NZ631479B2 - Method and apparatus for controlling the flotation process of pyrite - containing sulphide ores - Google Patents

Abstract

Method and apparatus for controlling the flotation process of sulphide ores including separation of sulphide minerals from pyrite in an alkaline environment created by lime. The method comprises measuring the molybdenum electrode potential of an aqueous slurry of the ore and adjusting the addition of lime based on the measured molybdenum electrode potential to maintain the molybdenum electrode potential of the slurry in a preselected range. The apparatus comprises means (6) for measuring the molybdenum electrode potential and a control unit (7) for controlling the addition of lime to the slurry based on the measured molybdenum electrode potential of the slurry. of lime based on the measured molybdenum electrode potential to maintain the molybdenum electrode potential of the slurry in a preselected range. The apparatus comprises means (6) for measuring the molybdenum electrode potential and a control unit (7) for controlling the addition of lime to the slurry based on the measured molybdenum electrode potential of the slurry.

Description

ANDAPPARATUSFORCONTROLUNGTHEFLOTAHON PROCESS OF PYRITE - CONTAINING SULPHIDE ORES FIELD OF THE INVENTION The invention relates to a method for con— trolling the flotation process of sulphide ores in— cluding separation of sulphide minerals from pyrite in an ne environment created by lime. The invention also relates to an apparatus for controlling such (lo— tation process.

BACKGROUND OF THE INVENTION ion process which includes separation of sulphide minerals from pyrite by adjusting limo (CaO) dosage is one of the most common ses used in concentration plants throughout the world. The pro— cess is used, for instance, in beneficiation of cop- per, copper-zinc, —nickel, copper-molybdenum, and complex ores.

Each flotation process has an l elec~ trochemical state that leads to the best possible met— allurgical performance. In ion practice, methods are known for controlling the feed of sulphidizinq agent (e.g. NaZS) based on the measurement of electro—' al potential (Eh) of an s ore slurry with the help of a platinum electrode. Examples of such methods are disclosed, for instance, in patent docu~ ments US 4011072 A and US 3883421 A. These methods rc— late to flotation processes aiming at sulphidizinq ox— idized forms of copper minerals. Such methods cannot be directly applied to flotation separation of sul— phide minerals from pyrite, since N825 applied in those methods would result in activation of pyrite flotation.

Lime addition in selective flotation of sul— phide minerals from pyrite is usually controlled based W0 2013/169140 on hydrogen ion concentration measured from the slur— ry, or based on the conductivity of the slurry. in spite of the high importance of separation of de minerals from pyrite, there are no examples of relia— ble implementation of such flotation control systems in industrial conditions. The reasons for this will be discussed in the ing.

Low ivity of glass electrodes with highly alkaline slurry is one of the problems. Selec— lO tive flotation of ~containing de ores is usually carried out at a pH of about 12.0-12.2.

Fouling of ode surface with films of Ca(OH)2 and mineral particles of the processed ore is another problem. Attempts have been made to clean the electrode surface mechanically or by washing with wa- ter or acid. These procedures significantly complicate the design of the measurement sensor. Still, they do not ensure reliable operation of the pyrite separation process.

The feasibility of eliminating sensor fouling by means of natural peeling of the sensor surface with the slurry flow is excluded because a glass electrode would break in such treatment.

High sensor nce (over lOOO MOhm) re- quires special ionometers with a esistance input and protection of connecting cables and connectors from the influence of electromagnetic fields of motors installed in the flotation building, as well as taking measures to prevent the ingress of moisture, vapours and steam condensation into the fixture with the help of which the sensor is installed into the slurry.

A glass electrode does not react on changes in the redox—potential of the slurry.

