ZA200507463B

ZA200507463B - Measuring froth stability

Info

Publication number: ZA200507463B
Application number: ZA200507463A
Authority: ZA
Inventors: Triffett Brett; Johannes Jacobus Le Roux Cilliers
Original assignee: Tech Resources Pty Ltd; Univ Manchester
Priority date: 2003-03-13
Filing date: 2005-09-28
Publication date: 2006-12-27
Also published as: AU2010212522B2; EP1613434B1; DK1613434T3; ATE509704T1; AU2003901142A0; AU2004218778A1; WO2004080600A1; EP1613434A4; PL1613434T3; EP1613434A1; AU2010212522A1; ES2371311T3

Abstract

A method of measuring froth stability (as described herein) of a froth in a cell of a flotation circuit for a slurry of a mined mineral containing valuable material and gangue materials is disclosed. The method includes a step of measuring one or more than one froth stability parameter using a measurement column arranged to extend downwardly through the froth in the cell to a location below an interface between the froth and the slurry in the cell. A method of controlling the operation of a flotation cell that is based on the froth stability measurement method is also disclosed.

Description

MEASURING FROTH STABILITY

The present invention relates to recovering valuable material from mined minerals by means of froth flotation of a slurry of the mined materials.

The presen-t invention relates particularly to a method of measuring froth stability in a cell of a flotation circuit for recovering valuable material from a slurry of mined minerals containing valuable material and gangue material.

The preserat invention also relates to an apparatus for measuxing froth stability.

The present invention also relates to a method o £ controlling the opexation of a flotation cell using froth stability as a contol parameter for the method.

It has been long understood that the froth phase: of a flotation cell has a significant influence on the overall performances of the flotation procesa.

A froth is a three phase structure comprising afr bubbles, solids and water. The bubbles are defined by a thin water film or lamellae, which separates two bubbles, while the intersection of three lamellae results in the formation of a narxow water channel called a Plateau border. The entire froth is therefore made up of a continuous network of narrow water channels in which wate x and solid particles can flow. The solids contained in th e froth are either valuable material attached to lamellae ox a mixture of valualble material and gangue material contained freely within the Plateau borders.

A froth 4s a highly dynamic system in which solids and water movement is governed by the following

W 0 2004/080600 PCT/AU2004/000311 processes:

J The flow of air bubbles from the pulp froth interface to the top surface of the froth. 5S Typically, 5-10% of the air entering the froth is carried over a cell weir into a concentrate launder and the other 90-95% leaves the top of the E£roth as bubbles burst. As the bubbles flow upwards they carry valuable material which is directly attached to the bubble lamellae. The upward flow of bubbles also drags a portion of the water contained in Plateau borders upwards along with its load of entrained a5 particles (both valuable material and gangue material) .

J Bubble coalescence. Water contained in the thin film lamellae def ining each bubble tends to flow towards the Plateau borders.

As this takes place the lamellae become thin, and eventually berezk, resulting in the coalescence of twos adjacent bubbles into a single larger lbbubble. The coalescence process re=leases attached particles into the Plateau borders. The thinning and rupture of lamellae at the top gurface of the froth results in bubbles bursting. This results in loss of air from 20 the froth and release of attached particles into the Plateau borders.

The term “froth stability” is understood herein to mean the ability of bubbles in a froth to resist coalescence and bursting.

A more stable froth will have less coalescence and bursting events, a smaller mean bubble size and may carry more water. All of these factors will ultimately determine the structure and vo lume of the froth (water, solids and air) carried over t he cell weir into the concentrate launder and therefore the recovery of attached and unattached (carried in Plateau border) particles - in other words, the valuable matearial recovery and concentrate grade.

It is evident from the above-described processes that a more stable froth will recover a greater amount of valuable material attached to bubbles and within the

Plateau borders.

Tt is also evident from the above that a more stable froth will also recover more gangues material.

Accordingly, from a viewpoint of maximising recovery and concentrate grade, there is an optimum froth stability for any given flotation cell and any given operating conditions for that cell.

