anionic flocculent. It is preferred that the method be carried out on a continuous basis.
With such an arrangement it is preferred that the method comprises, aerating the liquor in an aeration tank, transferring the aerated liquor from the aeration tank into a flotation tank, and allowing floes of the suspended solids to form and float to the surface of the flotation tank.
It is preferred that the method comprises adding the flocculent to the aerated liquor in an outlet section of the aeration tank or as the aerated liquor flows between the aeration tank and the flotation tank.
It is preferred particularly that the method comprises transferring the aerated liquor containing the flocculent into a draft tube having open upper and lower ends located in the flotation tank.
It is preferred particularly that the height and the diameter of the draft tube be selected to provide sufficient residence time to allow the floes to form and to float upwardly in the draft tube before the suspended solids reach the lower end of the draft tube.
The present invention is described further by way of example with reference to the accompanying drawings in which:
Figure 1 illustrates schematically an apparatus for carrying out a preferred embodiment of the method of the invention; Figure 2 is a top plan view of the apparatus shown in Figure 1; and
Figure 3 illustrates schematically an apparatus for carrying out another preferred embodiment of the method of the inventio .
With reference to Figure 1, in accordance with a preferred embodiment of the method of the invention, operated on a continuous basis, a liquor containing suspended solids is fed into an aeration tank 5 and is aerated by any suitable means (not shown) . By way of example, the inlet feed of liquor may be sprayed onto the surface of the liquor in the aeration tank 5. A motor- driven impeller 7 is located in the aeration tank 5 and is operated to mix the aerated liquor.
The aerated liquor is discharged from the aeration tank 5 through a conduit 9 and is introduced into an upper section of an open-ended draft tube 11 located centrally in a settling tank 13. A predetermined amount of a polyelectrolyte flocculent is added to the aerated liquor through a line 10 as the aerated liquor flows through the conduit 9.
The aerated liquor dosed with flocculent flows downwardly after being introduced into the draft tube 11 and progressively floes of the suspended solids and air bubbles form and float towards the upper end of the draft tube II.
The floes are periodically skimmed from the surface by means of a motor-driven radial scraper blade 17 which feeds the floes into a radial launder 19.
The amount and type of the polyelectrolyte flocculent and the height and diameter of the draft tube 11 are selected so that substantially all the suspended solids agglomerate to form floes prior to reaching the lower end of the draft tube 11.
The clarified liquor flows downwardly from the lower end of the draft tube 11 and is discharged continuously from an outlet 21 positioned in a lower section of the settling tank 13.
In order to evaluate the preferred embodiment of the method of the invention as described above the applicant carried out experiments on an effluent liquor containing a suspension of wood fibres obtained from a particle board manufacturer.
In a first series of experiments the liquor was aerated and there was no addition of flocculent. It was found that a homogenous suspension of solids was formed with no separation of the solids from the liquor.
In a second series of experiments the liquor was dosed with flocculent and there was no aeration of the liquor. It was found that some of the floes of suspended solids that formed floated towards the surface and other floes sank towards the bottom of the settling tank 13. As a consequence, there was unsatisfactory separation of the suspended solids from the liquor.
In a third series of experiments the liquor was aerated and then dosed with flocculent in accordance with the preferred embodiment of the method of the invention. It was found that the suspended solids quickly agglomerated into floes that floated to the surface of the liquor.
With reference to Figure 3, the other preferred embodiment of the method of the invention shown in the figure is similar to that shown in Figures 1 and 2.
In this connection, a liquor containing suspended solids is fed into and aerated in an aeration tank 31, the aerated liquor is dosed with a predetermined amount of a polyelectrolyte flocculent delivered by means of a circuit 34 into the aeration tank 31, and thereafter the dosed and aerated liquor is transferred by means of a conduit 33 into a settling tank 35. In the settling tank 35 floes of suspended solids and air bubbles form and float to the surface and are periodically skimmed from the surface by means of a motor driven radial scraper blade 35 into a discharge chute 37.
A particular feature of the embodiment shown in Figure 3 is that the aeration tank 31 is divided by means of a baffle 39 into a feed chamber 41 and an aeration chamber 43. The liquor containing suspended solids is fed into an upper section of the feed chamber 41 through the line 36 and mixed therein by means of an agitator (not shown) , and the mixed liquor containing suspended solids is transferred by means of a pump 45 through a circuit 47 to a cyclone 49 positioned above the aeration chamber 43. The cyclone 49 directs a spray of the mixed liquor containing suspended solids into the aeration chamber 43 such that the action of the spray contacting the surface of the liquor in the aeration chamber 43 promoted aeration of the liquor. The liquor level in the aeration tank 31 is controlled so that liquor can flow over the upper edge of the baffle 39 between the aeration chamber 43 and the feed chamber 41.
Many modifications may be made to the preferred embodiments of the method of the invention described with reference to the drawings without departing from the spirit and scope of the invention.