Special researches conducted in a concentra— tion plant beneficiating Cu—Zn ore confirmed the unre— liability of using conventional s control with a pH sensor during the separation of copper minerals 2012/000398 from pyrite. The measurement results of the industrial sensor installed directly in a flotation cell and the measurement results of a pH sensor installed in a test flow—through cuvette were compared. The trend of the sensor installed in the flotation cell demonstrated first a gradual decrease of pH values and then a total failure of the pH control system. Thus there is a great risk that the pH sensor installed directly in the flotation cell misinforms the process l op— erator. instability and low efficiency ot pH based control of flotation s during separation of sul— phide minerals front pyrite has also been discovered when analysing the operation of another industrial concentration plant treating complex ore.

A second industrially ented way of con- trolling the ion separation of sulphide minerals from pyrite is to adjust the CaO dosage according to the slurry conductivity value. Taking into t the particularities of the ionic composition of flotation slurries, this method has numerous disadvantages.

Apart from the residual concentration of CaO, the con— ductivity of the slurry is also considerably influ- enced by the amount of ZnSOa electrolyte dosage into the slurry, which is widely used, especially when treating Zn~containing ores, as well as by any dosage of other reagents. Apart from HP and OH” .ions, the slurry conductivity is also influenced by the e components of the processed ore and the composition of circulation water, which may contain Na+, K‘, Cl‘, 323 SOf', szof‘, SqOJ', 80f- and many other ions. A close correlation can be observed in an industrial — trator plant between the slurry conductivity and the electrochemical potential within short time periods, but this correlation falls almost to zero within a couple of days.

In a Finnish industrial concentration plant, in order to l the operation of a conductometric analyser, manual slurry pH control of the industrial slurry is performed daily every 3—4 hours in the la— boratory. Hence the control method is ous.

A control method based on conductometric mon— itoring of the residual CaO concentration does not ate the disadvantage of sensor element fouling with films of Ca(OH)2 and mineral particles ot the processed ore. tes are often used as collectors in flotation of sulphide ores. entation of a KloLa— tion method comprising pyrite depression by means 01 lime provides for preventing the oxidation oi xanthate ions into dixanthoqenide, which is a pyrite collector: ZX' a X2 + 2e“ (1) In other words, the pyrite depression process also depends on the electrochemical potential of the slurry, the value of which should be aimed at shifting the on (1) to the left side. This fact is not taken into account when implementing the present py- rite separation process control, which is realised in practice only by controlling the tration of EV ions in the slurry based on a selective glass elec— trode for gfii measurement. This can be considered as the main technological drawback of the current process of separating sulphide minerals from pyrite. This fact has also been verified in practice. During different operation periods in an rial concentration plant, with the same “optimum” pH value 12.0—12.5, ochemical potential values of different heights were registered. Higher electrochemical potentials were found to result in higher pyrite floatability and disruption of flotation selectivity.

The object of the present invention is to me the problems faced in the prior art.

More precisely, the object of the present invention is to improve the control of conditions in a flotation process that comprises selective separation of sulphide minerals from pyrite in an alkaline environment created by addition of lime.

The ing objects are to be read ctively with the object of at least providing the public with a useful alternative.

SUMMARY According to the present invention, a method for controlling the flotation. process of sulphide ores including separation of sulphide minerals from pyrite in an alkaline environment created by lime comprises measuring the molybdenum electrode potential of an aqueous slurry of the ore and adjusting the addition of lime based on the measured molybdenum electrode potential to maintain the molybdenum electrode potential of the slurry in a preselected range.

Preferably, the molybdenum ode and a reference electrode (Ag/AgCl) are placed at a point where the slurry is in flow, for instance, in a feed line or in an intensively agitated section of a flotation cell. This prevents fouling of the electrode surface with Ca(OH)2 films and mineral particles of the processed .

Reliability of electric ements can be increased by' using' a low—resistance electrode, preferably‘ one having a resistance below 1.0 ohm.

The optimum range for the molybdenum ode potential, which is used as the preselected range in an automatic control loop, can be defined experimentally in each case.

According to the present invention, an apparatus for controlling the flotation process of sulphide ores including separation of sulphide ls from pyrite in an alkaline environment created by lime comprises means for measuring the molybdenum electrode potential of an aqueous slurry and means for control- ling the addition of lime based on the ed molyb— denum electrode potential to maintain the molybdenum electrode potential of the slurry in a ected range.