The term “operating conditions” is understood herein to mean: (a) chemical cond itions (frother, collector, PH and other modifiers or contaminants) of the cell; (b) grade of hydr-ophobic particles in the cell feed (valuabl.e material and gangue material); (¢) slimes and cXay content in the cell feed: (d) particle size of the cell feed;

(e) air rate for the cell; and (£) pulp density of the slurry supplied to the cell.

Each of thesie variables can change rapidly or gradually over time and can significantly influence froth stability and the ovexall flotation performance.

A method by which froth stability can be measured online in a flotation circuit for the purposes of process monitoring and control would add great value to any flotation operation.

The present invention provides such a method.

According to the present invention there is provided a method of measuring froth stability (as described herein) of a froth in a cell of a flotation circuit for a slurry of a mined mineral containing valuable material and gangue material, which method includes & step of measuring one or more than one froth stability parameter using a measurement column arranged to extend downwardly through the froth in the cell to a 55 location below an interface between the froth and the slurry in the cell.

The froth stability parameter may be any parameter that provicles information on the stability of the froth in the cell that can (a) be measured directly by means of the column or (b) be derived from measurements made using the columm.

Two preferxed froth stability parameters that can be measured directly by means of the column are: (a) the rate or velocity of movement of froth vp the column from a pre-determined starting height to a maximum height of the £roth in the column; and (b) “the maximum height attained by the froth in +he columm.

Prefexably the method includes washing the column to collapse the £rxoth in the column to the pre-determ-ined starting height, for example the interface between the slurry and the froth, and thereafter repeating the abwove- described measurement step and measuring one or more than one froth stabi. lity parameter.

According to the present invention there is also provided an apparatus for measuring froth stability of a froth in a flotation cell in a plant and for controll. ing operating condzitions of a flotation cell which includes: (a) a measurement column arranged to extend downwardly through the froth in the cell to a locztion below zn interface between the froth and the slurry in the cell; and (b) a means for measuring froth stability parameters directly by means of the column or indirectly from measurements made -using the column; and (e) a means for processing data measured directly or indirectly from the column and adjusting one or more than one of thea operating conditions of the cell (as described herein) to optimize cell performance.

According to the present invention there i.s also

- 6 =~ provided a method of controlling the operation of a flotation ce 11 which includes the steps of: (a) measuring froth stability (as desc=ribed herein) of a froth in the cell in accordance with the method described above; (b) inputting froth stability data into a model that relates froth stability and %&he performance of the cell (in terms of recovery of valuable material and concentrate grade) to assess the cell performance; and (¢) adjusting one or more than one off the operating conditions of the cell (as described herein) to optimize cell performance. whe term “froth stability data” is understood herein to mmean data that is directly measured bly means of the column ox ig derived from directly measured data.

Preferably the method includes repeating the measuremen.t of the froth stability during the course of the operat-ion of the cell and adjusting operati.ng conditionss of the cell based on the froth stabi. lity data.

The model may be any suitable model t=hat relates froth stability and the performance of the cell (in terms of recovery of valuable material and concentratce grade) to assess the cell performance.

The model may be a fundamental model derived from theoretical considerations.

Alternatively, the model may be base«d On comparing measured froth stability data and data on the historical operation of the cell.

One particular model is a model that is being developed by the applicant.

The development of the model has been supported by testwork carried out by the applicant to determine how to measure selected froth stability parameters in a single laboratory batch flotation cell and along the rougher bank of a flotation circuit at one of the mines operat.ed by the applicamt.

As indicated above, the model relates £roth stability and the performance of the cell (in terms of recovery of valuable material and concentrate grade).

The model is a fundamental model and is based on foam physics and interprets the effect of froth structure on flotation. The model links the flow rate of -valuable material, gangue material, and water to froth st xucture.

The mass flow rate of valuable material, gangue material, and water are related to the flow rate of bubble surface area amd the total volumetric flow rate of Platerau borders overflowing the weir. These last two parameterss can be estima ted through analysis of video images of thie overfl owing froth.