Claims

CLAIMS :
1. A method of separating suspended solids from a liquor by flotation comprising:
(a) aerating the liquor;
(b) thereafter adding a flocculent to the aerated liquor to form floes of the suspended solids and air bubbles in the liquor; and
(c) allowing the floes to float to the surface of the liquor.
2. The method defined in claim 1 comprising, aerating the liquor in an aeration tank, transferring the aerated liquor from the aeration tank into a flotation tank, and allowing floes of the suspended solids to form and float to the surface of the flotation tank.
3. The method defined in claim 2 comprising, adding the flocculent to the aerated liquor in an outlet section of the flotation tank or as the aerated liquor flows between the aeration tank and the flotation tank.
4. The method defined in claim 2 or claim 3 further comprising, adding liquor to be aerated to the mixing tank as the aerated liquor is transferred to the flotation tank so that the method operates on a continuous basis.
5. The method defined in any one of claims 2 to 4 comprising, aerating the liquor by spraying the liquor to be added to the aeration tank onto the surface of the liquor in the aeration tank.
6. The method defined in any one of claims 2 to 5 comprising, transferring the aerated liquor containing the flocculent into a draft tube having open upper and lower ends located in the flotation tank.
7. The method defined in claim 6, wherein the height and the diameter of the draft tube are selected to provide sufficient residence time to allow the floes to form and to float upwardly in the draft tube before the suspended solids reach the lower end of the draft tube.
8. The method defined in any one of claims 2 to 7 further comprising, removing floes from the surface of the flotation tank and discharging clarified liquor from the flotation tank.
9. The method defined in any one of the preceding claims, wherein the flocculent is a polyelectrolyte flocculent.
PCT/AU1993/000373 1992-07-23 1993-07-23 Flotation method WO1994002252A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU45505/93A AU4550593A (en) 1992-07-23 1993-07-23 Flotation method

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPL3716 1992-07-23
AUPL371692 1992-07-23

Publications (1)

Publication Number Publication Date
WO1994002252A1 true WO1994002252A1 (en) 1994-02-03

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ID=3776311

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Application Number Title Priority Date Filing Date
PCT/AU1993/000373 WO1994002252A1 (en) 1992-07-23 1993-07-23 Flotation method

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ZA (1) ZA935335B (en)

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1444026A (en) * 1973-08-02 1976-07-28 Water Res Centre Method of clarifying impure water
US4071447A (en) * 1975-04-16 1978-01-31 Swift & Company Dewatering of wastewater treatment wastes
GB1522188A (en) * 1974-10-17 1978-08-23 Swift & Co Apparatus and method for removing pollutants from wastewater
US4193869A (en) * 1974-11-21 1980-03-18 Milton Brucker Wastewater and wastewater solid processing system
US4214987A (en) * 1976-12-21 1980-07-29 Dravo Corporation Two stage wastewater flotation
US4220612A (en) * 1979-04-23 1980-09-02 Envirotech Corporation Flotation cell feed duct
EP0248519A2 (en) * 1986-05-30 1987-12-09 Petrolite Corporation Flotation-aid composition and method of use thereof
US5009792A (en) * 1989-10-24 1991-04-23 Norsk Hydro A.S. Method for clarifying aqueous salt solutions

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1444026A (en) * 1973-08-02 1976-07-28 Water Res Centre Method of clarifying impure water
GB1522188A (en) * 1974-10-17 1978-08-23 Swift & Co Apparatus and method for removing pollutants from wastewater
US4193869A (en) * 1974-11-21 1980-03-18 Milton Brucker Wastewater and wastewater solid processing system
US4071447A (en) * 1975-04-16 1978-01-31 Swift & Company Dewatering of wastewater treatment wastes
US4214987A (en) * 1976-12-21 1980-07-29 Dravo Corporation Two stage wastewater flotation
US4220612A (en) * 1979-04-23 1980-09-02 Envirotech Corporation Flotation cell feed duct
EP0248519A2 (en) * 1986-05-30 1987-12-09 Petrolite Corporation Flotation-aid composition and method of use thereof
US5009792A (en) * 1989-10-24 1991-04-23 Norsk Hydro A.S. Method for clarifying aqueous salt solutions

Also Published As

Publication number Publication date
ZA935335B (en) 1994-02-14

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