Preferably, the means for controlling the ad— dition of lime comprise means for comparing the meas— ured enum electrode potential with the prese— lected range and means for changing the feed rate of lO lime to the slurry if the Heasured molybdenum elec— trode ial deviates from the preselected range.

BRIEF DESCRIPTION OF THE DRAWINGS In the following the principles of the inven- tion are ned with reference to the appended drawings, where: Fig. l is a schematic representation of a control system. for a flotation process according to the present invention.

Fig. 2 is a diagram illustrating three— dimensionally lead losses with tailings as a function of pH and molybdenum electrode potential.

Fig. 3 is a diagram illustrating copper con- centrate grade and copper losses with tailings as a on of enum electrode potential.

Fig. 4 is a diagram illustrating the final copper concentrate grade in the form of isolines as a function of molybdenum electrode potential and pH.

DETAILED DESCRIPTION OF THE INVENTION Stemming from the physical-chemical nature of the flotation process in separating de minerals from pyrite, the new control method comprises adjust— ing lime dosage based on the molybdenum electrode po— tential ed from the ore slurry. The possibility of pH control using metal—oxide electrodes is well— W0 2013/169140 known from the theory of electrochemistry, but it has not before been used in the t context.

Formation of molybdenum electrode potential is determined by an electrochemical reaction: M002 + H20 = M003 +2H+ + 2e" (2).

Since H? ion participates in the on (2), the molybdenum electrode potential simultaneously controls the pH and the redox potential of the slurry.

Redox potential measurement indicates the re— duction/oxidation potential of a solution. Redox po— tential is obtained by ing the electrode poten— tial of a redox ode against 51 reference elec— l5 trode. Usually, a platinum electrode is used in the ement. However, platinum electrode is very un- stable in terms of slurry composition; for instance, a platinum electrode is influenced by the concentration of oxygen and hydrogen in the slurry. um elec— 'trode is very sensitive to ions of bivalent iron, which often appear in ore slurries. The instability of the properties of platinum electrode is associated with the method of its manufacture: presence of atomic impurities from other metals in platinum,' electrode shape, method of its surface processing.

In a flotation system for pyrite—containinq copper ores, the ore is first d and ground with lime usually added as an aqueous solution to depress pyrite. The ore is then treated in a primary ELotation 3O circuit after a suitable copper collector and frother have been added. The copper rougher trate thus obtained contains most of the copper of the ore. This copper rougher concentrate is then subjected to sever— al stages of cleaner flotation, usually' after a re— qrind operation, to produce a finished copper concen— trate. The new control method can be used at any stage of a flotation process used for separation of copper, W0 2013/169140 or any other valuable sulphide minerals, such as Zn, Pb, Mo, Ni, from pyrite in an alkaline environment created by lime.

The principles of the ion process and ‘5 the control system according to the present invention are illustrated in Fig. 1. An aqueous ore slurry is fed to a flotation cell 1 via a slurry feed Line 2.

Lime or lime milk is added to the slurry via a lime, feed line 3 in an ore mill (not shown), in a condi— lO tioner (not shown) and/or in the flotation cell 1. The goal of flotation is to separate valuable sulphide minerals from pyrite and gangue minerals such that the former are transferred to trate 4 and the latter are transferred to tailings 5.

The redox~potential of the slurry is measured by measuring means 6 which comprise, among other , a nmlybdenum electrode and a reference elec- trode, preferably an Ag/AgCl-electrode. Both elec— trodes are placed either in the slurry feed Line ? or in the flotation cell 1. It is important the elec— trodes are placed at a point where the slurry is in motion.

The measuring means 6 provide a ement signal, which is transmitted to a control unit 7. The control unit 7 compares the measured molybdenum elec— trode potential with a preselected range given to the molybdenum ode potential. If the ed value is not within the preselected range, the control unit 7 transmits a l signal to an actuator 8 control— ling the lime feed. ageously, the optimum range for molyb- denum electrode potential to be used as the preselect— ed range in the control system should be defined ex— perimentally in each case.