The teastwork program carried out at the applicant’s mine involved the use of a column 30cm square by 165cm high constructed of perspex. The objective of the program was to investigate how to measure fxoth stabil ity parameters.

The column was inserted into the pulp phase to a depth of 30cm and an operator manually recorded the level of the rising froth with time.

At the end of the test, when the froth had reached a stable maximum height, the data was entered into a spreadsheet and the appropriate parameters were calculated.

Figuxe 1 shows a typical column froth height versus time curve generated during the testwork. The= graph has raw data as well as a "fitted model" for the data. The fit ted model is a separate model to the previously des cribed model.

Of significance is the close fit of the fitted model to the raw data. 1S

The fitted model has the form shown in equation (1) where Ho i & the maximum height the froth reaches and 1 is a fitted stability parameter.

H=H, (1-e"%/") Equation (1)

Other models may be appropriate also.

Figure 2 and 3 are graphs of column froth height versus time for selected operating conditions.

What is clear from Figures 2 and 3 is that alterations to operating conditions resulted in significantly different froth stability curves. The se differences can be used to clearly explain differenc.es in metallurgical performance, ie recovery and concentra.te grade, of a cell.

An extension of the froth stability curves discussed abo-ve comes with consideration of the bursting fraction (1 - a) of the froth.

If all of the air entering the froth from the pulp was retained in the froth then the rise velocity within the coluxm would be equal to the superficial gas velocity Jy (where Jg equals the gas flow rate per unit area of the col-umm). Thig would be the case if bubbles at the surface of the froth did not burst and release their contained air. This is obviously not the case with only & small fraction of the airflow retained in the froth.

It may be expected that the value of a in the column and the value of a for the entire cell at a given froth depth will be different. The relationship between « in the column and the actual a achieved for the entire cell is the subject of current research.

Givem the considerations in the preceding paragraph, the following equation can be presented, relating the E£roth rise velocity (u) to the superficial gas velocity and the fraction of air retained in the fro th {o) :

U = Jg (1-a) Equation (2)

Given that the instantaneous rice velocity cam be calculated from the froth stability curve and the superficial gas velocity can be measured, then the instantaneous bursting fraction (l-a) can be calculated for a given f£ roth height.

The result is a plot of alpha versus height shown in Figure 4.

These graphs take the form: a = a; (1-H/H) Equation (3) where a; is the fraction of airflow retained in the froth at a froth height of =ero.

Using equatdions 1, 2 and 3 the following additional equations can be developed to assist with interpretation of the datas

Ho = ® Jg Ox Equation (4)

U = J4 0; - H/T Equation (5) ¥ = H¢/Jy Equation (6) where I is the dynamic froth stability factor.

In summary, the above-described testwork determined how to measure two particular froth stability parameters, namely the maximum height attained by the froth in the column and the rate or velocity of movement of froth up the column from a pre-determined starting height to a maximum height of the froth in the column.

Figure 5 is a conceptual diagram of an apparatus for measuring froth stability in a flotation cell in a plant and for controlling operating conditions of a flotation cell.

The main, but not only, operating conditions that can be adjusted in wmesponse to froth stability measurements include reagents (frother, collector, pH modifier or other modifier), air rate, pulp density, particle size and oxxe blend. with refemence to Figure 5, the apparatus includes a column ( 6) that is constructed from 300mm diameter perspex pipe with a wear resistant and replaceable HDPE extension piece (9) which, in use, is inserted into the pulp in a cell.

While the original column used in the testwork at the applicant's mine was square, it is anticipated that a circular column will provide better movement of the froth as there is no interferences from the corners. Having said this, a square column would still suffice.

The column (6) is constructed in a number of sections so the measurement height of the column can be reduced if necessary.

The maximum height shown in Figure 5 will allow for two metres of froth, which might typically be expected in a high grade rougher ce 11, whereas a shorter column might be used for a scavenger cell where less froth is generated.

Figure 5 illustr-ates a gridmesh walkway above the cell on which to secure the column (6). This may not always be the case and an alternate securing arrangement may be required. The coluum (6) is secured to the gridmesh wia a sscuring plate (7) and the depth that the column is inserted into tke pulp can be adjusted slightly via the level adjustment Joolts (8).