L0 (_fi The invention is further illustrated below by reference to specific examples. However, the scope of W0 2013/169140 the t invention is not limited to these exam- ples.

EXAMPLE 1 A comparative evaluation of three different control methods that can be used in selective flota- tion separation of sulphide minerals from pyrite in a lime environment was carried out in an rial con— centration plant with the help of neural k mod— cling. The concentration plant in question benefi- clates Cu—Zn ore. Neural networks, with their remarka— ble ability to derive meaning from complicated or im— precise data, are a feasible tool for extracting pat— terns and detecting trends that are too complex to be noticed by either humans or other computer techniques.

The evaluated three methods comprise control— ling the conditions in flotation process based on: pH control, conductemetric , and redbx—potential (Eh). Measurements of redox-potential and pH were per— formed by installing the respective electrodes ln a flow—through cell in a Chena® system installed in the slurry flow fed into a rougher copper flotation. These results were ed with results of conductometric measurement system which was led at the same process point. Information on metal content, section lead and reagent dosage was received from Outotec Pro~ scon® automation system during the period of conduct— ing the tests.

The results of the neural network modeling of the sensitivity of each process control method are given in Tables 1—3. In each table, s load pre- sents the load of the observed process stage in terms of tons of ore per hour. Fe in feed (or Cu, Zn, Pb, S in feed) presents the iron content (or copper, zinc, lead, r t) in the incoming ore. Xanthate consumed (or ZnSOq, CaO consumed) presents the amount of xanthate (or ZnSOa, CaO) consumed in the ore mill.

W0 2013/169140 Table 1 shows the neural network model for pH control, Table 2 shows the neural network model for conductometric method and Table 3 shows the neural network model for redox potential (Eh) based control system.

As expected, the method ing process control based on pH (Table l) responds to CaO consump» tion and copper content of the ore in the first place and to other changes in the composition of the pro~ lO cessed ore in the last place.

The method employing process control based on tometric method (Table 2) responds to ZnSOa feed and to zinc and copper contents of the ore in the first place.

The s control based on the redox poten— tial (Table 3) responds to the composition of the pro— cessed raw als in the first place. This explains the reason of the optimality' of this parameter~ when implementing the control method according to the pre— sent ion.

The neural network model for Eh parameter is noted for its better appropriateness for the discussed site. The correlation factor for the model is evaluat— ed as R = 0.947. For the flotation process control based on pH the model appropriateness is ted as R 2 0.657. When using a conductometric method, the value of R is 0.889.

EXAMPLE 2 The optimality of using molybdenum electrode potential in flotation control was further confirmed by comparative tests with molybdenum. and pH elec— trodes. The tests were performed in a 1concentration plant treating polymetal ores. Fig. 2 shows the re— sponse of an output function — lead losses with tail— ings (8(Pbll - during neural network modeling against the change of the slurry pH and the electrochemical potential measured using a molybdenum electrode. From Fig. 2 one can clearly see the availability of an op- timum molybdenum ode potential at which lead losses with tailings are minimal, whereas this is not the case with pH values. On the shown se surface there is almost no influence of pH value variation, or there is a linear dependency necessitating reduction of pH value in order to decrease the loss of Lead with tailings, in which case increased pyrite floatabiiity is inevitable.

EXAMPLE 3 The method according to the present ion was tested during the treatment of Cu—Zn pyrite ore in an industrial concentration plant in a copper flota— tion circuit where CaO is fed into ore mills. Apart from CaO, Zn804 is also fed into the ore mills for sphalerite sion, and xanthate is used as a col— lector for copper minerals. ation of molybdenum electrode potential with the produced copper concen— trate grade B(Cu) and copper losses with the circuit tailings 6(Cu) is presented in Fig. 3. The figure re— veals an optimum of molybdenum electrode potentials at an area around -325 mV, where the highest copper con— centrate grade and the minimum copper losses with tailings are achieved. When the molybdenum eLectrode potential is higher than the optimum, process parame— ters are lly lower due to the shift of the reac— tion (1) balance to the right side. According to the present invention, high molybdenum electrode potential necessitates increased CaO addition. Process paramew ters are decreased as well with low molybdenum elec— trode potentials, which is explained by the Formation of complex nds of type )Xfl' in this area.

Formation of said complex has been confirmed by spe— cial electrochemical measurements in rougher copper flotation. se of the activity of the ionic form W0 2013/169140 of xanthate is a reason for the increase of copper losses with section tailings.

The advantage of controlling the molybdenum ode potentials in the implementation of the pre— sent method compared to controlling the pH parameter is further med by Fig. 4. The figure shows a plane in the coordinate system of molybdenum electrode potential and pH in which isolines of the final copper concentrate grade are plotted. A clear dependence 0L copper concentrate grade and molybdenum electrode po— tential variation can be observed. The dependence of copper concentrate grade and pH is much weaker.

EXAMPLE 4 The l method according to the t invention was tested during treatment of pyrite- containing copper ore in an industrial concentration plant in the coarse copper concentrate cleaner cir— cuit, where CaO is fed into a d mill.

The correlation of process parameters - pro~ duced copper concentrate grade B(Cu) and copper losses in the circuit tailings 6(Cu) - and molybdenum elec— trode ials followed a similar pattern as in Fig. 3. The area of optimum values of molybdenum electrode ials was found to be close to the area of opti— mum values of molybdenum electrode potentials discov— ered in Example 3. Control measurements of hydrogen parameter value in that area pond to pH = 12.2.

The above results indicate that it is possi— ble to optimize the selective flotation of sulphide minerals from pyrite by measuring the molybdenum elec- trode potential and by adjusting the lime addition based on the measured electrode potential. it is evident that the optimum molybdenum electrode potential may vary in different concentra— tion plants based on the differences in the ore compo— sition and other process conditions. That is why the W0 2013/169140 optimum range of molybdenum electrode potential shouid be separately defined for each individual case.

It is obvious to a person skilled in the art that with the ement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples bed above; instead they may vary within the scope of the claims.

Claims (11)

WHAT IS CLAIMED IS

1. A method for controlling the flotation process of sulphide ores including separation of sulphide minerals from pyrite in an alkaline environment created by lime, characterized by measuring the molybdenum electrode potential of an aqueous slurry of the ore and adjusting the addition of lime based. on the measured molybdenum electrode potential to in the molybdenum electrode potential of the slurry in a preselected range.

2. A method according to claim 1, characterized by measuring the molybdenum electrode potential while the slurry is in flow.

3. A. method. according to claim. 1 or 2, characterized by using a low—resistance molybdenum electrode.

4. A method according to claim 3, wherein the electrode has a resistance below 1.0 ohm.

5. A method according to any one of claims 1 to 4, characterized by experimentally ng the optimum range for the molybdenum electrode potential to be used as the preselected range.

6. An apparatus for controlling the ion process of sulphide ores including separation of sulphide minerals from pyrite in an alkaline environment created by lime, wherein the apparatus comprises means for measuring the enum electrode potential of an s slurry of the ore and means for lling the addition of lime based on the measured molybdenum electrode potential to in the molybdenum electrode ial of the slurry in a preselected range.

7. An apparatus according to claim 6, wherein the means for measuring the molybdenum electrode potential of the slurry comprise a enum electrode and a reference electrode placed at a point in the process where the slurry is in flow.

8. An apparatus according to claim 6 or 7, wherein the molybdenum electrode is a low—resistance ode.

9. An tus according to claim 8, wherein the electrode has a resistance below 1.0 ohm.

10. An apparatus according to Claim 6, wherein the means for controlling the addition of lime comprise means for comparing the measured molybdenum electrode potential with the ected range and means for changing the feed rate of lime to the slurry if the measured enum electrode potential deviates from the preselected range.

11. A method according to claim 1, substantially as herein. bed with. reference to any one of the Examples and/or