When the column (6) is used at its maximum height the adjustable length tie down bars are required to minimise any bending of the column as a result of the pulp movement at the base.

If the column is used in a shortened form the tie down bars may not be required.

In use, the froth height inside the column (6) is measured by an ultrasonic level sensor, although any other suitable means of continuously monitoring the froth level will suffice.

In this case, the f roth height data is monitored by a commercially available C'itect monitoring and control system, which collects the data and performs the calculation of the froth stability parameters described previously.

Any other suitable means of continuously logging and calculating the appropriate froth stability parameters for process control purposes will suffice.

Froth stability data is supplied to the above- described model that relates froth stability and the performance of the cell (in terms of recovery of valuable material and concentrate grade) and the model assesses the cell performance and, if recuired, initiates adjustments to selected operating conditions of the cell to improve the cell performance.

Once the froth stability parameters are calculated to a satisfactorw level of accuracy in a first measurement cycle, a water =olenoid valve (2) is actuated to wash down the froth. The measurement sequence, data input to the model, and adj-ustment of cell operating conditions is then repeated.. Typically, the sequence requires a 20-60 minute per-iod and can be repeated on a continuous or periodic basi.s during the operation of the cell. The measurement sequmence period may be any suitable period.

Many modificatioras may be made to the preferred embodiment of the present dnvention described above without departing from the spirit and scope of the invention.

Claims

CLAIMS:

1. A method of measuring froth stability (as described herein) of a froth in a —ell of a flotation circuit for a slurry of a mined mimeral containing valuable material and gangue material, which method includes a step of measuring one Ox more than one froth stability parameter using a measur-ement column arranged to extend downwardly through the froth in the cell to a location below an interface between the froth and the slurry in the cell. .

2. The method defined in claim 1 wherein the froth stability parameter is any paramet-er that provides information on the stability of the froth in the cell that can (a) be measured directly by means of the column or (b) be derived from measurements made using the column.

3. The method defined in cllaim 1 or claim 2 wherein the froth stability parameters th at can be measured directly by means of the column imclude the rate or velocity of movement of froth up the column from 2 pre- determined starting height to a maximum height of the froth in the column.

4. The method defined in any one of the preceding claims wherein the froth stability parameters that can be measured directly by means of the column include the maximum height attained by the fxroth in the column above a pre-determined starting height.

5. The method defined in claim 3 or claim 4 includes washing the column to collapse the froth in the column to the pre-determined starting height at the end of a measurement step and thereafter repeating the measurement step and measuring one or more than one froth stability parameter.

6. An apparatus for measuring froth stability of a froth in a flotation cell in a plant and for controlling operating conditions of a flotation cell which includes: S (a) a measurement column arranged to extend dovnwardly through the froth in the cell to ‘a location below an interface between the froth and the slurry in tlae cell; and

10 . (b) a means for measuring froth stability parameters directly by means of the column or indirectly from measurements made using the column; and 1s (c) a means for processing data measured directly or indirectly from the column and adjusting one or more thax one of the operating conditions of tlhe cell (as described herein) to optimmize cell performance.

7. A method of controlling the op eration of a flotation cell which includes the steps of: (a) measuring froth stability (as described herein) of a froth in thes cell in accordance with the method defined in any one of claims 1 to 6; (b) inputting froth stability data into a model that relates froth stability and the performance of the cell «in terms of recovery of valuable material and concentrate grade) to assess the cell performance; and

(c) adjusting one or more than ore of the operating conditions of the cell (as described herein) to optimizee cell performance.

8. The method defined in claim 7 inc ludes repeating the measurement of the froth stability during the course of %he operation of the cell and adjusting operating conclitions of the cell based on the froth sxtability data.

9. The method defined in claim 6 or claim 7 wherein the model is a model that relates froth stability and the per formance of the cell (in terms of recovesry of valuable mat erial and concentrate grade) to assess he cell performance.